Researchers dramatically downsize technology for fingerprinting drugs
and other chemicals
Tiny photonic chip could fit comfortably within the tip of a finger

Date:
August 28, 2020
Source:
Texas A&M University
Summary:
Researchers have invented a new technology that can drastically
downsize the apparatus used for Raman spectroscopy, a well-known
technique that uses light to identify the molecular makeup of
compounds.



FULL STORY ==========================================================================
As new infectious diseases emerge and spread, one of the best shots
against novel pathogens is finding new medicines or vaccines. But before
drugs can be used as potential cures, they have to be painstakingly
screened for composition, safety and purity, among other things. Thus,
there is an increasing demand for technologies that can characterize
chemical compounds quickly and in real time.


========================================================================== Addressing this unmet need, researchers at Texas A&M University have now invented a new technology that can drastically downsize the apparatus
used for Raman spectroscopy, a well-known technique that uses light to
identify the molecular makeup of compounds.

"Raman benchtop setups can be up to a meter long depending on the level
of spectroscopic resolution needed," said Dr. Pao-Tai Lin, assistant
professor in the Department of Electrical and Computer Engineering and
the Department of Materials Science and Engineering. "We have designed
a system that can potentially replace these bulky benchtops with a
tiny photonic chip that can snugly fit within the tip of a finger."
In addition, Lin said that their innovative photonic device is also
capable of high-throughput, real-time chemical characterization and
despite its size, is at least 10 times more sensitive than conventional benchtop Raman spectroscopy systems.

A description of their study is in the May issue of the journal Analytical Chemistry.

The basis of Raman spectroscopy is the scattering of light by
molecules. When hit by light of a certain frequency, molecules perform a
dance, rotating and vibrating upon absorbing the energy from the incident
beam. When they lose their excess energy, molecules emit a lower-energy
light, which is characteristic of their shape and size. This scattered
light, known as the Raman spectra, contains the fingerprints of the
molecules within a sample.



========================================================================== Typical benchtops for Raman spectroscopy contain an assortment of optical instruments, including lenses and gratings, for manipulating light. These "free-space" optical components take a lot of space and are a barrier for
many applications where chemical sensing is required within tiny spaces
or locations that are hard to reach. Also, benchtops can be prohibitive
for real-time chemical characterization.

As an alternative to traditional lab-based benchtop systems, Lin and his
team turned to tube-like conduits, called waveguides, that can transport
light with very little loss of energy. While many materials can be used
to make ultrathin waveguides, the researchers chose a material called
aluminum nitride since it produces a low Raman background signal and is
less likely to interfere with the Raman signal coming from a test sample
of interest.

To create the optical waveguide, the researchers employed a technique
used by industry for drawing circuit patterns on silicon wafers. First,
using ultraviolet light, they spun a light-sensitive material, called
NR9, onto a surface made of silica. Next, by using ionized gas molecules,
they bombarded and coated aluminum nitride along the pattern formed by
the NR9. Finally, they washed the assembly with acetone, leaving behind
an aluminum waveguide that was just tens of microns in diameter.

For testing the optical waveguide as a Raman sensor, the research team transported a laser beam through the aluminum nitride waveguide and
illuminated a test sample containing a mixture of organic molecules. Upon examining the scattered light, the researchers found that they could
discern each type of molecule within the sample based on the Raman spectra
and with a sensitivity of at least 10 times more than traditional Raman benchtops.

Lin noted since their optical waveguides have very fine width, many of
them can be loaded onto a single photonic chip. This architecture, he
said, is very conducive to high-throughput, real-time chemical sensing
needed for drug development.

"Our optical waveguide design provides a novel platform for
monitoring the chemical composition of compounds quickly, reliably
and continuously. Also, these waveguides can be easily manufactured at
an industrial scale by leveraging the already existing techniques to
make semiconductor devices," said Lin. "This technology, we believe,
has a direct benefit for not just pharmaceutical industries but even
for other industries, like petroleum, where our sensors can be put
along underground pipes to monitor the composition of hydrocarbons."
Other contributors to this research are Megan Makela from the Department
of Materials Science and Engineering; and Paul Gordon, Dandan Tu, Cyril Soliman, Dr. Gerard Cote' and Dr. Kristen Maitland from the Department
of Biomedical Engineering.


========================================================================== Story Source: Materials provided by Texas_A&M_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Megan Makela, Paul Gordon, Dandan Tu, Cyril Soliman, Gerard
L. Cote',
Kristen Maitland, Pao Tai Lin. Benzene Derivatives Analysis Using
Aluminum Nitride Waveguide Raman Sensors. Analytical Chemistry,
2020; 92 (13): 8917 DOI: 10.1021/acs.analchem.0c00809 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200828144421.htm

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