Abstract: Disclosed herein are integrated photonics systems (3800) for biosensing including an interrogator photonic circuit (3802) and cartridge (3804) and methods using these systems. The cartridge (3804) comprises a sensor photonic integrated subcircuit. The cartridge (3804) is configured to receive a biological sample. The interrogator photonic circuit (3802) is optically coupled to the cartridge (3804) an comprises: (i) a light source (3806) configured to generate light; and (ii) one or more waveguides configured to carry the light, wherein the light is used to determine a characteristic of the biological sample in the cartridge (3804). A system can have an assembly of a plurality of modular photonic integrated subcircuits. Each subcircuit can be pre-fabricated and can be configured to transfer light to and receive light from another subcircuit based on the first functionality.