We report on the photorefractive properties of tin-silica slab waveguides, deposited on vitreous-SiO 2 by means of sol-gel dip-coating technique. The basic composition of these amorphous binary systems is 75 SiO 2 -25 SnO 2 mol% with 1 mol% of Eu 3+ ions. Europium was chosen as an optical probe of the glass structure. These guiding structures exhibit low propagation losses (around 0.5 dB/cm at 633 nm) and a high refractive index modulation, as large as -1.5 × 10 − 3 under the UV irradiation of a KrF excimer laser source at λ = 248 nm, suitable for writing waveguide gratings.

In this paper, we review the literature on optical evanescent field sensing in resonant cavities where aptamers are used as biochemical receptors. The combined advantages of highly sensitive whispering gallery mode resonator (WGMR)-based transducers, and of the unique properties of aptamers make this approach extremely interesting in the medical field, where there is a particularly high need for devices able to provide real time diagnosis for cancer, infectious diseases, or strokes. However, despite the superior performances of aptamers compared to antibodies and WGMR to other evanescent sensors, there is not much literature combining both types of receptors and transducers. Up to now, the WGMR that have been used are silica microspheres and silicon oxynitride (SiON) ring resonators.

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