Nucleic acids are fixed or immobilized to non-porous solid supports (substrates), and include systems containing such supports and arrays with fixed or immobilized nucleic acids. These compositions are useful for nucleic acid analyses and a host of applications, including, for example, detection, mutational analysis and quantification. The non-porous solid supports can be transparent or translucent, and the surfaces can be treated with agents to fix or immobilize the nucleic acids. Such agents include, for example, amine providing compounds, epoxy compounds and acid solutions. The fixed or immobilized nucleic acids can be unlabeled, or labeled with at least one non-radioactive signaling moiety, such as the case when the nucleic acids are double-stranded.