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Second harmonic correlation spectroscopy: a method for determining surface binding kinetics and thermodynamics.

These studies describe the implementation of second harmonic correlation spectroscopy (SHCS) to measure the adsorption and desorption kinetics of molecular species associated with a surface. Specifically, the local fluctuations of the measured second harmonic (SH) signal were used to determine the binding kinetics and thermodynamics of (S)-(+)-1,1'-bi-2-napthol SBN intercalation into a 1,2-dioleoyl-sn-glycero-3-phosphocoline (DOPC) bilayer. In order to determine the adsorption and desorption rates, the SH signal was collected above saturation concentration at steady-state equilibrium as a function of time. The autocorrelated SH signal was then fit to a correlation model developed for molecules binding at a surface when there is no contribution from molecules in solution. The measured adsorption rate for SBN to DOPC was 2.7 ± 0.2 × 10(3) s(-1) M(-1) and the desorption rate was 9 ± 4 × 10(-4) s(-1). The kinetic rates as well as the calculated equilibrium binding constant, 3.0 ± 1.3 × 10(6) M(-1) obtained from SHCS were compared with those obtained from a conventional binding isotherm and found to be statistically consistent. The primary advantage of using SHCS is both the absorption and desorption rates were determined in the same experiment using only a single bulk concentration of SBN. The results of these studies demonstrate that SHCS can be used to provide accurate kinetic and thermodynamic binding data in a label-free manner in lieu of conventional isotherm studies, especially where time and analyte are scarce.