Fluorescent Biolabels Research Articles

Encapsulation of Carbon Dots in a Core-Shell Mesh through Coaxial Direct Ink Writing for Improved Crop Growth.

Through coaxial direct ink writing, we fabricated a core-shell mesh system for the controlled release of carbon dots (C-dots). In the core ink, we developed an ink formulation with tuned viscosity using hydroxypropyl cellulose and polyethylene glycol to host C-dots. Polycaprolactone was employed as the main shell material, in combination with sodium alginate, to control the degradation rate of the shell. We investigated the degradation profile of the 3D-printed meshes and tracked the weekly release of C-dots in an aqueous medium by spectrofluorometry. We tested the efficacy of the C-dot release on plants by placing the meshes in transparent soil with Triticum aestivum L. seeds. We observed the in vivo translocation of the C-dots in the plant using confocal microscopy. We measured the root elongation and shoot length to assess the effect of C-dots on plant growth. Our study revealed that the plants exposed to C-dots grew 2.5-fold faster than the control group, indicating that C-dots are promising nanofertilizers for aggrotech and non-toxic fluorescent biolabels for in vivo applications.

Synthesis and Photoluminescence Characterization of 3- MPA Capped CdZnTe Quantum Dots

3-MPA capped CdZnTe alloy quantum dots synthesized using Na2TeO3 as the tellurium source under open atmosphere conditions in aqueous medium. The optical and photoluminescence properties of the CdZnTe quantum dots characterized using UV-Visible absorption and Photoluminescence spectrum. An excitonic peak at 527 nm observed in the absorption spectrum. Tauc relation and Urbach relation were employed to find the bandgap energy and urbach energy of the CdZnTe quantum dot. The quantum dot particle size was estimated using the bandgap energy from Tauc plot employing tight binding approximation, which was 4.75 nm. A high intense emission peak at 567 nm obtained in the photoluminescence spectrum. The emission peaks correspond to yellow fluorescence. The CIE chromaticity diagram gives color coordinate at (0.41,0.56) with a color purity of 92%. The high intense yellow fluorescent CdZnTe quantum can placed as potential candidates for fluorescent probes, biolabeling and cell imaging applications.

Nanodiamonds: A Versatile Drug-Delivery System in the Recent Therapeutics Scenario

Nanodiamonds (ND) belong to the nano-carbon family, which involves several synthesis, post-synthesis methods, and other modifications for ND preparation. NDs have played vital role both inside and outside of medicine in recent years. The study of NDs has stated in early 1960s, NDs are smaller particles with a size of about 4-5 nm with confined size distribution, large-scale synthesis at lower costs relying on the carbon explosives ignition, apparent surface functional design along with bio-conjugation and extreme biocompatibility. It has been predicted that the ND's magnetic characteristics will contribute to the up-growth of various therapeutic promoters for delivery vehicles, diagnostic probes, gene therapy, tissue scaffolds, anti-bacterial and anti-viral treatments, and devices like nano-robots. Furthermore, the wide applications of biotechnology have displayed the potential usage of NDs in certain bioanalytical needs like fluorescent bio labeling through fluorescent and protein purification of proteins. In this current review, the determination of ND's design, property, classes, constancy, organization, surface modification, biocompatibility, and its applications in the biomedical field have penned. The usage of ND as anti-neoplastic agents and in other health related formulations have displayed exceptional results for future growth. Additionally, NDs provide other functionalities such as production of biodegradable surgical devices of bone, the assassination of drug resistant microbes and viruses, tissue engineering scaffolds, and aids in the delivery of genetic matter into the nucleus of cells.

