A cell-surface-anchored DNA probe coupled with hybridization chain reaction enzyme-free dual signal amplification for sensitive electrochemical detection of the cellular microenvironment.

The cellular microenvironment plays key roles in regulating physiological processes. However, it is still a challenge to detect it with quantification. Here, a simple, biocompatible, and universal strategy based on cell surface-anchored specific DNAzymes and hybridization chain reaction enzyme-free signal amplification for cellular microenvironment electrochemical detection is presented. In this strategy, the cell could be captured on the surface of the electrode via aptamer-target recognition. On the other hand, the DNAzyme hybridized with the substrate strand as a metal ion probe was anchored on the surface of the cell. In the presence of metal ions, the substrate strand could be cleaved into two fragments by the DNAzyme and released from the cell surface. Then, the DNA modified gold nanoparticles (AuNPs) could be captured on the electrode. Subsequently, an alternative hybridization reaction of two hairpin probes was triggered by the carried initiators forming nicked double helices. For signal readout, hemin could be inserted into the double-helix DNA long chain via electrostatic interaction, which could electro-reduce hydrogen peroxide to generate an electrochemical signal. Based on the intrinsic advantages of DNAzymes, including rapid kinetics, high sensitivity, and high selectivity, and the signal amplification strategy, this method should be able to monitor and semi-quantify target metal ions in the cellular microenvironment. Furthermore, this method shows potential for various targets by employing different DNA probes in the cellular microenvironment, providing a platform for bioanalysis.