With a light meter
and an app on his smartphone, researcher Jijo Vallooran is
measuring the
intensity of the birefringence signal of a sample.
(Image: Laboratory
Prof. R. Mezzenga / ETH Zurich)
(December 13, 2015) ETH
researchers led by Raffaele Mezzenga have developed a new diagnostic method. It
is based on Birefringence, the ability of substances to change the polarisation
state of light. With this method, doctors around the world can easily, rapidly
and reliably detect malaria, Ebola or HIV to name only a few.
Nothing could be simpler: a drop of blood is placed on a
special carrier substance; after a wait of a few minutes, the slide is placed
on a device that emits polarised light thanks to an inexpensive polarisation
filter. It is covered with a lid containing a second polarisation filter, which
blocks the light from all materials except crystalline or materials with
directional properties. If light is visible through the cross-polariser filter,
a positive diagnosis is made. Through this an immediate ‘yes or no’ screening
is possible. It is also possible to measure the light intensity, and thus the
amount of the pathogen, through a simple light meter plugged into a smartphone
and controlled via an app.
What sounds almost like science fiction has now become
reality. The research group led by Raffaele Mezzenga, Professor of Food and
Soft Materials, has recently published a scientific paper in which it
introduces a new rapid test that can detect not only malaria parasites but also
viruses such as HIV or Ebola, diverse bacteria or biomarkers, like glucose or
cholesterol.
Birefringence
pattern of a sample positive to Ebola infection.
(Image: ETH
Zurich/Jijo Vallooran)
The detection methods are not only extremely fast; they are
also considerably less expensive when compared with other detection methods.
The polarisation device costs just CHF 20, says Jijo Vallooran, first author of
the paper, which has just been published in the journal Advanced Functional
Materials.
Exploited
birefringence
Although the concept behind this new technology is very
general and appears so easy to operate, the scientific basis underlying the
invention of the ETH researchers is extremely complex.
The scientists use the phenomenon of birefringence of
polarised light from the lipid based lyotropic liquid crystals, which consist
of self-assembled structures of fat molecules in water. The group of Prof.
Mezzenga has been working with these liquid crystals for long time and exploits
them also for other applications, such as drug delivery and protein
crystallisation.
Prototype of the
cross-polarization device.
(Image: ETH Zurich / Jijo Vallooran)
Lyotropic liquid crystals organise themselves into special
networks with unique symmetry, which means that their basic motif repeats
itself periodically. In the case of liquid crystal cubic phases, the channels
are made of lipid bilayer membranes in water and have a diameter of just a few
nanometres, so only few free water molecules are available in the liquid
crystal, whereas the majority is bound to the channel walls. These liquid
crystal cubic phases are isotropic, or so to say, do not have any birefringent
properties, which means that if a slide with a layer of lyotropic liquid
crystal films is placed under a light source that allows polarised light to pass
through, it appears black when observed through another polarizer tilted at
90°.