Fluorescence Phenomena in Amyloid and Amyloidogenic Bionanostructures

Nanoscale optical labeling is an advanced bioimaging tool. It is mostly based on fluorescence (FL) phenomena and enables the visualization of single biocells, bacteria, viruses, and biological tissues, providing monitoring of functional biosystems in vitro and in vivo, and the imaging-guided transportation of drug molecules. There is a variety of FL biolabels such as organic molecular dyes, genetically encoded fluorescent proteins (green fluorescent protein and homologs), semiconductor quantum dots, carbon dots, plasmonic metal gold-based nanostructures and more. In this review, a new generation of FL biolabels based on the recently found biophotonic effects of visible FL are described. This intrinsic FL phenomenon is observed in any peptide/protein materials folded into β-sheet secondary structures, irrespective of their composition, complexity, and origin. The FL effect has been observed both in natural amyloid fibrils, associated with neurodegenerative diseases (Alzheimer’s, Parkinson’s, and more), and diverse synthetic peptide/protein structures subjected to thermally induced biological refolding helix-like→β-sheet. This approach allowed us to develop a new generation of FL peptide/protein bionanodots radiating multicolor, tunable, visible FL, covering the entire visible spectrum in the range of 400–700 nm. Newly developed biocompatible nanoscale biomarkers are considered as a promising tool for emerging precise biomedicine and advanced medical nanotechnologies (high-resolution bioimaging, light diagnostics, therapy, optogenetics, and health monitoring).

Aqueous Synthesis of Lead Halide Perovskite Nanocrystals with High Water Stability and Bright Photoluminescence.

Lead halide perovskite nanocrystals (NCs) have attracted intense attention because of their excellent optoelectronic properties. The ionic nature of halide perovskites makes them highly vulnerable to water. Encapsulation of perovskite NCs with inorganic or organic materials has been reported to enhance their stability; however, they often suffer from large aggregation size, low water solubility, and difficulty for further surface functionalization. Here, we report a facile aqueous process to synthesize water-soluble CsPbBr3/Cs4PbBr6 NCs with the assistance of a fluorocarbon agent (FCA), which features a novel mechanism of the perovskite crystallization at the oil/water interface and direct perovskite NCs/FCA self-assembly in an aqueous environment. The products exhibit a high absolute photoluminescence quantum yield (PLQY) of ∼80% in water with the PL lasting for weeks. Through successive ionic layer adsorption and reaction, BaSO4 was further applied to encapsulate the NCs, which greatly enhanced their stability in phosphate-buffered saline solutions. The high stability in water and saline solution, high PLQY, and tunable emission wavelength, together with the successful demonstration of brain tissue labeling and PL under X-ray excitation, make our perovskite NCs a promising choice for X-ray fluorescent biolabels.

Green upconversion nanoparticles for 2, 4- dichlorophenoxyacetic acid and fenitrothion detection

Upconversion fluorescence analysis is an increasingly popular novel technique with biological and biomedical applications owing to its high detection sensitivity, non-invasive mode and superior photo-stability. Herein, water-soluble green β-NaYF4:Yb, Er UCNPs were prepared via a facile wet-chemical technique, then conjugated with rabbit anti-2, 4-dichlorophenoxyacetic acid immunoglobulin G (2, 4-D-IgG) and rabbit anti-fenitrothion IgG (fenitrothion-IgG), respectively. The content of 2, 4-D-IgG and fenitrothion-IgG in labeled-samples were quantitatively analyzed by the Coomassie-Brilliant-Blue method. The 2, 4-D-IgG (or fenitrothion-IgG) labeled with β-NaYF4:Yb, Er UCNPs conjugates can be used as fluorescent bio-labels for the detection of 2, 4-D and fenitrothion under 980 nm near-infrared excitation. An immunochromatographic strip was then successfully constructed based on the antibody-UCNPs conjugates. The detection limits of 2, 4-D and fenitrothion pesticide residues were 5 ng/mL and 11 ng/mL, respectively. The experimental results indicate that the biocompatible green UCNPs have great advantages as bio-labeling materials for low-molecular-weight pesticide residue analysis.

Carbon Dots for Single-Molecule Imaging of the Nucleolus

Carbon dots are newly discovered bright fluorescent biolabeling probes that nonspecifically bind to multiple cellular structures. Here we report yellow-orange emissive carbon dots that spontaneously localize inside the nucleolus of HeLa cells, specifically binding to the RNA. Single-particle measurements of carbon dots show fluorescence-intensity fluctuations with superior brightness and photostability. These optical properties were used for performing blinking-assisted localization microscopy that shows organization of the nucleolar RNA with improved resolution. Our study opens up the opportunity for single-molecule imaging and super-resolution microscopy applications using fluorescent carbon dots.

