Selective Detection of Chromate and Permanganate Ions Using Gallic Acid Capped CaF2:Tb3+ Nanocrystals

In this study, we have developed ligand-sensitized Ln3+-doped nanocrystals (NCs) for the selective sensing of Cr2O7 2- and MnO4 - ions in nanomolar concentrations. This is accomplished with the gallic acid capped-CaF2:Tb3+ NCs. These NCs display bright green emission through an efficient energy transfer from surface functionalized gallic acid molecules to Tb3+ ions upon UV light excitation. The luminescence from Tb3+ ions are selectively quenched by the addition of Cr2O7 2- and MnO4 - anions. The reduction in the luminescence intensity is found to be quite selective, as the addition of other strong oxidizing species (I-, F-, Br-, Cl-, PO3 2-, SO4 2-, VO3 -, WO4 2-, IO3 -, ClO4 -,) had minimal impact on the luminescence intensity of Tb3+ ions. The calculated limit of detection from the experimental results (for the 3σ/slope criterion) is 77 nM and 55 nM for K2Cr2O7 and KMnO4, respectively. The findings show that tuning the resonance energy transfer (RET) between analytes and Tb3+ inside the NCs serves as a tool for the detection of dichromate and permanganate ions selectively.

Temperature-Dependent Luminescence of Nd3+-Doped Carbon Nanodots for Nanothermometry

Noncontact optical nanothermometers operating within the biological transparency windows are required to study temperature-sensitive biological phenomena at the nanoscale. Nanoparticles containing rare-earth ions such as Nd3+ have been reported to be efficient luminescence-based ratiometric thermometers, however often limited by poor water solubility and concentration-related quenching effects. Herein, we introduce a new type of nanothermometer, obtained by employing low-dimensional carbon nanodots (CNDs) as matrices to host Nd3+ ions (NdCNDs). By means of a one-pot procedure, small (∼7-12 nm), water-soluble nanoparticles were obtained, with high (15 wt %) Nd3+ loading. This stable metal-CND system features temperature-dependent photoluminescence in the second biological window (BW II) upon irradiation at 808 nm, thereby allowing accurate and reversible (heating/cooling) temperature measurements with good sensitivity and thermal resolution. The system possesses remarkable biocompatibility in vitro and promising performance at a high penetration depth in tissue models.

Magnetic Hydroxyapatite Nanoparticles in Regenerative Medicine and Nanomedicine

This review focuses on the latest advancements in magnetic hydroxyapatite (mHA) nanoparticles and their potential applications in nanomedicine and regenerative medicine. mHA nanoparticles have gained significant interest over the last few years for their great potential, offering advanced multi-therapeutic strategies because of their biocompatibility, bioactivity, and unique physicochemical features, enabling on-demand activation and control. The most relevant synthetic methods to obtain magnetic apatite-based materials, either in the form of iron-doped HA nanoparticles showing intrinsic magnetic properties or composite/hybrid compounds between HA and superparamagnetic metal oxide nanoparticles, are described as highlighting structure-property correlations. Following this, this review discusses the application of various magnetic hydroxyapatite nanomaterials in bone regeneration and nanomedicine. Finally, novel perspectives are investigated with respect to the ability of mHA nanoparticles to improve nanocarriers with homogeneous structures to promote multifunctional biological applications, such as cell stimulation and instruction, antimicrobial activity, and drug release with on-demand triggering.

Fabrication of Europium-Doped CaF2 Films via Sol-Gel Synthesis as Down-Shifting Layers for Solar Cell Applications

In the present work, an in-depth study on the sol-gel process for the fabrication of Eu-doped CaF2 materials in the form of thin films has been addressed for the production of down-shifting layers. Fine-tuning of the operative parameters, such as the annealing temperature, substrate nature and doping ion percentage, has been finalized in order to obtain Eu(III)-doped CaF2 thin films via a reproducible and selective solution process for down-shifting applications. An accurate balance of such parameters allows for obtaining films with high uniformity in terms of both their structural and compositional features. The starting point of the synthesis is the use of a mixture of Ca(hfa)2•diglyme•H2O and Eu(hfa)3•diglyme adducts, with a suited ratio to produce 5%, 10% and 15% Eu-doped CaF2 films, in a water/ethanol solution. A full investigation of the structural, morphological and compositional features of the films, inspected using X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX), respectively, has stated a correlation between the annealing temperature and the structural characteristics and morphology of the CaF2 thin films. Interestingly, crystalline CaF2 films are obtained at quite low temperatures of 350-400 °C. The down-shifting properties, validated by taking luminescence measurements under UV excitation, have allowed us to correlate the local environment in terms of the degree of symmetry around the europium ions with the relative doping ion percentages.

