To achieve optimal virus detection using surface plasmon resonance (SPR), a leading SPR manufacturer is relying on glass prisms with a high-quality gold thin film sensor custom grown in the LTA laboratory (Fig.1).
Basic research provides the basis for subsequent applied research and development. In the same way, instrumentation and expertise tailored for basic research projects can provide new insights into technical challenges of industrial nature. The NCCR MaNEP, through the sustained, focused effort on fundamental research related to materials with novel electronic properties, has created an attractive reservoir of tools and expertise. We can name in particular surface science, metallurgy, local probe microscopy, among many other scientific branches. These technology domains are today critical for applied research. And for many firms, there is a strong dependence of industrial innovation upon extramural technological knowledge. In the same way, access to high-end equipment remains a hurdle for several firms, even for companies with the required absorptive capacity to exploit outside knowledge of a more intermediate sort, such as basic research findings. While economists assume that technological knowledge which is in the public domain is a public good, they ignore the costs and difficulties related to learning and applying a given technology.
The LTA was precisely created to remove those barriers and to facilitate the knowledge transfer in a timely and effective way. In the present case, basic-research-induced technological knowledge has been successfully applied to the development of dedicated thin films for surface plasmon resonance of very high resolution.
Optical biosensors based on SPR – a high sensitive optical method of analysis – enable unprecedented real time investigations of interacting biomolecules (nucleic acids, proteins, peptides). Ground-breaking studies highlight the capabilities of modified SPR-based imaging techniques for the detection of single viruses and for the visualization of viral binding events. Optimized SPR microscopy with digital background subtraction allows the precise observation of particles only a few tens of nanometres in size (20 – 200nm).
Most viruses range between 20nm to 400nm in diameter, with coronaviruses, including the Covid-19, measuring around 100nm. They are detected in the SPR Kretschmann geometry, where light travelling through a prism is reflected from the backside of the gold coated face (Fig. 2). The properties of the reflected light change depending on the species binding to the outer-side of the reflecting gold layer. Using a CCD detector, the whole coated surface can be monitored, thus allowing the analysis of up to several thousand surface processes simultaneously.
The sensitivity of the above SPR virus detection scheme critically depends on the quality of the gold thin film. The coating characteristics, such as thickness and roughness of the gold layer, strongly influence the SPR signal. Defects and inhomogeneities cause artefacts which affect the plasmonic properties. State-of-the-art coating technology is thus needed to guarantee the sensitivity of the sensor unit, especially for particles below 100nm in size.
Producing such films requires specific equipment and multiple expertise in thin film growth, in AFM microscopy for surface characterization, in profilometry and X-ray analysis for film thickness calibration, among others.
The LTA was able to provide timely innovative support for this leading SPR manufacturer owing to its simple organization and single point of entry to access unique competences of the Faculty of Science of the University of Geneva and the HES-SO hepia.