Graphene quantum dot-enabled dual-modal fluorescence/ colorimetry detection of formaldehyde

While methods for gaseous formaldehyde (HCHO) detection are well-established, rapid and sensitive sensing in aqueous matrices remains a challenge. To address this gap, we developed a dual-mode sensing platform based on a nitrogen-doped graphene quantum dots/o-phenylenediamine-Ag + (NGQD/OPD-Ag + ) system for HCHO analysis in aqueous matrices. In this system, Ag + catalyzes the oxidation of OPD, whose product quenches NGQD fluorescence via a FRET mechanism. The presence of HCHO inhibits this oxidation, resulting in complementary ratiometric fluorescence and colorimetric signal changes. This method achieved high sensitivity with detection limits of 0.54 μ M (fluorescence) and 1.33 μ M (colorimetry), excellent selectivity, and was successfully applied for the visual detection of HCHO in real water samples using a smartphone-integrated paper sensor. This work provides a robust and practical solution for rapid on-site monitoring of HCHO in in aqueous matrices. • Nitrogen doped graphene quantum dots have strong fluorescence emission. • Colorimetry and ratio fluorescence dual-modal fluorescence/colorimetry sensing platform for rapid field detection of HCHO. • Ratio fluorescence sensor can overcome the drawback of a signal sensing. • Smartphone and test strip are combined to visually detect HCHO in the environment.