A novel sensor array with ability to respectively identify phenol and ketone for the precise discrimination of origins of raw Pu-erh and its counterfeiting.

Most reported sensor arrays for teas were based on the sensing of phenolic hydroxyl group on tea polyphenols. In this work, a novel sensor array was developed based on the simultaneous sensing of phenols and ketones, for the enhanced discrimination of tea polyphenols with/without ketone, and then for the efficient discrimination of raw Pu-erh teas from different origins and the counterfeit, combined with machine learning. This sensor array is consisting of four channels. Channel A is carbon dots, room-temperature carbon nanoparticles (RT-CNPs), whose fluorescence can be quenched by ketone; Channel B is the chromogenic agent, 2,4-Dinitrophenylhydrazine (DNPH), which can combine with ketone to undergo absorption spectral changes. Tea polyphenols without ketone have little effect on Channel A and Channel B. Channel C (RT-CNPs + nanozyme) and Channel D (DNPH + nanozyme) are the addition of nanozyme with polyphenol oxidase activity to Channel A and Channel B. The nanozyme can catalyze the oxidation of phenols to the quinones, which means Channel C and D can react to tea polyphenols with phenols or ketones. Based on the different quenching efficiency of various tea polyphenols on the carbon dots, differences in the color due to the ketone combination with DNPH, and differences in the degrees of tea polyphenol's oxidation by the nanozyme, the proposed four-channel sensor array achieved the enhanced discrimination of tea polyphenols. This sensing technology which can simultaneously recognize phenols and ketones, has an excellent applicating prospects in the recognition and distinguish of tea and its derivatives (such as tea drinks), with oxidation and transformation of tea polyphenols.