On-site rapid screening of ethylene etonitazene via a versatile conjugated-polymer fluorescence platform

We report a versatile conjugated-polymer fluorescence platform for rapid on-site screening of ethylene etonitazene (EE), an emerging nitazene opioid that remains inadequately covered by existing rapid screening tools. EE induced pronounced fluorescence quenching of the donor-acceptor conjugated polymer PFBT-MI through an inner-filter-effect-dominated response, with photoinduced electron transfer as a possible secondary pathway. The resulting response was translated into complementary fluorometric, smartphone-assisted and paper-based formats, affording limits of detection of 1.78, 12.41 and 14.83 μM, respectively. This sensor exhibited a preferential response toward nitazene-type structures over representative non-nitazene psychoactive substances and common interferents, enabled reliable analysis across different aqueous matrices, and demonstrated a versatile analytical strategy that combines quantitative analysis with portable and visually accessible readouts for the rapid screening of emerging nitazene opioids.