Design And Preparation Of Nanoparticles With Fluorescence In Multi-spectral Region For Biological Detection

Along with continual advances in nanotechnology and exploration by researchers,countless new-style fluorescent nanomaterials have sprung up in recent two decades,and they are widely used in the fields of chemical catalysis,photoelectric device and solar cells.Owing to the fluorescence emission in multi-spectral region,high quantum yields,low cytotoxicity and excellent fluorescence stability,a new-type of fluorescent nanomaterials with good biocompatibility have drawn greater attention by scientists,and they exhibit broad prospect of application in the fields of medical treatment,clinical diagnosis,bioimaging and biosensing.Nanomaterials with fluorescence in multispectral region play a pivotal role and have deeply promoted technical progress in the areas above.Therefore,it possesses great theoretic and practical significance to design and prepare differentfunctional nanomaterials with different fluorescence wavelengths and further to apply them in the fields of clinical diagnosis,bioimaging and biosensing.In this thesis,we are focusing on the biological detection applications of nanoparticles with fluorescence in multi-spectral region.We also investigated the influence of the synthetic conditions,size and composition of nanoparticles on the fluorescent property for preparing nanoparticles with different fluorescent wavelengths.Besides,we also explore the feasibility and actual result of fluorescent nanoparticles in biological detection.These series of nanoparticles could provide a potential as a new type of fluorescent nanomaterials for biological detection.Firstly,EuS nanocrystals(NCs)with dual functions of fluorescent and magnetic were prepared through amine reducing approach.EuCl3·6H2O and 1-Dodecanethiol were used as Eu and S sources,and the alkyl amines(OLA)and alkyl acids(OA)as stabilizing agent,we develop a one-pot method to synthesize EuS nanocrystals with divalent value of Eu.The resultant EuS NCs show blue emission(peaking at 403 nm with 2.8% quantum yield)and paramagnetic properties at room temperature.By adjusting experimental conditions,the morphologies of EuS NCs could be tunable as nanowires,nanorods and nanospheres,while these EuS NCs also maintain fluorescent and magnetic properties.In order to expand the biological applications,the resultant EuS NCs are modified with amphiphilic block copolymer F127 and transferred from oil to water phase.The EuS NCs demonstrated excellent biocompatibility as well as preservation of their luminescence and paramagnetic properties.The EuS NCs offer multifunction and great advantages such as bright luminescence,paramagnetic,controllable morphologies,and good biocompatibility for the potential applications in the field of simultaneous magnetic resonance and fluorescence bioimaging.Secondly,using Ag nanodots(AgNDs)as templates,we prepared gold nanodots(AuNDs)with red fluorescence through the galvanic exchange reaction.The asprepared AuNDs show a diameter smaller than 2.5 nm and exhibit red fluorescence(quantum yields ~10%)with the emission peak at 608 nm.The MTT assay and histopathological examination results indicate that AuNDs possess very low toxicity.The as-prepared AuNDs could be used in bioimaging application in PC12 neural cells.Experimental results show that AuNDs could uptake into cells and mainly distribute in the lysosomes.After injected into the sciatic nerve of rat for even 10 days,the AuNDs still well maintained fluorescent properties.The AuNDs were further conjugated with cholera toxin B(CTB),which is a highly sensitive retrograde neural tracer,to form CTB-AuNDs complex.CTB-AuNDs can be taken up and retrogradely transported by neurons in the peripheral nervous system of rats.CTB–AuNDs possess excellent advantages such as high photoluminescence intensity,good optical stability,long life time and non-toxicity.Thus,as a targeting regent for neural cells,CTB–AuNDs demonstrate reliable fluorescent retrograde tracers.Thirdly,we designed branched polyethylenimine(PEI)with surface segmental modification of sulfydryl group(SH-PEI).Using SH-PEI as ligand,hydrazine hydrate as reducing agent,HAu Cl4 as source of Au,we developed to prepare near-infrared region(NIR)fluorescent SH-PEI-AuNDs through a simple “bottom-up” chemical route.The fluorescence of the SH-PEI-AuNDs can be tunable from the visible red(wavelength of 609 nm)to NIR(wavelength of 811 nm)corresponding to the increasing size of the AuNDs.The SH-PEI were designed as the ligands to synthesize AuNDs based on the following reasons.Firstly,compared with PEI,SH-PEI showed significantly lower cytotoxicity after the amine groups are partly modified with sulfydryl groups.Secondly,when the sulfydryl groups of SH-PEI anchors on the surface of Au NDs,the amine terminal groups of SH-PEI are towards water phase.This structure not only can endow AuNDs with excellent stabilities but also make Au NDs possess positive charge.Finally,and more importantly,the SH-PEI-AuNDs with positive charges and low cytotoxicity can be used as a kind of perfect DNA carrier for combining with negative charged DNA to form the complex via electrostatic interactions,and protect DNA to be uptaken by cells to realize gene transfection.Finally,in order to obtain nanomaterials with longer fluorescent wavelength in NIR region,we introduce Cu element into system to prepare Au/Cu alloy nanodots with fluorescent properties in the second near-infrared region(NIR-II).The as-prepared Au/Cu alloy nanodots show a diameter of 2.7 nm and possess NIR-II fluorescence emission at 1080 nm.The Au/Cu alloy nanodots exhibit relatively high quantum yields(~2%),which are 5 times higher than that of the commercial carbon nanotube.More interesting,Au/Cu alloy nanodots show tunable luminescence from NIR-I(811 nm)to NIR-II(1130 nm)corresponding to increasing the content Cu element in the nanodots.The Au/Cu alloy nanodots with high photoluminescence intensity,good fluorescence stability and low cytotoxicity can be used as an excellent NIR-II fluorescent probe for potential applications in the field of in vivo NIR-II fluorescent imaging.