Autofluorescence-Free Live-Cell Imaging Using Terbium Nanoparticles

Potential Biomedical Applications of Terbium-Based Nanoparticles (TbNPs): A Review on Recent Advancement

The scientific world is increasingly focusing on rare earth metal oxide nanomaterials due to their consequential biological prospects, navigated by breakthroughs in biomedical applications. Terbium belongs to rare earth elements (lanthanide series) and possesses remarkably strong luminescence at lower energy emission and signal transduction properties, ushering in wide applications for diagnostic measurements (i.e., bioimaging, biosensors, fluorescence imaging, etc.) in the biomedical sectors. In addition, the theranostic applications of terbium-based nanoparticles further permit the targeted delivery of drugs to the specific site of the disease. Furthermore, the antimicrobial properties of terbium nanoparticles induced via reactive oxygen species (ROS) cause oxidative damage to the cell membrane and nuclei of living organisms, ion release, and surface charge interaction, thus further creating or exhibiting excellent antioxidant characteristics. Moreover, the recent applications of terbium nanoparticles in tissue engineering, wound healing, anticancer activity, etc., due to angiogenesis, cell proliferation, promotion of growth factors, biocompatibility, cytotoxicity mitigation, and anti-inflammatory potentials, make this nanoparticle anticipate a future epoch of nanomaterials. Terbium nanoparticles stand as a game changer in the realm of biomedical research, proffering a wide array of possibilities, from revolutionary imaging techniques to advanced drug delivery systems. Their unique properties, including luminescence, magnetic characteristics, and biocompatibility, have redefined the boundaries of what can be achieved in biomedicine. This review primarily delves into various mechanisms involved in biomedical applications via terbium-based nanoparticles due to their physicochemical characteristics. This review article further explains the potential biomedical applications of terbium nanoparticles with in-depth significant mechanisms from the individual literature. This review additionally stands as the first instance to furnish a "single-platted" comprehensive acquaintance of terbium nanoparticles in shaping the future of healthcare as well as potential limitations and overcoming strategies that require exploration before being trialed in clinical settings.

Therapeutic potentials of terbium hydroxide nanorods for amelioration of hypoxia-reperfusion injury in cardiomyocytes

Myocardial hypoxia reperfusion (H/R) injury is the paradoxical exacerbation of myocardial damage, caused by the sudden restoration of blood flow to hypoxia affected myocardium. It is a critical contributor of acute myocardial infarction, which can lead to cardiac failure. Despite the current pharmacological advancements, clinical translation of cardioprotective therapies have proven challenging. As a result, researchers are looking for alternative approaches to counter the disease. In this regard, nanotechnology, with its versatile applications in biology and medicine, can confer broad prospects for treatment of myocardial H/R injury. Herein, we attempted to explore whether a well-established pro-angiogenic nanoparticle, terbium hydroxide nanorods (THNR) can ameliorate myocardial H/R injury. For this study, in vitro H/R-injury model was established in rat cardiomyocytes (H9c2 cells). Our investigations demonstrated that THNR enhance cardiomyocyte survival against H/R-induced cell death. This pro-survival effect of THNR is associated with reduction of oxidative stress, lipid peroxidation, calcium overload, restoration of cytoskeletal integrity and mitochondrial membrane potential as well as augmentation of cellular anti-oxidant enzymes such as glutathione-s-transferase (GST) and superoxide dismutase (SOD) to counter H/R injury. Molecular analysis revealed that the above observations are traceable to the predominant activation of PI3K-AKT-mTOR and ERK-MEK signalling pathways by THNR. Concurrently, THNR also exhibit apoptosis inhibitory effects mainly by suppression of pro-apoptotic proteins like Cytochrome C, Caspase 3, Bax and p53 with simultaneous restoration of anti-apoptotic protein, Bcl-2 and Survivin. Thus, considering the above attributes, we firmly believe that THNR have the potential to be developed as an alternative approach for amelioration of H/R injury in cardiomyocytes.

