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Rice UniversityCBEN
Center for Biological and Environmental Nanotechnology

Measuring Nanoparticles in Biological and Environmental Settings

Figure 9.1.18

The dipole density (A) and potential (B) of a supported DOPC membrane as determined by analysis of electrostatic interactions measured with the AFM.

By developing new analytical methods, Theme 1 enables engineers in Theme 2 and Theme 3 to determine the structure, reactivity and dynamics of their materials.  The crux of the analysis problem can be found in the nature of the wet/dry interface.  The inorganic materials themselves (e.g. the ‘dry’ side) can be analyzed using electron microscopy, x-ray diffraction, and other tools common in solid state chemistry; unfortunately, these methods all destroy the more fragile ‘wet’ side.  Examination of the ‘wet’ interface using conventional solution phase methods often fails as the nanomaterial components interferes with the process.  As a result, to reach CBEN’s systems goals requires that its researchers constantly reinvent and rework characterization tools in order to manage the complex structure of nanoparticle -biological-environmental systems.  Equally important as CBEN’s research has matured is the importance of examining these issues in real-time using techniques that capture change.

This project area has over the years supported a diverse array of method development including spectroscopic analysis, chromatography, ultracentrifugation, force microscopy and most recently single molecule imaging techniques. This year, Hafner has continued his work to characterize the fundamental nature of the cell membrane, in particular its electrostatic features.  Several years ago, Hafner and Colvin found that nanoparticles preferentially deposit on supported membranes; the origins of these general phenomena were not apparent at the time but other CBEN researchers (Drezek, Alvarez) hypothesized such interactions were precursors for important cellular responses.  To quantitatively understand these interactions, the Hafner group has been working to more accurately measure the membrane potential and map this onto nanoparticles interactions using atomic force microscopy.  Matthews and Colvin CBEN researchers have also used conventional biophysical tools to examine the solution phase properties of bioconjugates; this effort was motivated initially by the need to distinguish between different stoichometries of nanoparticles-protein complexes.  More recently, due in part to the interest in separating Gold/Gold Sulfide particles in Theme 2, this effort has expanded to include quantitative AUC methods.  Finally, a growing area of attention has been the use of single molecule methods that track nanoparticles motion directly in environmental and biological media.  Link and Colvin have demonstrated the use of fluorescence to measure the dynamic light scattering from single particles; this information allowed them to determine the size of nanocrystalline magnetite both before, during and after the magnetic separations of interest in Theme 3.  Pasquali and Colvin have used nanoparticle tracking of fluorescent magnetite to measure intrinsic nanoparticle diffusion and related this to nanoparticle size.

In the remaining two years of funding, efforts in this project area will have three goals.  The first is to generate research publications that are general and summative in their presentation.  The second is to connect these methods to improved engineering outcomes. Finally, investigators will develop real value by translating their methods across themes.  AUC, for example, will be applied to studies of the nano-environmental complex while Link’s single molecule techniques will be adapted for cellular systems. Pasquali will complement this work by evaluating the dynamics of nanoparticles including nanotubes in complex media.

Participating Researchers: