This Small Business Innovation Research Phase I project will develop a robust, portable, low-power plasmonic mercury monitor capable of measuring ambient (nanograms per cubic meter) levels of mercury in air. Environmental monitoring of mercury is a $600 million market, with an estimated $200 million spent on instruments. Incumbent instruments are adapted from automated laboratory methods requiring bulky equipment, frequent calibration, inert gasses, and high power. The method to be developed, based on gold nanoparticle films, can lower costs to operators and expand monitoring to areas currently underserved by existing systems. Of particular note are artisanal mining sites, which represent the single largest source of mercury emissions. To expand mercury monitoring to these sites and other remote settings, a drastically less expensive, easier to operate, and more robust mercury sensing platform is needed. Beyond mercury, plasmonic sensors based on nanoparticle films have the potential to address the broader ($4 billion) chemical and biological sensing markets.<br/><br/>The intellectual merit of this project derives from the development of a new sensing platform based on the localized surface plasmon resonance (LSPR) of a gold nanoparticle film. Harnessing the unique optical properties of noble metal nanoparticles for use in highly sensitive analytical instruments requires an improved understanding of the science and properly engineered controls. Mercury sensing with gold nanoparticles provides an ideal first target for this platform. The specific aims of this project are to: improve the nanoparticle film fabrication; investigate new optical configurations to interrogate the films with light; and test and develop a packaging and control systems to handle and analyze air samples at ambient concentration levels. This research will result in a prototype plasmonic mercury sensor with a unique combination of portability and sensitivity. It will be a valuable tool in characterizing the environmental behavior of mercury and the risks to human health. Beyond mercury, the advances anticipated for this plasmonic detection platform will apply to a wide variety of chemical and biological analytes.