Visible-light-excited and europium-emissive nanoparticles for highly-luminescent bioimaging in vivo

Silica-Based Materials Containing Inorganic Red/NIR Emitters and Their Application in Biomedicine

The low absorption of biological substances and living tissues in the red/near-infrared region (therapeutic window) makes luminophores emitting in the range of ~650-1350 nm favorable for in vitro and in vivo imaging. In contrast to commonly used organic dyes, inorganic red/NIR emitters, including ruthenium complexes, quantum dots, lanthanide compounds, and octahedral cluster complexes of molybdenum and tungsten, not only exhibit excellent emission in the desired region but also possess additional functional properties, such as photosensitization of the singlet oxygen generation process, upconversion luminescence, photoactivated effects, and so on. However, despite their outstanding functional applicability, they share the same drawback-instability in aqueous media under physiological conditions, especially without additional modifications. One of the most effective and thus widely used types of modification is incorporation into silica, which is (1) easy to obtain, (2) biocompatible, and (3) non-toxic. In addition, the variety of morphological characteristics, along with simple surface modification, provides room for creativity in the development of various multifunctional diagnostic/therapeutic platforms. In this review, we have highlighted biomedical applications of silica-based materials containing red/NIR-emitting compounds.

Immunotoxicity of metal and metal oxide nanoparticles: from toxic mechanisms to metabolism and outcomes

The influence of metal and metal oxide nanomaterials on various fields since their discovery has been remarkable. They have unique properties, and therefore, have been employed in specific applications, including biomedicine. However, their potential health risks cannot be ignored. Several studies have shown that exposure to metal and metal oxide nanoparticles can lead to immunotoxicity. Different types of metals and metal oxide nanoparticles may have a negative impact on the immune system through various mechanisms, such as inflammation, oxidative stress, autophagy, and apoptosis. As an essential factor in determining the function and fate of immune cells, immunometabolism may also be an essential target for these nanoparticles to exert immunotoxic effects in vivo. In addition, the biodegradation and metabolic outcomes of metal and metal oxide nanoparticles are also important considerations in assessing their immunotoxic effects. Herein, we focus on the cellular mechanism of the immunotoxic effects and toxic effects of different types of metal and metal oxide nanoparticles, as well as the metabolism and outcomes of these nanoparticles in vivo. Also, we discuss the relationship between the possible regulatory effect of nanoparticles on immunometabolism and their immunotoxic effects. Finally, we present perspectives on the future research and development direction of metal and metal oxide nanomaterials to promote scientific research on the health risks of nanomaterials and reduce their adverse effects on human health.

Eggshell Derived Europium Doped Hydroxyapatite Nanoparticles for Cell Imaging Application

Hen's eggshell, a biological waste product, was turned into a cell imaging probe: europium doped hydroxyapatite (HAp: Eu) nanoparticle using hydrothermal method. Luminescence of the synthesized nanoparticle was studied for various doping concentrations of the lanthanide ion europium (Eu³⁺). Eu doped HAp showed a hexagonal crystal structure and rod-shaped morphology. Well-defined emission peaks of europium, corresponding to the substitution of Eu³⁺ at the Ca²⁺(I) site of HAp, were confirmed from the samples' photoluminescence (PL) spectra. Good biocompatibility up to 500 μg/mL of the samples indicates their potential applications in bioimaging. Synthesized nanoparticles were internalized and used for in vitro imaging of the PC12 cells without any surface modification. The materials' use as a potential in vivo imaging agent is proposed from the haemolysis study.

