Combined therapy using multiple approaches has been demonstrated to be a promising route for cancer therapy. To achieve enhanced antiproliferation efficacy under hypoxic condition, here we report a novel hybrid system by integrating dual-model photodynamic therapies (dual-PDT) in one system. First, we attached core–shell structured up-conversion nanoparticles (UCNPs, NaGdF4:Yb,Tm@NaGdF4) on graphitic-phase carbon nitride (g-C3N4) nanosheets (one photosensitizer). Then, the as-fabricated nanocomposite and carbon dots (another photosensitizer) were assembled in ZIF-8 metal–organic frameworks through an in situ growth process, realizing the dual-photosensitizer hybrid system employed for PDT via stepwise water splitting. In this system, the UCNPs can convert deep-penetration and low-energy near-infrared light to higher-energy ultraviolet–visible emission, which matches well with the absorption range of the photosensitizers for reactive oxygen species (ROS) generation without sacrificing its efficacy under ZIF-8 shell protection. Furthermore, the UV light emitted from UCNPs allows successive activation of g-C3N4 and carbon dots, and the visible light from carbon dots upon UV light excitation once again activate g-C3N4 to produce ROS, which keeps the principle of energy conservation thus achieving maximized use of the light. This dual-PDT system exhibits excellent antitumor efficiency superior to any single modality, verified vividly by in vitro and in vivo assay.Keywords: carbon dots; g-C3N4; MOFs; synergistic therapy; up-conversion;

Rare-earth-doped up-conversion nanoparticles (UCNPs), which are capable of converting infrared light to shorter-wavelength photons, have attracted worldwide attention due to their unique characteristics. However, the emission brightness of UCNPs is greatly limited by the unsatisfactory absorptivity of lanthanide ions. Herein, we adopted a novel strategy to enhance the up-conversion intensity using NIR dye IR-808 as an antenna to sensitize the core–shell–shell structured NaGdF4:Yb,Er@NaGdF4:Yb@NaNdF4:Yb UCNPs. When excited with 808 nm light, the IR-808 emitted a broadband peak, which perfectly overlapped with the absorption of Nd3+ and Yb3+ ions. Thus, the active shell of NaNdF4:Yb can efficiently capture the emitted NIR photons and transfer them to the transition layer of NaGdF4:Yb. The transition layer acted as an energy bridge to connect the active shell and up-converting zone, avoiding the energy back-transfer from the activators to Nd3+ ions. The optimized dye sensitization combined with the well-designed core–shell–shell structure tremendously enhances the NIR photon absorptivity of UCNPs and eliminates the deleterious cross-relaxation between the activators and sensitizers, eventually leading to dramatic enhancement of the up-conversion intensity. This study provides a new insight into the dye-sensitized up-conversion luminescence of rare earth-based nanoparticles and facilitates their practical applications.

Low tissue penetration depth of the excited light and complicated synthetic procedures greatly hinder the clinical application of photodynamic therapy (PDT). Here we present a facile and mass production route to fabricate Yb3+/Tm3+ co-doped BiOBr nanosheets. In contrast to the complicated combination of photosensitizers (PSs) with up-conversion nanoparticles (UCNPs), which generates a PDT effect by a fluorescence resonance energy transfer process from UCNPs to PSs upon near-infrared light excitation, this as-synthesized material can be self-activated by deep-penetrating 980 nm laser light to produce a large amount of reactive oxygen species, giving rise to a high PDT efficiency which has been proven by in vitro and in vivo therapeutic assays. Surface modification of the BiOBr:Yb,Tm nanosheets with polyethylene glycol endows the system with improved biocompatibility. Through the combination of inherent fluorescence and CT imaging properties, an imaging-monitored therapeutic system has been realized. The system overcomes the problems of low tissue penetration depth, complicated structure-induced low efficiency, and potential safety concerns. Our finding presents the first demonstration of a self-activated nanoplatform for targeted and noninvasive deep-cancer therapy.

