Unique Fluorescence Properties Research Articles

Hot injection synthesis of core-shell upconversion nanoparticles for bioimaging application

In recent years, lanthanide-containing upconversion nanoparticles (UCNPs) have aroused the extensive interest in bioimaging due to their unique upconversion fluorescent properties, such as the high tissue penetration depth, good biocompatibility, low auto-fluorescence, and high imaging sensitivity. In this work, we synthesize a series of NaYF<sub>4</sub>:Yb, Tm@NaYF<sub>4</sub> core-shell structured nanoparticles with various shell thicknesses. A “hot injection” strategy is introduced to fabricate the core-shell UCNPs through using high boiling-point mixtures (sodium/rare-earth trifluoroacetates dissolved in oleic acid and octadecene at 150 °C) as shell precursor solutions. The as-synthesized UCNPs are characterized by transmission electron microscope, particle size analysis and fluorescence spectra. The experimental results show that the shell thickness of UCNPs can be well controlled within a range from 4.2 nm to 32.6 nm by simply tuning the added quantity of the shell precursors. Meanwhile, the upconversion luminescence intensity of NaYF<sub>4</sub>:Yb, Tm@NaYF<sub>4</sub> shows tens times higher than that of NaYF<sub>4</sub>:Yb, Tm owing to the effective suppression of surface quenching. The optimized thickness of the shell is determined to be 22.7 nm. An ultrathick inert shell (>22.7 nm) is not beneficial to upconversion luminescence mainly due to a strong scattering effect. In addition, the in vitro upconversion luminescent bioimaging application is demonstrated by using the as-synthesized core-shell structured UCNPs. Typically, the prepared OA capped UCNPs are dispersed in HCl solution to obtain hydrophilic ones, followed by polyethylene glycol (PEG) modification to improve their biological compatibility. The hydrophilic NaYF<sub>4</sub>:Yb, Tm@NaYF<sub>4</sub>@PEG nanostructures (denoted as UCNP@PEG) show a good biocompatibility with HeLa cells, as the viability of HeLa cells do not decrease obviously when the concentration of UCNP@PEG increases to 0.2 mg/mL. Then, we evaluate the upconversion luminescent signals of UCNP@PEG in HeLa cells under the excitation of 980 nm laser. An obviously increasing upconversion luminescent signal can be observed in HeLa cells with the incubation time increasing from 0.5 h to 6.0 h, indicating that the UCNP@PEG can be used as an excellent luminescence probe for cell imaging and monitoring the cell endocytosis process. All in all, we offer an efficient “hot injection” strategy of fabricating the core-shell structured UCNPs with various shell thickness for improving the upconversion efficiency of UCNPs, which will pave the way for new bioimaging and medical applications.

Quinoline- and isoquinoline-derived ligand design on TQEN (N,N,N',N'-tetrakis(2-quinolylmethyl)ethylenediamine) platform for fluorescent sensing of specific metal ions and phosphate species.

Rational molecular structure alterations of TQEN (N,N,N',N'-tetrakis(2-quinolylmethyl)ethylenediamine) produced variable fluorescent sensors for specific metal ions and phosphate species. Utilization of methoxy-substituted quinoline and isoquinoline chromophores, conformational restriction and multidentate coordination structure allow discrimination between Zn2+ and Cd2+. Pyrophosphate (P2O74-, PPi) and phosphate (PO43-) also are selectively detected with dinuclear Zn2+ complexes of tetrakisquinoline-based ligands. Differential stability and structure of the metal complexes, as well as resulting fluorescence enhancement mechanism, such as intramolecular excimer formation via change in coordination geometry, play key roles in the discrimination of target ions.

Preparation and biological imaging of fluorescent hydroxyapatite nanoparticles with poly(2-ethyl-2-oxazoline) through surface-initiated cationic ring-opening polymerization.

Fluorescent hydroxyapatite (HAp) nanoparticles have received significant attention in biomedical fields due to their outstanding advantages, such as low immunogenicity, excellent biocompatibility and biodegradability. However, fluorescent HAp nanoparticles with well controlled size and morphology are coated with hydrophobic molecules and their biomedical applications are largely restricted by their poor dispersibility in physiological solutions. Therefore, surface modification of these hydrophobic fluorescent HAp nanoparticles to render them water dispersibility is of utmost importance for biomedical applications. In this work, we reported for the first time for preparation of water-dispersible hydrophilic fluorescent Eu3+-doped HAp nanoparticles (named as HAp-PEOTx) through the cationic ring-opening polymerization using hydrophilic and biocompatible 2-ethyl-2-oxazoline (EOTx) as the monomer. The characterization techniques, such as nuclear magnetic resonance (NMR) spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) have been used to characterize these samples. Results confirmed that we could successfully obtain the hydrophilic fluorescent HAp-PEOTx composites through the strategy described above. These fluorescent HAp-PEOTx composites display great water dispersibility, unique fluorescent properties and excellent biocompatibility, making them promising for in vitro bioimaging applications.

