Cater to the call of on-site, quantitative, and low-cost food formaldehyde detection: A paper-based sensor by timing Congo red decoloration

Given the illegal formaldehyde (FA) contamination in seafood/aqueous products, the instrument-free, chemical-free, low-cost sensor that enables on-site FA detection is of great interest. We have developed a paper-based analytical device (PAD) sensor to detect FA on-site for easy operation by integrating FA-responsive dye decoloration reaction on filter paper and timing decoloration time for quantitative signal interpretation. This innovative dry chemical PAD sensor can be easily prepared. The on-site FA detection is performed by dropping a drop of the sample into the sensor sampling zone and timing the decoloration time, respectively. The difference in decoloration time between a fictitious blank (5.0 μM) and an FA standard is proportional to the FA concentration in the range of 10–700 μM with a detection limit of 5.6 μM. The utility and effectiveness of this PAD sensor has been verified by applying it to seafood, paper cups, and water samples with the supports of official method validation.