Near-infrared carbon dots for cell imaging and detecting ciprofloxacin by label-free fluorescence sensor based on aptamer

A label-free fluorescence sensor based on near-infrared carbon dots (NIR-CDs) and aptamer is described for the highly sensitive and selective detection of ciprofloxacin (CIP). NIR-CDs were synthesized from polyethyleneimine and reduced glutathione by one-step hydrothermal method. The electrostatic interaction between the positively charged carbon dots and the negatively charged aptamer resulted in fluorescence quenching. After the addition of CIP, the specific binding between CIP aptamer and CIP was stronger, resulting in fluorescence recovery. Under the optimal experimental conditions, the recovered fluorescence intensity has a linear relationship with the concentration of CIP in the range 0.5–800 ng/mL, and the detection limit is 0.167 ng/mL. The prepared carbon dots have excellent optical properties and biocompatibility, and due to their emission characteristics in the near-infrared window, they can be used for biological imaging, which has also been confirmed in the experiment. The feasibility of the label-free fluorescence sensor for the detection of CIP is also proved by confocal fluorescence imaging. The detection results of CIP determination in milk by this sensor are satisfactory, indicating that the developed sensor has great application potential. Graphical abstract