High sensitivity glucose detection at extremely low concentrations using a MoS2-based field-effect transistor

2D Materials in Advanced Electronic Biosensors for Point-of-Care Devices

Since two-dimensionalal (2D) materials have distinct chemical and physical properties, they are widely used in various sectors of modern technologies. In the domain of diagnostic biodevices, particularly for point-of-care (PoC) biomedical diagnostics, 2D-based field-effect transistor biosensors (bio-FETs) demonstrate substantial potential. Here, in this review article, the operational mechanisms and detection capabilities of biosensing devices utilizing graphene, transition metal dichalcogenides (TMDCs), black phosphorus, and other 2D materials are addressed in detail. The incorporation of these materials into FET-based biosensors offers significant advantages, including low detection limits (LOD), real-time monitoring, label-free diagnosis, and exceptional selectivity. The review also highlights the diverse applications of these biosensors, ranging from conventional to wearable devices, underscoring the versatility of 2D material-based FET devices. Additionally, the review provides a comprehensive assessment of the limitations and challenges faced by these devices, along with insights into future prospects and advancements. Notably, a detailed comparison of FET-based biosensors is tabulated along with various other biosensing platforms and their working mechanisms. Ultimately, this review aims to stimulate further research and innovation in this field while educating the scientific community about the latest advancements in 2D materials-based biosensors.

Unleashing the potential of tungsten disulfide: Current trends in biosensing and nanomedicine applications

The discovery of graphene ignites a great deal of interest in the research and advancement of two-dimensional (2D) layered materials. Within it, semiconducting transition metal dichalcogenides (TMDCs) are highly regarded due to their exceptional electrical and optoelectronic properties. Tungsten disulfide (WS2) is a TMDC with intriguing properties, such as biocompatibility, tunable bandgap, and outstanding photoelectric characteristics. These features make it a potential candidate for chemical sensing, biosensing, and tumor therapy. Despite the numerous reviews on the synthesis and application of TMDCs in the biomedical field, no comprehensive study still summarizes and unifies the research trends of WS2 from synthesis to biomedical applications. Therefore, this review aims to present a complete and thorough analysis of the current research trends in WS2 across several biomedical domains, including biosensing and nanomedicine, covering antibacterial applications, tissue engineering, drug delivery, and anticancer treatments. Finally, this review also discusses the potential opportunities and obstacles associated with WS2 to deliver a new outlook for advancing its progress in biomedical research.

One-step hydrothermal synthesis of CuS/MoS2 composite for use as an electrochemical non-enzymatic glucose sensor

Early diagnosis may be crucial for the prevention of chronic diabetes mellitus. For that herein, we prepared a CuS/MoS2 composite for a non-enzymatic glucose sensor through a one-step hydrothermal method owing to the synergetic effect of CuS/MoS2. The surface morphology of CuS/MoS2 was studied by Field Emission Scanning Electron Microscopy (FESEM) and Cs-corrected Scanning Transmission Electron Microscopy (Cs-STEM). The crystallinity and surface composition of CuS/MoS2 were analyzed by X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) respectively. The working electrode was prepared from CuS/MoS2 electrocatalyst, and for that dispersed solution of electrocatalyst was used to fabricate the material-loaded glassy carbon electrode (GC). CuS/MoS2 composite shows the viability of electrocatalyst to oxidize glucose in an alkaline solution with sensitivity and detection limit of 252.71 μA mM-1 cm-2 and 1.52 μM respectively. The proposed glucose sensor showed reasonable stability and potential selectivity during electrochemical analysis. Accordingly, the CuS/MoS2 composite has potential as a viable material for glucose sensing in diluted human serum.

An integrated wearable sticker based on extended-gate AlGaN/GaN high electron mobility transistors for real-time cortisol detection in human sweat

Cortisol hormone imbalances can be detected through non-invasive sweat monitoring using field-effect transistor (FET) biosensors, which provide rapid and sensitive detection. However, challenges like skin compatibility and integration with sweat collection have hindered FET biosensors as wearable sensing platforms. In this study, we present an integrated wearable sticker for real-time cortisol detection based on an extended-gate AlGaN/GaN high electron mobility transistor (HEMT) combined with a soft bottom substrate and flexible channel for sweat collection. The developed devices exhibit excellent linearity (R2 = 0.990) and a high sensitivity of 1.245 μA dec-1 for cortisol sensing from 1 nM to 100 μM in high-ionic-strength solution, with successful cortisol detection demonstrated using authentic human sweat samples. Additionally, the chip's microminiature design effectively reduces bending impact during the wearable process of traditional soft binding sweat sensors. The extendedgate structure design of the HEMT chip enhances both width-to-length ratio and active sensing area, resulting in an exceptionally low detection limit of 100 fM. Futhermore, due to GaN material's inherent stability, this device exhibits long-term stability with sustained performance within a certain attenuation range even after 60 days. These stickers possess small, lightweight, and portable features that enable real-time cortisol detection within 5 minutes through direct sweat collection. The application of this technology holds great potential in the field of personal health management, facilitating users to conveniently monitor their mental and physical conditions.

