Issue 1, Volume 1
September 2007

Biology and Chemistry in the Physics Department?

By Jan Liphardt, Liphardt@physics.berkeley.edu

More-or-less complete part lists are now available for many biological systems, from E. coli to mice to humans. The "butterfly-counting" phase of biology is over. The focus of biology is changing to discovering the basic physical principles that govern biological systems. Biologists are now beginning to use words like flux, noise, and force in their papers.

There is a relevant parallel development, the increased control over "hard" nanoscale systems. The key idea is that finite size effects can be used to create new materials with unusual optical, magnetic, and mechanical properties for research and industry. Examples include carbon nanotubes, quantum dots, and semiconductor nanowires. My background is in single-molecule biophysics. I've been in the Berkeley Physics Dept. for 3 years. I joined the department because I wanted to learn about the properties of nanoscale systems and the tools that are used to characterize them. Another benefit is the ability to take on physics graduate students; their quantitative skills are essential in contemporary biophysics research.

Jessica Walter, a physics graduate student in my lab, has recently figured out how to synthesize light-powered bacteria. When these bacteria are illuminated with a green laser, they convert the light into a chemical potential and then into mechanical work: they swim when illuminated. It seems simple, but it can only be done if physical concepts are applied to this system. By modeling the E. coli bacterium as an electrical circuit with several batteries, capacitors, and resistors, Jessica was able to figure out how to modulate energy fluxes in these cells to make them light-responsive.

Aleksandra Radenovic, a physics postdoc, collaborated with Peidong Yang in the Chemistry Department to build a new kind of microscope. She used optical tweezers to pick up individual semiconductor nanowires. By choosing the material and trapping the wavelength just right, she did something more. The potassium niobate nanowires were able to frequency-double the trapping light: coherent green light radiated out both ends of the nanowires when they were optically confined by an infra-red laser. In this way, she invented a raster-scannable source of coherent visible radiation, which was featured on the cover of Nature in June.

Of course, these new opportunities and playing-fields for physicists also mean that we have to keep rethinking how we teach our students. Recently, the Advanced 111 Lab (many of you will be familiar with it!) has been significantly updated — numerous faculty, staff, students, and donors such as SRI International are involved in this effort. Among other things, most of the course materials are now online. Several new experiments are being developed, such as magneto-optical trapping of atoms, a ’Brownian motion and intracellular transport’ lab, and an ’optical trapping of cells’ lab. We are collaborating with MIT to make these experiments (and related materials) accessible to other universities around the world, and this effort is being funded by Microsoft Research. If you are in town, drop by and see what we are doing at Berkeley (tea and cookies are still at 4 pm), and if you are not in town, come visit!

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