A facile approach to synthesis carbon quantum dots-doped P25 visible-light driven photocatalyst with improved NO removal performance

The water-soluble carbon quantum dots (CQDs) and a novel composite photocatalyst CQDs/P25 have been prepared by a one-step electrochemical-microwave method. The experimental result shows that the photocatalytic degradation of NO by this new kind of CQDs/P25 composite reaches 71%, which is approximately 1.65 times than that of the pure P25 at room temperature. The initial concentration of NO pollutants is 10 ppm. The photocatalytic efficiency of the composite catalyst achieves the highest when the content of CQDs is 1%. It can be concluded that the CQDs extend the light absorption range and adjust the band gap of pure P25. The high photocatalytic performance of this new kind of photocatalyst can be mainly attributed to the unique up-conversion fluorescence property, nanometer size effect and surface activity effect.

The Biomolecular Corona in 2D and Reverse: Patterning Metal–Phenolic Networks on Proteins, Lipids, Nucleic Acids, Polysaccharides, and Fingerprints

AbstractThe adsorption of biomolecules onto nanomaterials can alter the performance of the nanomaterials in vitro and in vivo. Recent studies have primarily focused on the protein “corona”, formed upon adsorption of proteins onto nanoparticles in biological fluids, which can change the biological fate of the nanoparticles. Conversely, interactions between nanomaterials and other classes of biomolecules namely, lipids, nucleic acids, and polysaccharides have received less attention despite their important roles in biology. A possible reason is the challenge associated with investigating biomolecule interactions with nanomaterials using current technologies. Herein, a protocol is developed for studying bio–nano interactions by depositing four classes of biomolecules (proteins, lipids, nucleic acids, and polysaccharides) and complex biological media (blood) onto planar substrates, followed by exposure to metal–phenolic network (MPN) complexes. The MPNs preferentially interact with the biomolecule over the inorganic substrate (glass), highlighting that patterned biomolecules can be used to engineer patterned MPNs. Subsequent formation of silver nanoparticles on the MPN films maintains the patterns and endows the films with unique reflectance and fluorescence properties, enabling visualization of latent fingerprints (i.e., invisible residual biomolecule patterns). This study demonstrates the potential complexity of the biomolecule corona as all classes of biomolecules can adsorb onto MPN‐based nanomaterials.

Synthesis and Spectral Properties of 8-Anilinonaphthalene-1-sulfonic Acid (ANS) Derivatives Prepared by Microwave-Assisted Copper(0)-Catalyzed Ullmann Reaction.

For decades, the dye 8-anilino-1-naphthalenesulfonic acid (ANS) has been used to study biological systems due to its environmentally sensitive fluorescent nature and propensity to bind to hydrophobic pockets of proteins. However, the syntheses of ANS and its derivatives have been low yielding, requiring harsh reaction conditions and long reaction times. We have developed efficient, mild microwave-assisted copper(0)-catalyzed Ullmann coupling conditions to synthesize ANS derivatives with yields of up to 74%. Many of these derivatives have spectral properties distinct from ANS, including improved and diminished quantum yields, different absorption and emission maxima, and complete loss of fluorescence. ANS derivatives with these unique fluorescence properties are useful tools to study biological systems.

Acid selective pro-dye for cellular compartments

A novel pro-dye approach for the acid-selective staining of the subcellular compartments for better permeability and selectivity was applied. The designed sensor has suitable physicochemical properties such as a large Stokes shift and a long-lived intracellular fluorescence. The Schiff base fragment was used for the acid-sensitive release of a fluorophore without affecting the overall stability of the biological systems. Due to the presence of an imine bond in its structure and its unique fluorescent properties, it can be presented as a “pro-dye” for acidic structures such as lysosomes. As a result of an imine bond cleavage, a new fluorescent compound is released, whose substantially shifted excitation and emission wavelengths enable a more selective and effective imaging of lysosomes and endosomes. The presented report provides the chemical, physicochemical and optical profiles as well as biological assays and theoretical calculations.