Field effect transistor based wearable biosensors for healthcare monitoring

The rapid advancement of wearable biosensors has revolutionized healthcare monitoring by screening in a non-invasive and continuous manner. Among various sensing techniques, field-effect transistor (FET)-based wearable biosensors attract increasing attention due to their advantages such as label-free detection, fast response, easy operation, and capability of integration. This review explores the innovative developments and applications of FET-based wearable biosensors for healthcare monitoring. Beginning with an introduction to the significance of wearable biosensors, the paper gives an overview of structural and operational principles of FETs, providing insights into their diverse classifications. Next, the paper discusses the fabrication methods, semiconductor surface modification techniques and gate surface functionalization strategies. This background lays the foundation for exploring specific FET-based biosensor designs, including enzyme, antibody and nanobody, aptamer, as well as ion-sensitive membrane sensors. Subsequently, the paper investigates the incorporation of FET-based biosensors in monitoring biomarkers present in physiological fluids such as sweat, tears, saliva, and skin interstitial fluid (ISF). Finally, we address challenges, technical issues, and opportunities related to FET-based biosensor applications. This comprehensive review underscores the transformative potential of FET-based wearable biosensors in healthcare monitoring. By offering a multidimensional perspective on device design, fabrication, functionalization and applications, this paper aims to serve as a valuable resource for researchers in the field of biosensing technology and personalized healthcare.

Non-invasive, ultrasensitive detection of glucose in saliva using metal oxide transistors

Transistor-based biosensors represent an emerging technology for inexpensive point-of-care testing (POCT) applications. However, the limited sensitivity of the current transistor technologies hinders their practical deployment. In this study, we developed tri-channel In2O3/ZnO heterojunction thin-film transistors (TFTs) featuring the surface-immobilized enzyme glucose oxidase to detect glucose in various biofluids. This unusual channel design facilitates strong coupling between the electrons transported along the buried In2O3/ZnO heterointerface and the electrostatic perturbations caused by the interactions between glucose and surface-immobilized glucose oxidase. The enzyme selectively binds to glucose, causing a change in charge density on the channel surface. By exploring this effect, the solid-state biosensing TFT (BioTFT) can selectively detect glucose in artificial and real saliva over a wide range of concentrations from 500 nM to 20 mM with limits of detection of ∼365 pM (artificial saliva) and ∼416 nM (real saliva) in less than 60 s. The specificity of the sensor towards glucose has been demonstrated against various interfering species in artificial saliva, further highlighting its unique capabilities. Moreover, the BioTFTs exhibited good operating stability upon storage for up to two weeks, with relative standard deviation (RSD) values ranging from 2.36% to 6.39% for 500 nM glucose concentration. Our BioTFTs are easy to manufacture with reliable operation, making them ideal for non-invasive POCT applications.

Flexible Bio-Electronic Hybrid Metal-Oxide Channel FET as a Glucose Sensor

A high-sensitivity flexible field-effect transistor (FET) based glucose sensor is fabricated that can surpass the conventional electrochemical glucometers in terms of sensitivity, limit of detection, and other performance parameters. The proposed biosensor is based on the FET operation with the advantage of amplification which provides a high sensitivity and a very low limit of detection. Hybrid metal oxide (ZnO and CuO) nanostructures have been synthesized in the form of hollow spheres (ZnO/CuO-NHS). The FET was fabricated by depositing ZnO/CuO-NHS on the interdigitated electrodes. Glucose oxidase (GOx) was immobilized successfully on the ZnO/CuO-NHS. Three different outputs of the sensor are examined, the FET current, the relative current change, and the drain voltage. The sensitivity of the sensor for each output type has been calculated. The readout circuit can convert the current change to the voltage change that has been used for wireless transmission. The sensor has a very low limit of detection of 30 nM with satisfactory reproducibility, good stability, and high selectivity. The electrical response of the FET biosensor towards the real human blood serum samples demonstrated that it can be offered as a potential device for glucose detection in any medical application.

Development of a portable smart Glucometer with two electrode bio-electronic test strip patch based on Cu/Au/rGO/PEDOT:PSS

Today, the importance of blood sugar monitoring in diabetic patients has created a global need to develop new glucometers. This article presents the fabrication of a portable smart glucometer for monitoring blood glucose with high sensitivity. The glucometer employs a bio-electronic test strip patch fabricated by the structure of Cu/Au/rGO/PEDOT: PSS on interdigitated electrodes. We demonstrate that this structure based on two-electrode can be superior to the three-electrode electrochemical test strips available in the market. It has good electro-catalytic properties that indicate high-performance sensing of blood glucose. The proposed bio-electronic glucometer can surpass the commercial electrochemical test strips in terms of response time, detection range, and limit of detection. Electronic modules used for the fabrication of smart glucometers, such as a power supply, analog to digital converter, OLED screen, and, wireless transmission module, are integrated onto a printed circuit board and packaged as a bio-electronics glucometer, enabling the comfortable handling of this blood glucose monitoring. The characteristics of active layers biosensors were investigated by SEM, and AFM. The glucometer can monitor glucose in the wide detection range of 0-100 mM, the limit of detection (1 µM) with a sensitivity of 5.65 mA mM^-1 and excellent sensing performance such as high selectivity, high reproducibility, and good stability of fabricated test strips. With 11 human blood and serum samples, the glucometer demonstrated high clinical accuracy with the best value of RSD of 0.012.

