Modulation of proteins by rare earth elements as a biotechnological tool

Although rare earth element (REE) complexes are often utilized in bioimaging due to their photo- and redox stability, magnetic and optical characteristics, they are also applied for pharmaceutical applications due to their interaction with macromolecules namely proteins. The possible implications induced by REEs through modification in the function or regulatory activity of the proteins trigger a variety of applications for these elements in biomedicine and biotechnology. Lanthanide complexes have particularly been applied as anti-biofilm agents, cancer inhibitors, potential inflammation inhibitors, metabolic elicitors, and helper agents in the cultivation of unculturable strains, drug delivery, tissue engineering, photodynamic, and radiation therapy. This paper overviews emerging applications of REEs in biotechnology, especially in biomedical imaging, tumor diagnosis, and treatment along with their potential toxic effects. Although significant advances in applying REEs have been made, there is a lack of comprehensive studies to identify the potential of all REEs in biotechnology since only four elements, Eu, Ce, Gd, and La, among 17 REEs have been mostly investigated. However, in depth research on ecotoxicology, environmental behavior, and biological functions of REEs in the health and disease status of living organisms is required to fill the vital gaps in our understanding of REEs applications.

Engineered upconversion nanocarriers for synergistic breast cancer imaging and therapy: Current state of art

Breast cancer is the most common type of cancer in women and is the second leading cause of cancer-related deaths worldwide. Early diagnosis and effective therapeutic interventions are critical determinants that can improve survival and quality of life in breast cancer patients. Nanotheranostics are emerging interventions that offer the dual benefit of in vivo diagnosis and therapeutics through a single nano-sized carrier. Rare earth metal-doped upconversion nanoparticles (UCNPs) with their ability to convert near-infrared light to visible light or UV light in vivo settings have gained special attraction due to their unique luminescence and tumor-targeting properties. In this review, we have discussed applications of UCNPs in drug and gene delivery, photothermal therapy (PTT), photodynamic therapy (PDT) and tumor targeting in breast cancer. Further, present challenges and future opportunities for UCNPs in breast cancer treatment have also been mentioned.

Facile synthesized NaGdF4 :Yb, Er peanut-shaped, highly biocompatible, colloidal upconversion nanospheres

A facile method was used for the synthesis of peanut-shaped very emissive NaGdF₄ :Yb, Er upconversion nanospheres (UCNSs) at lower temperatures with uniform size distribution. Crystallographic structure, phase purity, morphology, thermal robustness, biocompatibility, colloidal stability, surface chemistry, optical properties, and luminesce properties were explored by X-ray diffraction (XRD), Scanning electron microscope (SEM), transmission electron microscope (TEM), zeta potential, Thermogravimetric/thermal differential analysis (TGA/DTA), Fourier transform infrared (FTIR), UV/visible and photoluminescence spectroscopic tools. XRD pattern verified the construction of a single-phase, highly-crystalline NaGdF₄ phase with a hexagonal structure. Peanut-shaped morphology of the sample was obtained from SEM micrographs which were validated from high-resolution TEM images, have an equatorial diameter of 170-200 nm and a length of 220-230 nm, with irregular size, monodispersed, porous structure, and rough surface of the particles. The positive zeta potential value exhibited good biocompatibility along with high colloidal stability as observed from the absorption spectrum. The prepared UCNSs revealed high dispersibility, irregular size peanut-shaped morphology, rough surface, good colloidal stability, and excellent biocompatibility in aqueous media. A hexagonal phase NaGdF₄ doped with Yb, and Er UCNSs revealed the characteristics of highly dominant emissions located at 520-525, 538-550, and 659-668 nm are corresponding to the ² H_11/2 →⁴ I_15/2 , ⁴ S_3/2 →⁴ I_15/2 , and ⁴ F_9/2 →⁴ I_15/2 transition of Er³⁺ ions, respectively, as a result of energy transfer from sensitizer Yb³⁺ ion to emitter Er³⁺ ion.

New up-conversion luminescence in molecular cyano-substituted naphthylsalophen lanthanide(iii) complexes

A new naphthylsalophen and its 3 : 2 ligand-to-lanthanide sandwich-type complexes were isolated. When excited at 380 nm, the complexes display the characteristic metal-centred emission for Nd^III, Er^III and Yb^III. Upon 980 nm excitation, in mixed lanthanide and the Er complexes, Er-centred upconversion emission at 543 and 656 nm is observed, with power densities as low as 2.18 W cm^-2.

