In this study, a new type of field-effect transistor (FET)-based biosensor is demonstrated to be able to overcome the problem of severe charge-screening effect caused by high ionic strength in solution and detect proteins in physiological environment. Antibody or aptamer-immobilized AlGaN/GaN high electron mobility transistors (HEMTs) are used to directly detect proteins, including HIV-1 RT, CEA, NT-proBNP and CRP, in 1X PBS (with 1%BSA) or human sera. The samples do not need any dilution or washing process to reduce the ionic strength. The sensor shows high sensitivity and the detection takes only 5 minutes. The designs of the sensor, the methodology of the measurement, and the working mechanism of the sensor are discussed and investigated. A theoretical model is proposed based on the finding of the experiments. This sensor is promising for point-of-care, home healthcare, and mobile diagnostic device.Field-effect transistors (FETs) attract great interest for biomolecular detection, due to their high sensitivity, small size, and label-free detection, which are suitable for point-of-care or personal homecare devices. Either planar or nanowire FET-based biosensors have been widely studied using various materials, such as Si 1 , GaN 2 , carbon nanotube (CNT) 3 , or graphene oxide 4 . Conventionally, FET-based biosensors with receptors (ex. antibody) immobilized on the gate region above the active channel of the FETs face an intrinsic issue, which is the severe charge screening effect in high ionic strength solutions, such as in serum or blood samples, leading to low sensitivity for direct detection of protein in the physiological environment. The Debye length in physiological salt environment (1X PBS) is near 0.7 nm, which is much smaller than the size of a regular IgG antibody (5~10 nm) 5 . In order to effectively detect proteins with receptor-immobilized FETs, the electrical measurements are usually conducted in diluted buffer solutions, such as in 0.1X PBS or 0.01X PBS, where the Debye lengths as 2.4 nm and 7.4 nm, respectively 1,6,7 . However, diluted ionic strength solution may cause the change in protein structure, resulting in the loss of protein activity, and the binding affinity as well. For most biological reactions, which occur in physiological high salt environment, a biosensor that can be used directly with physiological samples is much favored. Besides, an additional washing process is needed for conventional FET-based biosensors to remove the unbound antigen before electrical measurement, which also increases the complexity of the whole sensor system. Therefore, direct detection of the target protein in physiological sample is very demanding.Previously, several groups have reported that conventional FET-based biosensors can effectively detect proteins in physiological salt environment, using alternative current (AC) signals in drain-source voltage (V ds ), in conjunction with a reference electrode, in a relatively high frequency [8][9][10][11] . The better sensitivity of AC signals compared to that o...

No abstract

In here, we have reviewed the major FET sensor methodologies developed for biosensing applications. Each of the methodologies offer different approaches to mitigate the effects of charge screening in high ionic strength solutions. We focus in detail on the study of high field gated FET biosensors developed to directly detect target analytes in physiological salt environments, without extensive sample pre-treatments. Several biomedical applications are illustrated in this review cum original research article, such as protein detection in buffer/serum/whole blood, nucleotide detection in buffer, whole cell-based sensor and characterization of biological tissues. The mechanism of detection beyond Debye length in high ionic strength solutions is investigated. The integrated portable biosensor system developed based on the high field gated FET biosensor demonstrates potential for clinical applications in point of care and home-care diagnostics.

This paper reports a high‐resolution, template‐free, and direct‐printing method of functional nanofiber on 3D surfaces using a self‐aligning nanojet (SA‐N) in near‐field electrospinning (NFES). In the lowest regime of NFES, the cone‐jet transition is induced by the surface current, which leads to a unique jetting configuration where the microscale Taylor cone (microcone) is formed on the surface of the spherical‐shape droplet. The microcone rapidly develops to the nanoscale jet where the tangential electric force dominates the kinematics of the charged jet. The spherical‐shape ejection boundary allows the jetting angle from 0° to ±90° in both convex and concave surfaces, enabling precise deposition of nanofiber regardless of the curvature of the 3D surfaces. Using SA‐N, precise printing of functional nanofiber is successfully demonstrated on various 3D geometries, including convex, concave, and inner surface of the 3D structure. The direct‐printing ability of nanofiber on 3D surfaces using SA‐N will be a promising strategy to utilize various functional polymers in flexible electronics, printed electronics, optics, and biomedical engineering.

