Rational Design Of Multidimensional Multilayered Upconversion Nanoarchitectures For Biomedical Applications

In this dissertation,we designed a new class of multidimensional,multilayered upconversion nanoarchitectures with different shapes,composition,and surface properties for bioanalytical and biomedical applications as follows:1.We rationally synthesized three-dimensional upconversion core-double-shell nanodendrites(UCNDs),including an active core(NaYF4:Yb,Er,Ca)capped by a transition layer(NaYF4:Yb,Ca)and an active outer shell(NaNdF4:Yb,Ca).The high concentration of Nd3+sensitizer in the outer dendritic shell enhances the luminescence intensity,while the transition layer enriched with Yb3+acts as an efficient energy migration network between the outer shell and inner core along with preventing the undesired quenching effects resulting from Nd3+.These unique structural and compositional merits enhanced the upconversion luminescence(UCL)of UCNDs by 5 and 15 times relative to NaYF4:Yb,Er,Ca@NaYF4:Yb,Ca truncated core-shell UCNPs and NaYF4:Yb,Er,Ca spherical core upconversion nanoparticles(UCNPs),respectively under excitation at 980 nm.The SiO2-COOH layer coated UCNDs(UCND@SiO2-COOH)were successfully used as efficient long-term luminescence probes for the in vitro and in vivo bioimaging without any significant toxicity.The uptake and retention of UCND@SiO2-COOH were almost found in the liver and spleen.This study may open the way towards the preparation of three-dimensional UCNDs nanostructures for biomedical applications.2.We developed a facile scalable approach that was presented for the rational design of multidimensional,multilayered sand-clock-like UCNPs(denoted as UCCKs)bounded with high index facets,with a tunable Nd3+content,and without a template or multiple complicated reaction steps.This was achieved using the seed-mediated growth and subsequent longitudinal direction epitaxial growth with the assistance of oleic acid and NH4F.The as-formed UCCKs composed of inner layer(NaYF4:Yb,Er,Ca),intermediate layer(NaYF4:Yb,Ca),and outer layer(NaNdF4:Yb,Ca).The outer shell,enriched with Nd3+sensitizer,augmented the near-infrared(NIR)photons absorption,whereas the intermediate shell,enriched with Yb3+,acted as a bridge for energy transfer from Nd3+to Er3+emitter in the inner core alongside with precluding any deleterious energy back-transfer from Er3+ or quenching effect from Nd3+.These unique structural and compositional properties of UCCKs endowed the UCL intensity of UCCKs by 22 and 10 times higher than that of hexagonal UCNPs core(NaYF4:Yb,Er,Ca)and hexagonal UCNPs core-shell(NaYF4:Yb,Er,Ca@NaYF4:Yb,Ca),respectively.Intriguingly,the UCL intensity increased significantly with increasing the content of Nd3+in the outer shell.The silica-coated UCCKs were used as excellent long-term luminescence probes for the in vitro bioimaging without any noteworthy cytotoxicity.The presented approach may pave the road for controlling the synthesis of multidimensional UCCKs for various applications.