Facile preparation of peroxidase-like core-shell nanorods and application as platform for colorimetric determination of glucose, insulin and glucose/insulin ratio.

To obtain sensitive analytical detection methods, many unique materials have been developed and made them promising candidates for biosensing. In this study, a type of core-shell gold nanorods, GNR@AuS/AuAgS/CuS, possessing peroxidase-like activity was prepared in a simple, facile manner. A colorimetric strategy for detection of blood glucose, insulin and differentiating type 1 and type 2 diabetes was developed based on the unique GNR@AuS/AuAgS/CuS. The sensitive colorimetric approach for detection of glucose in the dynamic range of 2.5-200 μM was first established based on the catalytic performance of GNR@AuS/AuAgS/CuS. Meanwhile, the catalytic activity of the peroxidase-like GNR@AuS/AuAgS/CuS can be regulated by introducing the high affinity and specific reaction between DNA aptamer and insulin on the surface of GNR@AuS/AuAgS/CuS, which allows the colorimetric assay to be extended to the detection of insulin, and a quantitative analysis of insulin based on the specific recognition can be implemented at the range from 0.014 to 1.08 μU/mL. Furthermore, colorimetric approach coupling peroxidase-like performance and specific recognition on the surface of GNR@AuS/AuAgS/CuS nanoparticles was developed to measure glucose/insulin ratio and directly differentiate type 1 and type 2 diabetes mellitus. Practical human serum samples were tested and only the glucose/insulin ratio greater than 2.2 (μU/mL) may lead to the appearance of color change. The coupling of this different bioassay on the same nanoparticles reflects the versatility and integration characteristics of the colorimetric assay and is highly promising for improving diabetes management.