DNA-based point accumulation for imaging in nanoscale topography (DNA-PAINT) is a method for overcoming the diffraction limit, for super-resolution imaging, using a simple reagent-based approach. Molecules of interest in the cell are labeled with antibodies that are attached to single DNA strands. Complementary DNA strands are labeled with fluorophores and introduced in solution; they transiently bind to their complementary strand on the antibody according to the binding kinetics. In this way, the binding and unbinding of labeled DNA strands induces the same blinking effect that occurs stochastically from the dyes in traditional dSTORM.
Recent developments in labeling have permitted identification of epigenetic sites by single-molecule fluorescence. The Nanoimager can image the sites of interest, mapping their density and consistency across DNA strands. The DNA is attached to a surface and sites for epigenetic modification can be marked out with fluorescent molecules, which are detected with high signal-to-noise by the Nanoimager. With four laser lines, the Nanoimager can image several molecular species bound to the DNA.
In this figure, we demonstrate the ability of the Nanoimager to easily obtain 20 nm resolution, by imaging binding sites on GATTA-PAINT nanorulers that are separated by 20 nm. Nanorulers with all three binding sites localized are indicated in gray. (Those with two out of three sites localized are in yellow, probably caused by no binding at this site during the acquisition period.) Imaging at this resolution requires drift correction, a feature comprehensively supported by the Nanoimager.
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