Wafer-Scale Uniform Carbon Nanotube Transistors for Ultrasensitive and Label-Free Detection of Disease Biomarkers

Mass Production of Carbon Nanotube Transistor Biosensors for Point-of-Care Tests

Low-dimensional semiconductor-based field-effect transistor (FET) biosensors are promising for label-free detection of biotargets while facing challenges in mass fabrication of devices and reliable reading of small signals. Here, we construct a reliable technology for mass production of semiconducting carbon nanotube (CNT) film and FET biosensors. High-uniformity randomly oriented CNT films were prepared through an improved immersion coating technique, and then, CNT FETs were fabricated with coefficient of performance variations within 6% on 4-in. wafers (within 9% interwafer) based on an industrial standard-level process. The CNT FET-based ion sensors demonstrated threshold voltage standard deviations within 5.1 mV at each ion concentration, enabling direct reading of the concentration information based on the drain current. By integrating bioprobes, we achieved detection of biosignals as low as 100 aM through a plug-and-play portable detection system. The reliable technology will contribute to commercial applications of CNT FET biosensors, especially in point-of-care tests.

WSe2 Negative Capacitance Field-Effect Transistor for Biosensing Applications

Field-effect transistor (FET) biosensors based on two-dimensional (2D) materials are highly sought after for their high sensitivity, label-free detection, fast response, and ease of on-chip integration. However, the subthreshold swing (SS) of FETs is constrained by the Boltzmann limit and cannot fall below 60 mV/dec, hindering sensor sensitivity enhancement. Additionally, the gate-leakage current of 2D material biosensors in liquid environments significantly increases, adversely affecting the detection accuracy and stability. Based on the principle of negative capacitance, this paper presents for the first time a two-dimensional material WSe2 negative capacitance field-effect transistor (NCFET) with a minimum subthreshold swing of 56 mV/dec in aqueous solution. The NCFET shows a significantly improved biosensor function. The pH detection sensitivity of the NCFET biosensor reaches 994 pH-1, nearly an order of magnitude higher than that of the traditional two-dimensional WSe2 FET biosensor. The Al2O3/HfZrO (HZO) bilayer dielectric in the NCFET not only contributes to negative capacitance characteristics in solution but also significantly reduces the leakage in solution. Utilizing an enzyme catalysis method, the WSe2 NCFET biosensor demonstrates a specific detection of glucose molecules, achieving a high sensitivity of 4800 A/A in a 5 mM glucose solution and a low detection limit (10-9 M). Further experiments also exhibit the ability of the biosensor to detect glucose in sweat.

Recent progress on field-effect transistor-based biosensors: device perspective

Over the last few decades, field-effect transistor (FET)-based biosensors have demonstrated great potential across various industries, including medical, food, agriculture, environmental, and military sectors. These biosensors leverage the electrical properties of transistors to detect a wide range of biomolecules, such as proteins, DNA, and antibodies. This article presents a comprehensive review of advancements in the architectures of FET-based biosensors aiming to enhance device performance in terms of sensitivity, detection time, and selectivity. The review encompasses an overview of emerging FET-based biosensors and useful guidelines to reach the best device dimensions, favorable design, and realization of FET-based biosensors. Consequently, it furnishes researchers with a detailed perspective on design considerations and applications for future generations of FET-based biosensors. Finally, this article proposes intriguing avenues for further research on the topology of FET-based biosensors.

Single-Molecule Electrical Profiling of Peptides and Proteins

In recent decades, there has been a significant increase in the application of single-molecule electrical analysis platforms in studying proteins and peptides. These advanced analysis methods have the potential for deep investigation of enzymatic working mechanisms and accurate monitoring of dynamic changes in protein configurations, which are often challenging to achieve in ensemble measurements. In this work, the prominent research progress in peptide and protein-related studies are surveyed using electronic devices with single-molecule/single-event sensitivity, including single-molecule junctions, single-molecule field-effect transistors, and nanopores. In particular, the successful commercial application of nanopores in DNA sequencing has made it one of the most promising techniques in protein sequencing at the single-molecule level. From single peptides to protein complexes, the correlation between their electrical characteristics, structures, and biological functions is gradually being established. This enables to distinguish different molecular configurations of these biomacromolecules through real-time electrical monitoring of their life activities, significantly improving the understanding of the mechanisms underlying various life processes.

A Strategy for Multigas Identification Using Multielectrical Parameters Extracted from a Single Carbon-Based Field-Effect Transistor Sensor

Given the widespread utilization of gas sensors across various industries, the detection of diverse and complex target gases presents a significant challenge in designing sensors with multigas detection capability. Although constructing a sensor array with widely used chemiresistive gas sensors is one solution, it is difficult for a single chemiresistive gas sensor to simultaneously detect different gases, as it can only detect a single target gas. The intrinsic reason for this bottleneck is that chemiresistive gas sensors rely entirely on the resistivity as the unique parameter to evaluate the diverse gas sensing properties of sensors, such as sensitivity, selectivity, etc. Herein, a field-effect transistor (FET) with abundant electrical parameters is employed to prepare a gas sensor for the detection of a variety of gases. Semiconducting carbon nanotubes (CNTs) are selected as the channel material, which is modified by Pd nanoparticles to enhance the gas sensing properties of the sensors. By extracting various electrical parameters such as transconductance, threshold voltage, etc. from the transfer characteristic curves of FET, a correlation between multielectrical parameters and various gas detection information is established for subsequent data analysis. Through the utilization of the principal component analysis algorithm, the identification of six gases can be finally achieved by relying solely on a single carbon-based FET-type gas sensor. We hope our work can solve the bottleneck of multigas identification by a single sensor in principle and is expected to reduce the system complexity and cost caused by the design of sensor arrays, offering a valuable guidance for multigas identification technology.

Label-Free Field Effect Transistors (FETs) for Fabrication of Point-of-Care (POC) Biomedical Detection Probes

Field effect transistors (FETs)-based detection probes are powerful platforms for quantification in biological media due to their sensitivity, ease of miniaturization, and ability to function in biological media. Especially, FET-based platforms have been utilized as promising probes for label-free detections with the potential for use in real-time monitoring. The integration of new materials in the FET-based probe enhances the analytical performance of the developed probes by increasing the active surface area, rejecting interfering agents, and providing the possibility for surface modification. Furthermore, the use of new materials eliminates the need for traditional labeling techniques, providing rapid and cost-effective detection of biological analytes. This review discusses the application of materials in the development of FET-based label-free systems for point-of-care (POC) analysis of different biomedical analytes from 2018 to 2024. The mechanism of action of the reported probes is discussed, as well as their pros and cons were also investigated. Also, the possible challenges and potential for the fabrication of commercial devices or methods for use in clinics were discussed.

