Optical biosensors have now proved to be sensitive and reliable devices as proved by the numerous commercial devices available. Label free biosensing systems are very interesting in the fields of research, drug discovery and point of care applications but they can suffer from a lack of sensitivity for the detection of small molecules. Nanostructuration is an elegant approach to lower the limit of detection by increasing the sensitive surface area. The optical sensing technique WIOS  developed at CSEM, which is based on evanescent wave refractometry, has been modified following two different strategies to enhance the sensitivity: 1)  formation of quasi-periodic nanostructures in silica by deep reactive ion etching using an etch mask made of self-assembled polymer micelles and 2) deposition of thin mesoporous films of nanoparticles.

With the appropriate choice of the polymer layer self assembly parameters and etching conditions, the silica layer is nanostructured in nano-pillars or nano-holes form. The samples were tested with the WIOS¹ instrument and the results show that the presence of a residual SiO₂ layer can hinder drastically the effect of the increased surface area. Careful control of the deposited layer and the etching conditions lead to an appreciable improvement for the non-specific adsorption of bovine serum albumin (BSA). Using the second approach, different sensing layers made of various metal oxides stabilized by a photo-crosslinkable polymer or sintered at high temperature have been compared. Improvements have been observed for non-specific adsorption of BSA. Finally, the nanostructured sensing surfaces were tested in a biosensor environmental application for the specific recognition of pesticides and antibiotics in water samples using adapted immunoassays.

[1] Wavelength-Interrogated Optical Sensing

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1. Nanostructured sol-gel surfaces
2. Fabrication of superhydrophobic surfaces with controlled topography and chemistry