Colorimetric-ratiometric fluorescence sensors dual-mode detection of ofloxacin based on Fe-Ni bimetallic metal-organic frameworks and carbon dots

Ofloxacin (OFL) is an effective antibiotic against bacteria. However, the overuse of ofloxacin can lead to residues in animal-derived foods, posing a potential threat to human health. Due to the issue of false positives in single-mode detection, it is crucial to establish a multi-mode method for accurate and sensitive detection of ofloxacin. Peroxidase-like active iron-nickel bimetallic organic framework (FeNi-MOF) and orange fluorescent carbon dots (OCDs) synthesized by a simple one-pot method were used to establish a dual-mode colorimetric/ratiometric fluorescence biosensor for the detection of ofloxacin residues. In colorimetric mode, in the presence of hydrogen peroxide (H₂O₂), FeNi-MOF can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to produce blue oxTMB. However, the fluorescence of OCDs at 588 nm will be quenched by oxTMB, thus forming a ratiometric fluorescence signal with the fluorescence of FeNi-MOF at 420 nm. The linear range of the dual-mode detection method was 10⁻⁷-10⁻² mg/mL, and the detection limits were 1.1 ng/kg (colorimetric) and 0.34 ng/kg (radiometric fluorescence). In addition, the constructed smartphone sensing platform is also well applied for on-site portable detection. Therefore, we have established a dual-mode sensor with high specificity, accuracy, and excellent anti-interference ability for OFL detection, and satisfactory results are also obtained in the actual spiked samples.