Directed assembly of particles using microfluidic droplets and bubbles

Assembly of particles into three dimensional structures is critical for a variety of advanced applications including photonics, optics, catalysis, MEMS, drug delivery and biosensing. Needless to say, a precise control over the structure and properties of three-dimensional particle assemblies is essential in maximizing the functionality that is afforded by the particles in these structures. One method that enables rapid, inexpensive and potentially scalable assembly of particles involves using fluid droplets and bubbles as structure directing agents. Recent advances in microfluidics allow for the formation of highly uniform and structured droplets and bubbles that can be used to direct the assembly of particles into three dimensional structures. In this review, we introduce the recent developments in using microfluidic techniques to generate highly uniform and complex droplets and bubbles, which are subsequently used to direct the assembly of various nano and microparticles. We also highlight a number of functional supraparticles that have been shown to exhibit unique photonic and sensing properties. We conclude this review by providing an outlook on the current challenges and opportunities that need to be addressed for these microfluidic-based approaches to have a broader impact as widely applicable methods for directed assembly of particles.