scientists and applied physicists collaborating at Harvard’s School of
Engineering and Applied Sciences (SEAS) have invented a new device that
can instantly identify an unknown liquid.
device, which fits in the palm of a hand and requires no power source,
exploits the chemical and optical properties of precisely nanostructured
materials to distinguish liquids by their surface tension.
finding, published in the Journal of the American Chemical Society
(JACS), offers a cheap, fast, and portable way to perform quality
control tests and diagnose liquid contaminants in the field.
encryption and sensors have become extremely sophisticated these days,
but this is a tool that will work anywhere, without extra equipment, and
with a very wide range of potential applications,” says co-principal
investigator Marko Lon?ar, Associate Professor of Electrical Engineering
to the litmus paper used in chemistry labs around the world to detect
the pH of a liquid, the new device changes color when it encounters a
liquid with a particular surface tension. A single chip can react
differently to a wide range of substances; it is also sensitive enough
to distinguish between two very closely related liquids.
hidden message can actually be “written” on a chip, revealing itself
only when exposed to exactly the right substance. Dipped in another
substance, the chip can display a different message altogether (see
highly selective wetting would be very difficult to achieve on a
two-dimensional surface,” explains lead author Ian B. Burgess, a
doctoral candidate in Lon?ar’s lab and in the Aizenberg
Biomineralization and Biomimetics Lab. “The optical and fluidic
properties we exploit here are unique to the 3D nanostructure of the
“Watermark Ink,” or “W-Ink,” concept relies on a precisely fabricated
material called an inverse opal. The inverse opal is a layered glass
structure with an internal network of ordered, interconnected air pores.
Lidiya Mishchenko (a graduate student at SEAS) and Benjamin D. Hatton
(a research appointee at SEAS and a technology development fellow at the
Wyss Institute for Biologically Inspired Engineering at Harvard),
recently perfected the production process of large-scale, highly ordered
factors determine whether the color changes upon the introduction of a
liquid: the surface chemistry and the degree of order in the pore
structure,” says Mishchenko, who works in the Aizenberg lab. “The more
ordered the structure, the more control you can have over whether or not
the liquid enters certain pores by just changing their surface
and his colleagues discovered that selectively treating parts of the
inverse opal with vaporized chemicals and oxygen plasma creates
variations in the reactive properties of the pores and channels, letting
certain liquids pass through while excluding others.
liquid into a pore changes the material’s optical properties, so the
natural color of the inverse opal shows up only in the dry regions.
chip is calibrated to recognize only certain liquids, but it can be
used over and over (provided the liquid evaporates between tests).
the hope of commercializing the W-Ink technology, the researchers are
currently developing more precisely calibrated chips and conducting
field tests with government partners for applications in quality
assurance and contaminant identification.
you want to detect forgeries,” says Burgess, “you can tune your sensor
to be acutely sensitive to one specific formulation, and then anything
that’s different stands out, regardless of the composition.”
immediate application would allow authorities to verify the fuel grade
of gasoline right at the pump. Burgess also envisions creating a chip
that tests bootleg liquor for toxic levels of methanol.
W-Ink technology would additionally be useful for identifying chemical
spills very quickly. A W-Ink chip that was calibrated to recognize a
range of toxic substances could be used to determine, on the spot,
whether the spill required special treatment.
device like this is not going to rival the selectivity of GC-MS [gas
chromatography-mass spectrometry],” remarks co-principal investigator
Joanna Aizenberg, the Amy Smith Berylson Professor of Materials Science
at SEAS and a core faculty member of the Wyss Institute.
the point is that if you want something in the field that requires no
power, is easy to use, and gives you an instant result, then the W-Ink
may be what you need.”
“W-Ink” research was supported by grants from: the Air Force Office of
Scientific Research; the Natural Sciences and Engineering Research
Council of Canada; and the U.S. Department of Homeland Security (DHS),
administered by the Oak Ridge Institute for Science and Education,
through an interagency agreement between the U.S. Department of Energy
microscopy was performed at Harvard’s Center for Nanoscale Systems,
part of the National Nanotechnology Infrastructure Network, which is
supported by the National Science Foundation.