Electrochemical Diazonium Grafted Surface for Protein Biosensing

Surface-based or electrochemical protein biosensors commonly use thiol-gold bonding to conjugate a designed binding protein (ligand) to the surface in order to evaluate analytes in the solution. As an example, antibodies, proteins, and other large polypeptides have been conjugated to gold surfaces that lead to successful biosensors. While thiol-gold surfaces have been shown to lead to successful biosensor surfaces, they have limited stability and long-term use, which can affect overall sensor performance. For example, thiol-gold surfaces can degrade (thiol decoupling) or the gold can become pitted. Surface damage in such forms presents numerous problems when paired with electrochemical impedance spectroscopy (EIS) or cyclic voltammetry (CV) when concerned with long term sensor stability.

To overcome the degradation of thiol-gold bonds, we created a more stable surface by electrochemically grafting diazonium functionalized surfaces. To build the surface, 4-carboxyphenyl diazonium salt was electrochemically grafted to a carbon surface creating a functional carboxylate. The N-terminus of a polypeptide is modified to the carboxyl-terminated surface via EDC/NHS chemistry. The surface was characterized using XPS, ATR-FTIR, and EIS. Long term surface stability of the 4-carboxyphenyl surface compared to thiol-gold surfaces indicated a stability increase over a one month period. The stability and viability of diazonium/protein surfaces has also been investigated and will be reported.