Development of a surface-enhanced Raman sensor for detection in complex mixtures.

Abstract

Surface-enhanced Raman scattering (SERS) is a powerful analytical signal transduction mechanism for the detection of analytes in aqueous environments, largely free from interfering water signals and capable of obtaining unique molecular signatures from structurally similar analytes. These characteristics make SERS ideal for the detection of analytes of interest from biological and environmental settings. To achieve the low limits of detection needed for biological and environmental analyte detection, new SERS platforms with the highest possible enhancement factors (EF) need to be developed. Traditionally, SERS has had limited analytical use because the analyte of interest must dwell on or near the Ag, Au or Cu surfaces, regardless of substrate EF. To overcome this limitation this work employs alkanethiol partition layers in combination with novel SERS platforms for the detection of environmental pollutants (eg. polychlorinated biphenyls and polycyclic aromatic hydrocarbons) and bioactive lipids. As the use of partition layers continues to increase and more SERS platforms with higher EF are developed, the use of SERS for analytical applications will increase. Overall, this work demonstrates the power of using novel SERS platforms combined with partition layers and reveals great promise for the future of environmental and biological sensing with SERS. Chapter One reviews the use of surface-enhanced Raman scattering detection in complex mixtures that have emerged in the last 10 years. SERS been employed for small molecule detection all the way to more complex systems, such as detection in living cells, and this chapter reviews the recent advancements and looks toward the future of SERS detection in biological systems. Chapter Two details the fabrication and characterization of new novel substrates for SERS sensing. In this chapter, three substrates are discussed, each with their own fabrication method and SERS sensing application. The majority of our SERS sensing schemes for non-traditional SERS analytes employ a partition layer-covered SERS substrate. In Chapter Three, I investigated what fundamental properties of an alkanethiol partition layer make it an ideal partition layer for particular analytes. I discovered both the thickness of the monolayer and the amount of disorder in the partition layer that allows for analyte partitioning and are critical for facilitating the analyte to dwell within the zone of enhancement for SERS. The last two chapters detail the implementation of partition layer-modified SERS substrates for detection in complex mixtures. Chapter Four demonstrates the use of partition layer-modified SERS substrates for the detection of environmental pollutants: polycyclic aromatic hydrocarbons, polychlorinated biphenyls and polybrominated diphenyl ethers. I was able to show that our substrate made it possible to detect and discriminate between structurally similar analytes in the presence of interfering species at environmentally relevant concentrations. The final chapter of this dissertation describes the steps I have taken towards SERS sensing in complex biological mixtures for the detection of bioactive lipids. The results of this investigation indicate that partition layer-modified AgFON substrates can facilitate the detection of phospholipids and secreted lipids at higher concentrations, but the SERS bands from the partition layer make detection of lipids at physiologically relevant concentrations challenging at this time.