Abstract: Based on digital imaging, a microfluidic paper chip for the rapid determination of the chlorogenic acid content in honeysuckle was developed and optimized by using carbon dots, which combines the high accuracy of fluorescence carbon dots and the high selectivity of molecularly imprinted polymers. Using nitrogen and sulfur co-doped carbon dots as a fluorescent sensing material and chlorogenic acid as a template molecule, a carbon dot-molecularly imprinted paper chip was made by synthesizing molecularly imprinted polymers on the hydrophilic surface of filter paper. Based on the redness, greenness, and blueness values of colored spots, the experimental conditions were optimized using single-factor experiments. The optimal preparation conditions were molar ratio of chlorogenic acid to 3-aminopropyltriethoxysilane (functional monomer) to ethyl orthosilicate (cross-linking agent) 1:8:8, addition of 1 mL of anhydrous ethanol and 0.2 mL of amino-modified carbon dot solution to 0.01 mmol of chlorogenic acid, and ultrasound-assisted polymerization for 35 min. The optimal color development conditions were sample volume 4 μL, and reaction time 15 min. Under the optimized conditions, a good linear relationship was obtained between the greenness value and chlorogenic acid concentration in the range of 0.025–0.15 mg/mL, with a determination coefficient of 0.991 8, and the detection limit of the method 0.020 6 mg/mL. The recoveries of chlorogenic acid spiked into honeysuckle were 90.77%–102.10%. The paper chip method has the advantages of low cost, good selectivity and rapidity (It can be completed within 20 min). It can be used as a supplementary method for the determination of chlorogenic acid in the field or under primitive conditions.

Key words: honeysuckle; chlorogenic acid; carbon dot; molecularly imprinted polymers; paper chip; rapid determination