Odorant binding proteins (OBPs) are small soluble proteins found in olfactory systems that are capable of binding several types of odorant molecules. Cantilevers based on polycrystalline diamond surfaces are very promising as chemical transducers. Here two methods were investigated for chemically grafting porcine OBPs on polycrystalline diamond surfaces for biosensor development. The first approach resulted in random orientation of the immobilized proteins over the surface. The second approach based on complexing a histidine-tag located on the protein with nickel allowed control of the proteins' orientation. Evidence confirming protein grafting was obtained using electrochemical impedance spectroscopy, fluorescence imaging and X-ray photoelectron spectroscopy. The chemical sensing performances of these OBP modified transducers were assessed. The second grafting method led to typically 20% more sensitive sensors, as a result of better access of ligands to the proteins active sites and also perhaps a better yield of protein immobilization. This new grafting method appears to be highly promising for further investigation of the ligand binding properties of OBPs in general and for the development of arrays of non-specific biosensors for artificial olfaction applications.

A new bio-sensing platform based on major uri- nary proteins (MUPs) from the mouse as chemical recognition elements has been developed. The transducers were surface acoustic devices coated with diamond nanoparticles as an inter- mediate layer enabling covalent attachment of the proteins. The resulting sensors detected 2,4-Dinitrotoluene, 4-Nitrotoluene, and 2-Isobutyl-3-methoxypyrazine at ppb levels. The best sensor showed a sensitivity of 24 000 Hz · ppm−1 to 2, 4-DNT when grafted with the protein MUP20. Trends in the sensitivity of the various VOC sensors were compared with the association constant values Ka of the proteins to target ligands measured by competitive assay in liquid phase. The system is able to detect analytes both in liquid as well as vapor phase and indicate that MUPs are robust bio-recognition elements that can be utilized in artificial olfaction applications

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