Dual-Targeting Peptide-Guided Approach for Precision Delivery and Cancer Monitoring by Using a Safe Upconversion Nanoplatform

Using Epstein-Barr virus (EBV)-induced cancer cells and HeLa cells as a comparative study model, a novel and safe dual-EBV-oncoproteins-targeting pH-responsive peptide engineering, coating, and guiding approach to achieve precision targeting and treatment strategy against EBV-associated cancers is introduced. Individual functional peptide sequences that specifically bind to two overexpressed EBV-specific oncoproteins, EBNA1 (a latent cellular protein) and LMP1 (a transmembrane protein), are engineered in three different ways and incorporated with a pH-sensitive tumor microenvironment (TME)-cleavable linker onto the upconversion nanoparticles (UCNP) NaGdF4:Yb3+, Er3+@NaGdF4 (UCNP-P n , n = 5, 6, and 7). A synergistic combination of the transmembrane LMP1 targeting ability and the pH responsiveness of UCNP-P n is found to give specific cancer differentiation with higher cellular uptake and accumulation in EBV-infected cells, thus a lower dose is needed and the side effects and health risks from treatment would be greatly reduced. It also gives responsive UC signal enhancement upon targeted dual-protein binding and shows efficacious EBV cancer inhibition in vitro and in vivo. This is the first example of simultaneous imaging and inhibition of two EBV latent proteins, and serves as a blueprint for next-generation peptide-guided precision delivery nanosystem for the safe monitoring and treatment against one specific cancer.

Cross Talk Between Autophagy and Apoptosis Contributes to ZnO Nanoparticle-Induced Human Osteosarcoma Cell Death

Killing osteosarcoma cells by zinc oxide nanoparticles (NPs) and its underlying subcellular mechanism are never studied. Here, it is found that the NPs induce cross talk between apoptosis and autophagy, which leads to osteosarcoma cell death. Specifically, the NP uptake promotes autophagy by inducing accumulation of autophagosomes along with impairment of lysosomal functions. The autophagy further causes the uptaken NPs to release zinc ions by promoting their dissolution. These intracellular zinc ions, together with those that are originally released from the extracellular NPs and flowed into the cells, collectively target and damage mitochondria to produce reactive oxygen species (ROS). Then the ROS inhibit cell proliferation by arresting S phase and trigger apoptosis by extrinsic and intrinsic pathways, ultimately leading to cell death. More importantly, suppression of the early stage autophagy restores cell viability by abolishing apoptosis whereas blockade of the late stage autophagy inversely enhances apoptosis. In contrast, inhibition of apoptosis shows a limited ability to restore cell viability but obviously enhance autophagy. Notably, cell viability is strongly ameliorated by the combination of inhibitors for both the late stage autophagy and the apoptosis. These findings provide a mechanistic understanding of the NP-directed autophagy and apoptosis in osteosarcoma cells.

Responsive upconversion nanoprobe for monitoring and inhibition of EBV-associated cancers via targeting EBNA1

Non-responsive emission enhancement is the disadvantage of upconversion nanomaterials (UCNM) when compared with conventional organic based agents for molecular imaging. We herein show a new strategy by conjugating NaGdF4:Yb3+,Er3+@NaGdF4 (UCNP) with peptides to achieve responsive UC emission enhancement upon binding to a targeted protein - EBNA1. EBNA1 is a well-known viral latent protein for the EBV-associated cancer. Peptide-coating of the functionalized core-shell nanoparticle diminishes upconverted emission intensity drastically. However, the peptide-coated UCNP shows selective and responsive UC emission enhancement via aggregation with the targeted protein. This phenomenon paves a new way for UCNM in molecular imaging.