Nanojet Trapping of a Single Sub-10 nm Upconverting Nanoparticle in the Full Liquid Water Temperature Range

Upconverting nanoparticles (UCNPs) have been used as optical probes in a great variety of scenarios ranging from cells to animal models. When optically trapped, a single UCNP can be remotely manipulated making possible, for instance, thermal scanning in the surroundings of a living cell. When conventional optics is used, the stability of an optically trapped UCNP is very limited. Its reduced size leads to optical potentials comparable to thermal energy, and up to now, stable optical trapping of a UCNP has been demonstrated only close to room temperature. This fact limits their use above room temperature, for instance, the use to investigate protein denaturalization that occurs in the 40-50 °C range. In this work, stable optical trapping of a single UCNP in the 20-90 °C range has been demonstrated by using a photonic nanojet. The use of an optically trapped microsphere makes it possible to overcome the diffraction limit producing another optical trap of smaller size and enhanced strength. This simple strategy leads not only to an improvement in the thermal stability of the optical trap but also to an enhancement of the emission intensity generated by the optically trapped UCNP.

When rare earth meets carbon nanodots: mechanisms, applications and outlook

Rare earth (RE) elements are widely used in the luminescence and magnetic fields by virtue of their abundant 4f electron configurations. However, the overall performance and aqueous stability of single-component RE materials need to be urgently improved to satisfy the requirements for multifunctional applications. Carbon nanodots (CNDs) are excellent nanocarriers with abundant functional surface groups, excellent hydrophilicity, unique photoluminescence (PL) and tunable features. Accordingly, RE-CND hybrids combine the merits of both RE and CNDs, which dramatically enhance their overall properties such as luminescent and magnetic-optical imaging performances, leading to highly promising practical applications in the future. Nevertheless, a comprehensive review focusing on the introduction and in-depth understanding of RE-CND hybrid materials has not been reported to date. This review endeavors to summarize the recent advances of RE-CNDs, including their interaction mechanisms, general synthetic strategies and applications in fluorescence, biosensing and multi-modal biomedical imaging. Finally, we present the current challenges and the possible application perspectives of newly developed RE-CND materials. We hope this review will inspire new design ideas and valuable references in this promising field in the future.

Luminescent and paramagnetic properties of nanoparticles shed light on their interactions with proteins

Nanoparticles have been recognized as promising tools for targeted drug-delivery and protein therapeutics. However, the mechanisms of protein-nanoparticle interaction and the dynamics underlying the binding process are poorly understood. Here, we present a general methodology for the characterization of protein-nanoparticle interaction on a molecular level. To this end we combined biophysical techniques including nuclear magnetic resonance (NMR), circular dichroism (CD), resonance energy transfer (RET) and surface plasmon resonance (SPR). Particularly, we analyzed molecular mechanisms and dynamics of the interaction of CaF2 nanoparticles with the prototypical calcium sensor calmodulin (CaM). We observed the transient formation of an intermediate encounter complex involving the structural region linking the two domains. Specific interaction of CaM with CaF2 NPs is driven by the N-terminal EF-hands, which seem to recognize Ca2+ on the surface of the nanoparticle. We conclude that CaF2 NP-CaM interaction is fully compatible with potential applications in nanomedicine. Overall, the methods presented in this work can be extended to other systems and may be useful to quantitatively characterize structural and dynamic features of protein-NP interactions with important implications for nanomedicine and nano-biotechnology.

Novel sol–gel fabrication of Yb3+/Tm3+ co-doped β-NaYF4 thin films and investigation of their upconversion properties

An innovative sol–gel process, using a mixture of Na(hfa)·tetraglyme and RE(hfa)₃·diglyme (RE = Y, Yb, Tm) complexes, has been optimized to produce upconverting β-NaYF₄:Yb³⁺/Tm³⁺ thin films.

Calcium-based biomaterials for diagnosis, treatment, and theranostics

Calcium-based biomaterials with good biosafety and bio-absorbability are promising for biomedical applications such as diagnosis, treatment, and theranostics.

