With co-funding from the Instrument Development for Biological Research and the Chemistry of Life Processes programs, the Chemical Measurement and Imaging program is supporting an EAGER award to Prof. Jason Hafner of Rice University, seeking new ways to characterize structures like biological membranes - the thin sheets of molecules that support many critical biological functions of living cells. While the external electrical properties of membranes are well understood, their internal electrical properties are not. One such internal property is the dipole potential, which arises from molecular alignment in the membrane. Although this potential has been studied for decades, it is among the least understood aspects of membranes. There is currently no definitive measure of the size of this potential, or even agreement about which components of the membrane create it. It has been hypothesized that this potential significantly affects membrane biology, but such a correlation has not been confirmed since there is currently no satisfactory way to measure the dipole potential. This project will further develop a recently discovered method to measure the membrane dipole potential using an atomic force microscope (AFM).
These activities will result in a quantitative tool to measure an important yet poorly understood property of biological membranes, the site of many critical biological functions and the actions of most drug molecules. Students will be supported and trained in an interdisciplinary manner in both experimental research and theoretical simulations. The research results and instrumentation concepts from this project will be used in 9th grade Integrated Physics and Chemistry (IPC) teacher training programs at Rice. The work will also provide research experiences for summer teacher interns in Prof. Hafner's laboratory.
The goal of this project was to explore the lipid membrane "dipole moment" - a voltage that exists inside cell membranes and is very difficult to measure - with an instrument called an atomic force microscope. During the course of the project, we found that the atomic force microscope measurements were unlikely to be useful for biological researchers who study cell membranes, so we changed our plan to find an optical method to evaluate the environment inside the membrane. We settled on a method called "Surface Enhanced Raman Spectroscopy" (SERS) which gives a great deal of chemical information but had not yet been applied to biological structures. To do so we encapuslated gold nanoparticles (which create SERS) with model biomembranes and studied their chemical structure. In addition to our work, this progress will be important for researchers who are using gold nanoparticles in medicine, such as for cancer detection and therapy. With a good chemical method to evaluate the biomolecules attached to nanoparticles, researchers can better target the nanoparticles to disease sites. The research results were also used to illustrate physics concepts in a high school teacher professional development collaboration with Houston Independent School District (HISD), in which 40 high school teachers improved their physics content knowledge, became proficient in teaching with inquiry methods, and received course materials and lesson plans for use at their school. This impact will reach hundreds of students in HISD, the larfourth largest school district in the US.
