Photoanalytical Chemistry Developments Of Gold Nanoparticle Involved New Resonance Energy Transfer Systems

As an early developed optical technique, resonance energy transfer (RET) has become a common method for the analytical detection and bioimage. In the RET process, energy donor chromophore can couple with energy acceptor chromophore through a dipole-dipole interaction, and the energy could be transferred to the acceptor in a non-radiative manner. The occurrence of this process is closely related to the distance between donor-acceptor pair. Therefore, RET is the powerful tool in the distance detection and their relative changes in a nanometer range, and has widely applications in the analysis of mutual interaction between biomacromolecules, cell physiology, immunoassay and etc. In the RET processes, rhodamine and its derivatives have quantum yield over 90%, therefore serve as a common energy transfer donor. However, using carbon quantum dots (CQDs) as energy donor is relatively less concerned. This is because, first the researches on the CQDs is still in the initial stage, and second the methods for the modification and functionalization of CQDs is limited. In the current established energy transfer process, gold nanoparticles (AuNPs) always be involved as energy acceptor in the RET process since it is easy to be synthesized and has unique localized surface free electrons. The AuNPs-involved RETs normally include nanometal surface energy transfer (NSET), plasmon resonance energy transfer (PRET) and metal enhanced fluorescence (MEF). Also, during the study on the process of RETs, the interrupting methods of RETs are restricted on the changes of donor, acceptor or the distance. This direct interruption has a demonstrable effect, but is it possible by using an indirect interrupting method? by which the observation of RETs would not directly influence the process.Concerning the as mentioned research status and dilemma, basing on the previous works, this thesis will focus on the synthesis and functionalization of CQDs, as well as the noble metal gold nanoparticle involved RET process. The main points of our work in this thesis are summarized as follows:1. A redox hydrothermal route to prepare high quantum yield carbon quantum dots as a potential energy donor in the energy transfer system. By choosing fullerene (C60) as carbon source and cetyltrimethylammonium bromide (CTAB) as passivant, highly PL CQDs were successfully prepared from by introducing H2O2 in aqueous NaOH under hydrothermal conditions. Transmission electronic microscope (TEM), dynamic light scattering (DLS) and gel permeation chromatogram (GPC) were used to confirm that the CQDs were spherical nanoparticles with uniform size distribution. Fourier transform infrared (FTIR) spectroscopy, X-ray photo electron spectroscopy (XPS) analysis, nuclear magnetic resonance (NMR) and raman spectrum were used to prove the existence of abundant carboxyl groups on the surface of this CQDs. The PL quantum yield (PLQY) of this CQDs could be as high as 80% by adjusting the synthesis routine (average PLQY was 66 ±14%). Under the excitation of 290 nm to 380 nm incident light, the emission peak of this CQDs was fixed to 395 nm. A further experiment indicated the unreplaceable role of CTAB to this highly PLQY CQDs. The involvement of CTAB could apparently decrease the non-radiative decay process and activate the radiative decay path. More experiments found the restriction of rotation could be used to improve the PL efficiency of CQDs. When different approaches were used to aggregate CQDs, the luminescence of CQDs exhibited a aggregation-induced emission enhancement property, which was the first time to report on the optical property of CQDs. This as-prepared CQDs could be considered as a potential energy donor. The success of the synthesis for this CQDs expand the choices of the do nor-acceptor pairs in the energy transfer system, and provide the possibility for further applications.2. Click-reaction-modified high quantum yield CQDs for biosensing via resonance energy transfere and targeting bioimaging. By introducing the method of organic synthesis, carboxyl CQDs were covalently bonded with propargylamine through the amidation reaction under the catalysis of 1,1'-carbonyldiimidazole (CDI). Confirmed by thin layer chromatography (TLC), purified by silica gel column chromatography and analyzed by FTIR spectroscopy, we ensured the alkynylation of CQDs was successful. The PLQY of the as-synthesized the alkynylated CQDs was 56 %, and the size distribution was 3.75±1.25 nm. Refering to the pervious work of our group, we decided to catalyze the "click" reaction between alkynylated CQDs and azido molecular beacon DNA by using nonstoichiometric copper chalcogenide nanocrystals (Cu2-xSySe1-y NCs, CuCNCs). Agarose gel electrophoresis confirmed the formation of CQDs-DNA complex. Further research carried out that the "click" reaction between CQDs and DNA would not influence the covalent conjugation between DNA and AuNPs. After we successfully formed the CQDs-DNA-AuNPs complex, a metal enhanced fluorescence (MEF) phenomenon was observed, the enhancing efficiency was 57%. We could realize the recongnization of single base-pair mismatch on the ring of the molecular beacon with the MEF. In further research, alkynylated CQDs was covalently bonded with nuclear targeting sequence (NLS). The NLS modified CQDs could specifically target the nuclei for cell image.3. Plasmonic resonance energy transfer (PRET) betweem rhodamine deriatives and AuNPs for copper, mercury ions detection. Mesoporous silica coated AuNPs (AuNPs@mSiO2) were synthsized by sodium hydrate etching on the silica layer. Scanning electronic microscope (SEM), Uv-Vis spectrophotometer and dynamic light scattering could be used to confirm the formation of silica layer and the mesoporous silica. The synthesized the rhodamine B hydrazide or the rhodamine B ethylenediamine was doped into the AuNPs@mSiO2 by molecular diffusion, and the PRET process was obersved when target ions was added to this system causing the ring open of rhodaminlactam derivatives. The addition of target ions could quenching the scattering light and the spectrum intensity significantly. This method could selectively recognize copper ions or mercury ions, and other eight interfering ions had no significant quenching effect. The electric field simulation of the rhodamine B doped AuNPs@mSiO2 indicated the rhodamine B had electric field interaction with AuNPs, which caused the scattering light quenching of the AuNPs.4. The establishment of a reversible enery transfer system between rhodamine derivatives and AuNPs. "Click" reaction was used to covalent bond azido tetramethylrhodamine (TAMRA) with surface alkynylated AuNPs, forming a bidirectional energy transfer system in which NSET and PRET could coexist. In this system, TAMRA was the energy donor in the NSET process and the energy acceptor in the PRET process, AuNPs was the energy acceptor in the NSET process and the energy donor in the PRET process. Fluorescence spectra confirmed the occurrence of the NSET and the dark field microscope and the light scattering spectrum system confirmed the coexistence of PRET in this system. Further theoritical calculations were used to simulated both process and proved that those two processes could theoretical coexist in one system. Evenmore, when altering the energy donor-acceptor pair to restrict the PRET process, the quenching efficiency of NSET could be influenced. This phenomenon indicated that these two energy transfer processes were not simply conbined together, some energy exchange also involved between them.In summary, this thesis mainly focused on a series of energy transfer processes which involved noble metal gold nanoparticles. Works on the synthesis and functionalization of energy donor and the establishment of new energy transfer system were done. From these design, more RET system could be developed. It is significant and important to realize a more simple and sensitive analytical detecting methods.