Coating a homogeneous layer outside the core nanoparticles has become a common method to improve the optical properties of nanoparticles. For rare earth ion-doped nanoparticles, although the homogeneous coating is found to enhance the upconversion luminescence, a large deviation in the reported enhancement amplitude, however, demonstrates the lack of a complete picture of the enhancement mechanism. In this work, we have performed steady-state and time-resolved spectroscopic studies on one of the most efficient upconversion nanosystems − β-NaYF4:Yb3+,Er3+ and β-NaYF4:Yb3+,Er3+@β-NaYF4 core/shell nanoparticles. Roles of the surface quenching centers, typically the high-frequency vibrational modes provided by the organic surfactants in the upconversion luminescence, are studied in detail. Our results show that excitation power density, once over a threshold, say ∼150 W/cm2 in this case, does have a non-negligible annealing effect, which may even lead to high luminescence upconversion intensity of the core nanoparticles compared to the shell-coated nanoparticles. The surface-related high-frequency vibrational modes play an important role in the upconversion process and in the laser annealing process, and the latter manifests itself in the difference of the laser annealing effect between the core and core/shell nanoparticles. From the upconversion luminescence kinetics analysis, it turns out that the luminescent centers of the core nanoparticle are severely quenched but homogeneous coating can effectively reduce the quenching, enhancing the upconversion luminescence. It is concluded that the upconversion emission spectrum, or more specifically the ratio between the red and green emissions, can be greatly altered by excitation power density for core nanoparticles but not for core/shell nanoparticles.

It is generally accepted that a lanthanide ions based upconversion material follows an activator low doping strategy (normally <3 mol%), because of the restriction of the harmful concentration quenching effect. Here, we demonstrate that this limitation can be broken in nanostructures. Simply by using an inert shell coating strategy, the concentration quenching effect for the activator (Er3+) could be eliminated and highly efficient upconversion luminescence realized in the activator fully doped nanostructure, e.g. NaErF4@NaYF4. More importantly, this novel nanostructure achieves some long-cherished desires, such as multiple-band co-excitation (∼800 nm, ∼980 nm and ∼1530 nm) and monochromic red emission. Proof-of-concept experiments are presented of the potential benefit of this structure in solar cells and anti-counterfeiting. This nanostructure offers new possibilities in realizing high upconversion emission and novel functionalities of lanthanide based nanomaterials.

Similar to many other anticancer therapies, photodynamic therapy (PDT) also suffers from the intrinsic cancer resistance mediated by cell survival pathways. These survival pathways are regulated by various proteins, among which anti-apoptotic protein Bcl-2 plays an important role in regulation of programmed cell death and has been proved to involve in protecting against oxidative stimuli. Confronted by this challenge, we propose and validate here a novel upconversion photosensitizing nanoplatform which enables significant reduction of cancer resistance and improve PDT efficacy. The upconversion nanophotosensitizer contains the photosensitizing molecules - Zinc phthalocyanine (ZnPc) and Bcl-2 inhibitor - ABT737 small molecules, denoted as ABT737@ZnPc-UCNPs. ABT737 molecules were encapsulated, in a pH sensitive way, into the nanoplatform through Poly (ethylene glycol)-Poly (l-histidine) diblock copolymers (PEG-b-PHis). This nanosystem exhibits the superiority of sensitizing tumor cells for PDT through adjuvant intervention strategy. Upon reaching to lysosomes, the acidic environment changes the solubility of PEG-b-PHis, resulting in the burst-release of ABT737 molecules which deplete the Bcl-2 level in tumor cells and leave the tumor cells out from the protection of anti-apoptotic survival pathway in advance. Owing to the sensitization effect of ABT737@ZnPc-UCNPs, the PDT therapeutic efficiency of cancer cells can be significantly potentiated in vitro and in vivo.

Correction for ‘In vivo 808 nm image-guided photodynamic therapy based on an upconversion theranostic nanoplatform’ by Xiaomin Liu, et al., Nanoscale, 2015, 7, 14914–14923.

