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pH Sensors, Biosensors and Systems
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pH Sensors, Biosensors and Systems

A topical collection in Chemosensors (ISSN 2227-9040). This collection belongs to the section "Applied Chemical Sensors".

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Editors

Dr. Pietro Salvo

E-Mail Website
Collection Editor
Institute of Clinical Physiology, Italian National Council of Research, Pisa, Italy
Interests: sensors; biosensors; field effect transistors; bioengineering; bioimaging
Special Issues, Collections and Topics in MDPI journals
Dr. Lorena Tedeschi

E-Mail Website
Collection Editor
Institute of Clinical Physiology, National Research Council, 56124 Pisa, Italy
Interests: conjugation and labelling of oligonucleotides and peptides for biosensing; theranostics and in-vitro pathway dissection
Special Issues, Collections and Topics in MDPI journals

Topical Collection Information

Dear Colleagues,

The pH value has a key role in the life of many living systems and chemical reactions in nature. Biology and microbiology (e.g., monitoring of bacteria, DNA, enzymes, aminoacids, and cells), environmental protection (e.g., characterization of waste and sea water), food and beverage quality control (e.g., monitoring of fermentation processes, characterization of fruit, drinking water and vegetables), pharmaceutical, cosmetics (quality control of creams, gels, and shampoos), medicine (e.g., monitoring and analysis of culture media, cancer, blood, and cytoplasm), and industry (e.g., chemical baths for paints and plating) are some of the fields where pH sensors have been extensively used to understand the nature of chemical processes, as well as to monitor quality and control safety.

Although paper test strips and glass electrodes are the most common pH sensors, many studies have focused on developing less fragile, miniaturized, and biocompatible sensors with higher sensitivity. The pH value can be measured through various approaches and materials, such as electrochemical and optical sensors, ion-selective field effect transistors (ISFETs), quantum dots, 2D materials, and organic compounds.

The aim of this Topical Collection is to collect the latest findings in the sensors, biosensors, and systems, including mathematical approaches and machine learning techniques, for the measurement of pH.

Dr. Pietro Salvo
Dr. Lorena Tedeschi
Collection Editors

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 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

  • pH sensors
  • pH biosensors
  • Chemical sensors
  • Optical sensors
  • Electrochemical sensors
  • Sensing materials (e.g., 2D, organic, inorganic compounds)
  • Transistors
  • pH sensing principles
  • Machine learning and deep learning

Published Papers (14 papers)

