Smartphone-based colorimetric detection of formaldehyde in the air

Adverse impacts of exposure to formaldehyde on human health significantly increases attention in monitoring formaldehyde concentrations in the air. Conventional formaldehyde detection methods typically rely on large and costly instruments and requires high skills of expertise, preventing it from being widely accessible to civilians. This study introduced a novel approach utilizing smartphone-based colorimetric analysis. Changes of green channel signals of digital images by a smartphone successfully capture variation of purple color of 4-amino-3-hydrazino-5-mercapto-1,2,4-triazol solution, which is proportional to formaldehyde concentrations. It is because that green and purple are complimentary color pairs. A calibration curve was established between green channel signals and formaldehyde concentrations, with a correlation coefficient of 0.98. Detection limit of the smartphone-based method is 0.008 mg/m³. Measurement errors decrease as formaldehyde concentrations increase, with median relative errors of 34%, 17%, and 6% for concentration ranges of 0–0.06 mg/m³, 0.06–0.12 mg/m³, and 0.12–0.35 mg/m³, respectively. This method replaced scientific instrumentation with ordinary items, greatly reducing cost and operation bars. It would provide an opportunity to realize onsite measurements for formaldehyde by occupants themselves and increase awareness of air quality for better health protection.