In this work, ultraporous silica layers with very low refractive indices (1,1-1,2) and thicknesses about one micrometer are prepared and integrated to two systems of sensors for different applications. The synthesis of the initial solution is optimized from the sol-gel standard two steps. Due to its high porosity, the deposited layer has two remarkable properties : low refractive index and low thermal conductivity. Our study is based on the establishment of two systems : a reverse symmetry waveguide and an heating microsystem. The achievement principle of the reverse symmetry waveguide is based on a stack of three layers with a central layer with higher refractive index than the surrounding media. The particularity of this guide is due to the index of the lower middle (ultraporous layer) which is lower than the upper middle. In an application to build a multilayer film type polyelectrolyte / protein and to test the depth of evanescent field sensing, poly-L-lysin and caseins multilayers are adsorbed on the waveguide surface. From the variation of the effective refractive index, one can determine the mass of biomolecules deposited and we show the sensitivity of this system. In the second application of the ultraporous layer, the technology of heating microsystem is based on the integration of this layer between metal resistance and its substrate. It is highlighting that this addition allows a better concentration of energy supplied.
