Abstract: An ingestible device includes a sample chamber configured to hold a sample, the sample chamber including a base having an aperture; a fluorometer separated from the sample chamber by the sample chamber base, the fluorometer including (I) a light source configured to emit excitation light, (II) a light guide configured to guide the excitation light from the light source to the sample, (III) a photodetector configured to detect emission light generated via the interaction of the excitation light with the sample. The photodetector is configured to receive the emission light from the sample through the aperture. Additionally, the fluorometer includes (IV) an emission filter between the aperture and the photodetector, the emission filter configured to (i) transmit the emission light incident thereon, and (ii) block excitation light incident thereon. In addition, the ingestible device includes a housing that houses the sample chamber and the fluorometer.