A “Neck-Formation” Strategy for an Antiquenching Magnetic/Upconversion Fluorescent Bimodal Cancer Probe

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.

Recent Advances in Magnetic Upconversion Nanocomposites for Bioapplications

The combination of magnetism and upconversion luminescent property into one single nanostructure is fascinating for biological fields, such as multimodal bioimaging, targeted drug delivery, and imaging-guided therapy. In this review, we will provide the state-of-the-art advances on magnetic upconversion nanocomposites towards their bioapplications. Their structure design, synthesis methods, surface engineering and applications in bioimaging, drug delivery, therapy as well as biodetection will be covered.

Advances in the application of upconversion nanoparticles for detecting and treating cancers

The detection and treatment of cancer cells at an early stage are crucial for prolonging the survival time and improving the quality of life of patients. Upconversion nanoparticles (UCNPs) have unique physical and chemical advantages and likely provide a platform for detecting and treating cancer cells at an early stage. In this paper, the principle of UCNPs as chemical sensors based on fluorescence resonance energy transfer (FRET) has been briefly introduced. Research progress in such chemical sensors for detecting and analyzing bioactive substances and heavy metal ions at the subcellular level has been summarized. The principle of UCNP-based nanoprobe-targeting of cancer cells has been described. The research progress in using nanocomposites for cancer cell detection, namely cancer cell targeted imaging and tissue staining, has been discussed. In the field of cancer treatment, the principles and research progress of UCNPs in photodynamic therapy and photothermal therapy of cancer cells are systematically discussed. Finally, the prospects for UCNPs and remaining challenges to UCNP application in the field of cancer diagnosis and treatment are briefly described. This review provides powerful theoretical guidance and useful practical information for the research and application of UCNPs in the field of cancer.

Multifunctional BaYbF5: Gd/Er upconversion nanoparticles for in vivo tri-modal upconversion optical, X-ray computed tomography and magnetic resonance imaging

Development of high-quality upconversion nanoparticles (UCNPs) with combination of the merits of multiple molecular imaging techniques, such as, upconversion luminescence (UCL) imaging, X-ray computed tomography (CT), and magnetic resonance (MR) imaging, could significantly improve the accuracy of biological diagnosis. In this work, multifunctional BaYbF₅: Gd/Er (50:2mol%) UCNPs were synthesized via a solvothermal method using oleic acid (OA) as surface ligands (denoted as OA-UCNPs). The OA-UCNPs were further treated by diluted HCl to form ligand-free UCNPs (LF-UCNPs) for later bioimaging applications. The cytotoxicity assay in HeLa cells shows low cell toxicity of these LF-UCNPs. Owing to the efficient UCL of BaYbF₅: Gd/Er, the LF-UCNPs were successfully used as luminescent bioprobe in UCL bioimaging. And, X-ray CT imaging reveals that BaYbF₅: Gd/Er UCNPs can act as potential contrast agents for detection of the liver and spleen in the live mice owing to the high-Z elements (e.g., Ba, Yb, and Gd) in host matrix. Moreover, with the addition of Gd, the as-designed UCNPs exhibit additional positive contrast enhancement in T₁-weighted MR imaging. These findings demonstrate that BaYbF₅: Gd/Er UCNPs are potential candidates for tri-modal imaging.

Nanomaterials for In Vivo Imaging

In vivo imaging, which enables us to peer deeply within living subjects, is producing tremendous opportunities both for clinical diagnostics and as a research tool. Contrast material is often required to clearly visualize the functional architecture of physiological structures. Recent advances in nanomaterials are becoming pivotal to generate the high-resolution, high-contrast images needed for accurate, precision diagnostics. Nanomaterials are playing major roles in imaging by delivering large imaging payloads, yielding improved sensitivity, multiplexing capacity, and modularity of design. Indeed, for several imaging modalities, nanomaterials are now not simply ancillary contrast entities, but are instead the original and sole source of image signal that make possible the modality's existence. We address the physicochemical makeup/design of nanomaterials through the lens of the physical properties that produce contrast signal for the cognate imaging modality-we stratify nanomaterials on the basis of their (i) magnetic, (ii) optical, (iii) acoustic, and/or (iv) nuclear properties. We evaluate them for their ability to provide relevant information under preclinical and clinical circumstances, their in vivo safety profiles (which are being incorporated into their chemical design), their modularity in being fused to create multimodal nanomaterials (spanning multiple different physical imaging modalities and therapeutic/theranostic capabilities), their key properties, and critically their likelihood to be clinically translated.

Multimodal cancer imaging using lanthanide-based upconversion nanoparticles

Multimodal nanoprobes that integrate different imaging modalities in one nano-system could offer synergistic effect over any modality alone to satisfy the higher requirements on the efficiency and accuracy for clinical diagnosis and medical research. Upconversion nanoparticles (UCNPs), particularly lanthanide (Ln)-based NPs have been regarded as an ideal building block for constructing multimodal bioprobes due to their fascinating properties. In this review, we first summarize recent advances in the optimizations of existing UCNPs. In particular, we highlight the applications of Ln-based UCNPs for multimodal cancer imaging in vitro and in vivo. The explorations of UCNPs-based multimodal nanoprobes for targeting diagnosis and imaging-guided therapeutics are also presented. Finally, the challenges and perspectives of Ln-based UCNPs in this rapid growing field are discussed.

