MOS capacitor for simple thiol based biosensor applications

Thiols attached to thin gold films provide the platform for many biosensors to detect DNA. Attachment of thiol to gold can cause stress in gold especially if the layer is thin, inducing a change in the work function of gold. We report here a simple method to estimate this effect of attaching thiol to gold by monitoring the flat-band voltage of a metal-oxide-semiconductor (MOS) capacitor with gold as the metal. Capacitance-voltage (CV) characteristics were measured on gold gated MOS before and after attaching thiol to gold. A negative shift in the CV was seen for 1-octadecanethiol, while the shift was positive for 4-flurothipohenol. The MOS capacitor showed an increased change in the work function for increasing duration of immersion of the sample in the thiol solution saturating at longer times. Effect of attaching DNA molecules to the thiol on the CV characteristic was also investigated.