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13 pages, 4035 KiB  
Communication
Use of Laccase Enzymes as Bio-Receptors for the Organic Dye Methylene Blue in a Surface Plasmon Resonance Biosensor
by Araceli Sánchez-Álvarez, Gabriela Elizabeth Quintanilla-Villanueva, Osvaldo Rodríguez-Quiroz, Melissa Marlene Rodríguez-Delgado, Juan Francisco Villarreal-Chiu, Analía Sicardi-Segade and Donato Luna-Moreno
Sensors 2024, 24(24), 8008; https://doi.org/10.3390/s24248008 (registering DOI) - 15 Dec 2024
Viewed by 108
Abstract
Methylene blue is a cationic organic dye commonly found in wastewater, groundwater, and surface water due to industrial discharge into the environment. This emerging pollutant is notably persistent and can pose risks to both human health and the environment. In this study, we [...] Read more.
Methylene blue is a cationic organic dye commonly found in wastewater, groundwater, and surface water due to industrial discharge into the environment. This emerging pollutant is notably persistent and can pose risks to both human health and the environment. In this study, we developed a Surface Plasmon Resonance Biosensor employing a BK7 prism coated with 3 nm chromium and 50 nm of gold in the Kretschmann configuration, specifically for the detection of methylene blue. For the first time, laccases immobilized on a gold surface were utilized as bio-receptors for this organic dye. The enzyme was immobilized using carbodiimide bonds with EDC/NHS crosslinkers, allowing for the analysis of samples with minimal preparation. The method demonstrated validation with a limit of detection (LOD) of 4.61 mg L−1 and a limit of quantification (LOQ) of 15.37 mg L−1, a working range of 0–100 mg L−1, and an R2 value of 0.9614 during real-time analysis. A rainwater sample spiked with methylene blue yielded a recovery rate of 122.46 ± 4.41%. The biosensor maintained a stable signal over 17 cycles and remained effective for 30 days at room temperature. Full article
(This article belongs to the Section Biosensors)
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Figure 1
<p>Chemical structure of methylene blue.</p>
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<p>Possible recognition process and first step of degradation of methylene blue by laccases.</p>
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<p>Immobilization process of laccases on the thin chromium–gold film chip. In the step 1, alkanethiols are added to the thin gold surface. In step 2, the EDC is added, forming an unstable intermediate. In step 3, the NHS is added, creating a sulfo-NHS ester. In step 4, NHS is replaced by the laccase through an amide bond.</p>
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<p>Assembly of the prism and the chip on the SPR equipment: (<b>a</b>) assembly of the prism, the chip with a thin gold film with the immobilized laccases, the prism and other components. (<b>b</b>) Set up of the prism, sample cell, chip with immobilized laccases and the other on the SPR equipment.</p>
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<p>Reflectance spectra obtained by angular sweep.</p>
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<p>Immobilization process of laccass from <span class="html-italic">Rhus vernicifera</span> in real-time by SPR.</p>
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<p>FTIR analysis of different stages of laccase immobilization.</p>
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<p>(<b>a</b>) SPR analysis of stocks with different concentrations of methylene blue. (<b>b</b>) Calibration curve and equation of a straight line.</p>
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<p>Comparison of the intensity of reflectance of solutions of methylene blue at day 1 and day 30.</p>
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14 pages, 2845 KiB  
Article
Detection and Quantification of DNA by Fluorophore-Induced Plasmonic Current: A Novel Sensing Approach
by Daniel R. Pierce, Zach Nichols, Clifton Cunningham, Sean Avryl Villaver, Abdullah Bajwah, Samuel Oluwarotimi, Herbert Halaa and Chris D. Geddes
Sensors 2024, 24(24), 7985; https://doi.org/10.3390/s24247985 (registering DOI) - 14 Dec 2024
Viewed by 225
Abstract
We report on the detection and quantification of aqueous DNA by a fluorophore-induced plasmonic current (FIPC) sensing method. FIPC is a mechanism described by our group in the literature where a fluorophore in close proximity to a plasmonically active metal nanoparticle film (MNF) [...] Read more.
We report on the detection and quantification of aqueous DNA by a fluorophore-induced plasmonic current (FIPC) sensing method. FIPC is a mechanism described by our group in the literature where a fluorophore in close proximity to a plasmonically active metal nanoparticle film (MNF) is able to couple with it, when in an excited state. This coupling produces enhanced fluorescent intensity from the fluorophore–MNF complex, and if conditions are met, a current is generated in the film that is intrinsically linked to the properties of the fluorophore in the complex. The magnitude of this induced current is related to the spectral properties of the film, the overlap between these film properties and those of the fluorophore, the spacing between the nanoparticles in the film, the excitation wavelength, and the polarization of the excitation source. Recent literature has shown that the FIPC system is ideal for aqueous ion sensing using turn-on fluorescent probes, and in this paper, we subsequently examine if it is possible to detect aqueous DNA also via a turn-on fluorescent probe, as well as other commercially available DNA detection strategies. We report the effects of DNA concentration, probe concentration, and probe characteristics on the development of an FIPC assay for the detection of non-specific DNA in aqueous solutions. Full article
(This article belongs to the Special Issue Optical Sensing for Environmental Monitoring—2nd Edition)
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Figure 1

Figure 1
<p>Absorption spectra of various solutions of ethidium bromide, ranging from 20 µM to 100 µM, both with and without the addition of 1 mg/mL DNA from a salmon sperm DNA stock solution. The solutions were allowed to mix for 30 min prior to analysis.</p>
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<p>Fluorescence emission spectra of various solutions of ethidium bromide, ranging from 20 µM to 100 µM, both with and without the addition of 1 mg/mL DNA from a salmon sperm DNA stock solution, excited at 365 nm. The solutions were allowed to mix for 30 min prior to analysis.</p>
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<p>Peak fluorescence emission spectra values for various solutions of ethidium bromide, ranging from 20 µM to 100 µM with the addition of 1 mg/mL DNA from a salmon sperm DNA stock solution, excited at 365 nm. The solutions were allowed to mix for 30 min prior to analysis. Data organized as the peak fluorescence intensity at 600 nm vs. concentration.</p>
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<p>Plasmonic current response of various solutions of ethidium bromide, ranging from 20 µM to 100 µM, both with and without the addition of 1 mg/mL DNA from a salmon sperm DNA stock solution, excited at 266 nm at 100 µW excitation power. The solutions were allowed to mix for 30 min prior to analysis.</p>
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<p>Plasmonic current response of various solutions of ethidium bromide, ranging from 20 µM to 100 µM with the addition of 1 mg/mL DNA from a salmon sperm DNA stock solution, excited at 266 nm at 100 µW excitation power. The solutions were allowed to mix for 30 min prior to analysis.</p>
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<p>Absorbance spectra of a 50µM solution of ethidium bromide mixed with varying concentrations of DNA from a salmon sperm DNA stock solution, ranging from 1 µg/mL to 10,000 µg/mL. The solutions were allowed to mix for 30 min prior to analysis.</p>
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<p>Fluorescence emission spectra of a 50 µM of ethidium bromide mixed with varying concentrations of DNA from a salmon sperm DNA stock solution, ranging from 1 µg/mL to 10,000 µg/mL, excited at 266 nm. The solutions were allowed to mix for 30 min prior to analysis.</p>
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<p>Peak fluorescence emission spectra values of a 50 µM of ethidium bromide solution mixed with varying concentrations of DNA from a salmon sperm DNA stock solution, ranging from 1 µg/mL to 10,000 µg/mL, excited at 266 nm. The solutions were allowed to mix for 30 min prior to analysis. Data shown as peak fluorescence intensity at 600 nm vs. DNA concentration.</p>
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<p>Plasmonic current response of a 50 µM of ethidium bromide solution mixed with varying concentrations of DNA from a salmon sperm DNA stock solution, ranging from 1 µg/mL to 10,000 µg/mL, excited at 266 nm at 100 µW power. The solutions were allowed to mix for 30 min prior to analysis.</p>
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<p>Absorbance spectra of various solutions of SYBR Green with varying concentrations of added DNA. Concentrations in μg/mL and mg/mL are related to DNA concentration added; 100×, 10× and 1× are related to the concentrations of SYBR Green.</p>
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<p>Fluorescence spectra of various solutions of SYBR Green with different concentrations of DNA added, excited at 473 nm. (<b>A</b>) 1× Concentration, (<b>B</b>) 10× Concentration and, (<b>C</b>) 100× Concentration of SYBR Green.</p>
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<p>FIPC responses for various solutions of SYBR Green with various amounts of DNA added, excited via a 473 nm (CW) laser, 10 mW power.</p>
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<p>FIPC response for 1× SYBR Green with added DNA, excited via 473 nm laser. Comparison between P and S polarized light for excitation.</p>
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<p>Standard curve obtained using 1× SYBR Green and various DNA concentrations (Left). In a blinded study, the sample values were found to be within 15% of their true value. Table detailing the raw responses and their calculated values (on the right). Each current response shown is the average of 10 values, n = 10.</p>
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11 pages, 3561 KiB  
Article
Enhanced Visible Light Controlled Glucose Photo-Reforming Using a Composite WO3/Ag/TiO2 Photoanode: Effect of Incorporated Plasmonic Ag Nanoparticles
by Katarzyna Jakubow-Piotrowska, Bartlomiej Witkowski, Piotr Wrobel, Krzysztof Miecznikowski and Jan Augustynski
Nanomaterials 2024, 14(24), 2001; https://doi.org/10.3390/nano14242001 - 13 Dec 2024
Viewed by 267
Abstract
WO3/Ag/TiO2 composite photoelectrodes were formed via the high-temperature calcination of a WO3 film, followed by the sputtering of a very thin silver film and deposition of an overlayer of commercial TiO2 nanoparticles. These synthetic photoanodes were characterized in [...] Read more.
