EGFET-Based Sensors for Bioanalytical Applications: A Review

Ultrasensitive and selective vancomycin detection using aptamer-modified multi-doped laser-induced graphene extended-gate field-effect transistor

Vancomycin (Van), a widely utilized glycopeptide antibiotic in clinical settings, necessitates precise bloodstream concentration monitoring due to its narrow therapeutic window, ensuring drug efficacy while preventing adverse effects. In this work, we have engineered an extended-gate field-effect transistor (EG-FET) sensor tailored for vancomycin detection. This novel sensor configuration comprises a detachable multi-doped graphene EG electrode sensing element paired with a commercial field-effect transistor (FET). The EG electrode design integrates a sophisticated multistage doping process, incorporating MnO2 and Au nanoparticles into laser-induced graphene (LIG), thereby augmenting both functional and electrical characteristics of LIG. To achieve specific recognition, a vancomycin aptamer is immobilized onto the electrode surface, enabling selective binding with vancomycin and translating this interaction into a measurable electrical signal. This collaborative mechanism empowers the EG-FET sensor to exhibit exceptional sensitivity and selectivity towards vancomycin. Notably, the sensor demonstrates a wide linear response ranging from 1 nM to 100 μM, spanning the entire therapeutic window of vancomycin (6-35 μM), boasting an impressive detection limit of 0.187 nM. We have innovated a portable wireless sensing system, coupled with a Janus membrane for expedited plasma separation, consolidating a portable platform dedicated to vancomycin sensing. Furthermore, we have realized the detection of vancomycin concentration in patient's blood using this sensor, and the results are reliable. This comprehensive study underscores the immense potential of multi-doped graphene EG-FET sensors in the realm of antibiotic detection, thereby contributing a pivotal tool towards the realization of precision medicine strategies.

Fast and label-free detection of procalcitonin in human serum for sepsis using a WTex-based extended-gate field-effect transistor biosensor

In this article, we present the first instance of depositing WTex-sensitive films with varying thicknesses (3, 4, and 5 nm) onto flexible polyimide substrates using radio-frequency sputtering. These films were used to create an extended-gate field-effect transistor (EGFET) for pH sensing and detecting procalcitonin (PCT) in the sera of patients with sepsis or bacterial infections. Among the films, the 4 nm WTex film exhibited high sensitivity (59.57 mV/pH), minimal hysteresis (∼0.8 mV), and a low drift rate (0.14 mV/h). Additionally, this WTex-based EGFET sensor retained a pH sensitivity of 59.2 mV/pH even after 180 days of operation and exhibited excellent mechanical flexibility, enduring 500 bending cycles without degradation. Moreover, PCT antibodies, activated using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide and N-hydroxysuccinimide, were immobilized on the WTex film functionalized with 3-aminopropyl triethoxysilane. This effective immobilization enabled the specific binding of PCT antigens. The WTex-based EGFET biosensor demonstrated high sensitivity (18.12 mV/pCPCT) across a wide dynamic range (1 fg/mL to 1 μg/mL). Furthermore, the PCT concentrations in patient sera, whether from individuals with or without sepsis or bacterial infections, measured by our biosensor were comparable to results obtained using clinical enzyme-linked immunosorbent assay kits.

Laser-induced multi-doped graphene extended-gate field-effect transistor sensor for enhanced detection of cystatin C

In this study, we amplified the capabilities of laser-induced graphene (LIG) by developing a multi-doped LIG extended-gated field-effect transistor (EG-FET) sensor. This sensor integrates a multi-doped LIG EG electrode array as a disposable sensing component with a standard MOSFET for reusable transduction. The multi-doped LIG was synthesized using a dual-approach: initially, by using a MnCl2-doped polyimide (MnCl2-PI) film through precursor compounding, and subsequently, by employing a CO2 laser to respectively in situ generate MnO2 nanoparticles and gold nanoparticles (Au NPs) via direct laser conversion. By incorporating the resultant multi-doped LIG (Au NPs/MnO2/LIG) as the EG electrode, we boosted its electrical efficiency and provided ideal sites for the papain immobilization. This facilitated the selective binding of protein complexes with cystatin C (Cys C), allowing for precise measurement. Notably, the sensor exhibited a robust linear correlation across a concentration range from 50 ag/μL to 0.25 ng/μL and achieved a detection limit of 50 ag/μL. These advancements not only address traditional limitations of LIG applications but also highlight the potential of LIG-based EG-FET portable devices for accurate and early screening of chronic kidney disease (CKD).

Brewer's Spent Grain-Cellulose-Coated Copper Electrode-Based Extended Gate Field-Effect Transistor for Nonenzymatic Glucose Detection toward Diagnosis of Diabetes Mellitus

The demand for environmentally friendly, reliable, and cost-effective electrodes for glucose sensor technology has become a major research area in the paradigm shift toward green electronics. In this regard, cellulose has emerged as a promising flexible biopolymer solution with unique properties such as biocompatibility, biodegradability, nontoxicity, renewability, and sustainability. Because of their large surface area and porous structure, fibrous cellulose substrates quickly adsorb and disperse analytes at detection sites. This work focuses on utilizing glyoxal-treated cellulose (derived from brewer's spent grain (BSG)) for the fabrication of extended gate field-effect transistor (EGFET)-based glucose sensors. This investigation extends to the utilization of BSG-cellulose for glucose detection in biomimicking electrolytes (phosphate buffer saline) to facilitate glucose detection in human blood samples. The fabricated electrode demonstrates a linear range of glucose detection from 1 to 13.5 mM with a Langmuir adsorption coefficient (K) of 0.102. Also, its selectivity toward glucose over interfering molecules such as sucrose, fructose, ascorbic acid, and uric acid under physiological conditions has been demonstrated. This cellulose-based EGFET electrode exhibits a sensitivity of 6.5 μA mM-1 cm-2 with a limit of detection (LOD) of 0.135 mM. Computational studies by density functional theory calculations confirmed the higher binding affinity of glucose molecules with glyoxal-modified cellulose (-0.95 eV) than with pristine cellulose (-0.46 eV). Here, the novelty lies in the fabrication of electrodes with biodegradable catalysts and their integration into the EGFET configuration.

Deep Learning-Based Kinetic Analysis in Paper-Based Analytical Cartridges Integrated with Field-Effect Transistors

This study explores the fusion of a field-effect transistor (FET), a paper-based analytical cartridge, and the computational power of deep learning (DL) for quantitative biosensing via kinetic analyses. The FET sensors address the low sensitivity challenge observed in paper analytical devices, enabling electrical measurements with kinetic data. The paper-based cartridge eliminates the need for surface chemistry required in FET sensors, ensuring economical operation (cost < $0.15/test). The DL analysis mitigates chronic challenges of FET biosensors such as sample matrix interference, by leveraging kinetic data from target-specific bioreactions. In our proof-of-concept demonstration, our DL-based analyses showcased a coefficient of variation of <6.46% and a decent concentration measurement correlation with an r2 value of >0.976 for cholesterol testing when blindly compared to results obtained from a CLIA-certified clinical laboratory. These integrated technologies have the potential to advance FET-based biosensors, potentially transforming point-of-care diagnostics and at-home testing through enhanced accessibility, ease-of-use, and accuracy.

