Optical Detection of Water Adulteration in Ethanol Using PCPDTBT-Conjugated Polymer Nanoparticles

The detection of water adulteration in ethanol biofuels is a persistent challenge due to ethanol's high affinity for water and the limitations of conventional analytical methods. In this study, we present an innovative optical sensing strategy using conjugated polymer nanoparticles (CPNs) composed of poly-[2,6-(4,4-bis-(2-ethylhexyl)-4<i>H</i>-cyclopenta-[2,1-b;3,4-b0]-dithiophene)-<i>alt</i>-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) for rapid and sensitive quantification of water content in ethanol blends. These nanoparticles were synthesized via nanoprecipitation and exhibited dual-emission bands centered at 679 and 846 nm, corresponding to nanoparticle fluorescence and aggregation-related emissions, respectively. Upon exposure to ethanol, destabilization of the CPN micelle structure and enhanced aggregation were observed, leading to pronounced changes in the emission profile. Notably, the emission intensity ratio (<i>I</i> ₆ ₇ ₉/<i>I</i> ₈ ₄ ₆) showed a strong linear correlation with the water concentration, enabling precise calibration for water detection and achieving limit of detection (LOD) and limit of quantification (LOQ) values of 0.4 and 1.3% (v/v), respectively. These findings demonstrate the strong potential of PCPDTBT CPNs as a sensitive and practical platform for the future development of analytical tools to assess biofuel quality and detect water adulteration in ethanol.