ABSTRACT
We review progress in the development of optical tweezers as sample manipulators for third-generation synchrotron radiation sources. X-ray microbeam small-and wide-angle scattering experiments discussed in this chapter have been performed by using a custom optical tweezers setup. We also outline opportunities for future technical and scientific developments of optical tweezers at third-generation synchrotron radiation sources and X-ray free-electron lasers. Synchrotron Radiation and Structural Proteomics Edited by Eugenia Pechkova and Christian Riekel Copyright © 2012 Pan Stanford Publishing Pte. Ltd. www.panstanford.com
6.1 INTRODUCTIONThe availability of intense microbeams and, more recently, nanobeams at third-generation synchrotron radiation (SR) sources allows probing local structures in hierarchically organized materials by small-angle and wide-angle X-ray scattering techniques (SAXS/WAXS) (Riekel, 2000; Paris, 2008; Riekel et al., 2009). These techniques have been applied to a variety of synthetic polymers (Riekel and Davies, 2005) and biological materials (Paris, 2008; Riekel et al., 2009) including protein microcrystals (Riekel et al., 2005). The small beam dimensions have also allowed the reduction of the investigated object dimension. Indeed it has become possible studying membrane protein crystals of a few micrometer dimensions which are difficult to crystallize (Riekel et al., 2005). Complementary imaging techniques such as X-ray microscopy and coherent X-ray diffraction imaging have contributed to an understanding of the structural properties of such systems (Huang et al., 2009; Lima et al., 2009). It is well known in biological research that single particle investigations (cells and biomolecules) may provide a more accurate understanding of the relation between the macroscopic functionalities and the microscopic properties, with respect to the averaged properties measured over a large population (Carlo et al., 2006; Knight, 2008). Such studies are best performed under in vitro or in vivo conditions to maintain macroscopic functionality. Although X-ray scattering techniques provide in principle excellent in situ capabilities for probing functional biological objects, radiation damage imposes usually experiments under cryoconditions (Lima et al., 2009). A possible alternative is to distribute the radiation dose across multiple copies of an object as already done in protein microcrystallography (Riekel et al., 2005). This calls for manipulation tools which allow both manipulating single objects under in situ conditions (e.g., a microfluidic cell) and provide sample replacement by handling a series of particles, one after another.Sample manipulation is commonly performed through mechanical contact which may induce mechanical deformations.