Polydiacetylene and imidazole mixed self-standing films for colorimetric detection of various volatile organic analytes

Polydiacetylens (PDAs) have attracted great attention for application in sensing field due to their unique fluorescence and colorimetric properties. Polydiacetylenes (PDAs) are important class of polymer that exists in two distinct phases namely metastable, non-fluorescent blue phase and stable, auto-fluorescent red phase under specific conditions. PDA is obtained through polymerization of diacetylene (DA) monomers, typically using UV irradiation that leads to photopolymerization of the diacetylene lipids. Herein, the diacetylene monomer 10, 12-tricosadiynoic acid (TCDA) and N-1-hexadecyl Imidazole have been used to prepare mixed films onto a filter paper surface using the self-standing technique and then polymerizes the mixed films to get blue phase by UV irradiation. The PDA and N-1-hexadecyl Imidazole mixed films in the blue phase exhibit rapid colorimetric/fluorescence response upon exposure to various volatile organic analytes. The colorimetric and fluorogenic responses of TCDA and N-1-hexadecyl Imidazole mixed films were investigated by UV-vis absorption spectroscopy, inverting fluorescence microscopy and RGB analysis. This study demonstrates that PDA and N-1-hexadecyl Imidazole mixed films can be a used for detection of various volatile organic analytes even in naked eye.

Analysis of UV photographs of the Shroud of Turin.

The Shroud of Turin is one of the most widely studied ancient relics in history. In this paper, recently published UV photographs of the Shroud are analyzed. It is shown that the Shroud exhibits very unique UV fluorescence properties, and fluoresces more on its right side than its left side. Also, where comparisons can be made, the Shroud fluoresces more on its dorsal side than its frontal side, and fluorescence is stronger near the center of the image on the Shroud than near the head or feet. Additional research is required to determine what produced these unique properties.

Fluorescence imaging for rapid monitoring of translocation behaviour of systemic markers in snap beans for automated crop/weed discrimination

Investigating the translocation behaviour of fluorescent markers is significant for the effective application of the markers in weed and crop differentiation. Snap bean was used as a model plant to study the systemic movement of Rhodamine B (Rh-B) in specialty crops for weed control. A fluorescence imaging system was developed to monitor the uptake and translocation of Rh-B from dyed snap bean seeds to bean plants. Bean samples were dyed using different concentrations of Rh-B solutions. As the concentration of Rh-B applied to the seeds increased, the fluorescent signal of the marker was at first enhanced, then weakened. After germination, this marker was observed from the stems of bean seedlings at stages of first leaf to multiple leaves over time. The fluorescence response on the hypocotyl was stronger than that on the epicotyl, while there was limited translocation observed in plant roots and leaves based on this fluorescence imaging system. The fluorescence peak at 590 nm, measured by a spectrometer (350–1050 nm), exhibited the greatest contrast between untreated and treated plant samples. The proposed crop signalling approach based on Rh-B emission was able to classify snap bean plants from different weeds (e.g. burning nettle, groundsel, and barley). The results demonstrate that fluorescence imaging technology is a rapid and effective approach to studying the real-time translocation behaviour of a signalling marker in a crop system. Based on the unique fluorescence property, visualisation of the marker in vivo specialty crops grown from Rh-B treated seeds provides potential for their successful application in early season weed discrimination. • Fluorescence imaging was used to characterise a signalling marker in snap beans. • The uptake of Rhodamine from dyed snap bean seeds to bean plants was observed. • The marker was detected from crop stems at first leaf stage to multiple leaves. • Snap bean plants were classified from different weeds based on crop signalling.

Review of Carbon and Graphene Quantum Dots for Sensing.

Carbon and graphene quantum dots (CQDs and GQDs), known as zero-dimensional (0D) nanomaterials, have been attracting increasing attention in sensing and bioimaging. Their unique electronic, fluorescent, photoluminescent, chemiluminescent, and electrochemiluminescent properties are what gives them potential in sensing. In this Review, we summarize the basic knowledge on CQDs and GQDs before focusing on their application to sensing thus far followed by a discussion of future directions for research into CQDs- and GQD-based nanomaterials in sensing. With regard to the latter, the authors suggest that with the potential of these nanomaterials in sensing more research is needed on understanding their optical properties and why the synthetic methods influence their properties so much, into methods of surface functionalization that provide greater selectivity in sensing and into new sensing concepts that utilize the virtues of these nanomaterials to give us new or better sensors that could not be achieved in other ways.

