Portable, quantitative, and sequential monitoring of copper ions and pyrophosphate based on a DNAzyme-Fe3O4 nanosystem and glucometer readout.

In this report, portable, quantitative, and sequential monitoring of copper ions and pyrophosphate (PPi) with a single sensor based on a DNAzyme-Fe3O4 system and glucometer readout was performed. Initially, streptavidin was functionalized on the surface of magnetic Fe3O4 spheres through glutaraldehyde. Then, an invertase-modified DNA Cu substrate was connected to the magnetic Fe3O4 spheres by a specific reaction between streptavidin and biotin. The sensing system was formed by a hybridization reaction between the Cu substrate and Cu enzyme. In the presence of Cu2+, Cu2+ will recognize the Cu DNA substrate and form an "off-on" signal switch, thereby resulting in the separation of invertase from the Fe3O4 nanospheres. PPi recognizes Cu2+ to form a Cu2+-PPi complex, resulting in an "on-off" signal switch. Under optimized conditions, linear detection ranges for Cu2+ and PPi of 0.01-5 and 0.5-10 µM, and detection limits for Cu2+ and PPi of 10 nM and 500 nM, respectively, were obtained. Good selectivity was achieved for the analysis of Cu2+ and PPi. Satisfactory results were achieved for this biosensor during the determination of Cu2+ in real tap samples and PPi in human urine samples. This verified that the sensor is portable and low cost, and can be applied to the sequential monitoring of multiple analytes with a single point-of-care biosensor.