Oxygen vacancy-rich Fe(MoO) combined with MWCNTs for electrochemical sensors of fentanyl and its analogs.

Hundreds of thousands of people dying from the abuse of fentanyl and its analogs. Hence, the development of an efficient and highly accurate detection method is extremely relevant and challenging. Therefore, we proposed the introduction of oxygen defects into Fe(MoO) nanoparticles for improving the catalyst performance and combining it with multi-walled carbon nanotubes (MWCNTs) for electrochemical detection of fentanyl and its analogs. Oxygen vacancy-rich Fe(MoO) (called r-Fe(MoO)) nanoparticles were successfully synthesized and characterized in detail by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectrometry (EDS), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Raman spectra, BET, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) and investigated by comparison with oxygen vacancy-poor Fe(MoO) (called p-Fe(MoO)). The obtained oxygen vacancy-rich Fe(MoO) was ultrasonically composited with MWCNTs for modification of glassy carbon electrodes (GCEs) used for the electrochemical detection of fentanyl and its analogs. The modified MWCNT-GCE showed ultrasensitivity to fentanyl, sufentanil, alfentanil, and acetylfentanyl with limits of detection (LOD) of 0.006 µmol·L, 0.008 µmol·L, 0.018 µmol·L, and 0.024 µmol·L, respectively, and could distinguish among the four drugs based on their peak voltages. Besides, the obtained r-Fe(MoO)/MWCNT composite also exhibited high repeatability, selectivity, and stability. It showed satisfactory detection performance on real samples, with recoveries of 70.53 ~ 94.85% and 50.98 ~ 82.54% in serum and urine for the four drugs in a concentration range 0.2 ~ 1 µM, respectively. The experimental results confirm that the introduction of oxygen vacancies effectively improves the sensitivity of fentanyl electrochemical detection, and this work provides some inspiration for the development of catalytic materials for electrochemical sensors with higher sensitivity.