Mapping of fluidic mixing in microdroplets with 1 micros time resolution using fluorescence lifetime imaging.
ABSTRACT Microdroplets generated in microfluidic channels hold great promise for use as substrates in high-throughput chemical and biological analysis. These water-in-oil compartments can serve as isolated reaction vessels, and since they can be generated at rates in excess of 1 kHz, thousands of assays can be carried out quickly and reproducibly. Nevertheless, sampling the large amount of information generated from these platforms still remains a significant challenge. For example, considering the high droplet generation rates and velocities, reproducibility and micrometer resolution are challenging requirements that must be fulfilled. Herein we combine confocal fluorescence lifetime imaging microscopy with a statistical implementation that permits the analysis of mixing phenomena within microdroplets with a temporal resolution of 1 mus. Importantly, such exquisite resolution is only possible as a result of the large number of droplets sampled and their high structural reproducibility.
Article: Microfluidics using spatially defined arrays of droplets in one, two, and three dimensions.[show abstract] [hide abstract]
ABSTRACT: Spatially defined arrays of droplets differ from bulk emulsions in that droplets in arrays can be indexed on the basis of one or more spatial variables to enable identification, monitoring, and addressability of individual droplets. Spatial indexing is critical in experiments with hundreds to millions of unique compartmentalized microscale processes--for example, in applications such as digital measurements of rare events in a large sample, high-throughput time-lapse studies of the contents of individual droplets, and controlled droplet-droplet interactions. This review describes approaches for spatially organizing and manipulating droplets in one-, two-, and three-dimensional structured arrays, including aspiration, laminar flow, droplet traps, the SlipChip, self-assembly, and optical or electrical fields. This review also presents techniques to analyze droplets in arrays and applications of spatially defined arrays, including time-lapse studies of chemical, enzymatic, and cellular processes, as well as further opportunities in chemical, biological, and engineering sciences, including perturbation/response experiments and personal and point-of-care diagnostics.Annual Review of Analytical Chemistry (2008) 06/2010; 4:59-81. · 9.05 Impact Factor
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ABSTRACT: The development of microfluidic platforms for performing chemistry and biology has in large part been driven by a range of potential benefits that accompany system miniaturisation. Advantages include the ability to efficiently process nano- to femoto- liter volumes of sample, facile integration of functional components, an intrinsic predisposition towards large-scale multiplexing, enhanced analytical throughput, improved control and reduced instrumental footprints. In recent years much interest has focussed on the development of droplet-based (or segmented flow) microfluidic systems and their potential as platforms in high-throughput experimentation. Here water-in-oil emulsions are made to spontaneously form in microfluidic channels as a result of capillary instabilities between the two immiscible phases. Importantly, microdroplets of precisely defined volumes and compositions can be generated at frequencies of several kHz. Furthermore, by encapsulating reagents of interest within isolated compartments separated by a continuous immiscible phase, both sample cross-talk and dispersion (diffusion- and Taylor-based) can be eliminated, which leads to minimal cross-contamination and the ability to time analytical processes with great accuracy. Additionally, since there is no contact between the contents of the droplets and the channel walls (which are wetted by the continuous phase) absorption and loss of reagents on the channel walls is prevented. Once droplets of this kind have been generated and processed, it is necessary to extract the required analytical information. In this respect the detection method of choice should be rapid, provide high-sensitivity and low limits of detection, be applicable to a range of molecular species, be non-destructive and be able to be integrated with microfluidic devices in a facile manner. To address this need we have developed a suite of experimental tools and protocols that enable the extraction of large amounts of photophysical information from small-volume environments, and are applicable to the analysis of a wide range of physical, chemical and biological parameters. Herein two examples of these methods are presented and applied to the detection of single cells and the mapping of mixing processes inside picoliter-volume droplets. We report the entire experimental process including microfluidic chip fabrication, the optical setup and the process of droplet generation and detection.Journal of Visualized Experiments 01/2011;