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2023

Jump to: 2022, 2021

12 pages, 1021 KiB  
Article
Variability Assessment of the Performance of MoS2-Based BioFETs
by Juan Cuesta-Lopez, Alejandro Toral-Lopez, Enrique G. Marin, Francisco G. Ruiz, Francisco Pasadas, Alberto Medina-Rull and Andres Godoy
Chemosensors 2023, 11(1), 57; https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors11010057 - 10 Jan 2023
Cited by 1 | Viewed by 1577
Abstract
Two-dimensional material (2DM)-based Field-Effect Transistors (FETs) have been postulated as a solid alternative for biosensing applications thanks to: (i) the possibility to enable chemical sensitivity by functionalization, (ii) an atomically thin active area which guarantees optimal electrostatic coupling between the sensing layer and [...] Read more.
Two-dimensional material (2DM)-based Field-Effect Transistors (FETs) have been postulated as a solid alternative for biosensing applications thanks to: (i) the possibility to enable chemical sensitivity by functionalization, (ii) an atomically thin active area which guarantees optimal electrostatic coupling between the sensing layer and the electronic active region, and (iii) their compatibility with large scale fabrication techniques. Although 2DM-based BioFETs have demonstrated notable sensing capabilities, other relevant aspects, such as the yield or device-to-device variability, will demand further evaluation in order to move them from lab-to-fab applications. Here, we focus on the latter aspect by analyzing the performance of MoS2-based BioFETs for the detection of DNA molecules. In particular, we explore the impact of the randomized location and activation of the receptor molecules at the sensing interface on the device response. Several sensing interface configurations are implemented, so as to evaluate the sensitivity dependence on device-to-device variability. Full article
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20 pages, 4974 KiB  
Article
Near-Infrared-Emitting Meso-Substituted Heptamethine Cyanine Dyes: From the Synthesis and Photophysics to Their Use in Bioimaging
by Louise Kommers Reimann, Daniela de Souza Fortes, Fabiano da Silveira Santos, Henrique de Castro Silva Junior, Ana Moira Morás, Dinara Jaqueline Moura, Rodrigo da Costa Duarte and Fabiano Severo Rodembusch
Chemosensors 2023, 11(1), 47; https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors11010047 - 05 Jan 2023
Cited by 4 | Viewed by 2397
Abstract
Heptamethine cyanine dyes were synthesized in good yields by the reaction between quaternary indoles and a pentamethinic salt, under mild reaction conditions minimizing photooxidation. These compounds were used as precursors to prepare meso-substituted derivatives. The cyanine dye precursors presented UV-Vis absorption, related [...] Read more.
Heptamethine cyanine dyes were synthesized in good yields by the reaction between quaternary indoles and a pentamethinic salt, under mild reaction conditions minimizing photooxidation. These compounds were used as precursors to prepare meso-substituted derivatives. The cyanine dye precursors presented UV-Vis absorption, related to fully allowed electronic transitions and fluorescence emission in the NIR region, without any evidence of aggregation in both ground and excited states. The substitution at the meso position showed a fundamental role in their photophysics, with the main absorption in the green-orange region related to the monomeric species. Moreover, the excited state photophysics presented emission profiles dependent on the excitation wavelengths, complicating the correlation of spectroscopy and structure. Density Functional Theory and OO-SCS-MP2 calculations under different solvation conditions revealed the heavy impact of conjugation effects on ground and excited states’ geometries and electronic configurations of these compounds. Finally, the observed photophysical features of the meso-substituted heptamethine cyanine dyes were successfully used to explore their application as fluorescent probes in biological media, allowing stable staining in live and fixed cells. Full article
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12 pages, 3027 KiB  
Article
Fully Transparent and Highly Sensitive pH Sensor Based on an a-IGZO Thin-Film Transistor with Coplanar Dual-Gate on Flexible Polyimide Substrates
by Tae-Hwan Hyun and Won-Ju Cho
Chemosensors 2023, 11(1), 46; https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors11010046 - 04 Jan 2023
Cited by 3 | Viewed by 1815
Abstract
In this paper, we propose a fully transparent and flexible high-performance pH sensor based on an amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) transducer with a coplanar dual-gate structure on polyimide substrates. The proposed pH sensor system features a transducer unit [...] Read more.
In this paper, we propose a fully transparent and flexible high-performance pH sensor based on an amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) transducer with a coplanar dual-gate structure on polyimide substrates. The proposed pH sensor system features a transducer unit consisting of a floating gate (FG), sensing gate (SG), and control gate (CG) on a polyimide (PI), and an extended gate (EG) sensing unit on a separate glass substrate. We designed a capacitive coupling between (SG) and (CG) through the FG of an a-IGZO TFT transducer to contribute to sensitivity amplification. The capacitance ratio (CSG/CCG) increases linearly with the area ratio; therefore, the amplification ratio of the pH sensitivity was easily controlled using the area ratio of SG/CG. The proposed sensor system improved the pH sensitivity by up to 359.28 mV/pH (CSG/CCG = 6.16) at room temperature (300 K), which is significantly larger than the Nernstian limit of 59.14 mV/pH. In addition, the non-ideal behavior, including hysteresis and drift effects, was evaluated to ensure stability and reliability. The amplification of sensitivity based on capacitive coupling was much higher than the increase in the hysteresis voltage and drift rate. Furthermore, we verified the flexibility of the a-IGZO coplanar dual-gate TFT transducer through a bending test, and the electrical properties were maintained without mechanical damage, even after repeated bending. Therefore, the proposed fully transparent and highly sensitive a-IGZO coplanar dual-gate TFT-based pH sensor could be a promising wearable and portable high-performance chemical sensor platform. Full article
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2022

