Direct Detection of Low Concentration DNA in High Ionic Strength Solution with AlGaN/GaN High Electron Mobility Transistors

Abstract

In this research, the direct detection of DNA sequences in physiological salt concentration by FET based biosensor has been investigated. Traditionally, most of the DNA detection methods are optical measurements, such as fluorescence or Raman spectroscopy which are always expensive, bulky and hard to quantify. In contrast with the traditional method, we use AlGaN/GaN high electron mobility transistor (HEMT) to detect the target ssDNA. The III-IV compound semiconductor based transistor is chemically inert and possess really high resistivity to high salt environment and has low possibility of corrosion. The HEMT device is fabricated with four mask: MESA, SD metal, final metal and gate opening and presents a 3D structure which isolates the transistor channel and gold sensing region.(fig 1.) Moreover, with the isolated gold sensing area, the transistor can be extremely small as the gold sensing region stays in the large area. This kind of FET having high transconductance gain, can significantly improve the S/N ratio and sensitivity. Current measured in PBS buffer serves as the baseline of the biosensor. Probe ssDNA is immobilized on the gold gate electrode positioned at a fixed distance from the transistor channel. Device is operated with 2V drain voltage and a tunable gate pulse voltage. As the complementary DNA concentration, ranging from 1fM to 100nM, is introduced, the current gain of the device changes accordingly. The sensor can efficiently detect target DNA down to a low concentration of 100 fM. This ultrahigh sensitivity and low S/N ratio characteristics exhibited by the sensor makes it a competitive alternate choice compared to the traditional existing sensors. The miniaturized device design and ease of fabrication and testing indicate the potential of the sensor to be used as a commercial DNA biosensor. Figure 1