Poster 7

Rongxin Huang UT-Physics

An Efficient Imaging Strategy for 3-D Scanning Probe Microscopy Scanning probe microscopy based on optical tweezers employs stochastic thermal motions of an optically trapped nano-particle as a natural scanner for three-dimensional imaging of objects with complex topography on the scale of hundreds of nanometers. This non-perturbing technique is especially suitable for imaging soft materials (e.g. biopolymer networks in their physiological conditions) with resolution an order of magnitude better than light microscopy. 3-D scanning probe microscopy is much more challenging than conventional 2-D surface scanning probe microscopy - such as AFM. The addition of the third dimension complicates the scanning paths and dramatically increases the scanning time required to obtain a complete object image. Imaging of soft biological materials, e.g. cell cytoskeletons or in vitro biopolymer networks, on a relevant length scale (a linear dimension on the order of 1 micron) becomes practically impossible. Scanning times approach several hours; drift in the sample and imaging instrument leads to image distortion. We used the fact that the volume fraction of biopolymer networks under physiological conditions is typically much less than 10% to develop a novel scanning strategy for exploring complex 3-D environments efficiently. During the imaging process, the probe particle is actively driven through vacant spaces (e.g. pores in a polymer network) and high-resolution thermal noise images are only acquired when the probe encounters an object (e.g. a polymer filament). We demonstrated the feasibility of this approach by imaging micron-sized microfluidic channels. The combination of active scanning and local high-resolution thermal noise imaging reduces the sampling time by at least an order of magnitude and preserves the high resolution capability of this technique. This paves the way for its application for imaging soft material systems.