Near-Infrared-Fluorescent Probes for Bioapplications Based on Silica-Coated Gold Nanobipyramids with Distance-Dependent Plasmon-Enhanced Fluorescence.

Optical antennas with anisotropic metal nanostructures are widely used in the field of fluorescence enhancement based on localized surface plasmons (LSPs). They overcome the intrinsic defects of low brightness of near-infrared (NIR) dyes and can be used to develop sensitive NIR sensors for bioapplications. Here, we demonstrate a novel NIR plasmon-enhanced fluorescence (PEF) system consisting of elongated gold nanobipyramids (Au NBPs) antennas, silica, and NIR dyes. Silica was chosen as the rigid spacer to regulate the distance between the metal nanostructures and dyes. Maximum enhancement was observed at a distance of approximately 17 nm. The enhanced fluorescence could be quenched by Cu2+ and recovered by pyrophosphate (PPi) owing to the strong affinity between PPi and Cu2+. Thus, the Au NBP@SiO2@Cy7 nanoparticles (NPs) detect PPi via "switch-on" fluorescence signals, with a detection limit of 80 nM in the aqueous phase. The probe not only detects PPi in living cells but also can be used for a microRNA assay with a detection limit of 8.4 pM by detecting PPi in rolling circle amplification (RCA). Additionally, gold nanorods (Au NRs) with the same longitudinal plasmon resonance wavelength (LPRW) as the Au NBPs were prepared to synthesize Au NR@SiO2@Cy7 NPs for comparison. The experimental and finite-different time-domain (FDTD) simulation results indicate that the stronger electric fields of Au NBPs contribute to a fluorescence enhancement that is several times higher than that of Au NRs, confirming the superior properties of Au NBPs as novel ideal substrates to develop PEF biosensors.

Solvatochromism, Reversible Chromism and Self-Assembly Effects of Heteroatom-Assisted Aggregation-Induced Enhanced Emission (AIEE) Compounds.

Two compounds, 9,10-bis[2-(quinolyl)vinyl]anthracene (BQVA) and 9,10-bis[2-(naphthalen-2-yl)vinyl]anthracene (BNVA), have been synthesised and investigated. Both of them have aggregation-induced enhanced emission (AIEE) properties. Heteroatom-assisted BQVA shows solvatochromism, reversible chromism properties and self-assembly effects. When increasing the solvent polarities, the green solution of BQVA turns to orange with a redshift of the fluorescence emission wavelengths from λ=527 to 565 nm. Notably, BQVA exhibits reversible chromism properties, including mechano- and thermochromism. The as-prepared BQVA powders show green fluorescence (λem=525 nm) and the colour can turn into orange (λem=573 nm) after grinding. Interestingly, the orange colour can return at high temperature. Based on these reversible chromism properties, a simple and convenient erasable board has been designed. Different from BQVA, non-heteroatom-assisted BNVA has no clear chromic processes. The results obtained from XRD, differential scanning calorimetry, single-crystal analysis and theoretical calculations indicate that the chromic processes depend on the heteroatoms in BQVA. Additionally, BQVA also exhibits excellent self-assembly effects in different solvents. Homogeneous nanospheres are formed in mixtures of tetrahydrofuran and water, which are then doped into silica nanoparticles and treated with 3-aminopropyltriethoxysilane to give amino-functionalised nanoparticles (BQVA-AFNPs). The BQVAAFNPs could be used to stain protein markers in polyacrylamide gel electrophoresis.

Color- and morphology-controlled self-assembly of new electron-donor-substituted aggregation-induced emission compounds.

