Forensic electrochemistry on a drop: bromocresol green-modified screen-printed platforms for dual colorimetric-electrochemical detection of scopolamine.

A novel bulk-modified screen-printed electrode (SPE) was developed by incorporating bromocresol green (BG) as a pH-responsive colorimetric reagent, directly into the graphite ink formulation to create an integrated dual-response sensing platform. This bulk modification strategy enables complementary electrochemical and colorimetric responses on a single disposable device (BG-SPE), eliminating the need for additional reagents or multi-step procedures. The platform was applied to the detection of scopolamine, a clinically relevant tropane alkaloid associated with both therapeutic use and drug-facilitated criminal activity. The BG-SPE sensor enabled rapid, portable preliminary visual screening followed by electrochemical confirmation and quantification of scopolamine in beverages and biological matrices. Differential pulse voltammetry provided a wide linear range from 5 to 80 µg mL-1, with limits of detection (3σ) and quantification (10σ) of 0.02 and 0.07 µg mL-1, respectively, alongside excellent repeatability (RSD < 7.0% for peak current and <2.0% for peak potential). Method validation in real beverage samples (whiskey) and synthetic biological fluids (saliva, urine, and vitreous humour) yielded recoveries close to 100% with negligible matrix effects. The bulk incorporation of BG into the ink formulation provided reproducible electrode fabrication, supporting the use of bulk-modified SPE for on-site forensic screening, while allowing both analytical responses to be generated from the same sensing interface. The bulk-modified SPE integrates visual screening and electrochemical confirmation and quantification within a single portable sensing platform, enabling complementary analytical information to be obtained from the same sensing interface without requiring addition reagents.