In-vitro cytotoxicity evaluation of surface design luminescent lanthanide core/shell nanocrystals

Lanthanide nanocrystals (NCs) are the most promising luminescent materials for bioapplications, but their use is hindered by difficulties in obtaining biocompatible and photoluminescence lanthanide NCs. To solve this problem, a simple and versatile strategy was developed for improving the luminescence efficiency with the hydrophilicity of the lanthanide NCs. In this study, the effects of shell formation on structural, morphological, and optical properties (optical absorption, band-gap energy, excitation, emission, and luminescent decay time) were evaluated. To improve the luminescence efficiency and aqueous dispersion, luminescent core-NCs were encapsulated with inert NaGdF4 and amorphous silica layers. These surface coating layers significantly improved the luminescence efficiency and dispersion of the core/shell NCs in which the silica surface provides a negatively charged surface to the NCs at physiological pH. Optical properties of these NCs strongly depend on the external change of NCs, demonstrating the impact of coating in improving the luminescence efficiency. The outcomes can be ascribed to the development of surface chemical bonds betweencore/shell and noncrystalline SiO2shell via GdOSi bridges, activating the ‘dormant’ Ce3+ and Tb3+ions on the surface of NCs. An intensive emission and good hydrophilic property from the active functional groups in solutions show a great potential for applications such as multi-analyte fluorescent biolabeling, optical biosensing, staining, display, and other optical technologies. The core/shell/SiO2 NCs showed higher nontoxicity and biocompatibility with respect to the core NCs because of biocompatible silica surface modification, facilitating entry into the living cells. Therefore, this developed synthesis approach might advance the field of biomolecule-based nanotechnology in near future.

In-vitro cytotoxicity and cellular uptake studies of luminescent functionalized core-shell nanospheres.

Monodispersed luminescent functionalized core-shell nanospheres (LFCSNs) were successfully synthesized and investigated for their cyto-toxic effect on human liver hepatocellular carcinoma cell line (HepG2 cells) by adopting MTT, DNA Ladder, TUNEL assay and qPCR based gene expressions through mRNA quantifications. The TUNEL and DNA ladder assays suggested an insignificant apoptosis in HepG2 cells due to the LFCSNs treatment. Further, the qPCR results also show that the mRNA expressions of cell cycle checkpoint gene p53 and apoptosis related gene (caspase-9) was up-regulated, while the antiapoptotic gene BCl-2 and apoptosis related genes FADD and CAS-3 (apoptosis effecter gene) were down-regulated in the LFCSNs treated cells. The nanospheres that were loaded into the cells confirm their intracellular uptake by light and fluorescent spectro-photometry and microscopy imaging analysis. The loaded nanospheres demonstrate an absolute resistance to photo-bleaching, which were applied for dynamic imaging to real-time tracking in-vitro cell migratory activity for continuous 24 and 48 h durations using a time-lapsed fluorescent microscope. These properties of LFCSNs could therefore promote applications in the area of fluorescent protein biolabeling and drug-delivery.

Synthesis, modification, bioconjugation of silica coated fluorescent quantum dots and their application for mycotoxin detection

To create bright and stable fluorescent biolabels for immunoassay detection of mycotoxin deoxynivalenol in food and feed, CdSe/CdS/ZnS core–shell quantum dots (QDs) were encapsulated in silica nanoparticles through a water-in-oil reverse microemulsion process. The optical properties and stability of the obtained silica coated QDs (QD@SiO2), modified with amino, carboxyl and epoxy groups and stabilized with polyethylene glycol fragments, were characterized in order to assess their bioapplicability. The developed co-condensation techniques allowed maintaining 80% of the initial fluorescent properties and yielded stable fluorescent labels that could be easily activated and bioconjugated. Further, the modified QD@SiO2 were efficiently conjugated with antibodies and applied as a novel label in a microtiter plate based immunoassay and a quantitative column-based rapid immunotest for deoxynivalenol detection with IC50 of 473 and 20ng/ml, respectively.