The great application potential of triangular silver nanoprisms (TSNPRs, also referred to as triangular silver nanoplates) is hampered by the lack of methods to produce well-defined tips with high monodispersity, with easily removable ligands. In this work, a simple one-step plasmon-mediated method was developed to prepare monodisperse high-quality TSNPRs. In this approach, the sole surface capping agent was the easily removable trisodium citrate. Differing from common strategies using complex polymers, OH− ions were used to improve the monodispersity of silver seeds, as well as to control the growth process through inhibiting the oxidation of silver nanoparticles. Using these monodisperse high-quality TSNPRs as building blocks, self-assembled TSNPRs consisting of six-tip based “hot spots” were realized for the first time as demonstrated in a high enhancement (∼107) of surface-enhanced Raman scattering (SERS). From the plasmon band shift versus the refractive index, ultra-high local surface plasmon resonance sensitivity (413 nm RIU−1 or 1.24 eV RIU−1, figure of merit (FOM) = 4.59) was reached at ∼630 nm, making these materials promising for chemical/biological sensing applications.

A new strategy for efficient in vivo image-guided photodynamic therapy (PDT) has been demonstrated utilizing a ligand-exchange constructed upconversion-C60 nanophotosensitizer. This theranostic platform is superior to the currently reported nanophotosensitizers in (i) directly bonding photosensitizer C60 to the surface of upconversion nanoparticles (UCNPs) by a smart ligand-exchange strategy, which greatly shortened the energy transfer distance and enhanced the 1O2 production, resulting in the improvement of the therapeutic effect; (ii) realizing in vivo NIR 808 nm image-guided PDT with both excitation (980 nm) and emission (808 nm) light falling in the biological window of tissues, which minimized auto-fluorescence, reduced light scatting and improved the imaging contrast and depth, and thus guaranteed noninvasive diagnostic accuracy. In vivo and ex vivo tests demonstrated its favorable bio-distribution, tumor-selectivity and high therapeutic efficacy. Owing to the effective ligand exchange strategy and the excellent intrinsic photophysical properties of C60, 1O2 production yield was improved, suggesting that a low 980 nm irradiation dosage (351 J cm−2) and a short treatment time (15 min) were sufficient to perform NIR (980 nm) to NIR (808 nm) image-guided PDT. Our work enriches the understanding of UCNP-based PDT nanophotosensitizers and highlights their potential use in future NIR image-guided noninvasive deep cancer therapy.

We provide the first demonstration of a near infrared light driven water oxidation reaction in a molecule-based artificial photosynthetic device using an upconversion nano-photosensitizer. One very attractive advantage of this system is that using NIR light irradiation does not cause significant photodamage, a serious problem in molecular based artificial photosynthesis under visible light irradiation.

Applying the Stöber method to directly coat noble metal nanoparticles (NPs) such as gold (Au) and silver (Ag) NPs with silica shells presents challenges, since the noble metal NPs are not stable in alcoholic solution and have low chemical affinity for silica. This paper describes a method which uses 11-mercaptoundecanoic acid (MUA) as a linker molecule between the silica shell and the noble metal NPs. MUA binds strongly to the surface of the NPs via a metal–S bond by replacing the standard capping agents on the surface of the NPs. Upon MUA stabilization, the NPs can be transferred into alcohol solution and show chemical affinity for silica. The MUA-modified NPs can be directly coated with thickness controlled, smooth and homogeneous silica shells via the standard Stöber method by varying the amount of tetraethoxysilane (TEOS). Compared with methods reported in the literature for the coating of such particles, this method can not only be used to successfully coat citrated-stabilized Au or Ag NPs, but can also be extended to encapsulate oleylamine (OA)-stabilized Au NPs and cetyltrimethylammonium bromide (CTAB)-stabilized Au nanorods (NRs) by using MUA to displace the original ligand on the surface of the NPs. Additionally, the obtained metal@SiO2 core–shell NPs have been successfully applied as plasmonic nanoantennas for fluorescence enhancement in metal@SiO2@fluorophore NPs.

