Conformational transition-induced simultaneous fluorescence enhancement of oxytetracycline and rhodamine B under a single excitation wavelength.

Since the abuse of antibiotic oxytetracycline (OTC) poses a serious threat to the environment and human health, it is of great importance to develop sensitive fluorescent probes for its rapid and in situ detection. Herein, a dual fluorescence response probe based on an aluminum-incorporated metal-organic framework (MOF) was presented for OTC assay. Unlike internal references that demonstrate an independent and stable fluorescence signal intensity in traditional dual-emissive probes, the fluorescence of rhodamine B immobilized in a prepared probe was gradually enhanced at a 585 nm emission wavelength with increasing concentrations of OTC under 405 nm excitation, while OTC also experienced an obvious fluorescence enhancement at a 521 nm emission wavelength due to a molecular conformation transition from the twisted to the extended state, realizing a molecular conformational transition-induced dual fluorescence enhancement for OTC detection under a single excitation wavelength. In addition to the mechanism exploration and double linear range for OTC quantification with nM level detection limits in solution, a paper-based portable test strip was successfully fabricated by loading the probe on glass fiber filter paper with an obvious fluorescence color change from orange to yellow upon increasing the addition of OTC. We expect that the proposed probe in this work would provide an example for the design of organic fluorophore-based sensors exhibiting multiple fluorescence responses under a single excitation.