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-Fe 3 O 4 system and glucometer readout was performed. Initially, streptavidin was functionalized on the surface of magnetic Fe 3 O 4 spheres through glutaraldehyde. Then, an invertase-modified DNA Cu substrate was connected to the magnetic Fe 3 O 4 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 Cu 2+ , Cu 2+ will recognize the Cu DNA substrate and form an “off-on” signal switch, thereby resulting in the separation of invertase from the Fe 3 O 4 nanospheres. PPi recognizes Cu 2+ to form a Cu 2+ -PPi complex, resulting in an “on-off” signal switch. Under optimized conditions, linear detection ranges for Cu 2+ and PPi of 0.01–5 and 0.5–10 μM, and detection limits for Cu 2+ and PPi of 10 nM and 500 nM, respectively, were obtained. Good selectivity was achieved for the analysis of Cu 2+ and PPi. Satisfactory results were achieved for this biosensor during the determination of Cu 2+ 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. Graphical abstract