Rapid electrochemical screening of levamisole in urine: toward forensic applications

Levamisole, once a common anthelmintic and now a frequent adulterant in street cocaine, has emerged as a silent marker of illicit drug use and exposure. Detecting it in biological samples remains difficult due to its rapid metabolism and low concentrations. Here, we introduce a rapid electrochemical biosensor that turns this challenge into an opportunity by exploiting the inhibitory power of levamisole on alkaline phosphatase (ALP). Using flexible screen-printed electrodes and a simple enzyme drop-casting step, the device converts enzyme inhibition into a measurable current drop, providing a direct electrochemical signature of levamisole. The biosensor displayed a limit of detection of 3.4 nM (≈0.8 ng mL^-1), limit of quantification of 11.5 nM (≈2.8 ng mL^-1), and RSD of 7 %, ensuring reproducible performance. To assess its applicability in biological matrices, the sensor was tested in artificial urine, chosen as a model fluid for potential for potential forensic and toxicological screening. The system maintained high sensitivity and selectivity, consistent with concentrations and interferents reported in urine. The method was further validated through the analysis of urine samples spiked with cocaine samples different percentages of levamisole, yielding recoveries between 89 and 95 %. This work presents the first ALP-based electrochemical biosensor for levamisole, offering a fast, low-cost, and portable platform that could support on-site forensic screening of cocaine adulteration and levamisole exposure, bridging the gap between laboratory toxicology and field-deployable diagnostics.