An internal filtration effect-based "off-on" probe for fluorescent and visual sensing of formaldehyde

Formaldehyde (FA) sensing in children's toys and water has great application prospects in the protection of home safety and the ecological environment. However, there has been no report heretofore addressing FA detection in children's toys. In this work, a fluorescent (FL) whitening agent (FWA), potassium dichromate, and sulfuric acid were proposed as an "off-on" probe (FPD) for FA sensing via FL and visual FL (VFL) methods. The FL emission of the FWA at 435 nm was quenched by Cr₂O₇^2- because of the internal filtration effect. The effect was interrupted after the addition of FA because Cr₂O₇^2- was reduced to Cr³⁺, accompanying the recovery of the FL emission of the FWA. The detection limit of FPD for FA via FL and VFL approaches was 2.03 and 85.5 μg L^-1, respectively. The proposed probe was successfully utilized for FA detection in crawling mats and building blocks as well as environmental water (verified by the UV method), indicating good adaptability. The FPD-based FL method might be a potential approach for FA detection due to the merits of high selectivity, anti-interference ability, and stability.