This Small Business Innovation Research (SBIR) Phase II project will develop a robust, in-line plasmonic sensor for the detection of mercury in natural gas. Mercury naturally contaminates natural gas at the parts per million levels and can corrode critical aluminum components in processing facilities. Heat exchangers at Liquid Natural Gas (LNG) plants have failed catastrophically due to mercury corrosion, costing hundreds of millions of dollars of damage and injuring workers. Current monitoring methods cannot operate at the high pressures found in the process gas lines, leading to inaccurate measurements and unreliable instruments. LNG is a growing share of global energy as natural gas replaces more carbon intensive fossil fuels. By 2020, 30 LNG plants will be operating world wide, for a total mercury monitoring market of $136 million. Mercury monitoring at petrochemical facilities broadly is a $216 million per year market. Mercury itself is a neurotoxin and a global pollutant; our sensor has the potential to aid in efforts to detect and remove mercury before it can impact human health. Beyond mercury, plasmonic sensing is a novel technology with applications for a variety of chemical and biological species.<br/><br/>The intellectual merit of this project derives from the utilization of a novel sensing platform based on the localized surface plasmon resonance (LSPR) of a gold nanoparticle film. It will build upon the success of the Phase I project, which demonstrated the suitability of LSPR sensors for the detection of elemental mercury vapor. This Phase II project will proceed along two objectives. The first objective will be to adapt the sensor for operations at high pressure; included in this objective is the redesign of key components of the system and the construction of a high-pressure test bench. The second objective is testing the LSPR sensor in a natural gas matrix; preliminary results indicate that LSPR mercury sensors response well in methane, but the full range of response and lifetime performance will be investigated in this project. Upon completion of these two objectives, field trials will commence. The full system will be certified for use in a gas plant and demonstrated at a suitable natural gas plant. A commercial prototype LSPR based natural gas mercury monitor will be realized upon completion of this project.