Syntheses And Applications Of Dendrimer-nanocomposites

Nanocomposites,consisting of different nanoparticles,have been great interested in materials science,biotechnology and biosenser as they not only posses excellent characteristics of nanoparticles but also may result many novel properties from the synergistic effect among the components.In this paper three kinds of dendrimer-nanocomposites were synthesized by linking nanoparticles/enzyme with fourth generation polyaminoamide(G4 PAMAM) dendrimer that possesses unique structure and properties.The nanoparticles and enzyme modified with PAMAM exhibited improvement performance significantly and provided a new protocol for preparation of polymer nanocomposites.The details are summarized as follows:(1) Silver nanoparticles(Ag NPs) with carboxyl groups were synthesized by using thioglycolic acid(TGA) as the stabilizer.The research of spectral characteristics of the nanoparticles showed that Ag NPs would cluster and get instable with overabundance of TGA.The optimum conditions for modification of the Ag NPs were determined also. Ag-PAMAM nanocomposites were synthesized by tethering G4 PAMAM on the surface of Ag NPs covalently,which enhanced the stability and solubility of Ag NPs in water greatly. (2) CdS quantum dots(QDs) were synthesized in aqueous solution by using TGA as the stabilizer and characterized by spectrophotometry.A new fluorescence analysis method for determination of Fe³⁺ ions was developed by using CdS QDs as fluorescence probes,based on the investigation of fluorescence quenching of the quantum dots by inorganic ions. Under the optimum conditions,the relative fluorescence intensity decreased linearly with the Fe³⁺ ions concentration in the range from 5×10^-7 M to 100×10^-7 M with a detection limit of 6×10^-8 M.A new mechanism for fluorescence quenching of CdS quantum dots by Fe³⁺ ions was established,which developed the fluorescence quenching theory.CdS-PAMAM nanocomposites were synthesized by the electrostatic adsorption between CdS QDs and PAMAM.The light stability of quantum dots in CdS-PAMAM was improved greatly as the surface of CdS nanocrystals was well modified and sufficiently protected by PAMAM.The research exhibited that the fluorescence intensity of CdS QDs enhanced obviously due to energy transfer between CdS QDs and PAMAM in the CdS-PAMAM composites.The composites with these excellent properties have great promise of applications in solar cell, photo-devices and biotechnology.(3) A novel looped enzyme-PAMAM nanohybrids were synthesized by tethering horseradish enzymes(HRP) on G4 PAMAM covalently.The procedure for preparing the looped nanohybrids was as follows:HRP tethers on PAMAM to form simple hybrids first, then the simple hybrids grow to form large one,and to looped nanohybrids finally. Electrochemical research showed a high stability of the looped HRP-PAMAM composites due to well biocompatibility of PAMAM.The current response of the glassy carbon electrode modified with sol-gel containing looped composites maintained over 70%that of original value over 10 weeks.H₂O₂ biosensors,based on the looped enzyme-PAMAM composites,were prepared and their electrocatalysis behaviors were also investigated.The results showed the excellent performance of the sensor in high current response,well stability and long-tern catalytic active retainment.This research provided a new kind of enzyme- PAMAM nanocomposites for bioreactor,enzyme engineering and biotechnology.