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 (W_adh), derived from the corresponding surface energies. The absence of a ΔG_ads − W_adh 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 W_adh values.