Date of Award

12-2013

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Biological Engineering

Advisor

Michael Mason

Second Committee Member

Doug Bousfield

Third Committee Member

Paul Millard

Abstract

Silver Nanoparticles have unique optical, conductivity, and biochemical properties. In this study the ability for silver nanoparticles to be embedded in a 3- dimensional porous substrate was assessed for two major uses; antimicrobial water filtration and surface enhanced Raman spectroscopy. First the silver nanoparticles were synthesized within paper as a substrate. The goal was to evenly and uniformly disperse the nanoparticles throughout the 3-D matrix of the paper. This was achieved by soaking the paper samples in a silver salt solution (either silver nitrate or silver chloride) and then reducing the silver ions by immersion of this sample into a reducing agent (ascorbic acid or sodium citrate). To optimize the uniform dispersal of nanoparticles within the paper, several parameters were altered in order to find the ideal conditions. Wood free 200 coated paper (WF 200) and blotter paper were two paper types compared, and different combinations of silver sources with reducing agents at varying concentrations were examined. Temperature of the reaction was also varied to determine temperature dependence. The uniformity of silver dispersion was assessed qualitatively through visual inspection, and quantitatively with grayscale analysis. The paper interior was imaged using cross-sectional SEM techniques, SEM detecting secondary electrons, and SEM detecting backscattered electrons. The presence of silver and other chemical constituents within the paper substrate were characterized using SEM with EDX. It was found silver was present throughout the substrate, as well as other paper constituents such as hydrocarbons, magnesium, copper, and silica. The specific amount of silver was measured via ash content analysis. Of the four samples tested silver content ranged from 6.8 to 16.5 mg Ag/ g paper. Silver chloride was determined to be ineffective as a silver source for this reduction due to the lack of uniformity it produced, but silver nitrate reduced by ascorbic acid or sodium citrate produced uniform nanoparticle dispersion in both WF200 paper and Blotter paper.

It was important that the silver nanoparticles be immobilized within the substrate and not able to leach into the environment. Two experiments were conducted to affirm that the silver had been immobilized. An effluent study was performed in which silver treated paper was soaked in water and the silver concentration within the water was measured periodically up to 30 days. From this effluent study the WF200 paper sample treated with 0.5M silver nitrate and 0.1M ascorbic acid retained the highest amount of silver (98% of total silver) after 30 days of soaking and the silver concentration in the effluent water was well within the EPA acceptable levels for drinking water. A second experiment assessing silver leaching was performed. In this experiment silver treated paper sample were placed onto agar inoculated with E. coli. There was no inhibition of bacterial growth in the area surrounding the paper sample confirming silver had not leached into the surroundings at toxic levels.

Next the silver paper samples were tested for their ability to act as an antimicrobial water filter. E. coli contaminated water was passed through each paper sample and the cell concentration in the filtered solution was measured. WF200 treated with 0.5M silver nitrate and 0.1M ascorbic acid had the greatest antimicrobial action, reducing the bacterial count by more than half.

The final application for the silver impregnated paper was to serve as a substrate for enhancing Raman signal. Using 4-Mercaptopyridine (4-MCP) as a test molecule deposited on the paper substrate, Raman measurements were taken. Comparison of tabulated literature values, and Raman measurements obtained from pure 4-MCP on glass, and 500μM 4-MCP on WF200 treated with 0.5M silver nitrate and 0.1M ascorbic acid showed enhancement of Raman signal confirming the silver treated paper was acting as an effective surface enhanced Raman scattering (SERS) substrate. The same concentration of 4-MCP on plain paper showed no visible enhancement.

From the results of the study it can be concluded that it is possible to uniformly synthesize silver nanoparticles within paper substrates. Furthermore these substrates could be optimized to serve as antimicrobial water filters, or alternatively SERS substrates.

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