An immobilization-free aptamer-based liquid sensing display for the label-free detection of illicit...

This study presents an alternating-current electroluminescent (ACEL) aptasensing display for label-free, smartphone-based detection of Δ⁹-tetrahydrocannabinol (THC) in saliva. The sensor integrates a graphene oxide (GO) film with a THC-specific DNA aptamer via rapid π-π interactions, establishing an immobilization-free recognition interface. The sensing mechanism is driven by the modulation of the Grotthuss proton-hopping pathway. Upon target binding, the aptamer undergoes a conformational change and detaches from the GO surface. This process results in a decrease in electroluminescence, which is both visually observable and quantifiable. The sensor exhibits a linear dynamic range from 0.5 to 100 ng/mL. Its detection limit of 0.15 ng/mL is well below the common regulatory thresholds for oral fluid (1 ng/mL). The assay achieves reliable responses within 10 min without the need for complex labeling or sample pretreatment. Selectivity tests confirmed that the sensor effectively discriminates THC from cannabidiol (CBD) and cannabinol (CBN). Furthermore, validation on pooled human saliva yielded excellent recovery (96-102%). These features, combined with its low-cost and intuitive visual readout, make this sensor-on-display platform highly suitable for point-of-need applications in forensic, clinical, and regulatory settings.