A rapid and ultrasensitive cardiac troponin I aptasensor based on an ion-sensitive field-effect transistor with extended gate

Acute myocardial infarction (AMI) is a life-threatening disease with a short course and a high mortality rate. However, it is still a great challenge to achieve the on-site diagnosis of this disease within minutes, meaning there is an urgent need to develop an efficient technology for realizing the rapid diagnosis and early warning of AMI in clinical emergencies. In this study, an ultrasensitive electrochemical aptasensor based on an extended-gate ion-sensitive field-effect transistor (EGISFET) was designed to achieve the quantitative assay of cardiac troponin I (cTnI), which is a highly sensitive and specific biomarker of AMI, within only 5 min. The EGISFET exhibits extremely high detection sensitivity due to its separated structure with a large sensing area and the surface-modified Prussian blue-gold nanoparticles (PB-AuNPs) composite, which serves as a signal magnifier and DNA loading platform for good electrocatalytic ability with a large specific area. Additionally, a target-induced strand-release strategy is proposed to shorten the recognition time of cTnI using a particular DNA strand. Under optimal conditions, the as-prepared aptasensor exhibits a wide linear range of 1-1000 pg/mL, an ultralow detection limit of 0.3 pg/mL, and reliable detection results in real serum samples. It is highly anticipated that this EGISFET-based aptasensor will have broad applications in the early warning and rapid diagnosis of AMI and other acute diseases in emergency treatment.

A simple and highly sensitive flexible sensor with extended-gate field-effect transistor for epinephrine detection utilizing InZnSnO sensing films

This study introduces a straightforward method for depositing InZnSnO films onto flexible polyimide substrates at room temperature, enabling their application in electrochemical pH sensing and the detection of epinephrine. A comprehensive analysis of these sensing films, spanning structural, morphological, compositional, and profiling characteristics, was conducted using diverse techniques, including X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectroscopy. The investigation into the influence of oxygen flow rates on the performance of InZnSnO sensitive films revealed a significant correlation between their structural properties and sensing capabilities. Notably, exposure to an oxygen flow rate of 30/2 (Ar/O2) the ratio of resulted in the InZnSnO sensitive film demonstrating outstanding pH sensitivity at 59.58 mV/pH within a broad pH range of 2-12, surpassing the performance observed with other oxygen flow rates. Moreover, under this specific condition, the film exhibited excellent stability, with a minimal drift rate of 0.14 mV/h at pH 7 and a low hysteresis voltage of 1.8 mV during a pH cycle of 7 → 4→7 → 10→7. Given the critical role of epinephrine in mammalian central nervous and hormone systems, monitoring its levels is essential for assessing human health. To facilitate the detection of epinephrine, we utilized the carboxyl group of 4-formylphenylboronic acid to enable a reaction with the amino group of the 3-aminopropyltriethoxysilane-coated InZnSnO film. Through optimization, the resulting InZnSnO-based flexible sensor displayed a broad and well-defined linear relationship within the concentration range of 10-7 to 0.1 μM. In practical applications, this sensor proved effective in analyzing epinephrine in human serum, showcasing notable selectivity, stability, and reproducibility. The promising outcomes of this study underscore the potential for future applications, leveraging the advantages of electrochemical sensors, including affordability, rapid response, and user-friendly operation.

Histones Classification Based on EGFET Signals

Dysregulation of histones has been implicated in several medical conditions, including various cancers and neurodegenerative disorders. Histone-specific biosensors are key in detecting and quantifying them, advancing our understanding of chromatin dynamics and epigenetic regulation for potential breakthroughs in cancer research and personalized medicine. The focus of this paper is on quantifying a biosensor's ability to distinguish between Human Histones (H4) and non-target analytes. Classification methods are used to provide complementary analysis to biosensor data derived from sensor manufactured using a KU7 RNA aptamer bonded to a gold electrode. The features found provide high classification performance (F1 score over 0.99) and suggest physical insights to the operation of the sensor not provided by typical analysis. Furthermore, machine learning techniques are used in an exploratory analysis to test the effects of faulty manufacturing or differences in testing environments on histone detection accuracy.

Low-Power Wearable Enabled by Extended Gate Field-Effect Transistors to Advance Vigilant Biochemical Sensing

Biochemical monitoring of sweat through vigilant wearable systems offers new opportunities for improved stress management. A low-power biochemical sensing platform has been developed to perform potentiometric sensing using extended gate field-effect transistors (EGFET) for wearable biochemical monitoring. In vitro validation of the EGFET-enabled electrochemistry was achieved by testing pH and electrolyte concentrations. As a model biochemical analyte and important stress biomarker, neuropeptide Y (NPY) detection was demonstrated with this sensing platform by using an anti-NPY aptamer. The sensor and system operation were optimized to meet the sensitivity requirements to monitor NPY in sweat in a range of 100 fM to 100 nM by comparing different gate drive voltages. The sensing electronics power was optimized to enable longer term operation allowing 11 days of continuous monitoring on a single charge using a 3.8 g 150 mAh lithium polymer battery. The sensitivity of this custom designed electronics system was found to be similar to a commercial benchtop system when the same NPY aptamer-based sensor was tested in artificial sweat. The results indicated the largest current signal change of 34.3% for 100 nM NPY compared to the baseline current. Selectivity was measured against the stress biomarker cortisol. The measurements were achieved with a resolution of 13.59 μA/decade concentration change of NPY. These initial results pave the way towards vigilant sensing of stress biomarkers in sweat using a wearable system.

Molecularly imprinted polymer-based extended-gate field-effect transistor chemosensors for selective determination of antiepileptic drug

Ultrathin molecularly imprinted polymer (MIP) films were deposited on the surfaces of ZnO nanorods (ZNRs) and nanosheets (ZNSs) by electropolymerization to afford extended-gate field-effect transistor sensors for detecting phenytoin (PHT) in plasma. Molecular imprinting efficiency was optimized by controlling the contents of functional monomers and the template in the precursor solution. PHT sensing was performed in plasma solutions with various concentrations by monitoring the drain current as a function of drain voltage under an applied gate voltage of 1.5 V. The reliability and reproducibility of the fabricated sensors were evaluated through a solution treatment process for complete PHT removal and PHT adsorption-removal cycling, while selectivity was examined by analyzing responses to chemicals with structures analogous to that of PHT. Compared with the ZNS/extracted-MIP sensor and sensors with non-imprinted polymer (NIP) films, the ZNR/extracted-MIP sensor showed superior responses to PHT-containing plasma due to selective PHT adsorption, achieving an imprinting factor of 4.23, detection limit of 12.9 ng/mL, quantitation limit of 53.0 ng/mL, and selectivity coefficients of 3-4 (against tramadol) and ~ 5 (against diphenhydramine). Therefore, we believe that the MIP-based ZNR sensing platform is promising for the practical detection of PHT and other drugs and evaluation of their proper dosages.

Evaluation of sensitivity of Extended Gate Field Effect Transistor -biosensor based on V2O5/GOx for glucose detection

The sensing modified electrode was prepared using glucose oxidase immobilized onto vanadium pentoxide xerogel with glass/FTO as support electrode to evaluate the possibility to construct a V2O5/GOx Extended Gate Field Effect Transistor biosensor. Previously, our studies exhibited a sensitivity of V2O5 of 58.1 mV/pH. The use of Nafion® onto V2O5/GOx caused a decrease of mass loss after several cycles compared to the modified electrode without Nafion® during the EQCM and cyclic voltammetrics studies. Electrical characterization of V2O5/GOx demonstrated a tendency to stability after 200 s as a function of applied current. In presence of glucose and in different pH, the current decreased when the glucose concentration increased due to the lower active sites of enzyme. After ten voltammetric cycles, the total charge tends to structural stability. In pH = 5.0, the modified electrode based on V2O5/GOx Extended Gate Field Effect Transistor presented more tendency to sensitivity in different concentration of glucose.