WO3/Ag/TiO2 composite photoelectrodes were formed via the high-temperature calcination of a WO3 film, followed by the sputtering of a very thin silver film and deposition of an overlayer of commercial TiO2 nanoparticles. These synthetic photoanodes were characterized in view of the oxidation of a model organic compound glucose combined with the generation of hydrogen at a platinum cathode. During prolonged photoelectrolysis under simulated solar light, these photoanodes demonstrated high and stable photocurrents of ca. 4 mA cm−2 due, on one hand, to the occurrence of the so-called photocurrent doubling and, on the other hand, to the plasmonic effect of Ag nanoparticles. The post-photoelectrolysis analyses of the electrolyte demonstrated the formation of high-value final glucose photo-reforming products, principally gluconic acid, erythrose and formic acid. Full article
(This article belongs to the Special Issue Hydrogen Production and Evolution Based on Nanocatalysts)
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Figure 1
<p>(<b>a</b>) A cross-sectional SEM image of the WO<sub>3</sub>/Ag/TiO<sub>2</sub> film electrode. (<b>b</b>) The X-ray diffraction pattern of a WO<sub>3</sub> film annealed at 550 °C with a perfect monoclinic crystalline structure. (<b>c</b>) A top-view SEM image of the WO<sub>3</sub> film covered with silver nanoparticles. (<b>d</b>) A particle size distribution histogram of Ag NPs. (<b>e</b>) A top-view SEM image of the WO<sub>3</sub>/Ag/TiO film.</p>
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<p>(<b>a</b>) Absorbance spectra of FTO substrates: bare (black), with a TiO<sub>2</sub> layer (violet), with a WO<sub>3</sub> layer (red), with a TiO<sub>2</sub> and WO<sub>3</sub> bilayer (green), and with Ag nanoparticles placed between the WO<sub>3</sub> and TiO<sub>2</sub> layers. (<b>b</b>) Relative absorbance spectra of the Ag-enhanced photoanode related to the reference FTO/WO<sub>3</sub>/TiO<sub>2</sub> sample.</p>
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<p>IPCE spectra for WO<sub>3</sub>, TiO<sub>2</sub>, WO<sub>3</sub>/Ag/TiO<sub>2</sub>, and WO<sub>3</sub>/TiO<sub>2</sub> photoanodes measured at 0.6 V vs. Ag/AgCl in a 0.01 M NaCl/Na<sub>2</sub>SO<sub>4</sub> electrolyte of pH 7 containing 0.01 M glucose.</p>
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<p>The photo-currents of glucose oxidation measured during 5 h long electrolysis conducted at 0.6 V vs. Ag/AgCl in a 0.01 M NaCl/Na<sub>2</sub>SO<sub>4</sub> electrolyte of pH 7, using WO<sub>3</sub>/Ag/TiO<sub>2</sub> and WO<sub>3</sub>/TiO<sub>2</sub> photoanodes irradiated with simulated AM 1.5 G solar light.</p>
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<p>Photocurrent densities vs. imposed potential (j-E) plots in a 0.01 M NaCl/Na<sub>2</sub>SO<sub>4</sub> electrolyte of pH 7 containing 0.01 M glucose using WO<sub>3</sub>, TiO<sub>2</sub>, WO<sub>3</sub>/TiO<sub>2</sub> and WO<sub>3</sub>/Ag/TiO<sub>2</sub> recorded under simulated AM 1.5G irradiation.</p>
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<p>Photocurrent-potential plots for the WO<sub>3</sub>/Ag/TiO<sub>2</sub> electrode recorded in a 0.01 M NaCl/Na<sub>2</sub>SO<sub>4</sub> electrolyte of pH 7 with 0.01 M glucose under 3 sun illumination from the front side (black curve) and from the back side (red curve).</p>
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<p>Concentrations (<b>a</b>) and Faradaic yields (<b>b</b>) of glucose photo-reforming products collected after electrolysis performed following the conditions depicted in the legend of <a href="#nanomaterials-14-02001-f003" class="html-fig">Figure 3</a>.</p>
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<p>The proposed reaction pathway of glucose reforming over the WO<sub>3</sub>/Ag/TiO<sub>2</sub> photoanode; products quantified in this work are shown in blue. (<b>A</b>) main pathway; (<b>B</b>) parallel pathway.</p>
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<p>The preparation process of WO<sub>3</sub>/Ag/TiO<sub>2</sub> film electrodes used in glucose photo-reforming experiments.</p>
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19 pages, 3244 KiB  
Article
An Advanced Sensing Approach to Biological Toxins with Localized Surface Plasmon Resonance Spectroscopy Based on Their Unique Protein Quaternary Structures
by Hirotaka Uzawa, Satoshi Kondo, Takehiro Nagatsuka, Yasuo Seto and Yoshihiro Nishida
Int. J. Mol. Sci. 2024, 25(24), 13352; https://doi.org/10.3390/ijms252413352 - 12 Dec 2024
Viewed by 425
Abstract
Botulinum neurotoxins (BoNTs), ricin, and many other biological toxins are called AB toxins possessing heterogeneous A and B subunits. We propose herein a quick and safe sensing approach to AB toxins based on their unique quaternary structures. The proposed approach utilizes IgG antibodies [...] Read more.
Botulinum neurotoxins (BoNTs), ricin, and many other biological toxins are called AB toxins possessing heterogeneous A and B subunits. We propose herein a quick and safe sensing approach to AB toxins based on their unique quaternary structures. The proposed approach utilizes IgG antibodies against their A-subunits in combination with those human cell-membrane glycolipids that act as the natural ligands of B-subunits. In practice, an IgG antibody against the A-subunit of a target toxin is selected from commercially available sources and immobilized on the surface of Au nanoparticles to constitute a multivalent IgG/Au nanoconjugate. The derived IgG/Au conjugate is used in the pretreatment process of test samples for deactivating biological toxins in the form of a ternary toxin/antibody/Au complex. This process is implemented in advance to reduce the risk of handling biological toxins in laboratory work. On the other hand, the human glycolipid is immobilized on a tiny glass plate and used as a biosensor chip. The biosensor chip is set in the chamber of a flow sensing system using localized surface plasmon resonance (LSPR) spectrometry available in portable size at relatively low cost. In principle, the LSPR sensing system enables us to perform a rapid and selective detection for different kinds of biological toxins if the human glycolipid is correctly selected and installed in the sensing system. In the present LSPR sensing approach, a target AB toxin may have been deactivated during the pretreatment process. The test sample containing the deactivated AB toxin becomes a real target to be analyzed by the sensing system. In the present, we describe the concept of employing the commercially available IgG antibody in the pretreatment process followed by a typical procedure for converting it into the multivalent antibody/Au nanoconjugate and its preliminary applications in the LSPR detection of a ricin homologue (RCA120) and BoNTs in different serotypes. The tested LSPR sensing approach has worked very well for the ricin homologue and certain serotypes of botulinum neurotoxins like BoNT/A, indicating that the prior deactivation process at their A-domains causes no significant damage to the function of their B-domains with respect to determining the host cell-membrane glycolipid. The experimental results also indicated that LSPR responses from these pretreated AB toxins are significantly amplified. That is obviously thanks to the presence of Au nanoparticles in the multivalent IgG/Au nanoconjugate. We suggest in conclusion that the proposed LSPR sensing approach will provide us with a safe and useful tool for the study of biological AB toxins based on their unique quaternary protein structures. Full article
(This article belongs to the Collection Feature Papers in Molecular Nanoscience)
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Figure 1
<p>A representation of biological AB toxins: (<b>a</b>) BoNTs and (<b>b</b>) ricin (RCA<sub>60</sub>) and RCA<sub>120</sub>, in which molecular shapes and sizes are roughly shown.</p>
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<p>LSPR sensing approaches to AB toxins using a sensor chip coated with human glycolipids. (<b>a</b>) The sensor chip is incorporated in a flow LSPR sensing system, which has a UV/Vis spectrometer and a cuvette holder [<a href="#B21-ijms-25-13352" class="html-bibr">21</a>,<a href="#B22-ijms-25-13352" class="html-bibr">22</a>]. (<b>b</b>) A biosensor chip for BoNTs coated with GT1b-Cer glycolipids. The human glycolipid is immobilized on a tiny glass substrate and used to capture the target toxins on the glass surface discriminating their heavy chains (Hc) (B-subunit of AB toxins). (<b>c</b>) An advanced sensing approach to AB toxins, which utilizes a multivalent IgG antibody/Au nanoconjugate together with the biosensor chip. Those test samples which may contain BoNTs or other AB toxins are treated with this multivalent IgG/Au conjugate in advance to block their Lc domains acting as a main body of toxins. The target toxins are trapped on the sensor chip in a sandwiched manner and analyzed in the flow LSPR sensing system. A part of the illustration was adapted with permission from reference [<a href="#B23-ijms-25-13352" class="html-bibr">23</a>]. Copyright 2021 American Chemical Society.</p>
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<p>A flow LSPR sensing system used in the present study. The flow LSPR sensing system is assembled of two major parts. One is for flow, sample injection, and waste receiver. The second is the optical LSPR sensing system composed of UV-VIS light source (tungsten-halogen lamp), cuvette holder, photodetector, and PC processor. The cuvette holder has a room for setting a glycolipid/Au glass plate for use as biosensor chip.</p>
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<p>A local structure of antibody/Au nanoconjugate (Au conjugate-2) around an amide linkage between the oligo-EG linker and Lys in the antibody Fc domain.</p>
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<p>LSPR sensorgrams of RCA<sub>120</sub> measured at three different concentrations after the pretreatment process of mixing with the multivalent IgG/Au nanoconjugate to block the A-subunit acting as a main body of biological toxin. RCA<sub>120</sub> is used as a less toxic substitute of ricin (RCA<sub>60</sub>). Sensorgrams of negative controls (influenza hemagglutinin, BSA, and antibody/Au conjugate) measured at ca. 100 ng/mL are also shown. After the pretreatment process, each test sample (250 μL) was injected at 500 s (waiting time) and then delivered with running HEPES buffer at 4 mL/h and processed on a PC software (<a href="#sec3-ijms-25-13352" class="html-sec">Section 3</a>).</p>
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<p>LSPR sensorgram of BoNT/A after pretreatment with the multivalent IgG antibody/Au nanoconjugate. The other serotypes (B and E) of BoNTs are also tested as one of the negative controls as listed in <a href="#ijms-25-13352-t002" class="html-table">Table 2</a> and show together with the target BoNT/A. In this experiment, each test sample was treated with the multivalent conjugate in advance and injected into the flow LSPR system with a waiting time of 500 s and flow rate of 4 mL/h (<a href="#sec3-ijms-25-13352" class="html-sec">Section 3</a>). Typical LSPR data are shown when measurements were repeatedly conducted (<a href="#app1-ijms-25-13352" class="html-app">Table S1, Supplemental Materials</a>).</p>
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<p>LSPR sensorgram of (<b>a</b>) BoNT/B and (<b>b</b>) BoNT/E after treatment with the multivalent IgG/Au nanoconjugate of the corresponding anti (BoNT/Lc chain) IgG antibody (entries 7~10, <a href="#ijms-25-13352-t002" class="html-table">Table 2</a>). The two serotypes were equally analyzed with injection time of 500 s and flow rate of 4 mL/h (<a href="#sec3-ijms-25-13352" class="html-sec">Section 3</a>). Typical LSPR data are shown when measurements were repeatedly conducted (<a href="#app1-ijms-25-13352" class="html-app">Table S1, Supplemental Materials</a>).</p>
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<p>An LSPR sensor chip carrying human cell membrane glycolipid (GT1b-Cer) and its notable function to capture and determine a target botulinum neurotoxin in combination with a multivalent IgG antibody/Au nanoconjugate. A part of the illustration was adapted with permission from ref. [<a href="#B26-ijms-25-13352" class="html-bibr">26</a>]. Copyright 2023 American Chemical Society.</p>
Full article ">Scheme 1
<p>Preparation of multivalent antibody/Au conjugates using an oligo-ethylene glycol (EG) alkanethiol linker (HS-(CH<sub>2</sub>)<sub>11</sub>-EG<sub>6</sub>-OCH<sub>2</sub>-COONHS).</p>
Full article ">Scheme 2
<p>Conjugation reaction between IgG Lys-amino groups and NHS-activated carboxylic acids on Au nanoparticles to prepare multivalent IgG/Au nanoconjugate (Au conjugate-2).</p>
Full article ">Scheme 3
<p>A pretreatment process for each test sample with the multivalent IgG antibody/Au nanoconjugate prior to flow LSPR sensing analysis. Before being applied in the flow LSPR sensing system, a test sample containing a target AB toxin is mixed with a multivalent antibody/Au conjugate (Au conjugate-2) in HEPES buffer to block the A-subunit of the target toxin in the form of a ternary toxin/antibody/Au complex (Au conjugate-3).</p>
Full article ">
19 pages, 5820 KiB  
Article
Studying the Effect of Reducing Agents on the Properties of Gold Nanoparticles and Their Integration into Hyaluronic Acid Hydrogels
by Elżbieta Adamska, Agata Kowalska, Anna Wcisło, Katarzyna Zima and Beata Grobelna
Molecules 2024, 29(24), 5837; https://doi.org/10.3390/molecules29245837 - 11 Dec 2024
Viewed by 326
Abstract
Gold nanoparticles (Au NPs) are a promising target for research due to their small size and the resulting plasmonic properties, which depend, among other things, on the chosen reducer. This is important because removing excess substrate from the reaction mixture is problematic. However, [...] Read more.