Investigation of the antibacterial effect, osteogenic activity, and tracing properties of hydroxyapatite co-doped with Tb3+ and Zn2

Hydroxyapatite (HA) is a biomimetic biomaterial that has been widely used in bone repair for many years. However, the increased risk of infection after surgery and long-time tracing for the material distribution and degradation during bone reconstruction remain challenges in the clinic. Zinc (Zn) is considered as an indispensable microelement for humans and is characterized with antibacterial action and osteogenic activity. Terbium (Tb), a rare-earth element, emits stable fluorescence under ultraviolet light. Here, Tb³⁺/Zn²⁺ co-doped hydroxyapatite (HA:Tb/Zn) was prepared to synchronously realize the antibacterial effect, osteogenic activity, and long-time tracing property. We found that HA:Tb/Zn had a strong antibacterial effect on both Gram-positive and Gram-negative clinical infectious bacteria, as well as improved osteogenic activity. HA:Tb/Zn also displayed stable green fluorescence in vitro and in vivo, which indicated great potential for recognizing the material changes during the bone reconstruction process. The combination of the ternary functions is of great significance to control the overuse of antibiotics and realize long-time tracing, and provide a versatile design on biomaterials in bone repair.

Switching to the brighter lane: pathways to boost the absorption of lanthanide-doped nanoparticles

Lanthanide-doped nanoparticles (LNPs) are speedily colonizing several research fields, such as biological (multimodal) imaging, photodynamic therapy, volumetric encoding displays, and photovoltaics. Yet, the electronic transitions of lanthanide ions obey the Laporte rule, which dramatically hampers their light absorption capabilities. As a result, the brightness of these species is severely restricted. This intrinsic poor absorption capability is the fundamental obstacle for untapping the full potential of LNPs in several of the aforementioned fields. Among others, three of the most promising physicochemical approaches that have arisen during last two decades to face the challenges of increasing LNP absorption are plasmonic enhancement, organic-dye sensitization, and coupling with semiconductors. The fundamental basis, remarkable highlights, and comparative achievements of each of these pathways for absorption enhancement are critically discussed in this minireview, which also includes a detailed discussion of the exciting perspectives ahead.

Enhancing FRET biosensing beyond 10 nm with photon avalanche nanoparticles

Förster Resonance Energy Transfer (FRET) between donor (D) and acceptor (A) molecules is a phenomenon commonly exploited to study or visualize biological interactions at the molecular level. However, commonly used organic D and A molecules often suffer from photobleaching and spectral bleed-through, and their spectral properties hinder quantitative analysis. Lanthanide-doped upconverting nanoparticles (UCNPs) as alternative D species offer significant improvements in terms of photostability, spectral purity and background-free luminescence detection, but they bring new challenges related to multiple donor ions existing in a single large size UCNP and the need for nanoparticle biofunctionalization. Considering the relatively short Förster distance (typically below 5-7 nm), it becomes a non-trivial task to assure sufficiently strong D-A interaction, which translates directly to the sensitivity of such bio-sensors. In this work we propose a solution to these issues, which employs the photon avalanche (PA) phenomenon in lanthanide-doped materials. Using theoretical modelling, we predict that these PA systems would be highly susceptible to the presence of A and that the estimated sensitivity range extends to distances 2 to 4 times longer (i.e. 10-25 nm) than those typically found in conventional FRET systems. This promises high sensitivity, low background and spectral or temporal biosensing, and provides the basis for a radically novel approach to combine luminescence imaging and self-normalized bio-molecular interaction sensing.

Time-Gated FRET Nanoprobes for Autofluorescence-Free Long-Term In Vivo Imaging of Developing Zebrafish

The zebrafish is an important vertebrate model for disease, drug discovery, toxicity, embryogenesis, and neuroscience. In vivo fluorescence microscopy can reveal cellular and subcellular details down to the molecular level with fluorescent proteins (FPs) currently the main tool for zebrafish imaging. However, long maturation times, low brightness, photobleaching, broad emission spectra, and sample autofluorescence are disadvantages that cannot be easily overcome by FPs. Here, a bright and photostable terbium-to-quantum dot (QD) Förster resonance energy transfer (FRET) nanoprobe with narrow and tunable emission bands for intracellular in vivo imaging is presented. The long photoluminescence (PL) lifetime enables time-gated (TG) detection without autofluorescence background. Intracellular four-color multiplexing with a single excitation wavelength and in situ assembly and FRET to mCherry demonstrate the versatility of the TG-FRET nanoprobes and the possibility of in vivo bioconjugation to FPs and combined nanoprobe-FP FRET sensing. Upon injection at the one-cell stage, FRET nanoprobes can be imaged in developing zebrafish embryos over seven days with toxicity similar to injected RNA and strongly improved signal-to-background ratios compared to non-TG imaging. This work provides a strategy for advancing in vivo fluorescence imaging applications beyond the capabilities of FPs.