A portable transistor immunosensor for fast identification of porcine epidemic diarrhea virus

Widespread distribution of porcine epidemic diarrhea virus (PEDV) has led to catastrophic losses to the global pig farming industry. As a result, there is an urgent need for rapid, sensitive and accurate tests for PEDV to enable timely and effective interventions. In the present study, we develop and validate a floating gate carbon nanotubes field-effect transistor (FG CNT-FET)-based portable immunosensor for rapid identification of PEDV in a sensitive and accurate manner. To improve the affinity, a unique PEDV spike protein-specific monoclonal antibody is prepared by purification, and subsequently modified on FG CNT-FET sensor to recognize PEDV. The developed FET biosensor enables highly sensitive detection (LoD: 8.1 fg/mL and 100.14 TCID50/mL for recombinant spike proteins and PEDV, respectively), as well as satisfactory specificity. Notably, an integrated portable platform consisting of a pluggable FG CNT-FET chip and a portable device can discriminate PEDV positive from negative samples and even identify PEDV and porcine deltacoronavirus within 1 min with 100% accuracy. The portable sensing platform offers the capability to quickly, sensitively and accurately identify PEDV, which further points to a possibility of point of care (POC) applications of large-scale surveillance in pig breeding facilities.

DNA-Based Nanomaterials for Analysis of Extracellular Vesicles

Extracellular vesicles (EVs) are cell-derived nanovesicles comprising a myriad of molecular cargo such as proteins and nucleic acids, playing essential roles in intercellular communication and physiological and pathological processes. EVs have received substantial attention as noninvasive biomarkers for disease diagnosis and prognosis. Owing to their ability to recognize protein and nucleic acid targets, DNA-based nanomaterials with excellent programmability and modifiability provide a promising tool for the sensitive and accurate detection of molecular cargo carried by EVs. In this perspective, recent advancements in EV analysis using a variety of DNA-based nanomaterials are summarized, which can be broadly classified into three categories: linear DNA probes, DNA nanostructures, and hybrid DNA nanomaterials. The design, construction, advantages, and disadvantages of different types of DNA nanomaterials, as well as their performance for detecting EVs are reviewed. The challenges and opportunities in the field of EV analysis by DNA nanomaterials are also discussed.

Ultra-sensitive and rapid detection of Salmonella enterica and Staphylococcus aureus to single-cell level by aptamer-functionalized carbon nanotube field-effect transistor biosensors

Foodborne diseases caused by Salmonella enterica (S. enterica) and Staphylococcus aureus (S. aureus) significantly impact public health, underscoring the imperative for highly sensitive, rapid, and accurate detection technologies to ensure food safety and prevent human diseases. Nanomaterials hold great promise in the development of high-sensitivity transistor biosensors. In this work, field-effect transistor (FET) comprising high-purity carbon nanotubes (CNTs) were fabricated and modified with corresponding nucleic acid aptamers for the high-affinity and selective capture of S. enterica and S. aureus. The aptamer-functionalized CNT-FET biosensor demonstrated ultra-sensitive and rapid detection of these foodborne pathogens. Experimental results indicated that the biosensor could detect S. enterica at a limit of detection (LOD) as low as 1 CFU in PBS buffer, and S. aureus at an LOD of 1.2 CFUs, achieving single-cell level detection accuracy with exceptional specificity. The biosensor exhibited a rapid response time, completing single detections within 200 s. Even in the presence of interference from six complex food matrices, the biosensor maintained its ultra-sensitive (3.1 CFUs) and rapid response (within 200 s) characteristics for both pathogens. The developed aptamer-functionalized CNT-FET biosensor demonstrates a capability for low-cost, ultra-sensitive, label-free, and rapid detection of low-abundance S. enterica and S. aureus in both buffer solutions and complex environments. This innovation holds significant potential for applying this detection technology to on-site rapid testing scenarios, offering a promising solution to the pressing need for efficient and reliable pathogen monitoring in various settings.

Ultrasensitive 3D Stacked Silicon Nanosheet Field-Effect Transistor Biosensor with Overcoming Debye Shielding Effect for Detection of DNA

Silicon nanowire field effect (SiNW-FET) biosensors have been successfully used in the detection of nucleic acids, proteins and other molecules owing to their advantages of ultra-high sensitivity, high specificity, and label-free and immediate response. However, the presence of the Debye shielding effect in semiconductor devices severely reduces their detection sensitivity. In this paper, a three-dimensional stacked silicon nanosheet FET (3D-SiNS-FET) biosensor was studied for the high-sensitivity detection of nucleic acids. Based on the mainstream Gate-All-Around (GAA) fenestration process, a three-dimensional stacked structure with an 8 nm cavity spacing was designed and prepared, allowing modification of probe molecules within the stacked cavities. Furthermore, the advantage of the three-dimensional space can realize the upper and lower complementary detection, which can overcome the Debye shielding effect and realize high-sensitivity Point of Care Testing (POCT) at high ionic strength. The experimental results show that the minimum detection limit for 12-base DNA (4 nM) at 1 × PBS is less than 10 zM, and at a high concentration of 1 µM DNA, the sensitivity of the 3D-SiNS-FET is approximately 10 times higher than that of the planar devices. This indicates that our device provides distinct advantages for detection, showing promise for future biosensor applications in clinical settings.

Plug-and-play smart transistor bio-chips implementing point-of-care diagnosis of AMI with modified CRISPR/Cas12a system

The point-of-care diagnosis of acute myocardial infarction (AMI), an extremely lethal disease with only a few hours of golden rescue time, is significant and urgently required. Here, we describe a plug-and-play carbon nanotube field effect transistor (CNT-FET) bio-chip supported with a smart portable readout for ultrasensitive and on-site testing of cardiac troponin I (cTnI), which is one of the most specific and valuable biomarkers of AMI. A modified clustered regularly interspaced short palindromic repeats (CRISPR)/Cas12a system, featuring the G-triplex structured reporter, was first combined with the CNT-FET to realize non-nucleic acid detection. Such a unique CNT-FET biosensor achieved the high sensitivity (LOD: 0.33 fg/mL), which is expected to give timely warning in the early stage of myocardial injury. In addition, a bilayer gate dielectric consisting of Y2O3/HfO2, employed into the passivation process, enabled the high environmental stability and repeatability of CNT-FET. More importantly, the homemade compact chip readout forged a field-deployable cTnI analytical tool, realizing "plasma-to-answer" performance for AMI patients in point-of-care testing scenarios. The developed technology holds promise to help doctors make clinical decisions faster, especially in remote areas.

