Enzyme-free unlabeled DNA logic circuits based on toehold-mediated strand displacement and split G-quadruplex enhanced fluorescence.

Adopting fluorescence of PPIX enhanced by a split G-quadruplex and toehold mediated strand displacement reaction, a series of unlabeled fluorescent logic gates is set up and some of them are cascaded into circuits. Controlled release of PPIX, which is also a photosensitizer in photodynamic diagnosis and therapy, is realized by this circuit, making it a wise choice for DNA computing.