Dual-response ratiometric fluorescent probe for visual and colorimetric detection of tetracycline

The massive residues of tetracycline (TC) have caused serious harm to the human body and the environment, so it is urgent to explore a portable, on-site, sensitive and selective method to detect TC. In this study, a dual response ratiometric fluorescent probe (S,O-C3N4QDs-CitNa-Eu3+) for detecting TC was constructed by mixing sodium citrate (CitNa), europium ion (Eu3+) and sulfur and oxygen co-doped graphite phase carbon nitride quantum dots (S,O-C3N4QDs) solution in a specific proportion. The S,O-C3N4QDs was initially synthesized by using citric acid and thiourea as the precursors via a hydrothermal route. The blue fluorescence of S,O-C3N4QDs (λem = 445 nm) was decreased while the red fluorescence of Eu3+ was increased (λem = 620 nm) own to the synergistic effect of internal filter effect, static quenching and antenna effect when TC was added to the mixed system containing CitNa and Eu3+. As a result, the ultra-sensitive detection of TC was realized from 0.25 to 120 μM with a detection limit of 1.3 nM. An obvious color change of the solution from blue to purple to red with continuous adding TC was observed such that the semi-quantitative detection of TC can be realized. Moreover, a smartphone APP monitoring platform based on test paper was constructed by using color scanning application, demonstrating that the ratiometric fluorescent probe constructed in this work has great potential in medical and environmental fields.