Enzyme-based detection of epoxides using colorimetric assay integrated with smartphone imaging

Epoxides are widely used chemicals, the determination of which is of paramount importance. Herein, we present an enzyme-based approach for noninstrumental detection of epoxides in standard solution and environmental samples. Halohydrin dehalogenase (HheC) as a biological recognition element and epichlorohydrin as a model analyte were evaluated for sensing. The detection is based on the color change of the pH indicator dye bromothymol blue caused by the HheC-catalyzed ring-opening of the epoxide substrate. The color change is then exploited for the determination of epoxide using a smartphone as an image acquisition and data processing device, eliminating the need for computer-based image analysis software. The color parameters were systematically evaluated to determine the optimum quantitative analytical parameter. Under optimal conditions, the proposed enzyme-based detection system showed a linear range of 0.13-2 mM with a detection limit of 0.07 mM and an assay time of 8 Min. In addition, the repeatability expressed as relative standard deviation was found to be below 5% (n = 6). Validation with gas chromatographic analyses showed that the proposed enzyme-based epoxide detection could be an alternative way in the quantitative determination of epoxides, and particularly useful in resource-limited settings.