A highly sensitive electrochemical cytosensor based on a triple signal amplification strategy using both nanozyme and DNAzyme.

The development of a sensitive cytosensor is beneficial for the early diagnosis and treatment of cancer. Herein, highly sensitive cytosensing was achieved by applying triple signal amplification strategies with Fe3O4@Au nanozymes and DNAzyme hybrids as electrochemical nanoprobes and toluidine blue (Tb) as the electron transfer medium. The Fe3O4@Au nanocomposites not only acted as nanozymes with excellent catalytic performance towards H2O2 reduction but also served as promising scaffolds to carry massive electroactive substances and DNA probes. The dual-functional DNA probes were designed with the sequence of hemin/G-quadruplex to serve as the DNAzyme and the sequence of aptamer to recognize cancer cells. Furthermore, Tb was also conjugated to the surface of the Fe3O4@Au nanohybrids, working as the electron transport medium to magnify the electrochemical response. With the above design, the Fe3O4@Au nanozymes and hemin/G-quadruplex DNAzyme efficiently co-catalyzed the reduction of H2O2 to accelerate the electron transfer of Tb, which realized triple signal amplification and finally improved the performance of the electrochemical cytosensor. The proposed cytosensor achieved a sensitive detection of HepG2 cells with a low detection limit of 20 cells mL-1, and could be potentially used as an effective analysis tool in early cancer diagnosis in the future.