Gold nanoparticles (Au NPs) are a promising target for research due to their small size and the resulting plasmonic properties, which depend, among other things, on the chosen reducer. This is important because removing excess substrate from the reaction mixture is problematic. However, Au NPs are an excellent component of various materials, enriching them with their unique features. One example is hydrogels, which provide a good, easily modifiable base for multiple applications such as cosmetics. For this purpose, various compounds, including hyaluronic acid (HA) and its derivatives, are distinguished by their high water-binding capacity and many characteristics resulting from their natural origin in organisms, including biocompatibility, biodegradability, and tissue regeneration. In this work Au NPs were synthesized using a green chemistry method, either by using onion extract as a reductant or chemically reducing them with sodium citrate. A complete characterization of the nanoparticles was carried out using the following methods: Fourier-Transform Infrared Spectroscopy (FT-IR), Electrophoretic (ELS), and Dynamic Light Scattering (DLS) as well as Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM). Their antioxidant activity was also tested using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH). The results showed that the synthesized nanoparticles enrich the hydrogels with antioxidant properties and new surface properties (depending on the reducing agent, they can be more hydrophilic or hydrophobic). Preliminary observations indicated low cytotoxicity of the nanomaterials in both liquid form and as a hydrogel component, as well as their lack of penetration through pig skin. The cosmetic properties of hydrogel masks were also confirmed, such as increasing skin hydration. Full article
(This article belongs to the Special Issue Synthesis of Nanomaterials and Their Applications in Biomedicine)
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Figure 1
<p>HPLC-UV chromatograms of onion extract acquired at 254 nm. Peak identification: 1—Gallic acid, 2—Myricetin, 3—Catechin, 4—Caffeic acid, 5—Quercetin, 6—Rutin.</p>
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<p>Synthesized colloids of Au NPs obtained with the reducer (<b>a</b>) onion extract; (<b>b</b>) sodium citrate.</p>
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<p>TEM images and diagrams of the particle diameter for Au NPs obtained using the reducer (<b>a</b>) onion extract; (<b>b</b>) sodium citrate on two scales: 50 and 200 nm.</p>
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<p>FT-IR spectra for Au NPs obtained using the reducer (<b>a</b>) onion extract, and (<b>b</b>) sodium citrate.</p>
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<p>DPPH radical scavenging activity of reducer and Au NPs obtained using onion extract ((<b>left</b>) diagram) and sodium citrate ((<b>right</b>) diagram) after 15 min, 1 h, and 1, 2, 3, 6, 7 days. Results are expressed in terms of mean ± SEM (<span class="html-italic">n</span> = 3).</p>
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<p>TEM images for hydrogel masks: (<b>a</b>) control and obtained using the reducer; (<b>b</b>) onion extract; (<b>c</b>) sodium citrate on a scale of 200 nm.</p>
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<p>SEM images for hydrogel masks: (<b>a</b>) control and obtained using the reducer; (<b>b</b>) onion extract; (<b>c</b>) sodium citrate with smaller (<b>left</b>) and larger (<b>right</b>) zoom.</p>
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<p>Water contact angle measurement results for: Au NPs obtained using the reducer (<b>a</b>) onion extract; (<b>b</b>) sodium citrate; (<b>c</b>) hydrogel mask (control, without NPs); (<b>d</b>) hydrogel mask Au NPs obtained using the onion extract; (<b>e</b>) hydrogel mask Au NPs obtained using the sodium citrate.</p>
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<p>Average results of (<b>a</b>) skin hydration level, (<b>b</b>) oil level, and (<b>c</b>) transepidermal water loss (TEWL), were obtained for the skin before, after 1 min, 15 min, and 1 week after applying a hydrogel mask (control, without NPs).</p>
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<p>The viability of the HaCaT epidermal cell line evaluated by the MTT assay after 24, 48, and 72 h of exposure to lower concentrations of (<b>a</b>) hydrogel citrate Au NPs, (<b>b</b>) hydrogel onion Au NPs, (<b>c</b>) liquid citrate Au NPs, and (<b>d</b>) liquid onion Au NPs. Data are expressed as mean values ± SD from three independent experiments. * <span class="html-italic">p</span> &lt; 0.05; ** <span class="html-italic">p</span> &lt; 0.01; *** <span class="html-italic">p</span> &lt; 0.001; **** <span class="html-italic">p</span> &lt; 0.0001 versus negative control (CTRL−). The positive control (CTRL+) was water for the liquid formulations or hydrogel without Au NPs for the hydrogel formulations.</p>
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<p>The viability of the HaCaT epidermal cell line evaluated by the MTT test after 24 h of exposure to high concentrations of (<b>a</b>) Au NPs citrate and (<b>b</b>) Au NPs onion. Data are expressed as mean values ± SD from three separate experiments. * <span class="html-italic">p</span> &lt; 0.05; ** <span class="html-italic">p</span> &lt; 0.01; **** <span class="html-italic">p</span> &lt; 0.0001 versus negative control (CTRL−). The positive control (CTRL+) was water for the liquid formulations.</p>
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<p>The IC<sub>50</sub> values calculated by a nonlinear regression analysis for HaCaT (<b>a</b>) Au NPs citrate; (<b>b</b>) Au NPs onion after 24 h of exposure to high concentrations. Data are expressed as means ± SD for three separate experiments. R<sup>2</sup>—coefficient of determination.</p>
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<p>Absorption spectra for Au NPs obtained using the reducer: (<b>a</b>) onion extract; (<b>b</b>) sodium citrate. 1—for the receiving solution from the Franz diffusion chamber and 2—for the solution of nanoparticles used as an ingredient in the hydrogel mask (initial).</p>
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<p>Scheme for obtaining HA-based hydrogels with Au NPs.</p>
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20 pages, 7845 KiB  
Article
Exploring Distinct Second-Order Data Approaches for Thiamine Quantification via Carbon Dot/Silver Nanoparticle FRET Reversion
by Rafael C. Castro, Ricardo N. M. J. Páscoa, M. Lúcia M. F. S. Saraiva, João L. M. Santos and David S. M. Ribeiro
Biosensors 2024, 14(12), 604; https://doi.org/10.3390/bios14120604 - 10 Dec 2024
Viewed by 346
Abstract
Accurate and selective monitoring of thiamine levels in multivitamin supplements is essential for preventing deficiencies and ensuring product quality. To achieve this, a Förster resonance energy transfer (FRET) system using carbon dots (CDs) as energy donors and citrate-stabilized silver nanoparticles (AgNPs) as energy [...] Read more.