Jump to: 2023, 2021

16 pages, 3901 KiB  
Article
Effects of Viscosity and Salt Interference for Planar Iridium Oxide and Silver Chloride pH Sensing Electrodes on Flexible Substrate
by Khengdauliu Chawang, Sen Bing and Jung-Chih Chiao
Chemosensors 2022, 10(9), 371; https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors10090371 - 17 Sep 2022
Cited by 5 | Viewed by 1767
Abstract
The equivalency of pH measurements between aqueous and non-aqueous or viscous solutions is of great interest in biomedical applications as well for processing food and pharmaceuticals. Commercial glass-type electrodes have practical limitations, such as bulky sizes and membrane clogging in viscous environments. In [...] Read more.
The equivalency of pH measurements between aqueous and non-aqueous or viscous solutions is of great interest in biomedical applications as well for processing food and pharmaceuticals. Commercial glass-type electrodes have practical limitations, such as bulky sizes and membrane clogging in viscous environments. In this study, planar and flexible electrochemical pH sensors with iridium oxide as the sensing film have been developed by sol-gel and oxidation processes. A reference electrode was prepared by screen printing Ag/AgCl ink on the same polyimide substrate. The small form factors of the planar flexible electrodes provide an advantage in small volume or conformal surface measurements. Cyclic voltammetry was performed in different pH solutions. The electrode originally produced a response of −70.1 mV/pH at room temperature in aqueous solutions. The sensitivities were reduced when salt was added into the buffer solutions, although output potentials were increased. Sensing performances in a wide range of viscous conditions with various concentrations of added salt have been analyzed to study their effects on pH-sensing responses. Suitable calibration techniques using aqueous buffer solutions were studied for output potentials and their respective pH readings in viscous salt-added solutions. The mechanisms affecting output potentials are explained and results matched well for two different thickening agents. Specificity to pH changes measured by the planar IrOx-Ag/AgCl pH electrodes showed how the potential-pH calibration should consider the interference effect of salt. The viscosity effects on pH reading errors became more pronounced as solution viscosity increased. Comparisons of pH readings to those from a commercial glass-bodied pH meter indicated that the planar electrodes provided predictable pH deviations that were confined to a limited range. The planar IrOx-Ag/AgCl electrodes on flexible polyimide substrates have mostly been demonstrated with aqueous solutions in various diagnostic and environmental monitoring applications. This work provides more insights into pH sensing performance when the fluid is viscous and contains salt, which often is the case in biomedical and food-processing applications. Full article
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11 pages, 18265 KiB  
Article
High-Performance Bidirectional Chemical Sensor Platform Using Double-Gate Ion-Sensitive Field-Effect Transistor with Microwave-Assisted Ni-Silicide Schottky-Barrier Source/Drain
by Yeong-Ung Kim and Won-Ju Cho
Chemosensors 2022, 10(4), 122; https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors10040122 - 24 Mar 2022
Cited by 2 | Viewed by 2371
Abstract
This study proposes a bidirectional chemical sensor platform using ambipolar double-gate ion-sensitive field-effect transistors (ISFET) with microwave-assisted Ni-silicide Schottky-barrier (SB) source and drain (S/D) on a fully depleted silicon-on-insulator (FDSOI) substrate. The microwave-assisted Ni-silicide SB S/D offer bidirectional turn-on characteristics for both p- [...] Read more.