A highly efficient upconversion-C60 nanoplatform was demonstrated for NIR imaging-guided photodynamic therapy of cancer.

The fact that the photoluminescence properties of quantum dots are always strongly influenced by the environment limits the scope of further progress in the field of QD’ bio-applications. In this paper, the effects of immunoglobulin G (IgG) on the photoluminescence properties and stability of water-soluble CdSe/ZnS core-shell quantum dots coated with amphiphilic poly (acrylic acid) (PAA) are studied. Photoluminescence (PL) spectra, UV-vis spectra and excited state lifetime measurements are used to characterize the influence of different protein molecules, such as IgG (goat anti-human IgG, rabbit anti-human IgG, human IgG, and goat anti-human IgG-human IgG conjugates), avidin and bovine serum albumin (BSA) on the PL properties of QDs. The PL intensity and stability of CdSe/ZnS are largely enhanced compared to that of pure CdSe/ZnS QDs when the IgG molecules are added into the QD solution. The PL intensity increases with increasing the IgG concentration, but there appears no influence on the PL peak and a full width at half maximum (FWHM). The PL evolution of QDs as a function of different protein molecules depends on the structure of protein molecules, which is used as a sensor to recognize human IgG. It is inferred that the interaction between PAA coating layer and IgG molecules results in the enhancement of PL intensity. The study of the effect of pH and ion strength on optical properties of QD-IgG mixed solution, compared with the pure QD solution, suggests that pH value and ion strength do not destroy the interaction between the PAA coating layer and IgG. Excited state lifetime analysis indicates that the PL enhancement comes from the passivation of surface of the QDs with the PAA coating layer. IgG molecules have no effects on the properties of the biological system but can increase the stability and PL intensity of CdSe/ZnS QDs, which will enlarge the application of QDs in biomedicine and other fields.

LRET-based optical biosensor of an aptamer-upconversion conjugate was constructed. It is demonstrated that photosensitized breakage and damage of aptamers are eliminated by employing UCNPs as donors, and the as-designed biosensor is specific and sensitive in the detection of ATP.

Multi-sized quantum dots (QDs) donors and tailor-made gold nanorods (GNRs) are employed to form a FRET nanoplatform for homogeneous immunoassays developed for analysis of multiple virus antigens. The single GNRs/multiple QDs nanocomposite based nanosensor offers a simple and sensitive approach for multiple analytes detection in a homogeneous format.

A highly efficient multifunctional nanoplatform for simultaneous upconversion luminescence (UCL) imaging and photodynamic therapy has been developed on the basis of selective energy transfer from multicolor luminescent NaYF4:Yb3+,Er3+ upconversion nanoparticles (UCNPs) to photosensitizers (PS). Different from popular approaches based on electrostatic or hydrophobic interactions, over 100 photosensitizing molecules were covalently bonded to every 20 nm UCNP, which significantly strengthened the UCNP–PS linkage and reduced the probability of leakage/desorption of the PS. Over 80% UCL was transferred to PS, and the singlet oxygen production was readily detected by its feature emission at 1270 nm. Tests performed on JAR choriocarcinoma and NIH 3T3 fibroblast cells verified the efficient endocytosis and photodynamic effect of the nanoplatform with 980 nm irradiation specific to JAR cancer cells. Our work highlights the promise of using UCNPs for potential image-guided cancer photodynamic therapy.Keywords: covalent bonding; energy transfer; fluorescence imaging; photodynamic therapy; singlet oxygen; upconversion nanoparticles

The concentration quenching threshold of upconversion luminescence was broken through for the first time via a designed strategy: spatial separation of the emitter doping area.

Tailor-designed Au/SiO2 core/shell nanoparticles are employed to enhance the efficiency of fluorescence resonance energy transfer based on quantum dots and R-phycoerythrin in solution.