1,3-Diketone Calix[4]arene Derivatives-A New Type of Versatile Ligands for Metal Complexes and Nanoparticles

The present review is aimed at highlighting outlooks for cyclophanic 1,3-diketones as a new type of versatile ligands and building blocks of the nanomaterial for sensing and bioimaging. Thus, the main synthetic routes for achieving the structural diversity of cyclophanic 1,3-diketones are discussed. The structural diversity is demonstrated by variation of both cyclophanic backbones (calix[4]arene, calix[4]resorcinarene and thiacalix[4]arene) and embedding of different substituents onto lower or upper macrocyclic rims. The structural features of the cyclophanic 1,3-diketones are correlated with their ability to form lanthanide complexes exhibiting both lanthanide-centered luminescence and magnetic relaxivity parameters convenient for contrast effect in magnetic resonance imaging (MRI). The revealed structure–property relationships and the applicability of facile one-pot transformation of the complexes to hydrophilic nanoparticles demonstrates the advantages of 1,3-diketone calix[4]arene ligands and their complexes in developing of nanomaterials for sensing and bioimaging.

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.

Adaptive changes induced by noble-metal nanostructures in vitro and in vivo

The unique features of noble-metal nanostructures (NMNs) are leading to unprecedented expansion of research and exploration of their application in therapeutics, diagnostics and bioimaging fields. With the ever-growing applications of NMNs, both therapeutic and environmental NMNs are likely to be exposed to tissues and organs, requiring careful studies towards their biological effects in vitro and in vivo. Upon NMNs exposure, tissues and cells may undergo a series of adaptive changes both in morphology and function. At the cellular level, the accumulation of NMNs in various subcellular organelles including lysosomes, endoplasmic reticulum, Golgi apparatus, mitochondria, and nucleus may interfere with their functions, causing changes in a variety of cellular functions, such as digestion, protein synthesis and secretion, energy metabolism, mitochondrial respiration, and proliferation. In animals, retention of NMNs in metabolic-, respiratory-, immune-related, and other organs can trigger significant physiological and pathological changes to these organs and influence their functions. Exploring how NMNs interact with tissues and cells and the underlying mechanisms are of vital importance for their future applications. Here, we illustrate the characteristics of NMNs-induced adaptive changes both in vitro and in vivo. Potential strategies in the design of NMNs are also discussed to take advantage of beneficial adaptive changes and avoid unfavorable changes for the proper implementation of these nanoplatforms.

A new approach to spectroscopic and structural studies of the nano-sized silicate-substituted hydroxyapatite doped with Eu3+ ions

Nanocrystalline silicate-substituted hydroxyapatites Ca10-xEux(PO4)4(SiO4)2(OH)2 (where x = 0.5, 1.0, 2.0, 5.0 mol%) doped with Eu3+ ions were synthesized using a microwave assisted hydrothermal method and heat-treated in the temperature range from 700 to 1000 °C. The concentration of optically active Eu3+ ions was established in the range of 0.5-5 mol% to investigate the preference of occupancy sites. The structural and morphological properties of the obtained biomaterials were determined by using XRD (X-Ray Powder Diffraction), TEM (Transmission Electron Microscopy) and SEM (Scanning Electron Microscopy) techniques as well as infrared (IR) spectroscopy. The average particle sizes were calculated to be in the range from 20 nm to 80 nm by the Rietveld method. The charge compensation mechanism in europium(iii)-doped silicate-substituted hydroxyapatite was proposed in the Kröger-Vink-notation. The luminescence properties (the emission, excitation spectra and emission kinetics) of the Eu3+ ion-doped apatite were recorded depending on the dopant concentration. The existence of Eu2+ ions was confirmed by the emission spectra.

Optimization of Red Luminescent Intensity in Eu3+-Doped Lanthanide Phosphors Using Genetic Algorithm

In this research, four steps including synthesis experiment, brightness evaluation, optimized calculation using brightness as fitness reference, and new calculated composition for the next preparation have been proceeded to find the brightest Eu³⁺ doped phosphors combined with chemical experiments and genetic algorithm (GA) calculation. The evolutionary operations, such as elitism, selection, crossover, and mutation, are applied to the compound combination. Feasible optimized combination would be obtained until the phosphor is found to be satisfactory. Through GA calculation and thd experimental process, the final luminescence enhancement factor of the optimal phosphor is up to 141% compared with the best one in the first generation. Thus, the GA calculation could be well applied to combinatorial chemistry to find the better phosphor. Additionally, the optimized phosphor is potentially applied as the fingerprint detection nanoparticle and dual-modal imaging agent of the CT/luminescent agent with high penetration and resolution.

