Target-driven rolling walker based electrochemical biosensor for ultrasensitive detection of circulating tumor DNA using doxorubicin@tetrahedron-Au tags.

In this study, a multiple-legged and highly integrated DNA rolling walker based electrochemical biosensor was developed for ultrasensitive ctDNA analysis through rolling circle amplification (RCA) with doxorubicin@tetrahedron-Au (DOX@TDN-Au) as electrochemical indicator. Upon target-driven RCA, the multiple-legged walker could move along with the predesigned track by strand displacement reactions, resulting in numbers of legs binding irreversibly to iStep probes. The binding of massive legs to iStep probes could effectively impede DOX@TDN-Au tags binding on the surface of sensor and then reached a "signal off" state. Benefiting from the highly amplified efficiency of rolling walker machine and DOX@TDN-Au tags, the established biosensor performed high sensitivity for target detection with a low limit of detection down to 0.29 fM. Moreover, the target ctDNA could hybridize with the ring and capture probe simultaneously, greatly enhancing the specificity of the developed biosensing method. Thus, this biosensing method is a promising tool for detection of ctDNA in the field of clinical diagnostic and tumor progression assessment.