Search

In this research, we have realized an electrical double layer (EDL) gated high electron mobility transistor (HEMT) as DNA sensor. The sensing area on the gate electrode which is separated from the transistor channel is immobilized with probe DNA to capture target DNA from physiological salt environment. The detection limit of the sensor can be as low as 1 fM with very high sensitivity. The specificity of the DNA sensor is also demonstrated by controlling the hybridization temperature. By choosing the hybridization temperature slightly lower than the melting temperature of the well-matched sequence, the binding ratio can be controlled between the fully-matched and mismatched one. The sensor has demonstrated specificity, with the ability to achieve single base mismatch resolution. The sensor has the potential for rapid DNA sensing applications in cells, biomarkers and viruses.

This study reports the development of an efficient and sensitive method to directly sense microRNA (miRNA) in high ionic strength solutions with the use of electrical double layer (EDL) gated AlGaN/GaN high electron mobility transistor (HEMT). This FET structure uses a complementary DNA probe functionalized gate electrode which is separated from the transistor channel. In this research, we focus on the detection of miRNA samples, miR-126, miR-208a and miR-21 which are biomarkers of cardiovascular diseases (CVD). The sensor has a dynamic range that is comparable to the clinically relevant concentration range with a detection limit as low as 1 fM. Selectivity of the sensor is demonstrated by evaluating sensor response at fully complementary and slightly mismatched sequences. The miniaturized sensor can be used in point of care or homecare diagnostics for rapid miRNA detection to evaluate CVDs at an early stage.

This study reports the fabrication and characterization of electrical double layer gated AlGaN/GaN High electron mobility (HEMT) biosensor array to capture, detect and count circulating tumor cells (CTCs) of colorectal cancer (CRC). GaN HEMT chips were assembled into a sensor array on a thermo-curable polymer substrate in a simple and robust packaging process. The array had multiple aptamer immobilized sensing sites and was highly sensitive and selective with up to single cell resolution. The present method can detect cells in their native electrolyte composition, in a very short time with extremely low cost compared to the conventional circulating tumor cell assays. The effect of cellular binding in different test environments was further studied and reported. The electrical response of the sensor was discovered to be relevant to the transmembrane potential of the cell. This whole cell sensor array has the potential to be used as a point-of-care diagnostic tool in varied applications such as detection of rare cells, pathogens and studying the dynamics of cellular interactions.

In this study, conductive polyaniline (PANI) was coated on Si3N4/Si substrates and reacted with hydroxyl radicals created by mixing ferrous ions and hydrogen peroxide in a buffer solution, as known as the Fenton reaction. The hydroxyl radicals reacted with PANI, resulting in the decreased conductivity of PANI. The reduction in the conductivity of PANI was found to be proportional to the concentration of hydroxyl radicals in the buffer solution. The concentration of hydroxyl radicals was calibrated by comparing the fluorescence intensities of the Amplex ultrared molecules oxidized by radicals and hydrogen peroxide via the catalysis of horseradish peroxidase (HRP), respectively. The conductivity change of the PANI shows a linear relationship to the concentration of hydroxyl radicals, ranging from 0.2 μM to 0.8 μM. The conductivity of PANI does not respond to either ferrous ions or hydrogen peroxide alone. Only when both ferrous ions and hydrogen peroxide are present in the solution, the conductivity of PANI decreases, indicating that the conductivity change of PANI is attributed to the existence of hydroxyl radicals. The simple process for the sensor fabrication allows the sensor to be cost-effective and disposable. This electronic sensor can detect one of the most important reactive oxygen species (ROS), the hydroxyl radical, and therefore is promising for studying oxidative stress.

AlGaN/GaN high electron mobility transistors (HEMTs) were used to sense the binding between double stranded DNA (dsDNA) and the severe acute respiratory syndrome coronavirus (SARS-CoV) nucleocapsid protein (N protein). The sensing signals were the drain current change of the HEMTs induced by the protein–dsDNA binding. Binding-site models using surface coverage ratios were utilized to analyze the signals from the HEMT-based sensors to extract the dissociation constants and predict the number of binding sites. Two dissociation constants, K D 1 = 0.0955 nM, K D 2 = 51.23 nM, were obtained by fitting the experimental results into the two-binding-site model. The result shows that this technique is more competitive than isotope-labeling electrophoretic mobility shift assay (EMSA). We demonstrated that AlGaN/GaN HEMTs were highly potential in constructing a semiconductor-based-sensor binding assay to extract the dissociation constants of nucleotide–protein interaction.