AlGaN/GaN high electron mobility transistors for protein-peptide binding affinity study

Construction of AlGaN/GaN high-electron-mobility transistor-based biosensor for ultrasensitive detection of SARS-CoV-2 spike proteins and virions

The COVID-19 pandemic has highlighted the need for rapid and sensitive detection of SARS-CoV-2. Here, we report an ultrasensitive SARS-CoV-2 immunosensor by integration of an AlGaN/GaN high-electron-mobility transistor (HEMT) and anti-SARS-CoV-2 spike protein antibody. The AlGaN/GaN HEMT immunosensor has demonstrated the capability to detect SARS-CoV-2 spike proteins at an impressively low concentration of 10-22 M. The sensor was also applied to pseudoviruses and SARS-CoV-2 ΔN virions that display the Spike proteins with a single virion particle sensitivity. These features validate the potential of AlGaN/GaN HEMT biosensors for point of care tests targeting SARS-CoV-2. This research not only provides the first HEMT biosensing platform for ultrasensitive and label-free detection of SARS-CoV-2.

An integrated electronic tag-based vertical flow assay (e-VFA) with micro-sieve and AlGaN/GaN HEMT sensors for multi-target detection in actual saliva

Vertical flow assay (VFA) is an effective point-of-care (POC) diagnostic tool for widespread application. Nevertheless, the lack of multi-target detection and multi-signal readout capability still remains a challenge. Herein, a brand new VFA scheme for multi-target saliva detection based on electronic tags was proposed, where AlGaN/GaN HEMT sensors modified with different bio-receptors as electronic tags endowed the VFA with multi-target detection capability. In addition, the use of electronic tags instead of optical tags allowed the VFA to simultaneously carry out direct multi-target readouts, which ensure effective POC diagnostics for saliva analysis. Moreover, by integrating a hydrophilically optimized micro-sieve, impurities like sticky filaments, epidermal cells and other large-scale charged particles in saliva were effectively screened, which enabled the direct detection of saliva using AlGaN/GaN HEMT sensors. Glucose, urea, and cortisol were selected to verify the feasibility of the multi-target e-VFA scheme, and the results showed that the limit of detection (LOD) was as low as 100 aM. The linear response was demonstrated in the dynamic range of 100 aM to 100 μM, and the specificity, long-term stability and validity of the actual saliva test were also verified. These results demonstrated that the as-proposed e-VFA has potential for application in saliva detection for simultaneous multi-target detection, and it is expected to achieve the real-time detection of more biological targets in saliva.

Saliva-based COVID-19 detection: A rapid antigen test of SARS-CoV-2 nucleocapsid protein using an electrical-double-layer gated field-effect transistor-based biosensing system

Facing the unstopped surges of COVID-19, an insufficient capacity of diagnostic testing jeopardizes the control of disease spread. Due to a centralized setting and a long turnaround, real-time reverse transcription polymerase chain reaction (real-time RT-PCR), the gold standard of viral detection, has fallen short in timely reflecting the epidemic status quo during an urgent outbreak. As such, a rapid screening tool is necessitated to help contain the spread of COVID-19 amid the countries where the vaccine implementations have not been widely deployed. In this work, we propose a saliva-based COVID-19 antigen test using the electrical double layer (EDL)-gated field-effect transistor-based biosensor (BioFET). The detection of SARS-CoV-2 nucleocapsid (N) protein is validated with limits of detection (LoDs) of 0.34 ng/mL (7.44 pM) and 0.14 ng/mL (2.96 pM) in 1× PBS and artificial saliva, respectively. The specificity is inspected with types of antigens, exhibiting low cross-reactivity among MERS-CoV, Influenza A virus, and Influenza B virus. This portable system is embedded with Bluetooth communication and user-friendly interfaces that are fully compatible with digital health, feasibly leading to an on-site turnaround, an effective management, and a proactive response taken by medical providers and frontline health workers.

