A novel signal-on fluorometric sensor based on metal ion-mediated carbon dots for formaldehyde determination and lysosome-targeted bioimaging

Formaldehyde (FA) can exist in living cells and is involved in many physiological processes within organelles, especially lysosome, which plays pivotal roles in the FA metabolism of living systems. Therefore, a technique for the rapid and effective detection of FA is in high demand. Herein, a novel signal-on fluorometric strategy for FA determination based on Ag+-mediated nitrogen–sulfur co-doped carbon dots (Ag-M-NSCDs) was developed. The FA-responsive sensor was facilely prepared through introducing Ag+ into the lignin-derived nitrogen–sulfur co-doped carbon dots (NSCDs), accompanied by fluorescence (FL) reduction. With the addition of the FA solution, the redox interaction between Ag+ and FA led to the generation of Ag nanoparticles (Ag NPs) and separation of Ag+ from the surface of NSCDs, both of which contributed to the remarkable FL recovery. Furthermore, the fluorometric sensing system can selectively and sensitively detect FA with a linear response in a concentration range of 0–500 μM (R2 = 0.997) and a low detection limit of 500 nM based on three times signal-to-noise criteria, which make the nanosensor favorable for monitoring FA in real water samples and live cells. Furthermore, it showed superior lysosomal targeting performance with a Pearson coefficient of 0.87, which demonstrates a new method for FA-related biological studies and bioanalysis.