Dual-Emissive Phosphorescent Polymer Probe for Accurate Temperature Sensing in Living Cells and Zebrafish Using Ratiometric and Phosphorescence Lifetime Imaging Microscopy

Temperature plays an important part in many biochemical processes. Accurate diagnosis and proper treatment usually depend on precise measurement of temperature. In this work, a dual-emissive phosphorescent polymer temperature probe, composed of iridium(III) complexes as temperature sensitive unit with phosphorescence lifetime of ∼500 ns and europium(III) complexes as reference unit with lifetime of ∼400 μs, has been rationally designed and synthesized. Upon the increase of the temperature, the luminescence intensity from the iridium(III) complexes is enhanced, while that from the europium(III) complexes remains unchanged, which makes it possible for the ratiometric detection of temperature. Furthermore, the polymer also displays a significant change in emission lifetime accompanied by the temperature variation. By utilizing the laser scanning confocal microscope and time-resolved luminescence imaging systems, ratiometric and time-resolved luminescence imaging in Hela cells and zebrafish have been carried out. Notably, the intensity ratio and long-lifetime-based imaging can offer higher sensitivity, decrease the detection limit, and minimize the background interference from biosamples.

Stable photoluminescence of lanthanide complexes in aqueous media through Metal-Organic Frameworks Nanoparticles with plugged surface

The photoluminescence stability of lanthanide complex in aqueous media is a prerequisite for diagnostics probes. The combination of building blocks working in concert to facilitate host-guest structures is now considered state of the art in surpassing this roadblock, yet there still remains a tremendous challenge. Here, a stable, highly-luminescent system was developed through trapping anionic complexes sensitized by tridentate pyridine-tetrazolate (pytz) ligands within the rigid framework of ZIF-8 (zeolitic imidazolate framework-8) particles (∼60 nm in size). The key to maintaining the stable luminescence of lanthanide complexes inside ZIF-8 frameworks is a stopcock design, i.e. stopper molecules (an imidazolium based ionic liquid) selectively plugged on the pore entrances located at the exterior surface of the ZIF-8 host, which protect both the host and the guests from deteriorations by surrounding ions/water molecules. Remarkably, the obtained Ln complex encapsulated ZIF-8 particles (Ln = terbium, europium) particles possessed high quantum yields (23.2% and 8.5%), large absorption cross-section (∼10^-12 cm²), and long luminescence lifetimes (1.9 and 3.0 ms) in PBS buffer. In addition, the system can realize single/multi-color encoding by altering the loading amounts and the weight ratios of complexes emitting at different wavelengths.

Demonstration of cellular imaging by using luminescent and anti-cytotoxic europium-doped hafnia nanocrystals

Luminescent nanoparticles are researched for their potential impact in medical science, but no materials approved for parenteral use have been available so far. To overcome this issue, we demonstrate that Eu3+-doped hafnium dioxide nanocrystals can be used as non-toxic, highly stable probes for cellular optical imaging and as radiosensitive materials for clinical treatment. Furthermore, viability and biocompatibility tests on artificially stressed cell cultures reveal their ability to buffer reactive oxygen species, proposing an anti-cytotoxic feature interesting for biomedical applications.

