Fentanyl, an extremely potent synthetic opioid, has flooded the illicit drug market in the US. First responders arriving at the scene of an overdose, or law enforcement officers conducting drug searches, need to know what compounds they’re dealing with to avoid potentially dangerous exposures. In an effort to provide a cost-effective, field-compatible method to detect fentanyl, researchers have developed an electrochemical sensor that takes as little as one minute to identify the drug (Anal. Chem. 2019, DOI: 10.1021/acs.analchem.9b00176).
Fentanyl suppresses breathing at high doses and is often cut into other drugs without users’ knowledge. Law enforcement already uses handheld Raman spectrometers and miniature mass spectrometers to classify unknown drug samples, including fentanyl, in the field, but prohibitive price tags limit the number of devices that local departments can afford.
Joseph Wang, of the University of California, San Diego, and colleagues viewed electrochemistry as an attractive option for fentanyl detection, having successfully created electrochemical sensors for field-based detection of gunshot residue and explosives. Electrochemical techniques can identify chemicals based on the voltage at which compounds are oxidized or reduced, causing a spike in electric current. These methods also offer a combination of fast response times, high sensitivity, and portable, low-cost instrumentation.
Wang’s team screen-printed sensors consisting of a carbon electrode and a silver-chloride reference electrode onto polyethylene terephthalate sheets. They treated the carbon electrodes with an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, to stabilize them and help fentanyl accumulate on the surface. These disposable sensor strips are easy to produce and cost only a few cents apiece, says Wang.
The researchers then applied laboratory samples of fentanyl to the strips and inserted them into a handheld electrochemical analyzer that delivers alternating cycles of increasing and decreasing voltage to the test strip. Fentanyl undergoes oxidation and reduction at specific voltages, which changes how much current passes through the carbon electrodes compared to the reference electrode, and generates a unique signature. This process could detect fentanyl in the presence of common cutting agents, and identified two common physiological metabolites of fentanyl, norfentanyl and 4-ANPP.
This is the first electrochemical method described for fentanyl detection and could pave the way for development of cost-effective, easy-to-use sensors with disposable test strips, similar to those used to monitor blood glucose, says Wang.
One limitation of this detection method is that unknown powders or other materials for testing would have to be sampled directly, which could put users at greater risk of exposure than with other field-based detectors that can scan samples through clear packaging. To mitigate sampling risk, first responders would need to ensure they handle the material carefully and wear proper personal protective equipment like gloves, eye protection, and face masks.
Additionally, the samples analyzed in this study are not representative of complex street drug samples, says chemist George M. Whitesides of Harvard University, whose group also developed a mobile electrochemical sensor for a number of human- and environmental-health related molecules. Still, this study is “an essential start” in the process of defining when and where this type of detection will be most beneficial, he says.