Piezoelectric crystal impedance analysis for investigating the modification processes of protein, cross-linker, and DNA on gold surface

The processes of surface modification on gold-coated piezoelectric quartz c rystal sensor have been in situ investigated by using the impedance analysi s technique. The changes of equivalent circuit parameters were used to inte rpret the different behaviors of successively modifying protein, cross-link er, and DNA onto a gold electrode surface. It was found that the frequency changes due to protein adsorption might be described as a sum of two expone ntial functions, compared with a first-order kinetic function exhibited in subsequent binding of cross-linker to protein. The kinetic parameters were fitted to these two cases. It was also shown that the DNA molecules binding to cross-linker gave rise to the changes of the density-viscosity and the dielectric constant, both being linearly related to DNA concentration in th e liquid when below 6.0 mu g m(-1). (C) 2000 Elsevier Science B.V. All righ ts reserved.