Reactive oxygen species (ROS) produced in the specific tumor site plays the key role in photodynamic therapy (PDT). Herein, a multifunctional nanoplatform is designed by absorbing ultrasmall upconversion nanoparticles (UCNPs) on mesoporous graphitic-phase carbon nitride (g-C3N4) coated superparamagnetic iron oxide nanospheres, then further modified with polyethylene glycol (PEG)molecules (abbreviated as Fe3O4@g-C3N4–UCNPs–PEG). The inert g-C3N4 layer between Fe3O4 core and outer UCNPs can substantially depress the quenching effect of Fe3O4 on the upconversion emission. Upon near-infrared (NIR) laser irradiation, the UCNPs convert the energy to the photosensitizer (g-C3N4 layer) through fluorescence resonance energy transfer process, thus producing a vast amount of ROS. In vitro experiment exhibits an obvious NIR-triggered cell inhibition due to the cellular uptake of nanoparticles and the effective PDT efficacy. Notably, this platform is responsive to magnetic field, which enables targeted delivery under the guidance of an external magnetic field and supervises the therapeutic effect by T1/T2-weighted dual-modal magnetic resonance imaging. Moreover, in vivo therapeutic effect reveals that the magnetism guided accumulation of Fe3O4@g-C3N4–UCNPs–PEG can almost trigger a complete tumor inhibition without any perceived side effects. The experiments emphasize that the excellent prospect of Fe3O4@g-C3N4–UCNPs–PEG as a magnetic targeted platform for PDT application.

Two major issues of finding the appropriate photosensitizer and raising the penetration depth of irradiation light exist in further developing of photodynamic therapy (PDT). The excited ultraviolet/visible (UV/vis) irradiation light has a relatively shallow depth of penetration and UV light itself may have sufficient energy to damage normal tissues; these are substantial limitations to successful cancer therapy. Herein, we for the first time report a novel multifunctional nanoplatform for a single 980 nm near-infrared (NIR) light-triggered PDT based on NaGdF4:Yb,Tm@NaGdF4 upconversion nanoparticles (UCNPs) integrated with bismuth oxyhalide (BiOCl) sheets, designated as UCNPs@BiOCl. And UCNPs@BiOCl was fabricated by a convenient, efficient, green, and inexpensive method. Excitingly, layered bismuth oxyhalide materials possess a high photocatalytic performance, unique layered structures and wide light response to a broad wavelength range of ultraviolet to visible light. And the loaded UCNPs can convert NIR light into UV/vis region emissions, which drives the pure water splitting of BiOCl sheets to produce plenty of reactive oxygen species (ROS) to damage tumor cells. The excellent antitumor efficiency of the complex has been evidently attested by comparing experimental results. Our work may make a contribution to the wide application of BiOCl-based materials in biomedicine.

Core–shell nanostructures consisting of plasmonic materials and lanthanide-doped upconversion nanoparticles (UCNPs) show promising applications in theranostics including bio-imaging, diagnosis and therapy. However, some challenges still remain in the synthetic control because of the non-coordination between energy transfer and photothermal therapy (PTT). Herein, we developed a novel type of thermal-fluorescent core–shell hybrid nanocomposite incorporating rare-earth Yb3+ and Er3+ ion doped GdOF as the shell and gold nanorods (GNRs) as the core, creating upconversion nanorods (UCNRs) of GNRs@GdOF:Yb3+,Er3+. In order to facilitate the absorption or excretion of UCNRs in vivo, we designed gold nanorods with lower aspect ratios by reducing the amount of CTAB in the growth solution. More importantly, under 980 nm near-infrared (NIR) light irradiation, the green and red emissions of GdOF:Yb3+,Er3+ generally overlap with the visible absorbance of GNRs; by altering the contents of Yb3+ and Er3+ ions appropriately, the localized surface plasmon resonance (LSPR) absorption of low aspect ratio GNRs under 980 nm NIR laser excitation can be enhanced for improving the PTT efficiency. Furthermore, in vitro and in vivo assays reveal that the composite has excellent bio-compatibility and cancer therapy efficiency. This multi-functional nanocomposite, which possesses upconversion luminescence and photothermal and biocompatibility properties, shows strong potential for application in bio-imaging and photothermal anti-cancer therapy.

