See scientist biological litmus paper invented to detect strains of ebola

Discs of souped-up filter paper could change
how we diagnose infections. To demonstrate
the power of the approach, which involves
embedding DNA from jellyfish and other
organisms into paper, its developers have
successfully used it to identify two strains of
Ebola.

Although far from being ready for testing in
west Africa, paper discs that detect the virus
are being developed for potential use as a
cheap, simple method to identify infected
people.
"It's a platform for a new class of diagnostics,
and a very clear and important practical
extension of synthetic biology, opening up a
whole generation of new technologies for
diagnosis," says Jim Collins of the Wyss
Institute for Biologically Inspired Engineering
at Harvard University in Boston,
Massachusetts.
The key to the technology is the ability to
print sequences of DNA on paper, then freeze-
dry and store the discs at room temperature.
The DNA is reactivated by adding water. Once
active, it enables the paper to change colour if
a chosen target – such as a segment of Ebola
viral RNA – is present in the water.
Test the rainbow
The target fragment binds to a gene switch in
the DNA, which triggers the production of a
colourful substance such as the protein that
gives jellyfish a green glow under ultraviolet
light, or proteins from bacteria that produce
colour changes visible to the naked eye. The
colour the paper changes to indicates which of
the target pathogens has been detected.
"We're extending the concept of litmus paper
to biochemical reactions, putting the power of
molecular biology onto paper," says Collins.
"It's actually very easy."
Keith Pardee, a colleague of Collins, improved
the test by inserting tailor-made gene
switches that prevent any colour change
happening unless a very specific target
molecule is present. Called toeholds, the
synthetic switches enabled the paper to
simultaneously test for 24 distinct regions of
viral RNA – many more than would have been
possible using only naturally occurring DNA
sequences. This provided a means to
distinguish between a synthetic version of the
Zaire strain of Ebola – the one responsible for
the west African epidemic – and a synthetic
version of another known as the Sudan strain.
The test identified the strains within 30
minutes, rivalling the speed of more expensive
and complex tests that use antibodies. Collins
estimates it cost just $21 to develop the
litmus sensor – the cost of buying the
sequences of DNA that detect the viral RNA.
The whole thing took just 12 hours to
assemble.