Piezoelectric crystal impedance analysis for investigating the changes of interfacial properties due to interaction of cobalt salt with DNA immobilized on biosensor

The interaction of a cobalt compound, tris(2,2'-bipyridyl)cobalt(III) perch lorate (Co(bpy)(3)(ClO4)(3).3H(2)O), with DNA immobilized on a biosensor ha s been investigated by using a piezoelectric impedance technique. The chang es of equivalent circuit parameters were used to characterize the changes o f the interfacial properties of the piezoelectric biosensor in the reaction system. It was found that the interaction of cobalt compound with double-s trained DNA (dsDNA) could be described by a sum of two exponential function s, suggesting two corresponding kinetic steps. As for dsDNA, the change of static capacitance showed a linear correlation with time. Comparative exper iments indicated that dsDNA with double-helical structure is more easily bo und with cobalt compound than single-strained DNA (ssDNA). From the frequen cy curve, some parameters related to this interaction, such as cross-linkin g ratio, binding ratio, and the maximum initial rate were roughly estimated to be 2%, 1.15, 0.72 Hz/s (or 0.12 Hz/s for ssDNA), respectively. The line ar relationship between the frequency change and the motional resistance wa s verified to reflect the changes of the density-viscosity in the biologica l reaction.