Synthesis And Characterization Of Upconversion Nanoparticles With Shell Structure And Hydrophilic Modification

Recently,nano-science is becoming an emerging technology with the continuous research of nanoparticles.The rare earth-doped upconversion nanoparticles have developed into a new type of biological materials used in photodynamic therapy and biological fluorescent probes.Compared with conventional light-emitting materials(such as organic dyes,semiconductor quantum dots,etc.),upconversion nanoparticles have its unique advantages.As we all know,"biological tissue optical window" in the 700-1300 nm,using infrared light can penetrate biological tissue with a good ability and not cause any light damage.Upconversion nanoparticles can not only be excited by near-infrared light,but also emit light from ultraviolet to near-infrared with different wavelengths.And it has narrow emission bands,large anti-Stokes shift and little light scattering.All these make it possible to have a good application of biomarkers,multimodal imaging and photodynamic therapy.Therefore,this article studied the effect of upconversion nanoparticles’ synthesis process on luminescence properties.Upconversion nanoparticles excited at 980 nm with a diode laser transfer energy to excite the photosensitizer by Forster Resonance Energy Transfer,in which upconversion nanoparticles are as the donor.And we use the hydrophilic-hydrophobic assembly to make upconversion nanoparticles and photosensitizer become water-soluble.And we also studied the ability of photosensitizer to generate singlet oxygen after excitation.In our study,we synthesized two phases upconversion nanoparticles and examined their luminescence properties,size and morphology under different synthetic conditions.And we choose β-NaYF4: Er3+,Yb3+ that has better luminescent properties to further research.To further enhance the luminescence intensity,upconversion nanoparticles with core–shell structure were also prepared and luminescence intensity increases an order of magnitude.Ligand-free has been used to prepare water dispersible upconversion nanoparticles.Three emissions bands around 520,540 and 650 nm are ascribed to 2H11/2 → 4I15/2,4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ ion.Shell structure makes 650 nm emission intensity significantly enhanced in order to as a better energy donor to provide energy.Because the absorption spectra of photosensitizer and the emission spectra of the nanoparticles are overlap,we choose the Chlorin e6 as the energy acceptor.Then we use the poloxamer(F188)to make nanoparticles and photosensitizers into a whole system of water-soluble by the hydrophilic-hydrophobic assembly.In 980 nm laser excitation,upconversion nanoparticles are excited and transfer energy to excite the photosensitizer by Forster Resonance Energy Transfer.So Chlorin(Ce6)is excited to produce singlet oxygen.