Dynamics in a Broad Scale
Speaker: Valentine I. Vullev, UCal, Riverside
Series: Other Events
Location: J223 Equad
Date/Time: Tuesday, October 25, 2011, 3:00 p.m. - 4:00 p.m.
Dynamics in a Broad Scale
Valentine I. Vullev
Departments of Bioengineering, Chemistry, and Biochemistry,
and Materials Science and Engineering Program
University of California, Riverside
Riverside, CA 92521, USA
Understanding and utilizing dynamics, at various time scales and system sizes, represent
an underlying theme for most research projects in my group. Subpicosecond charge separation
(at a molecular scale) and millisecond to second fluid dynamics (in microfluidic devices, at
micrometer and millimeter scales) represent some of the extreme length and time scales that we
investigate. A range of synthetic, analytical, design and fabrication techniques, broadly used in
my lab, offer a liaison between basic science and applied engineering.
Nonlithographic fabrication, print-and-peel (PAP), allows for expedient and facile device
prototyping, offering key venues for expanding of the microfludics application beyond their
current realm. This presentation will review the development of PAP and focus on the means
for utilizing fluid dynamics for time-resolved spectroscopy. The laminar nature of microflows
characterized with low Reynolds numbers, allowed us to rely solely on steady-state imaging for
extracting excited-state kinetics of luminescent systems, demonstrating space-domain timeresolved
spectroscopy. Our microfluidics work in bacterial biosensing lead us to an important
insight about the dynamics of staining as a key characteristic of bacterial species. We observed
that, under certain conditions, the kinetics of fluorescence staining, quantified as a time constant
of the bacterium-induced emission enhancement, does not manifest concentration dependence.
Concurrently, the kinetics did depend on the bacterium and on the staining dye and was
statistically discernable for many of the different species that we investigated. This finding
presents an important venue for bringing the bioanalytical methodologies beyond their centuryold
tradition of Boolean logic.
In relevance to solar energy conversion, the second part of the talk will focus on the
kinetics of photoinduced charge transfer mediated by biomimetic and bioinspired systems.
Protein-mediated electron-transfer processes sustain a broad range of redox functions in
biological systems, such as respiration and photosynthesis. Therefore, such biological systems
are indispensable âworkingâ? models for molecular design and for the development of materials
for solar-energy-conversion and electronics applications. Modulation of charge transfer by local
electric fields presents an alternative approach for achieving long-lived charge-separated states.
Macromolecular electrets provide local field gradients in the order of 0.1 GV/m and degeneracy
of charge-transfer states essential for directionality of electron and hole entrainment. (Electrets
are the electrostatic equivalent of magnets: i.e., they possess ordered electric dipoles.) The
presentation will cover our designs of bioinspired electrets and discuss their properties.
The third part of the talk will cover our advances in single-molecule force-modulated
kinetics. This methodology offers unique capability for direct observation of a range of
structure-function relations. For example, it is the only experimental approach that allows direct
estimation of the displacements of the transition states during bimolecular interactions. Despite
the conceptual simplicity of single-molecule force techniques, certain experimental design
challenges, which will be discussed, have prevented such methodologies from becoming
routinely used tools. Employing controlled surface chemistry, for example, allows us to address
some of these issues.