Ultrasensitive detection of tetracycline using the disruption of crosslink-enhanced emission and inner-filter effect-induced phosphorescence quenching of carbonized polymer dots.

Accumulation of tetracycline (TC) in the environment and food may lead to potential health risks and the emergence of antibiotic-resistant bacteria. To meet the demand for sensitivity, ease of use, and portability in detecting TCs, we fabricated a green phosphorescent film consisting of crosslinked polymer-integrated carbon dots (named carbonized polymer dots, CPD) and polyvinyl alcohol (PVA) polymers for ultrasensitive sensing of TCs via the inner filter effect-mediated phosphorescence quenching and the disruption of the crosslink-enhanced emission (CEE) effect by TC. To create polymer structures on the carbon dots for interaction with PVA, CPDs were synthesized via low-temperature hydrothermal treatment using citric acid and cysteine. Compared to products with oxidized sulfur or no sulfur doping, the incorporation of nitrogen and sulfur in CPDs was found to effectively facilitate intersystem crossing, significantly enhancing phosphorescence. By measuring the phosphorescence properties of compounds inside and outside the dialysis bag at different dialysis times, we confirmed that crosslinking interactions between CPD and PVA polymers can create a rigid environment to amplify the phosphorescence of sub-luminophores (e.g., hydroxyl, carboxyl, and amino groups) through the CEE effect. These features make the CPD/PVA film an effective tool for phosphorescence turn-off detection of TC, offering a wide linear detection range (1 nM-1 mM), a low limit of detection (0.7 nM), and good selectivity over potential interfering substances, such as metal ions, amino acids, fatty acids, and lactose. Our finding indicates that the TC-triggered phosphorescence quenching of the CPD/PVA film originates from TC-mediated IFE effect and TC-disrupted CEE effect. The CPD/PVA film was shown to establish a linear calibration curve to quantify TC in drinking water and milk samples with good recoveries (84 %-120 %).