Fluorescence correlation spectroscopy (FCS) setup for short-time diffusion and microrheology studies in soft and biological materials

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Soft and living materials have a few common characteristics. First, they exhibit self-assembly on length scales spanning the nanoscale and the microscale. Second, they are easily driven out of equilibrium by external stimuli - forces, food - and they can achieve different non-equilibrium steady states as a function of the energy injection. Third, the role of hydrodynamic interactions (where macromolecular motions affect the flow of the surrounding solvent, which in turn affects the motions of other macromolecules) is often very important. In order to quantify the role of hydrodynamic interactions (HI), it is critical to be able to track motions on short timescales, during which inter-molecular collisions are rare, at long times where the molecule has fully experienced the environment, and at all intermediate timescales. In my laboratory, we use well-honed fluorescence confocal microscopy and high-speed optical imaging techniques to elucidate structures and study both slow and fast dynamics of large, micron-scale colloidal suspensions. As part of this strategy, we use pulsed-field gradient NMR as a powerful way to study slow dynamics (i.e. long-time diffusivities) of nanoscale macromolecular systems such as proteins, polysaccharides, and macromolecular complexes. There is, however, a gap in our measurement capabilities: we are missing the short-time window (microseconds to milliseconds) for studying the fast dynamics (i.e., short-time and intermediate-time self-diffusivities) of nanoscale macromolecular systems. The current proposal is a request for detectors, a hardware cross- and auto-correlator and a control computer in order to carry out fluorescence correlation spectroscopy (FCS) measurements in house. We have the optics (lenses and filters), a high-quality optics table, and a stable 488nm (blue), 50 mW laser, neutral density filters and power meter, and most importantly, the knowhow to construct the FCS system. What we are lacking and what we require to construct a fully operational FCS system are two detectors, the correlator hardware and a control computer. The FCS system will be utilized by a vibrant collaboration within the Biophysics group at Memorial in the study of macromolecular motions, that includes soft condensed matter physicists, physical chemists, biochemists, and simulation experts. This equipment will be essential for progressing and expanding the capacity of my NSERC-funded research programs to make major advances and further the development of my trainees to become skillful and competitive highly qualified personnel (HQP).