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 Fe 3 O 4 @Au nanozymes and DNAzyme hybrids as electrochemical nanoprobes and toluidine blue (Tb) as the electron transfer medium. The Fe 3 O 4 @Au nanocomposites not only acted as nanozymes with excellent catalytic performance towards H 2 O 2 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 Fe 3 O 4 @Au nanohybrids, working as the electron transport medium to magnify the electrochemical response. With the above design, the Fe 3 O 4 @Au nanozymes and hemin/G-quadruplex DNAzyme efficiently co-catalyzed the reduction of H 2 O 2 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.