Field-effect Transistor Sensor Research Articles

Planar Junctionless Field-Effect Transistor for Detecting Biomolecular Interactions.

Label-free field-effect transistor-based immunosensors are promising candidates for proteomics and peptidomics-based diagnostics and therapeutics due to their high multiplexing capability, fast response time, and ability to increase the sensor sensitivity due to the short length of peptides. In this work, planar junctionless field-effect transistor sensors (FETs) were fabricated and characterized for pH sensing. The device with SiO2 gate oxide has shown voltage sensitivity of 41.8 ± 1.4, 39.9 ± 1.4, 39.0 ± 1.1, and 37.6 ± 1.0 mV/pH for constant drain currents of 5, 10, 20, and 50 nA, respectively, with a drain to source voltage of 0.05 V. The drift analysis shows a stability over time of −18 nA/h (pH 7.75), −3.5 nA/h (pH 6.84), −0.5 nA/h (pH 4.91), 0.5 nA/h (pH 3.43), corresponding to a pH drift of −0.45, −0.09, −0.01, and 0.01 per h. Theoretical modeling and simulation resulted in a mean value of the surface states of 3.8 × 1015/cm2 with a standard deviation of 3.6 × 1015/cm2. We have experimentally verified the number of surface sites due to APTES, peptide, and protein immobilization, which is in line with the theoretical calculations for FETs to be used for detecting peptide-protein interactions for future applications.

Improvement in long-term stability of field effect transistor biosensor in aqueous environments using a combination of silane and reduced graphene oxide coating

A field-effect transistor (FET) biosensor that can directly detect target molecules is a promising diagnostic tool for healthcare and medical applications. However, the immersion of FET sensors in aqueous physiological environments for the long-term stability might damage the insulating layer of silicon dioxide, resulting in the degradation of the sensor response reproducibility. In this study, to improve the durability of the sensor response for long-term immersion in aqueous solution, we examined the effectiveness of reduced graphene oxide (rGO) coating on the gate insulator of FET sensors. The rGO coating was applied to the gate surface of the FET biosensor modified with an amino-terminated self-assembled monolayer by two steps: deposition of graphene oxide (GO) dispersion onto the monolayer-modified surface and subsequent thermal reduction of GO. The transconductance of both GO-coated and rGO-coated FETs remained unchanged after incubation under physiological conditions, suggesting that graphene prevents cations in the electrolytes from invading the gate insulator of the FET. Furthermore, functionalizing the rGO-coated FET surface enabled specific detection of target molecule.

Microstructural Control of Soluble Acene Crystals for Field-Effect Transistor Gas Sensors.

Microstructural control during the solution processing of small-molecule semiconductors (namely, soluble acene) is important for enhancing the performance of field-effect transistors (FET) and sensors. This focused review introduces strategies to enhance the gas-sensing properties (sensitivity, recovery, selectivity, and stability) of soluble acene FET sensors by considering their sensing mechanism. Defects, such as grain boundaries and crystal edges, provide diffusion pathways for target gas molecules to reach the semiconductor-dielectric interface, thereby enhancing sensitivity and recovery. Representative studies on grain boundary engineering, patterning, and pore generation in the formation of soluble acene crystals are reviewed. The phase separation and microstructure of soluble acene/polymer blends for enhancing gas-sensing performance are also reviewed. Finally, flexible gas sensors using soluble acenes and soluble acene/polymer blends are introduced, and future research perspectives in this field are suggested.

Adsorption and sensing performances of Rh-embedded PtSe2 monolayer upon CO and HCHO in dry-type reactors: A first-principles study

