Study On Chemical And Biochemical Sensors Based On Fluorescence Excited State Intramolecular Proton Transfer And Energy Transfer

Improving the selectivity of chemosensors is recognized as a difficult problem in the field of chemical sensing technology. Searching for novel fluorescent molecular recognition ionophores with high selectivity has attracted large attention of current analytical chemistry. The fluorescent compounds, containing 2-2'-hydroxyphenyl function group, such as benzoxazole, benzothiazole and quinazolinone, can exhibit excited state intramolecular proton transfer (ESIPT) reaction. Fluorescent dyes that exhibit excited state intramolecular proton transfer (ESIPT) reactions have attracted great interest for several decades because such compounds show good photo-physical properties such as intense fluorescence, large Stokes shifts and significant photostability. They have the trend of combining with some metal ions. When the binding occurs, the ESIPT process would be blocked, causing the change of fluorescent signal. And we can get the analytical information from the change of fluorescent signal. Therefore, studying the fluorophores exhibited ESIPT reaction, as the molecular recognition ionphores for fluorescent chemical sensor, remains task of theoretical and practical significance. On the other hand, immunoreaction is the most selective reaction in the chemical and biochemical field. In order to improve the sensors'selectivity, many chemists are interested in biology field, and focus on the combination of chemistry and biology, leading to a new study section of biochemistry. For example, the chemical compounds that have been labeled with antigen and antibody will connect with each other by immunoreaction, yielding a new supramolecule. Then the energy or structures of the chemical compounds might change, providing the analytical signal for the preparation of biochemical sensors.Taking the aforementioned information as research objectives, this thesis mainly accomplished three research tasks that have been divided into two parts. Its contents include following. Part one mainly describes fluorescent chemical sensors based on fluorophores that exhibit ESIPT reaction.(1)A highly selective fluorescent sensor for Cu2+ based on 2-(2'-hydroxyphenyl)- benzoxazole in a poly (vinyl chloride) matrix. The effect of the composition of the sensor membrane has been studied and results shown that optode membrane composition consisting of 2% HPBO, 5% NaTPB, 62% DOS, and 31% PVC (w/w) provides the best response for Cu2+. The sensor showed excellent selectivity for a wide range of transition, alkali, alkaline metals and common cations. Meanwhile, the contents of Cu²⁺ in river sample were determined by the proposed sensor. The Cu²⁺ can be linearly determined in the range of 4.0×10^-8 M-5.0×10^-5 M.(2)2-(2′, 5′-di-hydroxyphenyl)-4(3H)-quinazolinone was synthesized as a fluorescent chemosensor for mercury (II). We compared the fluorescence spectra of DHPQ with2-(2′-hydroxy-5′-methylphenyl)-4(3H)-quinazolinone (MeHPQ) and 2-(2′-hydroxylphenyl)-4(3H)-quinazolinone (HPQ), for their structures are similar with DHPQ, and results show that DHPQ provides the best response to Hg²⁺, because DHPQ has two hydroxyl groups, which make it easier to be deprotonated and bound with Hg²⁺and shows larger changes of the fluorescent signal than that of HPQ. The Hg²⁺ can be linearly determined in the range of 8×10–7 M-2×10–4 M.In part two, fluorescent immunoassay via resonance energy transfer between CdTe quantum dots and core-hell fluorescent nanoparticles doped with rhodamine B was investigated. The emission wavelength of CdTe quantum dots is close to the excitation wavelength of rhodamine B, which is the basic condition for the fluorescence resonance energy transfer (FRET) happening. The FRET occurs between quantum dots (QDs) donors with rhodamine B acceptors by combining CdTe QDs labeled with goat-anti-human IgG to core-hell fluorescent nanoparticles doped with rhodamine B labeled with human IgG. With the decrease of the concentration of detected human IgG, the fluorescent intensity of the CdTe quantum dots would decrease and the fluorescent intensity of the core-hell fluorescent nanoparticles doped with rhodamine B would increase.