Integration of protein processing steps on a droplet microfluidics platform for MALDI-MS analysis.

A droplet-based (digital) microfluidics platform has been developed to prepare and purify protein samples for measurement by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Liquid droplets are moved in air by sequentially applying an electric potential to an array of electrodes patterned beneath a hydrophobic dielectric layer. We show that a complete integrated sequence of protein processing steps can be performed on this platform, including disulfide reduction, alkylation, and enzymatic digestion, followed by cocrystallization with a MALDI matrix and analysis of the sample in situ by MALDI-MS. Proteins carbonic anhydrase, cytochrome c, and ubiquitin were used to demonstrate the digestion and postdigestion steps; insulin, serum albumin, and lysozyme were used to illustrate the complete sequence of protein processing steps available with the platform. Several functional improvements in the platform are reported, notably, the incorporation of acetonitrile in the protein droplets to facilitate movement, and patterning the device surfaces to optimize sample crystallization. The method is fast, simple, repeatable, and results in lower reagent consumption and sample loss than conventional techniques for proteomics sample preparation.

Transport of live yeast and zebrafish embryo on a droplet digital microfluidic platform.

We demonstrate the first programmed transport of live yeast (Saccharomyces cerevisiae) and a zebrafish embryo (Danio rerio) within droplets in a two-plate digital microfluidic device. The yeast remained viable after transport, and the actuated droplets left no yeast behind. A zebrafish embryo transported 2 hours after fertilization developed normally and hatched. Dechorionation was demonstrated by mixing a droplet of digestive reagent droplet with a droplet containing the embryo. These results demonstrate the potential for using a droplet microfluidic device as an alternative to microwell plates for yeast and zebrafish assays.