Extended-Gate FET Biosensor Based on GaN Micropillar Array and Polycrystalline Layer: Application to Hg2+ Detection in Human Urine

Owing to the separation of field-effect transistor (FET) devices from sensing environments, extended-gate FET (EGFET) biosensor features high stability and low cost. Herein, a highly sensitive EGFET biosensor based on a GaN micropillar array and polycrystalline layer (GMP) was fabricated, which was prepared by using simple one-step low-temperature MOCVD growth. In order to improve the sensitivity and detection limit of EGFET biosensor, the surface area and the electrical conductivity of extended-gate electrode can be increased by the micropillar array and the polycrystalline layer, respectively. The designed GMP-EGFET biosensor was modified with l-cysteine and applied for Hg2+ detection with a low limit of detection (LOD) of 1 ng/L, a high sensitivity of -16.3 mV/lg(μg/L) and a wide linear range (1 ng/L-24.5 μg/L). In addition, the detection of Hg2+ in human urine was realized with an LOD of 10 ng/L, which was more than 30 times lower than that of reported sensors. To our knowledge, it is the first time that GMP was used as extended-gate of EGFET biosensor.

Pyrene Derivative Incorporated Ni MOF as an Enzyme Mimic for Noninvasive Salivary Glucose Detection Toward Diagnosis of Diabetes Mellitus

Herein, we demonstrate the detection of glucose in a noninvasive and nonenzymatic manner by utilizing an extended gate field-effect transistor (EGFET) based on the organic molecule pyrene phosphonic acid (PyP4OH8) incorporated nickel metal-organic framework (NiOM-MOF). The prepared electrode responds selectively to glucose instead of sucrose, fructose, maltose, ascorbic acid, and uric acid in a 1× phosphate buffer saline solution. Also, utilizing the scanning Kelvin probe system, the sensing electrode's work function (Φ) is measured to validate the glucose-sensing mechanism. The sensitivity, detection range, response time, limit of detection, and limit of quantification of the electrode are determined to be 24.5 μA mM-1 cm-2, 20 μM to 10 mM, less than 5 s, 2.73 μM, and 8.27 μM, respectively. Most interestingly, the developed electrode follows the Michaelis-Menten kinetics, and the calculated rate constant (km) 0.07 mM indicates a higher affinity of NiOM-MOF toward glucose. The real-time analysis has revealed that the prepared electrode is sensitive to detect glucose in real human saliva, and it can be an alternative device for the noninvasive detection of glucose. Overall, the outcomes of the EGFET studies demonstrate that the prepared electrodes are well-suited for expeditious detection of glucose levels in saliva.

Nonenzymatic Potentiometric Detection of Ascorbic Acid with Porphyrin/ZnO-Functionalized Laser-Induced Graphene as an Electrode of EGFET Sensors

Laser-induced graphene (LIG) has emerged as a highly versatile material with significant potential in the development of electrochemical sensors. In this paper, we investigate the use of LIG and LIG functionalized with ZnO and porphyrins-ZnO as the gate electrodes of the extended gate field effect transistors (EGFETs). The resultant sensors exhibit remarkable sensitivity and selectivity, particularly toward ascorbic acid. The intrinsic sensitivity of LIG undergoes a notable enhancement through the incorporation of hybrid organic-inorganic materials. Among the variations tested, the LIG electrode coated with zinc tetraphenylporphyrin-capped ZnO nanoparticles demonstrates superior performance, reaching a limit of detection of approximately 3 nM. Furthermore, the signal ratio for 5 μM ascorbic acid relative to the same concentration of dopamine exceeds 250. The practical applicability of these sensors is demonstrated through the detection of ascorbic acid in real-world samples, specifically in a commercially available food supplement containing l-arginine. Notably, formulations with added vitamin C exhibit signals at least 25 times larger than those without, underscoring the sensors' capability to discern and quantify the presence of ascorbic acid in complex matrices. This research not only highlights the enhanced performance of LIG-based sensors through functionalization but also underscores their potential for practical applications in the analysis of vitamin-rich supplements.

Current and future technologies for monitoring cultured meat: A review

The high population growth rate, massive animal food consumption, fast economic progress, and limited food resources could lead to a food crisis in the future. There is a huge requirement for dietary proteins including cultured meat is being progressed to fulfill the need for meat-derived proteins in the diet. However, production of cultured meat requires monitoring numerous bioprocess parameters. This review presents a comprehensive overview of various widely adopted techniques (optical, spectroscopic, electrochemical, capacitive, FETs, resistive, microscopy, and ultrasound) for monitoring physical, chemical, and biological parameters that can improve the bioprocess control in cultured meat. The methods, operating principle, merits/demerits, and the main open challenges are reviewed with the aim to support the readers in advancing knowledge on novel sensing systems for cultured meat applications.

Micro- and nano-devices for electrochemical sensing

Electrode miniaturization has profoundly revolutionized the field of electrochemical sensing, opening up unprecedented opportunities for probing biological events with a high spatial and temporal resolution, integrating electrochemical systems with microfluidics, and designing arrays for multiplexed sensing. Several technological issues posed by the desire for downsizing have been addressed so far, leading to micrometric and nanometric sensing systems with different degrees of maturity. However, there is still an endless margin for researchers to improve current strategies and cope with demanding sensing fields, such as lab-on-a-chip devices and multi-array sensors, brain chemistry, and cell monitoring. In this review, we present current trends in the design of micro-/nano-electrochemical sensors and cutting-edge applications reported in the last 10 years. Micro- and nanosensors are divided into four categories depending on the transduction mechanism, e.g., amperometric, impedimetric, potentiometric, and transistor-based, to best guide the reader through the different detection strategies and highlight major advancements as well as still unaddressed demands in electrochemical sensing.

Graphical Abstract

Metal-Oxide FET Biosensor for Point-of-Care Testing: Overview and Perspective

Metal-oxide semiconducting materials are promising for building high-performance field-effect transistor (FET) based biochemical sensors. The existence of well-established top-down scalable manufacturing processes enables the reliable production of cost-effective yet high-performance sensors, two key considerations toward the translation of such devices in real-life applications. Metal-oxide semiconductor FET biochemical sensors are especially well-suited to the development of Point-of-Care testing (PoCT) devices, as illustrated by the rapidly growing body of reports in the field. Yet, metal-oxide semiconductor FET sensors remain confined to date, mainly in academia. Toward accelerating the real-life translation of this exciting technology, we review the current literature and discuss the critical features underpinning the successful development of metal-oxide semiconductor FET-based PoCT devices that meet the stringent performance, manufacturing, and regulatory requirements of PoCT.

Label-free and portable field-effect sensor for monitoring RT-LAMP products to detect SARS-CoV-2 in wastewater

The COVID-19 pandemic caused by the coronavirus SARS-CoV-2 has proven the need for developing reliable and affordable technologies to detect pathogens. Particularly, the detecting the genome in wastewater could be an indicator of the transmission rate to alert on new outbreaks. However, wastewater-based epidemiology remains a technological challenge to develop affordable technologies for sensing pathogens. In this work, we introduce a label-free and portable field-effect transistor (FET)-based sensor to detect N and ORF1ab genes of the SARS-CoV-2 genome. Our sensor integrates the reverse transcription loop-mediated isothermal amplification (RT-LAMP) reaction as a cost-effective molecular detection exhibiting high specificity. The detection relies upon pH changes, due to the RT-LAMP reaction products, which are detected through a simple, but effective, extended-gate FET sensor (EGFET). We evaluate the proposed device by measuring real wastewater samples to detect the presence of SARS-CoV-2 genome, achieving a limit of detection of 0.31 × 10⁻³ ng/μL for end-point measurement. Moreover, we find the ability of the sensor to perform real-time-like analysis, showing that the RT-LAMP reaction provides a good response after 15 min for concentrations as low as 0.37 ng/μL. Hence, we show that our EGFET sensor offers a powerful tool to detect the presence of the SARS-CoV-2 genome with a naked-eye method, in a straightforward way than the conventional molecular methods for wastewater analysis.

