A nanoporous silicon-based label-free DNA biosensor was fabricated to monitor rapidly enteric adenovirus types 40 and 41, a leading cause of viral gastroenteritis in children. Nanoporous silicon (NPS) was formed by an anodic etching process in a mixture solution containing hydrofluoric acid and ethanol. The polypyrrole (PPy) film was directly electropolymerized on The NPS substrate. Twenty-five base pairs of probe DNA (pDNA), derived from the fiber gene, was electrochemically doped on the PPy-coated NPS substrate. The conductivity change due to the immobilized pDNA and hybridized target DNA (tDNA) was expressed as an arbitrary factor, γ, which is a normalized numerical term used for the selective quantification of the tDNA. γ was inversely proportional to the concentration of complementary tDNA, but independent of the non-complementary tDNA. The sensitivity slope for detecting tDNAc was -1.54 μM(-1), based on the factor γ in the range of 0.4 to 1.0 μM of tDNA. The surface roughness was characterized using atomic force microscopy.