Aptamer-functionalized field-effect transistor biosensors for disease diagnosis and environmental monitoring

Nano-biosensors that are composed of recognition molecules and nanomaterials have been extensively utilized in disease diagnosis, health management, and environmental monitoring. As a type of nano-biosensors, molecular specificity field-effect transistor (FET) biosensors with signal amplification capability exhibit prominent advantages including fast response speed, ease of miniaturization, and integration, promising their high sensitivity for molecules detection and identification. With intrinsic characteristics of high stability and structural tunability, aptamer has become one of the most commonly applied biological recognition units in the FET sensing fields. This review summarizes the recent progress of FET biosensors based on aptamer functionalized nanomaterials in medical diagnosis and environmental monitoring. The structure, sensing principles, preparation methods, and functionalization strategies of aptamer modified FET biosensors were comprehensively summarized. The relationship between structure and sensing performance of FET biosensors was reviewed. Furthermore, the challenges and future perspectives of FET biosensors were also discussed, so as to provide support for the future development of efficient healthcare management and environmental monitoring devices.

Synthesis of a novel carboxybetaine copolymer with different spacer lengths and inhibition of nonspecific protein adsorption on its polymer film

Herein, we designed and synthesized a thermally stable carboxybetaine copolymer with a one- or three-carbon spacer between ammonium and carboxylate groups (CBMA1 and CBMA3) to create an anti-nonspecific adsorption surface with the ability to immobilize antibodies. A series of controlled poly(N,N-dimethylaminoethyl methacrylate) was successfully prepared using reversible addition-fragmentation chain-transfer (RAFT) polymerization and was derived to carboxybetaine copolymers of poly(CBMA1-co-CBMA3) [P(CBMA1/CBMA3)] with various CBMA1 contents, including the homopolymers of CBMA1 and CBMA3. Thermal stability of the carboxybetaine (co)polymers was higher than that of the carboxybetaine polymer with a two-carbon spacer (PCBMA2). Further, we also evaluated nonspecific protein adsorption in fetal bovine serum and antibody immobilization on the substrate coated with P(CBMA1/CBMA3) copolymers using surface plasmon resonance (SPR) analysis. As the CBMA1 content increased, nonspecific protein adsorption on the P(CBMA1/CBMA3) copolymer surface decreased. Similarly, the immobilization amount of the antibody decreased as the CBMA1 content increased. However, the figure of merit (FOM), defined as the ratio of the amount of antibody immobilization to that of nonspecific protein adsorption, depended on the CBMA3 content; FOM was higher when the CBMA3 content was 20-40% than those of CBMA1 and CBMA3 homopolymers. These findings will help enhance the sensitivity of the analysis using molecular interaction measurement devices, such as SPR and quartz crystal microbalance.

Polyethylene Glycol Functionalized Silicon Nanowire Field-Effect Transistor Biosensor for Glucose Detection

Accurate monitoring of blood glucose levels is crucial for the diagnosis of diabetes patients. In this paper, we proposed a simple "mixed-catalyzer layer" modified silicon nanowire field-effect transistor biosensor that enabled direct detection of glucose with low-charge in high ionic strength solutions. A stable screening system was established to overcome Debye screening effect by forming a porous biopolymer layer with polyethylene glycol (PEG) modified on the surface of SiNW. The experimental results show that when the optimal ratio (APTMS:silane-PEG = 2:1) modified the surface of silicon nanowires, glucose oxidase can detect glucose in the concentration range of 10 nM to 10 mM. The sensitivity of the biosensor is calculated to be 0.47 μAcm^-2mM^-1, its fast response time not exceeding 8 s, and the detection limit is up to 10 nM. This glucose sensor has the advantages of high sensitivity, strong specificity and fast real-time response. Therefore, it has a potential clinical application prospect in disease diagnosis.

Development of MoS2-ZnO heterostructures: an efficient bifunctional catalyst for the detection of glucose and degradation of toxic organic dyes

The heterostructure catalyst MoS2-ZnO possesses binary properties and provides a novel platform for the remediation of environmental as well as health issues.

Blood glucose sensing by back gated transistor strips sensitized by CuO hollow spheres and rGO

In this work, a highly sensitive flexible glucose sensor based on a field effect transistor (FET) has been fabricated. It is shown that the proposed flexible transistor can be used as new non-enzymatic blood glucose test strips. CuO hollow-spheres decorated with reduced graphene oxide have been synthesized using the hydrothermal method. The shells of the hollow micro-spheres are formed by nanostructures. The synthesized nanostructured hollow micro-spheres (rGO/CuO-NHS) are deposited on a flexible PET substrate between interdigitated electrodes as the channel of a back gate transistor. The channel concentration and the FET bias are optimized so that the sensor exhibits extremely low limit of detection and high sensitivity. The combination of selective porous CuO hollow spheres and the high surface to volume ratio of their nanostructured shells with the high mobility and high conductivity rGO led to faster and higher charge-transfer capability and superior electro-catalyst activity for glucose oxidation. The glucose-dependent electrical responses of the sensor is measured in both resistive and transistor action modes. The amplification of the current by the induced electric field of the gate in the proposed FET-based biosensor provides advantages such as higher sensitivity and lower limit of detection compared to the resistive sensor. The flexible glucose sensor has a sensitivity of 600 μA μM^-1 and a limit of detection of 1 nM with high reproducibility, good stability, and highly selectivity. The high accuracy response of the biosensor towards the real blood serum samples showed that it can be used as a test strip for glucose detection in real blood samples.