Addressing Signal Drift and Screening for Detection of Biomarkers with Carbon Nanotube Transistors

Electrical biosensors, including transistor-based devices (i.e., BioFETs), have the potential to offer versatile biomarker detection in a simple, low-cost, scalable, and point-of-care manner. Semiconducting carbon nanotubes (CNTs) are among the most explored nanomaterial candidates for BioFETs due to their high electrical sensitivity and compatibility with diverse fabrication approaches. However, when operating in solutions at biologically relevant ionic strengths, CNT-based BioFETs suffer from debilitating levels of signal drift and charge screening, which are often unaccounted for or sidestepped (but not addressed) by testing in diluted solutions. In this work, we present an ultrasensitive CNT-based BioFET called the D4-TFT, an immunoassay with an electrical readout, which overcomes charge screening and drift-related limitations of BioFETs. In high ionic strength solution (1X PBS), the D4-TFT repeatedly and stably detects subfemtomolar biomarker concentrations in a point-of-care form factor by increasing the sensing distance in solution (Debye length) and mitigating signal drift effects. Debye length screening and biofouling effects are overcome using a poly(ethylene glycol)-like polymer brush interface (POEGMA) above the device into which antibodies are printed. Simultaneous testing of a control device having no antibodies printed over the CNT channel confirms successful detection of the target biomarker via an on-current shift caused by antibody sandwich formation. Drift in the target signal is mitigated by a combination of: (1) maximizing sensitivity by appropriate passivation alongside the polymer brush coating; (2) using a stable electrical testing configuration; and (3) enforcing a rigorous testing methodology that relies on infrequent DC sweeps rather than static or AC measurements. These improvements are realized in a relatively simple device using printed CNTs and antibodies for a low-cost, versatile platform for the ongoing pursuit of point-of-care BioFETs.

Nanomaterials-Based Field-Effect Transistor for Protein Sensing: New Advances

It is crucial for early stage medical diagnostics to identify disease biomarkers at ultralow concentrations. A wide range of analytes can be identified using low-dimensional materials to build highly sensitive, targeted, label-free, field-effect transistor (FET) biosensors. Two-dimensional (2D) materials are preferable for high-performance biosensing because of their dramatic change in resistivity upon analyte adsorption or biomarker detection, tunable electronic properties, high surface activities, adequate stability, and layer-dependent semiconducting properties. We give a succinct overview of interesting applications for protein sensing with various architectural styles, such as 2D transition metal dichalcogenides (TMDs)-based FETs that include carbon nanotubes (CNTs), graphene (Gr), reduced graphene oxide (rGr), 2D transition-metal carbides (MXene), and Gr/MXene heterostructures. Because it might enable individuals to perform better, this review will be an important contribution to the field of medical science. These achievements demonstrate point-of-care diagnostics' abilities to detect biomarkers at ultrahigh performance levels. A summary of the present opportunities and challenges appears in the conclusion.

Power and Sensitivity Management of Carbon Nanotube Transistor Glucose Biosensors

Continuous glucose monitoring (CGM), which is significant for the daily management of diabetes, requires a low-power-consumption sensor system that can track low nanomolar levels of glucose in physiological fluids, such as sweat and tears. However, traditional electrochemical methods are limited to analytes in micromolar to millimolar ranges and entail high power consumption. Carbon nanotube (CNT) film field-effect transistors (FETs) are promising for constructing extremely sensitive biosensors, but their wide applications in CGM are limited by the strong screening effect of physiological fluids and the zero charge of glucose molecules. In this study, we demonstrate a glucose aptamer-modified CNT FET biosensor to realize a highly sensitive CGM system with sub-nW power consumption by applying a suitable gate voltage. A positive gate voltage can enlarge the effective Debye screening length at the double layer to reduce the local ion population nearby and then improve the sensitivity of the FET-based biosensors by 5 times. We construct CNT FET sensors for CGM with a limit of detection of 0.5 fM, a record dynamic range up to 109, and a power consumption down to ∼100 pW. The proposed field-modulated sensing performance scheme is applicable to other aptamer-based FET biosensors for detecting neutral or less charged molecules and opens opportunities to develop facilely modulated, highly sensitive, low-power, and noninvasive CGM systems.

Sensitive and rapid detection of bacterial endotoxin with a functional carbon nanotube field-effect transistor biosensor

Endotoxin in the blood can cause unexplained fever, and even death due to endotoxemia and bacteremia. Rapid and sensitive detection of endotoxin has become a priority event to intervene in the occurrence of dangerous diseases in time. In this context, a carbon nanotubes-based field-effect transistor (CNTs FET) nanosensor is developed to realize the rapid, label-free and sensitive detection of endotoxin. The CNTs FET was fabricated by assembling the polymer-sorted high-purity semiconductor CNT films onto the sensing channel. In order to improve the detection sensitivity, carboxylated graphene quantum dots (cGQDs) were coupled to the CNT surface via the poly-l-lysine (PLL). After that, polymyxin B (PMB), which is highly specific for endotoxin, was covalently combined with cGQDs, thus enabling the capture and detection of endotoxin. The method not only displayed an extremely low level of limitation of detection in PBS (4.6 fg/mL) and serum (30.3 fg/mL), respectively, with superior resistance to interference, but also enabled the analysis of Gram-negative bacterial infections in blood samples in a short duration of time. Meanwhile, the receiver operating characteristic curve (ROC) proved the superior diagnostic accuracy of this method (AUC = 0.990). Considering its excellent performance, the constructed CNTs FET biosensor is a promising tool to provide early warning of disease for clinical Gram-negative bacteremia and endotoxemia.