The biosafety of lanthanide upconversion nanomaterials

The association between the chemo-physical properties of UCNPs and their biodistribution, excretion, and toxic effects is presented in this review.

Highly biocompatible zwitterionic phospholipids coated upconversion nanoparticles for efficient bioimaging

The potential of upconversion nanoparticles (UCNPs) in various biomedical applications, including immunoassays, biomedical imaging, and molecular sensing, requires their surface derivatized to be hydrophilic and biocompatible. Here, a new family of compact zwitterionic ligand systems composed with functional phospholipids was designed and used for the surface modification of UCNPs. The zwitterionic UCNPs are hydrophilic, compact, and easily functionalized. It was proved that zwitterionic phospholipids could provide UCNPs with not only extended pH and salt stability but also little nonspecific interactions to positively and negatively charged proteins, low nonspecific adhesion in live-cell imaging process. Most notably, the efficient in vivo tumor imaging performance and long blood circulation half-life suggests the excellent biocompatibility for in vivo imaging of the zwitterionic UCNPs.

Functionalized upconversion nanoparticles: versatile nanoplatforms for translational research

The design, application, and translation of targeted multimodality molecular imaging probes based on nanotechnology have attracted increasing attentions during the last decade and will continue to play vital roles in cancer diagnosis and personalized medicine. With the growing awareness of drawbacks of traditional organic dyes and quantum dots, biocompatible lanthanide ion doped upconversion nanoparticles have emerged as promising candidates for clinically translatable imaging probes, owing to their unique features that are suitable for future targeted multimodal imaging in living subjects. In this review, we summarized the recent advances in the field of functionalized upconversion nanoparticles (f-UCNP) for biological imaging and therapy in vivo, and discussed the future research directions, obstacles ahead, and the potential use of f-UCNP in translational research.

Computed tomography imaging-guided radiotherapy by targeting upconversion nanocubes with significant imaging and radiosensitization enhancements

The clinical potentials of radiotherapy could not be achieved completely because of the inaccurate positioning and inherent radioresistance of tumours. In this study, a novel active-targeting upconversion theranostic agent (arginine-glycine-aspartic acid-labelled BaYbF₅: 2% Er³⁺ nanocube) was developed for the first time to address these clinical demands. Heavy metal-based nanocubes (~10 nm) are potential theranostic agents with bifunctional features: computed tomography (CT) contrast agents for targeted tumour imaging and irradiation dose enhancers in tumours during radiotherapy. Remarkably, they showed low toxicity and excellent performance in active-targeting CT imaging and CT imaging-guided radiosensitizing therapy, which could greatly concentrate and enlarge the irradiation dose deposition in tumours to enhance therapeutic efficacy and minimize the damage to surrounding tissues.

Iron oxide-induced thermal effects on solid-state upconversion emissions in NaYF4:Yb,Er nanocrystals

Multifunctional materials exhibiting photon upconversion show promising applications for biological imaging and sensing. In this study, we examine the solid-state upconversion emission of NaYF4:Yb,Er nanoparticles in the presence of iron oxide nanoparticles. Fe3O4 nanoparticles (6 nm) were mixed with NaYF4:Yb,Er nanoparticles (either 10 or 50 nm) in varying proportions by drying chloroform solutions of nanoparticles onto glass slides. Upconversion spectra were acquired, and a laser power-dependent emission was observed and correlated with the iron oxide content in the mixture. Changes in the lattice temperature of the upconverting particles were monitored by careful observation of the relative intensities of the (2)H11/2 and (4)S3/2 →( 4)I15/2 transitions. The emission characteristics observed are consistent with an iron oxide-induced thermal effect that is dependent on both the laser power and the proportion of iron oxide. The results highlight that the thermal effects of mixed nanoparticle systems should be considered in the design of luminescent upconverting hybrid materials.

Lanthanide-doped luminescent nano-bioprobes: from fundamentals to biodetection

Trivalent lanthanide (Ln(3+))-doped luminescent inorganic nanoparticles (NPs), characterized by long-lived luminescence, large Stokes and/or anti-Stokes shifts, narrow emission bands and high photochemical stability, are considered to be promising candidates as luminescent bioprobes in biomedicine and biotechnology. In this feature article, we provide a brief overview of the most recent advances in Ln(3+)-doped luminescent inorganic NPs as sensors, which covers from their chemical and physical fundamentals to biodetection, such as controlled synthesis methodology, surface modification chemistry, optical physics, and their promising applications in diverse bioassays, with an emphasis on heterogeneous and homogeneous in vitro biodetection. Finally, some of the most important emerging trends and future efforts toward this active research field are also proposed.

