Microfluidic platform for monitoring Saccharomyces cerevisiae mutation accumulation.

Mutations in DNA have large-ranging consequences, from evolution to disease. Many mechanisms contribute to mutational processes such as dysfunctions in DNA repair pathways and exogenous or endogenous mutagen exposures. Model organisms and mutation accumulation (MA) experiments are indispensable to study mutagenesis. Classical MA is, however, time consuming and laborious. To fill the need for more efficient approaches to characterize mutational profiles, we have developed an innovative microfluidic-based system that automatizes MA culturing over many generations in budding yeast. This unique experimental tool, coupled with high-throughput sequencing, reduces by one order of magnitude the time required for genome-wide measurements of mutational profiles, while also parallelizing and simplifying the cell culture. To validate our approach, we performed microfluidic MA experiments on two different genetic backgrounds, a wild-type strain and a base-excision DNA repair ung1 mutant characterized by a well-defined mutational profile. We show that the microfluidic device allows for mutation accumulation comparable to the traditional method on plate. Our approach thus paves the way to massively-parallel MA experiments with minimal human intervention that can be used to investigate mutational processes at the origin of human diseases and to identify mutagenic compounds relevant for medical and environmental research.

Quantifying the sol-gel process and detecting toxic gas in an array of anchored microfluidic droplets.

The detection of toxic gases is becoming an important element in tackling increased air pollution. This has led to the development of gas sensors based on porous solid materials, which are produced using sol-gel chemistry and functionalized to change their optical qualities when in contact with the gas. In this context it is interesting to explore how microfluidics can be used to miniaturize these sensors, to improve their sensitivity and dynamic range, or to multiplex many gas measurements on a single chip. In this article we show how the sol-gel process can be implemented using anchored droplet microfluidics. The sensor material is partitioned into droplets while in the sol phase and maintained using capillary anchors. The ability to hold the droplets in place first allows us to study the sol-gel process. We use an original rheology method, which consists of observing the flows within stationary droplets that are submitted to an external flow, to measure the gelation time of the droplets. These measurements show a gelation time that decreases from 50 minutes to below 10 minutes as the temperature increases from 20 to 50 °C. We also measure the shrinkage of individual gel beads after gelation and find that this syneresis process is nearly finished after about 12 hours, leading to a final bead size that is 50% smaller than the initial droplet. Finally, we show that the beads can be functionalized and used to detect the presence of formaldehyde. These results first provide a new way to observe the physics of the sol-gel process in a well-controlled and quantitative fashion. Moreover they highlight how the coupling of microfluidics and sol-gel chemistry can be used to detect toxic gases, in view of answering the challenges surrounding gas detection in real-world settings.