An extended gate field-effect transistor (EG-FET) type non-enzymatic glucose sensor with inkjet-printed copper oxide nanoparticles

Abstract

We develop a disposable and cost-effective non-enzymatic glucose sensor consisting of an extended gate field effect transistor (EG-FET) to obtain effortless operation. The sensor is fabricated by printing, gold (Au) precursor ink and copper oxide nanoparticles (CuO NPs) inks using a commercial inkjet printer on a flexible Polyimide (PI) substrate. First, sensing properties are tested electrochemically. The sensor shows a sensitivity of 728.5 μA cm−2 mM−1 and a detection limit of 0.01 mM with a correlation coefficient (R) of 0.998. The observed linear dynamic range is from 0.5 to 7 mM. After that, the sensing electrode is adapted to the EG-FET. Two linear response ranges extend from 0.1 to 4 mM of a low concentration range of glucose with a sensitivity of 1295 μA cm−2 mM−1, and from 5 to 30 mM of a high concentration range of glucose with a sensitivity of 164 μA cm−2 mM−1 are observed. The EG-FET approach can enhance the detection sensitivities using amplification for a low concentration glucose range and extending a detection range for high concentration glucose. The presented work demonstrates that simply printed CuO NPs sensors can be used at low cost for disposable wide-range glucose detection devices.

Article Highlights

Construction of cellulose-based highly sensitive extended-gate field effect chiral sensor

Chiral recognition is an emerging field of modern chemical analysis, and the development of health-related fields depends on the production of enantiomers. Cellulose is a kind of natural polymer material with certain chiral recognition ability. Limited by the chiral recognition ability of natural cellulose itself, more cellulose derivatives have been gradually developed for chiral recognition and separation. Based on the difference in action between cellulose derivatives and enantiomers, this work synthesized cellulose-tris(4-methylphenylcarbamate) (CMPC) chiral recognition mediators and a CMPC-functionalized extended-gate organic field effect transistor (EG-OFET) was constructed for the first time. Three chiral molecules were selected as model analytes to evaluate the enantiomeric recognition ability of the platform, including threonine (Thr), 2-chloromandelic acid (CA), and 1,2-diphenylethylenediamine (DPEA). The detection limit for 1,2-diphenylethylenediamine (DPEA) is down to 10-13 M. Through the amplification effect of the EG-OFET platform, the difference in the interaction between CMPC and three chiral molecules with different structures is converted into a current signal output. At the same time, the enantiomer discrimination mechanism of CMPC was further studied by means of spectroscopy and nuclear magnetic resonance.

Effect of Electrode Modification with Chitosan and Nafion® on the Efficiency of Real-Time Enzyme Glucose Biosensors Based on ZnO Tetrapods

Noninvasive, continuous glucose detection can provide some insights into daily fluctuations in blood glucose levels, which can help us balance diet, exercise, and medication. Since current commercially available glucose sensors can barely provide real-time glucose monitoring and usually imply different invasive sampling, there is an extraordinary need to develop new harmless methods for detecting glucose in non-invasive body fluids. Therefore, it is crucial to design (bio)sensors that can detect very low levels of glucose (down to tens of µM) normally found in sweat or tears. Apart from the selection of materials with high catalytic activity for glucose oxidation, it is also important to pay considerable attention to the electrode functionalization process, as it significantly contributes to the overall detection efficiency. In this study, the (ZnO tetrapods) ZnO TPs-based electrodes were functionalized with Nafion and chitosan polymers to compare their glucose detection efficiency. Cyclic voltammetry (CV) measurements have shown that chitosan-modified ZnO TPs require a lower applied potential for glucose oxidation, which may be due to the larger size of chitosan micelles (compared to Nafion micelles), and thus easier penetration of glucose through the chitosan membrane. However, despite this, both ZnO TPs modified with chitosan and Nafion membranes, provided quite similar glucose detection parameters (sensitivities, 7.5 µA mM-1 cm-1 and 19.2 µA mM-1 cm-1, and limits of detection, 24.4 µM and 22.2 µM, respectively). Our results show that both electrodes have a high potential for accurate real-time sweat/tears glucose detection.

Remote Floating-Gate Field-Effect Transistor with 2-Dimensional Reduced Graphene Oxide Sensing Layer for Reliable Detection of SARS-CoV-2 Spike Proteins

Despite intensive research of nanomaterials-based field-effect transistors (FETs) as a rapid diagnostic tool, it remains to be seen for FET sensors to be used for clinical applications due to a lack of stability, reliability, reproducibility, and scalability for mass production. Herein, we propose a remote floating-gate (RFG) FET configuration to eliminate device-to-device variations of two-dimensional reduced graphene oxide (rGO) sensing surfaces and most of the instability at the solution interface. Also, critical mechanistic factors behind the electrochemical instability of rGO such as severe drift and hysteresis were identified through extensive studies on rGO-solution interfaces varied by rGO thickness, coverage, and reduction temperature. rGO surfaces in our RFGFET structure displayed a Nernstian response of 54 mV/pH (from pH 2 to 11) with a 90% yield (9 samples out of total 10), coefficient of variation (CV) < 3%, and a low drift rate of 2%, all of which were calculated from the absolute measurement values. As proof-of-concept, we demonstrated highly reliable, reproducible, and label-free detection of spike proteins of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in a saliva-relevant media with concentrations ranging from 500 fg/mL to 5 μg/mL, with an R² value of 0.984 and CV < 3%, and a guaranteed limit of detection at a few pg/mL. Taken together, this new platform may have an immense effect on positioning FET bioelectronics in a clinical setting for detecting SARS-CoV-2.

Ion-Selective Organic Electrochemical Transistors: Recent Progress and Challenges

The charged species inside biofluids (blood, interstitial fluid, sweat, saliva, urine, etc.) can reflect the human body's physiological conditions and thus be adopted to diagnose various diseases early. Among all personalized health management applications, ion-selective organic electrochemical transistors (IS-OECTs) have shown tremendous potential in point-of-care testing of biofluids due to low cost, ease of fabrication, high signal amplification, and low detection limit. Moreover, IS-OECTs exhibit excellent flexibility and biocompatibility that enable their application in wearable bioelectronics for continuous health monitoring. In this review, the working principle of IS-OECTs and the recent studies of IS-OECTs for performance improvement are reviewed. Specifically, contemporary studies on material design and device optimization to enhance the sensitivity of IS-OECTs are discussed. In addition, the progress toward the commercialization of IS-OECTs is highlighted, and the recently proposed solutions or alternatives are summarized. The main challenges and perspectives for fully exploiting IS-OECTs toward future preventive and personal medical devices are addressed.

