Determination of norfloxacin residues in foods by exploiting the coffee‐ring effect and paper‐based microfluidics device coupling with smartphone‐based detection.

By utilizing the coffee‐ring effect and microfluidic paper‐based analytical devices (µPADs), this study improved the sensitivity of the determination of norfloxacin in four different food matrices. Micro‐PADs in this study were fabricated by designing and embedding wax channels onto cellulose‐based filter paper through printing and subjecting the paper to heat to allow the wax to penetrate the paper. Determination of norfloxacin concentration in food samples was achieved by monitoring the colorimetric reaction that occurred between norfloxacin and the added iron (III) nitrate nonahydrate in 5 mM ammonia in each reaction chamber. A transition metal hydroxide was formed through this reaction that resulted in the formation of a solid precipitate to enable the antibiotic to bind to the iron molecule via coordination chemistry. This metal ion–antibiotic complex generated a visible color change. Following the colorimetric reaction, images were taken and subsequently analyzed via ImageJ to determine the relative pixel intensity that was used to infer norfloxacin concentration. The analytical sensitivity of this device was determined to be as low as 50 ppm when analyzing the inner‐ring reaction, and as low as 5 ppm when analyzing the outer coffee ring thereby allowing for an alternative cheaper, faster, and more user‐friendly method to detect norfloxacin than the conventional methods. Practical Application: This novel paper‐based microfluidic device can achieve the detection of antibiotic residues in agrifoods in a faster, cheaper, and more user‐friendly manner. [ABSTRACT FROM AUTHOR]