Surface assembly and redox dissolution of silver nanoparticles monitored by evanescent wave cavity ring-down spectroscopy

The adsorption kinetics of Ag nanoparticles on a silica surface modified with poly-L-lysine (PLL) have been measured in situ by following the interfacial optical absorbance at 405 nm by evanescent wave cavity ringdown spectroscopy (EW-CRDS). Sensitivity toward nanoparticle detection is enhanced due to the plasmon resonance of the Ag nanoparticles. The redox-dissolution kinetics of the immobilized nanoparticles have been investigated by two distinct approaches. First, IrCl62- was generated electrochemically from IrCl62- by a chronoamperometric potential step in a thin-layer cell configuration formed between the silica surface and a Pt macroelectrode. The oxidative dissolution kinetics were obtained by monitoring the EW-CRDS signal as the nanoparticles dissolved. The reaction kinetics were extracted by complementary finite element modeling of diffusional and reaction processes. The second method of dissolution investigated involved the injection of IrCl62-(aq) directly at the surface by means of a microcapillary located close to the evanescent field. © 2008 American Chemical Society