Proteins make the invisible visible

DOUGLAS FARMER, SENIOR EDITOR doug.farmer@photonics.com

Changes in the proteins inside a cell may indicate the presence of a particular disease or condition, and these changes have been historically difficult to track. For many years, it was believed that light in the visible range (>320 nm) was not absorbed by proteins, but recent research has shown that this is not the case. Invasive techniques of investigation, such as the injection of fluorophores, can seriously damage the area being studied. However, recent experiments show that electrically charged amino acids exhibit increased absorption potential — and proteins can thus be studied in their natural state.

Researchers at the Indian Institute of Technology Guwahati recently showed that, when charged positively or negatively, headgroups (the bulky parts of molecules) of amino acids can dramatically improve the absorption of these proteins in the UV-VIS range. This phenomenon is called protein charge transfer spectra (ProCharTS), which has also been shown to produce luminescence.

Authors Amrendra Kumar and Rajaram Swaminathan write in our cover story in this edition that using the ProCharTS process makes anomalies visible in proteins that would not be visible via other techniques. The process also allows a view of the conglomeration of proteins that can forewarn of Alzheimer’s, Parkinson’s, and other neurodegenerative diseases. Read more about what the researchers’ experiments have uncovered here.

Elsewhere in this edition of BioPhotonics, Duncan Stacey and Xiaoguang Wang unveil their work in using liquid crystal sensors for rapidly diagnosing COVID-19. At the outset of the pandemic, reverse-transcription polymerase chain reaction (RT-PCR) tests were distributed, but they can take up to 48 hours to perform. By using liquid crystal sensors and a stage controller, the researchers were able to swiftly detect the ssRNA of the virus. The presence of these molecules affects the visible light that can then be detected by the sensor. Learn what this means for the future of virus detection here.

Another technology with growing use in medicine is quantum cascade lasers, which are pumped by mid-infrared light sources. Authors Panagiotis Georgiadis, Olivier Landry, Alex Kenich, and Miltiadis Vasileiadis write that as QCLs have increased in power while remaining small in size, their portability has made them a reference point for spectroscopy of liquid samples, biomarker monitoring, pathogen detection, and drug development. Find out about the possibilities presented by QCLs here.

Elsewhere, Pierre Fereyre and Antoine Adam relate how OCT has matured, making the technique useful not only in ophthalmology but also in cardiology and dermatology. In OCT, low-coherence light is used to obtain images in two or three dimensions. Many optical components of these systems are available off the shelf. Get more information here.

Finally, it is vital to have a system of standard measurement to determine the viability of results, regardless of the technology used, argues Lili Wang in “Biopinion,” specifically pointing to flow cytometry. While this technique has long been used to observe groups of cells and other particles, the uniformity of measurement has been hindered. Wang notes that a consortium of scientific interests is working to correct this problem. Read about the scope of these efforts here.

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