A dual response organogel system based on an iridium complex and a Eu(iii) hybrid for volatile acid and organic amine vapors

A thiophene-based hybrid organogel system consisting of complex iridium (Ir) and EuCl₃·6H₂O was designed and synthesized to realize dual responses to volatile acids and organic amine vapors. The photophysical properties and self-assembly of compound 1 and the hybrid organogel were also studied. Compound 1 could gelate some organic solvents and self-assemble into 3D nanofibers in the gels. The stable hybrid organogel 1-Ir-Eu could be obtained after addition of complex Ir and EuCl₃·6H₂O. FTIR spectral results showed that the hydrogen bond still remained even upon addition of complex Ir, EuCl₃·6H₂O, NaOH and CF₃COOH to organogel 1. Interestingly, the emission properties of the hybrid organogel 1-Ir-Eu could undergo interconversion between cyan light and red light via addition of NaOH and CF₃COOH. The emission properties of xerogel film 1-Ir-Eu obtained in the presence of NaOH could also undergo fast and reversible transition in response to volatile acids such as CF₃COOH, formic acid, acetic acid, propionic acid and organic amine vapors such as ammonium hydroxide, Et₃N, tripropylamine, and ethylenediamine. The emission spectral change of Ir-Eu in the organogel or xerogel in the presence of base and acid demonstrated the formation of a new complex between complex Ir and EuCl₃·6H₂O. This dual-response process could be repeated many times. Contact angle experiment results further showed the morphology and internal components of the xerogel film surface in the process of response to gaseous CF₃COOH and Et₃N. This work provides a method for producing multifunctional supramolecular materials for sensing volatile acids and organic amine vapors.

A near-infrared phosphorescent iridium(iii) complex for imaging of cysteine and homocysteine in living cells and in vivo

A novel NIR-emitting iridium(iii) complex was developed to detect Cys/Hcy levels in vitro and in vivo.

A Eu(3+)/Gd(3+)-EDTA-doped structurally controllable hollow mesoporous carbon for improving the oral bioavailability of insoluble drugs and in vivo tracing

A structurally controllable fluorescence-labeled hollow mesoporous carbon (HMC) was simply prepared to improve the oral bioavailability of insoluble drugs and further trace their delivery process in vivo. The hollow structure was derived from an inverse replica process using mesoporous silica as a template and the fluorescent label was prepared by doping the carboxylated HMC with a confinement of Eu(3+)/Gd(3+)-EDTA. The physicochemical properties of the composites were systematically characterized by transmission electron microscopy, Fourier transform infrared spectroscopy and photoluminescence spectra tests prior to studying their effects on drug-release behavior and biodistribution. As a result, the thickness of the carrier's shell was adjusted from 70 nm to 130 nm and the maximum drug loading was up to 73.6%. The model drug carvedilol (CAR) showed sustained release behavior compared to CAR commercial capsules, and the dissolution rate slowed down as the shells got thicker. AUC0-48h and Tmax were enlarged 2.2 and 6.5 fold, respectively, which demonstrated that oral bioavailability was successfully improved. Bioimaging tests showed that the novel carbon vehicle had a long residence time in the gastrointestinal tract. In short, the newly designed HMC is a promising drug carrier for both oral bioavailability improvement and in vivo tracing.

Core–shell BaYbF5:Tm@BaGdF5:Yb,Tm nanocrystals for in vivo trimodal UCL/CT/MR imaging

PEGylated core–shell BaYbF₅:Tm@BaGdF₅:Yb,Tm nanocrystals have been constructed and successfully applied in UCL imaging, CT imaging and MR imaging.

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.

Faster Synthesis of Beta-Diketonate Ternary Europium Complexes: Elapsed Times & Reaction Yields

β-diketonates are customary bidentate ligands in highly luminescent ternary europium complexes, such as Eu(β-diketonate)₃(L)₂, where L stands for a nonionic ligand. Usually, the syntheses of these complexes start by adding, to an europium salt such as EuCl₃(H₂O)₆, three equivalents of β-diketonate ligands to form the complexes Eu(β-diketonate)₃(H₂O)₂. The nonionic ligands are subsequently added to form the target complexes Eu(β-diketonate)₃(L)₂. However, the Eu(β-diketonate)₃(H₂O)₂ intermediates are frequently both difficult and slow to purify by recrystallization, a step which usually takes a long time, varying from days to several weeks, depending on the chosen β-diketonate. In this article, we advance a novel synthetic technique which does not use Eu(β-diketonate)₃(H₂O)₂ as an intermediate. Instead, we start by adding 4 equivalents of a monodentate nonionic ligand L straight to EuCl₃(H₂O)₆ to form a new intermediate: EuCl₃(L)₄(H₂O)_n, with n being either 3 or 4. The advantage is that these intermediates can now be easily, quickly, and efficiently purified. The β-diketonates are then carefully added to this intermediate to form the target complexes Eu(β-diketonate)₃(L)₂. For the cases studied, the 20-day average elapsed time reduced to 10 days for the faster synthesis, together with an improvement in the overall yield from 42% to 69%.

