Friday, May 4, 2018

Waveguide-enhanced Raman platform promises rapid diagnosis of disease

Sensor chips: chemically adaptable to detect small molecules

Portable and easy-to-use photonics devices can potentially offer substantial advantages in the diagnosis and prevention of disease, and a new project at the University of Southampton Optoelectronics Research Centre (ORC) could see a significant new step made towards this goal.
Supported with £1 million from the EPSRC Healthcare Technologies Programme, ORC and its collaborators at Southampton's Department of Chemistry and the UK Defence Science and Technology Laboratory (Dstl) intend to develop a low-cost instrument suitable for use in GP surgeries, hospital wards, or in remote communities, using cheap, disposable plug-in sensor chips.
These chips will be chemically adaptable to detect small molecules, proteins or DNA, with fluid samples simply being dropped onto the sensor surface, to rapidly detect infection and diagnose disease.
According to ORC, the new project will build upon research by Southampton's Zilong Wang on waveguide-enhanced Raman spectroscopy (WERS), along with work on biochemical detection currently underway between the University and Dstl.
In principle WERS offers a solution to the inherent issue of low sensitivity to which Raman spectroscopy is prone. Rather than employing free-space optical components, WERS incorporates Raman spectroscopy into a waveguide structure, allowing the waveguide to transport incident light, excite Raman scattering, and collect the emission.
Wang's research, published as part of his PhD studies at Southampton, demonstrated how guided light in a suitable dielectric thin-film waveguide can be squeezed to dimensions similar to its wavelength, which results in a large optical intensity over a long propagation range. Analyte molecules close to the waveguide's surface then interact with the evanescent field of the waveguide, becoming Raman excited and allowing their emission to be collected.
Environmental monitoring and security
This effect could be particularly valuable for analytical applications in real-world biological sensors, if it allows detection of particular species to be made through repeatable activity over relatively large enhanced surfaces, rather than the highly localized enhancements often employed to produce single-molecule detection.
"Highly specific, sensitive sensors interfaced with portable, easy-to use, low-cost instruments are needed for rapid point-of-care infection diagnostics, leading to better targeted therapy, shorter time to treatment and reduced morbidity," notes OFC in its WERS research literature.
"We aim to realize a generic, flexible, compact sensing platform with high sensitivity and selectivity, building upon our recent work on WERS to realise a sensor chip which shows surface enhancements comparable to those of surface-enhanced Raman spectroscopy, with improved application flexibility and manufacturability. These will have wide application in the diagnosis of disease."
As well as point-of-care applications, the platform could also prove valuable in broader settings such as environmental monitoring and border security, and should be readily configurable for new locations and analytical challenges.
In its project announcement, ORC indicated that the sensor will first be demonstrated using clinical samples from volunteers who have been exposed to controlled experimental infections in the NIHR Southampton Clinical Research Facility, and will also be assessed as a potential method of analysis for international priority pathogens such as Ebola and plague.

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