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Nanomaterials-Based Sensors for Biomedical Monitoring
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Nanomaterials-Based Sensors for Biomedical Monitoring

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Biosensors".

Deadline for manuscript submissions: closed (25 December 2024) | Viewed by 8130

Special Issue Editor

Dr. Claudia Lopes

E-Mail Website
Guest Editor
Centro de Física das Universidades do Minho e Porto, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal
Interests: nanomaterials; biomedical sensing; nanotecnology; flexible dry-electrodes

Special Issue Information

Dear Colleagues,

The development of new optimized sensing devices is crucial for modern preventive medicine, being primarily responsible for high-resolution monitoring of human biochemical and bioelectrical activity. New approaches based on flexible devices easily integrated into wearable technologies with improved biomedical sensing performance are key to diversifying and expanding the application of non-invasive physiological monitoring in new opportunities.

For the medical device industry, it is very important to obtain the right type of sensor, which lasts for a long time and assists in recording high-quality signals. The design of the base unit is one of the most critical aspects of biomedical sensor reliability. The sensor comprises the first stage of the signal chain and, therefore, plays a key role in the overall noise and performance of the acquisition system. It is very difficult (almost impossible) to improve the fidelity and signal-to-noise ratio of the signal beyond this point.

The ability to produce new materials sculpted at the nanoscale offers the possibility to target very specific functions with biocompatibility, lightness, comfort, and integrated usability. Based on the success of nanotechnology applied to biomedical sensors, this specific topic of the Special Issue aims to bring an improved and significant contribution to the field of sensing, including, but not limited to, the following topics:

  • Nanomaterials-based sensors for bioelectrical detection;
  • Nanomaterials-based sensors for biochemical detection;
  • New technologies applied to the development of nanomaterials-based sensors;
  • New designs for biomedical health monitoring systems.

Dr. Claudia Lopes
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sensors is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • nanomaterials synthesis
  • thin films
  • biomedical sensing
  • chemical, biological and physical sensors
  • physiological monitoring
  • wearable devices
  • preventive medicine and diagnosis
  • rehabilitation

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Further information on MDPI's Special Issue polices can be found here.

Published Papers (4 papers)