Preparation, characterization and luminescence properties of core-shell ternary terbium composites SiO2(600)@Tb(MABA-Si)•L

Two novel core-shell structure ternary terbium composites SiO₂₍₆₀₀₎@Tb(MABA-Si)·L(L:dipy/phen) nanometre luminescence materials were prepared by ternary terbium complexes Tb(MABA-Si)·L₂·(ClO₄)₃·2H₂O shell grafted onto the surface of SiO₂ microspheres. And corresponding ternary terbium complexes were synthesized using (CONH(CH₂)₃Si(OCH₂CH₃)₃)₂ (denoted as MABA-Si) as first ligand and L as second ligand coordinated with terbium perchlorate. The as-synthesized products were characterized by means of IR spectra, ¹HNMR, element analysis, molar conductivity, SEM and TEM. It was found that the first ligand MABA-Si of terbium ternary complex hydrolysed to generate the Si-OH and the Si-OH condensate with the Si-OH on the surface of SiO₂ microspheres; then ligand MABA-Si grafted onto the surface of SiO₂ microspheres. The diameter of SiO₂ core of SiO₂₍₆₀₀₎@Tb(MABA-Si)·L was approximately 600 nm. Interestingly, the luminescence properties demonstrate that the two core-shell structure ternary terbium composites SiO₂₍₆₀₀₎Tb(MABA-Si)·L(dipy/phen) exhibit strong emission intensities, which are 2.49 and 3.35 times higher than that of the corresponding complexes Tb(MABA-Si)·L₂·(ClO₄)₃·2H₂O, respectively. Luminescence decay curves show that core-shell structure ternary terbium composites have longer lifetime. Excellent luminescence properties enable the core-shell materials to have potential applications in medicine, industry, luminescent fibres and various biomaterials fields.

Stable ICG-loaded upconversion nanoparticles: silica core/shell theranostic nanoplatform for dual-modal upconversion and photoacoustic imaging together with photothermal therapy

We report here the design and multiple functions of a new hierarchical nanotheronostic platform consisting of an upconversion nanoparticle (UCNP) core: shell with an additional mesoporous silica (mSiO2) matrix load shell containing sealed, high concentration of ICG molecules. We demonstrate that this UCNP@mSiO2-ICG nanoplatform can perform the following multiple functions under NIR excitation at 800 nm: 1) Light harvesting by the UCNP shell containing Nd and subsequent energy transfer to Er in the Core to produce efficient green and red upconversion luminescence for optical imaging; 2) Efficient nonradiative relaxation and local heating produced by concentration quenching in aggregated ICG imbedded in the mesopourous silica shell to enable both photoacoustic imaging and photothermal therapy. Compared to pure ICG, sealing of mesoporous silica platforms prevents the leak-out and improves the stability of ICG by protecting from rapid hydrolysis. Under 800 nm laser excitation, we performed both optical and photoacoustic (PA) imaging in vitro and in vivo. Our results demonstrated that UCNP@mSiO2-ICG with sealed structures could be systemically delivered to brain vessels, with a long circulation time. In addition, these nanoplatforms were capable of producing strong hyperthermia efforts to kill cancer cells and hela cells under 800 nm laser irradiation.

cis-Platinum pro-drug-attached CuFeS2 nanoplates for in vivo photothermal/photoacoustic imaging and chemotherapy/photothermal therapy of cancer

Photothermal therapy (PTT) has attracted considerable attention in cancer treatment. Herein, the facile synthesis of copper iron sulfide (chalcopyrite, CuFeS₂) nanoplates (NPs) with well-defined shape was achieved by a template-mediated method. Chitosan (CS), a linear cationic polysaccharide, was used to improve the physiological stability and biocompatibility. CuFeS₂ NPs with strong near-infrared (NIR) absorbance enabled contrasts in photothermal and photoacoustic (PA) imaging. In vitro and in vivo tumor ablation studies further demonstrated that CS-functionalized CuFeS₂ (CuFeS₂-CS) NPs could convert 808 nm NIR light into heat for PTT with a photothermal conversion efficiency up to 30.5%, which was clearly higher than that of CuS NPs (only 21.4%). Furthermore, CuFeS₂-CS NPs could also load cis-platinum pro-drug (CuFeS₂-CS-Pt), and CuFeS₂-CS-Pt showed a better synergistic therapeutic effect with respect to either chemotherapy or PTT.

