DNA-templated Ag nanoclusters as fluorescent probes for sensing and intracellular imaging of hydroxyl radicals.

We have developed a simple, rapid and label-free sensor for the essential biological OH radicals based on the fluorescence quenching of DNA-templated Ag nanoclusters (DNA-Ag NCs). The OH radicals generated from the Fenton reagent attack and cleave the DNA template, which disturbs the microenvironments around Ag NCs, resulting in spontaneous aggregation due to the lack of stabilization and further the quenching of the Ag NCs fluorescence. These changes in fluorescence intensity allow sensing of OH radicals with good sensitivity and selectivity under optimal conditions. The sensor can be also applied for quantifying the radical scavenging action of antioxidants. Various characterizations including absorption spectra, fluorescence lifetimes, light scattering (LS) spectra, transmission electron microscopy (TEM), dark field light scattering imaging, and circular dichroism (CD) spectrometry have been employed to illustrate the proposed sensing mechanism. Further investigations demonstrate that the fluorescent probe could penetrate into intact cell membranes to selectively detect intracellular OH radicals induced by the phorbol myristate acetate (PMA) stimulation. These advantageous characteristics make the fluorescent DNA-Ag NCs potentially useful as a new candidate to monitor OH in broad biosystems.