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Research

15 pages, 2400 KiB  
Article
Design of Bio-Optical Transceiver for In Vivo Biomedical Sensor Applications
by Dimitrios Makrakis, Oussama Abderrahmane Dambri and Abdelhakim Senhaji Hafid
Sensors 2024, 24(8), 2584; https://doi.org/10.3390/s24082584 - 18 Apr 2024
Viewed by 1857
Abstract
This paper presents an enhanced version of our previously developed bio-optical transceiver, presenting a significant advancement in nanosensor technology. Using self-assembled polymers, this nanodevice is capable of electron detection while maintaining biocompatibility, an essential feature for in vivo medical biosensors. This enhancement finds [...] Read more.
This paper presents an enhanced version of our previously developed bio-optical transceiver, presenting a significant advancement in nanosensor technology. Using self-assembled polymers, this nanodevice is capable of electron detection while maintaining biocompatibility, an essential feature for in vivo medical biosensors. This enhancement finds significance in the field of infectious disease control, particularly in the early detection of respiratory viruses, including high-threat pathogens such as SARS-CoV-2. The proposed system harnesses bioluminescence by converting electric signaling to visible blue light, effectively opening the path of linking nano-sized mechanisms to larger-scale systems, thereby pushing the boundaries of in vivo biomedical sensing. The performance evaluation of our technology is analytical and is based on the use of Markov chains, through which we assess the bit error probability. The calculated improvements indicate that this technology qualifies as a forerunner in terms of supporting the communication needs of smaller, safer, and more efficient manufactured sensor technologies for in vivo medical applications. Full article
(This article belongs to the Special Issue Nanomaterials-Based Sensors for Biomedical Monitoring)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>The designed bio-optical transceiver for wired nano-communication networks.</p> Full article ">Figure 2
<p>The Decision Feedback version of the proposed ISD receiver; D represents a 1-bit delay storage unit.</p> Full article ">Figure 3
<p>The Markov chain of the studied scenario, where <span class="html-italic">L</span> = 1 for the proposed DF receiver.</p> Full article ">Figure 4
<p>Bit error probability as function of SNR in dB for ISD and DF versions when opening 1000 calcium channels.</p> Full article ">Figure 5
<p>Bit error probability as function of SNR in dB for the DF version when opening different numbers of calcium channels.</p> Full article ">
14 pages, 1396 KiB  
Article
Dopamine Measurement Using Engineered CNT–CQD–Polymer Coatings on Pt Microelectrodes
by Mahdieh Darroudi, Kevin A. White, Matthew A. Crocker and Brian N. Kim
Sensors 2024, 24(6), 1893; https://doi.org/10.3390/s24061893 - 15 Mar 2024
Cited by 2 | Viewed by 1859
Abstract
This study aims to develop a microelectrode array-based neural probe that can record dopamine activity with high stability and sensitivity. To mimic the high stability of the gold standard method (carbon fiber electrodes), the microfabricated platinum microelectrode is coated with carbon-based nanomaterials. Carboxyl-functionalized [...] Read more.
This study aims to develop a microelectrode array-based neural probe that can record dopamine activity with high stability and sensitivity. To mimic the high stability of the gold standard method (carbon fiber electrodes), the microfabricated platinum microelectrode is coated with carbon-based nanomaterials. Carboxyl-functionalized multi-walled carbon nanotubes (COOH-MWCNTs) and carbon quantum dots (CQDs) were selected for this purpose, while a conductive polymer like poly (3-4-ethylene dioxythiophene) (PEDOT) or polypyrrole (PPy) serves as a stable interface between the platinum of the electrode and the carbon-based nanomaterials through a co-electrodeposition process. Based on our comparison between different conducting polymers and the addition of CQD, the CNT–CQD–PPy modified microelectrode outperforms its counterparts: CNT–CQD–PEDOT, CNT–PPy, CNT–PEDOT, and bare Pt microelectrode. The CNT–CQD–PPy modified microelectrode has a higher conductivity, stability, and sensitivity while achieving a remarkable limit of detection (LOD) of 35.20 ± 0.77 nM. Using fast-scan cyclic voltammetry (FSCV), these modified electrodes successfully measured dopamine’s redox peaks while exhibiting consistent and reliable responses over extensive use. This electrode modification not only paves the way for real-time, precise dopamine sensing using microfabricated electrodes but also offers a novel electrochemical sensor for in vivo studies of neural network dynamics and neurological disorders. Full article
(This article belongs to the Special Issue Nanomaterials-Based Sensors for Biomedical Monitoring)
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Figure 1