MoS2 and MoS2 Nanocomposites for Adsorption and Photodegradation of Water Pollutants: A Review

The need for fresh and conveniently treated water has become a major concern in recent years. Molybdenum disulfide (MoS₂) nanomaterials are attracting attention in various fields, such as energy, hydrogen production, and water decontamination. This review provides an overview of the recent developments in MoS₂-based nanomaterials for water treatment via adsorption and photodegradation. Primary attention is given to the structure, properties, and major methods for the synthesis and modification of MoS₂, aiming for efficient water-contaminant removal. The combination of MoS₂ with other components results in nanocomposites that can be separated easily or that present enhanced adsorptive and photocatalytic properties. The performance of these materials in the adsorption of heavy metal ions and organic contaminants, such as dyes and drugs, is reviewed. The review also summarizes current progress in the photocatalytic degradation of various water pollutants, using MoS₂-based nanomaterials under UV-VIS light irradiation. MoS₂-based materials showed good activity after several reuse cycles and in real water scenarios. Regarding the ecotoxicity of the MoS₂, the number of studies is still limited, and more work is needed to effectively evaluate the risks of using this nanomaterial in water treatment.

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

Advancement and Challenges of Biosensing Using Field Effect Transistors

Field-effect transistors (FETs) have become eminent electronic devices for biosensing applications owing to their high sensitivity, faster response and availability of advanced fabrication techniques for their production. The device physics of this sensor is now well understood due to the emergence of several numerical modelling and simulation papers over the years. The pace of advancement along with the knowhow of theoretical concepts proved to be highly effective in detecting deadly pathogens, especially the SARS-CoV-2 spike protein of the coronavirus with the onset of the (coronavirus disease of 2019) COVID-19 pandemic. However, the advancement in the sensing system is also accompanied by various hurdles that degrade the performance. In this review, we have explored all these challenges and how these are tackled with innovative approaches, techniques and device modifications that have also raised the detection sensitivity and specificity. The functional materials of the device are also structurally modified towards improving the surface area and minimizing power dissipation for developing miniaturized microarrays applicable in ultra large scale integration (ULSI) technology. Several theoretical models and simulations have also been carried out in this domain which have given a deeper insight on the electron transport mechanism in these devices and provided the direction for optimizing performance.

Design and Analysis of Highly Sensitive LSPR-Based Metal–Insulator–Metal Nano-Discs as a Biosensor for Fast Detection of SARS-CoV-2

For over 2 years, the coronavirus has been the most urgent challenge to humanity, and the development of rapid and accurate detection methods is crucial to control these viruses. Here, a 3D FDTD simulation of Au/SiO2/Au metal–insulator–metal (MIM) nanostructures as a biosensor was performed. The strong coupling between the two plasmonic interfaces in the Au/SiO2/Au cavity helped us to obtain relatively higher sensitivity. The attachment of SARS-CoV-2 changed the refractive index, which was used to detect SARS-CoV-2. Due to the higher overlapping of plasmonic mode with the environment of nano-discs, a higher sensitivity of 312.8 nm/RIU was obtained. The peak wavelength of the proposed structure shifted by approximately 47 nm when the surrounding medium refractive index changed from 1.35 (no binding) to 1.5 (full binding). Consequently, the SPR peak intensity variation can be used as another sensing mechanism to detect SARS-CoV-2. Finally, the previously reported refractive index changes for various concentrations of the SARS-CoV-2 S-glycoprotein solution were used to evaluate the performance of the designed biosensor.

Aptamer-Functionalized Carbon Nanotube Field-Effect Transistor Biosensors for Alzheimer's Disease Serum Biomarker Detection

Blood-biomarker-based tests are highly important for the early clinical diagnosis of Alzheimer's disease (AD) and the treatment and care of AD patients, but the complex serum environment and extremely low abundance of AD blood protein biomarkers present challenges. Nanomaterials are promising for constructing highly sensitive transistor-based biosensors due to their small size. However, such biosensors are difficult to fabricate on a large scale and suffer from the lack of combined optimization of reproducibility and sensitivity in complex physiological fluids. In this work, field-effect transistor (FET) biosensors based on highly uniform semiconducting carbon nanotube (CNT) thin films are mass produced to achieve highly sensitive and selective detection of the AD core blood biomarkers of β-amyloid (Aβ). The combination of the mass-produced CNT FET sensors and oligonucleotide aptamers as efficient bioreceptors enables reliable and reproducible sub-femtomolar detection in full human serum for Aβ₄₂ and Aβ₄₀ peptides and has outperformed other methods reported to date. The adsorption of biological substrates to the sensor was significantly reduced by multiple blocking steps, resulting in selectivity ratios of up to 730% (Aβ₄₀) and 800% (Aβ₄₂). The aptamer-functionalized CNT FET biosensor exhibits a large dynamic range (>10⁴), rapid response time (several minutes), and low variation (<10%) and can be delivered as a low-cost and rapid clinical detection technology for the early diagnosis and mass screening of AD. This platform will help bring complex laboratory-based and expensive diagnostic tools to the point of care.

