Universal Platform for Ratiometric Sensing Based on Catalytically Induced Inner-Filter Effect by Cu²⁺

Integrating two kinds of fluorescent probes in one system to develop a ratiometric sensing platform is of prime importance for achieving an accurate assay. Inspired by the efficient overlapped spectrum of 2-aminoterephthalic acid (PTA-NH 2 ) and 2,3-diaminophenazine (DAP), a new sensitive ratiometric fluorescent sensor has been developed for Cu 2+ on the basis of in situ converting o -phenylenediamine (OPD) into DAP through the catalysis of Cu 2+ . Here, the presence of Cu 2+ induced the emission of DAP, which acted as an energy acceptor to inhibit the emission of PTA-NH 2 . This dual-emission reverse change ratiometric profile based on the inner-filter effect improved sensitivity and accuracy, and the highly sensitive determination of Cu 2+ with a detection limit of 1.7 nmol·L –1 was obtained. The proposed sensing platform displayed the wide range of detection of Cu 2+ from 5 to 200 nmol·L –1 by modulating the reaction time between Cu 2+ and OPD. Moreover, based on the specific interaction between glutathione (GSH) and Cu 2+, this fluorescent sensor showed high response toward GSH in a range of 0.5–80 μmol·L –1 with a detection limit of 0.16 μmol·L –1 . The successful construction of this simple ratiometric sensing platform without the participation of enzymes provides a new route for the detection of small biological molecules that are closely related to human health.