Rh(III)-Catalyzed Sequential C-H Amination/Annulation Cascade Reactions: Synthesis of Multisubstituted Benzimidazoles.

An efficient and practical method to construct benzimidazoles via Rh(III)-catalyzed sequential C-H amination and annulation cascade reaction has been developed. The cascade reaction displays high step, atom, and redox economy, is compatible with the air, and has good functional group tolerance and high efficiency. The titled products can be easily further converted into imidazo[4,5-c]acridines, which were observed unique fluorescent properties.

Preparation of CQDs with hydroxyl function for Fe 3+ detection

Owing to its excellent fluorescence stability, unique up-conversion fluorescence properties and biocompatibility, carbon-quantum dots (CQDs) have become a research hot spot in the field of carbon materials. This study used a series of different preparation strategies to synthesise CQDs such as microwave method, solvothermal method and hydrothermal method. The prepared quantum dots can be further applied to design and metal ion detection. It is worth noting that the CQDs prepared by the hydrothermal method are evenly distributed in the range of 2-3 nm without any agglomeration. Fluorescence quenching was performed by Fe 3+ , and the introduction of PO 4 3- ion could increase the fluorescence intensity of CQDs-Fe 3+ system. Furthermore, CQDs were hydroxyl functionalised by treating with ethanol. The functionalised CQDs synthesised by solvothermal method greatly enhanced the fluorescence intensity.

Crystal structure of the blue fluorescent protein with a Leu-Leu-Gly tri-peptide chromophore derived from the purple chromoprotein of Stichodactyla haddoni.

Chromoproteins are a good source of engineered biological tools. We previously reported the development of a blue fluorescent protein, termed shBFP, which was derived from a purple chromoprotein shCP found in the sea anemone Stichodacyla haddoni. shBFP contains a Leu63-Leu64-Gly65 tri-peptide chromophore, and shows maximum excitation and emission wavelengths at 401 nm and 458 nm, along with a high quantum yield. How this chromophore endows shBFP with the unique fluorescence property in the absence of a hydroxyphenyl ring remained unclear. Here, we present the crystal structures of shCP and shBFP at 1.9- and 2.05-Å resolution, respectively. Both proteins crystallized as similar tetramers, but they are more likely to function as dimers in solution. The chromophore in shCP shows a trans-conformation and its non-planarity is similar to most other homologues. The shBFP chromophore also contains an imidazolidone moiety in its structure, but there are a smaller number of conjugated double bonds compared to shCP. Consequently, the chromophore may prefer absorbing shorter wavelength lights in the UV region, followed by the emission of blue fluorescence. These observations provide new insights into the molecular basis that correlates chromophore conformation with light absorption and fluorescence emission for the development of improved biomarkers.

Construction of NaYF4:Eu@carbon dots nanocomposites for multifunctional applications

The combination of carbon dots (CDs) and rare-earth ions has attracted increasing attention due to their unique fluorescence properties. Herein, CDs are incorporated with NaYF4:Eu to form stable NaYF4:Eu@CDs nanocomposites by a simple sol-gel route. It has been demonstrated that CDs are successfully embedded in the silica layer outside NaYF4:Eu nanoparticles. These nanocomposites exhibit characteristic emissions of both CDs and NaYF4:Eu under a single excitation wavelength. By using their dual-emissive properties, the nanocomposites can act as ratiometric fluorescent sensor for selective detection of Fe3+ ions in the range of 0–350 μM. The temperature-dependent luminescent property of the nanocomposites makes them also suitable as thermometers in the range from 377 to 467 K. In addition, the luminescent color can be regularly adjusted by tuning the mass ratio of NaYF4:Eu to CDs. This combing strategy enables us to achieve dual emission of CDs and Eu3+ ions in nanocrystals, opening an avenue towards multifunctional applications in widespread fields.

Intracellular Delivery of Nanoparticles Mediated by Lactoferricin Cell-Penetrating Peptides in an Endocytic Pathway.

Cell-penetrating peptides (CPPs) containing a preponderance of basic amino acids are able to deliver biologically active macromolecules and nanomaterials into live cells. Quantum dots (QDs) are nanoparticles with unique fluorescence properties that have found wide application in biomedical imaging. In this study, we demonstrate transduction of an L6 CPP (RRWQWR) derived from bovine lactoferricin (LFcin) into human lung cancer cells. L6 noncovalently interacts with QDs to form stable complexes. L6/QD complexes enter cells most efficiently when prepared at a nitrogen/phosphate ratio of 60. Mechanistic studies indicate that L6/QD complexes enter cells by endocytosis. Treatment with 1,2-benzisothiazol-3(2H)-one (BIT), an industrial preservative that enhances uptake of certain CPPs, does not affect L6 CPP-mediated protein transduction efficiency. L6 and L6/QD complexes are not cytotoxic. These results indicate that L6 LFcin might be an efficient and safe nanoshuttle for nanoparticles or nanomedicines in biomedical applications.

