Glowing beads make tiny bar
Technology Research News
Researchers from Corning, Inc. have found
a way to form tiny barcoded beads that are small enough to be embedded
in ink and attached to DNA molecules.
The beads measure 100 by 20 by 20 microns, which is just at the
edge of invisible. A micron is one thousandth of a millimeter.
The researchers made the coded beads by fusing together glass
doped, or mixed, with lanthanide metal oxide ions. These metal oxides
glow at certain wavelengths under ultraviolet light. Stripes of oxide
that glow different colors can be used to make codes.
The researchers have proved that 100 billion unique barcodes are
possible using the method, said Joydeep Lahiri, manager of biochemical
sciences at Corning. "This could be pushed further," he added
The microbeads could be be embedded in inks as a way to tag currency
and other documents to protect against counterfeiting, said Lahiri. They
could also be used for security purposes in everything from automobile
paint to explosives, he said.
The beads can also be used to keep track of different types of
DNA or other molecules in drug discovery experiments, according to Lahiri.
The researchers made the beads by fusing together glass doped
with lanthanide, drawing the mixture into a fiber, etching the fiber with
a laser, then breaking the beads along the cuts by putting them in an
ultrasonic water bath, said Lahiri.
There were three keys to developing the beads, said Lahiri.
The first was developing brightly-fluorescent glasses with good
surface chemistry that did not interfere with organic labels, he said.
DNA is often tagged with dye and identified by shining light on the dye
and measuring the wavelength of the resulting glow.
It was a challenge to figure out which doped glasses "have distinguishable
fluorescence to enable their decoding, but also do not interfere with
the fluorescence emitted from biological materials," said Lahiri.
The second key was finding a way to fuse and consistently draw
miles of banded ribbon fiber, he said. "Not only are they rectangular
ribbons, but [at 20 microns] these are probably the thinnest structured
glass fibers ever drawn," Lahiri said.
The third was being able to scribe the thin fibers. The researchers
used a laser that put out light pulses that lasted only a few million
billionths of a second.
Making the beads required the researchers to combine their knowledge
of specialty glassy materials, optical fiber, surface chemistry and biochemistry,
The researchers tested the microbeads in a gene expression assay,
which determines which genes are expressed by a cell, said Lahiri.
The researchers' next step is to synthesize DNA and peptides on
the beads. Biological assays, or experiments, like studies of gene expression
or drug-protein interactions, can then be performed on the attached organic
molecules, Lahiri said. "If we do the synthesis of the DNA or peptides
on the coded microbeads [scientists can] order DNA attached to the encoded
beads," he said.
The researchers have done some neat work that expands the still-limited
repertoire of encoded bead technologies, said Shuming Nie, an associate
professor of biomedical engineering at the Georgia Institute of Technology
and Emory University.
The researchers have found "a novel method for fabricating microbarcodes,"
said Nie. "The most striking feature is perhaps the fiber bundling and
pulling process, a new procedure that would not be anticipated from previous
barcoding studies," he said.
The microbarcodes will be useful for applications like security
tagging, but it is not yet clear if there are biological applications
for the relatively large microbarcodes, Nie added.
The material has some drawbacks that may limit its practical use,
Nie said. It emits light at multiple wavelengths, is relatively inefficient
at absorbing light, and its long excited-state lifetimes will limit how
quickly the codes can be read out, he said.
The technology could be ready for commercial use in three to six
years, according to Lahiri.
Lahiri's research colleagues were Matthew J. Dejneka, Alexander
Streltsov, Santona Pal, Anthony G. Frutos, Christie L. Powell, Kevin Yost,
Po Ki Yuen and Uwe Muller. The research appeared in the January 6, 2003
issue of the Proceedings of the National Academy of Sciences. The research
was funded by Corning.
Timeline: 3-6 years
TRN Categories: Biotechnology; Materials Science and Engineering
Story Type: News
Related Elements: Technical paper, "Tiny Glowing Barcode
Beads," Proceedings of the National Academy of Sciences, January 6, 2003.
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