Fluorescence; fluorescent sensors; fluoride sensors; metal cation sensors; bioimaging
Fluorescence spectroscopy has been considered to be one of the most important research techniques in modern analytical chemistry, biochemistry, and biophysics. At present, fluorescence is a dominant methodology widely used in a great number of research domains, including biotechnology, medical diagnostics, genetic analysis, DNA sequencing, flow cytometry, and forensic analysis, to name just a few. In the past decade, with the rapid development of fluorescence microscopy, there has been a considerable growth in applying fluorescence technique to cellular imaging. The distinguished merits of fluorescence techniques, such as high sensitivity, non-invasiveness, low cytotoxicity, low cost, and convenience, make it a promising tool to replace radioactive tracers for most biochemical measurements, avoiding the high expense and difficulties of handling radioactive tracers. Among the wide range of applications of fluorescence technique, fluorescent sensing of various cations and anions is one of the most important and active areas. This dissertation is all about developing fluorescent sensors for physiologically significant ions, including F-, K+, Fe3+, and Ca2+. All of these sensors demonstrate fluorescence "turn-on" response upon interacting with their respective ions, which makes them much more appealing than those based on fluorescence quenching mechanisms. In Chapter II, a novel highly selective fluorescence turn-on F- sensor (FS), comprised of a fluorene platform serving as the chromophore, and two 1,2,3-triazolium groups functioning as the signaling moieties, is described. The function of FS is established on the basis of deprotonation of the C-H bonds of 1,2,3-triazolium groups, which makes FS the first reported anion sensor based on the deprotonation of a C-H bond. Easy-to-prepare test strips were prepared for determining F- in aqueous media, providing an inexpensive and convenient approach to estimate whether the concentration of F- contained in drinking water is at a safe level. Chapter III contains an optimized synthesis of a reported K+-selective group (TAC), and the development of two TAC-based fluorescence turn-on K+ sensors (KS1 and KS2). The synthetic route of TAC is shortened and its overall yield is enhanced from 3.6% to 19.5%. Both KS1 and KS2 exhibited excellent selectivity toward K+ over other physiological metal cations, high sensitivity for K+ sensing, and pH insensitivity in the physiological pH range. Confocal fluorescence microscopy experiments demonstrate that they are capable of sensing K+ within living cells. 2PA determination reveals that KS2 has a desirable 2PA cross section of 500 GM at 940 nm, which makes it a two-photon red-emitting fluorescent sensor for K+. Chapter IV describes the development of a novel BODIPY-based fluorescence turn-on Fe3+ sensor (FeS). FeS is a conjugate of two moieties, a BODIPY platform serving as the fluorophore and a 1,10-diaza-18-crown-6 based cryptand acting as the Fe3+ recognition moiety. FeS displays good selectivity, high sensitivity, reversibility, and pH insensitivity toward Fe3+ sensing. Based on its excellent performance in determining Fe3+ and very low cytotoxicity, FeS was effectively applied to sensing Fe3+ in living cells. In Chapter V, a new BODIPY-based fluorescence turn-on sensor (CaS) was designed and synthesized for selectively and sensitively determining Ca2+. CaS is comprised of two moieties, a BODIPY fluorophore and a Ca2+ complexing unit. CaS demonstrated selective fluorescence turn-on response towards Ca2+ over other biological metal cations. Moreover, CaS exhibited desirable sensitivity for Ca2+ detection, which makes it more suitable for extracellular Ca2+ determination. In addition, CaS was insensitive to the pH of the physiological environment, especially in the pH range of blood and serum. Therefore, CaS has potential to be applied to sensing Ca2+ ions in extracellular environments. Chapter VI discusses potential future work of KS2 and CaS, following the results achieved in this dissertation. Based on the desirable performances of both sensors in sensing their respective ions, future work could largely be focused on their applications in cellular imaging.
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Doctor of Philosophy (Ph.D.)
College of Sciences
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Dissertations, Academic -- Sciences; Sciences -- Dissertations, Academic
Sui, Binglin, "Fluorescence Off-On Sensors for F-, K+, Fe3+, and Ca2+ Ions" (2014). Electronic Theses and Dissertations. 1250.