Development of a stable sensing interface for an electrochemical impedance label-free DNA hybridisation biosensor

摘要

The performance of a DNA hybridisation biosensor relies greatly on the stability and selectivity of the sensing interface. This thesis explores several different DNA interface constructs on both gold and silicon surfaces for the development of an electrochemical impedance label-free DNA sensor. The gold sensing interface is comprised of a mixed self-assembled monolayer of single-stranded probe DNA and a diluent, mercaptoethanol. Using electrochemical impedance spectroscopy, the recognition interface was shown to display a good ability to differentiate between different target DNA analytes. However, the surface chemistry was found to be chemically unstable, thus making the sensor unreliable. Silicon sensing interfaces were formed by attaching single-stranded probe DNA to undecylenic acid on p-type Si(111). This surface chemistry showed good selectivity towards complementary DNA but impedance measurements were found to suffer from interference attributed to oxide growth underneath the grafted undecylenic acid monolayer. A novel silicon interface was trialed by attaching alkyne-tagged single-stranded DNA onto a 1,8-nonadiyne modified p-type Si(111) surface via a one-pot tandem ‘click’ reaction. With the addition of an antifouling layer comprised of bovine serum albumin, the recognition interface shows good discrimination between complementary, non-complementary and single-base mismatch target DNA using Faradaic impedance. This surface chemistry was translated onto poorly doped n-type Si(111) to investigate field-induced effects upon the formation of a DNA duplex. DNA hybridisation was found to result in a positive shift in open circuit potential (OCP). This was attributed to the increase in upward band bending due to the extra negative charge from the DNA at the silicon-electrolyte interface, bringing the silicon electrode further into depletion. OCP results were supported by a positive shift of the flat band potential obtained via AC impedance measurements.