To design more effective CIEEL (chemically initiated electron exchange luminescence) systems demands a complete picture of the dynamics of the chemiluminescence, which is often a challenge. In this work, photoluminescence of the methyl m-oxybenzoate anion – the authentic emitter of AMPPD (3-[2-spiroadamantane]-4-methoxy-4-[3-phosphoryloxy]-phenyl-1,2-dioxetane) in aqueous solvent has been studied. Combining the effect of solvent properties, e.g. pH value, and spectroscopic studies employing steady-state and ultrafast time-resolved emission and absorption and 1H NMR techniques, a novel mechanism is proposed. We conclude that the deviation of emission peaks between chemiluminescence and photoluminescence of the authentic emitter of AMPPD i.e. the methyl m-oxybenzoate anion, in alkaline aqueous solvents is due to its hydrolysis, rather than the hydrogen-bonding effect as has been assumed so far. Besides, the hydrogen-bonding is suggested to play a key role in significantly decreasing the chemiluminescence yield of AMPPD in aqueous solution by shortening the lifetime of the excited authentic emitter to 10 ps order of magnitude – three orders of magnitude shorter than the previously reported value (∼10 ns). These results shed light on the chemiluminescence dynamics of AMPPD and facilitate the design of more effective CIEEL systems.

Highly sensitive, multi-analyte assay is a long-standing challenge for a single fiber-optic evanescent wave biosensor (FOB). In this paper, we report the first realization of such kind of FOB using CdSe/ZnS core/shell quantum dots (QDs) as labels. A direct binding assay model between antibody and antigen was employed to demonstrate the advantages of using QDs, instead of conventional fluorescein isothiocyanate (FITC), in lifting the sensitivity. Especially, multiplexed immunoassay was demonstrated in a single fiber FOB constructed with four differently sized QDs. Furthermore, the phenomenon that the affinity of the QD-labeled human IgG (QD-IgG) with goat anti-human IgG (anti-IgG) was lower than that of the FITC-labeled human IgG (FITC-IgG) was investigated and was ascribed to the differences in size and mass of the two. Our study indicates that the affinity could be improved by controlling the amount of IgG binding on QDs.

Water-soluble pure hexagonal-phase NaYF4:Yb3+,Er3+/Tm3+ nanoparticles were obtained by an ionothermal method for the first time which offers a new alternative in synthesizing such materials.

Water-soluble and carboxyl-functionalized up-converting rare-earth nanoparticles (UCNPs) are obtained via an efficient surface–ligand-exchange procedure. Hexanedioic acid molecules are employed to replace the original hydrophobic ligands in diethylene glycol solvent at high temperature. Various characterizations indicate the ligand-exchange process has negligible adverse effect on the quality of the UCNPs. The resulting hydrophilic UCNPs show small size, strong up-converting emission and high water stability. The specific molecular recognition capacity of avidin-modified hydrophilic UCNPs confirms that hydrophilic UCNPs are suitable for potential biological labeling.Hexanedioic acid is used to replace the original hydrophobic ligands on the surface of up-converting rare-earth nanoparticles via an efficient ligand-exchange approach, the resulting carboxyl-functionalized UCNPs are suitable for biological applications.

Yb and Er codoped LaF3 nanocrystals were synthesized and studied. The upconversion luminescence properties of nanocrystals capped with different ligands are mainly dependent on the ligands, especially for the red emission which is sensitive to the nonradiative relaxation. The chelation between the ligands and rare earth ions can affect the morphology and fluorescent properties of samples. The chelating ligands will reduce the nonradiative quenching by isolating the RE ions from surrounding environment. So the upconversion luminescence properties of the samples vary correspondingly.

