Wet electrostatics and biomolecular self-assembly Gerard C. L. Wong, University of Illinois at Urbana Champaign, DMR Ring-like stains are commonly observed in dried drops of coffee. This ‘coffee ring’ phenomenon has been observed in general for dried colloid solutions. We show that when a droplet of DNA solution is dried on a surface instead, which is how many DNA microarrays are created, a ‘coffee-ring’ is also formed, but contrary to intuition, the extended DNA molecules form a liquid crystal with concentric chain orientations to minimize energy. Essentially all the DNA is concentrated in a thin annular ring at the droplet edge. Moreover, the DNA is organized into a periodic zig-zag pattern due to the stress from drying. An understanding of these effects can lead to improved reproducibility in ‘gene chip’ microarrays, in which DNA droplets are sequentially deposited onto a surface for hybridization studies. Magnified polarizing microscopy image of pattern formation in a dried droplet with fluorescently labeled tracer DNA. The liquid crystalline pattern shown is found in ‘coffee-ring’-like deposits from drying drops of DNA solution

Wet electrostatics and biomolecular self-assembly Gerard C. L. Wong, University of Illinois at Urbana Champaign DMR Electrostatics interactions are important in biology and colloid science. For example, all nucleic acids (DNA, RNA) is charged. All cell membranes are charged. Most proteins are charged. While electrostatics are well understood in a vacuum (say for example, Coulomb’s Law from High School physics), these interactions are extremely complicated in water. (This is largely due to the long-range nature of the interaction and the entropy of free ions.) An understanding of these interactions is important for a wide range of applications, including gene therapy, cancer vaccines, water purification technologies, and emerging biomimetic strategies for growing semiconductor nanocrystals based on our understanding of how bones and abalone shells are grown in nature.

Education: Researchers with a wide range of backgrounds contributed to this research program. This includes 6 undergraduates (Rynae Boler, Chrysa Prestia, Michael Strohman, Chuck Vrasich, Aaron Goodman, and David Lee), 2 graduate students (Olena Zribi, Nathan Schmidt) and 1 post-doctoral researcher (Ivan Smalyukh). Ivan and Olena are the main contributors to this work. At least three of the undergraduates will be co-authors on manuscripts this year (Michael, Aaron, David). Two of our undergraduates have graduated: Michael has gone on to graduate school at Stanford University, and Aaron has gone on to medical school at Emory University. Wet electrostatics and biomolecular self-assembly Gerard C. L. Wong, University of Illinois at Urbana Champaign, DMR Societal Impact: The effect we observe need to be accounted for in the design of ‘gene chip’ DNA arrays in which multiple DNA droplets are 'spotted' on glass surfaces for subsequent hybridization studies. Since essentially all the DNA is concentrated in a thin annular ring with almost no DNA in the center of the dried drop, it is possible for these studies to get false negatives by ‘missing’ all the DNA in a ring stain even if perfect center-of-mass alignment between droplets is achieved.

Soft matter physics can be translational research. Our fundamental research on the physics of electrostatics in water will also impinge on an unsolved biomedical problem. Cystic fibrosis (CF) is the most common fatal, inherited disease in the United States. The average life expectancy is under 30 years. Electrostatic binding and inactivation of antibacterial cationic proteins to anionic polymers in the airways (ex. lysozyme and actin) contributes to long term infections and lung destruction in CF. Our fundamental understanding of this binding may lead to new therapeutic strategies. We currently have seven undergraduates actively doing research in this multicisciplinary program, and their experiments range from protein purification to antibacterial assays, and x-ray scattering experiments. At present we are experimenting with a new model for undergraduate research. Not only will we introduce our engineering and physics students to biology, we will also introduce engineering and physics to biology students, by bringing them into our research labs. (Rynae and David are from Materials Science, Chrysa, Elizabeth, Michael, Chuck and Aaron are from Molecular Biology.) It is hoped that more of them will wind up being interested in multi-disciplinary research through engineering. Wet electrostatics and biomolecular self-assembly Gerard C. L. Wong, University of Illinois at Urbana Champaign, DMR