Review on two-dimensional material-based field-effect transistor biosensors: accomplishments, mechanisms, and perspectives.

Field-effect transistor (FET) is regarded as the most promising candidate for the next-generation biosensor, benefiting from the advantages of label-free, easy operation, low cost, easy integration, and direct detection of biomarkers in liquid environments. With the burgeoning advances in nanotechnology and biotechnology, researchers are trying to improve the sensitivity of FET biosensors and broaden their application scenarios from multiple strategies. In order to enable researchers to understand and apply FET biosensors deeply, focusing on the multidisciplinary technical details, the iteration and evolution of FET biosensors are reviewed from exploring the sensing mechanism in detecting biomolecules (research direction 1), the response signal type (research direction 2), the sensing performance optimization (research direction 3), and the integration strategy (research direction 4). Aiming at each research direction, forward perspectives and dialectical evaluations are summarized to enlighten rewarding investigations.

Ultrasensitive Detection of Interleukin 6 by Using Silicon Nanowire Field-Effect Transistors.

Interleukin 6 (IL-6) has been regarded as a biomarker that can be applied as a predictor for the severity of COVID-19-infected patients. The IL-6 level also correlates well with respiratory dysfunction and mortality risk. In this work, three silanization approaches and two types of biorecognition elements were used on the silicon nanowire field-effect transistors (SiNW-FETs) to investigate and compare the sensing performance on the detection of IL-6. Experimental data revealed that the mixed-SAMs-modified silica surface could have superior surface morphology to APTES-modified and APS-modified silica surfaces. According to the data on detecting various concentrations of IL-6, the detection range of the aptamer-functionalized SiNW-FET was broader than that of the antibody-functionalized SiNW-FET. In addition, the lowest concentration of valid detection for the aptamer-functionalized SiNW-FET was 2.1 pg/mL, two orders of magnitude lower than the antibody-functionalized SiNW-FET. The detection range of the aptamer-functionalized SiNW-FET covered the concentration of IL-6, which could be used to predict fatal outcomes of COVID-19. The detection results in the buffer showed that the anti-IL-6 aptamer could produce better detection results on the SiNW-FETs, indicating its great opportunity in applications for sensing clinical samples.

Real-time COVID-19 detection via graphite oxide-based field-effect transistor biosensors decorated with Pt/Pd nanoparticles.

Coronavirus 2019 (COVID-19) spreads an extremely infectious disease where there is no specific treatment. COVID-19 virus had a rapid and unexpected spread rate which resulted in critical difficulties for public health and unprecedented daily life disruption. Thus, accurate, rapid, and early diagnosis of COVID-19 virus is critical to maintain public health safety. A graphite oxide-based field-effect transistor (GO-FET) was fabricated and functionalized with COVID-19 antibody for the purpose of real-time detection of COVID-19 spike protein antigen. Thermal evaporation process was used to deposit the gold electrodes on the surface of the sensor substrate. Graphite oxide channel was placed between the gold electrodes. Bimetallic nanoparticles of platinum and palladium were generated via an ultra-high vacuum (UHV) compatible system by sputtering and inert-gas condensation technique. The biosensor graphite oxide channel was immobilized with specific antibodies against the COVID-19 spike protein to achieve selectivity and specificity. This technique uses the attractive semiconductor characteristics of the graphite oxide-based materials resulting in highly specific and sensitive detection of COVID-19 spike protein. The GO-FET biosensor was decorated with bimetallic nanoparticles of platinum and palladium to investigate the improvement in the sensor sensitivity. The in-house developed biosensor limit of detection (LOD) is 1 fg/mL of COVID-19 spike antigen in phosphate-buffered saline (PBS). Moreover, magnetic labelled SARS-CoV-2 spike antibody were studied to investigate any enhancement in the sensor performance. The results indicate the successful fabrication of a promising field effect transistor biosensor for COVID-19 diagnosis.

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.

Convection Driven Ultrarapid Protein Detection via Nanobody-Functionalized Organic Electrochemical Transistors.

Conventional biosensors rely on the diffusion-dominated transport of the target analyte to the sensor surface. Consequently, they require an incubation step that may take several hours to allow for the capture of analyte molecules by sensor biorecognition sites. This incubation step is a primary cause of long sample-to-result times. Here, alternating current electrothermal flow (ACET) is integrated in an organic electrochemical transistor (OECT)-based sensor to accelerate the device operation. ACET is applied to the gate electrode functionalized with nanobody-SpyCatcher fusion proteins. Using the SARS-CoV-2 spike protein in human saliva as an example target, it is shown that ACET enables protein recognition within only 2 min of sample exposure, supporting its use in clinical practice. The ACET integrated sensor exhibits better selectivity, higher sensitivity, and lower limit of detection than the equivalent sensor with diffusion-dominated operation. The performance of ACET integrated sensors is compared with two types of organic semiconductors in the channel and grounds for device-to-device variations are investigated. The results provide guidelines for the channel material choice in OECT-based biochemical sensors, and demonstrate that ACET integration substantially decreases the detection speed while increasing the sensitivity and selectivity of transistor-based sensors.