A triple-aptamer tetrahedral DNA nanostructures based carbon-nanotube-array transistor biosensor for rapid virus detection

Outbreaks of infectious viruses cause enormous challenges to global public health. Recently, the coronavirus disease 2019 (COVID-19) induced by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has severely threatened human health and resulted in the global pandemic. A strategy to detect SARS-CoV-2 with both fast sensing speed and high accuracy is urgently required. Here, rapid detection of SARS-CoV-2 antigen using carbon-nanotube-array-based thin-film transistor (CNT-array-based TFT) biosensors merged with tetrahedral DNA nanostructures (TDNs) and triple aptamers is demonstrated for the first time. Compared with CNT-network-based TFT biosensors and metal-electrode-based CNT-TFT biosensors, the response of CNT-array-based TFT biosensors can be enhanced up to 102% for SARS-CoV-2 receptor-binding domain (RBD) detection, which is supported by its sensing mechanism. By combining TDNs with triple aptamers, the biosensor has realized the wildtype SARS-CoV-2 RBD detection in a broad detection range spanning eight orders of magnitude with a low limit of detection (LOD) of 10 aM (6 copies/μL) owing to the improved protein capture efficiency. Moreover, the triple-aptamer biosensor platform has achieved the detection of SARS-CoV-2 Omicron RBD in a low LOD of 6 aM (3.6 copies/μL). Additionally, the CNT-array-based TFT biosensors have exhibited excellent specificity, enabling identification among SARS-CoV-2 antigen, SARS-CoV antigen and MERS-CoV antigen. The platform of CNT-array-based TFT biosensors combined with TDNs and triple aptamers provides a high-performance and rapid approach for SARS-CoV-2 detection, and its versatility by altering specific aptamers enables the possibility for rapid virus detection.

Methods gold standard in clinic millifluidics multiplexed extended gate field-effect transistor biosensor with gold nanoantennae as signal amplifiers

We present a portable multiplexed biosensor platform based on the extended gate field-effect transistor and demonstrate its amplified response thanks to gold nanoparticle-based bioconjugates introduced as a part of the immunoassay. The platform comprises a disposable chip hosting an array of 32 extended gate electrodes, a readout module based on a single transistor operating in constant charge mode, and a multiplexer to scan sensing electrodes one-by-one. Although employing only off-the-shelf electronic components, our platform achieves sensitivities comparable to fully customized nanofabricated potentiometric sensors. In particular, it reaches a detection limit of 0.2 fM for the pure molecular assay when sensing horseradish peroxidase-linked secondary antibody (∼0.4 nM reached by standard microplate methods). Furthermore, with the gold nanoparticle bioconjugation format, we demonstrate ca. 5-fold amplification of the potentiometric response compared to a pure molecular assay, at the detection limit of 13.3 fM. Finally, we elaborate on the mechanism of this amplification and propose that nanoparticle-mediated disruption of the diffusion barrier layer is the main contributor to the potentiometric signal enhancement. These results show the great potential of our portable, sensitive, and cost-efficient biosensor for multidimensional diagnostics in the clinical and laboratory settings, including e.g., serological tests or pathogen screening.

Alzheimer's Disease Biomarker Detection Using Field Effect Transistor-Based Biosensor

Alzheimer's disease (AD) is closely related to neurodegeneration, leading to dementia and cognitive impairment, especially in people aged > 65 years old. The detection of biomarkers plays a pivotal role in the diagnosis and treatment of AD, particularly at the onset stage. Field-effect transistor (FET)-based sensors are emerging devices that have drawn considerable attention due to their crucial ability to recognize various biomarkers at ultra-low concentrations. Thus, FET is broadly manipulated for AD biomarker detection. In this review, an overview of typical FET features and their operational mechanisms is described in detail. In addition, a summary of AD biomarker detection and the applicability of FET biosensors in this research field are outlined and discussed. Furthermore, the trends and future prospects of FET devices in AD diagnostic applications are also discussed.

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.

Multi-Body Biomarker Entrapment System: An All-Encompassing Tool for Ultrasensitive Disease Diagnosis and Epidemic Screening

Ultrasensitive identification of biomarkers in biofluids is essential for the precise diagnosis of diseases. For the gold standard approaches, polymerase chain reaction and enzyme-linked immunosorbent assay, cumbersome operational steps hinder their point-of-care applications. Here, a bionic biomarker entrapment system (BioES) is implemented, which employs a multi-body Y-shaped tetrahedral DNA probe immobilized on carbon nanotube transistors. Clinical identification of endometriosis is successfully realized by detecting an estrogen receptor, ERβ, from the lesion tissue of endometriosis patients and establishing a standard diagnosis procedure. The multi-body Y-shaped BioES achieves a theoretical limit of detection (LoD) of 6.74 aM and a limit of quantification of 141 aM in a complex protein milieu. Furthermore, the BioES is optimized into a multi-site recognition module for enhanced binding efficiency, realizing the first identification of monkeypox virus antigen A35R and unamplified detection of circulating tumor DNA of breast cancer in serum. The rigid and compact probe framework with synergy effect enables the BioES to target A35R and DNA with a LoD down to 991 and 0.21 aM, respectively. Owing to its versatility for proteins and nucleic acids as well as ease of manipulation and ultra-sensitivity, the BioES can be leveraged as an all-encompassing tool for population-wide screening of epidemics and clinical disease diagnosis.

Direct, ultrafast, and sensitive detection of environmental pathogenic microorganisms based on a graphene biosensor

Pathogenic microorganisms in the environment pose a serious threat to global human health. This study developed a reduced graphene oxide (rGO)-field effect transistor (FET) biosensor to realize the rapid and sensitive detection of pathogenic microorganisms. The rGO-FET sensors were prepared by in-situ thermal reduction method, and biorecognition elements were immobilized using a crosslinking agent to realize the surface functionalization of rGO. The rGO-FET biosensors can detect Escherichia coli O157:H7 as low as 1.4 CFU mL-1 within 46 s. The normalized current response was linearly correlated with E. coli concentration in the range of 1.4-1.4 × 107 CFU mL-1. The normalized current response of E. coli O157:H7 was about an order of magnitude higher than those of other microorganisms, indicating that the biosensor has good specificity. The current loss rates of the unmodified rGO-FET sensors and the biosensors modified with anti-E. coli O157:H7 after 30 days of storage at 4 °C were approximately 8% and 15%, respectively. Most importantly, the rGO-FET biosensors can directly detect real samples without pretreatment. Compared with other technologies, the rGO-FET biosensors can detect pathogenic microorganisms with a wider linear range in a shorter time, which is of great importance for the rapid warning and control of pathogenic microorganisms in the environment.

