Enhanced catechol biosensing on metal oxide nanocrystal sensitized graphite nanoelectrodes through preferential molecular adsorption

Amperometric biosensors offer a viable platform for phenol trace level detection in water with potential for miniaturization and automation, towards a cost-effective analytical monitor. In this work, we rationally designed and computationally analysed two laccase biosensors based on NiO(100) and α-Fe2O3(110) nanocrystals (NCs) sensitized carbon paste electrodes (CPEs) for selective electrochemical detection of catechol. Investigation of nanoelectrode surface for catechol sensing is advantageous to design efficient detection platforms for analytes in water. Incorporation of metal-oxide NCs in more common CPEs enabled reduction of their overpotential and improved the sensitivity of detection. Excellent dispersion of 11 nm-sized NiO NCs in CPE was obtained compared to cluster type α-Fe2O3 NCs with effective Randles-Sevcik surface area being 0.089 and 0.051 cm2 respectively, as against 0.027 cm2 for bare CPE. We performed adsorption energy calculations of different aminoacids on prevalent oxide NC surfaces that showed preferred molecular arrangements and stronger binding for NiO(100) plane amidst competitive adsorption by water, enabling shorter electron transfer distance for reversible catechol oxidation on the electrode surface, and thereby its faster detection. Our electrocatalytic studies also pointed to additional catechol oxidation facilitation through co-operative redox couples of Cu(I)/Cu(II) and Ni(II)/Ni(III) on laccase-CPE-NiO(100) electrode. The biosensor response reached steady state within 6 s, one of the shortest reported in literature with low detection limit of 0.95 μM and sensitivity of 1.415 A M−1 cm−2. From the different performance studies and the real sample analyses, NiO NC modified CPE could be proposed as a competent material for catechol biosensing.