Programming cascaded recycling amplifications for highly sensitive and label-free electrochemical sensing of transcription factors in tumor cells.

The monitoring of transcription factors (TFs) is critical for understanding the regulation of gene transcriptions. Here, by programming nucleic acid sequence-based and cascaded recycling amplifications, we developed a sensitive and non-label electrochemical biosensor for detecting TFs from tumor cell extracts. The binding of the target nuclear factor-kappa B p50 (NF-κB p50) with the dsDNA probes protects them from being digested by exonuclease III for subsequent initiation of three cascaded recycling cycles, which causes the generation of tremendous free G-quadruplex special sequences on the sensing electrode. Such G-quadruplexes can specifically bind and confine hemin within the vicinity of the sensor, generating substantially enhanced reduction current to achieve determination of NF-κB p50 within the range from 0.5 pM to 5 nM with the detection limit down to 0.13 pM. The proposed sensing system also has high selectivity and it can be used to interrogate the presence of NF-κB p50 in tumor cell extracts, demonstrating its potential for disease diagnosis and gene transcription-related studies.