Photodynamic therapy (PDT) is a novel technique that has been extensively employed in cancer treatment; it utilizes reactive oxygen species to kill malignant cells. However, poor performance of the photosensitizer itself, limited penetration depth and the overexpression of glutathione (GSH) in cancer cells are the major obstacles facing the actual clinical application of PDT. Inspired by the challenges mentioned above, here we propose multifunctional nanoparticles utilizing mesoporous manganese silicate (MnSiO3)-coated upconversion nanoparticles (UCNPs) as nanocarriers for loading highly fluorescent graphitic-phase carbon nitride quantum dots (g-C3N4 QDs) to simultaneously act as a photosensitive drug and imaging agent. Surface modification of the nanoparticles with polyethylene glycol (PEG) endows the samples (denoted as UMCNs-PEG) with excellent biocompatibility and long-term in vivo circulation. Taking advantage of the inherent performance of the as-synthesized nanoparticles, multimodality imaging, including upconversion luminescence (UCL), computed tomography (CT) and magnetic resonance imaging (MRI), has been achieved; this is conducive to providing effective treatment information by real-time monitoring. In vivo photodynamic therapy to achieve effective tumor inhibition was then realized without inducing significant toxicity to treated mice. As a result, this work provides a novel paradigm with highly integrated functionalities which not only exhibits excellent prospects for imaging-guided photodynamic anticancer therapy but also encourages further exploration of new types of multifunctional nanoparticles for biomedical applications.

To enhance the total emission intensity, particularly the red emission of Yb,Er co-doped nanoparticles for red light activated photodynamic therapy (PDT), we doped Mn2+ ions into the NaGdF4:Yb,Er core, and subsequently coated the NaGdF4:Yb active shell to fabricate core–shell structured, up-conversion nanoparticles of NaGdF4:Yb,Er,Mn@NaGdF4:Yb (abbreviated as UCNPs). A novel and facile encapsulation method with gelatin has been proposed to transfer oleic acid (OA) stabilized UCNPs into an aqueous solution and simultaneously decorate zinc phthalocyanine (ZnPc) photosensitizer molecules. In the encapsulation process, ZnPc molecules are wrapped in the interlaced net structure of the peptide chain from gelatin, forming the UCNPs@gel–ZnPc nanocomposite. The nanoplatform has high emission intensity and excellent biocompatibility, as was expected. More importantly, the enhanced red emission of UCNPs has significant overlap with the UV absorbance of ZnPc; therefore, it can effectively activate the sensitizer to produce a large amount of singlet oxygen reactive oxygen species (ROS, 1O2) to kill cancer cells, which has evidently been verified by the in vitro results. Combined with the inherent up-conversion luminescence (UCL) imaging properties, this UCNPs@gel–ZnPc nanoplatform could have potential application in PDT and imaging fields.

Near-infrared (NIR) light-induced cancer therapy has gained considerable interest, but pure inorganic anti-cancer platforms usually suffer from degradation issues. Here, we designed metal–organic frameworks (MOFs) of Fe3O4/ZIF-8-Au25 (IZA) nanospheres through a green and economic procedure. The encapsulated Fe3O4 nanocrystals not only produce hyperthemal effects upon NIR light irradiation to effectively kill tumor cells, but also present targeting and MRI imaging capability. More importantly, the attached ultrasmall Au25(SR)18− clusters (about 2.5 nm) produce highly reactive singlet oxygen (1O2) to cause photodynamic effects through direct sensitization under NIR light irradiation. Furthermore, the Au25(SR)18− clusters also give a hand to the hyperthemal effect as photothermal fortifiers. This nanoplatform exhibits high biocompatibility and an enhanced synergistic therapeutic effect superior to any single therapy, as verified by in vitro and in vivo assay. This image-guided therapy based on a metal–organic framework may stimulate interest in developing other kinds of metal–organic materials with multifunctionality for tumor diagnosis and therapy.

Multifunctional composites have gained significant interest due to their unique properties which show potential in biological imaging and therapeutics. However, the design of an efficient combination of multiple diagnostic and therapeutic modes is still a challenge. In this contribution, Y2O3:Yb,Er@mSiO2 double-shelled hollow spheres (DSHSs) with up-conversion fluorescence have been successfully prepared through a facile integrated sacrifice template method, followed by a calcination process. It is found that the double-shelled structure with large specific surface area and uniform shape is composed of an inner shell of luminescent Y2O3:Yb,Er and an outer mesoporous silica shell. Ultra small CuxS nanoparticles (about 2.5 nm) served as photothermal agents, and a chemotherapeutic agent (doxorubicin, DOX) was then attached onto the surface of mesoporous silica, forming a DOX–DSHS–CuxS composite. The composite exhibits high anti-cancer efficacy due to the synergistic photothermal therapy (PTT) induced by the attached CuxS nanoparticles and the enhanced chemotherapy promoted by the heat from the CuxS-based PTT when irradiated by 980 nm near-infrared (NIR) light. Moreover, the composite shows excellent in vitro and in vivo X-ray computed tomography (CT) and up-conversion fluorescence (UCL) imaging properties owing to the doped rare earth ions, thus making it possible to achieve the target of imaging-guided synergistic therapy.

