A metal-free, in particular tin-free, silane-terminated polyurethane which is useful in adhesives or sealant compositions is obtained by reacting at least one aliphatic secondary aminoalkylalkoxysilane of formula . The resulting novel oxides can be formed as dense films or coatings with very high strain-to-crack values, or as nanoparticles, depending primarily upon the concentration of the reactants. An optical path extends through the first deformable lens and to the sensor.