Detection of SO2 at the ppm Level with Localized Surface Plasmon Resonance (LSPR) Sensing

Abstract

Detection and monitoring of SO2 is important because it is a representative toxic gas in the atmospheric environment that is emitted from industrial and natural processes. Localized surface plasmon resonance (LSPR) sensing is a promising method to develop a robust and low-cost sensor for gaseous species. However, with conventional LSPR sensing, inorganic gases including SO2 are not detectable at the ppm level. In this study, we developed Au-nanopatterned chips coated with porous silica, which enabled detection of SO2 gas at ppm levels using the LSPR sensing system. The Au nanopattern was optimized using a finite-difference time-domain simulation and fabricated on quartz substrates using electron beam lithography. The Au-nanopatterned chips were coated with porous silica by the sol-gel method, which enables detection of 20 ppm of SO2. The sensitivity of the porous-silica-coated chip was four times higher than that of the uncoated chip. Modification of the porous silica layer with 3-aminopropyltrimethoxysilane (APTMS) using chemical vapor deposition further enhanced the sensitivity to SO2 gas, which was 13 times higher than that of the unmodified porous-silica-coated chip. Depth profiles by X-ray photoelectron spectroscopy indicated that APTMS was uniformly introduced into the porous silica layer. This study demonstrates that porous silica coatings on Au-nanopatterned chips and their additional modification with functional groups are potentially important to develop a low-cost and sensitive sensor for inorganic gases such as SO2.