No abstract

Fibrinogen found in blood plasma is an important protein biomarker for potentially fatal diseases such as cardiovascular diseases. This study focuses on the development of an assay to detect plasmatic fibrinogen using electrical double layer gated AlGaN/GaN high electron mobility transistor biosensors without complex sample pre-treatment methods used in the traditional assays. The test results in buffer solution and clinical plasma samples show high sensitivity, specificity, and dynamic range. The sensor exhibits an ultra-low detection limit of 0.5 g/l and a detection range of 0.5–4.5 g/l in 1× PBS with 1% BSA. The concentration dependent sensor signal in human serum samples demonstrates the specificity to fibrinogen in a highly dense matrix of background proteins. The sensor does not require complicated automation, and quantitative results are obtained in 5 min with <5 μl sample volume. This sensing technique is ideal for speedy blood based diagnostics such as POC (point of care) tests, homecare tests, or personalized healthcare.

and calibrate the sensors before detecting target gases. Second, a gas sensor's performance also depends on the system optimization, such as signal chain design, power consumption, etc., and sensor's operating conditions, such as temperature, humidity, pressure, test chamber design, etc. Finally, all sensors age, drift in performance, and ultimately fail at the end of their life. The cost of operation can be significantly decreased by effectively predicting the sensor's life and reducing unnecessary sensor replacements. In this research work, we fabricate a simple, low-cost, low-power consuming, and robust gas sensor that can detect Hydrogen (H 2 ) gas at a very low concentrations with enhanced sensitivity.Hydrogen (H 2 ) gas is a promising clean and green energy source. H 2 gas, with properties such as high energy density, renewability, and eco-friendly nature, is rising as a potential candidate to replace conventional fossil fuels in the automotive and industrial applications field. [1][2][3] Nevertheless, the low combustion energy (0.02 meJ) and wide flammable range (4-75%) of H 2 gas raise safety concerns and warrant an easy, quick, and reliable leakage detection method. [4,5] Typical commercial H 2 gas sensors employ metal oxide materials, such as SnO 2 , ZnO, and TiO 2 , due to their higher sensitivity toward detecting H 2 . [6][7][8] However, these sensors suffer from high operating temperatures (typically 200-500 °C) and usually have low selectivity. Other than conventional materials, conductive polymers have been studied as alternative sensing materials in chemical sensing to leverage simple processing, chemical versatility, and wide availability. [9] Poly(3,4-ethylene dioxythiophene) doped with polystyrene sulfonate (PEDOT: PSS) is the most commonly used conductive polymer which has attracted significant interest due to its high electrical conductivity, high stability, and ease in the processing. [10] The electrical property of PEDOT: PSS can be tailored via redox reactions and charge transfer due to doping. [11][12][13][14] PEDOT: PSS doped with nanocarbon materials is expected to achieve enhanced sensing properties owing to their high surface-to-volume ratio. Graphene (Gr), among various nanocarbon materials, is the most widely used because of its exceptional physical, chemical, mechanical, and electrical properties. [15][16][17][18] Although pristine graphene has proved low sensitivity toward detecting H 2 molecules, [15,19] chemically modified graphene/PEDOT: PSS nanocomposite films have demonstrated enhanced sensing response with a much shorter response and recovery time. [20] When suspended as a nanoscale bridge, In this study, the hydrogen gas (H 2 ) sensing mechanism of suspended graphene (Gr)/ Poly(3,4-ethylene dioxythiophene): Poly(styrene sulfonate) -Polyethylene oxide (PEDOT: PSS-PEO) composite nanoscale channels precisely patterned with near-field electrospinning is investigated. Suspended Gr/PEDOT: PSS-PEO nanoscale channels not only have a higher surface-to-volume ratio for easy diffusion...

According to the statistics published by the World Health Organization (WHO) in 2011, cardiovascular disease (CVD) is the leading cause of death globally. Recent studies suggest that the level of C-reactive protein can be an important indicator of a person’s risk for cardiovascular disease. In this study, we detect low concentration of C-reactive protein (1 fM) electronically by immobilizing CRP-specific aptamer on the AlGaN/GaN HEMT based biosensor, showing that this technique is promising for biosensor applications.