Spatially resolved DNA brushes on a chip: gene activation by enzymatic cascade.

We assemble on a chip spatially resolved DNA polymer brushes with density that can be controlled along continuous gradients, from dilute to dense packing, with 20-30 nm between DNA molecules. Investigation of DNA digestion in a approximately 1 kb DNA brush showed that endonucleases can digest within the brush, yet their activity is impeded at high DNA density and for restriction sites near the bottom. Local gene activation-a form of switch-was then demonstrated by a digestion-ligation cascade between two spatially resolved DNA brushes, leading to the in situ expression of green fluorescent protein upon a diffusion-controlled DNA swapping.