Photoluminescence Properties of Eu-Doped MIL-53(Fe) Obtained by Solvothermal Synthesis.

We report the facial synthesis of Eu-doped MIL-53(Fe) elongated hexagonal dipyramid by solvothermal reaction of Fe(NO₃)₃, Eu(NO₃)₃ and terephthalic acid (TPA) in the presence of N,N-dimethylformamide (DMF). The as-synthesized samples were characterized by XRD, Raman, FT-IR, PL, and SEM. From XRD and Raman results, metal replacement (Eu) with the metal ion (Fe) in the crystal lattice may change the high crystallinity of the MIL-53(Fe) structure, and all the metal ions were incorporated into the structures of MIL-53(Fe) as well as replaced Fe ion or located at interstitial site. From PL result, Eu-doped MIL-53(Fe) showed unique Eu fluorescence properties with high emission intensity, thus enabling it to be a promising functional probe for fluorescent imaging.

Two stimulus-responsive carbazole-substituted D–π–A pyrone compounds exhibiting mechanochromism and solvatochromism

Two D–A compounds were designed and synthesized from 2,6-dimethyl-4-pyrone and carbazole compounds. Both of them exhibited unique fluorescence properties in the aggregated state. Red shifts of the spectrum of 102 nm and 130 nm were observed for BCSP and CSP on changing the solvent from n-hexane to N,N-dimethylformamide (DMF), viz. solvatochromism. This phenomenon induced by the intramolecular charge transfer (ICT) effect was confirmed by density functional theory calculations. Interestingly, they both displayed excellent blue-shifted mechanochromic behavior, which was investigated by powder x-ray diffraction (PXRD) analysis. The results of this study provide a new avenue for the design of organic mechanochromic materials that exhibit a blue-shifting chromatic trend. Based on the unusual response of the solid fluorescence to external mechanical forces, we believe that these materials may be useful in various regards for potential applications.

Integration of fluorescence imaging and electrochemical biosensing for both qualitative location and quantitative detection of cancer cells

In this work, DNA-templated silver nanoclusters (DNA-AgNCs) with unique fluorescent and electrochemical properties are prepared as dual signal probes for both qualitative imaging and quantitative detection of cancer cells in an integrated system. ITO electrode that has good light transmittance and electric conductivity is employed as a substrate for dual analysis of cancer cells. ITO electrode is firstly modified by AS1141 aptamer, which could selectively bind to nucleolin overexpressed on the surface of a model breast cancer cell, MCF-7 cell line. The composite of mucin 1 antibody (anti-MUC1) and DNA-AgNCs then binds to MUC1 on the surface of captured MCF-7 cell, forming a sandwich-like structure. Therefore, our method allows noninvasive fluorescence imaging and amplified electrochemical detection using a single labeling platform, providing a biocompatible and highly specific method for adequate analysis of cancer cells. Experimental results demonstrate that strong red fluorescence of DNA-AgNCs clearly displays the loading of cancer cells on ITO electrode after dual recognition, and amplified electrochemical signals of DNA-AgNCs enable improved sensitivity toward quantitative analysis with a detection limit of 3 cells.

Polydiacetylene Capacitive Artificial Nose.

Polydiacetylenes are a class of conjugated polymers exhibiting unique color and fluorescence properties and employed as useful sensing vehicles. Here we demonstrate for the first time that the dielectric properties of polydiacetylenes can be exploited for vapor sensing. Specifically, electrodes coated with polydiacetylenes, embedded within a porous polyvinylpyrrolidone (PVP) matrix, exhibit significant capacitance transformations upon exposure to different vapors. The capacitive response of the polydiacetylene/PVP films depended upon both the structures of the diacetylene monomer and the extent of ultraviolet irradiation (i.e., polymerization), underscoring a unique sensing mechanism affected by conjugation, structure, and dielectric properties of the polydiacetylene/polymer matrix. Importantly, the variability of polydiacetylene structures allows vapor identification through an array-based pattern recognition (i.e., artificial nose). This study opens new avenues for applications of polydiacetylene systems, particularly pointing to their dielectric properties as powerful sensing determinants.