Atomic layer deposition-fabricated two-dimensional MoO3-WO3 nanohybrid thin-film electrode for ultrasensitive and interference-free detection of dopamine

Atomically thin two-dimensional (2D) semiconductors and their hybrid electrodes show great promise in the advancement of neural sensors for detecting neurotransmitters either through implantation on the brain's surface or by direct detection in biological fluids. This research demonstrated the fabrication of a sub-10 nm thick 2D MoO₃-WO₃ heterostructure electrode via atomic layer deposition (ALD) for the first time to detect dopamine (DA). The developed thin-film with uniform surface morphology possessed monoclinic and orthorhombic crystal structures of WO₃ and MoO₃, respectively, with the presence of oxygen vacancies and their sub-stoichiometric phases. The MoO₃-WO₃ sensor showed excellent catalytic activity for the interference-free detection of DA by suppressing the redox activity of common interferences, ascorbic acid (AA) and uric acid (UA). The ultra-sensitivity of DA oxidation can be ascribed to the effective electrostatic interaction and chemical coordination between the positively charged DA (at pH 7.0) and the MoO₃-WO₃. In contrast, the predominant electrostatic repulsive force between the negatively charged AA and UA (at pH 7.0) and the MoO₃-WO₃ suppressed their electrochemical responses. The sensor showed a nanomolar detection limit (20 nM) and a wide linear range for DA detection, which is highly appropriate for its determination in biological samples. Additionally, the sensor demonstrated excellent electrochemical stability, high reproducibility, and good recoveries of DA determination in diluted human serum samples.