Precisely shaped polymeric particles and structures are widely used for applications in photonic materials, MEMS, biomaterials and self-assembly. Current approaches for particle synthesis are either batch processes or flow-through microfluidic schemes that are based on two-phase systems, limiting the throughput, shape and functionality of the particles. We report a one-phase method that combines the advantages of microscope projection photolithography and microfluidics to continuously form morphologically complex or multifunctional particles down to the colloidal length scale. Exploiting the inhibition of free-radical polymerization near PDMS surfaces, we are able to repeatedly pattern and flow rows of particles in less than 0.1 s, affording a throughput of near 100 particles per second using the simplest of device designs. Polymerization was also carried out across laminar, co-flowing streams to generate Janus particles containing different chemistries, whose relative proportions could be easily tuned. This new high-throughput technique offers unprecedented control over particle size, shape and anisotropy.

High-throughput screening for genetic analysis, combinatorial chemistry, and clinical diagnostics benefits from multiplexing, which allows for the simultaneous assay of several analytes but necessitates an encoding scheme for molecular identification. Current approaches for multiplexed analysis involve complicated or expensive processes for encoding, functionalizing, or decoding active substrates (particles or surfaces) and often yield a very limited number of analyte-specific codes. We present a method based on continuous-flow lithography that combines particle synthesis and encoding and probe incorporation into a single process to generate multifunctional particles bearing over a million unique codes. By using such particles, we demonstrate a multiplexed, single-fluorescence detection of DNA oligomers with encoded particle libraries that can be scanned rapidly in a flow-through microfluidic channel. Furthermore, we demonstrate with high specificity the same multiplexed detection using individual multiprobe particles.

Polymeric particles in custom designed geometries and with tunable chemical anisotropy are expected to enable a variety of new technologies in diverse areas such as photonics, diagnostics and functional materials. We present a simple, high throughput and high resolution microfluidic method to synthesize such polymeric particles. Building off earlier work that we have done on continuous flow lithography (CFL) (D. Dendukuri, D. C. Pregibon, J. Collins, T. A. Hatton, P. S. Doyle, Nat. Mater., 2006, 5, 365-369; ref. 1), we have devised and implemented a new setup that uses compressed air driven flows in preference to syringe pumps to synthesize particles using a technique that we call stop-flow lithography (SFL). A flowing stream of oligomer is stopped before polymerizing an array of particles into it, providing for much improved resolution over particles synthesized in flow. The formed particles are then flushed out at high flow rates before the cycle of stop-polymerize-flow is repeated. The high flow rates enable orders-of-magnitude improvements in particle throughput over CFL. However, the deformation of the PDMS elastomer due to the imposed pressure restricts how quickly the flow can be stopped before each polymerization event. We have developed a simple model that captures the dependence of the time required to stop the flow on geometric parameters such as the height, length and width of the microchannel, as well as on the externally imposed pressure. Further, we show that SFL proves to be superior to CFL even for the synthesis of chemically anisotropic particles with sharp interfaces between distinct sections.