Multicolor (Vis-NIR) mesoporous silica nanospheres linked with lanthanide complexes using 2-(5-bromothiophen)imidazo[4,5-f][1,10]phenanthroline for in vitro bioimaging

A novel mesoporous nanosphere functionalized with 3-(aminopropyl)triethoxysilane (APTES) and 2-(5-bromothiophen)imidazo[4,5-f][1,10]phenanthroline (5-Br-Tip) was synthesized (denoted as Tip-MSS). With the coordinating function of the 5-Br-Tip to lanthanide (Ln) ions, for the first time, LnL3(5-Br-Tip) complexes were linked to the mesoporous nanospheres. The derived materials, named Ln-Tip-MSS (Ln = Eu, Tb, Sm, Nd, Yb), were characterized by Fourier-transform infrared (FT-IR) spectroscopy, TEM, XRD (wide-angle and small-angle), N2 adsorption/desorption analysis, and fluorescence spectroscopy. Upon excitation in the ligand absorption, the Ln-Tip-MSS nanomaterials show characteristic visible (Eu, Tb, Sm) and NIR (Sm, Nd, Yb) luminescence (multicolor emission covered from 450 nm to 1400 nm spectral region). Of importance is that, with low cytotoxicity and good biocompatibility given by the methyl thiazolyl tetrazolium (MTT) assay, the Eu-Tip-MSS was successfully applied to cell imaging in vitro based on the Eu(3+) luminescence (under 405 nm excitation).

Direct electrospinning construction of nanocables with electrical conductive-magnetic core and insulative-photoluminescent sheath

A new nanostructure of luminescent-electrical-magnetic trifunctional nanocables has been successfully fabricated by specially designed coaxial spinnerets electrospinning technology.

Enantiomers of cysteine-modified SeNPs (d/lSeNPs) as inhibitors of metal-induced Aβ aggregation in Alzheimer's disease

Chiral molecules, which selectively target and inhibit amyloid β-peptide (Aβ) aggregation, have potential use as therapeutic agents for the treatment of Alzheimer's disease (AD).

Multifunctional nanomesoporous materials with upconversion (in vivo) and downconversion (in vitro) luminescence imaging based on mesoporous capping UCNPs and linking lanthanide complexes

A series of new multifunctional nanomesoporous materials based on upconversion nanophosphors NaYF4:Yb,Tm@NaGdF4 (UCNPs) and lanthanide complexes were designed and synthesized through mesoporous capping UCNPs nanophosphors and linking lanthanide (Ln) complexes. The obtained UCNPs@mSiO2-Ln(dbm)4 (Ln = Eu, Sm, Er, Nd, Yb) materials can achieve downconversion and upconversion luminescence to show multicolor emission (covering the spectral region from 450 nm to 1700 nm) under visible-light excitation and 980 nm excitation, respectively. In addition, low cytotoxicity and good biocompatibility was found as determined by methyl thiazolyl tetrazolium assay, and the nanomesoporous materials were successfully applied to cell imaging in vitro based on Eu(3+) luminescence (under 405 nm excitation) and small animal imaging based on Tm(3+) luminescence (under 980 nm excitation). The doped Gd(3+) ion endows the nanomesoporous materials UCNPs@mSiO2-Ln(dbm)4 with effective T1 signal enhancement, which affords them as potential magnetic resonance imaging (MRI) contrast agents. Therefore, our results may provide more exciting opportunities for multimodal bioimaging and multifunctional applications.