Study On Functionalization Of Gold Nanoclusters And Its Application In Optical Sensors

Fluorescent gold nanoclusters(GNC) as a new class of fluorophores had attracted more and more attention due to their unique molecule-like properties and outstanding physical and chemical properties. Taking advantages of gold nanoclusters, such as superior fluorescence stability, excellent sensitivity, biocompatibility, sub-nanometer size and ease of synthesis, it had been successfully applied to fluorescence detection, catalytic, biosensing and bioimaging. However, these previous reviews focused on either one kind of gold nanoclusters with fixed emission length or the application about just one function. There were a variety of challenges remains when it was applied in multicomponent detection, biology complex reactions catalyzing and cancer diagnosing and therapying. Therefore, we had taken many studies for spectral expansion, multifunctional and multi-informatization of gold naoclusters, aiming to provide information and practical basis for the gold nanoclusters functional studies.The negatively charged double gold nanoclusters(D-GNCs) was synthesised based on mixing bovine serum albumin stabled nanoclusters and lysine stabled gold nanoclusters at appropriate ratio. Then, the D-GNCs was assembled on the surface of graphite oxide sheets which was modified with anino group to form positive charge initially through electrostatic interaction. The double gold nanoclusters/graphene oxide(D-GNCs/GO) could be successfully prepared. The study demonstrated that the interaction between GNC@Lys and GNC@BSA increased the fluorescence intensity of GNC@BSA. The secondary structure of stabilizer BSA could be distinctly changed under the influence of GO, for which the exposure degree of the core surrounded by BSA was increased. Because of the unique optical properties of DGNCs/GO, it could be used as fluorescent probe for Hg2+ detection. The sensitivity and reaction rate were both improved nearly twice times than that of single GNC@BSA and D-GNCs respectively. The fluorescence peak intensity linearly decreased with increasing Hg2+ concentration in the range of 1.0 × 10-5 to 5.0 × 10-13 mol·L-1 with a detection limit of 1.8 × 10-13 mol·L-1(S/N = 3). It had been successfully applied to detection of Hg2+ in water.Gold nanoclusters/glucose oxidase/graphene oxide(GNC/GOD/GO) multifunctional catalyst was prepared by introducing the negatively charged mimic enzyme GNC@BSA and natural enzyme GOD onto GO-NH3+ sheets through electrostatic interaction. The secondary structure of BSA and GOD were changed under the influence of GO, for which the stability of GNC@BSA was not only improved but also the catalytic activity of the multifunctional enzyme was greatly accelerated. With the cooperation between GNC and GOD,two steps interaction including the decomposition of hydrogen peroxide and oxidation of glucose was completed. Owing to the greatly synergistic catalytic effect between GNC and GOD, the nanosensor based on the hybrid displayed an ultrasensitive fluorescence response to glucose. The fluorescence peak intensity linearly decreased with the increase of glucose concentration in the range of 1.1×10-2 to 1.6 ×10-7 mol·L-1 with a detection limit of 6.8 ×10-8mol·L-1(S/N=3). It had been successfully applied in detection of glucose in real serum samples. The proposed method has higher long-term stability, sensitivity, repeatability and stability when compared with present glucose sensors.Multifunctional nanoplatform that was safe and combining thermal therapy and fluorescence imaging together was highly demanded in cancer theranostic. Herein the dual functional magnetic fluorescent microsphere(Si O2@GNC-Si O2@Fe3O4) was successfully synthesized by a double-coated Si O2 approach. The monodisperse magnetic nanoparticle which was modified with carboxyl group to increase the repulsion among particles and to prevent them from aggregatting initially were used as seeds in the first layer of Si O2 which could separate Fe3O4 and GNC from each other. The imaging guided GNC were act as cores in the second layer of Si O2 by which could greatly enhance the fluorescence intensity of the microsphere. The nanocomposite exhibited high photothermal effect and fluorescence intensity. The solution temperature of Si O2@GNC-Si O2@Fe3O4 at a concentration of 0.20 mg· m L-1 could be raised to 42℃ only within 10 min at the laser power of 500 m W. The fluorescence peak intensity linearly decreased with the increase of temperature in the range of 10~45℃, so the GNC could not only act as fluorescence label but also used as thermometer to indicate local temperature changing.Otherwise, the multi-emissive fluorescent complex, multi-functional gold nanoclusters catalyst and multi-informational magnetic fluorescent microsphere were fabricated in this work. They not only opened a new avenue for fabrication of fluorescent hybrids, but also provided approaches for design and synthesis of GNC-based multifunctional catalyst and multiinformatization microspere. They held great potential application in spectral encoding, multicomponent analysis, biological complex reaction catalysis and diseases diagnosing and threapying.