Quantum dots (QDs) are widely used in the immune detection. Yet, the sensitivity and specificity of the immune detection are not satisfactory because the binding sites of QDs onto antibody (Ab) are often arbitrary and the influence of the large surface electronic potential energy of QDs on the directly conjugated Ab is nonnegligible. In this work, we provide a “flexible” coupling method, in which protein G (PG) is selected as the flexible bridge between the QDs and the Hepatitis B virus surface antibody (HBsAb), to improve the sensitivity and specificity of the fluoroimmunoassay compared to the directly covalent conjugation. Successful coupling of the HBsAb to our highly luminescent CdTe/CdS core/shell QDs is proven with Gel electrophoresis and atomic force microscopy (AFM). The assay results, based on the microelisa well plate as matrix to immobilize the sandwich structure, show that both sensitivity and specificity can be improved greatly through the flexible coupled QDs–PG–Ab conjugates.

Morphology impact on the upconverted luminescence of ZnO:Er3+ nanocrystals was studied with controllable morphology of nanorod, prickly sphere-like, column-like, branch rod, prism-like, and grain-like, prepared via the cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal process. The upconversion emission of Er3+ with 980 nm excitation demonstrated morphology sensitivity which was related with the local environments of Er3+ ions in ZnO and doping efficiency. Under ultraviolet (UV) direct excitation, where exciton and defect emissions of ZnO appeared, morphology sensitivity was discussed in terms of surface-to-volume ratios.

In this paper, green and red up-conversion emissions of Er3+–Yb3+ co-doped TiO2 nanocrystals were reported. The phase structure, particle size and optical properties of Er3+–Yb3+ co-doped TiO2 nanocrystals samples were characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis–NIR absorption spectra and photoluminescence (PL) spectra. Green and red up-conversion emissions in the range of 520–570 nm (2H11/2, 4S3/2→4I15/2) and 640–690 nm (4F9/2→4I15/2) were observed for the Er3+–Yb3+ co-doped TiO2 nanocrystals. The visible up-conversion mechanism and temperature dependence of up-conversion emission for Er3+ in TiO2 nanocrystals were discussed in detail.

Surface effects on nanoparticles have been explored by picosecond time-resolved spectroscopy using Ce3+ ions doped in yttrium aluminum garnet (YAG) nano-phosphors (NPS) as a probe. Non-exponential decays have been observed over the entire emission band that could be fitted well with four decay components varying from ∼150 ps to ∼70 ns. These components have been assigned to originate from sites different in distance from the surface. Surface quenching effects have been found to be negligible when the luminescence centers are more than 7 nm away from the surface.Time-resolved spectroscopy of the nanoparticle surface effect on the embedded rare earth ions

Strong red upconversion luminescence of rare-earth ions doped in nanocrystals is desirable for the biological/biomedical applications. In this paper, we describe the great enhancement of red upconversion emission (4F9/2 → 4I15/2 transition of Er3+ ion) in NaYF4:Yb3+, Er3+ nanocrystals at low doping level, which is ascribed to the effectiveness of the multiphonon relaxation process due to the existence of citrate as a chelator and cross relaxation between Er3+ ions. The dissolution−recrystallization transformation, governing both the intrinsic crystalline phase (cubic and/or hexagonal phase) and the growth regime (thermodynamic vs kinetic), is responsible for the phase control of the NaYF4 crystals. The possible formation mechanism of the NaYF4 crystals and the role of trisodium citrate which acts as a chelating agent and shape modifier are discussed in detail. It is also found that the α → β phase transition is favored by the high molar ratio of fluoride to lanthanide and high hydrothermal temperature as well as long hydrothermal time.

3-Mercaptopropionic acid stabilized CdTe/CdS core/shell quantum dots (QDs) were prepared in an aqueous solution following the synthetic route of successive ion layer adsorption and reaction. The photoluminescence quantum yield of the CdTe QDs could reach 40%, from 8% of the bare core, via the control of the shell thickness. The CdTe/CdS QDs exhibited also a significant red shift of emission and excitation peaks when the shell layer grew. The experiments revealed that the CdTe/CdS QDs evolved from type I to type II core/shell structures with the increase of the shell thickness, and the evolution process is affected by the core size, shell thickness, surface quality of the core and shell, as unraveled by steady-state and time-resolved spectroscopy. The lack of photoluminescence lifetime lengthening was ascribed to the surface influence of the shell.

