Colorimetric detection of sugars based on gold nanoparticle formation

In this paper gold nanoparticles (Au-NPs) have been used as colorimetric reporters for the detection of sugars. The synthesis of Au-NPs has been obtained in presence of glucose as reducing agent in different conditions, allowing the formation of pink or blue coloured NPs, and has been employed in the design of two colorimetric assays. Both assays rely on the analyte induced intensity increase (without any shift) of the NPs plasmon band absorption. The “pink assay” is based on the sugar assisted chemical synthesis of NPs and it represents a simple one-step colorimetric approach to the quantification of all potentially reducing sugars (sucrose included) with a LOD of 10 μM.The “blue assay” is based on the Au-NP synthesis catalysed by the enzyme glucose oxidase and it is specific for glucose, with a LOD of 5 μM. Compared to the classical bi-enzymatic (glucose oxidase/peroxidase) optical assay, it uses only one enzyme and does not suffer of the bleaching of the final colour because the reporter Au-NPs are very stable.