A facile strategy for synthesis of porous Cu2O nanospheres and application as nanozymes in colorimetric biosensing

Abstract

Due to the unique advantages, developing a rapid, simple and economical synthetic strategy for porous nanomaterials is of great interest. In this work, for the first time, using sodium hypochlorite as a green oxidant, urea was oxidized to CO₂ as a carbon source to prepare the fine-particle crosslinked Cu-precursors, which could be further reduced by sodium ascorbate into pure Cu₂O nanospheres (NPs) with a porous morphology at room temperature. Interestingly, our study reveals that introduction of an appropriate amount of MgCl₂ into the raw materials can tune the pore sizes and surface area, but has no influence on the phase purity of the resulting Cu₂O NPs. Significantly, all the synthesized Cu₂O NPs exhibited intrinsic peroxidase-like activity with higher affinity towards both 3,3,5,5-tetramethylbenzidine (TMB) and H₂O₂ than horseradish peroxidase (HRP) due to the highly porous morphology and the electrostatic attraction towards TMB. The colorimetric detection of glucose based on the resulting porous Cu₂O NPs presented a limit of detection (LOD) of 2.19 μM with a broad linear range from 1–1000 μM, much better than many recently reported composite-based nanozymes. Meanwhile, this nanozyme system was utilized to detect L-cysteine, exhibiting a LOD value as low as 0.81 μM within a linear range from 0 to 10 μM. More interesting, this sensing system shows high sensitivity and excellent selectivity in determining glucose and L-cysteine, which is suitable for detecting serum samples with reliable results. Therefore, the present study not only develops a simple strategy to prepare Cu₂O NPs with controllable porous structure, but also indicates its promising applications in bioscience and disease diagnosis.