Final Report Summary - WIPFAB (Wideband Integrated Photonics For Accessible Biomedical Diagnostics)
The WIPFAB project set out to advance photonic materials, fabrication processes and optofluidic devices to create platform technologies for application to healthcare diagnostics in point-of-care settings where complex instrumentation may be scarce. The convergence of advanced microfabrication techniques, new materials and novel approaches to biochemical analysis was exploited to create miniaturised biosensor and cytometry devices and demonstrate applications in medicine and environmental monitoring, while generating knowledge which will also benefit telecommunications and consumer photonics. In biochemical analysis the ideal molecular “fingerprint” region for optical spectroscopy is dominated by the mid-infrared (MIR) spectral region from 2 to 13 microns, and biosensor and lab-on-chip technologies have been hampered by the lack of an integrated photonic (waveguide) platform which can operate over the MIR. In WIPFAB we realised germanium telluride and zinc selenide glass waveguide devices suitable for extended MIR surface molecular absorption spectroscopy. These materials have low toxicity and we have demonstrated their monolithic integration on silicon, important for transfer to low-cost mass-manufacture, integrated with paper-based fluidics for simple sample delivery, and demonstrated application to analgesics. MIR studies of lung surfactants, with Southampton General Hospital, showed that the lecithin/sphingomyelin ratio can be assessed rapidly using evanescent spectroscopy which may lead to better treatment of new-born babies suffering from Infant Respiratory Distress Syndrome. In an application to water quality monitoring, we have demonstrated the application of waveguide chips to the detection of cyanotoxins from algal blooms in lakes with collaborators at Tsinghua University, China. Raman spectroscopy is complementary to MIR spectroscopy for biochemical identification, with simpler operation in aqueous media but offering very low signals for the monomolecular films usually employed in biosensing. Surface-enhanced Raman spectroscopy (SERS) has achieved huge enhancements in signal strength, and thence excellent detection limit, but employs complex and fragile noble metal nanostructures. WIPFAB has simulated and realised novel purely dielectric high index waveguides of nanoscale thickness with no nanostructuring, used a systems-approach power budget analysis and shown these to have comparable performance to SERS, applying them to spectroscopy of monomolecular films, and demonstrating potential for low-cost instrumentation. The confluence of integrated fluidics with integrated photonics to create miniature, low-cost, mass-manufacturable optofluidic chips offers great potential for low-maintenance high performance systems for chemical analysis and biosensing. WIPFAB has established an integrated waveguide/fluidic platform technology for flow-cytometry of immunoassay beads and biological cells using silicon process technology and deep reactive ion etching (DRIE). This has incorporated inertial focussing for bead placement and monolithically integrated waveguide lenses to focus laser light in the flow stream, and has achieved multi-angle scattering and fluorescent measurements. Extracellular vesicles in blood have been identified as important biomarkers of disease and, working with Southampton General Hospital, we have contributed to the standardisation of flow cytometers for these small particle applications and realised an on-chip flow cytometer for extracellular vesicle identification. In summary, WIPFAB has realised several new waveguide materials, fabrication processes and device designs, including optofluidic, Raman and MIR absorption platform technologies and demonstrated applications of clinical interest which may be applied to as yet unforeseen clinical, environmental, telecommunications and consumer photonics applications.