Surface-plasmon-resonance-enhanced cavity ring-down detection

摘要

The cavity ring-down technique is used to probe the absolute optical response of the localized surface plasmon resonance (SPR) of a gold nanoparticle distribution to adsorption of trichloroethylene (TCE) and perchloroethylene (PCE) from the gas phase.Extended Mie theory for a coated sphere with a particle-size-dependent dielectric function is used to elucidate size-dispersion effects,the size-dependence of the SPR sensitivity to adsorption,and the kinetics of adsorption.An approximate Gaussian distribution of nanospheres with a mean diameter of 4.5 nm and a standard deviation of 1.1 nm,as determined by atomic force microscopy,is provided by the intrinsic granularity of an ultrathin,gold film,having a nominal thickness of approx=0.18 nm.The cavity ring-down measurements employ a linear resonator with an intracavity flow cell,which is formed by a pair of ultrasmooth,fused-silica optical flats at Brewster's angle,where the Au film is present on a single flat.The total system intrinsic loss is dominated by the film extinction,while the angled flats alone contribute only approx=5X10~(-5)/flat to the total loss.Based on a relative ring-down time precision of 0.1 for ensembles averages of 25 laser shots from a pulsed optical parametric oscillator,the minimum detectable concentrations of PCE and TCE obtained by probing the SPR response are found to be 2 and 7X10~(-8) mol/L,respectively,based on a 30 s integration time.