Liphardt Lab Research
We're a biophysics lab. Our research focuses on understanding and controlling energy and information fluxes in biological systems. Our model systems range from E. coli bacteria to, in collaboration with other labs, eukaryotic cells such as Thymocytes. Current projects include super-resolution studies of protein clustering in membranes and single-molecule studies of movement of materials through biological pores and channels. We also develop tools for characterizing cells and molecules, such as super-resolution light microscopy and interacting gold nanoparticles ("Plasmon rulers"). The lab is located in Stanley Hall, very close to the Campanile.
Patterns, Energy and Information
Self-assembly of Chemotaxis Proteins in E. coli
In collaboration with Eric Betzig, Hari Shroff, and Ned Wingreen, we are using super-resolution light microscopy to investigate how membrane proteins assemble and how they make patterns in membranes. Our overall goal is to relate biological spatial organization to function. The image shows a single E. coli cell expressing labeled Tar chemotaxis receptors. Each dot corresponds to one protein.
New Tools for Measurement and Control
Plasmon Rulers: a new tool for measuring molecular distances
A key problem in biophysics is the measurement of nm scale distances. In collaboration with the lab of Paul Alivisatos, we have been using characterizing the distance dependence of the plasmon resonance between two gold (or silver) nanoparticles. Unlike conventional dyes, noble metal nanoparticles do not blink or bleach, making it possible to track them, or use them to measure distances, for arbitrary durations. For an overview of our ongoing plasmon resonance work, please see the meeting report in Science 308 (2005).
Optical control of cellular proton-motive-force
We synthesize light powered and controlled forms of the E. coli bacterium to help us understand the conversion of light into mechanical work in biological systems. The images below show a single E. coli cell that is stuck to a surface and that rotates when illuminated with green light. The cell uses the Proteorhodopsin light powered pump to harvest photons, creating a proton-motive-force, that in turn drives the flagellar motor.
Optical Trapping and Manipulation of Nanowires
Semiconductor nanowires have unique optical and electronic properties. We're collaborating with the lab of Peidong Yang to find new ways of manipulating nanowires, and assembling them in to 3-D heterostructures. Primarily, we use optical tweezers to grab nanowires and fuse them to other wires and objects.
Polymer Physics; Nucleic Acids
Mechanical properties of RNA
RNA molecules perform many activities in the cell, including structural scaffolding, information transfer (e.g. mRNA and tRNA), and catalysis (e.g. catalysis of the peptide bond during protein synthesis). We would like to learn how RNA folds, and characterize the mechanical properties of RNA, such as resistance to mechanical stresses and strains.
Forces inside DNA loops
Imagine grabbing a single piece of DNA and trying to bend it. What are the forces needed to do that? We use force sensors with optical readout to directly measure the forces inside small, highly strained DNA loops.
