Custom density fluorescent tracer fabrication via microfluidics

A microfluidic system for creating custom density tracer particles with low polydispersity is described in which the particle density can be fine-tuned by varying the salt concentration in the core of a double-emulsion droplet. The droplets are generated in a glass-capillary, co-flow device and then solidified lithographically for use in a variety of flow experiments, including particle-image velocimetry and multi-phase flows. The novel use of solidified, double-emulsion droplets for flow tracers provides precise control of particle density, size, shape and fluorescent properties in a form that can be easily implemented in standard, macroscale laboratory settings.