Recent years have seen considerable progress in the development of microfluidic systems for use in the chemical and biological sciences. At a primary level, interest has been stimulated by the fact that physical processes can be more easily controlled and harnessed when instrumental dimensions are reduced to the micron scale. For example, it is well recognized that when compared to macroscale instruments, microfluidic systems engender a number of distinct advantages with respect to speed, analytical throughput, reagent usage, process control, automation and operational and configurational flexibility. In general terms, such systems define new operational paradigms and provide predictions about how molecular synthesis and analysis might be revolutionized in the coming years.   

Nanomaterials exhibit optical and electronic properties that depend on their size and shape, and are seen as tailored precursors for functional materials in biological sensing and optoelectronics. These critical dependencies indicate that ‘bottom-up’ approaches for nanomaterial synthesis must provide for fine control of the physical dimensions of the final product. Synthetic routes have attracted interest owing to their versatility and ease of use, but for many applications deviations about the mean particle diameter must be <1% to achieve the desired selectivity. This is beyond the tolerance of standard macroscale syntheses, and it is almost always necessary to use some form of post-treatment to extract the desired particle size.

Microfluidic systems provide an ideal medium for nanoparticle production. Since both mass and thermal transfer are rapid, temperatures may be defined with precision or varied on short timescales. Additionally, reagents can be rapidly and efficiently mixed to ensure homogeneous reaction environments, while allowing for additional reagents to be added at predefined times. My lecture will describe how we have utilized microfluidic reactors to perform highly efficient nanomaterial synthesis. Specifically, I will describe the controlled synthesis of fluorescent nanoparticles using continuous flows. Through incorporation of on-line detectors and efficient control algorithms the ‘intelligent’ synthesis of nanoparticles of varying size, shape and size-distribution becomes possible. Furthermore, I will discuss how droplets, formed when laminar streams of reagents are injected into an immiscible carrier fluid, can be used to synthesize a range of nanocrystalline materials including CdSe, all-inorganic perovskites, PbS and CuInS2 nanoparticles. Such droplets define picoliter volumes, with each acting as individual reaction vessels. Significantly, variation of the cross-sectional dimensions of microchannels can be used to regulate droplet volumes, with flow rate variations allowing control of reagent concentrations.