Max Planck scientists develop fundamentals for new microfluidic and nanofluidic devices
Atomic (or scanning) force microscopy images of liquid morphologies on silicon substrates with rectangular surface channels which have a width of about one micrometer. On the left, the liquid does not enter the channels but forms large lemon-shaped droplets overlying the channels (dark stripes). On the right, the liquid enters the channels and forms extended filaments separated by essentially empty channel segments (dark stripes). In the bottom row, several parallel surface channels can be seen in both images; in the top row, there is only one such channel with a single droplet (left) or filament (right). Close inspection of the upper right image reveals (i) that this filament is connected to thin wedges along the lower channel corners and (ii) that the contact line bounding the meniscus of the filament is pinned to the upper channel edges. Image: Max Planck Institute for Colloids and Interfaces
Morphology diagram as a function of the aspect ratio X of the channel and the contact angle q which characterizes the interaction between substrate material and liquid. This diagram contains seven different morphology regimes which involve localized droplets (D), extended filaments (F), and thin wedges (W) in the lower channel corners. The diagram represents a complete classification of all possible wetting morphologies and should be universal, i.e., it should apply to different liquids and substrate materials. Image: Max Planck Institute of Colloids and Interfaces
The labs of the future will be "labs-on-a-chip", i.e., integrated chemical and biochemical laboratories shrunk down to the size of a computer chip. An essential prerequisite for such labs are appropriate microcompartments for the confinement of very small amounts of liquids and chemical reagents. Directly accessible surface channels, which can be fabricated by available photolithographic methods, represent an appealing design principle for such microcompartments and, thus, provide a new route towards open microfluidic and nanofluidic systems. Scientists from the Max Planck Institute of Colloids and Interfaces, the Max Planck Institute of Dynamics and Selforganization and the University of California in Santa Barbara have shown that such open systems are possible in general but only if the geometry of the surface channels is carefully matched with their wettability (PNAS 102, 1848-1852 (2005).
Many research groups around the world work towards the construction of "labs-on-a-chip" in order to integrate chemical and biochemical analyzers on the micrometer or even nanometer scale. These devices will significantly change the way in which research is performed in the life sciences since they offer the ability to work with much smaller reagent volumes, much shorter reaction times, and the possibility of massive parallel processing. In general, this should lead to increased throughput and, thus, to reduced cost of (bio)chemical analysis. In addition, such integrated labs-on-a-chip have many potential applications in biomedicine and bioengineering. In the context of biomedicine, for example, they could provide fast and detailed analysis of blood samples in the physicians office without the need to wait several days before the sample has been returned from specialized laboratories. Other applications include customized chips for space travel in order to monitor microbes inside spacecraft or to detect life on other planets.
Dr. Bernd Wirsing | EurekAlert!
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