The SUPREME-B objective is to develop a new kind of biosensors based on all-semiconductor plasmonics

Making the right diagnosis in the case of illness is a crucial but not easy task, and generally, relies on invasive medical testing. Several alternative techniques have recently emerged, notably analysis based on the use of surface plasmon resonances (SPR). The basis: a metallic surface with an analyte is exposed to a reflected light. The analyte concentration is measured through the modification of the medium refractive index that affects the surface plasmon polariton, thus the reflected light properties (wavelength, angle, phase and intensity). The weak sensitivity to small size molecules, is the major limitation of SPR biosensors. Therefore, localised surface plasmon resonance (LSPR) systems have been recently proposed. Such systems are mainly based on gold nanoparticles and used in the visible or near infrared wavelength range, to increase the sensitivity. However, to extend the detection range into the infrared, it is essential to achieve a higher LSPR intensity, i.e. a higher sensitivity and easier molecule identification due to their specific infrared spectral signatures. Technically, the best performances are obtained by Surface Enhanced Raman Scattering (SERS), which is difficult to integrate and quite expensive, or by Surface Enhanced Infrared Absorption (SEIRA) which is a more direct and innovative technique.

Highly doped semiconductors (HDSC) are the best candidate for SEIRA, or infrared SPR, but their use is at an infancy stage. Recently we have demonstrated the potential of using HDSC for LSPR applications in the infrared range, theoretically and experimentally. We have generated LSPR in the infrared using highly doped InAsSb layers grown lattice-matched on GaSb substrates. Indeed, we have theoretically predicted a sensitivity critical point one order of magnitude higher compared to gold systems, explained by a higher plasmonic field exaltation due to the distinct HDSC permittivity, e.g. a real part with low negative values combined with a low imaginary part. Furthermore, nanostructured HDSC are easy to integrate with light sources and/or detectors or integrated spectrometers to form lab on chips at a reduced cost. HDSC appear as an ideal choice for infrared plasmonics.
At the end of the project we will have achieved:

  • The Design and fabrication of an optimised HDSC-based LSPR device, to reach resonances in the 6-15 µm IR range for SEIRA or SPR measurements, with at least one-order-of-magnitude enhancement of the near electromagnetic field of the LSPR compared to the state-of-art.
  • The integration of the HDSC-based LSPR structure to a label-free biosensor (without label molecule which amplifies the target signal) by functionalising the surface of the InAsSb resonators.

The final structure should be:

Structure-finaleFig. 1: Experimental setup for LSPR biosensing measurements. Front illuminated experiments will be performed through PDMS layer. Back illuminated experiments will be performed through the GaSb substrate.