Based on the first-principles method, we theoretically analyze the Rh-embedded PtSe2 (Rh-PtSe2) monolayer as a potential gas sensor in this paper, for detection of CO and HCHO in the dry-type reactor to evaluate its operation status. The Rh-embedding behavior is performed by substituting a Se atom at the topmost Se layer of the pristine PtSe2 monolayer, and we find that the Rh atom can be stably and energy-favorably embedded in the PtSe2 monolayer with the formation energy (Eform) of −0.53 eV. Chemisorption is identified for the CO and HCHO system, with the adsorption energy (Ead) as −1.89 and −1.05 eV, respectively. The electronic property analysis reveals that the Rh-PtSe2 monolayer can be a promising resistance-type sensor or a field-effect transistor sensor for detection of two gas species, with good sensing response or selectivity. This theoretical work can pave the way to further investigate the sensing application of Rh-PtSe2 monolayer upon toxic gases in the dry-type reactors, and related experimental research can verify our findings and to confirm that Rh-PtSe2 monolayer is a promising sensing candidate to evaluate the operation status of the dry-type reactors in the power system.

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.

Technical Perspectives on Applications of Biologically Coupled Gate Field-Effect Transistors.

Biosensing technologies are required for point-of-care testing (POCT). We determine some physical parameters such as molecular charge and mass, redox potential, and reflective index for measuring biological phenomena. Among such technologies, biologically coupled gate field-effect transistor (Bio-FET) sensors are a promising candidate as a type of potentiometric biosensor for the POCT because they enable the direct detection of ionic and biomolecular charges in a miniaturized device. However, we need to reconsider some technical issues of Bio-FET sensors to expand their possible use for biosensing in the future. In this perspective, the technical issues of Bio-FET sensors are pointed out, focusing on the shielding effect, pH signals, and unique parameters of FETs for biosensing. Moreover, other attractive features of Bio-FET sensors are described in this perspective, such as the integration and the semiconductive materials used for the Bio-FET sensors.

A novel room temperature SO2 gas sensor based on TiO2/rGO buried-gate FET

Gas sensors are able to detect the type and concentration of flammable, explosive, toxic gases (e.g. NO2, SO2, NH3), showing wide applications in petroleum, chemical, medical, transportation and safety protections in the domestic and industrial environment. Currently, the SO2 gas sensors are mainly based on metal oxide semiconductors. However, its operating temperature is generally much higher than room temperature, and the operation at higher temperature often requires complex circuits and high power consumption. A novel room temperature (RT) SO2 gas sensor based on buried-gate field effect transistor (FET) and interdigitated electrode structure with titanium dioxide (TiO2) nanoparticles and reduced graphene oxide (rGO) composite materials as gas-sensitive layer, has been fabricated and demonstrated in this paper. The TiO2/rGO FET sensor shows a relative high responsivity (3.46%) to 20 part per million (ppm) SO2 gas, under a source-drain voltage of 2 V and a zero gate voltage. Experimental results have shown that the responsivity and response-recovery time of the sensor could be controlled by the source-drain voltage. This paper demonstrates the feasibility of TiO2/rGO nanocomposite as a gas-sensing material for high-performance SO2 gas sensors. In addition, this approach would provide a feasible way for the realization of miniaturized, integrated and high-performance SO2 gas sensors.

Detecting the Bitterness of Milk-Protein-Derived Peptides Using an Electronic Tongue

Bitterness is a considerable limiting factor for the application of bioactive peptides in the food industry. The objective of this study was to compare the level of bitterness of milk-protein-derived peptides using an electronic tongue (E-tongue). Liquid milk protein concentrate (LMPC) was prepared from ultra-heat-treated skimmed cow’s milk. It was initially hydrolyzed with different concentrations of trypsin, namely, 0.008 g·L−1, 0.016 g·L−1 and 0.032 g·L−1. In a later exercise, tryptic-hydrolyzed LMPC (LMPC-T) was further hydrolyzed using Lactobacillus bulgaricus and Streptococcus thermophilus. The effect of glucose in microbial hydrolysis was studied. The bitterness of peptides was evaluated with respect to quinine, a standard bittering agent. The level of bitterness of the peptides after microbial hydrolysis of LMPC-T (LMPC-T-F and LMPC-T-FG) was evaluated using a potentiometric E-tongue equipped with a sensor array that had seven chemically modified field-effect transistor sensors. The results of the measurements were evaluated using principal component analysis (PCA), and subsequently, a classification of the models was built using the linear discriminant analysis (LDA) method. The bitterness of peptides in LMPC-T-F and LMPC-T-FG was increased with the increase in the concentration of trypsin. The bitterness of peptides was reduced in LMPC-T-FG compared with LMPC-T-F. The potential application of the E-tongue using a standard model solution with quinine was shown to follow the bitterness of peptides.