Rapid and label-free detection of the troponin in human serum by a TiN-based extended-gate field-effect transistor biosensor

In this article, the TiN sensitive film as a sensing membrane was deposited onto n+-type Si substrate by a DC sputtering technique for extended-gate field-effect transistor (EGFET) pH sensors and detection of cardiac troponin-I (cTn-I) in the patient sera for the first time. The crystal structure, Raman spectrum, element profile, surface roughness, and surface morphology of the TiN sensitive film were characterized by X-ray diffraction, Raman spectroscopy, secondary ion mass spectroscopy, atomic force microscopy, and scanning electron microscopy, respectively. The sensing performance of the TiN sensitive film is correlated with its relative structural feature. A high sensitivity of 57.49 mV/pH, a small hysteresis voltage of ∼1 mV, and a low drift rate of 0.31 mV/h were obtained in the TiN sensitive film. In addition, the pH sensitivity of this TiN EGFET sensor was preserved approximately 57 mV/pH after operation time of 180 days. Subsequently, the cTn-I antibodies with carboxyl groups activated by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) along with N-hydroxysuccinimide (NHS) were immobilized on the TiN sensitive film functionalizing with 3-aminopropyl triethoxysilane (APTES). After obtaining the successful immobilization of cTn-I antibodies on the TiN EGFET biosensor, the cTn-I antigen specifically binds with its relative antibody. The cTn-I EGFET biosensor showed a high sensitivity of 21.88 mV/pCcTn-I in a wide dynamic range of 0.01-100 ng/mL. Furthermore, the concentrations of cTn-I in patient sera measured by our TiN EGFET biosensors are comparable to those determined by commercial enzyme-linked immuno-sorbent assay kits.

Nanomaterial-Based Biosensors using Field-Effect Transistors: A Review

Field-effect transistor biosensors (Bio-FET) have attracted great interest in recent years owing to their distinctive properties like high sensitivity, good selectivity, and easy integration into portable and wearable electronic devices. Bio-FET performance mainly relies on the constituent components such as the bio-recognition layer and the transducer, which ensures device stability, sensitivity, and lifetime. Nanomaterial-based Bio-FETs are excellent candidates for biosensing applications. This review discusses the basic concepts, function, and working principles of Bio-FETs, and focuses on the progress of recent research in Bio-FETs in the sensing of neurotransmitters, glucose, nucleic acids, proteins, viruses, and cancer biomarkers using nanomaterials. Finally, challenges in the development of Bio-FETs, as well as an outlook on the prospects of nano Bio-FET-based sensing in various fields, are discussed.

Towards Multi-Analyte Detection with Field-Effect Capacitors Modified with Tobacco Mosaic Virus Bioparticles as Enzyme Nanocarriers

Utilizing an appropriate enzyme immobilization strategy is crucial for designing enzyme-based biosensors. Plant virus-like particles represent ideal nanoscaffolds for an extremely dense and precise immobilization of enzymes, due to their regular shape, high surface-to-volume ratio and high density of surface binding sites. In the present work, tobacco mosaic virus (TMV) particles were applied for the co-immobilization of penicillinase and urease onto the gate surface of a field-effect electrolyte-insulator-semiconductor capacitor (EISCAP) with a p-Si-SiO₂-Ta₂O₅ layer structure for the sequential detection of penicillin and urea. The TMV-assisted bi-enzyme EISCAP biosensor exhibited a high urea and penicillin sensitivity of 54 and 85 mV/dec, respectively, in the concentration range of 0.1-3 mM. For comparison, the characteristics of single-enzyme EISCAP biosensors modified with TMV particles immobilized with either penicillinase or urease were also investigated. The surface morphology of the TMV-modified Ta₂O₅-gate was analyzed by scanning electron microscopy. Additionally, the bi-enzyme EISCAP was applied to mimic an XOR (Exclusive OR) enzyme logic gate.

Sensing of C-Reactive Protein Using an Extended-Gate Field-Effect Transistor with a Tungsten Disulfide-Doped Peptide-Imprinted Conductive Polymer Coating

C-reactive protein (CRP) is a non-specific biomarker of inflammation and may be associated with cardiovascular disease. In recent studies, systemic inflammatory responses have also been observed in cases of coronavirus disease 2019 (COVID-19). Molecularly imprinted polymers (MIPs) have been developed to replace natural antibodies with polymeric materials that have low cost and high stability and could thus be suitable for use in a home-care system. In this work, a MIP-based electrochemical sensing system for measuring CRP was developed. Such a system can be integrated with microfluidics and electronics for lab-on-a-chip technology. MIP composition was optimized using various imprinting template (CRP peptide) concentrations. Tungsten disulfide (WS₂) was doped into the MIPs. Doping not only enhances the electrochemical response accompanying the recognition of the template molecules but also raises the top of the sensing range from 1.0 pg/mL to 1.0 ng/mL of the imprinted peptide. The calibration curve of the WS₂-doped peptide-imprinted polymer-coated electrodes in the extended-gate field-effect transistor platform was obtained and used for the measurement of CRP concentration in real human serum.

Glucose biosensors in clinical practice: principles, limits and perspectives of currently used devices

The demand of glucose monitoring devices and even of updated guidelines for the management of diabetic patients is dramatically increasing due to the progressive rise in the prevalence of diabetes mellitus and the need to prevent its complications. Even though the introduction of the first glucose sensor occurred decades ago, important advances both from the technological and clinical point of view have contributed to a substantial improvement in quality healthcare. This review aims to bring together purely technological and clinical aspects of interest in the field of glucose devices by proposing a roadmap in glucose monitoring and management of patients with diabetes. Also, it prospects other biological fluids to be examined as further options in diabetes care, and suggests, throughout the technology innovation process, future directions to improve the follow-up, treatment, and clinical outcomes of patients.

Laser Illumination Adjustments for Signal-to-Noise Ratio and Spatial Resolution Enhancement in Static 2D Chemical Images of NbOx/IGZO/ITO/Glass Light-Addressable Potentiometric Sensors

In a previous study, a thin In-Ga-Zn-oxide light addressable potentiometric sensor (IGZO LAPS) was indicated to have the advantages of low interference from ambient light, a high photocurrent and transfer efficiency, and a low cost. However, illumination optimization to obtain two-dimensional (2D) chemical images with better spatial resolutions has not been fully investigated. The trigger current and AC-modulated frequency of a 405-nm laser used to illuminate the fabricated IGZO LAPS were modified to check the photocurrent of the sensing area and SU8–2005 masking area, obtaining spatial resolution-related functions for the first time. The trigger current of illumination was adjusted from 0.020 to 0.030 A to compromise between an acceptable photocurrent and the integrity of the SU8–2005 masking layer. The photocurrent (PC) and differential photocurrent (DPC) versus scanning length (SL) controlled by an X-Y stage were used to check the resolved critical dimensions (CDs). The difference between resolved CD and optically measured CD (e.g., delta CD) measured at an AC frequency of 500 Hz revealed overall smaller values, supporting precise measurement in 2D imaging. The signal-to-noise ratio (SNR) has an optimized range of 2.0 to 2.15 for a better resolution for step spacings of both 10 and 2 μm in the scanning procedure to construct static 2D images. Under illumination conditions with a trigger current of 0.025 A and at an AC frequency of 500 Hz, the spatial resolution can be reduced to 10 μm from the pattern width of 6 μm. This developed methodology provides a quantitative evaluation with further optimization in spatial resolution without an extra cost for applications requiring a high spatial resolution, such as single-cell activity.

