An analyte detection system and method for the detection of one or more analytes in a sample, the analytes selected from the group consisting of explosives, narcotics, gunshot residue, organophosphate reagents, and toxic industrial chemicals, based on a capillary action in a sample card. The sample card includes a housing with at least one cavity made of flexible material, a sample substrate for collecting the sample with a portion of the substrate exposed from outside the housing, at least one test capsule in the cavity and an absorbent pad. The test capsule(s), the sample substrate, and the absorbent pad comprise at least one or more reagents. The test capsule(s) is ruptured with a rupture mechanism upon inserting the sample card into a reader device. The absorbent pad absorbs a liquid from the test capsule and delivers the same to the sample substrate. The reagent(s) from any of the test capsule(s), the sample substrate, and the absorbent pad chemically react with the analyte(s) in the sample thus providing their optical detection. The sample card is automatically tested within the reader device which supplies one or more light sources, records and processes an optical signal produced by the chemical reaction, and outputs a test result.