Angewandte Chemie International Edition 2009, 48, 2376–2378
Tracking Individual Particles
Electrochemical technique follows the motion of individual microparticles in space and time
Contact: Richard G. Compton, University of Oxford (UK)
Registered journalists may download the original article here:
A Method for the Positioning and Tracking of Small Moving Particles
bacteria are able to “swim” through liquids by means of a flagellum.
When doing this, some bacteria follow attractants, some flee from
harmful substances, and others align themselves using light, gravity, or
magnetic fields. These processes may also play a role in infections.
Following a swimming bacterium without influencing its motion is
difficult. Nanotechnology researchers are also interested in determining
the motion of nanoparticles, which would be useful for the development
of nanomotors, for example. A team from the Universities of Oxford and Cambridge
(UK) has now developed a new, electrochemical method for
locating microscale objects as they move through a liquid. As they report
in the journal Angewandte Chemie, researchers led by Richard G.
Compton were able to use an array of microelectrodes to follow the
two-dimensional motion of a tiny, individual basalt sphere in space and
British researchers’ new process is based on a simple arrangement of
four tiny electrodes (150×150 µm) at the bottom of a small cell. Each
electrode can be addressed individually. In order to demonstrate that
their approach works, the researchers carried out experiments with a
basalt sphere with a diameter of about 330 µm. They used a magnet
underneath the base of the cell to move the magnetic basalt sphere. The
magnet was positioned by means of a stepper motor.
the cell is a solution containing an electroactive compound. When the
sphere comes close to one of the microelectrodes, it gets in the way of
the molecules of this compound, which are trying to get to the
electrode. This disruption of the diffusion field changes the current
response of the electrode. The presence of the sphere is detectable up
to a distance of 0.5 mm from the electrode. The sphere was put into many
different positions and the corresponding current response curves of the
electrodes were recorded. At the same time, the researchers documented
the corresponding positions of the spheres with video. This allowed them
to calibrate their measurements so that the position of the spheres
could be determined by means of the current response curves of the
researchers would now like to reduce the scale of their technique. They
are developing electrode arrays for a spatial resolution at the
submicrometer level, which would also allow them to follow significantly
smaller particles with sub-microsecond resolution.