An Array of On-Chip Integrated, Individually Addressable Capacitive Field-Effect Sensors with Control Gate: Design and Modelling

The on-chip integration of multiple biochemical sensors based on field-effect electrolyte-insulator-semiconductor capacitors (EISCAP) is challenging due to technological difficulties in realization of electrically isolated EISCAPs on the same Si chip. In this work, we present a new simple design for an array of on-chip integrated, individually electrically addressable EISCAPs with an additional control gate (CG-EISCAP). The existence of the CG enables an addressable activation or deactivation of on-chip integrated individual CG-EISCAPs by simple electrical switching the CG of each sensor in various setups, and makes the new design capable for multianalyte detection without cross-talk effects between the sensors in the array. The new designed CG-EISCAP chip was modelled in so-called floating/short-circuited and floating/capacitively-coupled setups, and the corresponding electrical equivalent circuits were developed. In addition, the capacitance-voltage curves of the CG-EISCAP chip in different setups were simulated and compared with that of a single EISCAP sensor. Moreover, the sensitivity of the CG-EISCAP chip to surface potential changes induced by biochemical reactions was simulated and an impact of different parameters, such as gate voltage, insulator thickness and doping concentration in Si, on the sensitivity has been discussed.

Detection of plant virus particles with a capacitive field-effect sensor

Plant viruses are major contributors to crop losses and induce high economic costs worldwide. For reliable, on-site and early detection of plant viral diseases, portable biosensors are of great interest. In this study, a field-effect SiO2-gate electrolyte-insulator-semiconductor (EIS) sensor was utilized for the label-free electrostatic detection of tobacco mosaic virus (TMV) particles as a model plant pathogen. The capacitive EIS sensor has been characterized regarding its TMV sensitivity by means of constant-capacitance method. The EIS sensor was able to detect biotinylated TMV particles from a solution with a TMV concentration as low as 0.025 nM. A good correlation between the registered EIS sensor signal and the density of adsorbed TMV particles assessed from scanning electron microscopy images of the SiO2-gate chip surface was observed. Additionally, the isoelectric point of the biotinylated TMV particles was determined via zeta potential measurements and the influence of ionic strength of the measurement solution on the TMV-modified EIS sensor signal has been studied.

Fabrication and Characterization of In0.9Ga0.1O EGFET pH Sensors

In this study, the In0.9Ga0.1O sensing membrane were deposited by using the RF magnetron sputtering at room temperature and combined with commercial MOSFETs as the extended gate field effect transistor (EGFET) pH sensors. The sensing performance of the In0.9Ga0.1O EGFET pH sensors were measured and analyzed in the pH value of range between 2 to 12. In the saturation region, the pH current sensitivity calculated from the linear relationship between the IDS and pH value was approximately 56.64 μA/pH corresponding to the linearity of 97.8%. In the linear region, the pH voltage sensitivity exhibited high sensitivity and linearity of 43.7 mV/pH and 96.3%, respectively. The In0.9Ga0.1O EGFET pH sensors were successfully fabricated and exhibited great linearity. The analyzed results indicated that the In0.9Ga0.1O was a robust material as a promising sensing membrane and effectively used for pH sensing detection application.

Fully Transparent and Sensitivity-Programmable Amorphous Indium-Gallium-Zinc-Oxide Thin-Film Transistor-Based Biosensor Platforms with Resistive Switching Memories

This paper presents a fully transparent and sensitivity-programmable biosensor based on an amorphous-indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) with embedded resistive switching memories (ReRAMs). The sensor comprises a control gate (CG) and a sensing gate (SG), each with a resistive switching (RS) memory connected, and a floating gate (FG) that modulates the channel conductance of the a-IGZO TFT. The resistive coupling between the RS memories connected to the CG and SG produces sensitivity properties that considerably exceed the limit of conventional ion-sensitive field-effect transistor (ISFET)-based sensors. The resistances of the embedded RS memories were determined by applying a voltage to the CG-FG and SG-FG structures independently and adjusting the compliance current. Sensors constructed using RS memories with different resistance ratios yielded a pH sensitivity of 50.5 mV/pH (R_CG:R_SG = 1:1), 105.2 mV/pH (R_CG:R_SG = 2:1), and 161.9 mV/pH (R_CG:R_SG = 3:1). Moreover, when the R_CG:R_SG = 3:1, the hysteresis voltage width (V_H) and drift rate were 54.4 mV and 32.9 mV/h, respectively. As the increases in V_H and drift rate are lower than the amplified sensitivity, the sensor performs capably. The proposed device is viable as a versatile sensing device capable of detecting various substances, such as cells, antigens, DNA, and gases.

Construction and Application of Graphene Oxide-Bovine Serum Albumin Modified Extended Gate Field Effect Transistor Chiral Sensor

Chirality is an essential natural attribute of organisms. Chiral molecules exhibit differences in biochemical processes, pharmacodynamics, and toxicological properties, and their enantioselective recognition plays an important role in explaining life science processes and guiding drug design. Herein, we developed an ultra-sensitive enantiomer recognition platform based on an extended-gate metal-oxide semiconductor field-effect-transistor (Nafion–GO@BSA–EG-MOSFET) that achieved effective chiral resolution of ultra-sensitive Lysine (Lys) and α-Methylbenzylamine (α-Met) enantiodiscrimination at the femtomole level. Bovine serum albumin (BSA) was immobilized on the surface of graphene oxide (GO) through amide bond coupling to prepare the GO@BSA complex. GO@BSA was drop-cast on deposited Au surfaces with a Nafion solution to afford the extended-gate sensing unit. Effective recognition of chiral enantiomers of mandelic acid (MA), tartaric acid (TA), tryptophan (Trp), Lys and α-Met was realized. Moreover, the introduction of GO reduced non-specific adsorption, and the chiral resolution concentration of α-Met reached the level of picomole in a 5-fold diluted fetal bovine serum (FBS). Finally, the chiral recognition mechanism of the as-fabricated sensor was proposed.

Recent Advances of Field-Effect Transistor Technology for Infectious Diseases

Field-effect transistor (FET) biosensors have been intensively researched toward label-free biomolecule sensing for different disease screening applications. High sensitivity, incredible miniaturization capability, promising extremely low minimum limit of detection (LoD) at the molecular level, integration with complementary metal oxide semiconductor (CMOS) technology and last but not least label-free operation were amongst the predominant motives for highlighting these sensors in the biosensor community. Although there are various diseases targeted by FET sensors for detection, infectious diseases are still the most demanding sector that needs higher precision in detection and integration for the realization of the diagnosis at the point of care (PoC). The COVID-19 pandemic, nevertheless, was an example of the escalated situation in terms of worldwide desperate need for fast, specific and reliable home test PoC devices for the timely screening of huge numbers of people to restrict the disease from further spread. This need spawned a wave of innovative approaches for early detection of COVID-19 antibodies in human swab or blood amongst which the FET biosensing gained much more attention due to their extraordinary LoD down to femtomolar (fM) with the comparatively faster response time. As the FET sensors are promising novel PoC devices with application in early diagnosis of various diseases and especially infectious diseases, in this research, we have reviewed the recent progress on developing FET sensors for infectious diseases diagnosis accompanied with a thorough discussion on the structure of Chem/BioFET sensors and the readout circuitry for output signal processing. This approach would help engineers and biologists to gain enough knowledge to initiate their design for accelerated innovations in response to the need for more efficient management of infectious diseases like COVID-19.

