An apparatus includes a process chip and a dynamic light scattering assembly. The process chip includes a fluid chamber including and an optically transmissive material adjacent to the fluid chamber. The process chip is to be removably positioned in relation to the dynamic light scattering assembly. The dynamic light scattering assembly is to direct the light through the optically transmissive material and into the fluid chamber. The dynamic light scattering assembly is further to receive light scattered by particles in fluid in the fluid chamber in response to the first optical fiber emitting light into the fluid chamber and thereby capture light scattering data. A processor determines viscosity of fluid in the fluid chamber based on the captured light scattering data. The processor also determines one or both of size or size distribution of particles in the fluid based the captured light scattering data.