Advances in field-effect biosensors towards point-of-use

The future of medical diagnostics calls for portable biosensors at the point of care, aiming to improve healthcare by reducing costs, improving access, and increasing quality-what is called the 'triple aim'. Developing point-of-care sensors that provide high sensitivity, detect multiple analytes, and provide real time measurements can expand access to medical diagnostics for all. Field-effect transistor (FET)-based biosensors have several advantages, including ultrahigh sensitivity, label-free and amplification-free detection, reduced cost and complexity, portability, and large-scale multiplexing. They can also be integrated into wearable or implantable devices and provide continuous, real-time monitoring of analytesin vivo, enabling early detection of biomarkers for disease diagnosis and management. This review analyzes advances in the sensitivity, parallelization, and reusability of FET biosensors, benchmarks the limit of detection of the state of the art, and discusses the challenges and opportunities of FET biosensors for future healthcare applications.

Functionalized carbon nanotube field-effect transistor biosensor for highly sensitive detection of exosomal protein

Since the exosomal protein level is related to many diseases, sensitive detection of exosomal protein is highly desirable. Here, we describe a polymer-sorted high-purity semiconducting carbon nanotubes (CNTs) films-based field-effect transistor (FET) biosensor for ultrasensitive and label-free detection of MUC1, a transmembrane protein highly expressed in breast cancer exosomes. Polymer-sorted semiconducting CNTs hold advantages including high purity (>99%), high CNT concentration, and short processing time (<1 h), but they are difficult to be stably functionalized with biomolecules because of lacking hanging bonds on their surface. To solve this issue, poly-lysine (PLL) was employed to modify the CNT films after they were deposited on the sensing channel surface of the fabricated FET chip. To specifically recognize the exosomal protein, sulfhydryl aptamer probes were immobilized on the gold nanoparticles (AuNPs) surface that was assembled on PLL substrate. The aptamer-modified CNT FET was capable of sensitively and selectively detecting exosomal MUC1 as high as 0.34 fg/mL. Moreover, the CNT FET biosensor was able to recognize breast cancer patients from healthy individuals by comparing the expression level of exosomal MUC1. The developed CNT FET biosensor is expected to be a novel assay for early diagnosis of cancer.

Nanomaterials-based biosensor and their applications: A review

A sensor can be called ideal or perfect if it is enriched with certain characteristics viz., superior detections range, high sensitivity, selectivity, resolution, reproducibility, repeatability, and response time with good flow. Recently, biosensors made of nanoparticles (NPs) have gained very high popularity due to their excellent applications in nearly all the fields of science and technology. The use of NPs in the biosensor is usually done to fill the gap between the converter and the bioreceptor, which is at the nanoscale. Simultaneously the uses of NPs and electrochemical techniques have led to the emergence of biosensors with high sensitivity and decomposition power. This review summarizes the development of biosensors made of NPssuch as noble metal NPs and metal oxide NPs, nanowires (NWs), nanorods (NRs), carbon nanotubes (CNTs), quantum dots (QDs), and dendrimers and their recent advancement in biosensing technology with the expansion of nanotechnology.

The Use of Crystalline Carbon-Based Nanomaterials (CBNs) in Various Biomedical Applications

This review study aims to present, in a condensed manner, the significance of the use of crystalline carbon-based nanomaterials in biomedical applications. Crystalline carbon-based nanomaterials, encompassing graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, and graphene quantum dots, have emerged as promising materials for the development of medical devices in various biomedical applications. These materials possess inorganic semiconducting attributes combined with organic π-π stacking features, allowing them to efficiently interact with biomolecules and present enhanced light responses. By harnessing these unique properties, carbon-based nanomaterials offer promising opportunities for future advancements in biomedicine. Recent studies have focused on the development of these nanomaterials for targeted drug delivery, cancer treatment, and biosensors. The conjugation and modification of carbon-based nanomaterials have led to significant advancements in a plethora of therapies and have addressed limitations in preclinical biomedical applications. Furthermore, the wide-ranging therapeutic advantages of carbon nanotubes have been thoroughly examined in the context of biomedical applications.

Amplification-Free Detection of SARS-CoV-2 Down to Single Virus Level by Portable Carbon Nanotube Biosensors

The rapid and sensitive detection of trace-level viruses in a simple and reliable way is of great importance for epidemic prevention and control. Here, a multi-functionalized floating gate carbon nanotube field effect transistor (FG-CNT FET) based biosensor is reported for the single virus level detection of SARS-CoV-2 virus antigen and RNA rapidly with a portable sensing platform. The aptamers functionalized sensors can detect SARS-CoV-2 antigens from unprocessed nasopharyngeal swab samples within 1 min. Meanwhile, enhanced by a multi-probe strategy, the FG-CNT FET-based biosensor can detect the long chain RNA directly without amplification down to single virus level within 1 min. The device, constructed with packaged sensor chips and a portable sensing terminal, can distinguish 10 COVID-19 patients from 10 healthy individuals in clinical tests both by the RNAs and antigens by a combination detection strategy with an combined overall percent agreement (OPA) close to 100%. The results provide a general and simple method to enhance the sensitivity of FET-based biochemical sensors for the detection of nucleic acid molecules and demonstrate that the CNT FG FET biosensor is a versatile and reliable integrated platform for ultrasensitive multibiomarker detection without amplification and has great potential for point-of-care (POC) clinical tests.

Nano-biosensor for SARS-CoV-2/COVID-19 detection: methods, mechanism and interface design

The epidemic of coronavirus disease 2019 (COVID-19) was a huge disaster to human society. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which led to COVID-19, has resulted in a large number of deaths. Even though the reverse transcription-polymerase chain reaction (RT-PCR) is the most efficient method for the detection of SARS-CoV-2, the disadvantages (such as long detection time, professional operators, expensive instruments, and laboratory equipment) limit its application. In this review, the different kinds of nano-biosensors based on surface-enhanced Raman scattering (SERS), surface plasmon resonance (SPR), field-effect transistor (FET), fluorescence methods, and electrochemical methods are summarized, starting with a concise description of their sensing mechanism. The different bioprobes (such as ACE2, S protein-antibody, IgG antibody, IgM antibody, and SARS-CoV-2 DNA probes) with different bio-principles are introduced. The key structural components of the biosensors are briefly introduced to give readers an understanding of the principles behind the testing methods. In particular, SARS-CoV-2-related RNA mutation detection and its challenges are also briefly described. We hope that this review will encourage readers with different research backgrounds to design SARS-CoV-2 nano-biosensors with high selectivity and sensitivity.

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.