In this report, mesoporous NaYF4:Yb,Er@Au–Pt(IV)-FA up-conversion nanoparticles (UCNPs) have been designed by attaching Au NPs and Pt(IV) pro-drugs on the surface of PEI hydrogel modified mesoporous NaYF4:Yb,Er nanospheres. Finally the molecules modified with folic acid (FA) improve the receptor-mediated endocytosis. Because of the doped rare earth ions in the host matrix, the as-synthesized platform exhibits excellent up-conversion luminescence (UCL) imaging and computed X-ray tomography (CT) imaging properties. Diverse methods including MTT assay, hemolysis experiments, and live/dead cell analysis were employed to evaluate the biocompatibility and ablation efficacy of the as-synthesized platform. It was found that the cytotoxicity of the platform can be tuned by eliminating the axial ligands reductively during intracellular endocytosis. Especially, under 980 nm near-infrared (NIR) irradiation, the platform shows excellent inhibition toward cancer cells due to the synergistic photothermal injury to enzymes and membrane integrity combined with the DNA binding of activated Pt(II) to avoid cell proliferation. The developed nanocomposite may thus be a promising imaging-guided synergistic anti-cancer platform.

Gd2O3:Ln@mSiO2 hollow nanospheres (Gd2O3:Ln hollow spheres coated by a mesoporous silica layer) were successfully synthesized through a self-template method using Gd(OH)CO3 as template to form hollow precursors (named HPs), which involved the incorporation of the rare earth compound into the interior of the hydrophilic carbon shell, followed by coating with a mesoporous silica shell, and subsequent calcination in air. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric and differential thermal analyses (TG-DTA), photoluminescence spectroscopy, kinetic decays as well as N2 adsorption/desorption were employed to characterize the composites. The results indicate that the uniform Gd2O3:Ln@mSiO2 composite with the particle size around 300 nm maintains the spherical morphology and good dispersibility of the precursor. Interestingly, the composite has a double-shell structure including an inner shell of Gd2O3 and an outer shell of mesoporous silica. Moreover, they also exhibit bright red (Eu3+, 5D0 → 7F2) down-conversion (DC) emission and characteristic up-conversion (UC) emissions of Yb3+/Er3+. Under beam excitation, the hollow structured sample emits, which should have potential applications in biomedicine and other fields.

In this study, uniform gadolinium fluoride microspheres with controllable phases and structures have been synthesized for the first time by a facile ion exchange process using Gd(OH)CO3 solid microspheres as precursors. It is found that the as-synthesized NaxGdyFx+3y samples, including orthorhombic GdF3, cubic Na5Gd9F32 and hexagonal NaGdF4, all consist of well dispersed microspheres with mesopores. After the conversion process, the products mainly inherit the size and shape of the precursors. Moreover, the used ethylene glycol (EG) plays a key role in the phase and structure of the final NaxGdyFx+3y mesoporous spheres by impacting the etching and ion exchange process. Based on the time-dependent experiments of gadolinium fluorides, the possible formation mechanism is discussed in detail. Under 273 nm UV excitation, NaxGdyFx+3y:2% Eu3+ shows bright red emissions due to efficient energy transfer from Gd3+ to Eu3+. NaxGdyFx+3y:17% Yb3+/3% Er3+ exhibits the characteristic up-conversion (UC) emissions of Er3+. It is noted that the highest DC and UC emission intensities of NaGdF4:Ln should be due to the hexagonal phase. The fluorescent NaxGdyFx+3y mesoporous microspheres show obvious drug (doxorubicin hydrochloride, DOX) storage/release properties and good biocompatibility, suggesting their potential application in biomedical fields.

