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

• Published in: The Journal of chemical physics 2004-01, Vol.120 (3), p.1585-1593
• Main Authors: Pipino, Andrew C R, Woodward, John T, Meuse, Curtis W, Silin, Vitalii
• Format: Article
• Language: English
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.1629279

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 approximately 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 approximately 5 x 10(-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 7 x 10(-8) mol/L, respectively, based on a 30 s integration time.