Monolithic Three-Dimensional Integration of Carbon Nanotube Circuits and Sensors for Smart Sensing Chips

Semiconducting carbon nanotube (CNT) film is a promising material for constructing high-performance complementary metal-oxide-semiconductor (CMOS) integrated circuits (ICs) and highly sensitive field-effect transistor (FET) bio/chemical sensors. Moreover, CNT logic transistors and sensors can be integrated through a compatible low-temperature fabrication process, providing enough thermal budget to construct monolithic three-dimensional (M3D) systems for smart sensors. However, an M3D sensing chip based on CNT film has not yet been demonstrated. In this work, we develop M3D technology to fabricate CNT CMOS ICs and CNT sensor arrays in two different layers; then, we demonstrate a preliminary M3D sensing system comprising CNT CMOS interfacing ICs in the bottom layer and CNT sensors in the upper layer through interlayer vias as links. As a typical example, a highly sensitive hydrogen sensing IC has been demonstrated to perform in situ sensing and processing functions through upper-layer FET-based hydrogen sensors exposed to the environment and bottom-layer CNT CMOS voltage-controlled oscillator (VCO) interfacing circuits. The M3D CNT sensing ICs convert hydrogen concentration information (8-128 ppm) to digital frequency information (0.78-1.11 GHz) with a sensitivity of 2.75 MHz/ppm. M3D sensing technology is expected to provide a universal sensing system for future smart sensing chips, including multitarget detection and ultralow power sensors.

Carbon Nanotube Field-Effect Transistor Biosensor with an Enlarged Gate Area for Ultra-Sensitive Detection of a Lung Cancer Biomarker

Carcinoembryonic antigen (CEA) is a recognized biomarker for lung cancer and can be used for early detection. However, the clinical value of CEA is not fully realized due to the rigorous requirement for high-sensitivity and wide-range detection methods. Field-effect transistor (FET) biosensors, as one of the potentially powerful platforms, may detect CEA with a significantly higher sensitivity than conventional clinical testing equipment, while their sensitivity and detection range for CEA are far below the requirement for early detection. Here, we construct a floating gate FET biosensor to detect CEA based on a semiconducting carbon nanotube (CNT) film combined with an undulating yttrium oxide (Y₂O₃) dielectric layer as the biosensing interface. Utilizing an undulating biosensing interface, the proposed device showed a wider detection range and optimized sensitivity and detection limit, which benefited from an increase of probe-binding sites on the sensing interface and an increase of electric double-layer capacitance, respectively. The outcomes of analytical studies confirm that the undulating Y₂O₃ provided the desired biosensing surface for probe immobilization and performance optimization of a CNT-FET biosensor toward CEA including a wide detection range from 1 fg/mL to 1 ng/mL, good linearity, and high sensitivity of 72 ag/mL. More crucially, the sensing platform can function normally in the complicated environment of fetal bovine serum, indicating its great promise for early lung cancer screening.

Two-Dimensional Transition Metal Dichalcogenide Tunnel Field-Effect Transistors for Biosensing Applications

Field-effect transistor (FET) biosensors based on two-dimensional (2D) materials have drawn significant attention due to their outstanding sensitivity. However, the Boltzmann distribution of electrons imposes a physical limit on the subthreshold swing (SS), and a 2D-material biosensor with sub-60 mV/dec SS has not been realized, which hinders further increase of the sensitivity of 2D-material FET biosensors. Here, we report tunnel FETs (TFETs) based on a SnSe₂/WSe₂ heterostructure and observe the tunneling effect of a 2D material in aqueous solution for the first time with an ultralow SS of 29 mV/dec. A bilayer dielectric (Al₂O₃/HfO₂) and graphene contacts, which significantly reduce the leakage current in solution and contact resistance, respectively, are crucial to the realization of the tunneling effect in solution. Then, we propose a novel biosensing method by using tunneling current as the sensing signal. The TFETs show an extremely high pH sensitivity of 895/pH due to ultralow SS, surpassing the sensitivity of FET biosensors based on a single 2D material (WSe₂) by 8-fold. Specific detection of glucose is realized, and the biosensors show a superb sensitivity (3158 A/A for 5 mM), wide sensing range (from 10^-9 to 10^-3 M), low detection limit (10^-9 M), and rapid response rate (11 s). The sensors also exhibit the ability of monitoring glucose in complex biofluid (sweat). This work provides a platform for ultrasensitive biosensing. The discovery of the tunneling effect of 2D materials in aqueous solution may stimulate further fundamental research and potential applications.

A micro-carbon nanotube transistor for ultra-sensitive, label-free, and rapid detection of Staphylococcal enterotoxin C in food

Staphylococcal enterotoxin C (SEC) is an enterotoxin produced by Staphylococcus aureus, which can cause intestinal diseases. Therefore, it is of great significance to develop a sensitive detection method for SEC to ensure food safety and prevent foodborne diseases in humans. A field-effect transistor (FET) based on high-purity carbon nanotubes (CNTs) was used as a transducer, and a nucleic acid aptamer with high affinity was used for recognition to capture the target. The results indicated that the biosensor achieved an ultra-low theoretical detection limit of 1.25 fg/mL in PBS, and its good specificity was verified by detecting target analogs. Three typical food homogenates were used as the solution to be measured to verify that the biosensor had a swift response time (within 5 min after sample addition). An additional study with a more significant basa fish sample response also showed excellent sensitivity (theoretical detection limit of 8.15 fg/mL) and a stable detection ratio. In summary, this CNT-FET biosensor enabled the label-free, ultra-sensitive, and fast detection of SEC in complex samples. The FET biosensors could be further used as a universal biosensor platform for the ultrasensitive detection of multiple biological toxic pollutants, thus considerably stopping the spread of harmful substances.

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.

Nanosensor-Driven Detection of Neuron-Derived Exosomal Aβ42 with Graphene Electrolyte-Gated Transistor for Alzheimer's Disease Diagnosis

Blood-based tests have sparked tremendous attention in non-invasive early diagnosis of Alzheimer's disease (AD), a most prevalent neurodegenerative malady worldwide. Despite significant progress in the methodologies for detecting AD core biomarkers such as Aβ₄₂ from serum/plasma, there remains cautious optimism going forward due to its controversial diagnostic value and disease relevance. Here, a graphene electrolyte-gated transistor biosensor is reported for the detection of serum neuron-derived exosomal Aβ₄₂ (NDE-Aβ₄₂), which is an emerging, compelling trove of blood biomarker for AD. Assisted by the antifouling strategy with the dual-blocking process, the noise against complex biological background was considerably reduced, forging an impressive sensitivity gain with a limit of detection of 447 ag/mL. An accurate detection of SH-SY5Y-derived exosomal Aβ₄₂ was also achieved with highly conformable enzyme-linked immunosorbent assay results. Importantly, the clinical analysis for 27 subjects revealed the immense diagnostic value of NDE-Aβ₄₂, which can outclass that of serum Aβ₄₂. The developed electronic assay demonstrates, for the first time, nanosensor-driven NDE-Aβ₄₂ detection, which enables a reliable discrimination of AD patients from non-AD individuals and even the differential diagnosis between AD and vascular dementia patients, with an accuracy of 100% and a Youden index of 1. This NDE-Aβ₄₂ biosensor defines a robust approach for blood-based confident AD ascertain.

