Recent Advances in Nanomaterial-Based and Colorimetric Technologies for Detecting Illicit Drugs and Environmental Toxins

The global surge in illicit drug use has intensified the demand for rapid, portable, and reliable on-site detection technologies. Traditional analytical approaches, such as laboratory-based instrumentation and biological sample assays, while accurate, are often constrained by high costs, long processing times, and the need for specialized equipment, rendering them unsuitable for field applications. This review highlights recent progress in chemical sensor technologies designed for the detection of widely misused drugs such as methamphetamine, cocaine, fentanyl, and heroin. Parallel advancements in the detection of environmental contaminants, particularly concerning micro- and nanoplastics, are also discussed. Emerging sensing platforms employing nanoparticle functionalization, graphene nanosheets, MXenes, metal–organic frameworks (MOFs), and supramolecular colorimetric assays demonstrate significant potential for achieving high sensitivity, selectivity, and operational simplicity in portable formats. These innovations enable real-time detection with minimal user expertise, thereby advancing applications in forensic analysis, environmental monitoring, and public health protection. The review also addresses current limitations related to detection accuracy, reagent stability, and matrix interferences and proposes future directions for optimizing sensor robustness and performance under diverse field conditions.