Electrospray preparation of Fe-PMMA films for one-drop analysis of thiocyanate a tobacco biomarker as a case study.

In this work, a single-step electrospray strategy for the fabrication of colorimetric films based on FeCl3 immobilized within a poly(methyl methacrylate) (PMMA) matrix was developed. Electrospray parameters were optimized to obtain stable and uniform coatings using sustainable and non-hazardous solvents. The films enable one-drop thiocyanate analysis as a case study, with a rapid response (1 min), monitored by microvolume UV-vis spectrophotometry. The method was successfully applied to saliva samples treated by an optimized in-tip solid-phase extraction procedure. Thiocyanate levels of 0.57 - 0.80 mM and 1.3 - 2.0 mM were found for non-smokers and smokers, respectively, allowing to discriminate between saliva samples from smoker and non-smoker volunteers. In addition, the film exhibited good storage stability at 4 °C for at least one month.