Spider silk: Nature’s Bio-Superlens

Extending the limit of the classical microscope’s resolution has been the holy grail of microscopy for over a century. Physical laws of light make it impossible to view objects smaller than 200nm – the smallest size of bacteria – using a normal microscope alone. However, superlenses that enable us to see beyond the current magnification have been the goal since the turn of the millennium.

After a team at Bangor University’s School of Electronic Engineering used a nanobead-derived superlens to break the perceived resolution barrier, the same team has achieved another world first. The team, led by Dr Zengbo Wang, and in colloboration with Professor Fritz Vollrath’s silk group at Oxford University’s Department of Zoology, has used a naturally occurring material – dragline silk of the golden web spider – as an additional superlens, applied to the surface of the material to be viewed, that provides an additional 2-3 times magnification.

This is the first time that a naturally occurring biological material has been used as a superlens.

In the paper, published in Nano Letters, the joint team reveals how they used a cylindrical piece of spider silk from the thumb sized Nephila spider as a lens.

Dr Zengbo Wang said: ‘We have proved that the resolution barrier of the microscope can be broken using a superlens, but production of manufactured superlenses involves some complex engineering processes that are not widely accessible to other researchers. This is why we have been interested in looking for a naturally occurring superlens provided by “Mother Nature”, which may exist around us, so that everyone can access superlenses.’

Professor Fritz Vollrath added: ‘It is very exciting to find yet another cutting-edge and totally novel use for a spider silk, which we have been studying for over two decades in my laboratory.’

These lenses could be used for seeing and viewing previously ‘invisible’ structures, including engineered nano-structures and biological micro-structures, as well as, potentially, native germs and viruses.

The natural cylindrical structure at micron- and submicron-scale makes silks ideal candidates – in this case, the individual filaments had diameters of one tenth of a thin human hair.

The spider filament enabled the group to view details on a microchip and Blu-ray disk that would be invisible using the unmodified optical microscope.

In much the same way as looking through a cylindrical glass or bottle, the clearest image only runs along the narrow strip directly opposite one’s line of vision – or, resting on the surface being viewed, the single filament provides a one-dimensional viewing image along its length.

Dr Wang explained: ‘The cylindrical silk lens has advantages in the larger field-of-view when compared to a microsphere superlens. Importantly for potential commercial applications, a spider-silk nanoscope would be robust and economical, which in turn could provide excellent manufacturing platforms for a wide range of applications.’