An Aptamer-Functionalised Schottky-Field Effect Transistor for the Detection of Proteins.

The outbreak of the coronavirus disease 2019 (COVID-19) in December 2019 has highlighted the need for a flexible sensing system that can quickly and accurately determine the presence of biomarkers associated with the disease. This sensing system also needs to be easily adaptable to incorporate both novel diseases as well as changes in the existing ones. Here we report the feasibility of using a simple, low-cost silicon field-effect transistor functionalised with aptamers and designed to attach to the spike protein of SARS-CoV2. It is shown that a linear response can be obtained in a concentration range of 100 fM to 10 pM. Furthermore, by using a larger range of source-drain potentials compared with other FET based sensors, it is possible to look at a wider range of device parameters to optimise the response.

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.

Ultraprecise Antigen 10-in-1 Pool Testing by Multiantibodies Transistor Assay.

Effective screening of infectious diseases requires a fast, cheap, and population-scale testing. Antigen pool testing can increase the test rate and shorten the screening time, thus being a valuable approach for epidemic prevention and control. However, the overall percent agreement (OPA) with polymerase chain reaction (PCR) is one-half to three-quarters, hampering it from being a comprehensive method, especially pool testing, beyond the gold-standard PCR. Here, a multiantibodies transistor assay is developed for sensitive and highly precise antigen pool testing. The multiantibodies capture SARS-CoV-2 spike S1 proteins with different configurations, resulting in an antigen-binding affinity down to 0.34 fM. The limit of detection reaches 3.5 × 10-17 g mL-1SARS-CoV-2 spike S1 protein in artificial saliva, 4-5 orders of magnitude lower than existing transistor sensors. The testing of 60 nasopharyngeal swabs exhibits ∼100% OPA with PCR within an average diagnoses time of 38.9 s. Owing to its highly precise feature, a portable integrated platform is fabricated, which achieves 10-in-1 pooled screening for high testing throughput. This work solves the long-standing problem of antigen pool testing, enabling it to be a valuable tool in precise diagnoses and population-wide screening of COVID-19 or other epidemics in the future.

Ultrasensitive Detection of COVID-19 Causative Virus (SARS-CoV-2) Spike Protein Using Laser Induced Graphene Field-Effect Transistor.

COVID-19 is a highly contagious human infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and the war with the virus is still underway. Since no specific drugs have been made available yet and there is an imbalance between supply and demand for vaccines, early diagnosis and isolation are essential to control the outbreak. Current nucleic acid testing methods require high sample quality and laboratory conditions, which cannot meet flexible applications. Here, we report a laser-induced graphene field-effect transistor (LIG-FET) for detecting SARS-CoV-2. The FET was manufactured by different reduction degree LIG, with an oyster reef-like porous graphene channel to enrich the binding point between the virus protein and sensing area. After immobilizing specific antibodies in the channel, the FET can detect the SARS-CoV-2 spike protein in 15 min at a concentration of 1 pg/mL in phosphate-buffered saline (PBS) and 1 ng/mL in human serum. In addition, the sensor shows great specificity to the spike protein of SARS-CoV-2. Our sensors can realize fast production for COVID-19 rapid testing, as each LIG-FET can be fabricated by a laser platform in seconds. It is the first time that LIG has realized a virus sensing FET without any sample pretreatment or labeling, which paves the way for low-cost and rapid detection of COVID-19.

Chemically Induced pH Perturbations for Analyzing Biological Barriers Using Ion-Sensitive Field-Effect Transistors.

Potentiometric pH measurements have long been used for the bioanalysis of biofluids, tissues, and cells. A glass pH electrode and ion-sensitive field-effect transistor (ISFET) can measure the time course of pH changes in a microenvironment as a result of physiological and biological activities. However, the signal interpretation of passive pH sensing is difficult because many biological activities influence the spatiotemporal distribution of pH in the microenvironment. Moreover, time course measurement suffers from stability because of gradual drifts in signaling. To address these issues, an active method of pH sensing was developed for the analysis of the cell barrier in vitro. The microenvironmental pH is temporarily perturbed by introducing a low concentration of weak acid (NH4+) or base (CH3COO-) to cells cultured on the gate insulator of ISFET using a superfusion system. Considering the pH perturbation originates from the semi-permeability of lipid bilayer plasma membranes, induced proton dynamics are used for analyzing the biomembrane barriers against ions and hydrated species following interaction with exogenous reagents. The unique feature of the method is the sensitivity to the formation of transmembrane pores as small as a proton (H+), enabling the analysis of cell-nanomaterial interactions at the molecular level. The new modality of cell analysis using ISFET is expected to be applied to nanomedicine, drug screening, and tissue engineering.

