Optical ratiometric sensor for alcohol measurements

The need for low-cost, robust alcohol sensors has increased with the renewed interest in alternative fuels as well as high-throughput screening of biological processes involving the production of ethanol. The goal of this research was to develop a miniaturized optical ratiometric ethanol sensor to be used for in situ measurements. The sensor is based on the fluorescent dye Nile Blue Chloride. When in solution, the dye exhibits a single fluorescence peak. However, a dual emission peak is observed upon physical immobilization of the dye in the hydrogel poly( ethylene glycol) dimethacrylate. The dual emission allows for ratiometric measurements, thus circumventing drawbacks associated with fluorescence intensity measurements such as signal variations due to dye bleaching, source intensity fluctuations, etc. In developing this sensor we investigated ethanol sensitivity; alcohol selectivity; response time; and cross-sensitivity with pH, polarity, and ionic strength. We found that the sensor is sensitive to a broad range of ethanol concentrations, namely 5% to 90% v/v. Due to the hydrogel's restrictive pore size, the sensor is sensitive to short-chain alcohols such as methanol, ethanol, and propanol, but lacks sensitivity to larger alcohols such as butanol and hexanol. We also found the sensor maintains full functionality after autoclaving. Sensor sensitivity to alcohol in solutions of varying ionic strength is negligible, whereas the solvent's polarity must be controlled to maintain meaningful results. The sensor is most sensitive in acidic and neutral environments, indicating promising use for yeast-based alcohol fermentations.