Functional expression of olfactory receptors using cell-free expression system for biomimetic sensors towards odorant detection

How to obtain sufficient functional olfactory receptors and coupled to transducers with high efficiency are crucial to biomimetic olfactory-based biosensors. In this study, a cell-free expression system was employed to prepare functional olfactory receptors that were utilized as sensitive elements for biomimetic olfactory receptor-based biosensors. A nematode olfactory receptor, ODR-10, was used as a model of olfactory receptors and expressed in Escherichia coli (E. coli) cell-free expression system. To improve the coupling efficiency and obtain the on-chip purification, a His6-tag was expressed as a fusion to ODR-10, which makes the expressed ODR-10 capable of selectively binding to the sensor surface modified with anti-His6-tag aptamers. Electrolyte-insulator-semiconductor (EIS) sensors were utilized as the transducer to measure the capacitance changes induced by the ODR-10 responding to its natural ligand, diacetyl. The results show that ODR-10 was successfully expressed using E. coli cell-free expression system and the expression could be promoted by adding 0.5% Brij58 as the detergent. Capacitance measurement results indicate that this olfactory receptor-based biosensor can detect diacetyl with high specificity and sensitivity. Concentration-dependent linear response to diacetyl ranging from 0.01 nM to 1 nM was obtained. The detection limit was as low as 0.01 nM. All the results demonstrated that the cell-free expression system provides a new approach for the preparation of functional olfactory receptors, which have great potential to be applied in biomimetic sensors towards chemical sensing.