DNA microarrays have proven extraordinarily powerful for differential expression studies across thousands of genes in a single experiment. Microarrays also have the potential for clinical applications, including the detection of infectious and immunological diseases and cancer, if they can be rendered both reliable and cost-effective. Here we report the first practical application of an active microarray based on integrated circuit technology, completely obviating the need for external measurement instrumentation while employing protocols compatible with traditional fluorescence-based surface bioassays. In a gene expression biodosimetry study, we determine the differential activity of genes from leucocytes in irradiated human blood. Quantum dots are used as fluorescence labels to realize filterless, time-gated fluorescence detection on an active complementary metal-oxide-semiconductor (CMOS) microarray with 100-pM sensitivity. Improvements in surface chemistry should allow sensitivities that approach the microarray hardware limit of less than 10 pM. Techniques for covalent attachment of DNA capture strands to the CMOS active microarrays allow integrated sensors to be placed in immediate proximity to hybridized analyte strands, maximizing photon collection efficiencies.