Sensitive fluorescence “off–on” switch system for catechins detection based on water-soluble polythiophene derivatives

Abstract

Because catechins (CCs) play an important role in human health, we proposed a new CCs detection method relying on a novel fluorescence “off–on” switch system. Water-soluble cationic polythiophene derivatives, denoted as poly 3-{[1-(2-hydrazino-2-oxopropyl)piperidin-4-ylidene]methyl}thiophene hydrochloride (PMTH·HCl), was prepared as a novel fluorescent material. Initially, the fluorescence of PMTH·HCl can be quenched by Cu²⁺ because of the spontaneous formation of Cu²⁺–PMTH·HCl assembling dyads, resulting in fluorescence turn off. Then, on the addition of CCs in Cu²⁺–PMTH·HCl, Cu²⁺ was separated from PMTH·HCl, producing free PMTH·HCl and stable complex Cu²⁺–CCs, resulting in the turn on of the fluorescence signal of PMTH·HCl. Meanwhile, the mechanisms of fluorescence quenching and recovery were discussed to provide new ideas for designing sensors based on water-soluble conjugated polymers. This fluorescence “off–on” signal was sensitive to the concentration of CCs. Under optimized conditions, the fluorescence intensity was linear to the concentration of CCs varying from 1.0 × 10⁻⁸ to 9.0 × 10⁻⁶ mol L⁻¹ (γ = 0.9968), with a detection limit of 3.34 × 10⁻⁹ mol L⁻¹. Therefore, an efficient, sensitive, highly selective and practically applicable detection system for CCs has been designed.