Analyte-sensing Particles and Impact of Plastics on Environmentally Abundant Bacteria

Nano and microscale materials exhibit exciting chemical, physical and biological properties that dictate how they function. Furthermore, their surface chemistry influences how they respond to a specific application and interact with their surroundings. In this dissertation, a technique used to synthesize tunable hybrid gold nanoparticles for environmental sensing applications by Raman is presented, as well as the fate of nano and microplastics when in the presence of an abundant bacteria in the aquatic environment.Gold nanoparticles are widely used in many applications due to their various properties, such as facile synthesis, biocompatibility, surface conjugation with various ligand types, and tunability. The tunable optical properties of gold nanoparticles make them very attractive to be used in sensing by Raman due to the existence of a phenomenon known as surface-enhanced Raman scattering (SERS). Surface-enhanced Raman scattering is a surface phenomenon that increases the intrinsically weak Raman signal. The enhancement of the Raman signal from molecules close to the surface of a rough metal substrate or of a plasmonic nanostructure occurs due to the enhancement of the incident electric field at the surface of the substrate. Tunable gold-coated carbon black nanoparticles (AuCB NPs) were synthesized using a simple colloidal-based approach at room temperature. Tuning the localized surface plasmon (LSP) to be in resonance with the incident laser source will give the highest Raman enhancement. AuCB NPs were exposed to two model analytes, Congo Red (CR) and 4-nitrobenzenethiol (4-NBT). CR interacted with the AuCB NP surface through charge interaction, while 4-NBT can bond to the gold surface through its thiol group. The AuCB NPs with the LSP most closely tuned to the incident laser source gave the highest Raman enhancement. Microplastics and nanoplastics have gotten much attention due to their ubiquitous en-vironmental presence. Microplastics adsorb molecules, such as contaminants, from their surroundings, forming a plastic corona. Cyanobacteria (blue-green algae) were found to be part of the plastic corona of plastics sampled in the aquatic environment. Cyanobacte-ria are important primary producers and can convert inert nitrogen into organic nitrogen. Any impact on this community might affect the structure and function of the delicately bal-anced aquatic ecosystem. We have exposed a freshwater (Synechococcus elongatus Nageli, PCC 7942) and a marine cyanobacterium (Synechococcus elongatus sp., PCC 7002) to polystyrene spheres that were about ten times bigger (microPS) and ten times smaller (nanoPS) than a bacterium cell, to investigate plastic size effect. Cryo- and regular scanning electron microscopy, fluorescence microscopy, and photography were used to analyze these samples. Marine and freshwater cyanobacteria released EPS (extracellular polymeric substances) and formed aggregates with nanoPS. As a result, these aggregates are sedimented, with the sedimentation being more intense in the marine system than in the freshwater system. When freshwater and marine cyanobacteria were exposed to the microPS, they attached to the microPS linking up a few particles together, forming hetero-aggregates. Cyanobacteria remained alive after exposure to these particles. Thus, particle size and salt concentration-dependent effects must be considered when analyzing cyano-bacteria response to the presence of nanoplastics. Lastly, we have used atomic force microscopy to measure the adhesion force be-tween two polymer types and a marine cyanobacteria lawn. Polystyrene and polymethyl methacrylate were the polymers chosen due to their abundance in the environment. Force per distance measurements were carried out on a liquid cell at biological pH. The adhe-sion force was about four times higher for the PS probe than for the PMMA probe. PS is hydrophobic, while PMMA is hydrophilic. Thus, hydrophobicity could be the cause for the difference in the adhesion force.