Simultaneous size and color tuning of polymer microparticles in a single-step microfluidic synthesis: particles for fluorescence labeling

In the droplet-based microfluidic synthesis, the formation, precise control and tuning of the droplet sizes are important parameters, and therefore construction of an appropriate microreactor for the generation of precise-sized droplets is crucial. Droplets, enclosed with functional additives, come into contact with UV light and initiate the polymerization reaction. In general, co-flow and flow focusing arrangements are widely used for generating the homogeneous particles. However, the size of the particles is always in the micrometer to millimeter range only. Considering this issue, here in this paper size controlled poly-tripropylene glycol diacrylate (poly-TPGDA) microparticles with a broad size range down to the micron are produced in a silicone holeplate based distinct micro cross-flow set-up. Different surfactants and their concentrations along with flow rate ratios of both immiscible phases play a crucial role in tuning the particle size in a wide range between 40 mm and 500 mm. Besides the size of the microparticles, a controlled composition of differently fluorescence active dyes tunes the fluorescent properties of microparticles by modifying the microfluidic arrangement. Mixing of the monochromatic fluorescent particles and multi-coloured particles of different sizes creates a huge range of patterns for multi-fluorescence labeling. Here we present the broad range of size as well as color tuned polymer microparticles in a single-step continuous microfluidic procedure, and characterize them by SEM, light microscopy and fluorescence microscopy.