Laser & photonics A light in the dark
The world has been testing for Covid-19 for so long now that the technology at work to produce results might feel rudimentary. The reality is that the ability to diagnose the disease is the result of years of research and development, especially in the case of point-of-care devices. Biophysicist and European Photonics Industry Consortium project leader Dr Elena Beletkaia explains the complex role photonics has played, and will continue to play, throughout this pandemic.
hese days, most people are familiar with the PCR test given to diagnose infection with the SARS-CoV-2 virus, but many may not realise the central role that photonics technologies play in enabling it. PCR, or polymerase chain reaction, is a biomolecular method used to amplify the DNA or RNA molecule of interest. The process involves multiple amplification cycles carried out by thermal cycling. But the detection of the viral genetic material is carried out using an optical system that analyses a fluorescent tag within the mixture of sample and reagents. This tag is released only in cases where the genetic material of interest is present in the mixture, and the optical system needed to detect it requires an excitation source, a photodetector, and multiple optical filters.
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The excitation sources can range from halogen lamps that emit broad-spectrum white light, to lasers that produce high-intensity light with a narrow bandwidth. While the use of laser sources is confined to collecting data from a small set of fluorophores, the halogen lamp allows a high level of multiplexing. However, to enable a halogen lamp source to analyse a broad range of fluorophores within the same system, it must be complemented with a set of narrow-bandpass filters. A common compromise is to use light-emitting diodes (LEDs).
A single LED or multiple can be present in a shuttle mechanism; arranged in an array, they can be used for individual or parallel excitation of fluorophores in the test. The detection of the signal is typically done with the use of a photodiode – a semiconductor that converts photons into an electrical current. Perhaps the most demanding part of the optical pass in a PCR machine is the combination of multiple lenses and filters. The high degree of spectral precision is what ensures the reproducibility and reliability of the obtained results. At the excitation site, it is critical to minimise spectral overlap between fluorescent probes.
Medical Device Developments /
www.nsmedicaldevices.com
Medical Device Developments /
www.nsmedicaldevices.com
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