Shell penetration/free energy-driven crosstalk between intelligent DNA nanomachines for ultrasensitive detection of circulating tumor cells

Because of the extraordinary rarity, CTC detection remains a technological challenge. In this contribution, a stimuli-responsive intelligent DNA nanomachine system is demonstrated for ultrasensitive and specific CTC detection via a shell penetration/free energy-driven autonomous circuit. The responsive toeholds designed in linear probes are shielded by protective DNA self-assembled outer shell and hidden inwards from the attack of fuel strands, proposing an innovative concept different from conventional DNA hairpin-based catalytic reactions. DNA machines are very stable in the 'OFF' state, almost completely suppressing the background fluorescence. A linear trigger can permeate through outer shell and ignite the inner responsive toeholds, achieving an amplification fluorescent signal. CTC is specifically screened in a linear response range of three orders of magnitude with a detection limit of 2 cells/200 μL with almost 100% accuracy, indicating 3.4~50-fold improvement in assay ability.