OPTICAL DETECTION OF MOLECULAR INTERACTIONS ON THE SURFACE OF MATERIALS INDEX-MATCHED TO WATER.

The idea to have highly effective autonomous sensors able to measure and share information about the quality of our environment, and particularly water, in our lakes and rivers, our water supply system and the outputs of municipal and industrial wastewater treatment systems is revolutionary and fascinating. These sensors could be densely deployed at multiple locations, and the information may be available to citizens through the Internet. This idyllic vision, nowadays, is far away from being reality, despite the huge effort made to develop innovative molecular sensors. The main challenges related to the realization of these autonomous sensors network are the biofouling, power supply and compactness. In fact, despite thousands of papers in literature about development of novel nanostractured materials for sensing, for instance, there is still not a single example of any of these device being used in direct contact with water for long-term environmental monitoring. The work presented in this thesis proposes a new kind of optical sensor that combines a fast and low cost method to detect water pollutant with good performance and robustness. In particular, this work is focused on the detection of small molecular pollutants, as oils compounds and surfactants. An innovative aspect of the proposed approach relies on the use of a novel class of materials as sensing substrate which have peculiar and fascinating optical properties: these are amorphous perfluorinated polymers with refractive index similar to that of water. When immersed in aqueous solutions, they provide extremely low reflection or scattering of light, hence they become barely visible. For this reason, this class of materials is called phantom. In this limit, when a thin molecular layer spontaneously adsorbs on the surfaces of these materials, the reflected or scattered light increases, providing the basis for optical detection of molecules. In this work, three different phantom materials made of perfluorinated polymers are exploited in the framework of the detection of water contaminants: a prism, microporous membranes and micro-beads, that represent the building blocks for the assembly of an invisible chromatography column. The membrane and the micro-beads were produced for the first time during this work. The use of fluoropolymer prism substrate for molecular detection was already proposed in recent works to realize label-free biosensors based on the functionalization of the surface with antibodies. Here I extend the exploitation of this system to the detection of molecular pollutant through their adsorption on the bare surface of the fluoropolymer materials, without the need of any surface treatment. Despite the lack of surface functionalization, a selectivity in the adsorption of various classes of molecules is demonstrated.