A Tri-Channel Oxide Transistor Concept for the Rapid Detection of Biomolecules Including the SARS-CoV-2 Spike Protein.

Solid-state transistor sensors that can detect biomolecules in real time are highly attractive for emerging bioanalytical applications. However, combining upscalable manufacturing with the required performance remains challenging. Here, an alternative biosensor transistor concept is developed, which relies on a solution-processed In2 O3 /ZnO semiconducting heterojunction featuring a geometrically engineered tri-channel architecture for the rapid, real-time detection of important biomolecules. The sensor combines a high electron mobility channel, attributed to the electronic properties of the In2 O3 /ZnO heterointerface, in close proximity to a sensing surface featuring tethered analyte receptors. The unusual tri-channel design enables strong coupling between the buried electron channel and electrostatic perturbations occurring during receptor-analyte interactions allowing for robust, real-time detection of biomolecules down to attomolar (am) concentrations. The experimental findings are corroborated by extensive device simulations, highlighting the unique advantages of the heterojunction tri-channel design. By functionalizing the surface of the geometrically engineered channel with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody receptors, real-time detection of the SARS-CoV-2 spike S1 protein down to am concentrations is demonstrated in under 2 min in physiological relevant conditions.

Laser-Induced Graphene-Functionalized Field-Effect Transistor-Based Biosensing: A Potent Candidate for COVID-19 Detection.

Speedy and on-time detection of coronavirus disease 2019 (COVID-19) is of high importance to control the pandemic effectively and stop its disastrous consequences. A widely available, reliable, label-free, and rapid test that can recognize tiny amounts of specific biomarkers might be the solution. Nanobiosensors are one of the most attractive candidates for this purpose. Integration of graphene with biosensing devices shifts the performance of these systems to an incomparable level. Between the various arrangements using this wonder material, field-effect transistors (FETs) display a precise detection even in complex samples. The emergence of pioneering biosensors for detecting a wide range of diseases especially COVID-19 created the incentive to prepare a review of the recent graphene-FET biosensing platforms. However, the graphene fabrication and transfer to the surface of the device is an imperative factor for researchers to take into account. Therefore, we also reviewed the common methods of manufacturing graphene for biosensing applications and discuss their advantages and disadvantages. One of the most recent synthesizing techniques - laser-induced graphene (LIG) - is attracting attention owing to its extraordinary benefits which are thoroughly explained in this article. Finally, a conclusion highlighting the current challenges is presented.

Sensing Inflammation Biomarkers with Electrolyte-Gated Organic Electronic Transistors.

An overview of cytokine biosensing is provided, with a focus on the opportunities provided by organic electronic platforms for monitoring these inflammation biomarkers which manifest at ultralow concentration levels in physiopathological conditions. Specifically, two of the field's state-of-the-art technologies-organic electrochemical transistors (OECTs) and electrolyte gated organic field effect transistors (EGOFETs)-and their use in sensing cytokines and other proteins associated with inflammation are a particular focus. The overview will include an introduction to current clinical and "gold standard" quantification techniques and their limitations in terms of cost, time, and required infrastructure. A critical review of recent progress with OECT- and EGOFET-based protein biosensors is presented, alongside a discussion onthe future of these technologies in the years and decades ahead. This is especially timely as the world grapples with limited healthcare diagnostics during the Coronavirus disease (COVID-19)pandemic where one of the worst-case scenarios for patients is the "cytokine storm." Clearly, low-cost point-of-care technologies provided by OECTs and EGOFETs can ease the global burden on healthcare systems and support professionals by providing unprecedented wealth of data that can help to monitor disease progression in real time.

2D materials as a diagnostic platform for the detection and sensing of the SARS-CoV-2 virus: a bird's-eye view.