Saliva-based COVID-19 detection: A rapid antigen test of SARS-CoV-2 nucleocapsid protein using an electrical-double-layer gated field-effect transistor-based biosensing system

Facing the unstopped surges of COVID-19, an insufficient capacity of diagnostic testing jeopardizes the control of disease spread. Due to a centralized setting and a long turnaround, real-time reverse transcription polymerase chain reaction (real-time RT-PCR), the gold standard of viral detection, has fallen short in timely reflecting the epidemic status quo during an urgent outbreak. As such, a rapid screening tool is necessitated to help contain the spread of COVID-19 amid the countries where the vaccine implementations have not been widely deployed. In this work, we propose a saliva-based COVID-19 antigen test using the electrical double layer (EDL)-gated field-effect transistor-based biosensor (BioFET). The detection of SARS-CoV-2 nucleocapsid (N) protein is validated with limits of detection (LoDs) of 0.34 ng/mL (7.44 pM) and 0.14 ng/mL (2.96 pM) in 1× PBS and artificial saliva, respectively. The specificity is inspected with types of antigens, exhibiting low cross-reactivity among MERS-CoV, Influenza A virus, and Influenza B virus. This portable system is embedded with Bluetooth communication and user-friendly interfaces that are fully compatible with digital health, feasibly leading to an on-site turnaround, an effective management, and a proactive response taken by medical providers and frontline health workers.

A Rapid Detection of COVID-19 Viral RNA in Human Saliva Using Electrical Double Layer-Gated Field-Effect Transistor-Based Biosensors

In light of the swift outspread and considerable mortality, coronavirus disease 2019 (COVID-19) necessitates a rapid screening tool and a precise diagnosis. Saliva is considered as an alternative specimen to detect the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) since the viral load is comparable to what are found in a throat and a nasal cavity. The electrical double layer (EDL)-gated field-effect transistor-based biosensor (BioFET) emerges as a promising candidate for salivary COVID-19 tests due to a high sensitivity, a portable configuration, a label-free operation, and a matrix insensitivity. In this work, the authors utilize EDL-gated BioFETs to detect complementary DNAs (cDNAs) and viral RNAs with various testing conditions such as switches of probes, temperature treatments, and matrices. The selectivity is confirmed with cDNA and noncomplementary DNA (ncDNA), exhibiting an eightfold difference in electrical signals. The matrix insensitivity is evaluated, and BioFETs successfully validate the detection of SARS-CoV-2 N-gene RNA down to 1 fm in diluted human saliva with a 95°C- and a 25°C-treatment, respectively. This proposed system has a high potential to be deployed for an on-site COVID-19 screening, improving the disease control and benefitting frontline healthcare system.

Rapid Drug-Screening Platform Using Field-Effect Transistor-Based Biosensors: A Study of Extracellular Drug Effects on Transmembrane Potentials

Ion channel-modulating drugs play an important role in treating cardiovascular diseases. Facing the demands for continuous monitoring of drug effectiveness, the conventional techniques have become limited when investigating a long-term cellular physiology. To address the challenge, we propose a drug-screening platform using the stretch-out electrical double layer (EDL)-gated field-effect transistor-based biosensors (BioFETs). In this work, BioFETs were utilized to amplify electrophysiological signals from the mammalian cardiomyocytes (H9c2). The stretch-out configuration avoided a chemical corrosion on FETs and prolonged the lifetime of a BioFET system. A physical model is presented to elucidate the signal response to a drug effect on a cell. Fibronectin and gelatin were coated on sensors and served as the adhesive layers where H9c2 cells attached. BioFETs demonstrated an ability to qualitatively distinguish a depolarization and a polarization of the cytomembranes. The signal responses to the changes of transmembrane potentials were monitored in real-time, and they were highly correlated. The effects of nifedipine and calcium ions on cellular electrophysiology were examined and discussed. Due to the capability of a rapid detection, a prolonged lifetime, and an excellent sensitivity to an electrical change, a stretch-out EDL-gated BioFET can be a drug-screening platform for ion channel modulators.

Low limit of detection of the AlGaN/GaN-based sensor by the Kelvin connection detection technique

The AlGaN/GaN-based sensor is a promising POCT (point-of-care-testing) device featuring miniaturization, low cost, and high sensitivity. BNP is an effective protein biomarker for the early diagnosis of HF (heart failure). In this work, a novel AlGaN/GaN device with the Kelvin connection structure and the corresponding detection technique was proposed. This technique can effectively suppress the background noise and improve the SNR (signal-to-noise ratio). A BNP detection experiment was carried out to verify the effectiveness of this technique. It is shown that compared with that of the traditional detection method, the LOD (limit of detection) was improved from 0.47 ng/mL to 1.29 pg/mL. The BNP detection experiment was also carried out with a traditional electrochemical Au-electrode sensor with the same surface functionalization steps. The AlGaN/GaN sensor showed a better LOD than the Au-electrode sensor. Moreover, the influence of AlGaN/GaN sensor package on background noise was investigated with the mechanism of the noise source revealed. Finally, based on the optimized package, the optimal SNR quiescent operating point of the AlGaN/GaN sensor was determined. By biasing the sensor at the optimal quiescent operating point and immobilizing the magnetic beads with anti-BNP on the gate of the AlGaN/GaN sensor, the LOD for BNP detection was further improved to 0.097 pg/mL.

