(625e) Determining the Size of Protein Conjugated Nanoparticles By Quantifying Brownian Motion

Determining the
Size of Protein Conjugated Nanoparticles by Quantifying Brownian Motion

Katherine N.
Clayton¹, Janelle W. Salameh², Julia G. Fraseur^2*,
Nelda Portalatin-Vasquez^2*, Alyssa Panitch², Steven T.
Wereley¹, Tamara L. Kinzer-Ursem²

¹School of Mechanical
Engineering, Purdue University

²Weldon School of
Biomedical Engineering, Purdue University

As the field of colloidal science
continues to expand, tools for rapid and accurate physiochemical
characterization of colloidal particles will become increasingly important. Here, we present Particle Scattering Diffusometry
(PSD), a nanoparticle measurement technique that uses low sample volumes that
can be integrated into micro- or nanofluidic systems.
Based on the fundamental principles of diffusion, gold nanoparticles (100 nm)
in a 4
mL sample volume 
(or less) undergoing Brownian motion are imaged under dark field
microscopy and recorded with a CCD camera for ~8 seconds then processed using a
MATLAB algorithm. The diffusion coefficient of the
particles is calculated by correlating successive particle images (at time Dt) to one another (cross-correlation, s_c) and the particle
image with itself (autocorrelation, s_a) at a magnification (M).

The
size of the gold nanoparticles is then calculated from the Stokes-Einstein
equation.

We initially characterized the size of gold
nanoparticles with calmodulin (CaM), bovine serum
albumin (BSA), and lysozyme (Lyso) conjugated to the
particle surface. PSD was used to calculate the diffusion coefficient, polydispersity,
and biomolecule layer thickness on the gold nanoparticles. Post-characterization,
the presence of protein monolayers on gold nanoparticle surfaces was measured
in order to investigate the sensitivity in diffusion coefficient measurements
of PSD. Differentiating the change in the gold nanoparticle diffusion
coefficient down to protein enables PSD to be used in lieu of common laboratory
workflows. Therefore, we are currently applying PSD for the detection of inflammatory
cytokines and characterization of proteins involved in learning and memory.

In summary, we have established a rapid (seconds)
and sensitive (protein monolayer) technology for characterizing
biomolecular surface modifications in very low sample volumes (microliters)
using instrumentation and tools that are common to most laboratory
settings. In this presentation we will to
discuss the development of the PSD technique, our current results and
challenges associated with PSD measurements, as well as future work to size particle samples
and as a tool for molecular diagnostics and characterizing protein dynamics.