Surface Functionalization Of NaYF : Yb, Er And Its Application

In recent years, many studies have focused on the up-conversion phosphorsNaYF4:Yb,Er due to their wide application prospect in biomedical applications suchas biosensing, diagnose and etc. Especially, the advantages of NaYF4:Yb,Er such asnarrow emission bands with large anti-Stokes shifts, high photostability, theavoidance of autofluorescence, less toxicity and greater penetration depth in tissuesmake NaYF4:Yb,Er NPs more suitable for biomarkers than the conventionally organicdyes and quantum dots. NaYF4:Yb,Er NPs has become one candidate of the mostpromising new generation materimals to achieve bio-labeling and bioimagingapplications. However, the poor water solubility, low luminescence efficiency ofas-synthesized NaYF4:Yb,Er NPs have limited its biomedical applications. In order tomeet their wide application in biological detection and medical imaging research,exploring the surface functionalization of NaYF4:Yb,Er NPs appears to be particularlyimportant.The main contents of this paper are as follows:(1) We present a universal protocol, ultrasonic separation under weak acid toremove the oleate ligand from the surface of OA-capped NPs. The reactionmechanism is as follows. The H+ion will attack the conjunction of the carboxyl andthe rear earth atom of NaYF4:Yb,Er NPs, that is electrophilic substitution, namely, H+ions and Lnx+of NaYF4:Yb,Er NPs compete against each other to combine withcarboxyl groups. What is more, H+ions’combination with oleate becomes much easyowing to the assistance of low power ultrasonic. The OA-capped NPs includingNaYF4:Yb,Er (18nm), NaGdF4:Yb,Er (8nm), CaF2:Yb,Er (10nm), PbS (7nm) andZnS (12nm) have carried out the transformation from oil-soluble to water-solublesuccessfully. The results were characterized by TEM, XRD, TGA, HNMR, FTIR andthe Zeta potential testing.(2) The results of zeta potential testing indicate that the newly prepared OA-freeNaYF4:Yb,Er NPs are the positive charged particles, which are reactive electrophilicmoiety. Then, we carry out the coupling of the freshly prepared water-soluble NaYF4:Yb,Er NPs with amino acid directly in order to illustrate the reaction activityof the freshly synthesized ligand-free NaYF4:Yb,Er NPs. The freshly preparedwater-soluble NaYF4:Yb,Er NPs have coupled with glutamic acid and lysinesuccessfully. The results were characterized by TEM, PL and the Zeta potential testingand the mechanism was also explained.(3) The synthesis scheme of heterostructure NaYF4:Yb,Er@Ag was created andprepared the double functional heterostructure of NaYF4:Yb,Er@Ag successfully. Theobtained samples were characterized by TEM, HRTEM PL. A series of experimentwas tried to explore the impact of the amount of silver nitrate to the morphology ofNaYF4,Yb,Er@Ag NPs.