Field-effect transistors for microfluidic interfacial biosensing

The project aims to explore the use of a metal-oxide-semiconductor field-effect transistor (MOSFET) in the detection of cells, bacteria, and biomolecules in a microfluidic channel.

Conventional biologically-sensitive FETs (BioFETs) typically utilise a functionalised biological layer, and a change in charge on the surface is the typical sensing mechanism, consequently leading to a change in gate potential and a detectable change in the transistor. An important side-effect of the accumulation of material on these functionalised surfaces is a change in local capacitance. The effect of this change in capacitance is usually in addition to the effect of the change in surface charge; both change the gate potential on the FET.

Capacitance sensing in microfluidic environments has previously been used to create functional sensors. These typically utilise a pair of electrodes either stacked in parallel across a channel or, more commonly due to manufacturing constraints, arranged in a co-planar or interdigitated fashion along the length of the channel. With these two electrodes capacitively coupled, a high-frequency signal applied to one will propagate to the other; a change in the local environment of these two electrodes will then change the properties of the dielectric between them, and this change in capacitance can then be monitored to detect these changes in local environment. However, given the above observations on the sensitivity of a FET-based sensor to changes in local dielectric properties, it is speculated that a sensor based solely on the detection of a change in local environment using a FET-based mechanism may present an effective biosensor.

In order to test this mechanism, its application in cytometry will first be assessed. This presents an application where no surface charge accumulation is required; the proposed mechanism will be assessed on its ability to detect the passage of cells through the microfluidic channel through detection of the change in local dielectric properties or other interfacial effects alone, without necessitating the accumulation of charge. This presents the following research questions, to be approached using a combination of simulation and experimental observation:

Can the proposed mechanism reliably detect the passage of biomolecules?
If so, can any other properties of the biomolecule be inferred from the readings?
How does the proposed sensor compare to existing cytometry mechanisms?

This novel sensing mechanism to the detection of biomolecules can have a wide range of applications, in particular for the fast, sensitive detection of pathogens, inflammation markers and cancer biomarkers, amongst other biomedical diagnostics applications.