Boron-doped diamond (BDD) is a popular material for electrodes and it exhibits metal-like conductivity when a sufficient quantity of boron atoms is incorporated in the diamond lattice. BDD has distinct advantages over alternative electrode materials. It has diamond’s chemical stability and biocompatibility in conjunction with excellent electrochemical characteristics including large potential window and low background current. Thus, BDD has great potential as an electrode material in electrochemical sensors for the detection of pharmaceutical compounds.

Of particular interest is the monitoring of the antidepressants venlafaxine (VF) and desvenlafaxine (DVF). These pharmaceuticals are prescribed to those suffering from major depressive disorder, generalized anxiety disorder, panic disorder and/or social anxiety disorder. However, they can have adverse effects on the health and behaviour of aquatic life, and harmful quantities have already been detected in nature. Monitoring of DVF and VF in a patient’s blood and urine is required to ensure correct dosage levels, which in turn could mitigate environmental pollution. An electrochemical sensor with BDD electrodes would be well-suited for this application.

In this research, two distinct BDD electrode materials were used for the electrochemical detection of VF and DVF. For initial experimentation, a robust and well-established free-standing BDD electrode type was utilized in a voltammetric study. Optimized detection conditions were achieved on hydrogen-terminated BDD for DVF and oxygen-terminated BDD for VF in a 0.1 M H2SO4 solution (pH 0.6), yielding limits of detection (LOD) of 0.31 µM and 0.17 µM and limits of quantification (LOQ) of 0.94 µM and 0.57 µM for VF and DVF, respectively. The scan rate study demonstrated that the oxidation reactions for both compounds are diffusion controlled. VF and DVF have excellent repeatability in the presence of several interfering compounds, such as inorganic ions, sucrose, glucose, and dopamine. To assess the suitability of the detection method, electroanalysis of VF and DVF in synthetic human serum, synthetic urine, and river water was conducted. Besides, a commercially available BDD electrode chip was employed for VF and DVF detection under optimized conditions. The measurement results of the different BDD electrodes were compared; in particular, when the less robust commercial electrode chip was used, larger values of LOD (1.9 µM and 8.0 µM) and LOQ (5.8 µM and 24.1 µM) were reached for VF and DVF, respectively. The fabrication of analogue BDD-based electrochemical sensors by utilizing direct inkjet printing of diamond nanoparticles on silicon substrates was evaluated in parallel. Various electrode designs were successfully printed, however subsequent chemical vapor deposition of thin-film BDD did not satisfy the required electrode quality. Notwithstanding, the use of a BDD electrode allows for the creation of a modification-free and promising practical method for VF and DVF detection.