This paper demonstrates a novel high sensitive FET biosensor array that can capture as well as count the number of captured Circulating Tumor Cells (CTCs) by the aptamer immobilized on the sensor. The FET used for this purpose is AlGaN/GaN HEMT (High Electron Mobility Transistor) because of its high sensitivity. Using a new and robust sensing technique the cell capture was able to be measured electrically and analyzed. The array enhances the capturing and detection capability of the sensors. The advantage of this sensor array is that the detection can be extended to any type of cells and cell lines to differentiate the normal and abnormal cells among them, and the behavior of cells can be studied in different kinds of mediums in which the cells are suspended.

Biosensors can be used as point of care testing devices. In order to do so, they must be compact, portable, highly sensitive and user friendly. Along with being highly sensitive, GaN HEMT also are biocompatible, high temperature tolerant, chemically resistive and have excellent electrical properties. These properties of HEMT makes it a candidate for rapid biosensing. CTC enumeration has been used as a prognostic marker for metastatic colorectal cancer (m-CRC). CTCs are migrating cells that are shed into the blood stream from primary and metastatic tumors. But cancer patients have only 1-10 CTCs per cc of blood which makes them hard to be detected among plethora of other blood cells. The HEMT biosensor array developed by our group overcomes this drawback by capturing CTCs and counting them electrically, with an accuracy of single cell binding.

The fabrication of AlGaN/GaN HEMT is done by forming mesa islands by ICP etching of epi-wafer which is followed by ohmic metal deposition, annealing and probing pad deposition. Finally individual chips of size 1mm X 1mm are embedded onto an epoxy substrate and interconnects are deposited making a planar sensing device. This fabricated chip is then passivated and only the gate electrode and channel regions are opened with an area of 10X60µm² using photolithography.

Aptamer is immobilized on the gate electrode and CTCs are allowed to be captured for 5~10 minutes. The cells bound on the aptamer are observed and the capture can be confirmed electrically by measuring the change in current gain compared to the aptamer current level and the change in current gain of HEMT sensor corresponds to the number of CTCs captured by the aptamer. In this way, CTC enumeration can be carried out using electrical measurement. This sensing technique is highly sensitive and can provide up to single cell resolution. Apart from rare migrating cells, abnormal cells and other cell based disease biomarkers can be detected and enumerated using our GaN HEMT based biosensor array.