This study proposes a bidirectional chemical sensor platform using ambipolar double-gate ion-sensitive field-effect transistors (ISFET) with microwave-assisted Ni-silicide Schottky-barrier (SB) source and drain (S/D) on a fully depleted silicon-on-insulator (FDSOI) substrate. The microwave-assisted Ni-silicide SB S/D offer bidirectional turn-on characteristics for both p- and n-type channel operations. The p- and n-type operations are characterized by high noise resistance as well as improved mobility and excellent drift performance, respectively. These features enable sensing regardless of the gate voltage polarity, thus contributing to the use of detection channels based on various target substances, such as cells, antigen-antibodies, DNA, and RNA. Additionally, the capacitive coupling effect existing between the top and bottom gates help achieve self-amplified pH sensitivity exceeding the Nernst limit of 59.14 mV/pH without any additional amplification circuitry. The ambipolar FET sensor performance was evaluated for bidirectional electrical characteristics, pH detection in the single-gate and double-gate modes, and reliability in continuous and repetitive operations. Considering the excellent characteristics confirmed through evaluation, the proposed ambipolar chemical sensor platform is expected to be applicable to various fields including biosensors. And through linkage with subsequent studies, various medical applications and precision detector operations for specific markers will be possible. Full article
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21 pages, 5716 KiB  
Article
Two-Dimensional Dy2O3-Pd-PDA/rGO Heterojunction Nanocomposite: Synergistic Effects of Hybridisation, UV Illumination and Relative Humidity on Hydrogen Gas Sensing
by Hanie Hashtroudi, Aimin Yu, Saulius Juodkazis and Mahnaz Shafiei
Chemosensors 2022, 10(2), 78; https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors10020078 - 14 Feb 2022
Cited by 10 | Viewed by 2620
Abstract
A two-dimensional (2D) Dy2O3-Pd-PDA/rGO heterojunction nanocomposite has been synthesised and tested for hydrogen (H2) gas sensing under various functioning conditions, including different H2 concentrations (50 ppm up to 6000 ppm), relative humidity (up to 25 %RH) [...] Read more.
A two-dimensional (2D) Dy2O3-Pd-PDA/rGO heterojunction nanocomposite has been synthesised and tested for hydrogen (H2) gas sensing under various functioning conditions, including different H2 concentrations (50 ppm up to 6000 ppm), relative humidity (up to 25 %RH) and working temperature (up to 200 °C). The material characterisation of Dy2O3-Pd-PDA/rGO nanocomposite performed using various techniques confirms uniform distribution of Pd NPs and 2D Dy2O3 nanostructures on multi-layered porous structure of PDA/rGO nanosheets (NSs) while forming a nanocomposite. Moreover, fundamental hydrogen sensing mechanisms, including the effect of UV illumination and relative humidity (%RH), are investigated. It is observed that the sensing performance is improved as the operating temperature increases from room temperature (RT = 30 °C) to the optimum temperature of 150 °C. The humidity effect investigation revealed a drastic enhancement in sensing parameters as the %RH increased up to 20%. The highest response was found to be 145.2% towards 5000 ppm H2 at 150 °C and 20 %RH under UV illumination (365 nm). This work offers a highly sensitive and selective hydrogen sensor based on a novel 2D nanocomposite using an environmentally friendly and energy-saving synthesis approach, enabling us to detect hydrogen molecules experimentally down to 50 ppm. Full article
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2021

