A β-d-galactose-guided fluorescent probe for selectively bioimaging endogenous formaldehyde in living HepG-2 cells

Abstract

A fluorescent probe NFP-G, with β-d-galactose as the targeted unit and hydrazine as the recognition group for formaldehyde (FA), was designed and synthesized for specifically detecting endogenous FA in HepG-2 cells via asialoglycoprotein receptor-mediated endocytosis. The experimental results show that probes NFP-G/NFP-A exhibited highly fluorescent responses toward FA, which could be ascribed to the restriction of the photoinduced electron transfer (PET) process by the formation of hydrazone. Good selectivity and competition of NFP-G toward FA over potentially interfering species ensure it an appropriate candidate for FA detection. The sensing mechanism of the probes toward FA was studied by theoretical calculation, high performance liquid chromatography and mass spectrum. The confocal bioimaging results reveal that NFP-G could selectively visualize the endogenous FA in asialoglycoprotein receptor overexpressed HepG-2 cells over other cells. Pretreated with β-galactosidase made both asialoglycoprotein receptor positive and negative cells display strong green fluorescence, revealing β-d-galactose is essential in targeting HepG-2 cells.