Upconversion nanoparticles and their composite nanostructures for biomedical imaging and cancer therapy

Upconversion nanoparticles (UCNPs), particularly lanthanide-doped nanocrystals, which emit high energy photons under excitation by the near-infrared (NIR) light, have found potential applications in many different fields, including biomedicine. Compared with traditional down-conversion fluorescence imaging, the NIR light excited upconversion luminescence (UCL) imaging relying on UCNPs exhibits improved tissue penetration depth, higher photochemical stability, and is free of auto-fluorescence background, which promises biomedical imaging with high sensitivity. On the other hand, the unique upconversion process of UCNPs may be utilized to activate photosensitive therapeutic agents for applications in cancer treatment. Moreover, the integration of UCNPs with other functional nanostructures could result in the obtained nanocomposites having highly enriched functionalities, useful in imaging-guided cancer therapies. This review article will focus on the biomedical imaging and cancer therapy applications of UCNPs and their nanocomposites, and discuss recent advances and future prospects in this emerging field.

High resolution fluorescence imaging of cancers using lanthanide ion-doped upconverting nanocrystals

During the last decade inorganic luminescent nanoparticles that emit visible light under near infrared (NIR) excitation (in the biological window) have played a relevant role for high resolution imaging of cancer. Indeed, semiconductor quantum dots (QDs) and metal nanoparticles, mostly gold nanorods (GNRs), are already commercially available for this purpose. In this work we review the role which is being played by a relatively new class of nanoparticles, based on lanthanide ion doped nanocrystals, to target and image cancer cells using upconversion fluorescence microscopy. These nanoparticles are insulating nanocrystals that are usually doped with small percentages of two different rare earth (lanthanide) ions: The excited donor ions (usually Yb3+ ion) that absorb the NIR excitation and the acceptor ions (usually Er3+, Ho3+ or Tm3+), that are responsible for the emitted visible (or also near infrared) radiation. The higher conversion efficiency of these nanoparticles in respect to those based on QDs and GNRs, as well as the almost independent excitation/emission properties from the particle size, make them particularly promising for fluorescence imaging. The different approaches of these novel nanoparticles devoted to "in vitro" and "in vivo" cancer imaging, selective targeting and treatment are examined in this review.

Water-stable NaLuF4-based upconversion nanophosphors with long-term validity for multimodal lymphatic imaging

Multimodal imaging is rapidly becoming an important tool for biomedical applications because it can compensate for the deficiencies of individual imaging modalities. Herein, multifunctional NaLuF(4)-based upconversion nanoparticles (Lu-UCNPs) were synthesized though a facile one-step microemulsion method under ambient condition. The doping of lanthanide ions (Gd(3+), Yb(3+) and Er(3+)/Tm(3+)) endows the Lu-UCNPs with high T(1)-enhancement, bright upconversion luminescence (UCL) emissions, and excellent X-ray absorption coefficient. Moreover, the as-prepared Lu-UCNPs are stable in water for more than six months, due to the protection of sodium glutamate and diethylene triamine pentacetate acid (DTPA) coordinating ligands on the surface. Lu-UCNPs have been successfully applied to the trimodal CT/MR/UCL lymphatic imaging on the modal of small animals. It is worth noting that Lu-UCNPs could be used for imaging even after preserving for over six months. In vitro transmission electron microscope (TEM), methyl thiazolyl tetrazolium (MTT) assay and histological analysis demonstrated that Lu-UCNPs exhibited low toxicity on living systems. Therefore, Lu-UCNPs could be multimodal agents for CT/MR/UCL imaging, and the concept can be served as a platform technology for the next-generation of probes for multimodal imaging.

18F-Labeled magnetic-upconversion nanophosphors via rare-Earth cation-assisted ligand assembly

A novel method of rare-earth cation-assisted ligand assembly has been developed to provide upconversion nanophosphors with T(1)-enhanced magnetic resonance (MR), radioactivity, and targeted recognition properties, making these nanoparticles potential candidates for multimodal bioimaging. The process of modifying the surface of the nanophosphors has been confirmed by transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, proton nuclear magnetic resonance, Fourier-transform infrared spectroscopy, energy-dispersive X-ray analysis, and so on. The versatility of this surface modification approach for incorporating functional molecules and fabricating fluorine-18-labeled magnetic-upconversion nanophosphors as multimodal bioprobes has been demonstrated by targeted cell imaging, in vivo upconversion luminescence, MR imaging, and positron emission tomography imaging of whole-body small animals.

Upconverting luminescent nanoparticles for use in bioconjugation and bioimaging

Upconverting luminescent nanoparticles (UCNPs) display the unique property of emitting visible light following photoexcitation with near-infrared laser light. This results in features such as virtually zero autofluorescence of (biological) matter and easy separation of the emission peaks from stray light. Other features include rather narrow emission bands, very high chemical stability, the lack of bleaching, and the absence of blinking effects. This article reviews the work performed in the past few years with UCNPs in terms of surface modifications, bioconjugation, and optical (cellular) imaging.