Integration of chemoselective ligation with enzymespecific catalysis: Saccharic colorimetric analysis using aminooxy/hydrazine-functionalized gold nanoparticles

Here we developed a saccharic colorimetric method based on the combination of chemoselective ligation and enzyme-specific catalysis using aminooxy/hydrazine-functionalized gold nanoparticles (AO/AuNPs or H/AuNPs). In the detection of galactose (Gal), galactohexodialdose (GHDA), the galactose oxidase (GalOx)-catalyzed product, has an aldehyde group, which allows it to chemoselectively react with an aminooxy or hydrazine group at the outer layer of AO/AuNPs or H/AuNPs by oxime/hydrazone click chemistry to form oxime or hydrozone. Consequently, through the specific recognition of 1, 4-phenylenediboronic acid (PDBA) on cis-diols, GHDA, which contains two pairs of hydroxyls in the cis form, can bind not only with AO/AuNPs or H/AuNPs, but also with PDBA to form boronate diester, thereby triggering the aggregation of AuNPs and causing the corresponding color change. As GalOx catalyzed specific substrates, the amount of Gal correlated with the production of GHDA and the extent of AuNPs aggregation, thus allowing a simple and easily operatable colorimetric method for Gal detection to be developed. Under the optimized experimental conditions, the ratios of absorbance at a wavelength of 617 nm to that at 536 nm vary linearly with the logarithmic values of Gal concentrations within a wide range of 500 nM to 5 mM. Moreover, this colorimetric method shows anti-interference capability and high sensitivity with a detection limit of 21 nM. Thus, a universal platform for accurate and specific colorimetric analysis can be established through the integration of chemoselective ligation with enzyme specific catalysis.