Novel Chemical Detection Strategies for Trichloroethylene and Perchloroethylene

Abstract

Novel applications of cavity ring-down spectroscopy (CRDS) to chemical detection are described. Using a linear optical resonator with an intra-cavity double-Brewster-window flow cell, CRDS is employed to probe the optical response to adsorption of the surface-plasmon resonance (SPR) of an ultra-thin (0.2 nm), nanostructured Au film. Detection limits for trichloroethylene (TCE), perchloroethylene (PCE), and NO 2 are found to be 7x10 -8 mol/L, 2x10 -8 mol/L, and 4 x 10 -9 mol/L, respectively. As the ultra-thin nanostructured film is well described by a distribution of nanospheres with a mean diameter of 4.5 nm, Mie theory is employed to account for some aspects of the optical response. In a second implementation of CRDS, evanescent wave CRDS (EW-CRDS) is used to detect TCE, cis-dichloroethylene (cis-DCE), and trans-DCE by probing the first C-H stretching overtones in the near-IR with a monolithic folded resonator (MFR), providing spectroscopic selectivity and a reversible response. In a comparison of EW-CRDS to previous sensing technologies, the sensitivity obtained using an unclad MFR for TCE detection is found to be comparable to that obtained with a long-effective-path-length optical waveguide using a TCE-enriching polysiloxane coating. By applying an analyte-enriching, protective coating to an MFR, EW-CRDS may provide a sensitive, selective, and robust technology for longterm environmental monitoring.