Microwave synthesis of Y2O3:Eu3+ nanophosphors: A study on the influence of dopant concentration and calcination temperature on structural and photoluminescence properties

Red fluorescent emitting monodispersed spherical Y2O3 nanophosphors with different Eu3+ doping concentrations (0–13mol%) are synthesized by a novel microwave assisted urea precipitation, which is recognized as a green, fast and reproducible synthesis method. The effect of Eu3+ doping and calcination temperature on the structural characteristics and luminescence properties of particles is investigated in detail. The as prepared powders have (Y,Eu)(OH)(CO3) structure which converts to Y2O3:Eu3+ from 500°C and become crystalline at higher temperatures. The crystallite size of nanophosphors increased from 15nm to 25nm as the calcination temperature increased from 700°C to 1050°C. The efficient incorporation of Eu3+ ions in cubic Y2O3 host matrix is confirmed by the calculated X-ray Powder diffraction (XRPD) structural parameters. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) micrographs show that the as obtained and calcined particles are spherical, monodispersed and non-agglomerated. The overall size of particles increases from 61±8nm to 86±9nm by increasing Eu3+ concentration from 0mol% to 13mol%. High resolution TEM revealed polycrystalline nature of calcined particles. The particles exhibit a strong red emission under ultraviolet (UV) excitation. The photoluminescence (PL) intensity of the peaks increases proportionally with Eu3+ concentration and the calcination temperature with no luminescence quenching phenomenon observed even for Y2O3:13%Eu3+. The fluorescent emission properties combined with the monodispersity and narrow size distribution characteristics make the Y2O3:Eu3+ heavy metal free nanophosphors applicable in fluorescence cell imaging and as fluorescence biolabels.

Dispersible crystalline nanobundles of YPO4 and Ln (Eu, Tb)-doped YPO4: rapid synthesis, optical properties and bio-probe applications

Undoped and Ln(3+) (Eu and Tb)-doped crystalline nanobundles of YPO4 were prepared by a facile microwave-assisted route with water as a solvent and without using any surfactant. TEM investigations reveal that the as-prepared powder consists of lenticular-shaped nanobundles (similar to 100 nm in diameter) made of very small nanorods with diameter less than 10 nm and length varying from 20 to 50 nm. Each nanorod in turn is single crystalline, as revealed by HRTEM imaging. The as-prepared nanobundles are easily dispersible in various solvents, especially water, without any surface functionalization, which is critical for various bio-probe applications like cell and tissue imaging. The Eu- and Tb-doped YPO4 nanobundles show good photoluminescence properties and were further evaluated for their use as fluorescent biolabels. Our results show that HeLa cells labelled with Eu- and Tb-doped YPO4 nanobundles show bright red (Eu) and green (Tb) intracellular luminescence under a confocal microscope. Concentration-and time-dependent MTT cell viability assays show that the nanobundles show low toxicity towards cells which makes them promising in bioimaging field.

Green Synthesis of Y2O3:Eu3+ Nanocrystals for Bioimaging

ABSTRACTRare earth (e.g., Eu, Er, Yb, Tm) doped Y2O3 nanocrystals are promising fluorescent bioimaging agents which can overcome well known problems of currently used organic dyes like photobleaching, phototoxicity, and light scattering. Furthermore, the alternative quantum dots (QDs) composed of heavy metals (e.g., CdSe) possess inherently low biocompatibility due to the heavy metal content. In the present work, monodisperse spherical Y2O3:Eu3+ nanocrystals were successfully synthesized by microwave assisted urea precipitation method followed by thermochemical treatment. This is a green, fast and reproducible synthesis method, which is surfactant and hazardous precursors free. The as prepared particles were non-aggregated, spherical particles with a narrow size distribution. The calcined particles have a polycrystalline structure preserving the monodispersity and the spherical morphology of the as prepared particles. After calcination of Y(OH)CO3:Eu3+ precursors at 900°C for 2 hours, a highly crystalline cubic Y2O3 structure was obtained. The Y2O3:Eu3+ spherical particles showed a strong red emission peak at 613nm due to the 5D0–7F2 forced electric dipole transition of Eu3+ ions under UV excitation (235 nm) as revealed by the photoluminescence analysis (PL). The effect of reaction time on size and photoluminescence properties of calcined particles and also the effect of reaction temperature and pressure on the size and the yield of the precipitation process have been studied. The intense red fluorescent emission, excellent stability and potential low toxicity make these QDs promising for applications in bio-related areas such as fluorescence cell imaging or fluorescence bio labels.

