Abstract
Use of immunoassay test strips for the detection of fentanyl in drug samples has become commonplace in harm reduction, law enforcement, public health, customs, and forensic science settings for testing drug product. With the increase of xylazine in the drug supply in recent years, use of xylazine test strips has also increased. As use of test strips expands, a desire to implement them for other drugs may emerge. However, since these strips are designed for urine testing, it is important to understand their applicability to testing drug product. In this work, we investigate the utility of seven types of urine immunoassay test strips - amphetamine, benzodiazepine, cocaine, methamphetamine, nitazene, opiate, and xylazine - for drug checking applications. Reproducibility, sensitivity, cross-reactivity, and the effect of prolonged exposure to elevated temperatures were studied. Generally, the tests were found to be reproducible, able to detect trace (μg/mL) levels of the analyte of interest, and minimally affected by prolonged storage at elevated temperatures. Nearly all tests showed cross-reactivity with compounds other than the analyte of interest, highlighting the need to better understand these limitations prior to implementation in a drug checking scenario. The viability of expired cocaine, fentanyl, and methamphetamine test strips was also interrogated, and little to no change in sensitivity was found even though the tests were multiple years expired.