Here's a summary of some current and past research interests. Hopefully it's not too long!

Emergent behavior in biofilms:

Biofilms are communities of bacteria stuck together in a secreted extracellular matrix (for example). Biofilms of the species B. subtilis use electrical signaling to control their growth rate, resulting in remarkable stop/start oscillatory growth (growth video and signaling video). These growth-inhibiting electrical signals propagate from cell to cell on a time scale of minutes.

By looking at these biofilms with single-cell resolution, I’ve found that not all cells participate in this signaling. And the cells that do are organized in space in a very interesting way: the spatial distribution of signaling cells in the biofilm sits at a transition point between a weakly connected network and fully connected one. At this point, the biofilm has clusters of signaling cells of all sizes from that of a single cell to nearly the size of the community itself. For this reason, such a state is said to be “scale-free”: there is no characteristic length scale to the size of a signaling cluster. The following figure summarizes these findings.

 
percolation_and_cluster_dist.png
 

This pattern of organization may have emerged as a way to balance the community-level benefit of propagating an electrical signal with the individual-level cost of signaling, as illustrated in the next figure showing the connectivity of a biofilm signaling network. This “scale-free” phenomenon is an example of what is called a critical state. Critical states also arise outside the living world, for example in liquid-to-gas phase transitions. In recent years, the topic of whether biological systems exist near critical states has generated controversy and some very interesting papers (eg bird flocks, neural networks, and nice reviews here and here ).

 
phase_curve.png
 

The above is a summary of a paper published here.

Nanopores:

Nanopores are tiny holes in thin membranes. You can detect single biomolecules (eg nucleic acids or proteins) by pushing them through the pore with an electric field (see this famous paper). People have used them to do many cool things (eg sequencing and very cool biophysics experiments like this and this). I’ve used them to measure the ~microsecond-long transit of single folded proteins (journal link and pdf) and to concentrate large DNAs in nanoscale waveguides for single-molecule sequencing (journal link and pdf).