Adsorption of Alkylthiol-Capped Gold Nanoparticles onto Alkylthiol Self-Assembled Monolayers:  An SPR Study

The kinetics of alkylthiol-capped gold nanoparticle (RS/Au−NP) adsorption to alkylthiol/Au self-assembled monolayers (RS/Au−SAMs) has been studied using SPR (surface plasmon resonance) spectroscopy. Variation of the alkylthiol chain terminus (CH3, COOH) and solvent (H2O, hexane) provides insight into the relative importance of solvation energies (in the context of surface energies) and RS/Au−NP structure on adsorption kinetics. The kinetics, fitted to the Langmuir kinetic model, yield adsorption and desorption rate constants. ΔG ads derived from kinetic data are compared to calculated values of work of adhesion (Wadh), derived from the corresponding surface energies. The absence of a ΔG ads − Wadh correlation arises because the measured kinetics are not reporting the approach to equilibrium and/or because there are factors (i.e., local chain packing defects, surface hydration differences, or particle−particle interactions) not accounted for in calculated Wadh values.