Ultrasensitive detection of exosomal miRNA with PMO-graphene quantum dots-functionalized field-effect transistor biosensor

SummaryCompared with the conventional DNA probe immobilization on the planar surface, nanoparticles-based DNA probes enable more RNA molecules to be anchored to the sensor surface, thereby improving the detection sensitivity. In this work, we report phosphorodiamidate morpholino oligomers (PMO)-graphene quantum dots (GQDs)-functionalized reduced graphene oxide (RGO) field effect transistor (FET) biosensors for ultrasensitive detection of exosomal microRNAs. After the RGO FET sensor was fabricated, polylysine (PLL) film was deposited onto the RGO surface. GQDs-PMO hybrid was prepared and covalently bound to PLL surface, enabling detection of exosomal microRNAs (miRNAs). The method achieved a detection limit as low as 85 aM and high specificity. Furthermore, the FET sensor was able to detect exosomal miRNAs in plasma samples and distinguish breast cancer samples from healthy samples. Compared with other methods, we use GQDs to further improve the sensitivity of FET, making it a potential tool for early diagnosis of breast cancer.

Lab-on-chip assay of tumour markers and human papilloma virus for cervical cancer detection at the point-of-care

Cervical cancer affects over half a million people worldwide each year, the majority of whom are in resource-limited settings where cytology screening is not available. As persistent human papilloma virus (HPV) infections are a key causative factor, detection of HPV strains now complements cytology where screening services exist. This work demonstrates the efficacy of a handheld Lab-on-Chip (LoC) device, with an external sample extraction process, in detecting cervical cancer from biopsy samples. The device is based on Ion-Sensitive Field-Effect Transistor (ISFET) sensors used in combination with loop-mediated isothermal amplification (LAMP) assays, to amplify HPV DNA and human telomerase reverse transcriptase (hTERT) mRNA. These markers were selected because of their high levels of expression in cervical cancer cells, but low to nil expression in normal cervical tissue. The achieved analytical sensitivity for the molecular targets resolved down to a single copy per reaction for the mRNA markers, achieving a limit of detection of 102 for hTERT. In the tissue samples, HPV-16 DNA was present in 4/5 malignant and 2/5 benign tissues, with HPV-18 DNA being present in 1/5 malignant and 1/5 benign tissues. hTERT mRNA was detected in all malignant and no benign tissues, with the demonstrated pilot data to indicate the potential for using the LoC in cervical cancer screening in resource-limited settings on a large scale.

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.

Fluorine-Terminated Polycrystalline Diamond Solution-Gate Field-Effect Transistor Sensor with Smaller Amount of Unexpectedly Generated Fluorocarbon Film Fabricated by Fluorine Gas Treatment.

In this study, a partially fluorine-terminated solution-gate field-effect transistor sensor with a smaller amount of unexpectedly generated fluorohydrocarbon film on a polycrystalline diamond channel is described. A conventional method utilizing inductively coupled plasma with fluorocarbon gas leads the hydrogen-terminated diamond to transfer to a partially fluorine-terminated diamond (C–F diamond); an unexpected fluorohydrocarbon film is formed on the surface of the diamond. To overcome this issue, we newly applied fluorine gas for the fluoridation of the diamond. Analytical results of X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry suggest that the fluorocarbon film does not exist or only a smaller amount of fluorocarbon film exists on the diamond surface. Conversely, the C–F diamond fabricated by the conventional method of inductively coupled plasma with a perfluoropropane gas (C3F8 gas) source possesses a certain amount of fluorocarbon film on its surface. The C–F diamond with a smaller amount of unexpectedly generated fluorohydrocarbon film possesses nearly ideal drain–source–voltage vs. gate–source–current characteristics, corresponding to metal–oxide–silicon semiconductor field-effect transistor theory. The results indicate that the fluorine gas (F2 gas) treatment proposed in this study effectively fabricates a C–F diamond sensor without unexpected semiconductor damage.