Accurate and selective monitoring of thiamine levels in multivitamin supplements is essential for preventing deficiencies and ensuring product quality. To achieve this, a Förster resonance energy transfer (FRET) system using carbon dots (CDs) as energy donors and citrate-stabilized silver nanoparticles (AgNPs) as energy acceptors was developed. The aqueous synthesis of AgNPs using microwave irradiation was optimized to obtain efficient plasmonic nanoparticles for FRET applications, targeting maximal absorbance intensity, stability, and wavelength alignment. Using a central composite orthogonal design (CCOD), the optimal conditions were identified as a 12.5 min microwave reaction time, a Ag molar ratio of 0.72, and a pH of 8.28. The FRET sensing scheme was applied for thiamine determination, where the vitamin’s presence impaired the FRET process, restoring CDs’ photoluminescence (PL) emission in a concentration-dependent manner. To mitigate interference from other vitamins, PL kinetic data and excitation–emission matrix (EEM) data were analyzed using unfolded partial least-squares (U-PLS) with the subsequent application of the residual bilinearization technique (RBL), achieving high sensitivity and specificity for thiamine detection. This method demonstrated its accuracy and robustness by attaining a determination coefficient (R2) of 0.952 and a relative error of prediction (REP%) of 11%. This novel method offers highly sensitive and interference-free thiamine detection, with significant potential for a wide range of analytical applications. Full article
(This article belongs to the Special Issue Nanoparticle-Based Biosensors for Detection)
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<p>Influence of experimental conditions on the absorbance intensity of AgNPs and their stability over 4 weeks: (<b>a</b>) MW reaction time (from 2.5 to 25 min), (<b>b</b>) Ag–citrate molar ratio (from 0.14 to 7), and (<b>c</b>) pH (from 6 to 9).</p>
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<p>(<b>a</b>) CDs’ absorption spectrum. (<b>b</b>) PL decay curve of CDs fixing the emission wavelength at 436 nm. (<b>c</b>) EEM spectra of CD solution with excitation wavelengths varying from 320 to 390 nm (with increments of 3 nm) and emission wavelengths from 400 to 550 nm. (<b>d</b>) CDs’ PL emission spectrum excited at 351 nm.</p>
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<p>(<b>a</b>) Absorption spectrum of the optimized silver nanoparticles; (<b>b</b>) caption of video frames showing AgNPs diffracting during measurement; (<b>c</b>) size distribution profile AgNPs, derived from the average of five measurements obtained through NTA (video captures).</p>
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<p>Assessment of the acceptor–donor FRET system. (<b>a</b>) PL spectra of CDs with varying volumes of AgNPs; (<b>b</b>) Stern–Volmer plot demonstrating the PL intensity ratio of CDs with different volumes of AgNPs.</p>
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<p>(<b>a</b>,<b>b</b>) Normalized absorption (grey line) and emission (blue line) spectra of citrate-stabilized AgNPs and CDs, respectively, displayed as a function of wavelength (<b>a</b>) and energy (<b>b</b>); (<b>c</b>) PL decay curves of CDs with varying volumes of AgNPs; (<b>d</b>) Stern–Volmer plot exhibiting the PL lifetimes ratio of CDs with different volumes of AgNPs.</p>
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<p>(<b>a</b>) PL emission spectra recorded after the addition of thiamine to AgNP–CD FRET assembly; (<b>b</b>) linear correlation between the PL signal recovery (<span class="html-italic">F/F<sub>0</sub></span>) and thiamine concentration.</p>
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<p>(<b>a</b>) Absorption and (<b>b</b>) emission spectra of AgNPs and CDs, respectively, upon adding increasing concentrations of thiamine.</p>
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<p>Three-dimensional (<b>a</b>,<b>b</b>) and two-dimensional (<b>c</b>,<b>d</b>) representations of PL emission plotted against wavelength and time for the AgNP–CD FRET system (<b>a</b>,<b>c</b>) and the interaction between the AgNP–CD FRET system and 1.25 mmol L<sup>−1</sup> of thiamine calibration solution (<b>b</b>,<b>d</b>).</p>
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<p>Thiamine calibration curve plot using kinetic fluorescence data and U-PLS.</p>
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<p>Three-dimensional (<b>a</b>,<b>b</b>) and two-dimensional (<b>c</b>,<b>d</b>) plots of the PL emission as a function of excitation wavelength and emission wavelength of AgNP–CD FRET system (<b>a</b>,<b>c</b>) and upon the interaction between the FRET system and 1.25 mmol L<sup>−1</sup> of thiamine calibration solution (<b>b</b>,<b>d</b>).</p>
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<p>Thiamine calibration curve plot using EEM fluorescence data and U-PLS.</p>
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14 pages, 2039 KiB  
Article
Widening of Dynamic Detection Range in Real-Time Angular-Interrogation Surface Plasmon Resonance Biosensor Based on Anisotropic Van Der Waals Heterojunction
by Xiantong Yu, Jing Ouyang, Zhao Li, Chaojun Shi, Longfei Wang, Jun Zhou and Min Chang
Biosensors 2024, 14(12), 601; https://doi.org/10.3390/bios14120601 - 8 Dec 2024
Viewed by 404
Abstract
Surface plasmon resonance (SPR) biosensors have experienced rapid development in recent years and have been widely applied in various fields. Angular-interrogation SPR biosensors play an important role in the field of biological detection due to their advantages of reliable results and high stability. [...] Read more.
Surface plasmon resonance (SPR) biosensors have experienced rapid development in recent years and have been widely applied in various fields. Angular-interrogation SPR biosensors play an important role in the field of biological detection due to their advantages of reliable results and high stability. However, angular-interrogation SPR biosensors also suffer from low detection sensitivity, poor real-time performance, and limited dynamic detection range, which seriously restricts their application and promotion. Therefore, we designed an angular-interrogation SPR biosensor based on black phosphorus (BP)/graphene two-dimensional (2D) van der Waals heterojunction (vdWhs). On the basis of using the angle-fixed method, this biosensor not only has good real-time performance but also detection sensitivity enhancement. The optical anisotropy characteristic of BP is used to widen the dynamic detection range of biosensors. The simulation results show that the maximum detection sensitivity of the proposed biosensor is 258.6 deg/RIU. Compared with the bare-Ag film structure biosensor, the detection sensitivity was enhanced by 209.2% by 2D vdWhs. The use of anisotropic 2D material BP can not only enhance the detection sensitivity but also widen the detection range. When the fixed incident angle is θ = 5 deg, a maximum dynamic detection range enhanced factor of 123.1% can be achieved, and a detection sensitivity of 185.2 deg/RIU in the corresponding interval can be obtained. The proposed biosensor in this study has potential broad application prospects in several fields, such as biological detection. Full article
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<p>Schematic diagram of 2D vdWhs-enhanced SPR device. The reflectance spectrum image in the figure (top right), with pseudo color representing the intensity distribution of the reflected light, and blue to red indicating the strength of the reflected light intensity.</p>
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<p>(<b>A</b>): The variation in reflectivity vs. the incident angle by varying different thicknesses of Ag film. The refractive index of the sample medium layer is set to 1.330 with an excitation wavelength of 632.8 nm. The layer number of the BP is five. (<b>B</b>): The variation in reflectivity vs. the incident angle by varying different BP layer numbers. The refractive index of the sample medium is set to 1.330 with an excitation wavelength of 632.8 nm. The thickness of the Ag film is 45 nm.</p>
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<p>(<b>A</b>): The variation in detection sensitivity <span class="html-italic">S</span> vs. the different BP layer numbers by varying different thicknesses of Ag film. The refractive index of the sample medium is set to 1.330–1.380 with an excitation wavelength at 632.8 nm. (<b>B</b>): The variation in <span class="html-italic">FOM</span> vs. the different BP layer numbers by varying different thicknesses of Ag film. The refractive index of the sample medium is set to 1.330–1.380 with an excitation wavelength of 632.8 nm.</p>
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<p>(<b>A</b>): The variation in detection sensitivity <span class="html-italic">S</span> vs. the angle <span class="html-italic">φ</span>. The refractive index of the sample medium is set to 1.330–1.380 with an excitation wavelength of 632.8 nm. (<b>B</b>): The variation in the SPR resonance angle <span class="html-italic">θ</span> vs. the refractive index of the sample by varying different BP layer numbers. The thickness of the Ag film is fixed at 53 nm with an excitation wavelength of 632.8 nm.</p>
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<p>(<b>A</b>): The electric field intensity distribution; (<b>B</b>) the y-component distribution of the electric field. The thickness of the Ag film is 50 nm, and the thickness of the BP and graphene is five-layer and monolayer, respectively, with an excitation wavelength of 632.8 nm.</p>
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<p>(<b>A</b>): The variation in the SPR resonance angle within <span class="html-italic">φ</span> for the range of 0–90 deg. (<b>B</b>) The variation in the SPR resonance angle within <span class="html-italic">φ</span> for the range of 90–180 deg. The thickness of the Ag film is 45 nm, and the thickness of the BP and graphene is five-layer and monolayer, respectively, with an excitation wavelength of 632.8 nm.</p>
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<p>(<b>A</b>): The variation in the reflectivity vs. the incident angle by the refractive index of the sample is 1.330 and 1.358 in <span class="html-italic">φ</span> = 80 deg. (<b>B</b>): The variation in the reflectivity vs. the incident angle by the refractive index of the sample is 1.335 and 1.363 in <span class="html-italic">φ</span> = 75 deg. With an excitation wavelength of 632.8 nm. The thickness of the Ag film is 45 nm, and the thickness of the BP and graphene is five-layer and monolayer, respectively.</p>
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<p>The SPR spectra and light intensity distribution as the refractive index of the detection medium of the proposed biosensors: (<b>A</b>), 1.330; (<b>B</b>), 1.341; (<b>C</b>), 1.352; (<b>D</b>), 1.363. The thickness of the Ag film is 45 nm, and the thickness of the BP and graphene is five-layer and monolayer, respectively, with an excitation wavelength of 632.8 nm.</p>
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18 pages, 2264 KiB  
Review
Advancements in Detection Methods for Salmonella in Food: A Comprehensive Review
by Aayushi Patel, Andrew Wolfram and Taseen S. Desin
Pathogens 2024, 13(12), 1075; https://doi.org/10.3390/pathogens13121075 - 7 Dec 2024
Viewed by 993
Abstract
Non-typhoidal Salmonella species are one of the leading causes of gastrointestinal disease in North America, leading to a significant burden on the healthcare system resulting in a huge economic impact. Consequently, early detection of Salmonella species in the food supply, in accordance with [...] Read more.
