Density modification in arrays of surface-attached nucleic acid molecules

An array of DNA molecules on a substrate comprising,

• a substrate that has a surface wherein the surface comprises regions and the regions comprise a plurality of DNA polymers attached to the surface of the substrate,
• wherein at least one region comprise a plurality of DNA polymers that are attached to first trifunctional linkers such that at least two DNA polymers are attached to one first trifunctional linker,
• wherein the first trifunctional linkers have three sites for attachment, wherein a first of the two DNA polymers is attached to one of the three sites of the first trifunctional linker, a second of the two DNA polymers is attached to a second of the three sites of the first trifunctional linker, and a third site of the first trifunctional linker is attached to a second trifunctional linker,
• wherein the second trifunctional linker has three sites for attachment, and wherein a first trifunctional linker is attached to one of the three sites of the second trifunctional linker, another first trifunctional linker is attached to a second of the three sites of the second trifunctional linker, and a third site of the second trifunctional linker is attached to the surface of the substrate, and
• wherein the trifunctional linker is a molecule according to the structure:
• wherein when X and Y are different, X and Y are selected from the group consisting of CH2, CHR1, phenyl, O, S, NH, and NR2, and in the case where X and Y are the same X and Y are selected from the group consisting of CH2, CHR2, and phenyl wherein R1 is selected from the group consisting of —OH, —CH3, —CH2OH, —CH2CH3, and —CH2CH2OH and R2 is selected from the group consisting of —CH3, —CH2CH3, and —CH2CH2CH3, n is an integer from 0 to 10, and A1 and A2 are DNA polymers.