Triple-Probe DNA Framework-Based Transistor for SARS-CoV-2 10-in-1 Pooled Testing.

Accurate and population-scale screening technology is crucial in the control and prevention of COVID-19, such as pooled testing with high overall testing efficiency. Nevertheless, pooled testing faces challenges in sensitivity and specificity due to diluted targets and increased contaminations. Here, we develop a graphene field-effect transistor sensor modified with triple-probe tetrahedral DNA framework (TDF) dimers for 10-in-1 pooled testing of SARS-CoV-2 RNA. The synergy effect of triple probes as well as the special nanostructure achieve a higher binding affinity, faster response, and better specificity. The detectable concentration reaches 0.025–0.05 copy μL–1 in unamplified samples, lower than that of the reverse transcript-polymerase chain reaction. Without a requirement of nucleic-acid amplification, the sensors identify all of the 14 positive cases in 30 nasopharyngeal swabs within an average diagnosis time of 74 s. Unamplified 10-in-1 pooled testing enabled by the triple-probe TDF dimer sensor has great potential in the screening of COVID-19 and other epidemic diseases.

ANN based approach for selective detection of breath acetone by using hybrid GO-FET sensor array

This research used hybrid graphene oxide (GO) field effect transistors (FETs) based sensor array to design an electronic nose (e-nose) for identifying exhaled breath acetone to diagnose diabetes mellitus through noninvasive route. Six back gated FET sensors were fabricated with hybrid channel of GO, WO3 and noble metals (Au, Pd and Pt) nanoparticles. The experiment was carried out by using four distinct forms of synthetic breath, each with a different level of interference. Linear discriminant analysis (LDA) and artificial neural networks (ANN) were utilized to classify and analyze the sensor response vector. In contrast, partial least square (PLS) and multiple linear regression (MLR) were used to evaluate the exact acetone concentration in synthetic breath. First, LDA was used to lower the dimensionality of the response vector, which was then provided as an input to the ANN model. ANN was performed with ten perceptrons model in the hidden layer and highest accuracy of 99.1% was achieved. Additionally, by using the loading plot of PLS, three sensors (Pt/WO3/GO, Pd/WO3/GO, and WO3/GO) had the ample use to predict the concentration of breath acetone. Moreover, the MLR approach with correlation coefficient (R2) of 0.9572 and root mean square error (RMSE) of 5.63% were used for obtaining the exact concentration of acetone. Consequently, e-nose with matrix of hybrid GO-FET sensors and pattern recognition algorithms (LDA, ANN, PLS and MLR) exhibited considerable ability in selective detection of acetone in synthetic breath.

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.

Concentration recognition of gas sensor with organic field-effect transistor assisted by artificial intelligence

Many gas analytes have been detected with organic field-effect transistor (OFET) sensors. However, most of the analytes are detected with known concentrations and few OFET sensors have been used to quantify analytes. Here, we integrated the multiple independent parameters of OFETs with artificial neural network (ANN) to quantify toxic H2S. The precise concentration recognition was confirmed as the difference between real and predicted values was less than 5%. The H2S sensors also showed high responsivity over 6500% at 150 ppm, and quick response in ten seconds. Moreover, the multiple parameters provided the possibility to differentiate eight different analytes. Thus, the artificial intelligence combined with OFET sensors realized precise quantification and fingerprint recognition of gas analytes for real applications.

Detection of carbohydrate antigen 19-9 by a diamond solution-gate field-effect transistor sensor

Detection of carbohydrate antigen 19-9 (CA19-9) via hydrogen-terminated diamond (H-diamond) solution-gate field-effect transistor (SGFET) sensor had been carried out for the first time. Linker molecule 1-pyrenebutyric acid–N-hydroxy succinimide ester (Pyr-NHS) was fixed on the surface of H-diamond by π-π bonding. Then, anti-CA19-9 antibody was immobilized with Pyr-NHS. After specific binding of CA19-9 and antibody, transfer characteristics of H-diamond SGFET exhibited a gate voltage shift in negative direction at the same output current. The sensitivity of sensor was obtained as −50.98 mV/Log10[antigen concentration]. The minimum detection concentration was 0.001 U/mL. This article illustrated a potential application of H-diamond SGFET sensor in CA19-9 detection.