Toward the Commercialization of Carbon Nanotube Field Effect Transistor Biosensors

The development of biosensors based on field-effect transistors (FETs) using atomically thick carbon nanotubes (CNTs) as a channel material has the potential to revolutionize the related field due to their small size, high sensitivity, label-free detection, and real-time monitoring capabilities. Despite extensive research efforts to improve the sensitivity, selectivity, and practicality of CNT FET-based biosensors, their commercialization has not yet been achieved due to the non-uniform and unstable device performance, difficulties in their fabrication, the immaturity of sensor packaging processes, and a lack of reliable modification methods. This review article focuses on the practical applications of CNT-based FET biosensors for the detection of ultra-low concentrations of biologically relevant molecules. We discuss the various factors that affect the sensors' performance in terms of materials, device architecture, and sensor packaging, highlighting the need for a robust commercial process that prioritizes product performance. Additionally, we review recent advances in the application of CNT FET biosensors for the ultra-sensitive detection of various biomarkers. Finally, we examine the key obstacles that currently hinder the large-scale deployment of these biosensors, aiming to identify the challenges that must be addressed for the future industrialization of CNT FET sensors.

High-intensity vector signals for detecting SARS-CoV-2 RNA using CRISPR/Cas13a couple with stabilized graphene field-effect transistor

False detection of SARS-CoV-2 is detrimental to epidemic prevention and control. The scalar nature of the detected signal and the imperfect target recognition property of developed methods are the root causes of generating false signals. Here, we reported a collaborative system of CRISPR-Cas13a coupling with the stabilized graphene field-effect transistor, providing high-intensity vector signals for detecting SARS-CoV-2. In this collaborative system, SARS-CoV-2 RNA generates a "big subtraction" signal with a right-shifted feature, whereas any untargets cause the left-shifted characteristic signal. Thus, the false detection of SARS-CoV-2 is eliminated. High sensitivity with 0.15 copies/μL was obtained. In addition, the wide concerned instability of the graphene field-effect transistor for biosensing in solution environment was solved by the hydrophobic treatment to its substrate, which should be a milestone in advancing it's engineering application. This collaborative system characterized by the high-intensity vector signal and amazing stability significantly advances the accurate SARS-CoV-2 detection from the aspect of signal nature.

Highly Stable InSe-FET Biosensor for Ultra-Sensitive Detection of Breast Cancer Biomarker CA125

Two-dimensional materials-based field-effect transistors (FETs) are promising biosensors because of their outstanding electrical properties, tunable band gap, high specific surface area, label-free detection, and potential miniaturization for portable diagnostic products. However, it is crucial for FET biosensors to have a high electrical performance and stability degradation in liquid environments for their practical application. Here, a high-performance InSe-FET biosensor is developed and demonstrated for the detection of the CA125 biomarker in clinical samples. The InSe-FET is integrated with a homemade microfluidic channel, exhibiting good electrical stability during the liquid channel process because of the passivation effect on the InSe channel. The InSe-FET biosensor is capable of the quantitative detection of the CA125 biomarker in breast cancer in the range of 0.01-1000 U/mL, with a detection time of 20 min. This work provides a universal detection tool for protein biomarker sensing. The detection results of the clinical samples demonstrate its promising application in early screenings of major diseases.

A Wireless, Regeneratable Cocaine Sensing Scheme Enabled by Allosteric Regulation of pH Sensitive Aptamers

A key challenge for achieving continuous biosensing with existing technologies is the poor reusability of the biorecognition interface due to the difficulty in the dissociation of analytes from the bioreceptors upon surface saturation. In this work, we introduce a regeneratable biosensing scheme enabled by allosteric regulation of a re-engineered pH sensitive anti-cocaine aptamer. The aptamer can regain its affinity with target analytes due to proton-promoted duplex-to-triplex transition in DNA configuration followed by the release of adsorbed analytes. A Pd/PdH_x electrode placed next to the sensor can enable the pH regulation of the local chemical environment via electrochemical reactions. Demonstration of a "flower-shaped", stretchable, and inductively coupled electronic system with sensing and energy harvesting capabilities provides a promising route to designing wireless devices in biointegrated forms. These advances have the potential for future development of electronic sensing platforms with on-chip regeneration capability for continuous, quantitative, and real-time monitoring of chemical and biological markers.

Fabrication and Functionalisation of Nanocarbon-Based Field-Effect Transistor Biosensors

Nanocarbon-based field-effect transistor (NC-FET) biosensors are at the forefront of future diagnostic technology. By integrating biological molecules with electrically conducting carbon-based platforms, high sensitivity real-time multiplexed sensing is possible. Combined with their small footprint, portability, ease of use, and label-free sensing mechanisms, NC-FETs are prime candidates for the rapidly expanding areas of point-of-care testing, environmental monitoring and biosensing as a whole. In this review we provide an overview of the basic operational mechanisms behind NC-FETs, synthesis and fabrication of FET devices, and developments in functionalisation strategies for biosensing applications.

Clustered Regularly Interspaced short palindromic repeats-Based Microfluidic System in Infectious Diseases Diagnosis: Current Status, Challenges, and Perspectives

Mitigating the spread of global infectious diseases requires rapid and accurate diagnostic tools. Conventional diagnostic techniques for infectious diseases typically require sophisticated equipment and are time consuming. Emerging clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated proteins (Cas) detection systems have shown remarkable potential as next-generation diagnostic tools to achieve rapid, sensitive, specific, and field-deployable diagnoses of infectious diseases, based on state-of-the-art microfluidic platforms. Therefore, a review of recent advances in CRISPR-based microfluidic systems for infectious diseases diagnosis is urgently required. This review highlights the mechanisms of CRISPR/Cas biosensing and cutting-edge microfluidic devices including paper, digital, and integrated wearable platforms. Strategies to simplify sample pretreatment, improve diagnostic performance, and achieve integrated detection are discussed. Current challenges and future perspectives contributing to the development of more effective CRISPR-based microfluidic diagnostic systems are also proposed.

