Discrimination in the aggregation kinetic of polyelectrolyte stabilized gold nanoparticles induced by cysteine and homocysteine

Cysteine and homocysteine are naturally occurring amino acids structurally similar (only one methylene difference) and metabolically linked. The development of simple and specific methods for their determination is attractive. Gold nanoparticles (GNP) have emerged as important colorimetric materials for their strongly distance-dependent optical properties. The analyte-induced aggregation of GNP shifts the surface plasmon resonance absorption peak towards longer wavelengths. Based on this feature, methods have been investigated for the detection of thiol-containing amino acids which always lack in specificity1. The present study shows that the aggregation kinetics of poly(styrenesulfonate) stabilized GNP can be differentiated significantly by increasing particle size from 10 to 20 nm, allowing the recognition of one methylene difference between Cys and Hcys. Such a differentiation have been optimized by tuning the chain length of the polyelectrolyte which affects its flexibility and therefore its attitude to wrapping around GNP2. The aim was to create a crowded layer able to maximize colloid stability and to discriminate the permeation of species with minimal difference in sterical hindrance. 1. Zhang, F.X.; Han, L.; Israel, L.B.; Daras, J.C.; Maye, M.M.; Ly, N.K.; Zhong, C.J. Analyst 2002, 127, 462-465. 2. Chodanowski, P.; Stoll, S. Macromolecules 2001, 34, 2320-2328.