Optical and structural studies of CaMoO4:Sm, CaMoO4:Sm@CaMoO4 and CaMoO4:Sm@CaMoO4@SiO2 core–shell nanoparticles

A simple polyol and Stober surface coating process was introduced to synthesize CaMoO4:Sm and their silica-coated CaMoO4:Sm nanoparticles. Powder X-ray diffraction (XRD) and different spectroscopic techniques were employed to investigate the structural and optical properties of as-prepared nanoparticles. The surface of CaMoO4:Sm nanoparticles was modified to alter the solubility of the nanoparticles and to study the influence of surface coating on emission spectra of samarium ions. Optical properties of these nanoparticles showed a strong dependence on the surface modification of nanoparticles, indicating the influence of coating in the enhancement of luminescent intensity. These results were attributed to the formation of chemical bonds between CaMoO4:Sm@ CaMoO4 core and non-crystalline SiO2 shell via Mo–O–Si bridges, which activate the ‘dormant’ Sm3+ ion on the surfaces of nanoparticles. It is, therefore, concluded that good hydrophilicity resulting from active functional groups in solutions and more intense luminescence enable doped core–shell nanoparticles to have great potential to be used as fluorescence biolabels in the future.

Mercaptopropionic acid-capped Mn(2+):ZnSe/ZnO quantum dots with both downconversion and upconversion emissions for bioimaging applications.

Doped quantum dots (d-dots) can serve as fluorescent biosensors and biolabels for biological applications. Our study describes a synthesis of mercaptopropionic acid (MPA)-capped Mn(2+):ZnSe/ZnO d-dots through a facile, cost-efficient hydrothermal route. The as-prepared water-soluble d-dots exhibit strong emission at ca. 580 nm, with a photoluminescence quantum yield (PLQY) as high as 31%, which is the highest value reported to date for such particles prepared via an aqueous route. They also exhibit upconversion emission when excited at 800 nm. With an overall diameter of around 6.7 nm, the d-dots could gain access to the cell nucleus without any surface decoration, demonstrating their promising broad applications as fluorescent labels.

DNA-Stabilized Silver Nanoclusters with High Yield of Dark State Probed by Fluorescence Saturation Spectroscopy

Polymer-stabilized silver nanoclusters have gained much attention as a promising higly fluorescent biolabels [1]. While a wide palette of DNA-stabilized nanoclusters has been created, a little attention has been paid to their excited state properties. Meantime, dark long-lived non-emitting states have gained increasing interest in ultrahigh resolution microscopy, transient state imaging, and optically modulated microscopy [2] in the last years. The photoinduced dark states are used to be probed by pump-probe spectroscopy. However, it requires relatively high concentrations and it is not easily applied for heterogeneous samples.We applied fluorescence saturation spectroscopy for determining the photophysical constants of DNA-stabilized silver nanoclusters. This method allows one to determine the photophysical parameters of the ground and excited states such as absorption cross section, rate of intersystem crossing and others. Herein we report on extremely high yield of 25% of the dark state observed for the yellow-emitting Ag nanoclusters formed on calf thymus DNA [3]. This result seems to be promising in further creating polymer-stabilizing Ag nanoclusters with specially designed structure providing high efficiency of the dark state formation.[1] Obliosca, J. M.; Liu, C.; Batson, R. A.; Babin, M. C.; Werner. J. H.; Yeh, H.-C. DNA/RNA Detection Using DNA-Templated Few-Atom Silver Nanoclusters. Biosensors 2013, 3, 185-200.[2] Richards, C. I.; Hsiang, J.-C.; Senapati, D.; Patel, S.; Yu, J.; Vosch, T.; Dickson, R. M. Optically Modulated Fluorophores for Selective Fluorescence Signal Recovery. Journal of the American Chemical Society 2009, 131 (13), 4619-4621.[3] Volkov, I. L.; Ramazanov, R. R.; Ubyvovk, E. V.; Rolich, V. I.; Kononov, A. I.; Kasyanenko, N. A. Fluorescent Silver Nanoclusters in Condensed DNA. ChemPhysChem 2013, DOI: 10.1002/cphc.201300673.

