A toehold-mediated strand displacement cascade-based DNA assay method via flow cytometry and magnetic separation.

Sensitive assay of EGFR T790M, a circulating tumor DNA marker in non-small-cell carcinoma, provides critical information for the decision of clinical treatments, evaluation of radiotherapy effect, and monitoring the progress of recurrence and metastasis. In this report, a novel flow cytometry-based sensing method is proposed for detecting T790M. The toehold-sequence hybridizes with the biotin-labeled initiator sequence and forms IT-dsDNA. The presence of a target induces the displacement of initiator-sequence from IT-dsDNA. The targets are continuously set free with the aid of a helper hairpin sequence for the next cycle. In tandem, the free initiator sequence starts the hybridization chain reaction, which binds the serial of fluorescence-labeled probe sequences. The products of the hybridization chain reaction are captured and separated by magnetic beads, which are finally assayed via flow cytometry. The capability to distinguish single-nucleotide polymorphism and the tolerance of complex matrix in blood serum indicate that this strategy has the promising potential to be applied in the liquid biopsy of clinical samples.