The enhancement of upconversion luminescence (UCL) of rare earth doped upconversion nanoparticles (UCNPs) in aqueous solution is particularly important and urgently required for a broad range of biomedical applications. Herein, an effective approach to achieve highly enhanced UCL from NaYF4:Yb3+,Tm3+ UCNPs in aqueous solution is presented. We demonstrate that UCL of these UCNPs can be enhanced more than 104-fold by using a mesoporous silica low refractive index resonant waveguide grating (low-n RWG) in contact with aqueous solution, which makes it well-suited for biomedical applications. The structure parameters of the low-n RWG are tuned via rigorous coupled-wave analysis simulation to ensure strong local excitation field to form atop the TiO2 surface of the low-n RWG, where UCNPs are deposited. As the low-n RWG is excited by a near-infrared laser at 976 nm to match its guided mode resonance (GMR) condition, UCL emitted from UCNPs is greatly enhanced thanks to the strong interaction between excitation local field and UCNPs. UCL emission of UCNPs can be further enhanced about two to four times when the UCL emission condition (wavelength and angle) matches with the GMR condition. Furthermore, we show that the presence of biotin molecules atop of the low-n RWG can be easily detected through UCL emission generated from streptavidin-functionalized UCNPs with the help of the streptavidin–biotin specific binding. The results indicate that the low-n RWG has high potential for UCL biosensing and bioimaging applications.

Lanthanide (Ln3+)–doped upconversion nanoparticles (UCNPs) offer an ennormous future for a broad range of biological applications over the conventional downconversion fluorescent probes such as organic dyes or quantum dots. Unfortunately, the efficiency of the anti−Stokes upconversion luminescence (UCL) process is typically much weaker than that of the Stokes downconversion emission. Albeit recent development in the synthesis of UCNPs, it is still a major challenge to produce a high−efficiency UCL, meeting the urgent need for practical applications of enhanced markers in biology. The poor quantum yield efficiency of UCL of UCNPs is mainly due to the fol-lowing reasons: (i) the low absorption coefficient of Ln3+ dopants, the specific Ln3+ used here being ytterbium (Yb3+), (ii) UCL quenching by high−energy oscillators due to surface defects, impurities, ligands, and solvent molecules, and (iii) the insufficient local excitation intensity in broad-field il-lumination to generate a highly efficient UCL. In order to tackle the problem of low absorption cross-section of Ln3+ ions, we first incorporate a new type of neodymium (Nd3+) sensitizer into UCNPs to promote their absorption cross-section at 793 nm. To minimize the UCL quenching induced by surface defects and surface ligands, the Nd3+-sensitized UCNPs are then coated with an inactive shell of NaYF4. Finally, the excitation light intensity in the vicinity of UCNPs can be greatly enhanced using a waveguide grating structure thanks to the guided mode resonance. Through the synergy of these three approaches, we show that the UCL intensity of UCNPs can be boosted by a million−fold compared with conventional Yb3+–doped UCNPs.

We report for the first time the preparation of luminescent lanthanide nanomaterial (LLN) linked bioconjugates and their application as a label tool for recognizing virus in the processing line of vaccine industrial fabrication. Several LLNs with the nanostructure forms of particles or rods/wires with europium (III) and terbium (III) ions in lattices of vanadate, phosphate and metal organic complex were prepared to develop novel fluorescent conjugates able to be applied as labels in fluorescence immunoassay analysis of virus/vaccine.With regard to the LLNs, we have successfully synthesized nanoparticles around 10 nm of YVO 4 : Eu(III), with high emission in the red spectral region, nanorod and nanowire of TbPO 4 • H 2 O and Eu 1−x Tb x PO 4 • H 2 O, width 5-7 nm and length 300 nm, showing very bright luminescence in green, and core/shell nanosized Eu(III) and Tb(III)/Eu(III) complexes with naphthoyl trifluoroacetone and tri-n-octylphosphineoxide (Eu.NTA.TOPO@PVP, Eu X Tb 1−X .NTA.TOPO). The appropriated core/shell structures can play a double role, one for enhancing luminescence efficiency and another for providing nanophosphors with better stability in water media for facilitating the penetration of nanophosphor core into a biomedical environment.The organic functionalizations of the obtained LLNs were done through their surface encapsulation with a functional polysiloxane including active groups such as amine (NH 2 ), thiocyanate (SCN) or mecarpto (SH). The properties of functional sol-gel matrix have great influence on the luminescence properties, especially luminescence intensity of YVO 4 : Eu(III), Eu.NTA.TOPO@PVP, TbPO 4 • H 2 O and Eu x Tb 1−x PO 4 • H 2 O. Bioconjugation processes of the functionalized LLNs have been studied with some bioactive molecules such as biotin, protein immunoglobulin G (IgG) or bovine serum albumin (BSA).The results of LLN-bioconjugate linking with IgG for recognizing virus (vaccine) will be presented in brief. It is consistent to state that the LLN bioconjugates prepared from YVO 4 : Eu(III)-nanoparticles, TbPO 4 • H 2 O nanorod or wire and EuNTA.TOPO@PVP nanosized core/shell complex could be used as labels for recognizing virus in diagnosis or in vaccine production by use of the fluorescence immunoassay (FIA) method. The fluorescence images of the incubated specimens consisting of LLN bioconjugate and vaccine fabricate could be obtained well in terms of sharpness, reproductivity and stability.

2021) Gold nanorods conjugated upconversion nanoparticles nanocomposites for simultaneous bioimaging, local temperature sensing and photothermal therapy of OML-1 oral cancer cells,