ISFET‐based sensors for (bio)chemical applications: A review

AbstractIon‐sensitive field effect transistor (ISFET) sensor is a hot topic these years, playing the combined roles of signal recognizer and converter for (bio)chemical analytes. In this review article, the basic concept, origination, and history of the ISFET sensor are presented. In addition, the common fabrication processes, the most‐used working principle (potentiometric, amperometric, and impedancemetric), and the techniques of gate functionality (physical, chemical, and biological) are discussed introducing the afterward signal transfer processes from ISFET to the terminals through different types of circuits. At last, the development and recent progress (until 2021) of ions and biomolecules (DNA molecules, antibodies, enzymatic substrates, and cell‐related secretions or metabolism) were introduced together with the outlook and facing obstacles (Debye screening, the wearability of ISFET, the multiplexed detections) before the commercialization of ISFET. This review article emphasizes the advantages of the developed ISFET sensors as miniaturization, low‐cost, all‐solid, highly sensitive, and easy operation for portable and multiplexed detections.

Silicon Nanowires Length and Numbers Dependence on Sensitivity of the Field-Effect Transistor Sensor for Hepatitis B Virus Surface Antigen Detection.

Silicon nanowire field effect transistor (NWFET) sensors have been demonstrated to have high sensitivity, are label free, and offer specific detection. This study explored the effect of nanowire dimensions on sensors’ sensitivity. We used sidewall spacer etching to fabricate polycrystalline silicon NWFET sensors. This method does not require expensive nanoscale exposure systems and reduces fabrication costs. We designed transistor sensors with nanowires of various lengths and numbers. Hepatitis B surface antigen (HBsAg) was used as the sensing target to explore the relationships of nanowire length and number with biomolecule detection. The experimental results revealed that the sensor with a 3 µm nanowire exhibited high sensitivity in detecting low concentrations of HBsAg. However, the sensor reached saturation when the biomolecule concentration exceeded 800 fg/mL. Sensors with 1.6 and 5 µm nanowires exhibited favorable linear sensing ranges at concentrations from 800 ag/mL to 800 pg/mL. The results regarding the number of nanowires revealed that the use of few nanowires in transistor sensors increases sensitivity. The results demonstrate the effects of nanowire dimensions on the silicon NWFET biosensors.

Adsorption of H2 and C2H2 onto Rh-decorated InN monolayer and the effect of applied electric field

InN monolayer with graphene-like morphology and desirable electronic property is a promising candidate for gas sensing application. In this paper, we study the adsorption and sensing performances of the Rh-decorated InN (Rh–InN) monolayer upon two typical dissolved gases in the transformers oil, namely H2 and C2H2, to explore its potential to evaluate the working condition of the transformers. Rh atom conducts n-doping on the pristine InN surface with E b of −2.01 eV. Also, chemisorption is determined for H2 and C2H2 adsorption on the Rh–InN surface given that the E ad of −0.88 and −2.15 eV, respectively. The opposite changing trend of E g in H2 and C2H2 systems manifests the resistance-based sensing mechanism for selective detection of two gas species. The applied electric field supports the work function analysis that an Rh–InN monolayer possesses a strong potential for field-effect transistor sensor application in terms of H2 and C2H2 detection, wherein the charge-transfer in the gas systems is tunable by altering the voltage. Moreover, the excessive electric field is not considered to be suggestible since it can impact the geometric stability of the Rh–InN monolayer. This theoretical work is meaningful to exploit novel sensing 2D materials to guarantee the good operation of the power system. Highlights Rh-decorating behaviors upon InN monolayer is studied. Expound the potential of Rh-InN monolayer for dissolved gas analysis in transformers. Analyze the effect of applied electric field on gas adsorptions.