On Chip Sensing of Biochemical Molecules with GaAs PIN Diodes

We demonstrate that Schottky contacted GaAs PIN conducting diode can be used as a viable sensor for detecting biochemically relevant molecules. The microfluidic chip contains an array of cylindrically shaped diodes, oriented so the liquid solution can be placed in a trough of the chip with the liquid surrounding the diodes. For the test of the functionality of the sensor, we use DI water, deuterated water, PBS solution, and a series of amino acid solutions with controlled pH levels. We focus our studies on the transport properties, including differential conductance and impedance spectroscopy. Also, we examine the C-V measurements as the various electrolytes and diode biasing conditions have different effects on the Debye length. Next, we address the issue of noise in such (bio)chemical sensors in relation to variations in the molecular structure of solid-liquid interface. Wealth of data coming from this sensor calls for the use of advanced data analysis techniques, so we demonstrate how one can use machine learning to optimize such sensor.