The Department of Biomedical Engineering, Johns Hopkins University School
of Medicine is using the NanoSight
LM10-HS system to study self-assembled polymer/DNA particles for drug delivery.
The main research interests of Dr Jordan Green of the Biomaterials and Drug
Delivery Laboratory are in cellular engineering and nanobiotechnology. Knowledge
of particle size is of particular value in the characterization of different
drug delivery systems. Having had previous experience using dynamic light scattering
techniques, Dr Green and his team now also use the complementary technique of
nanoparticle tracking analysis from NanoSight. NTA provides insight into their
samples particularly those with polydisperse behavior.
The laboratory chose the NanoSight LM10-HS system equipped with an EMCCD high
sensitivity camera and a 404 nm laser for particle sizing analysis. In a typical
study, particle solutions were diluted in DI water to adjust the sample concentration
to a level such that there were approximately 30-60 light scattering centers
in the visual analysis window. A sixty second movie containing the Brownian
motion tracking of each individual particle was recorded. The movie was processed
to enable detection of a least 250 particle tracks per sample. The NTA analysis
gives a direct number-averaged distribution of the particle size as well as
absolute particle concentration. The mean, standard deviation and mode of the
particles is then calculated.
In this method, each individual particle is independently sized so that a direct
number-averaged mean can be calculated. As each particle is counted, a mode,
or the peak in the number distribution, can also be calculated. For monodisperse
particle populations, both DLS and NTA measured the same values for particle
size. However, NTA allowed finer distinction between peaks in samples that were
polydisperse. The uniformity of polymeric nanoparticle distribution is thought
to be a property of the polymer structure, and in particular, of the polymer
terminal group. Changes to polymer terminal group were also found to dramatically
change gene delivery efficacy of these nanoparticles in 2-D and 3-D cell systems.
Dr Green said that “To our knowledge, this is the first time that NTA
has been used for self-assembled polymer/DNA particles. Our results highlight
its utility, especially when combined with traditional DLS analysis.”