Non-typhoidal Salmonella species are one of the leading causes of gastrointestinal disease in North America, leading to a significant burden on the healthcare system resulting in a huge economic impact. Consequently, early detection of Salmonella species in the food supply, in accordance with food safety regulations, is crucial for protecting public health, preventing outbreaks, and avoiding serious economic losses. A variety of techniques have been employed to detect the presence of this pathogen in the food supply, including culture-based, immunological, and molecular methods. The present review summarizes these methods and highlights recent updates on promising emerging technologies, including aptasensors, Surface Plasmon Resonance (SPR), and Surface Enhanced Raman Spectroscopy (SERS). Full article
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<p>Schematic illustration of aptamer-based electrochemical biosensor construction used for detection of <span class="html-italic">Salmonella</span>. GCE was modified with GO and GNPs for biocompatibility and high electron transfer properties. Then, thiolated aptamer ssDNA was attached to the surface, capable of capturing <span class="html-italic">Salmonella</span>. Created in BioRender. Wolfram, A. (2024) <a href="https://BioRender.com/r18r866" target="_blank">https://BioRender.com/r18r866</a> (accessed on 23 November 2024).</p>
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<p>Schematic representation of the detection of bacteria using the gold nanoparticle-aptamer-based localized surface plasmon resonance (SPR) sensing chip. Created in BioRender. Wolfram, A. (2024) <a href="https://BioRender.com/c38m504" target="_blank">https://BioRender.com/c38m504</a> (accessed on 5 December 2024).</p>
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<p>Schematic illustration of the CRISPR-SERS biosensor. DNA was extracted from <span class="html-italic">S.</span> Typhimurium and used to trigger the CRISPR system after binding with Cas12a-crRNA duplex for cleavage. The Raman signal reporter consists of ssDNA and Rox molecular which will be cleaved to decrease Raman intensity following wash out from SERS substrate. Without <span class="html-italic">S.</span> Typhimurium present, Cas12a/ccRNA would not initiate the cleavage activity of the probe, resulting in no detectable change in the Raman signal. Created in BioRender. Wolfram, A. (2024) <a href="https://BioRender.com/k99l567" target="_blank">https://BioRender.com/k99l567</a> (accessed on 23 November 2024).</p>
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<p>Schematic illustration of a bacteriophage detecting, infecting, and lysing bacteria like <span class="html-italic">Salmonella</span>. Created in BioRender. Wolfram, A. (2024) <a href="https://BioRender.com/g33l156" target="_blank">https://BioRender.com/g33l156</a> (accessed on 23 November 2024).</p>
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<p>A comparison of the Limits of Detection (LoD) across various technologies used for the Detection of <span class="html-italic">Salmonella</span> species. All LoDs were converted to CFU/mL from CFU/g using 1g to 1 mL conversion based on the density of water.</p>
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<p>A comparison of the total time required across various technologies used for the detection of <span class="html-italic">Salmonella</span> species. The average reported detection time for each method (including any enrichment time) was used to create this chart.</p>
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<p>Factoring both Limits of Detection (LoD) and total detection time (including enrichment) for comparison of the various detection methods of <span class="html-italic">Salmonella</span> species. Lower total values have lower LoDs and total detection times. All LoDs were converted to CFU/mL from CFU/g using 1 g to 1 mL conversion based on the density of water.</p>
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13 pages, 2174 KiB  
Article
Leveraging Femtosecond Laser Ablation for Tunable Near-Infrared Optical Properties in MoS2-Gold Nanocomposites
by Ilya A. Zavidovskiy, Ilya V. Martynov, Daniil I. Tselikov, Alexander V. Syuy, Anton A. Popov, Sergey M. Novikov, Andrei V. Kabashin, Aleksey V. Arsenin, Gleb I. Tselikov, Valentyn S. Volkov and Alexey D. Bolshakov
Nanomaterials 2024, 14(23), 1961; https://doi.org/10.3390/nano14231961 - 6 Dec 2024
Viewed by 521
Abstract
Transition metal dichalcogenides (TMDCs), particularly molybdenum disulfide (MoS2), have gained significant attention in the field of optoelectronics and photonics due to their unique electronic and optical properties. The integration of TMDCs with plasmonic materials allows to tailor the optical response and [...] Read more.
Transition metal dichalcogenides (TMDCs), particularly molybdenum disulfide (MoS2), have gained significant attention in the field of optoelectronics and photonics due to their unique electronic and optical properties. The integration of TMDCs with plasmonic materials allows to tailor the optical response and offers significant advantages for photonic applications. This study presents a novel approach to synthesize MoS2-Au nanocomposites utilizing femtosecond laser ablation in liquid to achieve tunable optical properties in the near-infrared (NIR) region. By adjusting ablation and fragmentation protocols, we successfully synthesize various core–shell and core–shell–satellite nanoparticle composites, such as MoS2/MoSxOy, MoSxOy/Au, and MoS2/MoSxOy/Au. UV-visible absorption spectroscopy unveils considerable changes in the optical response of the particles depending on the fabrication regime due to structural modifications. Hybrid nanoparticles exhibit enhanced photothermal properties when subjected to NIR-I laser irradiation, demonstrating potential benefits for selective photothermal therapy. Our findings underscore that the engineered nanocomposites not only facilitate green synthesis but also pave the way for tailored therapeutic applications, highlighting their role as promising candidates in the field of nanophotonics and cancer treatment. Full article
(This article belongs to the Special Issue Optical Composites, Nanophotonics and Metamaterials)
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<p>Schematic representation of the one-, two-, and three-step processes as well as solution mixing for the synthesis of pristine and hybrid MoS<sub>2</sub>/Au NPs.</p>
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<p>TEM characterization of one-step synthesized NPs. (<b>a</b>,<b>d</b>) TEM images of the ablated MoS<sub>2</sub> (<b>a</b>) and Au (<b>d</b>) NPs. Scale bar, 50 nm. (<b>b</b>,<b>e</b>) Size distributions of MoS<sub>2</sub> (<b>b</b>) and Au (<b>e</b>) NPs. (<b>c</b>,<b>f</b>) SAED patterns of MoS<sub>2</sub> (<b>c</b>) and Au (<b>f</b>) NPs.</p>
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<p>Characterization of two- and three-step synthesized NPs and Raman spectroscopy data. TEM images of (<b>a</b>) “Au in MoS<sub>2</sub>”, (<b>b</b>)“MoS<sub>2</sub> in Au”, and (<b>c</b>) “MoS<sub>2</sub>:Au co-fragmented” NPs. Scale bar, 50 nm. Size distributions of (<b>d</b>) “Au in MoS<sub>2</sub>”, (<b>e</b>) “MoS<sub>2</sub> in Au”, and (<b>f</b>) “MoS<sub>2</sub>:Au co-fragmented” NPs. Turquoise bars represent Au NPs, while orange bars represent MoS<sub>2</sub>-based NPs. (<b>g</b>) Raman spectra of the NPs. Violet, brown- and green-colored numbers indicate the positions of the peaks related to MoS<sub>2</sub>, MoS<sub>x</sub>O<sub>y</sub>, and MoO<sub>x</sub>, respectively. Inset shows the magnified low-intensity peaks of the MoS<sub>2</sub> sample.</p>
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<p>High-angle annular dark-field imaging (upper left panels) and EDX maps of “MoS<sub>2</sub>” (<b>a</b>), “MoS<sub>2</sub> in Au” (<b>b</b>), and “Au in MoS<sub>2</sub>” (<b>c</b>) NPs. Scale bar, 20 nm.</p>
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<p>Optical absorption and photoheating. (<b>a</b>) UV-visible extinction spectra. Red dotted line indicates the photoheating laser wavelength. (<b>b</b>–<b>g</b>) Photoheating dynamics. ΔT<sub>max</sub> and PCE notations indicate the values of maximum temperature increases observed throughout the heating and photothermal conversion efficiencies. The plots are presented in the following order: (<b>b</b>) MoS2, (<b>c</b>) Au, (<b>d</b>) MoS<sub>2</sub> in Au, (<b>e</b>) Au in MoS<sub>2</sub>, (<b>f</b>) MoS<sub>2</sub>:Au co-fragmented, (<b>g</b>) MoS<sub>2</sub>+Au.</p>
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12 pages, 10856 KiB  
Article
Multi-Resonant Full-Solar-Spectrum Perfect Metamaterial Absorber
by Zhe Shen and Junfan Ni
Nanomaterials 2024, 14(23), 1959; https://doi.org/10.3390/nano14231959 - 6 Dec 2024
Viewed by 359
Abstract
Currently, perfect absorption properties of metamaterials have attracted widespread interest in the area of solar energy. Ultra-broadband absorption, incidence angle insensitivity, and polarization independence are key performance indicators in the design of the absorbers. In this work, we proposed a metamaterial absorber based [...] Read more.
Currently, perfect absorption properties of metamaterials have attracted widespread interest in the area of solar energy. Ultra-broadband absorption, incidence angle insensitivity, and polarization independence are key performance indicators in the design of the absorbers. In this work, we proposed a metamaterial absorber based on the absorption mechanism with multiple resonances, including propagation surface plasmon resonance (PSPR), localized surface plasmon resonance (LSPR), electric dipole resonance (EDR), and magnetic dipole resonance (MDR). The absorber, consisting of composite nanocylinders and a microcavity, can perform solar energy full-spectrum absorption. The proposed absorber obtained high absorption (>95%) from 272 nm to 2742 nm at normal incidence. The weighted absorption rate of the absorber at air mass 1.5 direct in the wavelength range of 280 nm to 3000 nm exceeds 98.5%. The ultra-broadband perfect absorption can be ascribed to the interaction of those resonances. The photothermal conversion efficiency of the absorber reaches 85.3% at 375 K. By analyzing the influence of the structural parameters on the absorption efficiency, the absorber exhibits excellent fault tolerance. In addition, the designed absorber is insensitive to polarization and variation in ambient refractive index and has an absorption rate of more than 80% at the incident angle of 50°. Our proposed absorber has great application potential in solar energy collection, photothermal conversion, and other related areas. Full article
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<p>(<b>a</b>) Schematic diagram of the proposed metamaterial absorber. Side (<b>b</b>) and top (<b>c</b>) view of the absorber unit.</p>
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<p>(<b>a</b>) The absorption spectrum of the absorber under normal incidence. (<b>b</b>) The absorption spectrum on the scale of absorption rate from 0.75 to 1. (<b>c</b>) The distribution of solar energy and energy absorbed by the absorber at AM 1.5D. (<b>d</b>) Solar energy is absorbed and unabsorbed by the absorber at AM 1.5D.</p>
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<p>Thermal emission spectrum of the absorber (red) and the ideal blackbody (black) from 2.5 µm to 20 µm at 375 K (dotted line) and 425 K (solid line).</p>
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<p>Electric field (<b>a</b>,<b>d</b>,<b>f</b>,<b>h</b>) and magnetic field (<b>b</b>,<b>e</b>,<b>g</b>,<b>i</b>) distributions of the metamaterial absorber in the x-z plane at 332 nm, 532 nm, 940 nm, and 2400 nm, respectively. (<b>c</b>) Charge and electrical field line distributions in the x-y plane at the red line in (<b>a</b>). The green color framed by the black dotted lines in (<b>a</b>) represents two pairs of local electric fields.</p>
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<p>(<b>a</b>) Absorption spectrum of the absorber (red), and the absorber without the SiO<sub>2</sub> layer (gray), and without composite nanocylinder (blue). (<b>b</b>) The absorption spectrum of the absorbers with the number of TiN nanodisk layers from 1 to 4.</p>
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<p>(<b>a</b>–<b>d</b>) Electric field distributions of the metamaterial absorbers with numbers of TiN nanodisk layers from 1 to 4 in the x-z plane at 2400 nm.</p>
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<p>(<b>a</b>–<b>d</b>) are absorption spectrum under the four cases of different thicknesses of SiO<sub>2</sub> nanodisk (h<sub>1</sub>), TiN nanodisk (h<sub>2</sub>), TiN film (h<sub>3</sub>), and SiO<sub>2</sub> film (h<sub>4</sub>).</p>
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<p>Absorption spectrum map of the absorbers at different structure periods (<b>a</b>) and nanocylinder radius (<b>b</b>). The write dotted lines donate the resonance wavelengths.</p>
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<p>(<b>a</b>) The absorption spectrum map of the absorber at different polarization angles (0–90°) of incidence. Absorption spectrum map of the absorber to different angles (0–70°) of incidence in TM mode (<b>b</b>) and TE mode (<b>c</b>).</p>
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<p>The absorption spectrum of the absorber at ambient refractive indexes from 1 to 1.3.</p>
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15 pages, 3030 KiB  
Article
Impact of Plant Species on the Synthesis and Characterization of Biogenic Silver Nanoparticles: A Comparative Study of Brassica oleracea, Corylus avellana, and Camellia sinensis
by Gülçin Demirel Bayik and Busenur Baykal
Nanomaterials 2024, 14(23), 1954; https://doi.org/10.3390/nano14231954 - 5 Dec 2024
Viewed by 419
Abstract
The choice of plant species is crucial, as different plants provide unique biomolecules that influence nanoparticle characteristics. Biomolecules in plant extracts, such as proteins, amino acids, enzymes, polysaccharides, alkaloids, tannins, phenolics, saponins, terpenoids, and vitamins, act as stabilizing and reducing agents. This study [...] Read more.
