Ultrasensitive detection of circulating tumor cells via DNA walker driven by a DNA circuit synergized with MOF-on-MOF nanozyme

Circulating tumor cells (CTCs) monitoring as a means of liquid biopsy can be effective in aiding the diagnosis, treatment monitoring, and prognosis of cancer. Herein, we fabricated a dual-mode cytosensor for ultrasensitive detection of CTCs via DNA walker powered by a DNA circuit and MOF-on-MOF nanozyme. The anti-EpCAM aptamer was hybridized with complementary DNA (cDNA) and modified onto the magnetic nanospheres (MNs). In the presence of CTCs, cDNA strand can be released by cell-aptamer specific recognition and was separated through a magnet to trigger the subsequent DNA walking process. In the DNA walking process, the cDNA strand could trigger cascade toehold-mediated DNA displacement reactions by fuel nanozymefunctionalized DNA strands and recycle to further accelerate the DNA circuit thus amplifying the output signal. What's more, since the MOF-on-MOF nanozyme had good peroxidase activity, electrochemical and colorimetric dual-mode signal output can be achieved in the presence of 3,3 ',5,5 '-tetramethylbenzidine (TMB) and hydrogen peroxide (H2O2) for CTCs determination through an ITO chamber. As a proof of concept, by virtue of the outstanding synergistic signal amplification of DNA walker and MOF-on-MOF nanozymes, the designed dual-mode cytosensor exhibited a comprehensive linear range of 5 to 5 x 105 cells/mL and a sensitivity of 5 cells/mL and performed well in complex environment. This work provided important references for further investigations on CTC-related diagnosis and individualized treatment.