A highly sensitive graphene oxide based label-free capacitive aptasensor for vanillin detection

Abstract

Biosynthetic production of vanillin via microbial biotransformation offers a low-cost alternative for manufacturers to meet the consumer demands for natural vanillin. However, identifying the high vanillin-producing microbial strains among multitudinous samples using the current analytical techniques such as liquid chromatography (LC) and mass spectroscopy (MS) is time consuming, cumbersome and costly. Here, we propose an alternative low-cost and rapid aptamer-based capacitive assay for sensitive and selective vanillin recognition based on the preferential binding affinity and stability of the aptamer-vanillin complex. This redox-free approach measures the changes in non-faradaic capacitance of transducing graphene-oxide (GO) activated gold electrodes immobilized with vanillin-specific aptamer. Aptamer-vanillin interaction on the GO surface alters the aptamer conformation causing surface charge redistribution detected via capacitance-frequency characteristics. The aptasensor showed a wide dynamic detection range of 10 pM-10 nM and a low limit of detection (LOD) of ~9.91 pM, which is the best reported so far. Finally, validation of the capacitive aptasensing against high-performance LC (HPLC) reference containing vanillin dissolved in a complex M9 medium with interfering compounds (ferulic acid and glycerol), to mimic typical microbial biotransformation, demonstrated good sensitivity and selectivity. The successful proof-of-concept can be translated to high-throughput electronic multi-analyte screening kits supplementary to existing analytical tools. Keywords: Graphene oxide, Capacitance, Aptamer, Vanillin, Biosensor, Synthetic biology