Recent advances in sensing technologies for fentanyl and its analogs: Challenges and future directions

• Review fentanyl and analog detection technologies. • Compare methods on the basis of sensitivity, selectivity, and portability. • Highlight uses of GC–MS, LC-MS, SERS, NMR, and electrochemical sensors. Fentanyl is a highly potent synthetic opioid which, along with structurally related analogs like carfentanil, is a significant driver of the global epidemic of opioid abuse. These compounds are often added in small amounts to other illicit drugs, found in misrepresented samples, or introduced through unintentional cross-contamination. Their low concentration, structural diversity, extreme potency, and occurrence in complex matrices like biological fluids increase the risk of fatal overdose and complicate their detection. The development of accurate, sensitive, and selective detection technologies is therefore crucial for applications in clinical diagnostics, forensics, public health surveillance, and law enforcement. This review discusses advanced sensors and analytical techniques for identifying fentanyl and its analogs, including colorimetric assays, immunoassays, electrochemical sensors, Raman spectroscopy, liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC–MS), nuclear magnetic resonance spectroscopy (NMR), and Fourier-transform infrared spectroscopy (FTIR). Each method is evaluated on the basis of its sensitivity, selectivity, ease of use, compatibility with complex matrices, stability, and ability to distinguish fentanyl from related analogs and other drugs of abuse. By detailing current advances and limitations in detection methodologies, this comprehensive overview of the field of fentanyl detection offers insights to guide the development of more effective and practical technologies tailored for diverse analytical and research settings.