Jump to: 2023, 2022

9 pages, 2756 KiB  
Communication
Potential Assessment of Dehydration during High-Intensity Training Using a Capacitance Sensor for Oral Mucosal Moisture: Evaluation of Elite Athletes in a Field-Based Survey
by Gen Tanabe, Tetsuya Hasunuma, Yuto Inai, Yasuo Takeuchi, Hiroaki Kobayashi, Kairi Hayashi, Shintaro Shimizu, Nana S Kamiya, Hiroshi Churei, Yuka I Sumita, Katsuhiko Suzuki, Naoki Moriya and Toshiaki Ueno
Chemosensors 2021, 9(8), 196; https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors9080196 - 28 Jul 2021
Cited by 1 | Viewed by 2359
Abstract
Background: The aim of this clinical study was to reveal the relationship between body dehydration and oral mucosa moisture measured by the use of a capacitance sensor for oral epithelial moisture. Methods: The following clinical parameters were recorded from each one of 19 [...] Read more.
Background: The aim of this clinical study was to reveal the relationship between body dehydration and oral mucosa moisture measured by the use of a capacitance sensor for oral epithelial moisture. Methods: The following clinical parameters were recorded from each one of 19 athletes in a one-week period of high-intensity exercise at the U-23 Triathlon Training Camp in summer and winter; body weight, urine specific gravity, oral mucosa moisture, subjective oral thirst, and subjective throat thirst (within 30 min after waking and before breakfast at 7:00 a.m. on Day2 and Day6). Results: There were no significant differences in the mean values of body weight, urine specific gravity, oral mucosa moisture, oral thirst, and throat thirst between Day2 and Day6 in both measurements in summer and winter. The oral mucosa moisture had a moderate negative correlation with urine specific gravity (p < 0.05, r = −0.45). Conclusions: This study suggests that oral mucosal moisture determined using an oral moisture-checking device could be a potential index for assessing dehydration during sports activities. Full article
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10 pages, 671 KiB  
Article
Optical pH Sensing in Milk: A Small Puzzle of Indicator Concentrations and the Best Detection Method
by Olga Voskoboynikova, Aleksey Sukhanov and Axel Duerkop
Chemosensors 2021, 9(7), 177; https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors9070177 - 12 Jul 2021
Cited by 6 | Viewed by 2944
Abstract
Optical chemical sensors can yield distinctively different responses that are dependent on the method applied for readout and evaluation. We therefore present a comprehensive study on the pH determined non-continuously with optical sensors in real milk samples by either photometry or colorimetry (via [...] Read more.
Optical chemical sensors can yield distinctively different responses that are dependent on the method applied for readout and evaluation. We therefore present a comprehensive study on the pH determined non-continuously with optical sensors in real milk samples by either photometry or colorimetry (via the RGB-readout of digital images) compared to the pH values obtained electrochemically by potentiometry. Additionally, the photometric determination of pH was conducted with single-wavelength and a dual wavelength ratiometric evaluation of the absorbance. It was found that both the precision and accuracy of the pH determined by photometry benefit from lower concentrations of bromocresol purple, which served as the pH indicator inside the sensor membrane. A further improvement is obtained by the ratiometric evaluation of the photometric sensor response. The pH values obtained from the colorimetric evaluation, however, gain in precision and accuracy if a higher concentration of the indicator is immobilized inside the sensor membrane. This has a major impact on the future fabrication of optical pH sensor membranes because they can be better tuned to match to the most precise and accurate range of the planned detection method. Full article
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10 pages, 1345 KiB  
Article
Development of Polydiacetylene-Based Testosterone Detection as a Model Sensing Platform for Water-Insoluble Hormone Analytes
by Jaewon Jung, Sung-Min An, Eun-Kyung Lim, Seung-Chul Kim, Beum-Soo An and Sungbaek Seo
Chemosensors 2021, 9(7), 176; https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors9070176 - 12 Jul 2021
Cited by 4 | Viewed by 2949
Abstract
We have developed a polydiacetylene (PDA)-based sensing platform to detect testosterone (T) as a potential biomarker of preterm birth. The insolubility of the steroid hormone in water, where PDA assemblies are dispersed, poses a major issue, since they can hardly interact with each [...] Read more.
