Polydiacetylenes (PDAs) have attracted great interest due to their spectacular chromatic transition in response to external stimuli. In particular, application of shear stress induces a colorimetric transition from a non-fluorescent blue phase to a fluorescent red phase. This turn-on fluorescence in response to mechanical stress is sensitive to very small forces, which are typically quite difficult to measure. The talk will detail some of the recent work in my group developing a fluorescent mechanical stress sensor for cell traction forces.
The talk will cover techniques developed to fabricate high quality PDA Langmuir films and tune their properties towards different sensitivity regimes. Using a modified Surface Forces Apparatus (SFA), PDA Langmuir films were found to be an order of magnitude more sensitive to shear stress compared to normal loads/stress. The stress sensitivity could be varied by surfactant chain length, headgroup functionality, and the binding of specific di- and tri-valent counterions. To demonstrate the utility of the sensing films, we studied the migration of the slime mold Physarum polycephalum. Stresses exerted by the slime mold induced the blue to red transition. The paths explored by the slime mold and stresses exerted were determined from the PDA fluorescent response and revealed some unusual features of the interaction. Finally, the structural differences between blue and red phase PDAs were examined using Grazing Incidence X-ray Diffraction, X-ray Reflectivity and Atomic Force Microscopy in order to obtain an improved understanding for rational design.
Tonya Kuhl is a professor and chair of chemical engineering and a faculty member of the biophysics and biomedical engineering graduate groups at the University of California, Davis. A chemical engineer by training with a BS from University of Arizona and a PhD from UCSB, Tonya’s research interests are in the general area of colloidal science and self-assembly. Her group combines high resolution force spectroscopy with x-ray and neutron scattering techniques to understand and design the properties and structure of interfaces and thin-films. She also co-developed and co-teaches the most popular elective course offered at UC Davis ECH 1 “The Design of Coffee” to over 2,000 undergraduates each year.