Figure 1
<p>Carbonized Pt microelectrode fabrication for FSCV-based dopamine detection. Photographs of (<b>a</b>) the probe and (<b>b</b>) tip of the probe taken using a Zeiss Examiner; schematic views of (<b>c</b>) the microfabricated Pt microelectrode and (<b>d</b>) the carbonized Pt microelectrode, 30 × 100 μm; and micrographs of (<b>e</b>) the bare Pt microelectrode and (<b>f</b>) carbonized Pt microelectrode, 30 × 100 μm.</p> Full article ">Figure 2
<p>Electrodeposition of carbon-based nanomaterials on Pt microelectrodes. Photographs of the (<b>a</b>) entire microelectrode assembly (5×); (<b>b</b>) bare Pt microelectrode (100 × 30 μm) before nanocomposite deposition (50×); and (<b>c</b>) CNT–PPy, (<b>d</b>) CNT–PEDOT, (<b>e</b>) CNT–CQD–PPy, and (<b>f</b>) CNT–CQDs–PEDOT layers uniformly deposited on the Pt microelectrode (50×). These images were taken using a Zeiss Examiner.</p> Full article ">Figure 3
<p>SEM images of CNT–CQD–PPy coated onto a Pt microelectrode (the scales are (<b>a</b>) 20 µm, (<b>b</b>) 1 µm, and (<b>c</b>) 200 nm) and (<b>d</b>) their EDAX analysis. SEM images of CNT–CQD–PEDOT coated onto a Pt microelectrode (the scales are (<b>e</b>) 20 µm, (<b>f</b>) 1 µm, and (<b>g</b>) 400 nm), and (<b>h</b>) their EDAX analysis.</p> Full article ">Figure 4
<p>Electrochemical analysis of nanocomposite-coated Pt microelectrodes: (<b>a</b>) CV diagrams at a scan rate of 100 mV/s; (<b>b</b>) FSCV of CNT–PPy, CNT–CQD–PPy, and Pt bare microelectrodes at a scan rate of 300 V/s; (<b>c</b>) FSCV of CNT–PEDOT, CNT–CQD–PEDOT, and Pt bare microelectrodes at a scan rate of 300 V/s.</p> Full article ">Figure 5
<p>Comparative Analysis of the CNT–CQD–PPy and CNT–CQD–PEDOT layers on Pt microelectrodes: (<b>a</b>) background-subtracted FSCVs with 1 μM dopamine, (<b>b</b>) background charging current (average background charging current (<span class="html-italic">n</span> = 3)), (<b>c</b>) mean anodic and cathodic peak currents with 1 μM dopamine (<span class="html-italic">n</span> = 3), and the experimental scan rate performance for (<b>d</b>) CNT–CQD–PPy (<span class="html-italic">n</span> = 3) and (<b>e</b>) CNT–CQD–PEDOT (<span class="html-italic">n</span> = 3) at a scan rate of 300 V/s.</p> Full article ">Figure 6
<p>Concentration dependence analysis. The dopamine sensitivity for (<b>a</b>) the CNT–CQD–PPy layer and (<b>b</b>) the CNT–CQD–PEDOT layer. The relationship between the anodic peak current and dopamine concentration for (<b>c</b>) the CNT–CQD–PPy layer and (<b>d</b>) the CNT–CQD–PEDOT layer. Both plots demonstrate a linear response within the 100 nM to 1 μM dopamine concentration range (<span class="html-italic">n</span> = 3) at a scan rate of 300 V/s.</p> Full article ">Figure 7
<p>Evaluation of electrode stability. Stability testing in PBS (1X) for (<b>a</b>) CNT–CQD–PPy (over a four-hour period, <span class="html-italic">n</span> = 3) and (<b>b</b>) CNT–CQD–PEDOT (over a one-hour period, <span class="html-italic">n</span> = 3). Continuous waveform application and measurements were performed within potential windows of −0.3 to 1.2 V at a scan rate of 300 V/s. Every 30 min, the microelectrodes were observed using an optical microscope. Microscopic images of the electrode before and after the stability test for (<b>c</b>) CNT–CQD–PPy and (<b>d</b>) CNT–CQD–PEDOT. Weekly repeated background-subtracted FSCV stability tests for (<b>e</b>) CNT–CQD–PPy and (<b>f</b>) CNT–CQD–PEDOT. Measurements were obtained at 7-day intervals within potential windows of −0.5 to 1.5 V at a scan rate of 300 V/s (<span class="html-italic">n</span> = 3). The arrows indicate the direction of drift during the stability test.</p> Full article ">
12 pages, 3917 KiB  
Article
Simultaneous Dry and Gel-Based High-Density Electroencephalography Recordings
by Patrique Fiedler, Uwe Graichen, Ellen Zimmer and Jens Haueisen
Sensors 2023, 23(24), 9745; https://doi.org/10.3390/s23249745 - 11 Dec 2023
Cited by 2 | Viewed by 2100
Abstract
Evaluations of new dry, high-density EEG caps have only been performed so far with serial measurements and not with simultaneous (parallel) measurements. For a first comparison of gel-based and dry electrode performance in simultaneous high-density EEG measurements, we developed a new EEG cap [...] Read more.
Evaluations of new dry, high-density EEG caps have only been performed so far with serial measurements and not with simultaneous (parallel) measurements. For a first comparison of gel-based and dry electrode performance in simultaneous high-density EEG measurements, we developed a new EEG cap comprising 64 gel-based and 64 dry electrodes and performed simultaneous measurements on ten volunteers. We analyzed electrode–skin impedances, resting state EEG, triggered eye blinks, and visual evoked potentials (VEPs). To overcome the issue of different electrode positions in the comparison of simultaneous measurements, we performed spatial frequency analysis of the simultaneously measured EEGs using spatial harmonic analysis (SPHARA). The impedances were 516 ± 429 kOhm (mean ± std) for the dry electrodes and 14 ± 8 kOhm for the gel-based electrodes. For the dry EEG electrodes, we obtained a channel reliability of 77%. We observed no differences between dry and gel-based recordings for the alpha peak frequency and the alpha power amplitude, as well as for the VEP peak amplitudes and latencies. For the VEP, the RMSD and the correlation coefficient between the gel-based and dry recordings were 1.7 ± 0.7 μV and 0.97 ± 0.03, respectively. We observed no differences in the cumulative power distributions of the spatial frequency components for the N75 and P100 VEP peaks. The differences for the N145 VEP peak were attributed to the different noise characteristics of gel-based and dry recordings. In conclusion, we provide evidence for the equivalence of simultaneous dry and gel-based high-density EEG measurements. Full article
(This article belongs to the Special Issue Nanomaterials-Based Sensors for Biomedical Monitoring)
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Figure 1

