Fluorescent probes for selective detection of ozone in plasma applications

This thesis presents an overview of the research activities undertaken during my PhD under the supervision of Dr. F. Iza from the School of Electronic, Electrical and Systems Engineering and Dr. B. Buckley from the Chemistry Department at Loughborough University. The thesis is divided as follows. The first chapter of the thesis presents an introduction to plasma and chemical probes as well as the motivation for developing fluorescent probes for plasma characterisation. Analytical techniques used during this work to analyse chemical substances are described in the second chapter. Results and discussions from the experiments are discussed in chapters 3 to 7. Conclusions and future work are presented in chapter 8. In chapter 9, experimental data is presented. In the last century, plasma has attracted the attention of numerous researchers. Due to the wide-range of applications of this ionised gas, people from different fields have focused their effort on studying plasma. Low-temperature plasmas have received growing attention in the last 50 years when the development in cold plasma devices made them more controllable. Plasma played (and continues to play) a critical role in the fabrication process of integrated circuits and recent advances in the generation of low-temperature atmospheric-pressure plasmas have resulted in the emergence of new applications including treatment of temperature sensitive surfaces and biological targets. During the first months at Loughborough I worked on the ozonolysis of various alkenes with air plasmas. This allowed me to familiarised myself with plasma as this was new to me and get a feeling of some of the challenges lying ahead. Nonetheless, the data I obtained was encouraging and I presented the results of batch and flow plasma-based ozonolysis of alkenes at the Technological Plasma Workshop held in Manchester in January 2012. Once I had familiarised myself with the plasma system, I worked on synthesising fluorescent probes to detect ozone, one of the many reactive species that are typically generated in oxygen containing plasmas. Details of the experiments conducted to date and most significant findings are discussed in this thesis

Fluorescence probe for determining the ozone dose delivered by plasmas

Plasma composition is typically studied by absorption and emission spectroscopy, mass spectrometry and computational studies. While these techniques provide valuable information about the chemical species in the gas phase, in many applications it is desirable to have a direct measurement of the dose of chemical species delivered to a particular target. In this work, we will use a fluorescent chemical probe in order to characterize actual flux of ozone experienced by a target exposed to plasma

Plasmas for organic synthesis and chemical probes for plasma diagnostics

Although organic chemistry plays a critical role in many plasma applications, there is room for further cross-fertilization between the two disciplines. Here we explore two possible avenues: (1) plasma physics as a new tool for the organic chemist and (2) organic compounds as diagnostics for the plasma physicist

Comparative study of chemical probes for ozone detection

Plasma composition is typically studied by absorption and emission spectroscopy, mass spectrometry and computational studies. While these techniques provide valuable information about the chemical species in the gas phase, in many applications it is desirable to have a direct measurement of the dose of chemical species delivered to a particular target. For this purpose, chemical probes are particularly interesting as they can provide an inexpensive means for determining the dose of a particular compound. A number of chemical probes have recently been used by the plasma community, particularly those working in plasma medicine and with plasmas interacting with liquids. Generally, however, these probes were not initially intended for use in plasma environments and therefore, it is important to assess their suitability and identify any selectivity issue that could affect the correct interpretation of the measurements. Here, we report on a comparative study of three chemical probes aimed at the quantitative detection of ozone (Table 1): Indigo Carmine and two DCF-derived fluorescent probes

Continuous flow ozonolysis using atmospheric plasma

Ozonolysis is widely used in organic synthesis to obtain aldehydes and ketones from alkenes, a process of great interest, for example, for the pharmaceutical industry. This reaction is more environmentally accepted than other alternative oxidations and it has good atom efficiency. Ozonolysis, however, has an important drawback; the ozonides generated as intermediates in the process are unstable and pose a risk of explosion. To minimize this risk, continuous flow processing can be used, as this eliminates the accumulation of large amounts of hazardous intermediates, thereby offering an alternative to batch processing that greatly enhances the control and safety of the ozonolysis process.1,2 Here we report on the results obtained with an air plasma-driven continuous-flow ozonolysis system. (... continues

Virtues and limitations of Pittsburgh green for ozone detection

A recently proposed 2′,7′-dichlorofluorescein (DCF)-derived fluorescent probe for the detection of ozone shows good selectivity against a number of reactive oxygen species and good pH stability for biological and environmental applications. It is found, however, that over oxidation of the fluorescent product (Pittsburgh green) can occur. This could render quantitative measurements inaccurate due to a reduction in fluorescence and overlapping fluorescence signals from over oxidation by-products and it requires careful experimental design. Although difficult to assess by fluorescence measurements, the over oxidation can be conveniently monitored by 1H NMR spectroscopy