Double-mesoporous core-shell nanosystems based on platinum nanoparticles functionalized with lanthanide complexes for in vivo magnetic resonance imaging and photothermal therapy

A double-mesoporous nanosystem was synthesized for treating as well as imaging cancer cells by using a simple and mild method. The mesoporous platinum (Pt) nanoparticles acting as a core show excellent photothermal effect under illumination with an 808 nm near infrared (NIR) laser. The mesoporous silica linked with a lanthanide (Gd) complex acting as a shell displays potential applications as a contrast agent for magnetic resonance imaging (MRI). The final mPt@mSiO₂-GdDTPA nanosystems exhibit good biocompatibility in vitro and in vivo, when investigated by methyl thiazolyl tetrazolium assay and histological and serum biochemistry analysis. The investigation of the photothermal effect shows that the mPt@mSiO₂-GdDTPA nanosystems exhibit an excellent photothermal therapy effect on HeLa cells and tumor-bearing mice. As theranostic agents, the nanosystems display a higher r₁ value than the medical contrast agent magnevist and were successfully applied to in vivo MRI of Kunming mice. Therefore, the first systematic study on the photothermal effect of nanosystems based on mesoporous Pt nanoparticles does encourage the potential applications of metal nanoparticles and hybrid nanocomposites for cancer bioimaging and therapy.

Dopamine-mediated photothermal theranostics combined with up-conversion platform under near infrared light

An organic-inorganic hybrid core-shell nanostructure, based on mesoporous silica coated upconversion core-shell nanoparticles (NaGdF4:Yb,Er@NaGdF4:Yb@mSiO2-Dopa abbreviated here as UCNP@mSiO2-Dopa) that stably incorporates dopamine (Dopa) in the silica layer was introduced as a theranostic nanoplatform for optical imaging guided photothermal therapy (PTT) using NIR excitation. Silica-attaching polyethylenimine make the Dopa transforms into an active form (transferred Dopa) that strongly absorbs light under single 980 nm irradiation. We show that the activated UCNP@mSiO2-Dopa nanoplatform is able to produce a pronounced photothermal effect, that elevates water temperature from room temperature to 41.8 °C within 2 minutes, while concurrently emitting strong upconverted luminescence (UCL) for visualized guidance under 980 nm laser. In addition, we demonstrate the application of the same UCNP@mSiO2-Dopa nanoplatform for magnetic resonance imaging (MRI) and x-ray computed tomography (CT) enabled by the gadolinium (Gd) element contained in the UCNP. Importantly, the in vitro and in vivo anti-cancer therapeutic effects have been shown efficacious, implying the use of the described nanoplatform as an effective multi-modal imaging enabled PTT agent. Results from the in vivo biodistribution of UCNPs@mSiO2, cellular live/dead assay, and histologic analysis of main organs of treated mice, reveal that the UCNP@mSiO2-Dopa agents are bio-compatible with low toxicity.

Multifunctional carbon dots for highly luminescent orange-emissive cellulose based composite phosphor construction and plant tissue imaging

A new class of carbon dot (CD) grafted cellulose hybrid phosphors has been prepared in a facile and fast process. The reddish-orange emissive CDs can be effectively dispersed in cellulose matrices through hydrogen binding, and thus highly efficient orange-emissive CD-based phosphors were successfully obtained with a quantum yield of 44%. Moreover, the affinity of CDs for binding cellulose provides them the feasibility for fluorescence mapping of cellulosic plant cell walls. Several model plant tissues have been employed to investigate the pathway of CDs. Confocal analysis demonstrated that plant tissues can readily absorb CDs from aqueous solutions and bind them with cellulose-rich structures. These studies may open up new avenues for the exploration of CDs in long-wavelength emissive solid-state lighting and plant tissue imaging.

Multifunctional Cu39S28 Hollow Nanopeanuts for In Vivo Targeted Photothermal Chemotherapy

Actively targeted hollow nanoparticles may play key roles in precise anti-cancer therapy. Here, unique Cu39S28 hollow nanopeanuts (HNPs) were synthesized via a facile one-step method and the formation mechanism was illustrated. The as-synthesized Cu39S28 HNPs exhibit outstanding photothermal conversion efficiency (41.1%) and drug storage capacity (DOX, 99.5 %). At the same time, the DOX drug loading nanocomposites have shown great sensitive response of release to either pH value or near infrared ray (NIR). In particular, the folic acid (FA) can easily conjugate with the synthesized Cu39S28 HNPs without further modification to get a targeted effect. The FA modified Cu39S28 HNPs showed an efficiently targeting effect in vitro and could considerably enhance the tumor-targeting effect more than 10 times in vivo. Moreover, the synthetical hyperthermia and drug release from Cu39S28 HNPs when under 808 nm laser could significantly improve the therapeutic efficacy compared with photothermal or chemotherapy alone both in vitro and in vivo. The histological studies in main organs also proved the well biocompatibility, while the tumor sites were in seriously destruction due to the accumulation of the nanocomposites and the combined photothermal chemo therapy effect. Therefore, the multi-functional nanocomposites is excellent antitumor agents due to their superb therapy effect in breast cancer.

