A simple but quantitative mathematical formalism for interpretation of surface plasmon resonance
(SPR) signals from adsorbed films of a wide variety of structures is presented. It can be used to estimate
adsorbed film thicknesses, surface coverages, or surface concentrations from the SPR response over the
entire range of film thicknesses without relying on calibration curves of response versus known thicknesses
or surface concentrations. This formalism is compared to more complex optical simulations. It is further
tested by (1) calibrating the response of two SPR spectrometers to changes in bulk index of refraction, (2)
using these calibrations with this formalism to predict responses to several well-characterized adlayer
structures (alkanethiolates and serum albumin on gold, propylamine on COOH-functionalized gold), and
then (3) comparing these predictions to measured SPR responses. Methods for estimating the refractive
index of the adlayer material are also discussed. Detection limits in both bulk and adsorption-based
analyses are discussed. The planar system used here has a detection limit of ∼0.003 nm in average film
thickness for adsorbates whose refractive index differs from that of the solvent by only 0.1. The temperature
sensitivities of these two SPR spectrometers are characterized and discussed in terms of detection limits.
Calorimetric measurements of metal adsorption energies directly provide the energies of metal atoms in supported metal nanoparticles. As the metal coverage increases, the particles grow, revealing the dependence of this energy on particle size, which is found to be much stronger than predicted with the usual Gibbs-Thompson relation. It is shown that this knowledge is crucial to accurately model long-term sintering rates of metal nanoparticles in catalysts.
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