The choice of plant species is crucial, as different plants provide unique biomolecules that influence nanoparticle characteristics. Biomolecules in plant extracts, such as proteins, amino acids, enzymes, polysaccharides, alkaloids, tannins, phenolics, saponins, terpenoids, and vitamins, act as stabilizing and reducing agents. This study explores the synthesis of silver nanoparticles (AgNPs) using leaf extracts from collard greens (Brassica oleracea var. acephala), hazelnut (Corylus avellana var. avellana), and green tea (Camellia sinensis). NPs were synthesized using silver nitrate (AgNO3) solution at two different molarities (1 mM and 5 mM) and characterized by UV–Vis spectroscopy, XRD, TEM, and FTIR. The Surface Plasmon Resonance (SPR) peaks appeared rapidly for hazelnut and green tea extracts, within 30 and 15 min, respectively, while collard greens extract failed to produce a distinct SPR peak. X-Ray Diffraction confirmed the formation of face-centered cubic silver. TEM analysis revealed high polydispersity and agglomeration in all samples, with particle size generally decreasing at higher AgNO3 concentrations. However, hazelnut extract showed a slight increase in size at higher molarity. Among all samples, green tea-derived AgNPs synthesized with 5 mM AgNO3 were the smallest and least polydisperse, highlighting the significant role of plant type in optimizing nanoparticle synthesis. Full article
(This article belongs to the Section Synthesis, Interfaces and Nanostructures)
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<p>Absorption spectra of nanoparticles synthesized by collard greens extract (<b>a</b>,<b>c</b>) 1 mM AgNO<sub>3</sub>; (<b>b</b>,<b>d</b>) 5 mM AgNO<sub>3</sub>.</p>
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<p>Absorption spectra of nanoparticles synthesized by collard greens extract (<b>a</b>,<b>c</b>) 1 mM AgNO<sub>3</sub>; (<b>b</b>,<b>d</b>) 5 mM AgNO<sub>3</sub>.</p>
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<p>Absorption spectra of nanoparticles synthesized by hazelnut extract (<b>a</b>,<b>c</b>) 1 mM AgNO<sub>3</sub>; (<b>b</b>,<b>d</b>) 5 mM AgNO<sub>3</sub>.</p>
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<p>Absorption spectra of nanoparticles synthesized by greentea extract (<b>a</b>,<b>c</b>) 1 mM AgNO<sub>3</sub>; (<b>b</b>,<b>d</b>) 5 mM AgNO<sub>3</sub>.</p>
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<p>XRD patterns of produced nanoparticles (<b>a</b>) 1 mM three plant species; (<b>b</b>) 5 mM three plant species.</p>
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<p>TEM, particle size distribution, and EDX spectrum of nanoparticles.</p>
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<p>FTIR spectra of produced AgNPs.</p>
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16 pages, 15984 KiB  
Article
Development of a Portable Optomechatronic System to Obtain the Characterization of Transparent Materials and Dielectric Thin Films
by Araceli Sánchez-Alvarez, Osvaldo Rodríguez-Quiroz, Gabriela Elizabeth Quintanilla-Villanueva, Melissa Marlene Rodríguez-Delgado, Juan Francisco Villarreal-Chiu, Oscar Javier Silva-Hernández and Donato Luna-Moreno
Optics 2024, 5(4), 595-610; https://doi.org/10.3390/opt5040044 - 5 Dec 2024
Viewed by 512
Abstract
This paper outlines the design and fabrication of a portable optomechatronic system based on the theta-2theta configuration, which explores various optical characterization techniques for transparent materials and dielectric thin films. These techniques include Brewster angle and Abelès-Brewster angle measurements, critical angle measurements, and [...] Read more.
This paper outlines the design and fabrication of a portable optomechatronic system based on the theta-2theta configuration, which explores various optical characterization techniques for transparent materials and dielectric thin films. These techniques include Brewster angle and Abelès-Brewster angle measurements, critical angle measurements, and the surface plasmon resonance technique. The system consists of a mechanical assembly of rotating stages, a semiconductor laser, a photodiode connected to a data acquisition card, and a user interface for controlling the stepper motor rotation stages. Utilizing a BK7 substrate, the motorized stage achieved a resolution of 0.010. The Brewster angle measured was 56.550, with a refractive index (n) of 1.5137. The relative error obtained was Δn/n = 3.82 × 10−4, with a sensitivity of 164.27 RIU/degree and an accuracy of 0.37/degree. Furthermore, the discrepancies between theoretical and experimental refractive indices for different prisms at 639 nm ranged from ±7 × 10−4 to ±73 × 10−4. After testing various samples, the system demonstrated its capability to perform fast, precise, and non-invasive measurements. Its portability allows for use in diverse environments and applications. Full article
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<p>Reflectance curve for a BK7 glass prism (<span class="html-italic">n</span> = 1.5149 at λ = 639 nm); the critical angle (<math display="inline"><semantics> <mrow> <msub> <mrow> <mi>θ</mi> </mrow> <mrow> <mi>C</mi> </mrow> </msub> </mrow> </semantics></math>) is at 41.3082 degrees, and for a SF6 glass prism (<span class="html-italic">n</span> = 1.7981 at λ = 639 nm) with an <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>θ</mi> </mrow> <mrow> <mi>C</mi> </mrow> </msub> </mrow> </semantics></math> = 33.7894.</p>
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<p>Reflectance curve of an interface of air (n = 1)/glass FS (fused silica, n = 1.4568), BK7 (n = 1.5149), SK16 (n = 1.6180), and SF6 (n = 1.7981) at λ = 639 nm, where the refractive index is related by the minimum reflectance angle (Brewster angle) at 55.53°, 56.57°, 58.28°, and 60.92°, respectively.</p>
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<p>Reflectance curve of a BK7 glass substrate and a step-shaped layer of MgF<sub>2</sub> (n = 1.3769 at λ = 639 nm) coating with thicknesses of 100, 250, and 500 nm. The intersection of the curves is at <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>θ</mi> </mrow> <mrow> <mi>B</mi> </mrow> </msub> <mo>=</mo> <mn>54.01</mn> <mo>°</mo> </mrow> </semantics></math>.</p>
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<p>SPR curve for different prisms: (<b>a</b>) FS and BK7 and (<b>b</b>) SK16 and SF6, with a 50 nm thickness gold coating (N = 0.1736–i3.4930 at λ = 639 nm) and an air and distilled water sample (n = 1.3314 at λ = 639 nm) for each.</p>
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<p>(<b>a</b>) Reflectance of an SPR sensor having a laser at 639 nm, a BK7 prism, a gold film (50 nm), and a distilled water sample. The edge angle of total internal reflection is <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>θ</mi> </mrow> <mrow> <mi>M</mi> </mrow> </msub> </mrow> </semantics></math> = 61.5070<math display="inline"><semantics> <mrow> <mo>°</mo> </mrow> </semantics></math>, the initial angle from full width to half maximum (FWHM) is <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>θ</mi> </mrow> <mrow> <mi>F</mi> <mi>W</mi> <mi>H</mi> <mi>M</mi> <mo>−</mo> <mi>L</mi> </mrow> </msub> <mo>=</mo> <mn>69.5993</mn> <mo>°</mo> <mo>,</mo> </mrow> </semantics></math> and the resonance angle is <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>θ</mi> </mrow> <mrow> <mi>r</mi> </mrow> </msub> </mrow> </semantics></math> = 71.5820° and <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>θ</mi> </mrow> <mrow> <mi>m</mi> </mrow> </msub> </mrow> </semantics></math> = π/2+ i|−0.3963| and is calculated by Snell’s law. (<b>b</b>) <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>n</mi> </mrow> <mrow> <mi>e</mi> <mi>f</mi> <mi>f</mi> </mrow> </msub> </mrow> </semantics></math> calculated from the filling percentage (0%, 5%, 10%, 15%, 20%, 25%) of the spherical particles (<math display="inline"><semantics> <mrow> <msub> <mrow> <mi>d</mi> </mrow> <mrow> <mi>p</mi> <mi>a</mi> <mi>r</mi> <mi>t</mi> </mrow> </msub> </mrow> </semantics></math> = 100 nm) of PS added to the distilled water. (<b>c</b>) <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>n</mi> </mrow> <mrow> <mi>e</mi> <mi>f</mi> <mi>f</mi> </mrow> </msub> </mrow> </semantics></math> corresponding to the number concentration. (<b>d</b>) Reflectance for the first three calculated <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>n</mi> </mrow> <mrow> <mi>e</mi> <mi>f</mi> <mi>f</mi> </mrow> </msub> </mrow> </semantics></math> (0%, 5%, 10%).</p>
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<p>SPR system. (<b>a</b>) Portable optomechatronic system; A, diode laser; B, linear polarizer; C, sample mount; D, photodiode container; E, motorized rotary stages; F, sheet metal cabinet; (<b>b</b>) photography of the SPR system.</p>
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<p>General system architecture.</p>
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<p>The alignment process. (<b>A</b>): retroreflection at 0 degrees.; (<b>B</b>): reflection at grazing incidence, 180 degrees; (<b>C</b>): initial reflection at 30 degrees.</p>
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<p>User interface. Real-time graph of reflected light of the flat surface of a BK7 prism.</p>
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<p>Critical angle measurements for a BK7 prism.</p>
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<p>Experimental Brewster angle measurement of FK5 (56.07°), BK7 (56.55°), SK16 (58.21°), and SF6 (60.82°) prisms and the estimation of their refractive index (1.4865, 1.5137, 1.6135, 1.7908, respectively, at λ = 639 nm).</p>
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<p>Reflectance measurement of a BK7 glass substrate and a step with MgF<sub>2</sub> coating. The Brewster angle of the MgF<sub>2</sub> film is the point where the reflectance curves coincide.</p>
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<p>Experimental SPR curves for (<b>a</b>) a BK7 prism/Au(50 nm)/air and (<b>b</b>) a BK7 prism/Cr(3 nm)/Au(50 nm)/air.</p>
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<p>Immobilization of laccases of the BK7 prism with a Cr/Au coating.</p>
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<p>(<b>a</b>) Theoretical distilled water sample (dotted blue line); experimental distilled water sample as reference (red line); and experimental sample of water with 100 nm diameter polystyrene particles (magenta line). (<b>b</b>) Obtaining the filling fraction (4.08%) from <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>n</mi> </mrow> <mrow> <mi>e</mi> <mi>f</mi> <mi>f</mi> </mrow> </msub> </mrow> </semantics></math> = 1.3418 RIU calculated from <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>θ</mi> </mrow> <mrow> <mi>r</mi> </mrow> </msub> </mrow> </semantics></math> = 71.7920°. Note: The experimental signals are aligned with the theoretical reference signal of distilled water.</p>
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<p>SPR curve related to the FK5 prism with an Ag coating and a microplastic solution of 0.1 and 1 µm of diameter.</p>
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11 pages, 4723 KiB  
Article
Phonon-Induced Wake Potential in a Graphene–Insulator –Graphene Structure
by Ana Kalinić, Ivan Radović, Lazar Karbunar, Vito Despoja and Zoran L. Mišković
Nanomaterials 2024, 14(23), 1951; https://doi.org/10.3390/nano14231951 - 5 Dec 2024
Viewed by 378
Abstract
The aim of this study is to explore the potential which arises in a graphene–insulator–graphene structure when an external charged particle is moving parallel to it with a speed smaller than the Fermi speed in graphene. This is achieved by employing the dynamic [...] Read more.