Long-term toxicological effects of persistent luminescence nanoparticles after intravenous injection in mice

The ZnGa_1.995Cr_0.005O₄ persistent luminescence nanoparticles offer the promise of revolutionary tools for biological imaging with applications such as cell tracking or tumor detection. They can be re-excited through living tissues by visible photons, allowing observations without any time constraints and avoiding the undesirable auto-fluorescence signals observed when fluorescent probes are used. Despite all these advantages, their uses demand extensive toxicological evaluation and control. With this purpose, mice were injected with a single intravenous administration of hydroxylated or PEGylated persistent luminescence nanoparticles at different concentrations and then a set of standard tests were carried out 1day, 1 month and 6 months after the administration. High concentrations of hydroxylated nanoparticles generate structural alterations at histology level, endoplasmic reticulum damage and oxidative stress in liver, as well as rising in white blood cells counts. A mechanism involving the endoplasmic reticulum damage could be the responsible of the observed injuries in case of ZGO-OH. On the contrary, no toxicological effects related to PEGylated nanoprobes treatment were noted during our in vivo experiments, denoting the protective effect of PEG-functionalization and thereby, their potential as biocompatible in vivo diagnostic probes.

A Photochemical Avenue to Photoluminescent N-Dots and their Upconversion Cell Imaging

A photochemical avenue to synthesize nitrogen-rich quantum dots (N-dots) using 2-azido imidazole as the starting material was established for the first time. A production yield of up to 92.7% was obtained. The N-dots were then fully characterized by elemental analysis, IR, XPS, XRD, AFM and TEM. On the basis of the N2 production and in situ IR results, the underlying mechanism for the photochemical formation of N-dots was proposed. These N-dots showed promising optical properties including wavelength-dependent upconversion photoluminescence, and were successfully used in upconversion cell imaging.

Dependence between cytotoxicity and dynamic subcellular localization of up-conversion nanoparticles with different surface charges

Intensive investigations have been devoted to lanthanide-doped upconversion nanoparticles (UCNPs), which have shown great potential in applications such as biomedical imaging and therapy.

Special properties of luminescent magnetic NaGdF4:Yb3+, Er3+ upconversion nanocubes with surface modifications

Gadolinium-based upconversion nanocubes with amine surface modification are made by a one-pot process. The interfacial effect on their behaviors are observed.

Lanthanide-Functionalized Hydrophilic Magnetic Hybrid Nanoparticles: Assembly, Magnetic Behaviour, and Photophysical Properties

The lanthanide-functionalized multifunctional hybrid nanoparticles combining the superparamagnetic core and the luminescent europium complex were successfully designed and assembled via layer-by-layer strategy in this work. It is noted that the hybrid nanoparticles were modified by a hydrophilic polymer polyethyleneimine (PEI) through hydrogen bonding which bestowed excellent hydrophilicity and biocompatibility on this material. A bright-red luminescence was observed by fluorescence microscopy, revealing that these magnetic-luminescent nanoparticles were both colloidally and chemically stable in PBS solution. Therefore, the nanocomposite with magnetic resonance response and fluorescence probe property is considered to be of great potential in multi-modal bioimaging and diagnostic applications.

