Date of Award

Summer 7-20-2021

Degree Type

Thesis

Degree Name

MS Physics

Department

Physics

Advisor

Jose L Lopez, Ph.D.

Committee Member

Gerald J. Buonopane, Ph.D.

Committee Member

M. Alper Sahiner, Ph.D.

Keywords

atmospheric plasmas, nonthermal plasmas, Atmospheric Pressure Plasma Jet (APPJ), plasma agriculture, DPPH antioxidant assay, essential oils

Abstract

Plasma agriculture is an increasingly diverse field, where effects of nonthermal or cold plasma are measured by their influence on plant physiology and growth rate. Effects range from sterilization, germination, increased growth rate, cell metabolism, and so forth. This study aims to investigate the understanding of the generation of specific reactive oxygen and nitrogen species (RONS) from a nonthermal atmospheric DBD helium-based plasma jet and identify quantifiable effects that can directly translate to different applications related to plasma agriculture. Basil plants were separated into treated and control groups and grown hydroponically. The treated plants received a 30 second exposure treatment biweekly treatment with an atmospheric pressure plasma jet (APPJ).  Plants were analyzed during the growing phase and then harvested after 8 weeks where steam distillation was utilized to extract essential oil from the leaves. The plasma jet was analyzed to characterize the excited species being produced using emission spectroscopy within the range of 300 - 800 nm. The change in pH from interactions with these excited species was measured by exposing water to the plasma jet and measuring pH. The extracted oil was analyzed using the DPPH antioxidant scavenging assay to determine percent antioxidant activity (AA%). The change in pH when using the plasma jet in water, determined that there is a substantial increase, then a decrease in pH over time when using the plasma jet to treat water. This is further supported by emission spectroscopy being able to identify the components of OH-, O-, N+, N2+ and He metastable which leads to the chemical formation of other reactive species such as NO, NO2,, and O2. These chemical species lead to the pH change seen when treated in water, and the effects noted throughout the study (growth rate increase, changes in AA%) are also supported in literature to be attributed to these different reactive species coming in contact with plant material. When compared to other research, these effects overlap with different plants as well as different jet treatments being used in the plasma agricultural research field. Through DPPH scavenging assay, the extracted oil from plasma treated basil plants had a higher average AA% (about 1 – 2%) which is hypothesized to be attributed from the different antioxidant components (Eugenol, Limonene, Ocimene) present in the basil being increased.  While concentrations of these components were not measured, it is proposed that the increase in AA% can be attributed to them based on previous research with plasma-treated basil.

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