Nanosensor networks for health-care applications

Functionalized transistors provide effective sensors for a variety of viruses (Zika, severe acute respiratory syndrome), toxins (botulinum), cancers (breast and prostate), and disease or injury biomarkers (troponin, cerebrospinal fluid). A hallmark of this approach is high specificity, rapid response (<5 minutes), and ability to be integrated with wireless data transmission capabilities. The ultimate goal is hand-held point-of-care detection that can streamline patient diagnosis.

An electronic enzyme-linked immunosorbent assay platform for protein analysis based on magnetic beads and AlGaN/GaN high electron mobility transistors

The AlGaN/GaN high electron mobility transistor (HEMT) biosensors have the characteristics of high sensitivity, stability and fast response in the detection of biomolecules.

Design and Demonstration of Tunable Amplified Sensitivity of AlGaN/GaN High Electron Mobility Transistor (HEMT)-Based Biosensors in Human Serum

We have developed a swift and simplistic protein immunoassay using aptamer functionalized AlGaN/GaN high electron mobility transistors (HEMTs). The unique design of the sensor facilitates protein detection in a physiological salt environment overcoming charge screening effects, without requiring sample preprocessing. This study reports a tunable and amplified sensitivity of solution-gated electric double layer (EDL) HEMT-based biosensors, which demonstrates significantly enhanced sensitivity by designing a smaller gap between the gate electrode and the detection, and by operating at higher gate voltage. Sensitivity is calculated by quantifying NT-proBNP, a clinical biomarker of heart failure, in buffer and untreated human serum samples. The biosensor depicts elevated sensitivity and high selectivity. Furthermore, detailed investigation of the amplified sensitivity in an increased ionic strength environment is conducted, and it is revealed that a high sensitivity of 80.54 mV/decade protein concentration can be achieved, which is much higher than that of previously reported FET biosensors. This sensor technology demonstrates immense potential in developing surface affinity sensors for clinical diagnostics.

A microfluidic platform integrated with field-effect transistors for enumeration of circulating tumor cells

Circulating tumor cells (CTCs) are one of the promising cancer biomarkers whose concentrations are measured not only in the initial diagnostic stages, but also as treatment progresses. However, the existing methods for CTC detection are relatively time-consuming and labor-intensive. In this study, a new microfluidic platform integrated with field-effect transistors (FETs) and chambers for the trapping of CTCs was developed. This novel design could not only trap CTCs from whole blood samples, but also enumerate them via FET sensing of CTC-specific aptamer-CTC complexes. The FET output signal was experimentally found to increase with the increasing number of captured CTCs. More importantly, the enumeration of spiked CTCs in blood samples could be achieved in accordance with the signals measured on the FET devices. We therefore believe that this automated system could be a useful tool for enumeration of CTCs.

An integrated microfluidic system with field-effect-transistor sensor arrays for detecting multiple cardiovascular biomarkers from clinical samples

Certain blood-borne biomarkers offer a potent methodology for understanding the risk of cardiovascular diseases (CVDs) with clinicians generally advocating the use of multiple biomarkers for proper risk assessment of CVDs. Herein four such CVDs biomarkers- C-reactive protein (CRP), N-terminal pro b-type natriuretic peptide (NT-proBNP), cardiac troponin I (cTnI), and fibrinogen- were rapidly (5 min) analyzed from clinical samples (~ 4 µL) on an integrated microfluidic platform equipped with 1) immobilized highly specific aptamer probes and 2) field-effect transistor (FET)-based sensor arrays. The calibration curve from the FET sensor arrays showed good agreement in the physiological concentration ranges for CRP (0.1-50 mg/L), NT-proBNP (50-10,000 pg/mL), cTnI (1-10,000 pg/mL), and fibrinogen (0.1-5 mg/mL). The developed prototype of this fully automated portable device requires minimal reagent and sample inputs and consequently shows great promise for next-generation point-of-care devices assaying multiple CVDs biomarkers in clinical samples.