Theranostic Upconversion Nanobeacons for Tumor mRNA Ratiometric Fluorescence Detection and Imaging-Monitored Drug Delivery

Remote optical detection and imaging of specific tumor-related biomarkers and simultaneous activation of therapy according to the expression level of the biomarkers in tumor site with theranostic probes should be an effective modality for treatment of cancers. Herein, an upconversion nanobeacon (UCNPs-MB/Dox) is proposed as a new theranostic nanoprobe to ratiometrically detect and visualize the thymidine kinase 1 (TK1) mRNA that can simultaneously trigger the Dox release to activate the chemotherapy accordingly. UCNPs-MB/Dox is constructed with the conjugation of a TK1 mRNA-specific molecular beacon (MB) bearing a quencher (BHQ-1) and an alkene handle modified upconversion nanoparticle (UCNP) through click reaction and subsequently loading with a chemotherapy drug (Dox). With this nanobeacon, quantitative ratiometric upconversion detection of the target with high sensitivity and selectivity as well as the target triggered Dox release in vitro is demonstrated. The sensitive and selective ratiometric detection and imaging of TK1 mRNA under the irradiation of near infrared light (980 nm) and the mRNA-dependent release of Dox for chemotherapy in the tumor MCF-7 cells and A549 cells are also shown. This work provides a smart and robust platform for gene-related tumor theranostics.

Near-Infrared Light-Mediated Photodynamic Therapy Nanoplatform by the Electrostatic Assembly of Upconversion Nanoparticles with Graphitic Carbon Nitride Quantum Dots

Photodynamic therapy (PDT) is a promising antitumor treatment that is based on photosensitizers. This therapy kills cancer cells by generating reactive oxygen species (ROS) after irradiation with specific laser wavelengths. Being a potential photosensitizer, graphitic carbon nitride (g-C₃N₄) quantum dots (QDs) are noncytotoxic. Although the use of g-C₃N₄ QDs is challenged by the limited tissue penetration of UV light, g-C₃N₄ QDs display excellent ultraviolet (UV) light-triggered cytotoxicity. The g-C₃N₄ QDs were synthesized using a solid-phase hydrothermal method. The well-distributed hydrophilic g-C₃N₄ can be combined with NaYF₄:Yb³⁺/Tm³⁺ upconversion nanoparticles via the positive ligand poly(l-lysine) to produce the final nanocomposite, NaYF₄:Yb/Tm-PLL@g-C₃N₄. Upconversion nanoparticles can transfer IR light into UV light and promote g-C₃N₄ to release blue-to-green visible light to generate different images. Moreover, g-C₃N₄ is a promising photosensitizer in PDT because g-C₃N₄ can transfer oxygen into toxic ROS. The singlet oxygen formed by g-C₃N₄ displays great potential for use in the treatment of cancer.

NaGd(MoO4)2 nanocrystals with diverse morphologies: controlled synthesis, growth mechanism, photoluminescence and thermometric properties

Pure tetragonal phase, uniform and well-crystallized sodium gadolinium molybdate (NaGd(MoO4)2) nanocrystals with diverse morphologies, e.g. nanocylinders, nanocubes and square nanoplates have been selectively synthesized via oleic acid-mediated hydrothermal method. The phase, structure, morphology and composition of the as-synthesized products are studied. Contents of both sodium molybdate and oleic acid of the precursor solutions are found to affect the morphologies of the products significantly, and oleic acid plays a key role in the morphology-controlled synthesis of NaGd(MoO4)2 nanocrystals with diverse morphologies. Growth mechanism of NaGd(MoO4)2 nanocrystals is proposed based on time-dependent morphology evolution and X-ray diffraction analysis. Morphology-dependent down-shifting photoluminescence properties of NaGd(MoO4)2: Eu(3+) nanocrystals, and upconversion photoluminescence properties of NaGd(MoO4)2: Yb(3+)/Er(3+) and Yb(3+)/Tm(3+) nanoplates are investigated in detail. Charge transfer band in the down-shifting excitation spectra shows a slight blue-shift, and the luminescence intensities and lifetimes of Eu(3+) are decreased gradually with the morphology of the nanocrystals varying from nanocubes to thin square nanoplates. Upconversion energy transfer mechanisms of NaGd(MoO4)2: Yb(3+)/Er(3+), Yb(3+)/Tm(3+) nanoplates are proposed based on the energy level scheme and power dependence of upconversion emissions. Thermometric properties of NaGd(MoO4)2: Yb(3+)/Er(3+) nanoplates are investigated, and the maximum sensitivity is determined to be 0.01333 K(-1) at 285 K.

