Signal-amplified molecularly imprinted electrochemical sensor using Cu2Fe(CN)6/Cu-benzenehexathiol metal-organic framework for ultra-sensitive detection of methadone and its metabolite EDDP.

Methadone and its metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) are key biomarkers in wastewater-based epidemiology studies for assessing illicit opioid consumption. Due to their extremely low concentrations in wastewater, conventional laboratory-based detection methods are time-consuming, complex, and require expensive instrumentation, making them unsuitable for rapid on-site analysis. Herein, we developed a signal-amplified molecularly imprinted electrochemical sensor based on a Cu2Fe(CN)6/Cu-benzenehexathiol conductive metal-organic framework (CB-MOF) composite for the ultrasensitive detection of methadone and EDDP. The composite exhibits a high electrochemical signal through in situ synthesis of a conductive MOF with an integrated Prussian-Blue-analog redox probe. Guided by density functional theory (DFT) and molecular dynamics simulations, p-aminobenzoic acid (PABA) was selected as the functional monomer to construct a molecularly imprinted recognition layer for specific target binding. The sensor demonstrated a wide linear detection range for EDDP from 2.78 ng/L to 277.4 mg L-1 and methadone from 309.5 ng/L to 309.5 mg L-1, with limits of detection as low as 99.86 pg/L and 3.28 ng/L, respectively. In addition, the sensor exhibited excellent stability, selectivity, reproducibility, regenerability, and applicability, offering robust support for the rapid on-site detection of opioids in municipal wastewater and river water.