Vertically Oriented Zinc Oxide Nanorod-Based Electrolyte-Gated Field-Effect Transistor for High-Performance Glucose Sensing

Nanomaterial-based biosensors are a promising fit for portable and field-deployable diagnosis sensor devices due to their mass production, miniaturization, and integration capabilities. However, the fabrication of highly stable and reproducible biosensor devices is challenging. In this work, we grow a vertically oriented architecture of zinc oxide nanorods onto the active working area (i.e., the channel between the source and drain) of a field-effect transistor (FET) using a low-temperature hydrothermal method. The glucose oxidase enzyme was immobilized on the zinc oxide nanorod surface by a physical adsorption method to fabricate the electrolyte-gated FET-based glucose biosensor. The electrical properties of the electrolyte-gated FET biosensor were measured with different glucose concentrations. We found a linear increase in current up to 80 mM glucose concentration with high sensitivity (74.78 μA/mMcm²) and a low detection limit (∼0.05 mM). We illustrate a highly reproducible fabrication process of zinc oxide nanorod-based FETs, where vertically grown nanorods with a higher surface-to-volume ratio enhance the enzyme immobilization, provide a microenvironment for longer enzyme activity, and translate to better glucose sensing parameters. Additionally, our electrolyte-gated FET biosensor showed promising application in freshly drawn mouse blood samples. These findings suggest a great opportunity to translate into practical high-performance biosensors for a broad range of analytes.

A Review of Transition Metal Dichalcogenides-Based Biosensors

Transition metal dichalcogenides (TMDCs) are widely used in biosensing applications due to their excellent physical and chemical properties. Due to the properties of biomaterial targets, the biggest challenge that biosensors face now is how to improve the sensitivity and stability. A lot of materials had been used to enhance the target signal. Among them, TMDCs show excellent performance in enhancing biosensing signals because of their metallic and semi-conducting electrical capabilities, tunable band gap, large specific surface area and so on. Here, we review different functionalization methods and research progress of TMDCs-based biosensors. The modification methods of TMDCs for biosensor fabrication mainly include two strategies: non-covalent and covalent interaction. The article summarizes the advantages and disadvantages of different modification strategies and their effects on biosensing performance. The authors present the challenges and issues that TMDCs need to be addressed in biosensor applications. Finally, the review expresses the positive application prospects of TMDCs-based biosensors in the future.

Two-Dimensional Field-Effect Transistor Sensors: The Road toward Commercialization

The evolutionary success in information technology has been sustained by the rapid growth of sensor technology. Recently, advances in sensor technology have promoted the ambitious requirement to build intelligent systems that can be controlled by external stimuli along with independent operation, adaptivity, and low energy expenditure. Among various sensing techniques, field-effect transistors (FETs) with channels made of two-dimensional (2D) materials attract increasing attention for advantages such as label-free detection, fast response, easy operation, and capability of integration. With atomic thickness, 2D materials restrict the carrier flow within the material surface and expose it directly to the external environment, leading to efficient signal acquisition and conversion. This review summarizes the latest advances of 2D-materials-based FET (2D FET) sensors in a comprehensive manner that contains the material, operating principles, fabrication technologies, proof-of-concept applications, and prototypes. First, a brief description of the background and fundamentals is provided. The subsequent contents summarize physical, chemical, and biological 2D FET sensors and their applications. Then, we highlight the challenges of their commercialization and discuss corresponding solution techniques. The following section presents a systematic survey of recent progress in developing commercial prototypes. Lastly, we summarize the long-standing efforts and prospective future development of 2D FET-based sensing systems toward commercialization.

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.

Effect of Al2O3 Passive Layer on Stability and Doping of MoS2 Field-Effect Transistor (FET) Biosensors

Molybdenum disulfide (MoS2) features a band gap of 1.3 eV (indirect) to 1.9 eV (direct). This tunable band gap renders MoS2 a suitable conducting channel for field-effect transistors (FETs). In addition, the highly sensitive surface potential in MoS2 layers allows the feasibility of FET applications in biosensors, where direct immobilization and detection of biological molecules are conducted in wet conditions. In this work, we report, for the first time, the degradation of chemical vapor deposition (CVD) grown MoS2 FET-based sensors in the presence of phosphate buffer and water, which caused false positive response in detection. We conclude the degradation was originated by physical delamination of MoS2 thin films from the SiO2 substrate. The problem was alleviated by coating the sensors with a 30 nm thick aluminum oxide (Al2O3) layer using atomic layer deposition technique (ALD). This passive oxide thin film not only acted as a protecting layer against the device degradation but also induced a strong n-doping onto MoS2, which permitted a facile method of detection in MoS2 FET-based sensors using a low-power mode chemiresistive I-V measurement at zero gate voltage (Vgate = 0 V). Additionally, the oxide layer provided available sites for facile functionalization with bioreceptors. As immunoreaction plays a key role in clinical diagnosis and environmental analysis, our work presented a promising application using such enhanced Al2O3-coated MoS2 chemiresistive biosensors for detection of HIgG with high sensitivity and selectivity. The biosensor was successfully applied to detect HIgG in artificial urine, a complex matrix containing organics and salts.

