Synthesis and Function of Ion-Selective Single-Molecule Fluorescent Imaging Molecules and Materials

Abstract

Neutrinos are fermion subatomic particles that interact only by weak subatomic forces—making them almost impossible to detect. However, they can be produced in specific radioactive decay reactions, such as beta decay. We hypothesize the detection of double beta decay through the tagging of the Ba2+ daughter ion from 136Xe (136Xe —136Ba2+ + 2ν + 2β). The proposal is to develop single-molecule fluorescence imaging (SFMI) technology to investigate gaseous chemical constituents in high-pressure gases (ca. 30-150 psi) at gas-solid interfaces. To achieve proper SMFI, heterogenous self-assembled monolayers (SAMs) containing fluorophores that operate under dry conditions and are turned on when a covalently attached binding domain captures Ba2+ pursued. Many technological advances in molecular sensors are required to achieve this goal. The background context and the contributions to the field are outlined in chapter 1. The key ideas behind the design of different crown ether chelating agents with diverse fluorophores to demonstrate a fluorescent response to Ba2+ cation is argued. SMFI is being applied in the search for neutrinoless double-beta decay (0νββ) through the development of novel barium sensing molecules that will be employed as the first dry-phase chemosensor to detect Ba2+ ions using the new method, which is still in progress. Chapter 2 discusses the synthesis of the first-generation barium chemosensor tags. Anthracene substituted aza-18-crown-6-ether has been shown to function in the dry phase with almost no intrinsic background from the unchelated state. Through fluorescence microscopy with single barium ions in the solution, the sensors perceive barium ions in dry films, opening the door to the detection of single ions in high-pressure xenon gas. By applying naphthalimide to (di)aza-crown-ether chemosensors in chapter 3, we developed simple, robust, and effective Ba2+ selective chemosensors that performed well in 136Xe gas under high pressure while achieving SFMI in polyacrylamide matrix. NMR spectroscopy and fluorescence experiments support the concept of photoinduced electron transfer for turn-on sensing. Using an oil-free microscopy technique, we succeeded in imaging Ba2+ ions within the large volumes of 136Xe for the first time, which is an essential step toward finding the hypothetical process known as 0νββ. In chapter 4, we explore the synthesis of the Hg2+ sensor. Mercury selective aminonapthalimide-aza-crown-ether sensor has an ion charge transfer mechanism, able to fluoresce selectively in a variety of solvents as well as cells and solvent-free matrices. Their significant selectivity for Hg2+ ions offers the potential for use as a functional chemosensor for trace mercury in various solvent-free matrices. Finally, in chapter 5, we discuss the preliminary approaches and data concerning the development of SAMs. The fine-tuning of functional chemosensors with SAMs at transparent dielectric surfaces may be accomplished by fluorescent monomer synthesis, APTES growth, the addition of spacer/functional molecule, and quality analysis of the monolayer formation by using different analytical techniques such as atomic force microscopy (AFM) and total internal reflection fluorescence (TIRF) microscopy. In summary, we have generated fluorescent dyes for dry phase sensing of Ba2+ in a gaseous Xe and examined the function of the monolayer formation for Ba-tagging using single-molecule fluorescent imaging tags (SMFI). Our current research focuses on the formation and identification of SAMs using analytical techniques, such as AFM and TIRF microscopy.