Surface modifications for the development of piezoimmunosensors.

Four different techniques for the immobilisation of proteins onto the gold electrode of a piezoelectric quartz crystal were investigated. The examined techniques were adsorption, avidin-biotin binding and two different types of covalent binding on self-assembled monolayers (SAM), dithiobis(succinimidylpropionate) (DSP) and a dextran modified thiol monolayer. The reaction of the immobilised proteins (bovine serum albumin (BSA) and anti-human IgG) with their specific antibodies, anti-BSA and hIgG (50 and 200 micrograms/ml) were studied using a quartz crystal microbalance and then compared. Many cycles of measurements were performed on the same crystal regenerating the gold surface with a solution of glycine.HCl, 100 mM, pH 2.1. The interactions of the immobilised reagents with non-specific antibodies were also studied. The adsorption protocol was the quickest, but did not allow regeneration with glycine.HCl. Thiol-dextran coated surfaces did not show any detectable response to non-specific reagents, but needed a very long and complicated protocol. DSP and avidin-biotin coating procedures were easy and not too long. They seemed to have the best characteristics of reproducibility among different crystals and possibility of regeneration of the coated surface, but the percentage of non-specific binding was high.