Highly sensitive AlGaN/GaN HEMT biosensors using an ethanolamine modification strategy for bioassay applications

In this paper, we propose a highly efficient surface modification strategy on an AlGaN/GaN high electron mobility transistor (HEMT), where ethanolamine (EA) was utilized to functionalize the surface of GaN and provided amphoteric amine groups for probe molecular immobilization for bioassay application. The molecular gated-AlGaN/GaN HEMT was utilized for pH and prostate-specific antigen (PSA) detection to verify its performance as a biosensor. Benefitting from the high coating quality on the GaN surface, the performance of our biosensor is drastically improved compared to other AlGaN/GaN HEMT based pH and PSA biosensors reported before. Our molecular gated-AlGaN/GaN HEMT biosensor has achieved good static electrical performance for pH sensing, such as high sensitivity, good linearity and chemical stability. Moreover, after further immobilization of PSA antibody onto the EA aminated GaN surface, the limit of detection (LOD) for PSA detection is as low as 1 fg mL⁻¹ in PBS buffer, which has reached an at least two orders of magnitude decrease compared to any other AlGaN/GaN HEMT based PSA biosensor reported before. And the sensitivity of our PSA biosensor has achieved a substantial increase, reaching up to 2.04% for 100 ng mL⁻¹. The measurements of pH and PSA utilizing the EA modified AlGaN/GaN HEMT biosensor indicate that the surface modification strategy on the GaN proposed in this paper can effectively improve the performance of the AlGaN/GaN HEMT based biosensor, which demonstrates a promising application prospect in the AlGaN/GaN HEMT based biological detection field.

We propose a highly efficient surface modification strategy on an AlGaN/GaN high electron mobility transistor, where ethanolamine was utilized to functionalize the surface of GaN and provided amphoteric amine groups for bioassay application.

Detection of C-reactive protein on an integrated microfluidic system by utilizing field-effect transistors and aptamers

Cardiovascular diseases (CVDs) cause more than 17 × 10⁶ deaths worldwide on a yearly basis. Early diagnosis of CVDs is therefore of great need. The C-reactive protein (CRP) is an important biomarker for analyzing the risks of CVDs. In this work, CRP-specific aptamers with high sensitivity and specificity and field-effect-transistor (FET) devices were used to recognize and detect CRP by using an integrated microfluidic system automatically while consuming less volumes of reagents and samples (about 5 μm). In order to package the FET device into the microfluidic chip, a new method to prevent liquid leakage was proposed. Sensitive detection of CRP has been demonstrated on the developed microfluidic system. It is the first time that aptamer-FET assays could be realized on an integrated microfluidic system. Experimental results showed that the aptamer-FET assay was capable of detecting CRP with concentrations ranging from 0.625 mg/l to 10.000 mg/l, which may be promising for early diagnosis of CVDs.

Group III nitride nanomaterials for biosensing

Biosensing has found wide applications in biological and medical research, and in clinical diagnosis, environmental monitoring and other analytical tasks. Recognized as novel and outstanding transducing materials because of their superior and unique physical/chemical properties, group III nitride (III-nitride) nanomaterials have been introduced into biosensor development with remarkable advancements achieved in the past few decades. This paper presents the first comprehensive review on biosensor development with III-nitride nanomaterials. The review starts with the introduction of the material properties and biocompatibility of III-nitrides that are useful for biosensing. The focus is then placed on surface treatments of III-nitrides, which lay the foundation for biosensing, and on biosensing mechanisms where the exceptional properties of III-nitride nanomaterials lead to superior biosensing performance. From a practical point of view, techniques for biosensor fabrication are then summarized. Finally, existing biosensing applications and future directions are discussed.

Electronic Biosensors Based on III-Nitride Semiconductors

We review recent advances of AlGaN/GaN high-electron-mobility transistor (HEMT)-based electronic biosensors. We discuss properties and fabrication of III-nitride-based biosensors. Because of their superior biocompatibility and aqueous stability, GaN-based devices are ready to be implemented as next-generation biosensors. We review surface properties, cleaning, and passivation as well as different pathways toward functionalization, and critically analyze III-nitride-based biosensors demonstrated in the literature, including those detecting DNA, bacteria, cancer antibodies, and toxins. We also discuss the high potential of these biosensors for monitoring living cardiac, fibroblast, and nerve cells. Finally, we report on current developments of covalent chemical functionalization of III-nitride devices. Our review concludes with a short outlook on future challenges and projected implementation directions of GaN-based HEMT biosensors.