Spectroscopic And Photoelectrochemical Properties Of Biomacromolecules-Semiconductor Nanoparticles Composites

In recent years,the integration of semiconductor nanoparticles and biological systems has attracted a great many concerns in biology and medicine field. Investigations of biomacromolecules-semiconductor nanoparticles conjugates(composites) will provide significant theoretical foundation for the biological study and medical diagnosis and assist the construction and operation of nano-molecular devices and biosesors.Besides,semiconductor nanoparticles as fluorescence biological probes play an important role in biological labeling, bio-imaging,and biological detection.Accordingly,the emphasis of this thesis is focused on investigating the biomacromolecules-semiconductor nanoparticles conjugates and semiconductor nanoparticles as fluorescence biological probes.These works can be divides into two parts:1.DNA/semiconductor nanoparticles composites were constructed utilizing DNA as the stabilizers and templates.The influence of DNA on the spectroscopic and phtoelectrochemical properties of the composites was investigated,and the interactions between DNA and semiconductor nanoparticles were discussed.2.Different kinds of fluorescence biological probes based on semiconductor nanoparticles were fabricated,and their photo-induced electron transfer with redox proteins were studied by spectroscopic characterizations.The influencing factors on the interactions were further investigated.The main results are summarized as follows:1.The interactions between DNA and semiconductor nanoparticles(1) In DNA/CdS nanoparticles composites,CdS nanopaticles were intergrated with DNA through electrostatic affinity;DNA scaffolds did not affect the energy band of CdS nanoparticles;CdS nanoparticles fabricated by ssDNA and dsDNA templates possessed a higher density of surface states than that by Na₄P₂O₇,which enhanced the fluorescence while restrained the photoelectrochemical response of CdS nanoparticles; the density of surface states in the composites fabricated by ssDNA was higher than that by dsDNA.(2) In DNA/ZnS nanoparticles composites,DNA scaffolds quenched the fluorescence of ZnS nanoparticles.Besides,the quenching due to ssDNA was stronger than that due to dsDNA.2.Photo-induced electron transfer between redox proteins and semiconductor nanoparticles(1) There were electrostatic interactions between cytochrome c and semiconductor nanoparticles.Ferricytochrome c captured the excited electrons of CdS and ZnS nanoparticles under photo-irradiation and was reduced to be ferrocytochrome c displayed by UV-Vis spectra,which diminished the radiative recombination of the holes and the excited electrons and quench the fluorescence.The fluorescence quenching efficiency of cytochrome c varied in different semiconductor nanoparticles systems.P₂O₇^4- and L-cysteine located at the nanoparticles/cytochrome c interface may act as "bridges" for the electron transfer,while in the systems protected by DNA, there was little electron transfer between cytochrome c and nanoparticles.(2) The interactions between horseradish peroxidase(HRP) and semiconductor nanoparticles included two parts:one is the hydrophobic interaction,which can enhance the fluorescence of semiconductor nanoparticles;the other is the electron transfer between Fe-protoporphyrin and semiconductor nanoparticles,which can quench the fluorescence of semiconductor nanoparticles.But the effects of electron transfer may be very small.