Securing Bio-Cyber Interface for the Internet of Bio-Nano Things using Particle Swarm Optimization and Artificial Neural Networks based parameter profiling

Internet of bio-nano things (IoBNT) is a novel communication paradigm where tiny, biocompatible and non-intrusive devices collect and sense biological signals from the environment and send them to data centers for processing through the internet. The concept of the IoBNT has stemmed from the combination of synthetic biology and nanotechnology tools which enable the fabrication of biological computing devices called Bio-nano things. Bio-nano things are nanoscale (1-100 nm) devices that are ideal for in vivo applications, where non-intrusive devices can reach hard-to-access areas of the human body (such as deep inside the tissue) to collect biological information. Bio-nano things work collaboratively in the form of a network called nanonetwork. The interconnection of the biological world and the cyber world of the Internet is made possible by a powerful hybrid device called Bio Cyber Interface. Bio Cyber Interface translates biochemical signals from in-body nanonetworks into electromagnetic signals and vice versa. Bio Cyber Interface can be designed using several technologies. In this paper, we have selected bio field-effect transistor (BioFET) technology, due to its characteristics of being fast, low-cost, and simple The main concern in this work is the security of IoBNT, which must be the preliminary requirement, especially for healthcare applications of IoBNT. Once the human body is accessible through the Internet, there is always a chance that it will be done with malicious intent. To address the issue of security in IoBNT, we propose a framework that utilizes Particle Swarm Optimization (PSO) algorithm to optimize Artificial Neural Networks (ANN) and to detect anomalous activities in the IoBNT transmission. Our proposed PSO-based ANN model was tested for the simulated dataset of BioFET based Bio Cyber Interface communication features. The results show an improved accuracy of 98.9% when compared with Adam based optimization function.

Low dimensional materials for glucose sensing

Biosensors are essential components for effective healthcare management. Since biological processes occur on molecular scales, nanomaterials and nanosensors intrinsically provide the most appropriate landscapes for developing biosensors. Low-dimensional materials have the advantage of offering high surface areas, increased reactivity and unique physicochemical properties for efficient and selective biosensing. So far, nanomaterials and nanodevices have offered significant prospects for glucose sensing. Targeted glucose biosensing using such low-dimensional materials enables much more effective monitoring of blood glucose levels, thus providing significantly better predictive diabetes diagnostics and management. In this review, recent advances in using low dimensional materials for sensing glucose are summarized. Sensing fundamentals are discussed, as well as invasive, minimally-invasive and non-invasive sensing methods. The effects of morphological characteristics and size-dependent properties of low dimensional materials are explored for glucose sensing, and the key performance parameters such as selectivity, stability and sensitivity are also discussed. Finally, the challenges and future opportunities that low dimensional materials can offer for glucose sensing are outlined.

Integrated contact lens sensor system based on multifunctional ultrathin MoS2 transistors

Smart contact lenses attract extensive interests due to their capability of directly monitoring physiological and ambient information. However, previous demonstrations usually lacked efficient sensor modalities, facile fabrication process, mechanical stability, or biocompatibility. Here, we demonstrate a flexible approach for fabrication of multifunctional smart contact lenses with an ultrathin MoS₂ transistors-based serpentine mesh sensor system. The integrated sensor systems contain a photodetector for receiving optical information, a glucose sensor for monitoring glucose level directly from tear fluid, and a temperature sensor for diagnosing potential corneal disease. Unlike traditional sensors and circuit chips sandwiched in the lens substrate, this serpentine mesh sensor system can be directly mounted onto the lenses and maintain direct contact with tears, delivering high detection sensitivity, while being mechanically robust and not interfering with either blinking or vision. Furthermore, the in vitro cytotoxicity tests reveal good biocompatibility, thus holding promise as next-generation soft electronics for healthcare and medical applications.

Solid State Sensors for Hydrogen Peroxide Detection

Hydrogen peroxide (H2O2) is a key molecule in numerous physiological, industrial, and environmental processes. H2O2 is monitored using various methods like colorimetry, luminescence, fluorescence, and electrochemical methods. Here, we aim to provide a comprehensive review of solid state sensors to monitor H2O2. The review covers three categories of sensors: chemiresistive, conductometric, and field effect transistors. A brief description of the sensing mechanisms of these sensors has been provided. All three sensor types are evaluated based on the sensing parameters like sensitivity, limit of detection, measuring range and response time. We highlight those sensors which have advanced the field by using innovative materials or sensor fabrication techniques. Finally, we discuss the limitations of current solid state sensors and the future directions for research and development in this exciting area.

Microfluidic tank assisted nicotine sensing property of field effect transistor composed of an atomically thin MoS2 channel

We investigated the sensor behavior of a field effect transistor, the channel of which is made of atomically thin MoS2 layers, focusing on the interaction of the MoS2 channel with the solution containing target molecules. For this purpose, we made a newly designed device in which the mask covered the electrodes of the source and the drain in order to make the solution contact only with the channel. In addition, a micro-fluid tank was fabricated above the channel as a solution reservoir. We examined the FET properties of this device for the sensing of the nicotine molecule for the development of a detection system for this molecule in the human body under in vivo conditions. We detected the sensor behavior both for the drop-cast process and for the condition where the channel contacts with the solution. The drain-current vs. gate-voltage variation of the MoS2-FET with the attachment of the nicotine molecule was clearly observed for both cases. For the latter case, the threshold voltage shifted in the negative gate-voltage direction with the increase of the concentration of the nicotine in the solution. This can be explained by the electron transfer from the molecule to the MoS2 channel, which was further confirmed by analyzing the X-ray photoemission spectroscopy and Raman spectroscopy together with the DFT calculation. The sensor can detect the variation of the nicotine concentration in the IPA solution by detecting the Vth change of the MoS2-FET.

