Rational design of a ratiometric indicator-displacement assay for the monitoring of chlortetracycline and intracellular imaging.

Chlortetracycline (CTC), one of the tetracyclic antibiotics, has been widely employed for the inhibition of bacteria. Due to the potential threat to human health posed by the residual CTC, the development of ratiometric fluorescent probes that can achieve accurate measurement and in-situ imaging is urgently needed but remains challenged. Here, a bovine serum albumin (BSA)-involved host-guest system was designed as the novel ratiometric probe (C3@BSA) for CTC based on the indicator-displacement assay principle. Significantly, the fluorescence difference between the CTC@BSA complex and other tetracyclic@BSA complexes ensured high selectivity of this probe. The indicator (C3) was rationally derived from a simple chalcone dye with weak binding affinity to BSA (1.7 × 104 M-1) compared with CTC (2.2 × 104 M-1). The sensing process can finish in 10 s with sensitive response (detection limit: 0.23 μM) and anti-interference capacities over common ions and amino acids. On this basis, the probe was successfully used to detect CTC in HeLa cells and B16 cells, where the distributions of CTC were displayed under a dual-channel imaging mode for the first time. Our research provided a novel ratiometric probe for CTC and an effective strategy for designing ratiometric fluorescent indicator-displacement assays.