Surface Potential-Controlled Oscillation in FET-Based Biosensors

Field-effect transistor (FET)-based biosensors have garnered significant attention for their label-free electrical detection of charged biomolecules. Whereas conventional output parameters such as threshold voltage and channel current have been widely used for the detection and quantitation of analytes of interest, they require bulky instruments and specialized readout circuits, which often limit point-of-care testing applications. In this study, we demonstrate a simple conversion method that transforms the surface potential into an oscillating signal as an output of the FET-based biosensor. The oscillation frequency is proposed as a parameter for FET-based biosensors owing to its intrinsic advantages of simple and compact implementation of readout circuits as well as high compatibility with neuromorphic applications. An extended-gate biosensor comprising an Al₂O₃-deposited sensing electrode and a readout transistor is connected to a ring oscillator that generates surface potential-controlled oscillation for pH sensing. Electrical measurement of the oscillation frequency as a function of pH reveals that the oscillation frequency can be used as a sensitive and reliable output parameter in FET-based biosensors for the detection of chemical and biological species. We confirmed that the oscillation frequency is directly correlated with the threshold voltage. For signal amplification, the effects of circuit parameters on pH sensitivity are investigated using different methods, including electrical measurements, analytical calculations, and circuit simulations. An Arduino board to measure the oscillation frequency is integrated with the proposed sensor to enable portable and real-time pH measurement for point-of-care testing applications.

Gold Nanoframe Array Electrode for Straightforward Detection of Hydrogen Peroxide

The nanostructuring of a sensing membrane is performed through colloidal nanosphere lithography (NSL) techniques with a tiny polystyrene nanobead template 100 nm in size. The solvent ratio adjustment has been proven to be effective in assisting the monolayer deposition of small templating particles with minimal defects. Two distinct structures, namely, a billowy gold nanostructure (BGN) where the nanobead template is left unetched and a gold nanoframe array (GNA) with a regular ring-like structure after template removal, are used for the extended-gate field-effect transistor (EGFET) electrodes. The GNA structure generates an electroactive surface area significantly (~20%) larger than its geometrical area as well as a greater surface roughness than the BGN. When integrated with the portable constant voltage–constant current (CVCC) FET circuitry for pH screening to determine the optimized measurement conditions for H2O2 sensing, the GNA sensing membrane also shows more improved Nernstian sensitivity at ~50 mV/pH than the BGN electrode. The more optimized sensitivity is then proven using the GNA in the detection of H2O2, the most common representative reactive oxygen species (ROS) involved in the environment, food, and neurodegenerative diseases, such as Parkinson´s and Alzheimer´s diseases. The GNA electrode has a sensitivity of 70.42 mV/log µM [H2O2] and a limit of detection (LoD) of 1.183 µM H2O2. The integrated ion sensing system employing unique, highly ordered gold array gate electrodes and a portable CVCC circuit system has shown a stable real-time output voltage signal, representing an alternative to bulky conventional FET devices for potential on-site H2O2 detection.

Biosensing based on field-effect transistors (FET): Recent progress and challenges

The use of field-Effect-Transistor (FET) type biosensing arrangements has been highlighted by researchers in the field of early biomarker detection and drug screening. Their non-metalized gate dielectrics that are exposed to an electrolyte solution cover the semiconductor material and actively transduce the biological changes on the surface. The efficiency of these novel devices in detecting different biomolecular analytes in a real-time, highly precise, specific, and label-free manner has been validated by numerous research studies. Considerable progress has been attained in designing FET devices, especially for biomedical diagnosis and cell-based assays in the past few decades. The exceptional electronic properties, compactness, and scalability of these novel tools are very desirable for designing rapid, label-free, and mass detection of biomolecules. With the incorporation of nanotechnology, the performance of biosensors based on FET boosts significantly, particularly, employment of nanomaterials such as graphene, metal nanoparticles, single and multi-walled carbon nanotubes, nanorods, and nanowires. Besides, their commercial availability, and high-quality production on a large-scale, turn them to be one of the most preferred sensing and screening platforms. This review presents the basic structural setup and working principle of different types of FET devices. We also focused on the latest progression regarding the use of FET biosensors for the recognition of viruses such as, recently emerged COVID-19, Influenza, Hepatitis B Virus, protein biomarkers, nucleic acids, bacteria, cells, and various ions. Additionally, an outline of the development of FET sensors for investigations related to drug development and the cellular investigation is also presented. Some technical strategies for enhancing the sensitivity and selectivity of detection in these devices are addressed as well. However, there are still certain challenges which are remained unaddressed concerning the performance and clinical use of transistor-based point-of-care (POC) instruments; accordingly, expectations about their future improvement for biosensing and cellular studies are argued at the end of this review.

A Reliable BioFET Immunosensor for Detection of p53 Tumour Suppressor in Physiological-Like Environment

The concentration of wild-type tumour suppressor p53_wt in cells and blood has a clinical significance for early diagnosis of some types of cancer. We developed a disposable, label-free, field-effect transistor-based immunosensor (BioFET), able to detect p53_wt in physiological buffer solutions, over a wide concentration range. Microfabricated, high-purity gold electrodes were used as single-use extended gates (EG), which avoid direct interaction between the transistor gate and the biological solution. Debye screening, which normally hampers target charge effect on the FET gate potential and, consequently, on the registered FET drain-source current, at physiological ionic strength, was overcome by incorporating a biomolecule-permeable polymer layer on the EG electrode surface. Determination of an unknown p53_wt concentration was obtained by calibrating the variation of the FET threshold voltage versus the target molecule concentration in buffer solution, with a sensitivity of 1.5 ± 0.2 mV/decade. The BioFET specificity was assessed by control experiments with proteins that may unspecifically bind at the EG surface, while 100pM p53_wt concentration was established as limit of detection. This work paves the way for fast and highly sensitive tools for p53_wt detection in physiological fluids, which deserve much interest in early cancer diagnosis and prognosis.

Suppression of Ionic Doping by Molecular Dopants in Conjugated Polymers for Improving Specificity and Sensitivity in Biosensing Applications

Ionic doping effects in conjugated polymers often cause nonspecific signaling and a low selectivity of bioelectronic sensing. Using remote-gate field-effect transistor characterization of molecular and ionic doping in poly(3-hexylthiophene) (P3HT) and acid-functionalized polythiophene, poly[3-(3-carboxypropyl) thiophene-2,5-diyl] (PT-COOH), we discovered that proton doping effects on the interfacial potential occurring in P3HT could be suppressed by sequentially doping P3HT by 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). To be specific, intrinsic pH sensitivity shown by pure P3HT (18 mV/pH in a range from pH 3 to 9) was fully dissipated for doped P3HT:F4TCNQ. However, F4TCNQ sequential doping instead increases pH sensitivity of acid-functionalized polythiophene, PT-COOH (40 mV/pH), compared to that of a pure PT-COOH (30 mV/pH). Interactions between polythiophene backbone and side chains, which constrain the activity of COOH, are weakened by stronger F4TCNQ doping leaving behind responsive COOH groups exposed to aqueous solutions. This is supported by the reduced pH sensitivity of PT-COOH sequentially doped by a weaker dopant, tetracyanoethylene (TCNE) (21 mV/pH). Thus, doping is shown to stabilize a nonpolar conjugated polymer to pH-induced fluctuations on one hand, and to activate a COOH side chain to pH-induced response on the other.

Capacitive Field-Effect EIS Chemical Sensors and Biosensors: A Status Report

Electrolyte-insulator-semiconductor (EIS) field-effect sensors belong to a new generation of electronic chips for biochemical sensing, enabling a direct electronic readout. The review gives an overview on recent advances and current trends in the research and development of chemical sensors and biosensors based on the capacitive field-effect EIS structure—the simplest field-effect device, which represents a biochemically sensitive capacitor. Fundamental concepts, physicochemical phenomena underlying the transduction mechanism and application of capacitive EIS sensors for the detection of pH, ion concentrations, and enzymatic reactions, as well as the label-free detection of charged molecules (nucleic acids, proteins, and polyelectrolytes) and nanoparticles, are presented and discussed.

