Label-free electrochemical biosensors for clinical diagnostic

We present the development of a high sensitivity, label-free, biosensor platform suitable for multiplexed point-of-care diagnostics. A sensor surface based on a carboxy-terminated oligo ethylene-glycol (OEG) self-assembled monolayer (SAM) was developed and fully characterised. Optimal conditions for antibody immobilisation were found for a buffer pH approximately one unit below the pI of the antibody, which yielded both higher antibody density on the sensor surface as well as higher sensor response to the antigen. At the same time the surface showed good resistance to non-specific adsorption of high concentrations of proteins. A non-faradaic electrochemical impedance spectroscopy biosensor to detect human chorionic gonadotropin (hCG) in full serum was demonstrated as a proof of concept. By using the phase of the impedance at 100 mHz as the sensor response, a linear relationship of the phase shift vs the logarithm of hCG concentration was established between 26 fM and 0.26 nM with a sensitivity of 0.6 degree per decade, which is a significant improvement over current state-of-the-art biosensor systems.