Working principles of DNA engineered nanomachine. (a) Structural diagram of DNA-logic gate TP nanomachine, which contains reporter toe, recognition toe 1, recognition toe 2 and DNA TP scaffold. Strand cS is completely complementary to strand S and a piece of sgc8c, whereas strand cF is completely complementary to strand F and a piece of sgc4f. (b) Scheme of aptamer-based 3D DNA nanomachine for targeted cell surface computing. Two aptamers recognize and bind to their membrane biomarkers, thus releasing cS and cF from respective recognition toes. Driven by DNA strand displacement reactions, the fluorescence signal in reporter toe switches to βONβ from its original quenched (OFF) state.