ChemInform Abstract: One‐Pot Tandem Synthesis of Fluorescent 5‐Naphthyl‐3(2H)‐furanones.

Abstract Fluorescent 3(2H)-furanones, 4-cyano-2,2-dialkyl-5-(1- or 2-)naphthyl-3(2H)-furanones, have been synthesized in 69–81% yield by a one-pot procedure, via the tandem reaction of tertiary cyanopropargylic alcohols with 1- and 2-naphthoic acids under mild transition-metal free conditions (Et3N, 20–25 °C for 48–192 h or 55–60 °C for 7–13 h, MeCN). The synthesized compounds fluoresce in the visible region (λmax=419–431 nm), thus being prospective fluorescent biolabels.

Controlled growth, intense upconversion emissions and concentration induced luminescence switching of bifunctional Tm3+ doped hexagonal NaYb0.55Gd0.45F4 nanorods

Bifunctional hexagonal Tm3+ doped NaYb0.55Gd0.45F4 nanorods with tunable size are prepared via in situ cation-exchange reaction using hydrothermal method. The measured field dependence of magnetization of the NaYb0.55Gd0.45F4 nanorods shows typical paramagnetic characteristics that can be ascribed to the non-interacting localized nature of the magnetic moment of rare-earth ions. When excited by a 980nm laser, these nanorods exhibit intense multi-color up-conversion (UC) emissions in infrared, red, blue and especially ultraviolet. In addition, luminescent switching between different UC emission wavelengths of 480nm and 450nm is observed by adjusting Tm3+ doping concentration. Based on power-dependent spectral analyses, it is found that with the increase of Tm3+ doping concentration, due to the suppressed saturation effect, the dominative UC process redistribute the populations at 1G4 and 1D2(Tm3+) states of Tm3+ ion resulting in the above luminescent switching. Our results indicate that bifunctional hexagonal NaYb1−xGdxF4 nanocrystals have potential applications in miniaturized solid-state light sources, optical processing sensors and fluorescent biolabels.

One-pot tandem synthesis of fluorescent 5-naphthyl-3(2H)-furanones

Fluorescent 3(2H)-furanones, 4-cyano-2,2-dialkyl-5-(1- or 2-)naphthyl-3(2H)-furanones, have been synthesized in 69–81% yield by a one-pot procedure, via the tandem reaction of tertiary cyanopropargylic alcohols with 1- and 2-naphthoic acids under mild transition-metal free conditions (Et3N, 20–25 °C for 48–192 h or 55–60 °C for 7–13 h, MeCN). The synthesized compounds fluoresce in the visible region (λmax=419–431 nm), thus being prospective fluorescent biolabels.

Hybrid nanoparticles for drug delivery and bioimaging: Mesoporous silica nanoparticles functionalized with carboxyl groups and a near-infrared fluorescent dye

The development of a drug delivery system with fluorescent biolabels is important in anti-cancer drug delivery application due to the potential for simultaneous diagnosis and treatment of diseases. Here, we reported the synthesis and multiple functionalization of mesoporous silica nanoparticle (MSN) for bioimaging and controlled drug release. After the functionalization with carboxyl group, the nanoparticles exhibited much better dispersity and stability in aqueous solution than MSN. Furthermore, a substantial doxorubicin (DOX) loading level was achieved and DOX-loaded nanoparticles exhibited noticeable pH-sensitive behavior with accelerated release of DOX in acidic environment. Compared with native DOX–MSN, DOX–MSN/COOH–Cy5 exhibited enhanced intracellular uptake efficacy and stronger effect on killing tumor cells. Meanwhile, it was observed that the MSN/COOH–Cy5 was able to locate in the cytoplasm of MCF-7 cells and could accumulate in tumor tissues for a long period of time. Overall, the functional nanoparticle could potentially be used for simultaneous controlled drug release and near-infrared fluorescent bioimaging.