Diamond micro-cantilevers as transducers for olfactory receptors - based biosensors: Application to the receptors M71 and OR7D4

Abstract : Two olfactory receptors (ORs), mouse M71 and chimpanzee OR7D4, were immobilized onto synthetic diamond transducers surfaces. 6His tagged M71 (6His-M71) was grafted using covalent attachment of nitriloacetic acid (NTA) as chelating agent, which could bind the 6His tagged receptor through nickel ions. OR7D4 was grafted through covalent bonding of hexanoic acid radical on diamond followed by EDC/NHS peptidic coupling to the receptor. Both grafting procedures were monitored by electrochemical impedance spectroscopy (EIS) on boron doped diamond (BDD) electrodes. Then the grafting protocols were applied to the surface of bulk diamond micro-cantilevers. The resulting sensors were assessed for odorant detection in the liquid phase using a Laser Doppler read-out system. The 6His-M71 based sensor was found to exhibit a good sensitivity to acetophenone, with a typical frequency shift near 100 Hz for 1 μM exposure, with a good selectivity against negative control 2-octanone. The OR7D4 based sensor showed a sensitivity of 200 Hz for exposures to 1 or 10 μM androstenone with a good selectivity against both non-ligands acetophenone and 2-octanone.