A new compact electrochemical method for analyzing complex protein films adsorbed on the surface of modified interdigitated gold electrodes

Abstract

A new electrochemical instrumentation for real-time impedance measurements has been developed. In a first series of experiments we investigated the adsorption and protein film formation of complex biological fluid (blood serum) on solid surfaces. Interdigitated gold electrodes were coated with a series of hydroxyl and methyl functionalized thiols. Thiols with different chain length were used in order to get different baseline capacitance values. Binding of serum protein was monitored in real-time by capacitance measurements. In addition serum protein adsorption was quantified on the basis of refractive index changes using surface plasmon resonance (SPR). The capacitance shift induced upon sera injection to hydroxyl terminated and methyl terminated surfaces did not correlate to the amount of adsorbed protein. We therefore draw the conclusion that the capacitance shift was correlated to presumed hydrophobic interactions, and possible conformational change, of the adsorbed protein films at the hydrophobic electrode surfaces. Another finding was that the formation of relatively thick protein films on the hydroxyl terminated surface was inactive with regard to the capacitance parameter. Measuring in real-time using the novel band-pass filter set-up for impedance measurements allows for detection of small changes in surface capacitance. The described model experiments with the use of a complex protein solution indicated a high degree of reliability also when very concentrated and complex protein mixture was used. Further development of the instrument to more specific biosensor application is one interesting possibility.