Concentrating viral particles in electric field could lead to rapid
9 May 2007
Engineers in the US have solved a critical bottleneck in the
transport and capture of virus nanoparticles, making possible a device that
could rapidly sample and detect infectious biological agents, such as
viruses. They used electric fields to drive viral particles in solution to
electrodes to give concentrations high enough for rapid detection.
advance may pave the way for an 'on-the-spot' virus detector, which would be
immensely helpful, especially in military and public-health applications,"
said Paschalis Alexandridis, Ph.D., professor in the Department of Chemical
and Biological Engineering in the University at Buffalo School of
Engineering and Applied Sciences and co-author on the research.
describing the results was published in the March issue of Langmuir (vol.
23, p. 3840).
The rapid detection of viruses in biological samples is of
increasing interest, particularly with the recent emergence of new viruses,
including SARS, West Nile virus and avian flu virus.
But because viral
particles are present at such low concentrations in biological samples, such
as blood, a device that can quickly and easily detect them has remained
Typical procedures involve using passive diffusion to get the
viral particles to bind to an antibody, a slow process that is not feasible
for many applications, such as on the battlefield, where quick results are
Scientists at the University of Wisconsin at Madison led by
Nicholas L. Abbott, Ph.D., a co-author on the paper and John T. and Magdalen
L. Sobota Professor of Chemical and Biological Engineering, previously had
demonstrated that liquid crystals can amplify signals from low
concentrations of viral particles, quickly indicating whether or not a virus
is present on a surface.
"The bottleneck was how to transport and capture
enough suspected viral particles onto a surface in a timely fashion so that
they could be detected," said Alexandridis. "During the acute phase of an
infection, the virus is at a very low concentration and relying on passive
diffusion to deposit the viral particles onto the detection surface can be
The researchers wanted to speed up the collection of
viral particles — in this case, of vesicular stomatitis virus, a common
animal virus — at the right place on a substrate, while also doing it in
media at physiological ionic strength.
The UB researchers used their
expertise in a technique called directed assembly, in which they design
external electrical and fluid flow fields in order to "drive" nanoparticles
to specific locations and in specific concentrations on a substrate.
paper shows that by using electrodes separated by just a few micrometers
together with electrothermally induced fluid flow, we can accelerate the
transport of viral particles from aqueous suspensions with physiological
ionic strength to specific points on a surface, allowing them to reach local
concentrations high enough to allow subsequent rapid detection,"
"We hypothesized that the application of these
external fields would cause the nanoparticles to act in a certain way. We
designed electrodes to generate the required forces for the system of
interest and then put our design to the test."
In the research, the UB
engineers used directed assembly to tailor dielectrophoretic forces, which
act through a nonuniform electric field, overcoming an obstacle that occurs
whenever nanoparticles are involved.
"When you work with microscopic
objects dispersed in a liquid, gravity is very important," explained
Alexandridis. "But at the nanoscale, gravity doesn't matter. So when you are
trying to manipulate matter at the nanoscale, electrical fields and fluid
fields may work best. By using directed assembly, we can tailor the forces
acting on the nanoparticles. The ability to use several forces acting in
tandem becomes important."
Electrical fields in particular, he said, are
advantageous because by designing the electrodes in a certain way, engineers
can control directionality and intensity of electrical forces acting on
The research was conducted with colleagues from Queen's
University at Kingston, Ontario, Canada and the University of Wisconsin at