Surface properties of nanoscale supramolecular particulates play important roles to determine their assembly behavior and functionalities. Their direct evaluation often evades the common structure examination techniques like x-ray/neutron diffraction and electron microscopy. Instead, they are often indirectly inferred or interpreted/rationalized based on the structure and property of the final products. In addition, the various non-covalent intermolecular interactions are intrinsically utilized in supramolecules design, synthesis and assembly. Their surface properties are expected to be highly susceptible to solvation/suspension media environments, a fact that is employed as an effective mean to achieve the complex structures and adaptive properties of a supramolecular material. Therefore, for experimental attempts of effective evaluation of surface properties of supramolecular nanoparticles, the critical requirements should include, but not limited to, non-invasive (in-situ) nature of measurement techniques used. It is prohibited in many cases to use common scanning probe techniques like atomic force microscopy (AFM).Laser light scattering serves as a viable tool for the purposes of in-situ experimental probe on supramolecular nanoparticles. The nanoscale hydrodynamics of particulates can be readily quantified with spectral broadening and shift of the light signal scattered from them, a form of Doppler Effect. In the present study, we demonstrate sensitivity and precision of the techniques using common proteins, the biological macromolecules inspire many synthesis efforts of supramolecules. Brownian motion and electrophoretic motion of protein molecules are directly evaluated in terms of their mean-square-displacement under thermal agitation and electrophoretic mobility under an electric field, respectively. From the measurement results, the surface characteristic of nanoparticles, such as surface area, surface charge density and electrostatic force/potential range (Debye length), can then calculated with Stokes-Einstein equation of translational friction force and Debye-H�ckel-Henry theory of electrophoretic effect. Furthermore, it is shown that the effects of solvation/suspension media can be assessed well within the measurement certainty. The observation is discussed in the context of the well-established electrostatic double layer (EDL) theory.

Surface properties of biological macromolecular nanoparticles revealed via their nanoscale hydrodynamics

248th National Meeting (2014)

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