A Selective and Sensitive Method for Colistin Detection by G-Quadruplex Ligand Competition

Colistin (COL) is a widely used antibiotic and is quite often used as a last-resort treatment option for treating multidrug-resistant Gram-negative bacterial infections. Due to its widespread use, COL accumulates in nature, which represents a novel ecological and health threat. However, there is currently no rapid and specific method available for titrating COL levels in collected samples. Herein, we report a simple chemiluminescence detection method based on the specific interaction between COL and a parallel G-quadruplex (G4). To this end, we exploit the catalytic properties of the G4/hemin DNAzyme, which is able to oxidize substrates to provide a readily monitored readout. The stronger affinity of G4 for COL versus hemin allows for the inactivation of the G4/hemin DNAzyme, which is used herein to quantify COL in solution. Through a series of optimizations, we identified the best G4 sequence (F3TC), oxidation substrate (luminol), and experimental conditions, which allow for the detection of COL over a broad concentration window, from 0.5 to 2,500 ng/mL, with a detection limit of 0.4 ng/mL and excellent selectivity against other antibiotics. Compared with existing methods, the proposed approach provides a simpler and label-free quantification of COL, which might serve as a valuable standard method for antibiotic detection, whose use was validated under real conditions herein.