Visual detection of formalin in food samples by using a microfluidic thread-based analytical device

Abstract

The use of formalin (FA) to maintain food freshness and storage time is illegal. FA intake causes chronic and acute effects on human health. In this work, the novel visual detection of FA in food samples by using a microfluidic thread-based analytical device (µTAD) was developed. This proposed method based on a sulfite assay where FA reacted with excess Na2SO3 to generate NaOH that was quantified on µTAD using acid-base titration. The µTAD was fabricated from an untreated 100 % cotton thread (20.0 cm) treated with phenolphthalein solution as an indicator and low and high concentrations of Potassium hydrogen phthalate (KHP) as a limiting agent. Both threads were tied together with a central knot before being attached to the woodblock platform before the analysis. The length of the color change (colorless to pink) on the µTAD was analyzed by the visual detection using the digital vernier caliper and ImageJ software (mode: distance measurement) using a captured image from a smartphone. Two linear calibration curves at low concentration (150–350 mg L−1) and high concentration (500–900 mg L−1) were achieved with the limit of quantification at 150 mg L−1. In addition, greater selectivity towards FA compared with potential interference ions was also observed. Furthermore, the developed µTAD was applied to analyze FA in food samples, and the results was agree with those obtained by the conventional method. Thus, the proposed µTAD can be used for developing a colorimetric detection platform for interesting trace chemical analysis.