Lanthanides: Applications in Cancer Diagnosis and Therapy

Lanthanide complexes are of increasing importance in cancer diagnosis and therapy, owing to the versatile chemical and magnetic properties of the lanthanide-ion 4f electronic configuration. Following the first implementation of gadolinium(III)-based contrast agents in magnetic resonance imaging in the 1980s, lanthanide-based small molecules and nanomaterials have been investigated as cytotoxic agents and inhibitors, in photodynamic therapy, radiation therapy, drug/gene delivery, biosensing, and bioimaging. As the potential utility of lanthanides in these areas continues to increase, this timely review of current applications will be useful to medicinal chemists and other investigators interested in the latest developments and trends in this emerging field.

Optically Monitoring Mineralization and Demineralization on Photoluminescent Bioactive Nanofibers

Bone regeneration and scaffold degradation do not usually follow the same rate, representing a daunting challenge in bone repair. Toward this end, we propose to use an external field such as light (in particular, a tissue-penetrating near-infrared light) to precisely monitor the degradation of the mineralized scaffold (demineralization) and the formation of apatite mineral (mineralization). Herein, CaTiO3:Yb(3+),Er(3+)@bioactive glass (CaTiO3:Yb(3+),Er(3+)@BG) nanofibers with upconversion (UC) photoluminescence (PL) were synthesized. Such nanofibers are biocompatible and can emit green and red light under 980 nm excitation. The UC PL intensity is quenched during the bone-like apatite formation on the surface of the nanofibers in simulated body fluid; more mineral formation on the nanofibers induces more rapid optical quenching of the UC PL. Furthermore, the quenched UC PL can recover back to its original magnitude when the apatite on the nanofibers is degraded. Our work suggests that it is possible to optically monitor the apatite mineralization and demineralization on the surface of nanofibers used in bone repair.

Cooperative adsorption of critical metal ions using archaeal poly-γ-glutamate

Antimony, beryllium, chromium, cobalt (Co), gallium (Ga), germanium, indium (In), lithium, niobium, tantalum, the platinoids, the rare-earth elements (including dysprosium, Dy), and tungsten are generally regarded to be critical (rare) metals, and the ions of some of these metals are stabilized in acidic solutions. We examined the adsorption capacities of three water-soluble functional polymers, namely archaeal poly-γ-glutamate (L-PGA), polyacrylate (PAC), and polyvinyl alcohol (PVA), for six valuable metal ions (Co(2+), Ni(2+), Mn(2+), Ga(3+), In(3+), and Dy(3+)). All three polymers showed apparently little or no capacity for divalent cations, whereas L-PGA and PAC showed the potential to adsorb trivalent cations, implying the beneficial valence-dependent selectivity of anionic polyelectrolytes with multiple carboxylates for metal ions. PVA did not adsorb metal ions, indicating that the crucial role played by carboxyl groups in the adsorption of crucial metal ions cannot be replaced by hydroxyl groups under the conditions. In addition, equilibrium studies using the non-ideal competitive adsorption model indicated that the potential for L-PGA to be used for the removal (or collection) of water-soluble critical metal ions (e.g., Ga(3+), In(3+), and Dy(3+)) was far superior to that of any other industrially-versatile PAC materials.

Improving the MR Imaging Sensitivity of Upconversion Nanoparticles by an Internal and External Incorporation of the Gd(3+) Strategy for in Vivo Tumor-Targeted Imaging

