Label-free pathogen detection by a deoxyribozyme cascade with visual signal readout

A colorimetric nucleic acid based test for label-free pathogen detection has been developed and used for the detection of the Zika virus. The test relies on nucleic acid sequence-based amplification (NASBA) of a viral RNA followed by interrogation of the amplicon by a cascade of deoxyribozymes constituting a visual split deoxyribozyme (vsDz) probe. The probe consists of a split phosphodiesterase deoxyribozyme, which forms its catalytic core upon binding to a specific amplicon fragment. The catalytically active complex recognizes and cleaves an inhibited peroxidase-like deoxyribozyme (PDz), thereby activating it. Active PDz catalyzes hydrogen peroxide-mediated oxidation of a colorless substrate into a colored product, thereby generating a visible signal. Viral RNA (10(6) copies/mL or higher) triggers intense color within 2 h. The test selectively differentiates between Zika and closely related dengue and West Nile viruses. The reported technology combines isothermal amplification and visual detection and therefore represents a basis for the future development of a cost-efficient and instrument-free method for point-of-care nucleic acid analysis.