The aim of this study is to explore the potential which arises in a graphene–insulator–graphene structure when an external charged particle is moving parallel to it with a speed smaller than the Fermi speed in graphene. This is achieved by employing the dynamic polarization function of graphene within the random phase approximation, where its π electrons are modeled as Dirac fermions, and utilizing a local dielectric function for bulk insulators. Three different insulators are considered: SiO2, HfO2, and Al2O3. It is observed that the wake potential is induced by the surface optical phonons originating from the insulator layer, and that total potential could be effectively decomposed into two components, each corresponding to different phonon branches, as long as those branches do not interact amongst themselves. Full article
(This article belongs to the Section Theory and Simulation of Nanostructures)
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<p>Illustration of the graphene–insulator–graphene setup featuring a point charge, <math display="inline"><semantics> <mrow> <mi>Z</mi> <mi>e</mi> </mrow> </semantics></math>, moving parallel to the <math display="inline"><semantics> <mi>x</mi> </semantics></math>-axis at a steady velocity <math display="inline"><semantics> <mrow> <mi>v</mi> <mo>,</mo> </mrow> </semantics></math> positioned at a consistent distance <math display="inline"><semantics> <mi>b</mi> </semantics></math> above the upper graphene layer. The polarization function of the top graphene layer situated in the <math display="inline"><semantics> <mrow> <msub> <mi>z</mi> <mn>2</mn> </msub> <mo>=</mo> <mrow> <mi>a</mi> <mo>/</mo> <mn>2</mn> </mrow> </mrow> </semantics></math> plane is denoted as <math display="inline"><semantics> <mrow> <msub> <mi>χ</mi> <mn>2</mn> </msub> <mo>,</mo> </mrow> </semantics></math> while that of the bottom layer at <math display="inline"><semantics> <mrow> <msub> <mi>z</mi> <mn>1</mn> </msub> <mo>=</mo> <mo>−</mo> <mrow> <mi>a</mi> <mo>/</mo> <mn>2</mn> </mrow> </mrow> </semantics></math> is represented by <math display="inline"><semantics> <mrow> <msub> <mi>χ</mi> <mn>1</mn> </msub> <mo>.</mo> </mrow> </semantics></math> The dielectric layer with a thickness of <math display="inline"><semantics> <mi>a</mi> </semantics></math> is characterized by its local dielectric function <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mi>s</mi> </msub> <mo stretchy="false">(</mo> <mi>ω</mi> <mo stretchy="false">)</mo> </mrow> </semantics></math>.</p>
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<p>The loss function <math display="inline"><semantics> <mrow> <mi>Im</mi> <mo stretchy="false">[</mo> <mo>−</mo> <mrow> <mn>1</mn> <mo>/</mo> <mrow> <mi>ε</mi> <mo stretchy="false">(</mo> <mi>q</mi> <mo>,</mo> <mi>ω</mi> <mo stretchy="false">)</mo> </mrow> </mrow> <mo stretchy="false">]</mo> </mrow> </semantics></math> (in arbitrary units) as a function of the wave number <math display="inline"><semantics> <mi>q</mi> </semantics></math> (in nm<sup>−1</sup>) and the excitation frequency <math display="inline"><semantics> <mi>ω</mi> </semantics></math> (in eV) for the graphene–insulator–graphene composite systems where the insulator is (<b>a</b>) SiO<sub>2</sub>, (<b>b</b>) HfO<sub>2</sub>, and (<b>c</b>) Al<sub>2</sub>O<sub>3</sub>. The magenta dotted lines depict the dispersion relations of three odd <math display="inline"><semantics> <mrow> <mo stretchy="false">(</mo> <msubsup> <mi>ω</mi> <mi>i</mi> <mo>−</mo> </msubsup> <mo>;</mo> <mo> </mo> <mi>i</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mn>2</mn> <mo>,</mo> <mn>3</mn> <mo stretchy="false">)</mo> </mrow> </semantics></math> plasmon–phonon modes, whereas the white dotted lines depict the dispersion relations of three even <math display="inline"><semantics> <mrow> <mo stretchy="false">(</mo> <msubsup> <mi>ω</mi> <mi>i</mi> <mo>+</mo> </msubsup> <mo>;</mo> <mo> </mo> <mi>i</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mn>2</mn> <mo>,</mo> <mn>3</mn> <mo stretchy="false">)</mo> </mrow> </semantics></math> plasmon–phonon modes. The white solid lines indicate the lower edge <math display="inline"><semantics> <mrow> <mo stretchy="false">(</mo> <mi>ω</mi> <mo>=</mo> <msub> <mi>v</mi> <mi>F</mi> </msub> <mo stretchy="false">(</mo> <mi>q</mi> <mo>−</mo> <mn>2</mn> <msub> <mi>k</mi> <mi>F</mi> </msub> <mo stretchy="false">)</mo> <mo stretchy="false">)</mo> </mrow> </semantics></math> and the upper edge <math display="inline"><semantics> <mrow> <mo stretchy="false">(</mo> <mi>ω</mi> <mo>=</mo> <msub> <mi>v</mi> <mi>F</mi> </msub> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </semantics></math> of the intraband <math display="inline"><semantics> <mrow> <mi>π</mi> <mo>*</mo> <mo>↔</mo> <mi>π</mi> <mo>*</mo> </mrow> </semantics></math> electron–hole excitations, in addition to the lower edge <math display="inline"><semantics> <mrow> <mo stretchy="false">(</mo> <mi>ω</mi> <mo>=</mo> <mn>2</mn> <msub> <mi>E</mi> <mi>F</mi> </msub> <mo>−</mo> <msub> <mi>v</mi> <mi>F</mi> </msub> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </semantics></math> of the interband <math display="inline"><semantics> <mrow> <mi>π</mi> <mo>↔</mo> <mi>π</mi> <mo>*</mo> </mrow> </semantics></math> electron–hole excitations in the Dirac cone approximation. The white dashed lines represent the <math display="inline"><semantics> <mrow> <mi>ω</mi> <mo>=</mo> <mn>0.5</mn> <msub> <mi>v</mi> <mi>F</mi> </msub> <mi>q</mi> </mrow> </semantics></math> lines, helping to visualize their intersections (marked with <math display="inline"><semantics> <mrow> <msubsup> <mi>q</mi> <mi>c</mi> <mrow> <mo stretchy="false">(</mo> <mi>i</mi> <mo stretchy="false">)</mo> </mrow> </msubsup> <mo>;</mo> <mo> </mo> <mi>i</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mn>2</mn> </mrow> </semantics></math>) with eigenmodes that contribute to the wake potential.</p>
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<p>The wake potential (in V) as a function of the <math display="inline"><semantics> <mrow> <mi>x</mi> <mo>−</mo> <mi>v</mi> <mi>t</mi> </mrow> </semantics></math> (in nm) with <math display="inline"><semantics> <mrow> <mi>y</mi> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math> in the graphene–insulator–graphene composite systems where the insulator is (<b>a</b>) SiO<sub>2</sub>, (<b>b</b>) HfO<sub>2</sub>, and (<b>c</b>) Al<sub>2</sub>O<sub>3</sub>. The thin black lines show total potential <math display="inline"><semantics> <mrow> <mo stretchy="false">(</mo> <msub> <mo>Φ</mo> <mrow> <mi>t</mi> <mi>o</mi> <mi>t</mi> </mrow> </msub> <mo stretchy="false">)</mo> </mrow> </semantics></math>, the medium red lines show potential when only the first phonon is observed <math display="inline"><semantics> <mrow> <mo stretchy="false">(</mo> <msubsup> <mo>Φ</mo> <mrow> <mi>t</mi> <mi>o</mi> <mi>t</mi> </mrow> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> </msubsup> <mo stretchy="false">)</mo> </mrow> </semantics></math>, the thick blue lines show potential when only the second phonon is present <math display="inline"><semantics> <mrow> <mo stretchy="false">(</mo> <msubsup> <mo>Φ</mo> <mrow> <mi>t</mi> <mi>o</mi> <mi>t</mi> </mrow> <mrow> <mo stretchy="false">(</mo> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </msubsup> <mo stretchy="false">)</mo> </mrow> </semantics></math>, and the green dotted lines are the sum of the red and the blue ones <math display="inline"><semantics> <mrow> <mo stretchy="false">(</mo> <msubsup> <mo>Φ</mo> <mrow> <mi>t</mi> <mi>o</mi> <mi>t</mi> </mrow> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> </msubsup> <mo>+</mo> <msubsup> <mo>Φ</mo> <mrow> <mi>t</mi> <mi>o</mi> <mi>t</mi> </mrow> <mrow> <mo stretchy="false">(</mo> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </msubsup> <mo stretchy="false">)</mo> </mrow> </semantics></math>. The characteristic wavelengths <math display="inline"><semantics> <mrow> <mo stretchy="false">(</mo> <msubsup> <mi>λ</mi> <mi>c</mi> <mrow> <mo stretchy="false">(</mo> <mi>i</mi> <mo stretchy="false">)</mo> </mrow> </msubsup> <mo>;</mo> <mo> </mo> <mi>i</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </semantics></math> are highlighted.</p>
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21 pages, 7677 KiB  
Article
Thermo-Responsive and Electroconductive Nano Au-PNiPAAm Hydrogel Nanocomposites: Influence of Synthesis Method and Nanoparticle Shape on Physicochemical Properties
by Nikolina Radojković, Jelena Spasojević, Zorica Kačarević-Popović, Una Stamenović, Vesna Vodnik, Goran Roglić and Aleksandra Radosavljević
Polymers 2024, 16(23), 3416; https://doi.org/10.3390/polym16233416 - 5 Dec 2024
Viewed by 537
Abstract
Hydrogel nanocomposites that respond to external stimuli and possess switchable electrical properties are considered as emerging materials with potential uses in electrical, electrochemical, and biological devices. This work reports the synthesis and characterization of thermo-responsive and electroconductive hydrogel nanocomposites based on poly(N [...] Read more.