Figure 1
<p>Photos of the assembled EEG cap on a volunteer (<b>a</b>), the dry multipin electrode (<b>b</b>), the commercial gel-based electrode (<b>c</b>), and the equidistant layout of the 64 gel-based (blue) and 64 dry (green) EEG channels (<b>d</b>).</p> Full article ">Figure 2
<p>Topographic distribution of the electrode–skin impedances of (<b>a</b>) the dry electrodes and (<b>b</b>) the gel-based electrodes shown at their respective individual location subsets.</p> Full article ">Figure 3
<p>Power spectral density (<b>a</b>) in the frequency range from 1 Hz to 40 Hz for the gel-based (blue) and dry (green) electrodes (solid lines: median; dotted lines: 25% and 75% quartiles). The grand average 2D interpolated topographic plots for the gel-based (<b>b</b>) and dry (<b>c</b>) electrodes show the alpha band power (shaded band area in (<b>a</b>)).</p> Full article ">Figure 4
<p>Overlay plot of spontaneous EEG recordings for the gel-based (blue) and dry (green) electrodes with triggered eye blinks of an exemplary volunteer recorded by the frontal electrodes at the 1L, 1LC, 1R, and 1RC positions and filtered by 1–40 Hz: (<b>a</b>) overlay of 50 s, and (<b>b</b>) overlay of 5 s.</p> Full article ">Figure 5
<p>The grand average of the pattern reversal visual evoked potential: (<b>a</b>,<b>b</b>) butterfly plots of gel-based (blue) and dry (green) electrodes, and (<b>c</b>) 2D interpolated topographic mapping of the three main peaks of the VEP (normalized to the respective maximum amplitude).</p> Full article ">Figure 6
<p>SPHARA analysis of the three main VEP peaks. Plots of the normalized cumulative power contributions of the spatial frequency components determined via SPHARA decomposition for the three main VEP peaks. (<b>a</b>) N75, (<b>b</b>) P100, and (<b>c</b>) N145 are displayed, recorded with gel-based (blue) and dry (green) electrodes.</p> Full article ">
16 pages, 4485 KiB  
Article
Enhancing the Longevity and Functionality of Ti-Ag Dry Electrodes for Remote Biomedical Applications: A Comprehensive Study
by Daniel Carvalho, Sandra Marques, Giorgia Siqueira, Armando Ferreira, João Santos, Dulce Geraldo, Cidália R. Castro, Ana V. Machado, Filipe Vaz and Cláudia Lopes
Sensors 2023, 23(19), 8321; https://doi.org/10.3390/s23198321 - 8 Oct 2023
Cited by 2 | Viewed by 1727
Abstract
This study aims to evaluate the lifespan of Ti-Ag dry electrodes prepared using flexible polytetrafluoroethylene (PTFE) substrates. Following previous studies, the electrodes were designed to be integrated into wearables for remote electromyography (EMG) monitoring and electrical stimulation (FES) therapy. Four types of Ti-Ag [...] Read more.
This study aims to evaluate the lifespan of Ti-Ag dry electrodes prepared using flexible polytetrafluoroethylene (PTFE) substrates. Following previous studies, the electrodes were designed to be integrated into wearables for remote electromyography (EMG) monitoring and electrical stimulation (FES) therapy. Four types of Ti-Ag electrodes were prepared by DC magnetron sputtering, using a pure-Ti target doped with a growing number of Ag pellets. After extensive characterization of their chemical composition and (micro)structural evolution, the Ti-Ag electrodes were immersed in an artificial sweat solution (standard ISO-3160-2) at 37 °C with constant stirring. Results revealed that all the Ti-Ag electrodes maintained their integrity and functionality for 24 h. Although there was a notable increase in electrical resistivity beyond this timeframe, the acquisition and transmission of (bio)signals remained viable for electrodes with Ag/Ti ratios below 0.23. However, electrodes with higher Ag content (Ag/Ti = 0.31) became insulators after 7 days of immersion due to excessive Ag release into the sweat solution. This study concludes that higher Ag/Ti atomic ratios result in heightened corrosion processes on the electrode’s surface, consequently diminishing their lifespan despite the advantages of incorporating Ag into their composition. This research highlights the critical importance of evaluating electrode longevity, especially in remote biomedical applications like smart wearables, where electrode performance over time is crucial for reliable and sustained monitoring and stimulation. Full article
(This article belongs to the Special Issue Nanomaterials-Based Sensors for Biomedical Monitoring)
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Figure 1

