A biomimetic taste biosensor based on bitter receptors synthesized and purified on chip from a cell-free expression system

Abstract

The conventional approaches for the preparation of receptor proteins towards chemical sensing are usually based on the expression of receptors in a heterologous cell system, which suffers from time-consuming, low efficiency, and complicated purification process. To address these limitations, in this study, a bitter receptor, T2R4, was synthesized and purified on chip from a cell-free protein expression system, which can be realized within a few hours. The bitter receptors were utilized as sensitive elements of a chemical biosensor for the detection of specific bitter substances. Quartz crystal microbalance (QCM) devices were used as transducers to monitor the process of sensor preparation and responses to different bitter substances by recoding the crystal resonant frequency shifts. The obtained results show that the dose-response curves of denatonium and crystal resonant frequency shifts are established in a wide linear range of 10 nM to 0.1 mM with a lower detection limit of 5 nM, which is superior to previous reports. Nearly 3 times of enhancement in sensitivity were achieved, which is calculated to be 4.96 kHz/mM. Such on-chip rapid synthesis and purification of receptors serve to achieve increased coupling efficiency and improved sensing performances. The combination of simple and rapid cell-free expression technique provides a very promising approach for the rapid and high-efficient development of receptor-based biosensors for chemical sensing.