The results of interaction between CdSe quantum dots and polyaniline were reported. Polyaniline effectively decreases the emission of CdSe quantum dots, and the CdSe luminescence lifetime is decreased by the addition of polyaniline. The mechanism of the emission observed in CdSe is assumed to result from the energy transfer and from the combination of surface-trapped electrons and holes energy is transferred from CdSe to polyaniline, and polyaniline occupies the hole sites.

This work presents that hydrophobic CdSe quantum dots (QDs) were successfully transferred from nonpolar organic solvent to biocompatible water buffer by liposome encapsulating technology. And this result has been confirmed via transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy, fluorescence mapping, and differential scanning calorimetry (DSC), respectively. TEM images showed that QDs have been encapsulated in the liposomes. PL spectroscopy indicated that hydrophobic CdSe QDs within liposome basically retain optical properties of free nanocrystals. Fluorescence mapping successfully showed intensity distribution of liposome entrapped luminescence QDs (QD-liposome). DSC data indicated that the enthalpy (ΔH) of the QD-liposome increased, suggesting the enhancement of hydrophobic interaction between lipid hydrophobic chains and organic ligands on the surface of QDs.

•A new biosensor was developed based on optical fiber and SERS nano-tags.•The biosensor can in situ detect biomarkers in the unprocessed whole blood.•The SERS nano-tags is effective NIR labels for application in the whole blood.•The optical fiber can eliminate light scattering effect from the blood composition.•The biosensor holds excellent reproducibility and stability.•The biosensor can detect the AFP from 50 to 500 ng/mL in unprocessed blood.Assay technologies capable of detecting biomarker concentrations in unprocessed whole blood samples are fundamental for applications in medical diagnostics. SERS nano-tags integrated fiber-optic biosensor (FOB) was realized for the first time for in situ immunoassay in whole blood. The reliability and sensitivity of this method rely, in a large extent, on the quality and properties of the SERS nano-tags. The constructed silica-coated Ag SERS nano-tags as labels were used in a rapid and specific in situ FOB immune sensor to detect alpha fetoprotein (AFP) in unprocessed blood samples. Preliminary results of in vivo and in situ dynamic observation of AFP of whole blood in wistar rat highlight the power of this new method.

•An immunoassay method was constructed by using UCNP-based FRET on a solid-substrate.•The approach successfully solved some shortcomings in the traditional immunoassays.•It is the first in situ solid-substrate-based immunoassay of whole blood samples.•A wide detection range of 0.75-60 μg/mL in whole blood samples was achieved.Despite their general clinical applications, current fluorescence-based immunoassays are confronted with serious challenges, e.g. the advance serum/ plasma separation and the tedious washing process in current heterogeneous approaches, and aggregation of particles, low sensitivity and the narrow linear range in homogeneous approaches. In this paper, these urgent problems were solved in a novel one-step in situ immunoassay of whole blood samples by combining the traditional fluorescence resonance energy transfer (FRET) technology (between upconversion nanoparticles (UCNPs) and gold nanoparticles (GNPs)) and the solid-substrate based immunoassay technology. The low detection limits of goat IgG (gIgG) as 0.042 μg/mL in buffers, 0.51 μg/mL in 20-fold diluted whole blood samples and a wide linear range from 0.75 μg/mL to 60 μg/mL in blood samples were achieved. To the best of our knowledge, it is the first one-step in situ solid-substrate-based immunoassay of whole blood samples with large linear detection range. This development provides a promising platform for a rapid and sensitive immunoassay of various bio-molecules directly in whole blood without tedious separation, washing steps and aggregation problems.