Figure 1
<p>Diffractograms of the thin films studied.</p> Full article ">Figure 2
<p>Cross-sectional images (<b>a<sub>i</sub></b>–<b>a<sub>iv</sub></b>) and top-view images (<b>b<sub>i</sub></b>–<b>b<sub>iv</sub></b>) of the Ti-Ag thin films produced with different Ag/Ti ratios.</p> Full article ">Figure 3
<p>Optical defects observed on the surface of an electrode with an Ag/Ti ratio of 0.31. (<b>a</b>) Image recorded by the optical microscope. (<b>b</b>) Image created by the MATLAB algorithm, marking the defects (black lines).</p> Full article ">Figure 4
<p>The percentage of surface defects on the electrodes after varying immersion durations in an artificial sweat solution.</p> Full article ">Figure 5
<p>FTIR spectra of the electrodes before and after immersion in artificial sweat solution and of PTFE.</p> Full article ">Figure 6
<p>Variation of Ti-Ag electrodes’ electrical resistivity after immersion in artificial sweat for different times.</p> Full article ">Figure 7
<p>Anodic stripping voltammograms of the different electrodes immersed in the sweat solution for 240 h, using the square-wave voltammetry technique with a deposition time of 120 s, a potential of −0.9 V, an equilibrium time of 5 s, and stirring at 300 rpm with a GCE electrode.</p> Full article ">Figure 8
<p>Concentration of Ag released into the artificial sweat solution after immersion. The values represent the average of the replicates over time.</p> Full article ">
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