Fe-Doping-Induced Magnetism in Nano-Hydroxyapatites

Doping of biocompatible nanomaterials with magnetic phases is currently one of the most promising strategies for the development of advanced magnetic biomaterials. However, especially in the case of iron-doped magnetic hydroxyapatites, it is not clear if the magnetic features come merely from the magnetic phases/ions used as dopants or from complex mechanisms involving interactions at the nanoscale. Here, we report an extensive chemical-physical and magnetic investigation of three hydroxyapatite nanocrystals doped with different iron species and containing small or no amounts of maghemite as a secondary phase. The association of several investigation techniques such as X-ray absorption spectroscopy, Mössbauer, magnetometry, and TEM allowed us to determine that the unusual magnetic properties of Fe^2+/3+-doped hydroxyapatites (FeHA) occur by a synergy of two different phenomena: i.e., (i) interacting superparamagnetism due to the interplay between iron-doped apatite and iron oxide nanoparticles as well as to the occurrence of dipolar interactions and (ii) interacting paramagnetism due to Fe³⁺ ions present in the superficial hydrated layer of the apatite nanophase and, to a lesser extent, paramagnetism due to isolated Fe³⁺ ions in the apatite lattice. We also show that a major player in the activation of the above phenomena is the oxidation of Fe²⁺ into Fe³⁺, as induced by the synthesis process, and their consequent specific positioning in the FeHA structure.

Sequential growth of CaF2:Yb,Er@CaF2:Gd nanoparticles for efficient magnetic resonance angiography and tumor diagnosis

It is a significant challenge to develop nanoscale magnetic resonance imaging (MRI) contrast agents with high performance of relaxation.

Citrate-stabilized lanthanide-doped nanoparticles: brain penetration and interaction with immune cells and neurons

Aim: To unravel key aspects of the use of lanthanide-doped nanoparticles (NPs) in biomedicine, the interaction with immune and brain cells. Materials & methods: Effects of citrate-stabilized CaF2 and SrF2: Yb, Er NPs (13–15 nm) on human dendritic cells and neurons were assessed in vitro. In vivo distribution was analyzed in mice at tissue and ultrastructural levels, and with glia immunophenotyping. Results: The NPs did not elicit dendritic cell activation and were internalized by cultured neurons, without viability changes. After intravenous injection, NPs were found in the brain parenchyma, without features of glial neuroinflammatory response. Conclusion: Lanthanide-doped NPs do not activate cells protagonists of systemic and brain immune responses, are endocytosed by neurons and can cross an intact blood–brain barrier.

Upconversion-luminescent/magnetic dual-functional sub-20 nm core–shell SrF2:Yb,Tm@CaF2:Gd heteronanoparticles

Combination of a high-efficiency upconversion luminescence core with a biocompatible magnetic shell endows hydrothermal-synthesized water-soluble nanoparticles with improved dual-modal bioimaging capabilities.

Multifunctional hollow CaF2:Yb(3+)/Er(3+)/Mn(2+)-poly(2-Aminoethyl methacrylate) microspheres for Pt(IV) pro-drug delivery and tri-modal imaging

Combining the multi-modal medical imaging with cancer therapy in one single system has attracted the great interests for theranostic purpose. In this paper, CaF2:Yb(3+)/Er(3+)/Mn(2+)-poly(2-Aminoethyl methacrylate) (UCHNs-PAMA) hybrid microspheres were successfully fabricated. The synthetic route to the nanocomposite based on a facile hydrothermal method for fabrication of hollow upconversion (UC) nanospheres at first and then post-filling the PAMA interiorly through photo-initiated polymerization. The UCHNs showed orange fluorescence under 980 nm near infrared (NIR) laser excitation, which provided the upconverting luminescence (UCL) imaging modality. Meanwhile, the presence of functional Mn(2+) and Yb(3+) offered the enhanced T1-weighted magnetic resonance (MR) and computed tomography (CT) imaging, respectively. Thanks to introducing amine groups-containing PAMA inside the hollow nanospheres, the Pt(IV) pro-drug, c,c,t-Pt(NH3)2Cl2(OOCCH2CH2COOH)2 (DSP), can be conveniently bonded on the polymer network to construct a nanoscale anti-cancer drug carrier. The UCHNs-PAMA-Pt(IV) nanocomposite shows effective inhibition for Hela cell line via MTT assay. In contrast, Pt(IV) pro-drug and UCHNs-PAMA microspheres behave little cytotoxicity to Hela cells. This should be attributed the fact that the anti-cancer ability can be recovered only when Pt(IV) pro-drug was reduced to Pt(II)-drug in cellular environment. Furthermore, the in vivo experiments on small mice also confirm that the hybrid microspheres have relatively low toxic side effects and high tumor inhibition rate. These findings show that the multifunctional hybrid microspheres have potential to be used as UCL/MR/CT tri-modal imaging contrast agent and anti-cancer drug carriers.

Imaging agents based on lanthanide doped nanoparticles

This review summarizes the recent progress of single and multimodal imaging agents based on lanthanide doped nanoparticles.