Enhancing electroanalytical performance of porous boron-doped diamond electrodes by increasing thickness for dopamine detection

Highlights: • Number of porous layers is a crucial factor influencing final BDD_porous properties. • Faster electron transfer kinetics observed with increased porous layer number. • The highest sensitivity and the lowest LOD for dopamine obtained on 5L-BDD_porous. • Enhanced selectivity demonstrated for 3L- and 5L-BDD_porous electrodes. • Stability of PLL layer differs depending on the electrode surface morphology. Novel porous boron-doped diamond (BDD_porous)-based materials have attracted lots of research interest due to their enhanced detection ability and biocompatibility, favouring them for use in neuroscience. This study reports on morphological, spectral, and electrochemical characterisation of three BDD_porous electrodes of different thickness given by a number of deposited layers (2, 3 and 5). These were prepared using microwave plasma-enhanced chemical vapour deposition on SiO₂ nanofiber-based scaffolds. Further, the effect of number of layers and poly-l-lysine coating, commonly employed in neuron cultivation experiments, on sensing properties of the neurotransmitter dopamine in a pH 7.4 phosphate buffer media was investigated. The boron doping level of ∼2 × 10²¹ atoms cm⁻³ and increased content of non-diamond (sp²) carbon in electrodes with more layers was evaluated by Raman spectroscopy. Cyclic voltammetric experiments revealed reduced working potential windows (from 2.4 V to 2.2 V), higher double-layer capacitance values (from 405 μF cm⁻² to 1060 μF cm⁻²), enhanced rates of electron transfer kinetics and larger effective surface areas (from 5.04 mm² to 7.72 mm²), when the number of porous layers increases. For dopamine, a significant boost in analytical performance was recognized with increasing number of layers using square-wave voltammetry: the highest sensitivity of 574.1 μA μmol⁻¹ L was achieved on a BDD_porous electrode with five layers and dropped to 35.9 μA μmol⁻¹ L when the number of layers decreased to two. Consequently, the lowest detection limit of 0.20 μmol L⁻¹ was obtained on a BDD_porous electrode with five layers. Moreover, on porous electrodes, enhanced selectivity for dopamine detection in the presence of ascorbic acid and uric acid was demonstrated. The application of poly-l-lysine coating on porous electrode surface resulted in a decrease in dopamine peak currents by 17% and 60% for modification times of 1 h and 15 h, respectively. Hence, both examined parameters, the number of deposited porous layers and the presence of poly-l-lysine coating, were proved to considerably affect the characteristics and performance of BDD_porous electrodes.