Worldwide infections and fatalities caused by the SARS-CoV-2 virus and its variants responsible for COVID-19 have significantly impeded the economic growth of many nations. People in many nations have lost their livelihoods, it has severely impacted international relations and, most importantly, health infrastructures across the world have been tormented. This pandemic has already left footprints on human psychology, traits, and priorities and is certainly going to lead towards a new world order in the future. As always, science and technology have come to the rescue of the human race. The prevention of infection by instant and repeated cleaning of surfaces that are most likely to be touched in daily life and sanitization drives using medically prescribed sanitizers and UV irradiation of textiles are the first steps to breaking the chain of transmission. However, the real challenge is to develop and uplift medical infrastructure, such as diagnostic tools capable of prompt diagnosis and instant and economic medical treatment that is available to the masses. Two-dimensional (2D) materials, such as graphene, are atomic sheets that have been in the news for quite some time due to their unprecedented electronic mobilities, high thermal conductivity, appreciable thermal stability, excellent anchoring capabilities, optical transparency, mechanical flexibility, and a unique capability to integrate with arbitrary surfaces. These attributes of 2D materials make them lucrative for use as an active material platform for authentic and prompt (within minutes) disease diagnosis via electrical or optical diagnostic tools or via electrochemical diagnosis. We present the opportunities provided by 2D materials as a platform for SARS-CoV-2 diagnosis.

Rapid Detection of SARS-CoV-2 Antigens Using High-Purity Semiconducting Single-Walled Carbon Nanotube-Based Field-Effect Transistors.

Early diagnosis of SARS-CoV-2 infection is critical for facilitating proper containment procedures, and a rapid, sensitive antigen assay is a critical step in curbing the pandemic. In this work, we report the use of a high-purity semiconducting (sc) single-walled carbon nanotube (SWCNT)-based field-effect transistor (FET) decorated with specific binding chemistry to assess the presence of SARS-CoV-2 antigens in clinical nasopharyngeal samples. Our SWCNT FET sensors, with functionalization of the anti-SARS-CoV-2 spike protein antibody (SAb) and anti-nucleocapsid protein antibody, detected the S antigen (SAg) and N antigen (NAg), reaching a limit of detection of 0.55 fg/mL for SAg and 0.016 fg/mL for NAg in calibration samples. SAb-functionalized FET sensors also exhibited good sensing performance in discriminating positive and negative clinical samples, indicating a proof of principle for use as a rapid COVID-19 antigen diagnostic tool with high analytical sensitivity and specificity at low cost.

Thin-film-transistor digital microfluidics for high value in vitro diagnostics at the point of need.

The latest developments in thin-film-transistor digital-microfluidics (TFT-DMF, also known by the commercial name aQdrop™) are reported, and proof of concept application to molecular diagnostics (e.g. for coronavirus disease, COVID-19) at the point-of-need demonstrated. The TFT-DMF array has 41 thousand independently addressable electrodes that are capable of manipulating large numbers of droplets of any size and shape, along any pathway to perform multiple parallel reactions. Droplets are continually tracked and adjusted through closed-loop feedback enabled by TFT based sensors at each array element. The sample-to-answer molecular in vitro diagnostic (IVD) test for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) includes nucleic acid extractions from saliva, removal of dsDNA and quantitative reverse transcription polymerase chain reaction (RT-PCR). This proof of concept illustrates how the highly configurable TFT-DMF technology can perform many reactions in parallel and thus support the processing of a range of sample types followed by multiple complex multi-step assays.

Rapid Detection of COVID-19 Causative Virus (SARS-CoV-2) in Human Nasopharyngeal Swab Specimens Using Field-Effect Transistor-Based Biosensor.

Coronavirus disease 2019 (COVID-19) is a newly emerging human infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, previously called 2019-nCoV). Based on the rapid increase in the rate of human infection, the World Health Organization (WHO) has classified the COVID-19 outbreak as a pandemic. Because no specific drugs or vaccines for COVID-19 are yet available, early diagnosis and management are crucial for containing the outbreak. Here, we report a field-effect transistor (FET)-based biosensing device for detecting SARS-CoV-2 in clinical samples. The sensor was produced by coating graphene sheets of the FET with a specific antibody against SARS-CoV-2 spike protein. The performance of the sensor was determined using antigen protein, cultured virus, and nasopharyngeal swab specimens from COVID-19 patients. Our FET device could detect the SARS-CoV-2 spike protein at concentrations of 1 fg/mL in phosphate-buffered saline and 100 fg/mL clinical transport medium. In addition, the FET sensor successfully detected SARS-CoV-2 in culture medium (limit of detection [LOD]: 1.6 × 101 pfu/mL) and clinical samples (LOD: 2.42 × 102 copies/mL). Thus, we have successfully fabricated a promising FET biosensor for SARS-CoV-2; our device is a highly sensitive immunological diagnostic method for COVID-19 that requires no sample pretreatment or labeling.