Non-Carbon 2D Materials-Based Field-Effect Transistor Biosensors: Recent Advances, Challenges, and Future Perspectives

In recent years, field-effect transistors (FETs) have been very promising for biosensor applications due to their high sensitivity, real-time applicability, scalability, and prospect of integrating measurement system on a chip. Non-carbon 2D materials, such as transition metal dichalcogenides (TMDCs), hexagonal boron nitride (h-BN), black phosphorus (BP), and metal oxides, are a group of new materials that have a huge potential in FET biosensor applications. In this work, we review the recent advances and remarkable studies of non-carbon 2D materials, in terms of their structures, preparations, properties and FET biosensor applications. We will also discuss the challenges facing non-carbon 2D materials-FET biosensors and their future perspectives.

A Review on the Use of Impedimetric Sensors for the Inspection of Food Quality

This paper exhibits a thorough review of the use of impedimetric sensors for the analysis of food quality. It helps to understand the contribution of some of the major types of impedimetric sensors that are used for this application. The deployment of impedimetric sensing prototypes has been advantageous due to their wide linear range of responses, detection of the target analyte at low concentrations, good stability, high accuracy and high reproducibility in the results. The choice of these sensors was classified on the basis of structure and the conductive material used to develop them. The first category included the use of nanomaterials such as graphene and metallic nanowires used to form the sensing devices. Different forms of graphene nanoparticles, such as nano-hybrids, nanosheets, and nano-powders, have been largely used to sense biomolecules in the micro-molar range. The use of conductive materials such as gold, copper, tungsten and tin to develop nanowire-based prototypes for the inspection of food quality has also been shown. The second category was based on conventional electromechanical circuits such as electronic noses and other smart systems. Within this sector, the standardized systems, such as electronic noses, and LC circuit -based systems have been explained. Finally, some of the challenges posed by the existing sensors have been listed out, along with an estimate of the increase in the number of sensors employed to assess food quality.

Environmental Analysis with 2D Transition-Metal Dichalcogenide-Based Field-Effect Transistors

Field-effect transistors (FETs) present highly sensitive, rapid, and in situ detection capability in chemical and biological analysis. Recently, two-dimensional (2D) transition-metal dichalcogenides (TMDCs) attract significant attention as FET channel due to their unique structures and outstanding properties. With the booming of studies on TMDC FETs, we aim to give a timely review on TMDC-based FET sensors for environmental analysis in different media. First, theoretical basics on TMDC and FET sensor are introduced. Then, recent advances of TMDC FET sensor for pollutant detection in gaseous and aqueous media are, respectively, discussed. At last, future perspectives and challenges in practical application and commercialization are given for TMDC FET sensors. This article provides an overview on TMDC sensors for a wide variety of analytes with an emphasize on the increasing demand of advanced sensing technologies in environmental analysis.

Enzyme-Free Glucose Biosensors Based on MoS2 Nanocomposites

High-performance glucose biosensors are highly desired for healthcare. To meet these demands, glucose biosensors, particularly enzyme-free glucose biosensors, have received much attention. Two-dimensional materials, e.g., graphene, with high surface area, excellent electrical properties, and good biocompatibility, have been the main focus of biosensor research in the last decade. This review presents the recent progress made in enzyme-free glucose biosensors based on MoS2 nanocomposites. Two different techniques for glucose detections are introduced, with an emphasis on electrochemical glucose biosensors. Challenges and future perspectives of MoS2 nanocomposite glucose biosensors are also discussed.

ISFET and Dex-AgNPs based portable sensor for reusable and real-time determinations of concanavalin A and glucose on smartphone

In this paper, a portable real-time sensing device was built for Concanavalin A (Con A) and glucose detection using a smartphone. The ion-sensitive field-effect transistor (ISFET) functioning at a low working point was selected as a small-size, low-power transducer, and dextran-capped silver nanoparticles (Dex-AgNPs) served as sensitive nanoprobes on the ISFET gate. Using the affinity between Con A and carbohydrates, Con A can be captured, and thus directly detected by the ISFET/Dex-AgNPs unit; then glucose can be determined indirectly by removing Con A from the ISFET/Dex-AgNPs/Con A unit via competition with dextran. The mechanism of this competition does less harm to the sensor, allows the reusability of the sensing device, and overcomes the Debye screening of the FET device in saline solutions. Powered by a button cell, the handheld device attains excellent Con A (0.16 ng mL^-1) and glucose (10 nM) detection limit, and can practically be used for at least 20 days.

MoS2-enabled dual-mode optoelectronic biosensor using a water soluble variant of μ-opioid receptor for opioid peptide detection

Owing to their unique electrical and optical properties, two-dimensional transition metal dichalcogenides have been extensively studied for their potential applications in biosensing. However, simultaneous utilization of both optical and electrical properties has been overlooked, yet it can offer enhanced accuracy and detection versitility. Here, we demonstrate a dual-mode optoelectronic biosensor based on monolayer molybdenum disulfide (MoS₂) capable of producing simultaneous electrical and optical readouts of biomolecular signals. On a single platform, the biosensor exhibits a tunable photonic Fano-type optical resonance while also functioning as a field-effect transistor (FET) based on a optically transparent gate electrode. Furthermore, chemical vapor deposition grown MoS₂ provides a clean surface for direct immobilization of a water-soluble variant of the μ-opioid receptor (wsMOR), via a nickel ion-mediated linker chemistry. We utilize a synthetic opioid peptide to show the operation of the electronic and optical sensing modes. The responses of both modes exhibit a similar trend with dynamic ranges of four orders of magnitude and detection limits of <1 nM. Our work explores the potential of a versatile multimodal sensing platform enabled by monolayer MoS₂, since the integration of electrical and optical sensors on the same chip can offer flexibility in read-out and improve the accuracy in detection of low concentration targets.

