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...
InSb and InAs1−xSbx epitaxial layers have been successfully grown on (100)GaAs substrates by molecular beam epitaxy. Remarkably good morphologies were obtained despite the large lattice mismatch (14%) between InSb and GaAs. Room-temperature electron mobilities as high as 57 000 cm2/V s were measured in InSb layers of about 5 μm thick with ND−NA∼1.6×1016 cm−3. The substrate temperature and Sb/In flux ratio were found to critically influence the quality of InSb epilayers. By employing dimeric instead of tetrameric sources, the composition of the InAs1−xSbx films was observed to be relatively independent of substrate temperature. Electron mobilities of 20 000 and 8800 cm2/V s, at 300 and 77 K, respectively, were obtained for a 1.6-μm-thick InAs1−xSbx (x=0.67) layer.
Mesa and planar GaN Schottky diode rectifiers with reverse breakdown voltages (V~~) up to 550V and >2000V, respectively, have been fabricated. The on-state resistance, RON, was 6mQ.cm2 and 0.8Llcmz, respectively, producing figure-of-merit values for (VRB)2/RoN in the range 5-48 MW.cm-2. At low biases the reverse leakage current was proportional to the size of the rectifying contact perimeter, while at high biases the current was proportional to the area of thk contact. These results suggest that at low reverse biases, the leakage is dominated by the surface component, while at higher biases the bulk component dominates.On-state voltages were 3.5V for the 550V diodes and 215 for the 2kV diodes. Reverse recovery times were <0.2ysec for devices switched from a forward current density of -500A.cm-2 to a reverse bias of 100V. DISCLAIMER
Epitaxial layers of InSb have been grown on Si substrates by molecular beam epitaxy. Room-temperature electron mobilities are 48 000 and 39 000 cm2/V s for 3.2 μm-thick InSb with and without a thin GaAs buffer, respectively. The corresponding carrier concentrations are 2.2×1016 and 2.7×1016 cm−3. A sample with an InSb thickness of 8 μm exhibited room-temperature mobilities as high as 55 000 cm2/V s with carrier concentrations of about 2.0×1016 cm−3. A sharp band-edge transmission spectrum is observed at room temperature for the 8 μm layer.
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