The present description provides, in some embodiments, an apparatus for mixing a fluid in a circuit having an inlet channel defining a flow path for a fluid including particulate matter, a first reagent channel in fluid communication with the inlet channel and defining a first reagent flow path for a first reagent, the inlet channel and first reagent channel configured to shear the fluid entering the first reagent channel from the inlet channel at a first junction, a shearing channel in fluid communication with the inlet channel and first reagent channel at the first junction, and a diffusion channel in fluid communication with the shearing channel at a second junction, the sheared fluid collectable into the diffusion channel such that the fluid is compressed at least in part by the first reagent to have a thickness close to a diameter of the particulate matter in the fluid.

A particulate matter detector includes a light emitter configured to emit light, a first, a second and a third waveguide, a waveguide splitter, a detector, and a controller. The third waveguide is free of cladding. The first waveguide is coupled to the light emitter and guides emitted light toward the waveguide splitter. The first waveguide includes an interrogation region formed by a cladding-free surface of the first waveguide. During a measurement phase, a first intensity of the light in the first waveguide is set for determining a change in the intensity of the light detected by the detector. An indication of an opacity of the surface of the first waveguide with accumulated particulate matter is output. During a cleaning phase, a second intensity of the light in the first waveguide is set for directing the accumulated particulate matter from the interrogation region to the third waveguide via optical forces.