Date of Award

1-1-2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Civil and Environmental Engineering

Specialization

Environmental Engineering

Department

Civil and Environmental Engineering

First Advisor

Vinka Oyanedel-Craver

Abstract

The objective of this study was to investigate the biofouling capacity and potential solutions for sensor devices in Narragansett Bay, Rhode Island. The dissertation was comprised of three main studies. First, the biofouling potential of several surface-enhanced Raman scat-tering (SERS)-based sensors was tested using zoospores from the common biofouling al-gae Ulva spp. Fluorescence microscopy was used to compare the adhesion of tubular Ulva spp. zoospores on commercial and novel SERS-based sensors including uncoated and gold (Au) silicon nanopillar array SERS substrates from Silmeco, Au coated carbon black nano-particle (AuCB NP) substrates, uncoated and Au sputter-coated in-house SERS created with a “flameless” Tesla-coil lighter, as well as uncoated and Au sputter-coated glass con-trols. In addition, chemical composition, contact angle, and roughness were measured to characterize each of the substrates. It was found that all SERS substrates except for the Au sputter-coated in house SERS biofouled less than the control. It was also determined that biofouling increased with hydrophobicity, roughness, and the presence of micro-refuges. Field emission scanning electron microscopy (FE-SEM) images of the zoospores adhered to the SERS substrates provided new insights on the glycoprotein adhesive secretion and cell flattening stages of the settlement process. The area of adhesive spreading was lowest for the AuCB NP, and highest for the uncoated glass. Zoospores adhered to AuCB NP substrates had a height greater than the glass and Au sputter-coated glass. The inverse was observed for spore area.

The second study analyzed the early phases of biofouling in a natural seawater envi-ronment. Samples were deployed in Narragansett Bay at¬¬ the University of Rhode Island Graduate School of Oceanography dock monitoring station and collected after 1 hour, 1 day, 1 week, and 4 weeks. Two potential anti-biofouling coatings for sensor housings (In-terlux Pacifica Plus Antifouling Paint and Sea Hawk Mission Bay copper-free antifouling coating), one novel nano-based sensor material (AuCB NP), and glass and silicon wafer controls were tested. One main focus of this study was to determine if X-ray photoelectron spectroscopy (XPS) is a promising technique for analyzing the conditioning layer and early biofilm formation in field samples. Samples were analyzed for atomic percent using XPS. Three dimensional renderings of biofilms were also produced using optical coherence to-mography (OCT). N1s and C1s XPS peaks were used as indicators of biofouling. The re-sults found increasing trends in the atomic percent of N1s over time for all samples except for the silicon wafers. C1s atomic percentages increased for the glass, silicon wafer, and AuCB NP substrates over time, however C1s decreased for the anti-biofouling paints. This study demonstrated the promising use of XPS as a method for studying the early phases of biofilm formation from field samples in marine environments.

The last study focused on the prevention and removal of biofouling on SERS sub-strates using electric potential. An in-house device consisting of copper electrodes was used to apply electric potentials of -0.5 V, -0.8 V and -1.0 V for 30 min to gold capped silicon nanopillar SERS substrates to detach adhered Ulva spp. zoospores. To prevent the adhe-sion of zoospores, a voltage of -0.3V was applied for 24 h using stainless steel electrodes. Fluorescence microscopy was used to quantify the surface area covered by biofouling, and FE-SEM was used to investigate the zoospore integrity after applying electric potential. Applying -0.5 V, -0.8 V and -1.0 V for 30 min showed a reduction in the area of the sub-strate covered by Ulva spp. by ~25%, ~20% and ~63%, respectively. The prevention study indicated a 91% reduction in Ulva spp. at the applied potential of -0.3 V for 24 h. FE-SEM observations indicated that zoospore integrity was affected by electric potentials of -0.5 V, -0.8 V and -1.0 V, however zoospores remained intact after applying -0.3 V for 24 h. These findings indicated that applying low-voltage electric potential to SERS substrates is a prom-ising method for biofouling control of Ulva spp. in marine environments.

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