Controlled Preparation of Single-Walled Carbon Nanotubes as Materials for Electronics

Single-walled carbon nanotubes (SWCNTs) are of particular interest as channel materials for field-effect transistors due to their unique structure and excellent properties. The controlled preparation of SWCNTs that meet the requirement of semiconducting and chiral purity, high density, and good alignment for high-performance electronics has become a key challenge in this field. In this Outlook, we outline the efforts in the preparation of SWCNTs for electronics from three main aspects, structure-controlled growth, selective sorting, and solution assembly, and discuss the remaining challenges and opportunities. We expect that this Outlook can provide some ideas for addressing the existing challenges and inspire the development of SWCNT-based high-performance electronics.

Passivation Strategies for Enhancing Solution-Gated Carbon Nanotube Field-Effect Transistor Biosensing Performance and Stability in Ionic Solutions

Interest in point-of-care diagnostics has led to increasing demand for the development of nanomaterial-based electronic biosensors such as biosensor field-effect transistors (BioFETs) due to their inherent simplicity, sensitivity, and scalability. The utility of BioFETs, which use electrical transduction to detect biological signals, is directly dependent upon their electrical stability in detection-relevant environments. BioFET device structures vary substantially, especially in electrode passivation modalities. Improper passivation of electronic components in ionic solutions can lead to excessive leakage currents and signal drift, thus presenting a hinderance to signal detectability. Here, we harness the sensitivity of nanomaterials to study the effects of various passivation strategies on the performance and stability of a transistor-based biosensing platform based on aerosol-jet-printed carbon nanotube thin-film transistors. Specifically, non-passivated devices were compared to devices passivated with photoresist (SU-8), dielectric (HfO₂), or photoresist + dielectric (SU-8 followed by HfO₂) and were evaluated primarily by initial performance metrics, large-scale device yield, and stability throughout long-duration cycling in phosphate buffered saline. We find that all three passivation conditions result in improved device performance compared to non-passivated devices, with the photoresist + dielectric strategy providing the lowest average leakage current in solution (~2 nA). Notably, the photoresist + dielectric strategy also results in the greatest yield of BioFET devices meeting our selected performance criteria on a wafer scale (~90%), the highest long-term stability in solution (<0.01% change in on-current), and the best average on/off-current ratio (~10⁴), hysteresis (~32 mV), and subthreshold swing (~192 mV/decade). This passivation schema has the potential to pave the path toward a truly high-yield, stable, and robust electrical biosensing platform.

Sensors Based on the Carbon Nanotube Field-Effect Transistors for Chemical and Biological Analyses

Nano biochemical sensors play an important role in detecting the biomarkers related to human diseases, and carbon nanotubes (CNTs) have become an important factor in promoting the vigorous development of this field due to their special structure and excellent electronic properties. This paper focuses on applying carbon nanotube field-effect transistor (CNT-FET) biochemical sensors to detect biomarkers. Firstly, the preparation method, physical and electronic properties and functional modification of CNTs are introduced. Then, the configuration and sensing mechanism of CNT-FETs are introduced. Finally, the latest progress in detecting nucleic acids, proteins, cells, gases and ions based on CNT-FET sensors is summarized.

Integrated Urinalysis Devices Based on Interface-Engineered Field-Effect Transistor Biosensors Incorporated With Electronic Circuits

Urinalysis is attractive in non-invasive early diagnosis of bladder cancer compared with clinical gold standard cystoscopy. However, the trace bladder tumor biomarkers in urine and the particularly complex urine environment pose significant challenges for urinalysis. Here, a clinically adoptable urinalysis device that integrates molecular-specificity indium gallium zinc oxide field-effect transistor (IGZO FET) biosensor arrays, a device control panel, and an internet terminal for directly analyzing five bladder-tumor-associated proteins in clinical urine samples, is reported for bladder cancer diagnosis and classification. The IGZO FET biosensors with engineered sensing interfaces provide high sensitivity and selectivity for identification of trace proteins in the complex urine environment. Integrating with a machine-learning algorithm, this device can identify bladder cancer with an accuracy of 95.0% in a cohort of 197 patients and 75 non-bladder cancer individuals, distinguishing cancer stages with an overall accuracy of 90.0% and assessing bladder cancer recurrence after surgical treatment. The non-invasive urinalysis device defines a robust technology for remote healthcare and personalized medicine.

Amplification-Free Detection of SARS-CoV-2 and Respiratory Syncytial Virus Using CRISPR Cas13a and Graphene Field-Effect Transistors

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) systems have recently received notable attention for their applications in nucleic acid detection. Despite many attempts, the majority of current CRISPR-based biosensors in infectious respiratory disease diagnostic applications still require target preamplifications. This study reports a new biosensor for amplification-free nucleic acid detection via harnessing the trans-cleavage mechanism of Cas13a and ultrasensitive graphene field-effect transistors (gFETs). CRISPR Cas13a-gFET achieves the detection of SARS-CoV-2 and respiratory syncytial virus (RSV) genome down to 1 attomolar without target preamplifications. Additionally, we validate the detection performance using clinical SARS-CoV-2 samples, including those with low viral loads (Ct value >30). Overall, these findings establish our CRISPR Cas13a-gFET among the most sensitive amplification-free nucleic acid diagnostic platforms to date.

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.

A handheld intelligent single-molecule binary bioelectronic system for fast and reliable immunometric point-of-care testing

Molecular tests are highly reliable and sensitive but lack portability and are not simple to use; conversely, easy-to-use antigenic tests still lack high performance. BioScreen combines single-molecule sensitivity and outstanding reliability with ultraportability and simplicity of use. This digital platform is capable of artificial intelligence-based binary classification at the limit of identification of a single marker/virus in 0.1 ml. The diagnostic sensitivity, specificity, and accuracy reach 99.2% as validated through 240 assays, including a pilot clinical trial. The versatile immunometric system can detect the SARS-CoV-2 virus, spike S1, and immunoglobulin G antigen proteins in saliva, blood serum, and swab. BioScreen has a small footprint comprising a disposable cartridge and a handheld electronic reader connected to a smart device. The sample handling is minimal, and the assay time to result is 21 min. Reliable and sensitive self-testing with an ultraportable and easy-to-use diagnostic system operated directly by a patient holds the potential to revolutionize point-of-care testing and early diagnosis.