We have developed a polydiacetylene (PDA)-based sensing platform to detect testosterone (T) as a potential biomarker of preterm birth. The insolubility of the steroid hormone in water, where PDA assemblies are dispersed, poses a major issue, since they can hardly interact with each other. To overcome this challenge, acetonitrile was used as a suitable solvent. In addition, to minimize false signals of PDA assemblies caused by the solvent, a mixture of acetonitrile and distilled water was selected. To prove a concept of PDA-based sensing platform for targeting T hormone, we conjugated anti-T antibodies to surface of PDA assemblies to induce selective binding between T and anti-T antibodies. The fluorescence sensory signaling of the PDA-anti-T antibody conjugate was selectively generated for T, over 3.4 times higher sensitivity of the signaling compared to that from other sex steroid hormones studied (β-estradiol and progesterone). Full article
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8 pages, 1391 KiB  
Communication
A Syringe-Based and Centrifugation-Free DNA Extraction Procedure for the Rapid Detection of Bacteria
by Taehwi Yoon, Seokjoon Kim, Jung Ho Kim and Ki Soo Park
Chemosensors 2021, 9(7), 167; https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors9070167 - 03 Jul 2021
Cited by 11 | Viewed by 4490
Abstract
Several bacteria are known to cause food poisoning; therefore, diagnostic systems that detect bacteria are essential. Nucleic acid-based testing methods that involve polymerase chain reaction (PCR) amplification are of great interest due to their high sensitivity and specificity. Herein, we developed a syringe-based [...] Read more.
Several bacteria are known to cause food poisoning; therefore, diagnostic systems that detect bacteria are essential. Nucleic acid-based testing methods that involve polymerase chain reaction (PCR) amplification are of great interest due to their high sensitivity and specificity. Herein, we developed a syringe-based one-step DNA extraction device that streamlines the extraction of genomic DNA (gDNA) from bacteria within 2 min, enabling versatile application of nucleic acid-based testing in the field. Notably, the bolt-nut structured case coupled with the syringe enables control of the volume of solution dispensed for enabling DNA extraction without the need for bulky centrifuge equipment. Using the proposed system, the gDNA of a model bacterium, Escherichia coli, was extracted at a good quantity and quality and amplified via PCR. The DNA extracted was comparable to that extracted via a centrifugation-based procedure. In addition, bacteria that were artificially spiked in common samples, including a work cloth, a work bench, and meat, were successfully detected with high accuracy. Full article
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16 pages, 3903 KiB  
Article
Cost-Effective Real-Time Metabolic Profiling of Cancer Cell Lines for Plate-Based Assays
by Wiktoria Blaszczak, Zhengchu Tan and Pawel Swietach
Chemosensors 2021, 9(6), 139; https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors9060139 - 13 Jun 2021
Cited by 6 | Viewed by 3114
Abstract
A fundamental phenotype of cancer cells is their metabolic profile, which is routinely described in terms of glycolytic and respiratory rates. Various devices and protocols have been designed to quantify glycolysis and respiration from the rates of acid production and oxygen utilization, respectively, [...] Read more.
A fundamental phenotype of cancer cells is their metabolic profile, which is routinely described in terms of glycolytic and respiratory rates. Various devices and protocols have been designed to quantify glycolysis and respiration from the rates of acid production and oxygen utilization, respectively, but many of these approaches have limitations, including concerns about their cost-ineffectiveness, inadequate normalization procedures, or short probing time-frames. As a result, many methods for measuring metabolism are incompatible with cell culture conditions, particularly in the context of high-throughput applications. Here, we present a simple plate-based approach for real-time measurements of acid production and oxygen depletion under typical culture conditions that enable metabolic monitoring for extended periods of time. Using this approach, it is possible to calculate metabolic fluxes and, uniquely, describe the system at steady-state. By controlling the conditions with respect to pH buffering, O2 diffusion, medium volume, and cell numbers, our workflow can accurately describe the metabolic phenotype of cells in terms of molar fluxes. This direct measure of glycolysis and respiration is conducive for between-runs and even between-laboratory comparisons. To illustrate the utility of this approach, we characterize the phenotype of pancreatic ductal adenocarcinoma cell lines and measure their response to a switch of metabolic substrate and the presence of metabolic inhibitors. In summary, the method can deliver a robust appraisal of metabolism in cell lines, with applications in drug screening and in quantitative studies of metabolic regulation. Full article
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7 pages, 2010 KiB  
Communication
High-Sensitivity pH Sensor Based on Coplanar Gate AlGaN/GaN Metal-Oxide-Semiconductor High Electron Mobility Transistor
by Seong-Kun Cho and Won-Ju Cho
Chemosensors 2021, 9(3), 42; https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors9030042 - 25 Feb 2021
Cited by 16 | Viewed by 2774
Abstract