The Leakage Mechanism of the Package of the AlGaN/GaN Liquid Sensor

Wide bandgap gallium nitride (GaN)-based devices have attracted a lot of attention in optoelectronics, power electronics, and sensing applications. AlGaN/GaN based sensors, featuring high-density and high-mobility two-dimensional electron gas (2DEG), have been demonstrated to be effective chemical sensors and biosensors in the liquid environment. One of the key factors limiting the wide adoption of the AlGaN/GaN liquid sensor is the package reliability issue. In this paper, the reliability of three types of sensor packaging materials (SiO₂/Si₃N₄, PI, and SiO₂/Si₃N₄/PI) on top of 5-μm metal are tested in Phosphate buffer saline (PBS) solution. By analyzing the I-V characteristics, it is found that the leakage currents within different regimes follow distinct leakage models, whereby the key factors limiting the leakage current are identified. Moreover, the physical mechanisms of the package failure are illustrated. The failure of the SiO₂/Si₃N₄ package is due to its porous structure such that ions in the solution can penetrate into the packaging material and reduce its resistivity. The failure of the PI package at a relatively low voltage (<3 V) is mainly due to the poor adhesion of PI to the AlGaN surface such that the solution can reach the electrode by the "lateral drilling" effect. The SiO₂/Si₃N₄/PI package achieves less than 10 μA leakage current at 5 V voltage stress because it combines the advantages of the SiO₂/Si₃N₄ and the PI packages. The analysis in this work can provide guidelines for the design and failure mechanism analysis of packaging materials.

Emerging Designs of Electronic Devices in Biomedicine

A long-standing goal of nanoelectronics is the development of integrated systems to be used in medicine as sensor, therapeutic, or theranostic devices. In this review, we examine the phenomena of transport and the interaction between electro-active charges and the material at the nanoscale. We then demonstrate how these mechanisms can be exploited to design and fabricate devices for applications in biomedicine and bioengineering. Specifically, we present and discuss electrochemical devices based on the interaction between ions and conductive polymers, such as organic electrochemical transistors (OFETs), electrolyte gated field-effect transistors (FETs), fin field-effect transistor (FinFETs), tunnelling field-effect transistors (TFETs), electrochemical lab-on-chips (LOCs). For these systems, we comment on their use in medicine.

Field-Effect Sensors for Virus Detection: From Ebola to SARS-CoV-2 and Plant Viral Enhancers

Coronavirus disease 2019 (COVID-19) is a novel human infectious disease provoked by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Currently, no specific vaccines or drugs against COVID-19 are available. Therefore, early diagnosis and treatment are essential in order to slow the virus spread and to contain the disease outbreak. Hence, new diagnostic tests and devices for virus detection in clinical samples that are faster, more accurate and reliable, easier and cost-efficient than existing ones are needed. Due to the small sizes, fast response time, label-free operation without the need for expensive and time-consuming labeling steps, the possibility of real-time and multiplexed measurements, robustness and portability (point-of-care and on-site testing), biosensors based on semiconductor field-effect devices (FEDs) are one of the most attractive platforms for an electrical detection of charged biomolecules and bioparticles by their intrinsic charge. In this review, recent advances and key developments in the field of label-free detection of viruses (including plant viruses) with various types of FEDs are presented. In recent years, however, certain plant viruses have also attracted additional interest for biosensor layouts: Their repetitive protein subunits arranged at nanometric spacing can be employed for coupling functional molecules. If used as adapters on sensor chip surfaces, they allow an efficient immobilization of analyte-specific recognition and detector elements such as antibodies and enzymes at highest surface densities. The display on plant viral bionanoparticles may also lead to long-time stabilization of sensor molecules upon repeated uses and has the potential to increase sensor performance substantially, compared to conventional layouts. This has been demonstrated in different proof-of-concept biosensor devices. Therefore, richly available plant viral particles, non-pathogenic for animals or humans, might gain novel importance if applied in receptor layers of FEDs. These perspectives are explained and discussed with regard to future detection strategies for COVID-19 and related viral diseases.

TiO2 Nano Flowers Based EGFET Sensor for pH Sensing

In this study, pH sensors were successfully fabricated on a fluorine-doped tin oxide substrate and grown via hydrothermal methods for 8 h for pH sensing characteristics. The morphology was obtained by high-resolution scanning electron microscopy and showed randomly oriented flower-like nanostructures. The TiO2 nanoflower pH sensors were measured over a pH range of 2–12. Results showed a high sensitivity of the TiO2 nano-flowers pH sensor, 2.7 (μA)1/2/pH, and a linear relationship between IDS and pH (regression of 0.9991). The relationship between voltage reference and pH displayed a sensitivity of a 46 mV/pH and a linear regression of 0.9989. The experimental result indicated that a flower-like TiO2 nanostructure extended gate field effect transistor (EGFET) pH sensor effectively detected the pH value.

Dynamic pH Sensor with Embedded Calibration Scheme by Advanced CMOS FinFET Technology

In this work, we present a novel pH sensor using efficient laterally coupled structure enabled by Complementary Metal-Oxide Semiconductor (CMOS) Fin Field-Effect Transistor (FinFET) processes. This new sensor features adjustable sensitivity, wide sensing range, multi-pad sensing capability and compatibility to advanced CMOS technologies. With a self-balanced readout scheme and proposed corresponding circuit, the proposed sensor is found to be easily embedded into integrated circuits (ICs) and expanded into sensors array. To ensure the robustness of this new device, the transient response and noise analysis are performed. In addition, an embedded calibration operation scheme is implemented to prevent the proposed sensing device from the background offset from process variation, providing reliable and stable sensing results.

Analytical Platform To Characterize Dopant Solution Concentrations, Charge Carrier Densities in Films and Interfaces, and Physical Diffusion in Polymers Utilizing Remote Field-Effect Transistors

Characterizing doping effects in a conductive polymer and physical diffusion in a passive polymer were performed using a remote-gate field-effect transistor (RG FET) detection system that was able to measure the electrical potential perturbation of a polymer film coupled to the gate of a silicon FET. Poly(3-hexylthiophene) (P3HT) film doped using various concentrations of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) solutions imposed additional positive potentials on the P3HT RG, resulting in a lower threshold voltage ( V_th) on the n-channel silicon FET. Changes in V_th were related to the induced hole concentrations and hole mobility in P3HT films by using our V_th shifting model for the RG FET. We discovered that the electron-donating P3HT and even inorganic materials, indium tin oxide and gold, showed similar electrical potential perturbations dependent on the concentration of F4TCNQ in overlying solutions as the dopant radical anions maximally covered the surfaces. This suggests that there are limited electroactive sites for F4TCNQ binding on electron donor surfaces which results in a similar number of positive charges in film materials forming dipoles with the F4TCNQ radical counteranions. The effect of electron acceptors such as 7,7,8,8-tetracyanoquinodimethane and tetracyanoethylene was compared to that of F4TCNQ in terms of V_th shift using our analytical tool, with differences attributed to acceptor size and reduction potential. Meanwhile, this FET analysis tool offered a means of monitoring the physical diffusion of small molecules, exemplified by F4TCNQ, in the passive polymer polystyrene, driven by concentration gradients. The technique allows for nondestructive, nonspectroscopic, ambient characterization of electron donor-acceptor interactions at surfaces.