Gd(3+)-ion-doped upconversion nanoparticles (UCNPs), integrating the advantages of upconversion luminescence and magnetic resonance imaging (MRI) modalities, are capturing increasing attention because they are promising to improve the accuracy of diagnosis. The embedded Gd(3+) ions in UCNPs, however, have an indistinct MRI enhancement owing to the inefficient exchange of magnetic fields with the surrounding water protons. In this study, a novel approach is developed to improve the MR imaging sensitivity of Gd(3+)-ion-doped UCNPs. Bovine serum albumin (BSA) bundled with DTPA-Gd(3+) (DTPA(Gd)) is synthesized both as the MR imaging sensitivity synergist and phase-transfer ligand for the surface engineering of UCNPs. The external Gd(3+) ion attachment strategy is found to significant improve the MR imaging sensitivity of Gd(3+)-ion-doped UCNPs. The relaxivity analysis shows that UCNPs@BSA·DTPA(Gd) exhibit higher relaxivity values than do UCNPs@BSA without DTPA(Gd) moieties. Another relaxivity study discloses a striking message that the relaxivity value does not always reflect the realistic MRI enhancement capability. The high concentration of Gd(3+)-ion-containing UCNPs with further surface-engineered BSA·DTPA(Gd) (denoted as UCNPs-H@BSA·DTPA(Gd)) exhibits a more pronounced MRI enhancement capability compared to the other two counterparts [UCNPs-N@BSA·DTPA(Gd) and UCNPs-L@BSA·DTPA(Gd) (-N and -L are denoted as zero and low concentrations of Gd(3+) ion doping, respectively)], even though it holds the lowest r1 of 1.56 s(-1) per mmol L(-1) of Gd(3+). The physicochemical properties of UCNPs are essentially maintained after BSA·DTPA(Gd) surface decoration with good colloidal stability, in addition to improving the MR imaging sensitivity. In vivo T1-weighted MRI shows potent tumor-enhanced MRI with UCNPs-H@BSA·DTPA(Gd). An in vivo biodistribution study indicates that it is gradually excreted from the body via hepatobiliary and renal processing with no obvious toxicity. It could therefore be concluded, with improved MR imaging sensitivity by an internal and external incorporation of Gd(3+) strategy, that UCNPs-H@BSA·DTPA(Gd) presents great potential as an alternative in tumor-targeted MR imaging.

The impact of structural variation in simple lanthanide binding peptides

A series of di-, tri- and tetra-peptides were synthesised using l- and d-glutamic acid in order to determine the effects of peptide length and stereochemistry on lanthanide binding affinity.

Near-infrared light-induced imaging and targeted anti-cancer therapy based on a yolk/shell structure

Yolk/shell mesoporous NaYF₄:Yb,Er@MgSiO₃–ZnPc–RGD spheres have been fabricated to combine photodynamic therapy (PDT) and bio-imaging for improved antitumor efficacy under NIR laser irradiation.

Giant enhancement of upconversion emission in (NaYF₄:Nd³⁺/Yb³⁺/Ho³⁺)/(NaYF₄:Nd³⁺/Yb³⁺) core/shell nanoparticles excited at 808 nm

In this work, colloidal hexagonal-phase (NaYF4:Nd3+/Yb3+/Ho3+)/(NaYF4:Nd3+/Yb3+) core/shell nanoparticles with intense visible upconversion emissions under 808-nm laser excitation were prepared. Compared with the core-only nanoparticles, a maximum 990-fold overall enhancement in the emission intensity of Ho3+ ions was achieved with the help of active-shell coating design, due to the significant increase in the near-infrared absorption and efficient energy transfer from Nd3+ primary-sensitizers to Ho3+ activators via Yb3+ bridging sensitizers. The luminescence-enhancement effect exhibited a strong dependence on the doping concentrations of NaYF4:Nd3+/Yb3+ active-shell. The optimal concentrations of Nd3+ and Yb3+ ions in the active-shell layer were found to be 30 and 5 mol. %, respectively. Moreover, the upconversion emission intensity of NaYF4:Nd3+/Yb3+-coated nanoparticles was about 2.5 times higher than the one coated with a NaYF4:Nd3+ active-shell.

Y2O3:Yb,Er@mSiO2-Cu(x)S double-shelled hollow spheres for enhanced chemo-/photothermal anti-cancer therapy and dual-modal imaging

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 Cu(x)S 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-Cu(x)S composite. The composite exhibits high anti-cancer efficacy due to the synergistic photothermal therapy (PTT) induced by the attached Cu(x)S nanoparticles and the enhanced chemotherapy promoted by the heat from the Cu(x)S-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.

Directional Plk1 inhibition-driven cell cycle interruption using amphiphilic thin-coated peptide-lanthanide upconversion nanomaterials as in vivo tumor suppressors

Polo-like kinase 1 (Plk1) is a major serine/threonine protein kinase which regulates key mitotic events.

The advances in applying inorganic fluorescent nanomaterials for the detection of hepatocellular carcinoma and other cancers

The advances, drawbacks and application suggestions of QDs, UCNPs and CDs in HCC and other cancer detection fields are discussed.

Upconverting nanoparticles: assessing the toxicity

Based on a survey of existing studies, low nanotoxicity of lanthanide doped upconverting nanoparticles holds promise for their safety and suitability for biomedical detection and imaging.