Microwave-assisted extraction, separation, and chromogenic detection of laced marijuana for presumptive point-of-interdiction testing†

Presumptive drug screening enables timely procurement of search and arrest warrants and represents a crucial first step in crime scene analysis. Screening also reduces the burden on forensic laboratories which often face insurmountable backlogs. In most scenarios, on-site presumptive drug screening relies on chemical field tests for initial identification. However, even when used appropriately, these test kits remain limited to subjective colorimetric analysis, produce false positive or negative results with excessive sample quantities, and are known to cross-react with numerous innocuous substances. Previous efforts to develop microfluidic devices that incorporate these chromogenic indicator reagents address only a few of the many challenges associated with these kits. This is especially true for samples where the drug of interest is present as a lacing agent. This work describes the development of a centrifugal microfluidic device capable of integrating facile sample preparation, by way of a 3D printed snap-on cartridge amenable to microwave assisted extraction, followed by chromatographic separation and chromogenic detection on-disc. As cannabis is among the most widely used controlled substance worldwide, and displays strong interference with these indicator reagents, mock samples of laced marijuana are used for a proof-of-concept demonstration. Post extraction, the microdevice completes high throughput metering just prior to simultaneous reaction with four of the most commonly employed microchemical tests, followed by objective image analysis in CIELAB (a device-independent color model). Separation and recovery of a representative controlled substance with 93% efficiency is achieved. Correct identification, according to hierarchical cluster analysis, of three illicit drugs (e.g., heroin, phencyclidine, and cocaine) in artificially laced samples is also demonstrated on-disc. The cost effective microdevice is capable of complete automation post-extraction, with a total analysis time (including extraction) of <8 min. Finally, sample consumption is minimized, thereby preventing the complete destruction of forensic evidence.