Integration of plasmonic nanostructures on waveguides

Abstract

Due to the limited sensitivity of many currently used single particle analyzation methods for the investigation of biological nanoparticles, such as exosomes and virions, many suffer from a bias towards the larger size ranges while sub 90 nm particles are potentially disregarded or less accurately analyzed. The division of Biological Physics at Chalmers has for the last couple of years been developing and testing a novel way of doing label-free biosensing. The method is based on waveguide evanescent-light microscopy using a silica core enveloped in a symmetric organic cladding with a refractive index matching that of water, which increases the sensitivity by minimizing the stray light background and allows for the label-free detection of single nanoparticles. A protocol for the integration of plasmonic nanostructures on this waveguide was developed to investigate the potential of plasmon enhanced single-particle waveguide evanescent-light microscopy as a mean of unveiling the elusive nature of small biological nanoparticles. The well-established methods of colloidal and hole-mask colloidal lithography were used and adjusted to suit the specific requirements posed by the sensitive surface of the waveguide chip. A recipe for the integration is presented and a proof-of-concept experimental setup was used to analyze the potential of this platform as a biosensor. It was found that the coupling of single wavelength lasers and the subsequent observation of nanostructure intensity shifts is possible, but the desired high sensitivity and reliability requires the transition to very intensity stable and continuous light sources to allow for spectroscopy measurements to be carried out.