Origami Chips: development and validation of a paper-based Lab-on-a-Chip device for the rapid and cost-effective detection of 4-methylmethcathinone (mephedrone) and its metabolite, 4-methylephedrine in urine

4-methylmethcathinone (mephedrone) has emerged in drug seizures as a new psychoactive substance (NPS) causing a public health risk of global concern. Currently, there are no commercial microfluidic devices for the selective detection of mephedrone and so this study presents a simple, low cost and portable paper-based Lab-on-a-Chip (LOC) device with colorimetric detection to fill this gap. Limits of detection for mephedrone in spiked urine and dissolved powder (aqueous) samples are clinically relevant at 4.34 ng mL-1 and 2.51 ng mL-1 respectively. No cross-reactivity for commonly encountered cutting agents, interferents and adulterants were detected. Mephedrone and its main metabolite were detectable in aqueous samples within 3 minutes. Stability and reproducibility measurements showed no significant difference in signal intensity over eight weeks and no significant difference within or between devices. The proposed device has the potential to provide cost-effective, rapid, on-site testing within forensic or clinical settings and therefore has wide global applicability.