Abstract: A system is provided for sensing an analyte in a breath sample. The system includes a breath bag, a cartridge and a base. The breath bag contains the breath sample. The bag includes a mouthpiece fixedly disposed on the breath bag. The cartridge includes an interactant that reacts with the analyte and generates a change in an optical characteristic relative to a reference. The base includes a flow path, a breath bag receiver for detachably receiving and retaining the mouthpiece of the breath bag in fluid communication with the flow path, and a cartridge receiver that detachably receives and retains the cartridge in the base, such that the base engages the cartridge so that the interactant is in fluid communication with the flow path.