Uniform LaF3 and LaCO3F hollow microspheres were successfully synthesized through a surfactant-free route by employing La(OH)CO3 colloidal microspheres as a sacrificial template and NaBF4 as the fluorine source. The synthetic process consists of two steps: the preparation of a La(OH)CO3 precursor via a facile urea-based precipitation and the following formation of lanthanide fluoride hollow microspheres under aqueous conditions at low temperature (50 °C) and short reaction time (3 h), without using any surfactant and catalyst. The formation of hollow spheres with controlled size can be assigned to the Kirkendall effect. It is found that the phase and structure of the products can be simply tuned by changing the pH values of the solution. Time-dependent experiments were employed to study the possible formation process. N2 adsorption/desorption results indicate the mesoporous nature of LaF3 hollow spheres. Yb3+/Er3+ (Ho3+) and Yb3+/Tm3+-doped LaF3 hollow spheres exhibit characteristic up-conversion (UC) emissions of Er3+ (Ho3+) and Tm3+ under 980 nm laser-diode excitation, and Ce3+/Tb3+-doped LaF3 and LaCO3F emit bright yellow-green and near-white light under UV irradiation, respectively. In particular, LaF3:Yb/Er and LaCO3F:Ce/Tb hollow microspheres exhibit obvious sustained and pH-dependent doxorubicin release properties. The luminescent properties of the carriers allow them to be tracked or monitored during the release or therapy process, suggesting their high potential in the biomedical field.

Uniform LaPO4:Ce/Tb mesoporous microspheres (MMs) have been successfully prepared by a facile mass production co-precipitation process under mild reaction conditions, without using any surfactant, catalyst or further heating treatment. Then, Au nanoparticles (NPs) were conjugated to polyetherimide (PEI) modified LaPO4:Ce/Tb MMs by electrostatic interactions. It was found that as-prepared LaPO4:Ce/Tb@Au composite consists of well-dispersed mesoporous microspheres with high surface area and narrow pore size distribution. Upon ultraviolet (UV) excitation, LaPO4:Ce/Tb and LaPO4:Ce/Tb@Au MMs exhibit the characteristic green emissions of Tb3+ ions. In addition, the good biocompatibility and sustained doxorubicin (DOX) release properties indicate its promise as a candidate in cancer therapy. In particular, under UV irradiation, a rapid DOX release was achieved due to the photothermal effect of Au NPs derived from the overlap of the green emission of Tb3+ and the surface plasmon resonance (SPR) band of gold NPs at about 530 nm. The MTT assay, cellular uptaken images, the anti-tumor therapy in vivo, and the histology examination results further proved that this novel multifunctional (mesoporous, luminescent, and thermal effect) drug delivery system should be a suitable candidate for cancer therapy carriers.

In this paper, uniform hollow mesoporous GdF3 micro/nanospheres were successfully prepared by a facile two-step synthesis route without using any surfactant, catalyst, and further calcination process. The precursor Gd(OH)CO3 spheres are prepared by a coprecipitation process. After that, uniform and size-tunable GdF3 hollow spheres were easily coprecipitated with NaBF4 at the sacrifice of the precursor with low temperature and short reaction time. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution TEM, N2 adsorption/desorption, and up-conversion (UC) photoluminescence spectra were used to characterize the as-obtained products. It is found that the initial pH value and NaBF4/Gd3+ molar ratios play important roles in the structures, sizes, and phases of the hollow products. The growth mechanism of the hollow spheres has been systematically investigated based on the Kirkendall effect. Under 980 nm IR laser excitation, UC luminescence of the as-prepared Yb3+/Er3+-codoped GdF3 hollow spheres can be changed by a simple adjustment of the concentration of the Yb3+ ion. Enhanced red emission is obtained by introducing Li+ ions in GdF3:Yb3+/Er3+. Furthermore, a doxorubicin release experiment and a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide cytotoxicity assay reveal that the product has potential application in drug delivery and targeted cancer therapy.Keywords: drug release; GdF3; hollow; luminescence; MTT; spheres;

