Fingerprinting drugs: Engineers reduce tech to tiny photonic chip

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 Pao-Tai Lin, assistant professor in the Department of Electrical & 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.

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