Determination of copper ions in herbal medicine based on click chemistry using an electronic balance as a readout

The amount of copper affects the quality of herbal medicine greatly, it is necessary to develop some simple and sensitive methods to detect copper for the remote or resource-limited area. An electronic balance is one of the most familiar equipment that can be found nearly in all laboratories. The presence of Cu(i) can catalyze azide-alkyne cycloaddition reaction (called as click chemistry) with high efficiency. In this study, a simple method had been developed to detect copper ions in herbal medicine using an electronic balance as a readout device based on click chemistry. Cu(ii) is reduced to Cu(i) by sodium ascorbate in situ, which induces the "click" reaction between azido-DNA modified magnetic beads (MB-DNA) and alkynyl-DNA modified platinum nanoparticles (Pt NP-DNA) and results in the fixing of the platinum nanoparticles on the beads (called as MB-Pt NPs). MB-Pt NPs can be separated by a magnetic frame easily and transferred into a drainage reaction device containing hydrogen peroxide. Then, hydrogen peroxide can be decomposed by Pt NPs modified on MB to generate oxygen, which increases the pressure in the drainage reaction device and forces the water in the system to be discharged. The weight of the discharged water can be easily and accurately measured by an electronic balance. The weight of the water has a linear relationship with Cu(ii) in the range of 2.0-200 μM and a detection limit of 0.83 μM under 30 min of collected time. This method does not need complicated and expensive instruments, skilled technicians, and a complex data processing process. The proposed method had been applied to detect copper ions in herbal medicine with satisfactory results.