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.
Colloidal gold and Eu -doped fluorescent microspheres were applied as labels to develop the immunochromatographic strips for detecting melamine in milk. Under the optimized condition, the visual detection limit of colloidal gold-immunochromatographic test strip (ICTS) was 150 μg/L of melamine in phosphate-buffered saline (PBS), although the visual detection limit of fluorescent nanoparticles (FN)-ICTS was 75 μg/L in PBS. As thermal acceleration test, FN-ICTS could be stored at 37 °C for at least 11 d before sample testing, but the color of the lines on colloidal gold-ICTS faded away after 7-d storage. The visual result of FN-ICTS was more stable than that of colloidal gold-ICTS, and the fluorescence intensity of the line on FN-ICTS could be maintained up to 30 d at 22 °C after sample testing. Once the immunochromatographic strips were used to detect melamine in milk, no negative effect of milk components on the performance of FN-ICTS was identified, whereas the performance of colloidal gold-ICTS was significantly influenced by milk matrix.
The screening of biological contaminants, chemical hazards and allergens in food products is critical to understanding the potential negative effects on human health. Intensive research has been conducted to develop various detection methods to monitor food safety and quality. However, most of these developed methods are costly and require supporting equipment and professional skills to perform the testing. Therefore, there is high demand to develop alternative and innovative methods that are affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and deliverable to fulfil the “ASSURED” criteria set by the World Health Organization (WHO). Colorimetric analysis can identify and determine the content of chemical elements/compounds in sample solutions by using various color reagents. This method has been used to detect and quantify specific pathogens, chemicals and hazards in foods for safety and quality control, which are suitable for use in laboratories and field studies. This chapter summarizes the recent advances in colorimetric analysis for assessing food safety and quality assurance, such as colorimetric detection of pathogens, toxins, parasites, antibiotic residues and chemical hazards in agri-food products. This chapter also conveys the current technical limitations and strategic research of colorimetric analysis required to further improve the performance of analytical assays in sensing food safety and quality control.
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