To design more effective CIEEL (chemically initiated electron exchange luminescence) systems demands a complete picture of the dynamics of the chemiluminescence, which is often a challenge. In this work, photoluminescence of the methyl m-oxybenzoate anion – the authentic emitter of AMPPD (3-[2-spiroadamantane]-4-methoxy-4-[3-phosphoryloxy]-phenyl-1,2-dioxetane) in aqueous solvent has been studied. Combining the effect of solvent properties, e.g. pH value, and spectroscopic studies employing steady-state and ultrafast time-resolved emission and absorption and 1H NMR techniques, a novel mechanism is proposed. We conclude that the deviation of emission peaks between chemiluminescence and photoluminescence of the authentic emitter of AMPPD i.e. the methyl m-oxybenzoate anion, in alkaline aqueous solvents is due to its hydrolysis, rather than the hydrogen-bonding effect as has been assumed so far. Besides, the hydrogen-bonding is suggested to play a key role in significantly decreasing the chemiluminescence yield of AMPPD in aqueous solution by shortening the lifetime of the excited authentic emitter to 10 ps order of magnitude – three orders of magnitude shorter than the previously reported value (∼10 ns). These results shed light on the chemiluminescence dynamics of AMPPD and facilitate the design of more effective CIEEL systems.

LRET-based optical biosensor of an aptamer-upconversion conjugate was constructed. It is demonstrated that photosensitized breakage and damage of aptamers are eliminated by employing UCNPs as donors, and the as-designed biosensor is specific and sensitive in the detection of ATP.

Tailor-designed Au/SiO2 core/shell nanoparticles are employed to enhance the efficiency of fluorescence resonance energy transfer based on quantum dots and R-phycoerythrin in solution.

Multi-sized quantum dots (QDs) donors and tailor-made gold nanorods (GNRs) are employed to form a FRET nanoplatform for homogeneous immunoassays developed for analysis of multiple virus antigens. The single GNRs/multiple QDs nanocomposite based nanosensor offers a simple and sensitive approach for multiple analytes detection in a homogeneous format.

A highly efficient upconversion-C60 nanoplatform was demonstrated for NIR imaging-guided photodynamic therapy of cancer.

Water-soluble pure hexagonal-phase NaYF4:Yb3+,Er3+/Tm3+ nanoparticles were obtained by an ionothermal method for the first time which offers a new alternative in synthesizing such materials.

We provide the first demonstration of a near infrared light driven water oxidation reaction in a molecule-based artificial photosynthetic device using an upconversion nano-photosensitizer. One very attractive advantage of this system is that using NIR light irradiation does not cause significant photodamage, a serious problem in molecular based artificial photosynthesis under visible light irradiation.

The concentration quenching threshold of upconversion luminescence was broken through for the first time via a designed strategy: spatial separation of the emitter doping area.

Applying the Stöber method to directly coat noble metal nanoparticles (NPs) such as gold (Au) and silver (Ag) NPs with silica shells presents challenges, since the noble metal NPs are not stable in alcoholic solution and have low chemical affinity for silica. This paper describes a method which uses 11-mercaptoundecanoic acid (MUA) as a linker molecule between the silica shell and the noble metal NPs. MUA binds strongly to the surface of the NPs via a metal–S bond by replacing the standard capping agents on the surface of the NPs. Upon MUA stabilization, the NPs can be transferred into alcohol solution and show chemical affinity for silica. The MUA-modified NPs can be directly coated with thickness controlled, smooth and homogeneous silica shells via the standard Stöber method by varying the amount of tetraethoxysilane (TEOS). Compared with methods reported in the literature for the coating of such particles, this method can not only be used to successfully coat citrated-stabilized Au or Ag NPs, but can also be extended to encapsulate oleylamine (OA)-stabilized Au NPs and cetyltrimethylammonium bromide (CTAB)-stabilized Au nanorods (NRs) by using MUA to displace the original ligand on the surface of the NPs. Additionally, the obtained metal@SiO2 core–shell NPs have been successfully applied as plasmonic nanoantennas for fluorescence enhancement in metal@SiO2@fluorophore NPs.