A novel bifunctional (fluorescent, mesoporous) hollow sphere was prepared by coating luminescent YBO3:Eu3+ nanoparticles onto uniform hollow mesoporous silica spheres (HMSs), derived from an etching strategy using spherical Fe3O4 as templates. The composites exhibit typical mesoporous shells, large interior space, high surface area, and well dispersed nanospheres with controlled size. In addition, the textural properties including the specific surface and pore volume can be easily altered by simply tuning of the spherical Fe3O4 cores. Upon ultraviolet (UV) excitation, the composite shows the characteristic 5D0–7F1–4 red emission lines of Eu3+ even after loading of the model drug. The composite with a large surface area and cavity was used as the host for loading the anticancer drug doxorubicin hydrochloride (DOX). It is observed that the multifunctional composites exhibit an obvious sustained release property and released in texture- and pH-sensitive patterns. Particularly, the down-conversion (DC) fluorescence intensity of the bifunctional vehicle increases with the release of drug molecules, making it possible to track the position and the drug release amount of the drug carrier system and to detect them by the change of fluorescence intensity.Keywords: drug release; hollow; luminescence; mesoporous; silica; YBO3:Eu3+;

Highly uniform α-NaYF4:Yb/Er hollow microspheres have been successfully prepared via a simple two-step route. First, the core–shell structured MF@Y(OH)CO3:Yb/Er precursor was fabricated by a urea-based homogeneous precipitation method using colloidal melamine formaldehyde (MF) microspheres as template. Then the Y(OH)CO3:Yb/Er precursor was transformed into hollow NaYF4:Yb/Er (α and β mixed phase) by a subsequent solvothermal method, and MF microspheres were dissolved in the solvent simultaneously. The mixed phase of NaYF4:Yb/Er was transferred into pure α-NaYF4:Yb/Er by calcination. The as-prepared hollow microspheres were well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrum (EDS), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and upconversion (UC) luminescence spectroscopy. It is found that the template can be removed without additional calcination or etching process. α-NaYF4:Yb/Er hollow microspheres exhibit bright upconversion (UC) luminescence under 980 nm laser diode (LD) excitation. Furthermore, the hollow microspheres show sustained and pH-dependent doxorubicin hydrochloride (DOX) release properties; in particular, the emission intensity increases with the release amount of drug, making the release process able to be tracked or monitored by the change of the emission intensity, which demonstrates the high potential of this kind of hollow fluorescent material in drug delivery fields.

Rare-earth-doped up-conversion nanoparticles (UCNPs), which are capable of converting infrared light to shorter-wavelength photons, have attracted worldwide attention due to their unique characteristics. However, the emission brightness of UCNPs is greatly limited by the unsatisfactory absorptivity of lanthanide ions. Herein, we adopted a novel strategy to enhance the up-conversion intensity using NIR dye IR-808 as an antenna to sensitize the core–shell–shell structured NaGdF4:Yb,Er@NaGdF4:Yb@NaNdF4:Yb UCNPs. When excited with 808 nm light, the IR-808 emitted a broadband peak, which perfectly overlapped with the absorption of Nd3+ and Yb3+ ions. Thus, the active shell of NaNdF4:Yb can efficiently capture the emitted NIR photons and transfer them to the transition layer of NaGdF4:Yb. The transition layer acted as an energy bridge to connect the active shell and up-converting zone, avoiding the energy back-transfer from the activators to Nd3+ ions. The optimized dye sensitization combined with the well-designed core–shell–shell structure tremendously enhances the NIR photon absorptivity of UCNPs and eliminates the deleterious cross-relaxation between the activators and sensitizers, eventually leading to dramatic enhancement of the up-conversion intensity. This study provides a new insight into the dye-sensitized up-conversion luminescence of rare earth-based nanoparticles and facilitates their practical applications.

To enhance the total emission intensity, particularly the red emission of Yb,Er co-doped nanoparticles for red light activated photodynamic therapy (PDT), we doped Mn2+ ions into the NaGdF4:Yb,Er core, and subsequently coated the NaGdF4:Yb active shell to fabricate core–shell structured, up-conversion nanoparticles of NaGdF4:Yb,Er,Mn@NaGdF4:Yb (abbreviated as UCNPs). A novel and facile encapsulation method with gelatin has been proposed to transfer oleic acid (OA) stabilized UCNPs into an aqueous solution and simultaneously decorate zinc phthalocyanine (ZnPc) photosensitizer molecules. In the encapsulation process, ZnPc molecules are wrapped in the interlaced net structure of the peptide chain from gelatin, forming the UCNPs@gel–ZnPc nanocomposite. The nanoplatform has high emission intensity and excellent biocompatibility, as was expected. More importantly, the enhanced red emission of UCNPs has significant overlap with the UV absorbance of ZnPc; therefore, it can effectively activate the sensitizer to produce a large amount of singlet oxygen reactive oxygen species (ROS, 1O2) to kill cancer cells, which has evidently been verified by the in vitro results. Combined with the inherent up-conversion luminescence (UCL) imaging properties, this UCNPs@gel–ZnPc nanoplatform could have potential application in PDT and imaging fields.

