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Applying microdroplets as label-free sensors for reactions inside the droplets

Hofmann, Tobias Wolfgang

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Droplet-based microfluidics offers tremendous capabilities for high-throughput-screening systems, but so far, the dearth of appropriate analytical assays has limited its widespread application. Here, we present a novel, label-free sensor method for the detection of biochemical reactions inside of micron-sized droplets. The method exploits the osmotically driven change in droplet size as a quantitative marker of the total osmolarity. Changes in osmolarity, which originate, for example, from the metabolic activity of cells, can be detected down to a few mOsm/l. We characterize the sensor system by investigating mixtures of two types of monodisperse aqueous droplets in oil, containing various, fixed amounts of solute. Differing concentrations of solute induce water flow between the droplets through the oil, compensating for the osmotic pressure until equilibrium is reached. The flux is mediated by the diffusion of reverse micelles and increases with increasing differences in solute concentration. We apply the method to monitor and quantify the metabolic activity of encapsulated yeast at the single cell level and demonstrate its use for live/dead assays. Due to its simple and broadly applicable principle, our novel sensor method provides a powerful analytical tool for screening applications, and advances the evolution of high-throughput-screening systems with droplet-microfluidics.

Item Type: Dissertation
Supervisor: Spatz, Prof. Dr. Joachim
Date of thesis defense: 8 February 2013
Date Deposited: 06 Mar 2013 13:09
Date: 28 February 2013
Faculties / Institutes: Fakultät für Chemie und Geowissenschaften > Institute of Physical Chemistry
Subjects: 530 Physics
600 Technology (Applied sciences)
Uncontrolled Keywords: microfluidics, droplet, osmosis
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