Metal-enhanced fluorometric formaldehyde assay based on the use of in-situ grown silver nanoparticles on silica-encapsulated carbon dots.

Fluorescent nanoparticles were prepared by encapsulating carbon dots (CDs) within silica spheres and then modifying these spheres with amino groups (CD@SiO2-NH2). On the basis of the silver mirror reaction, Ag+ assembled on the surface of CD@SiO2-NH2 is reduced to silver nanoparticles (AgNPs) by formaldehyde. The in-situ grown AgNPs cause a visually distinguishable fluorescence enhancement. This metal-enhanced effect was investigated by transmission electron microscopy and spectroscopic characterization, and the relevant conditions were optimized. CD@SiO2-NH2-Ag+ fluorescent probes were loaded onto nano-sponge pieces for the analysis of formaldehyde gas. The blue fluorescence emission (peaking at 466 nm) in response to formaldehyde is greatly enhanced (up to 5.2 times) over other species. There is a linear relationship between the fluorescence enhancement and formaldehyde gas concentration in the range of 10 ppb to 1 ppm, and the detection limit is 3 ppb. The fluorimetric assay needs 30 min for the reaction, and the fluorescent nano-sponge pieces are disposable. Graphical abstractSchematic representation of the metal-enhanced fluorescence (MEF) induced by in-situ grown silver nanoparticles on silica-encapsulated carbon dots, and its application in formaldehyde gas assays.