A system for detecting presence of an organism having an enzyme in a sample, comprising: a cartridge for containing the sample and a substrate such that the enzyme can react with the substrate to produce a biological molecule; a partitioning element mounted in a recess in a base of the cartridge, the partitioning element allowing partitioning of the biological molecule thereinto; a light source for irradiating the biological molecule partitioned into the partitioning element; and, a detector for detecting fluorescence of the biological molecule partitioned into the partitioning element, the detected fluorescence being indicative of presence of the organism in the sample; wherein the light source is in a raised cartridge mount of the system that mates with the recess in the base of the cartridge. Also provided is a method for calibrating said system and quality control cartridges for use in same.