Gastrointestinal tract detection methods, devices and systems

A device, comprising:

• a diffractive optics sensor, comprising:
• a diffraction grating;
• an analyte-binding agent linked to a surface of the diffraction grating, wherein the analyte-binding agent is capable of binding to the analyte;
• and
• a detector configured to detect light diffracted by the diffraction grating,
• wherein:
• the device is configured so that, when the analyte is bound to the analyte-binding agent, a diffraction pattern of light diffracted by the diffraction grating changes;
• at least one of the following holds:
• the device further comprises a light source configured so that light emitted by the light source impinges on the diffraction grating with an angle of incidence of from 30° to 80° measured from the surface of the diffraction grating;
• the diffraction grating comprises a series of grooves comprising adjacent recessed portions, and raised portions of the grooves have a depth from about 1 nm to about 1000 nm;
• the diffraction grating has a period of from 0.5 micron to 50 microns;
• the diffraction pattern comprises light in a plurality of diffraction orders, and the detector detects an intensity of light in one or more of the diffraction orders;
• and
• the device is an ingestible device.