Methods of immobilizing nucleic acid on a solid surface for us in nucleic acid hybridization assays is disclosed. The methods of the invention comprise reacting a modified nucleic acid strand comprising a variable portion and an anchor portion wherein the variable portion comprises a nucleotide sequence having a selected base sequence and the anchor portion comprises at least one nucleotide base modified with a primary amine function or nucleotide base equivalent having a primary amine function and reacting the modified nucleic acid strand with a free aldehyde group of the solid surface in the presence of a reducing agent to form complexes of the modified nucleic acid strand and at least a portion of the free aldehyde groups on the solid surface.