Towards integrated surface-enhanced Raman spectroscopy of anionic pollutants in water

Ensuring the quality of water reserves is essential to guarantee not only the safety of the citizens of a country but also the prosperity of a nation. At the same time, human activity produces often contamination of water reserves as a side-effect. Contamination events generate important economical and health consequences such as restricted access to water for bath or consumption, intoxication, destruction of local fauna and flora, and reduction of the trust of the users in the water companies. Traditional drinking water quality monitoring by the water providers requires periodic sample collection, preparation and analysis in specialized laboratories. Consequently, the first alarm after a contamination event is often given by the consumers and not by the water companies. Sensor technology and “smart water-supply networks” can help to reduce the time response to contamination events. The ideal sensor to be integrated in a smart water supply network should have low-size, low-cost, low-maintenance and long lifetime. Furthermore, the need of sample preparation should be avoided, and the sensor should provide early detection and identification of the pollutant agents. The experiments described in this thesis were carried out as part of the WaterPrint project, which pursued the design and fabrication of an optical sensor for the real-time detection and fingerprinting of pollutants in the water distribution network.

The thesis is organized in 7 chapters. Chapter 1 presents the necessary theory to understand the different experiments contained in the subsequent chapters. Chapter 2 demonstrates surface-enhanced Raman spectroscopy (SERS) of anionic pollutants in water using modified commercial gold-based SERS substrates. Chapter 3 explores the fabrication of different depletion-zone Isotachophoresis (dzITP) devices based on polydimethylsiloxane (PDMS) and Nafion®. Chapter 4 demonstrates the fabrication of gold plasmonic antenna arrays on fused-silica substrates using electron-beam lithography (EBL). Chapter 5 demonstrates waveguide Raman spectroscopy using Al2O3, Si3N4 and TiO2 channel waveguides in both TE and TM polarizations. Chapter 6 explores the fabrication of plasmonic antennas on integrated waveguides for SERS. Finally, chapter 7 presents the main conclusions of this work and introduces multiple research directions for the continuation of the experiments presented in this thesis.