Unravelling the physisorption characteristics of H2S molecule on biaxially strained single-layer MoS2

Sensing ultra-low levels of toxic chemicals such as H₂S is crucial for many technological applications. In this report, employing density functional theory (DFT) calculations, we shed light on the underlying physical phenomena involved in the adsorption and sensing of the H₂S molecule on both pristine and strained single-layer molybdenum disulfide (SL-MoS₂) substrates. We demonstrate that the H₂S molecule is physisorbed on SL-MoS₂ for all values of strain, i.e. from -8% to +8%, with a modest electron transfer, ranging from 0.023e^- to 0.062e^-, from the molecule to the SL-MoS₂. According to our calculations, the electron-donating behaviour of the H₂S molecule is halved under compressive strains. Moreover, we calculate the optical properties upon H₂S adsorption and reveal the electron energy loss (EEL) spectra for various concentrations of the H₂S molecule which may serve as potential probes for detecting H₂S molecules in prospective sensing applications based on SL-MoS₂.

Non-Enzymatic Impedimetric Sensor Based on 3-Aminophenylboronic Acid Functionalized Screen-Printed Carbon Electrode for Highly Sensitive Glucose Detection

A highly sensitive glucose sensor was prepared by a one-step method using 3-aminophenyl boronic acid as a unit of recognition and a screen-printed carbon electrode (SPCE) as an electrochemical transducer. Scanning Electron Microscopy confirmed the success of the functionalization of the SPCE due to the presence of clusters of boronic acid distributed on the carbon surface. In agreement with the Electrochemical Impedance Spectroscopy (EIS) tests performed before and after the functionalization, Cyclic Voltammetry results indicated that the electroactivity of the electrode decreased 37.9% owing to the presence of the poly phenylboronic acid on the electrode surface. EIS revealed that the sensor was capable to selectively detect glucose at a broad range of concentrations (limit of detection of 8.53 × 10-9 M), not recognizing fructose and sucrose. The device presented a stable impedimetric response when immediately prepared but suffered the influence of the storage time and some interfering species (dopamine, NaCl and animal serum). The response time at optimized conditions was estimated to be equal to 4.0 ± 0.6 s.

Flexible Molybdenum Disulfide (MoS2) Atomic Layers for Wearable Electronics and Optoelectronics

Flexible, stretchable, and bendable materials, including inorganic semiconductors, organic polymers, graphene, and transition metal dichalcogenides (TMDs), are attracting great attention in such areas as wearable electronics, biomedical technologies, foldable displays, and wearable point-of-care biosensors for healthcare. Among a broad range of layered TMDs, atomically thin layered molybdenum disulfide (MoS₂) has been of particular interest, due to its exceptional electronic properties, including tunable bandgap and charge carrier mobility. MoS₂ atomic layers can be used as a channel or a gate dielectric for fabricating atomically thin field-effect transistors (FETs) for electronic and optoelectronic devices. This review briefly introduces the processing and spectroscopic characterization of large-area MoS₂ atomically thin layers. The review summarizes the different strategies in enhancing the charge carrier mobility and switching speed of MoS₂ FETs by integrating high-κ dielectrics, encapsulating layers, and other 2D van der Waals layered materials into flexible MoS₂ device structures. The photoluminescence (PL) of MoS₂ atomic layers has, after chemical treatment, been dramatically improved to near-unity quantum yield. Ultraflexible and wearable active-matrix organic light-emitting diode (AM-OLED) displays and wafer-scale flexible resistive random-access memory (RRAM) arrays have been assembled using flexible MoS₂ transistors. The review discusses the overall recent progress made in developing MoS₂ based flexible FETs, OLED displays, nonvolatile memory (NVM) devices, piezoelectric nanogenerators (PNGs), and sensors for wearable electronic and optoelectronic devices. Finally, it outlines the perspectives and tremendous opportunities offered by a large family of atomically thin-layered TMDs.

Current and future envision on developing biosensors aided by 2D molybdenum disulfide (MoS2) productions

Two-dimensional (2D) layered nanomaterials have triggered an intensive interest due to the fascinating physiochemical properties with the exceptional physical, optical and electrical characteristics that transpired from the quantum size effect of their ultra-thin structure. Among the family of 2D nanomaterials, molybdenum disulfide (MoS₂) features distinct characteristics related to the existence of direct energy bandgap, which significantly lowers the leakage current and surpasses other 2D materials. In this overview, we expatiate the novel strategies to synthesize MoS₂ that cover techniques such as liquid exfoliation, chemical vapour deposition, mechanical exfoliation, hydrothermal reaction, and Van Der Waal epitaxial growth on the substrate. We extend the discussion on the recent progress in biosensing applications of the produced MoS₂, highlighting the important surface-to-volume of ultrathin MoS₂ structure, which enhances the overall performance of the devices. Further, envisioned the missing piece with the current MoS₂-based biosensors towards developing the future strategies.

Chemical sensing with 2D materials

During the last decade, two-dimensional materials (2DMs) have attracted great attention due to their unique chemical and physical properties, which make them appealing platforms for diverse applications in sensing of gas, metal ions as well as relevant chemical entities.