An ultrasensitive electrochemical impedance-based biosensor using insect odorant receptors to detect odorants

Herein, we present that insect odorant receptors reconstituted into the lipid bilayers of liposomes can be successfully immobilized onto a gold surface and selectively and sensitively detect odorant molecules. The odorant receptors (OrXs) Or10a, Or22a, and Or71a from the common fruit fly, Drosophila melanogaster, were recombinantly expressed, purified and integrated into nano-liposomes (100-200 nm). These liposomes were covalently attached to the self-assembled monolayers (SAMs) of a 6-mercaptohexanoic acid (MHA)-modified gold surface. X-ray Photo Electron Spectroscopy (XPS) and Quartz Crystal Microbalance with Dissipation (QCM-D) measurements confirmed the successful modification of the gold surface and immobilization of liposomes. Atomic Force Microscopy (AFM) revealed that the liposomes were covalently attached to the surface without any disruption of vesicles. The liposomes tethered to the gold sensor surface were then treated with a range of known ligands of various concentrations. We demonstrated by Electrochemical Impedance Spectroscopy (EIS) that an OrX/liposome EIS sensor can sensitively and selectively detect its known ligand to femtomolar concentrations by detecting a change in electrical signal upon binding. Our study is the first step towards using purified insect odorant receptors alone in biosensors to enable the development of novel ultrasensitive volatile sensors for medical diagnostic, air quality, food safety and border security applications.