Blood glucose monitoring is an essential but painful component of diabetes management, so it is urgent to develop simple, convenient, and noninvasive glucose monitoring methods as alternatives. Because the glucose level in urine is directly related to the blood glucose, urine can be an alternative for blood glucose monitoring. Herein, we report the development of a new and highly sensitive noninvasive colorimetric assay to detect the glucose content in urine samples using gold bipyramids (GBPs). The principle of this method is to utilize hydrogen peroxide (H2O2), the oxidation product of glucose, to etch GBPs, where the urine glucose will be quantified based on the displacement of the absorption peak of GBPs. The unique morphology (sharp tips) and etching mechanism (from tips) of GBPs determine the high sensitivity of this assay. Under optimal conditions, this colorimetric assay shows a dynamic range of 0.5-250 μM and a detection limit of 0.34 μM for artificial urine samples. This detection capability is ideal when sample dilution is necessary. Another advantage is that the color change of the GBP solution in this assay is convenient for the visual readout of the urine glucose semiquantitatively by the naked eye. Furthermore, it has been demonstrated here that the iodide ion has the horseradish peroxidase (HRP) activity and can be used alone to promote the reduction reaction of H2O2, which eliminates the use of HRP enzymes, simplifies the reaction, and reduces costs. The role of iodide ions has been studied and mainly attributed as a catalyst with I2 as the reaction intermediate, which reduced the activation energy for the reduction of H2O2.
Keywords: LSPR; colorimetric assay; glucose oxidase; gold bipyramids; iodide; urine glucose.