Hydrogel nanocomposites that respond to external stimuli and possess switchable electrical properties are considered as emerging materials with potential uses in electrical, electrochemical, and biological devices. This work reports the synthesis and characterization of thermo-responsive and electroconductive hydrogel nanocomposites based on poly(N-isopropylacrylamide) (PNiPAAm) and gold nanoparticles (nanospheres—AuNPs and nanorods—AuNRs) using two different synthetic techniques. Method I involved γ-irradiation-induced crosslinking of a polymer matrix (hydrogel), followed by radiolytic in situ formation of gold nanoparticles, while Method II included the chemical synthesis of nanoparticles, followed by radiolytic formation of a polymer matrix around the gold nanoparticles. UV–Vis spectral studies revealed the presence of local surface plasmon resonance (LSPR) bands characteristic of nanoparticles of different shapes, confirming their formation and stability inside the polymer matrix. Morphological, structural, and physicochemical analyses indicated the existence of a stable porous polymer matrix, the formation of nanoparticles with a face-centered cubic structure, increased swelling capacity, and a slightly higher volume phase transition temperature (VPTT) for the hydrogel nanocomposites. Comparative electrochemical impedance spectroscopy (EIS) showed an increase in conductivity for the nano Au-PNiPAAm hydrogel nanocomposites compared to the PNiPAAm hydrogel, with a considerable rise detected above the VPTT. By reverting to room temperature, the conductivity decreased, indicating that the investigated hydrogel nanocomposites exhibited a remarkable reversible “on–off” thermo-switchable mechanism. The highest conductivity was observed for the sample with rod-shaped gold nanoparticles. The research findings, which include optical, structural, morphological, and physicochemical characterization, evaluation of the efficiency of the chosen synthesis methods, and conductivity testing, provide a starting point for future research on the given nanocomposite materials with integrated multifunctionality. Full article
(This article belongs to the Special Issue Polymer Hydrogels: Synthesis, Properties and Applications)
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<p>Schematic representation of synthesis: Method I (<b>a</b>), Method II (<b>b</b>), and photographs of nano Au-PNiPAAm hydrogel nanocomposites obtained by Method II (<b>c</b>).</p>
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<p>UV–Vis absorption spectra of AuNPs-PNiPAAm (<b>a</b>) and AuNRs-PNiPAAm (<b>b</b>) hydrogel nanocomposites obtained by Method I.</p>
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<p>UV–Vis absorption spectra of chemically synthesized colloidal dispersion of AuNPs and AuNRs (<b>a</b>), AuNPs-PNiPAAm (<b>b</b>), and AuNRs-PNiPAAm (<b>c</b>) hydrogel nanocomposites obtained by Method II.</p>
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<p>TEM micrographs of chemically synthesized AuNPs (<b>a</b>) and AuNRs (<b>b</b>), with corresponding particle size distribution (PSD, (<b>a</b>,<b>b</b>) upper-left insets), HRTEM images ((<b>a</b>,<b>b</b>) upper-right insets), and SAED ((<b>a</b>,<b>b</b>) lower-right insets), and FE-SEM micrographs of the AuNPs-PNiPAAm hydrogel nanocomposites obtained by the Method I (<b>c</b>) and AuNRs-PNiPAAm hydrogel nanocomposites obtained by the Method II (<b>d</b>).</p>
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<p>The swelling behavior (<b>a</b>–<b>c</b>), temperature dependence of <span class="html-italic">SD<sub>eq</sub></span> (<b>d</b>–<b>f</b>), and deswelling curves (<b>g</b>–<b>i</b>) of AuNPs-PNiPAAm and AuNRs-PNiPAAm hydrogel nanocomposites.</p>
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<p>XRD patterns (<b>a</b>) and FTIR spectra (<b>b</b>) of nano Au-PNiPAAm hydrogel nanocomposites.</p>
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<p>Bode plots of the impedance magnitude (<b>a</b>–<b>c</b>) and Nyquist plots for the real and the imaginary impedances (<b>d</b>–<b>f</b>) for PNiPAAm hydrogel and AuNPs-PNiPAAm and AuNRs-PNiPAAm hydrogel nanocomposites (c(NPs) = 2.5 × 10<sup>−4</sup> mol/dm<sup>3</sup>) obtained by Method II (<span style="color:red">•</span> Initial T = 25 °C, <span style="color:#5BDF41">•</span> T = 40 °C, <span style="color:#0C2DF4">•</span> Final T = 25 °C).</p>
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<p>An equivalent electrical circuit used for the impedance plot fitting of the hydrogel nanocomposites.</p>
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<p>The electrical conductivity (<b>a</b>) and resistance (<b>b</b>) of PNiPAAm hydrogel and nano Au-PNiPAAm hydrogel nanocomposites.</p>
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10 pages, 1980 KiB  
Article
Gain Saturation of Encapsulated CdTe-Ag Quantum Dot Composite in SiO2
by Minwoo Kim, Agna Antony, Inhong Kim, Minju Kim and Kwangseuk Kyhm
Nanomaterials 2024, 14(23), 1950; https://doi.org/10.3390/nano14231950 - 4 Dec 2024
Viewed by 558
Abstract
Amplified spontaneous emission of CdTe and CdTe-Ag quantum dot composites were compared for increasing the optical stripe length, whereby optical gain coefficients for various emission wavelengths were obtained. In the case of CdTe-Ag nanoparticle composites, we observed that plasmonic coupling causes both optical [...] Read more.
Amplified spontaneous emission of CdTe and CdTe-Ag quantum dot composites were compared for increasing the optical stripe length, whereby optical gain coefficients for various emission wavelengths were obtained. In the case of CdTe-Ag nanoparticle composites, we observed that plasmonic coupling causes both optical enhancement and quenching at different wavelengths, where the amplified spontaneous emission intensity becomes enhanced at short wavelengths but suppressed at long wavelengths (>600 nm). To analyze the logistic stripe length dependence of amplified spontaneous emission intensity, we used a differential method to obtain the gain coefficient beyond the amplification range. This analysis enabled us to find the limit of the commonly used fitting method in terms of a threshold length and a saturation length, where amplification begins and saturation ends, respectively. Full article
(This article belongs to the Section Nanophotonics Materials and Devices)
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<p>(<b>a</b>) CdTe-Ag QD composites encapsulated with SiO<sub>2</sub> are shown schematically with a Scanning Electron Microscopy (SEM) image. (<b>b</b>) The absorption spectrum of CdTe QDs, Ag QDs, and QD composites with 1:1 (CdTe:Ag) and 1:10 ratios. (<b>c</b>) The intensity distribution of an optical stripe. (<b>d</b>) The experimental setup of the VSLM for<math display="inline"><semantics> <mrow> <mtext> </mtext> <mi>x</mi> <mo>≈</mo> <mn>0</mn> <mtext> </mtext> </mrow> </semantics></math>and <math display="inline"><semantics> <mrow> <mi>x</mi> <mo>&gt;</mo> <mn>0</mn> </mrow> </semantics></math>.</p>
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<p>(<b>a</b>) Edge emission spectrum of CdTe QDs for increasing stripe lengths at 4 K. Inset shows edge emission at 0 <math display="inline"><semantics> <mrow> <mi mathvariant="sans-serif">μ</mi> </mrow> </semantics></math>m stripe length. (<b>b</b>) <math display="inline"><semantics> <mrow> <mi>d</mi> <mi>I</mi> <mo>(</mo> <mi>λ</mi> <mo>,</mo> <mi>x</mi> <mo>)</mo> <mo>/</mo> <mi>d</mi> <mi>x</mi> </mrow> </semantics></math> spectrum at different stripe lengths. (<b>c</b>) Stripe length-dependent edge emission intensity at various wavelengths. Inset shows edge emission intensity in log scale. (<b>d</b>) Stripe length dependence of <math display="inline"><semantics> <mrow> <mi>d</mi> <mi>I</mi> <mo>(</mo> <mi>λ</mi> <mo>,</mo> <mi>x</mi> <mo>)</mo> <mo>/</mo> <mi>d</mi> <mi>x</mi> </mrow> </semantics></math> at different wavelengths. Short stripe length range (<span class="html-italic">x</span> &lt; <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>x</mi> </mrow> <mrow> <mi mathvariant="normal">t</mi> <mi mathvariant="normal">h</mi> </mrow> </msub> </mrow> </semantics></math>) is shown in inset.</p>
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<p>(<b>a</b>) Edge emission spectrum of CdTe QDs and CdTe-Ag QD composites at 1:1 and 1:10 ratios. (<b>b</b>) Stripe length dependence of edge emission intensity (in log scale) selected at wavelength of 730 nm for CdTe QDs and CdTe-Ag QD composites at 1:1 and 1:10 ratios. (<b>c</b>) Variation of <math display="inline"><semantics> <mrow> <mi>d</mi> <mi>I</mi> <mo>(</mo> <mi>λ</mi> <mo>,</mo> <mi>x</mi> <mo>)</mo> <mo>/</mo> <mi>d</mi> <mi>x</mi> </mrow> </semantics></math> with stripe length for CdTe QDs and CdTe-Ag QD composites at 1:1 and 1:10 ratios at wavelength of 730 nm. (<b>d</b>–<b>f</b>) Gain spectrum of CdTe QDs and CdTe-Ag QD composite at 1:1 and 1:10 ratios obtained using fitting method shown in Equation (2) and differential method shown in Equation (3).</p>
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