Precision Low Cost Phase Sensitive Optical Sensor for Detecting Carbon Nanoparticle Degradation

Phase sensitive detection (PSD) is a powerful technique to extract low amplitude signals from noisy data. Commercially available lock-in amplifiers that employ this technique are expensive and cost-prohibitive for several applications where accuracy is desired with low cost instrumentation. In this manuscript we present a novel dual switch based phase sensitive detection scheme to distinguish the contrast of a reflecting surface. The circuit is sensitive enough to distinguish various shades of gray colored (darkness) text printed on a sheet of regular printer paper, even in presence of high intensity background light. We report the measurement of concentration of a solution of carbon nanoparticles in water, with potential application as a toxicity sensor or biosensor for various enzymes that could cause degradation of carbon nanoparticles.