An ingestible capsule for detecting cancerous and non-cancerous tissues in a colon of patient is disclosed. The capsule has a radiation source integrated into the capsule body for illuminating tissues within a colon of the patient. Tissues of the colon are irradiated with radiation from the radiation source to elicit a fluorescence response, and a photon detector measures photons of the fluorescence response. Intensity and fluorescence lifetime of the fluorescence response is determined based on measured photons. A system employing the capsule is configured to distinguish cancerous and non-cancerous tissues based on the determined fluorescence lifetime of the fluorescence response.