Quantification of glucose via in situ growth of Cu₂O/Ag nanoparticles

The monitoring of glucose levels in blood is extremely important for the effective control of diabetes. Nanomaterial-based approaches for the quantification of glucose typically require two steps: material preparation and the actual glucose measurement. Herein, we report a single-step method that combines these functions via the in situ growth of Cu₂O/Ag nanoparticles (NPs). Mechanistically, we use glucose itself to reduce Cu²⁺ and Ag⁺ ions that are stabilized with 3-mercaptopropionic acid (3-MPA) and bovine serum albumin (BSA) under alkaline conditions to form Cu₂O/Ag NPs and produce a color change in solution due to plasmonic resonance at 400 nm, which can be related back to the concentration of glucose. We study several factors in this reaction, including the molar ratios of the metal ions and 3-MPA, the reaction time, and the temperature to control the synthesis of the Cu₂O/Ag NPs and thus their sensitivity toward glucose. Introducing BSA into the system is a key factor for the quantification of glucose in blood without pretreatment, improving the probe's limit of detection and reducing the sample volumes to 1 μL. This colorimetric assay based on Cu₂O/Ag NPs exhibits excellent sensitivity and specificity toward glucose, and a linear relationship with glucose concentrations ranging from 15 to 300 μM and a limit of detection of 9.2 μM. As proof of concept, we demonstrated that the Cu₂O/Ag NP probes could successfully detect glucose in two representative blood samples by neglecting interferences from various common species, demonstrating the potential of this technique in point-of-care analysis.