Preparation And Research Of Polyacrylic Acid-Functionalized Rare Earth(La³⁺,Nd³⁺,Eu³⁺,Gd³⁺)-doped Nanocrystals

With the tremendous development in optical emissice probes in the past decades fluoresenct bioimaging has become a demanding area in diagnosis and treatment of a variety of diseases. Organic dyes and quantum dots are most widely used optical probes in clinical diagnostic applications while both have some limitation. For example, organic dyes are easily subject to photo-bleaching and luminescence blinking in view of the mutability of conjugationg π–electrons. The toxicity of QDs caused by heavy mental ions will hinder their biological uses seriously. lanthanide nanoparticles(Ln NPs) had become a rising star in fluorescent bioimaging owing to their remarkable features, high photochemical stability, high PL quantum yield, and low toxicity.Water solubility of nanomaterials is a prerequisite for biomedical applications, so are lanthanide luminescent bioprobes. Inorganic and organic surface modification can be applied to transform the hydrophobic as-synthesized Ln NPs to hydrophilic and stabilize the colloidal dispersion. Nevertheless, these methods for surface modification still have some limitations – either needs complicated procedure, or has low QY that has a great impact on high-contrast bioimaging and fluorescence background, or the as-prepared dispersion had poor stability. Consequently, it is necessary to develop a facile synthetic procedure to obtain stable and high luminescent Ln NP aqueous dispersions. The studies were carried out in this paper as follows:(1)Ultrasmall LaF3: Eu nanocrystals(NCs) were prepared by a one-pot hydrothermal method using PAA as surface modification agent. The LaF3:Eu@PAA NCs are well dispersed in water. The as-prepared dispersions have excellent stability that could last for two months without precipitation. Meanwhile, the dispersions have a high absolute quantum yield of 66%. Furthermore, the NCs show no significant cytotoxicity for concentrations up to 1000 μg ml-1.(2)Monodisperse GdF3:Eu NCs encapsulated by polyacrylic acid(GdF3:Eu@PAA NCs) were prepared via a modified one-pot hydrothermal method. The GdF3:Eu@PAA NCs are well dispersed in water and the as-prepared dispersion have a high absolute quantum yield of 57%. In addition, Gd3+ ions could offer positive-contrast enhancement, which opens the door for modal imaging using Gd-containing NCs.(3)Ultrafine and water-dispersible LaF3: Nd NPs are synthesized via a one-step facile hydrothermal approach using PAA as modifier. The near-infrared to the near-infrared emission endow the obtained NCs with promising applications in biolabels and bioimaging. We compared the morphology and optical properties of LaF3:Nd NCs with that of La F3:Nd@PAA NCs. The effect on the fluorescent performance of the doping ions concentration, reaction time, and reaction temperature are studied systematically.