Development of Multifunctional Biopolymeric Auto-Fluorescent Micro- and Nanogels as a Platform for Biomedical Applications

The emerging field of theranostics for advanced healthcare has raised the demand for effective and safe delivery systems consisting of therapeutics and diagnostics agents in a single monarchy. This requires the development of multi-functional bio-polymeric systems for efficient image-guided therapeutics. This study reports the development of size-controlled (micro-to-nano) auto-fluorescent biopolymeric hydrogel particles of chitosan and hydroxyethyl cellulose (HEC) synthesized using water-in-oil emulsion polymerization technique. Sustainable resource linseed oil-based polyol is introduced as an element of hydrophobicity with an aim to facilitate their ability to traverse the blood-brain barrier (BBB). These nanogels are demonstrated to have salient features such as biocompatibility, stability, high cellular uptake by a variety of host cells, and ability to transmigrate across an in vitro BBB model. Interestingly, these unique nanogel particles exhibited auto-fluorescence at a wide range of wavelengths 450-780 nm on excitation at 405 nm whereas excitation at 710 nm gives emission at 810 nm. In conclusion, this study proposes the developed bio-polymeric fluorescent micro- and nano- gels as a potential theranostic tool for central nervous system (CNS) drug delivery and image-guided therapy.

Recent Advances in Luminescence Imaging of Biological Systems Using Lanthanide(III) Luminescent Complexes

The use of luminescence in biological systems allows one to diagnose diseases and understand cellular processes. Molecular systems, particularly lanthanide(III) complexes, have emerged as an attractive system for application in cellular luminescence imaging due to their long emission lifetimes, high brightness, possibility of controlling the spectroscopic properties at the molecular level, and tailoring of the ligand structure that adds sensing and therapeutic capabilities. This review aims to provide a background in luminescence imaging and lanthanide spectroscopy and discuss selected examples from the recent literature on lanthanide(III) luminescent complexes in cellular luminescence imaging, published in the period 2016-2020. Finally, the challenges and future directions that are pointing for the development of compounds that are capable of executing multiple functions and the use of light in regions where tissues and cells have low absorption will be discussed.

Recent Progress in Time-Resolved Biosensing and Bioimaging Based on Lanthanide-Doped Nanoparticles

Luminescent nanomaterials have attracted great attention in luminescence-based bioanalysis due to their abundant optical and tunable surface physicochemical properties. However, luminescent nanomaterials often suffer from serious autofluorescence and light scattering interference when applied to complex biological samples. Time-resolved luminescence methodology can efficiently eliminate autofluorescence and light scattering interference by collecting the luminescence signal of a long-lived probe after the background signals decays completely. Lanthanides have a unique [Xe]4f^N electronic configuration and ladder-like energy states, which endow lanthanide-doped nanoparticles with many desirable optical properties, such as long luminescence lifetimes, large Stokes/anti-Stokes shifts, and sharp emission bands. Due to their long luminescence lifetimes, lanthanide-doped nanoparticles are widely used for high-sensitive biosensing and high-contrast bioimaging via time-resolved luminescence methodology. In this review, recent progress in the development of lanthanide-doped nanoparticles and their application in time-resolved biosensing and bioimaging are summarized. At the end of this review, the current challenges and perspectives of lanthanide-doped nanoparticles for time-resolved bioapplications are discussed.

Single-Nanoparticle Cell Barcoding by Tunable FRET from Lanthanides to Quantum Dots

Fluorescence barcoding based on nanoparticles provides many advantages for multiparameter imaging. However, creating different concentration‐independent codes without mixing various nanoparticles and by using single‐wavelength excitation and emission for multiplexed cellular imaging is extremely challenging. Herein, we report the development of quantum dots (QDs) with two different SiO₂ shell thicknesses (6 and 12 nm) that are coated with two different lanthanide complexes (Tb and Eu). FRET from the Tb or Eu donors to the QD acceptors resulted in four distinct photoluminescence (PL) decays, which were encoded by simple time‐gated (TG) PL intensity detection in three individual temporal detection windows. The well‐defined single‐nanoparticle codes were used for live cell imaging and a one‐measurement distinction of four different cells in a single field of view. This single‐color barcoding strategy opens new opportunities for multiplexed labeling and tracking of cells.