Preparation,Assembly And Fluorescent Sensing Of Upconversion Nanomaterials

Lanthanide-based upconversion nanoparticles can emit high-energy photons under excitation by near-infrared(NIR)low-energy light.Upconversion nanoparticles(UCNPs)possess many advantages,such as high chemical and optical stability,low toxicity,deep light-penetration under NIR excitation,minimal photodamage to living organisms,and nearly-zero background auto-fluorescence.They have been widely explored in recent years for their potential applications in nanomedicine.The present dissertation firstly prepared RE3+ doped KSc2F7 UC nanomaterials with strong luminescence,uniform size and controlled morphology,and studied the effect of reaction parameters on the formation mechanism of the nanomaterials.To expand the functionality,we synthesized various KSc2F7 based multifunctional nanomaterials with the same experimental method,and carried out a series of investigations into the modification of the aspect ratios.The details are as following:(1)For the first time,we synthesized the orthorhombic phase KSc2F7:20%Yb/2%Er nanorods and further studied the crystal structure and morphology evolution,as well as their upconversion(UC)properties under varying F-contents and reaction temperatures.The effect of other experimental parameters,such as reaction time,OA contents and the value of OA/OM on morphology and crystalline phase was also researched.Different from ?-NaYF4:20%Yb/2%Er nanorods that usually give strong green UC luminescence,strong red UC emission was observed in KSc2F7:Yb/Er nanorods under 980 nm laser excitation.Their UC mechanisms were further analyzed and compared.This study provides a novel type of rare earth nanorods with strong red UC emissions which has great potentials in high resolution 3-dimensional bioimaging,color displays,solid-state lasers,and photocatalysis.(2)A novel route was developed by doping rare-earth ions(RE3+)of large ionic radius(such as La3+,Ce3+,Sm3+,Eu3+,Tb3+,Dy3+,Yb3+ and Lu3+)for aspect ratio modification of the KSc2F7 nanocrystals(NCs).The results revealed that the shape could be readily tuned from one-dimensional long nanorods to zero-dimensional ultrasmall nanospheres.The aspect ratio of the NCs could be adjusted over a broad range from 45 to 1 by changing the dopant or doping concentration.It is interestingly found that doping lanthanide with larger ionic radius is equivalent to increasing the amount of the dopant on the aspect ratio evolution.The NCs doped with different RE3+ also exhibited multifunctionality,including upconversion(UC)and downconversion(DC)emissions as well as paramagnetic properties.Fluorescence resonance energy transfer(FRET)-based methods have gained considerable attention for biological detections because of their simplicity and high sensitivity.Conventional down-conversion fluorescent materials,including organic dyes and quantum dots,require ultraviolet or blue excitation wavelengths.Many biological samples show auto fluorescence under such conditions,which decreases the sensitivity of detection.Upconversion nanoparticles appear as a breakthrough to resolve the problem,which can penetrate deep tissues without causing sample damage and avoid auto fluorescence from biological samples.Thus,upconversion materials show potential to be used for FRET based sensing.We have carried out some preliminary work:(1)A novel FRET-based probe,y-cyclodextrin modified oleic acid-NaYF4:Yb,Ho upconversion nanoparticles functionalized with a rhodamine B derivative(RBD),has been achieved for Fe3+-sensing in aqueous solution with high sensitivity and selectivity.In comparison with the atomic absorption spectrophotometry(AAS)method,the relative standard deviations(RSDs)showed acceptable practicability for the detection of serum iron,proving the potentiality of this strategy for practical applications.(2)UCNPs can be morphology,structure and properties of the modified nanoparticles were stufunctionalized with citrate modified p-CD,which increases its water-solubility.The died by TEM,HRTEM,XRD,XPS and UCL.Based on fluorescence resonance energy transfer between ?-cyclodextrin derivative-assembled upconversion nanoparticels and rhodamine B,a novel strategy was proposed for highly sensitive and selective cholesterol-sensing in human serum.