Colloidal silica particles were deposited on a glass substrate to produce h
igh-capacity porous supports for high-density DNA probe arrays. Porous surf
aces were used to increase the addressable surface area and number of probe
s available for hybridization. Surfaces derived from 70-100 nm size particl
es deposited in films from 0.15 to 2 microns thick exhibited excellent perf
ormance in light-directed oligonucleotide synthesis. Evaluation of these su
bstrates in a genotyping assay is reported.