A test module for performing a genetic diagnostic assay, the test module having an outer casing dimensioned for hand-held portability, the outer casing having a receptacle for a biological sample containing target nucleic acid sequences, an array of chambers containing probes for hybridization with the target nucleic acid sequences to form probe-target hybrids, a flow-path extending from the inlet to the probes, and, a reagent reservoir containing a reagent for addition to the sample in the flow-path upstream of the probes, wherein, each of the chambers contains less than 270 picograms of probe and the reagent reservoir has a volume less than 1000,000,000 cubic microns.