Microdroplet Sensor for Point-of-Care-Testing of Glycemic Index Using Gold-Amylase Nanocomposite

Biosynthesis of gold-amylase nanocomposites (Au-Am-NC) has been achieved wherein the gold ions are reduced with the help of thiol groups of the $\alpha $ -amylase enzyme to engender metal-enzyme link. The Au-Am-NC, thus synthesized ( $\sim 30$ nm) could easily degrade the starch iodine (SI) complex generated, which is eventually translated into a prototype for the determination of the glycemic index (GI) of a starch source. In a way, in situ hydrolysis of SI complex is achieved inside the droplet with the help of the Au-Am-NC, which breaks the $\alpha -1$ , 4 glycosidic bonds of the starch molecules to liberate iodine from helical SI complexes. Experiments uncover that the color intensity of the microdroplets decreases as the enzymatic activity of the nanocomposite increase. The variation in color intensity of droplets is correlated to the GI of various starch sources. Interestingly, an SI droplet of soluble starch shows more fading than wheat, corn, and waxy corn starch. The high branch density of waxy corn starch reduces the hydrolysis rate, showing less SI droplet color fading. The methodology has shown the potential to be translated into a biomedical device to determine the GI of various edible starch sources.