The sensitivity of conventional ion-sensitive field-effect transistors is limited to the Nernst limit (59.14 mV/pH). In this study, we developed a pH sensor platform based on a coplanar gate AlGaN/GaN metal-oxide-semiconductor (MOS) high electron mobility transistor (HEMT) using the resistive coupling effect to [...] Read more.
The sensitivity of conventional ion-sensitive field-effect transistors is limited to the Nernst limit (59.14 mV/pH). In this study, we developed a pH sensor platform based on a coplanar gate AlGaN/GaN metal-oxide-semiconductor (MOS) high electron mobility transistor (HEMT) using the resistive coupling effect to overcome the Nernst limit. For resistive coupling, a coplanar gate comprising a control gate (CG) and a sensing gate (SG) was designed. We investigated the amplification of the pH sensitivity with the change in the magnitude of a resistance connected in series to each CG and SG via Silvaco TCAD simulations. In addition, a disposable extended gate was applied as a cost-effective sensor platform that helped prevent damages due to direct exposure of the AlGaN/GaN MOS HEMT to chemical solutions. The pH sensor based on the coplanar gate AlGaN/GaN MOS HEMT exhibited a pH sensitivity considerably higher than the Nernst limit, dependent on the ratio of the series resistance connected to the CG and SG, as well as excellent reliability and stability with non-ideal behavior. The pH sensor developed in this study is expected to be readily integrated with wide transmission bandwidth, high temperature, and high-power electronics as a highly sensitive biosensor platform. Full article
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17 pages, 1161 KiB  
Review
Recent Advances in Optical, Electrochemical and Field Effect pH Sensors
by Federico Vivaldi, Pietro Salvo, Noemi Poma, Andrea Bonini, Denise Biagini, Lorenzo Del Noce, Bernardo Melai, Fabio Lisi and Fabio Di Francesco
Chemosensors 2021, 9(2), 33; https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors9020033 - 05 Feb 2021
Cited by 35 | Viewed by 5968
Abstract
Although its first definition dates back to more than a century ago, pH and its measurement are still studied for improving the performance of current sensors in everyday analysis. The gold standard is the glass electrode, but its intrinsic fragility and need of [...] Read more.
Although its first definition dates back to more than a century ago, pH and its measurement are still studied for improving the performance of current sensors in everyday analysis. The gold standard is the glass electrode, but its intrinsic fragility and need of frequent calibration are pushing the research field towards alternative sensitive devices and materials. In this review, we describe the most recent optical, electrochemical, and transistor-based sensors to provide an overview on the status of the scientific efforts towards pH sensing. Full article
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32 pages, 33096 KiB  
Review
Recent Advances in Perylene Diimide-Based Active Materials in Electrical Mode Gas Sensing
by Salman Ali, Akhil Gupta, Mahnaz Shafiei and Steven J. Langford
Chemosensors 2021, 9(2), 30; https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors9020030 - 01 Feb 2021
Cited by 25 | Viewed by 4636
Abstract
This review provides an update on advances in the area of electrical mode sensors using organic small molecule n-type semiconductors based on perylene. Among small organic molecules, perylene diimides (PDIs) are an important class of materials due to their outstanding thermal, chemical, [...] Read more.
This review provides an update on advances in the area of electrical mode sensors using organic small molecule n-type semiconductors based on perylene. Among small organic molecules, perylene diimides (PDIs) are an important class of materials due to their outstanding thermal, chemical, electronic, and optical properties, all of which make them promising candidates for a wide range of organic electronic devices including sensors, organic solar cells, organic field-effect transistors, and organic light-emitting diodes. This is mainly due to their electron-withdrawing nature and significant charge transfer properties. Perylene-based sensors of this type show high sensing performance towards various analytes, particularly reducing gases like ammonia and hydrazine, but there are several issues that need to be addressed including the selectivity towards a specific gas, the effect of relative humidity, and operating temperature. In this review, we focus on the strategies and design principles applied to the gas-sensing performance of PDI-based devices, including resistive sensors, amperometric sensors, and operating at room temperature. The device properties and sensing mechanisms for different analytes, focusing on hydrazine and ammonia, are studied in detail, and some future research perspectives are discussed for this promising field. We hope the discussed results and examples inspire new forms of molecular engineering and begin to open opportunities for other rylene diimide classes to be applied as active materials. Full article
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