Imaging and Characterization of Self-Assembled Soft Nanostructures
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Imaging and Characterization of Self-Assembled Soft Nanostructures Elizabeth F. de Souza1 and Omar Teschke2 1 PUC-Campinas, Faculdade de Química, Rodovia D. Pedro I, km 136, Parque das Universidades, Campinas, SP 13086-900, Brazil 2 UNICAMP, Instituto de Física Gleb Wataghin, Cidade Universitária Zeferino Vaz, Barão Geraldo, Campinas, SP, 13083-970, Brazil ABSTRACT Long-ranged double layer interactions and specific tip penetration through the scanned layers should be considered when atomic force microscopy (AFM) is used to probe soft samples such as surfactants or biological material within liquid media. Therefore, AFM imaging of soft nanostructures requires a careful adjust of the applied force and the scanning velocity. A paramount advantage of this technique is that cells immersed in liquids can be imaged under physiological conditions. On the other hand, confocal Raman microscopy (CRM) allows the realtime monitoring and chemical characterization of compounds also in a noncontact manner. The three-dimensional distribution of substances can be recorded by CRM with high spatial resolution by scanning a tightly focused laser beam over the sample. By combining of these two techniques (AFM and CRM), it is possible to obtain relevant information on formation processes, characteristics and behavior of soft self-assembled nanostructures and of cells on hydrophilic or hydrophobic surfaces under physiological conditions. INTRODUCTION Surfaces and interfaces are often facilitating chemical and physical changes and this function becomes more important if the size of matter is decreased down to the micro- and nanometer scale. A wide variety of chemical, physical and biological processes occur at liquidliquid or liquid-solid interfaces where soft nanometric structures are self-assembled. Even at room temperature, subtle changes in chemistry, pressure or temperature can strongly influence the physical or chemical properties of soft matter systems. Most of the biologically relevant matter is formed by soft matter and it is not surprising that an enormous diversity of biochemical processes exist in nature [1]. AFM has been increasingly used in biosciences. Theoretically, it combines the two most important aspects for studying structure-function relationships of biological specimens: highresolution imaging with high signal-to-noise ratio in the molecular/sub-molecular scale and the ability to operate in aqueous environments without any chemical fixation [2-4]. Beyond being an imaging device, AFM has evolved as an instrument for measuring molecular electrostatic and van der Waals interaction forces. However, it is important to ensure that imaging forces between the tip and sample are generally of similar magnitudes, because higher forces would lead to sample distortion or even destruction. Finally, a proper interpretation of the force-distance curves between interacting surfaces in AFM requires bacterial immobilization that fully preserves the chemical and structural integrity of the cell surface [5]. The potential of
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