Microfluidic Reference Electrode for Use in BioFET Sensor Systems

Abstract

<p>Biosensors, used in medical diagnostics, increasingly use genomic information (DNA) to rapidly and accurately determine the species present in the sample. Since, the DNA inherently has a negative charge, electrical methods provide a direct technique to sense it. This transduction has been achieved by using a biological Field-Effect-Transistor (BioFET) structure, where hybridization of a single stranded DNA (indicative of the biological species) with a complementary strand from the sample solution causes a change in the transistor characteristics that could be read out electrically. The accuracy of sensing using the BioFET is critically dependent on imposition of a highly stable potential which is performed using a reference electrode.</p> <p>Design and fabrication of a miniaturized silver/silver chloride (Ag/AgCI) reference electrode is introduced in this thesis for use in BioFET. The electrode consists of Ag/AgCl wire which is embedded into a PDMS microchannel enclosed by a microcontact printed nanoporous polycarbonate membrane. The microchannel is filled with KCI solution as the internal solution.</p> <p>By modifying the electrodeposition method, nanosheet AgCI structure was grown rather than the conventional globular morphology. The bare Ag/AgCl potential drift with the former morphology was found to be</p> <p>In conclusion, a modified electrodeposition method and free-diffusion liquid junction micro fluidic reference electrode is proposed to improve the stability and extend the lifetime of a reference electrode with very low potential drift.</p>