In this study, uniform gadolinium fluoride microspheres with controllable phases and structures have been synthesized for the first time by a facile ion exchange process using Gd(OH)CO3 solid microspheres as precursors. It is found that the as-synthesized NaxGdyFx+3y samples, including orthorhombic GdF3, cubic Na5Gd9F32 and hexagonal NaGdF4, all consist of well dispersed microspheres with mesopores. After the conversion process, the products mainly inherit the size and shape of the precursors. Moreover, the used ethylene glycol (EG) plays a key role in the phase and structure of the final NaxGdyFx+3y mesoporous spheres by impacting the etching and ion exchange process. Based on the time-dependent experiments of gadolinium fluorides, the possible formation mechanism is discussed in detail. Under 273 nm UV excitation, NaxGdyFx+3y:2% Eu3+ shows bright red emissions due to efficient energy transfer from Gd3+ to Eu3+. NaxGdyFx+3y:17% Yb3+/3% Er3+ exhibits the characteristic up-conversion (UC) emissions of Er3+. It is noted that the highest DC and UC emission intensities of NaGdF4:Ln should be due to the hexagonal phase. The fluorescent NaxGdyFx+3y mesoporous microspheres show obvious drug (doxorubicin hydrochloride, DOX) storage/release properties and good biocompatibility, suggesting their potential application in biomedical fields.

Gd2O3:Ln@mSiO2 hollow nanospheres (Gd2O3:Ln hollow spheres coated by a mesoporous silica layer) were successfully synthesized through a self-template method using Gd(OH)CO3 as template to form hollow precursors (named HPs), which involved the incorporation of the rare earth compound into the interior of the hydrophilic carbon shell, followed by coating with a mesoporous silica shell, and subsequent calcination in air. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric and differential thermal analyses (TG-DTA), photoluminescence spectroscopy, kinetic decays as well as N2 adsorption/desorption were employed to characterize the composites. The results indicate that the uniform Gd2O3:Ln@mSiO2 composite with the particle size around 300 nm maintains the spherical morphology and good dispersibility of the precursor. Interestingly, the composite has a double-shell structure including an inner shell of Gd2O3 and an outer shell of mesoporous silica. Moreover, they also exhibit bright red (Eu3+, 5D0 → 7F2) down-conversion (DC) emission and characteristic up-conversion (UC) emissions of Yb3+/Er3+. Under beam excitation, the hollow structured sample emits, which should have potential applications in biomedicine and other fields.

Two major issues of finding the appropriate photosensitizer and raising the penetration depth of irradiation light exist in further developing of photodynamic therapy (PDT). The excited ultraviolet/visible (UV/vis) irradiation light has a relatively shallow depth of penetration and UV light itself may have sufficient energy to damage normal tissues; these are substantial limitations to successful cancer therapy. Herein, we for the first time report a novel multifunctional nanoplatform for a single 980 nm near-infrared (NIR) light-triggered PDT based on NaGdF4:Yb,Tm@NaGdF4 upconversion nanoparticles (UCNPs) integrated with bismuth oxyhalide (BiOCl) sheets, designated as UCNPs@BiOCl. And UCNPs@BiOCl was fabricated by a convenient, efficient, green, and inexpensive method. Excitingly, layered bismuth oxyhalide materials possess a high photocatalytic performance, unique layered structures and wide light response to a broad wavelength range of ultraviolet to visible light. And the loaded UCNPs can convert NIR light into UV/vis region emissions, which drives the pure water splitting of BiOCl sheets to produce plenty of reactive oxygen species (ROS) to damage tumor cells. The excellent antitumor efficiency of the complex has been evidently attested by comparing experimental results. Our work may make a contribution to the wide application of BiOCl-based materials in biomedicine.