One of the applications of microfluidics that we are investigating is the study of metastable fluids. We work with deeply supercooled water, which is still liquid at temperatures around -37 ºC. Producing supercooled water at such temperatures remains challenging despite decades of experimental research, but we demonstrated that using microfludics we can develop better methods for producing and handling supercooled water.
We recently developed a high-accuracy and high-speed instrument for studying supercooled water by investigating how statistical ensembles (more than 10 000 systems) of ~100-micron diameter drops of water freeze by homogenous nucleation of ice. This experimental platform is faster and more reliable than any other previous instruments for the study of ice nucleation.
Using this instrument we have performed some of the most accurate measurements of the rate of homogenous nucleation of ice in supercooled water; we also measured the rates of heterogeneous ice nucleation due to immersed solid particles with high accuracy and over extended temperature ranges. Another fundamental question that we investigated is whether electric fields have an effect on the homogenous nucleation of ice in supercooled water; we did not observe any effects, despite applying the largest electric fields ever used in this type of experiment.
One of the major goals of the lab-on-a-chip community is the integration of all instrumentation into a small portable device that, ideally, would also be simple and significantly cheaper. Another major goal is to find applications and systems that work best integrated in a microscale system. Achieving these goals requires creative designs that have no counterpart in a macroscale setup.
We have built a liquid-core liquid-cladding lens in which the laminar flow of two unmixed fluids provides a dynamically variable interface of optical quality (Figure 4). The curvature of the interface between liquids is generated by the expansion of fluid streamlines in a wider region of a microfluidic channel. One advantage of this type of lens design is that it can be easily integrated in a microfluidic chip – since it is made of fluids rather than of solid optics. We have shown that this type of lens has very good quality compared with other adaptive lenses designed for microanalytical applications.
We explore the use of different techniques to facilitate the study of the worm Caenorhabditis elegans, a popular model organism in modern biology (Figure 5). The general characteristics of the microfluidics devices are that:
We use magnetic levitation to explore whether the nematode C. elegans can be a useful model organism for diseases related to the accumulation of fat. The accumulation of excess fat is associated with a number of adverse medical conditions, including liver failure due to hepatotoxicity, obesity, and fatty liver disease. The accumulation of fat changes the density of the worm which is then measured with magnetic levitation. The levitation height of the worms between the two magnets is proportional to their density and therefore, their fat content (Figure 6).