Four electron-donor-substituted aggregation-induced emission (AIE) compounds, N,N'-bis(4-methoxylsalicylidene)-p-phenylenediamine (BSPD-OMe), N,N'-bis(4-methylsalicylidene)-p-phenylenediamine (BSPD-Me), N,N'-bis(salicylidene)-p-phenylenediamine (BSPD), and N,N'-bis(4-hydroxylsalicylidene)-p-phenylenediamine (BSPD-OH), are designed and synthesized. They are all found to exhibit controlled self-assembly behaviors and good thermal properties. By changing the terminal electron-donor groups, they are controlled to self-assemble into three emission colors (green, yellow, and orange) and four morphologies (microblocks, microparticles, microrods, and nanowires) in THF/water mixtures. Their self-assembled structures were investigated with scanning electron microscopy (SEM), fluorescent microscopy images, transmission electron microscopy (TEM), and powder X-ray diffraction (PXRD) techniques. In addition, the emission colors of BSPD-OH can be successfully controlled to three colors (green → yellow → orange) through simply changing the water fraction (fw). Their thermal gravimetric analysis (TGA) results indicate that their thermal decomposition temperatures (Td, corresponding to 5% weight loss) range from 282 to 319 °C. Their differential scanning calorimetry (DSC) data show that BSPD-OH bears a glass-transition temperature (Tg) of 118 °C. The good Td and Tg values will ensure them to be luminogens for organic light-emitting diodes (OLEDs). The theoretical calculations and single-crystal X-ray diffraction (XRD) analysis of BSPD-OMe and BSPD suggest that the stronger electron donor substituent can twist the molecular conformation, decrease the degree of π conjugation, increase the energy gap, and then induce the emission colors' blue shift and morphology variation. The results are meaningful in controlling the emission colors and self-assembly shapes of these derivatives, and they also provide a novel but facile way to get color-tunable AIE luminogens for OLEDs.

Design and application of anthracene derivative with aggregation-induced emission charateristics for visualization and monitoring of erythropoietin unfolding.

Erythropoietin (EPO) is an attractive protein-unfolding/folding model because of its high degree of unfolding and folding reversibility and intermediate size. Due to its function for regulating red blood cell production by stimulating late erythroid precursor cells, EPO presents obvious values to biological research. A nonemissive anthracene derivative, that is 9,10-bis[4-(3-sulfonatopropoxyl)-styryl]anthracene sodium salt (BSPSA), with aggregation-induced emission (AIE) charateristics shows a novel phenomenon of AIE when EPO is added. The AIE biosensor for EPO shows the limit of detection is 1 × 10(-9) M. Utilizing the AIE feature of BSPSA, the unfolding process of EPO using guanidine hydrochloride is monitored, which indicates three steps for the folding structures of EPO to transform to random coil. Computational modeling suggests that the BSPSA luminogens prefer docking in the hydrophobic cavity in the EPO folding structures, and the assembly of BSPSA in this cavity makes the AIE available, making the monitoring of unfolding of EPO possible.

Core-shell gold nanocubes for point mutation detection based on plasmon-enhanced fluorescence.

Point mutation, with a permanent change in nucleic acid sequences, can affect the expression of genetic information forming the basis for numerous human genetic diseases, which makes its detection crucially important. Here, we reported a simple and sensitive method for point mutation detection, which employs a core-shell gold nanocube (Au NC) based on plasmon-enhanced fluorescence (PEF). For the generation of PEF, a Au NC was chosen as a core and silica as a spacer layer to adjust the distance between the Au NC and the dye of 5-carboxyfluorescein. Cu2+ quenched fluorescence by the interaction with the dye, while a "turn-on" signal was observed with the presence of pyrophosphate (PPi) owing to the strong affinity between Cu2+ and PPi, which subsequently achieved sensitive and selective detection of PPi. The experiment and theoretical simulations indicated that the enhanced signal was generated from square scattering cross sections and multiple corners, which could also be applied to cell imaging. Moreover, the rolling circle amplification coupled with ligase chain reaction (L-RCA) assay was also performed, which generated a circular DNA to initiate the RCA reaction accompanied by the generation of PPi that can be detected by the PEF sensor. Therefore, point mutation (C to T) can be detected based on fluorescence changes with a detection limit of 1.3 pM. This is a specific, simple, and economical method for point mutation detection, which overcomes the shortcomings of traditional detections of RCA products and point mutation.

A comparative study of plasmonic-enhanced single-molecule fluorescence induced by gold nanoantennas and its application for illuminating telomerase.

A comparative study of plasmonic-enhanced single-molecule fluorescence (PESMF) induced by four gold nanoantennas is reported. The gold triangular nanoplate (Au TNP) is the optimal PESMF substrate for Cy5.5 owing to its sharpest point and strongest electric fields. The Au TNP is chosen for the preparation of a telomerase sensor.

Silica-coated triangular gold nanoprisms as distance-dependent plasmon-enhanced fluorescence-based probes for biochemical applications.

Plasmon-enhanced fluorescence (PEF)-based anisotropic nanostructures are considered extremely promising tools for improving the inherent problems of traditional fluorophores and for detecting important biomolecules with high sensitivity. Herein, a novel triangular gold nanoprism (AuNPR)-based fluorescence probe, AuNPR@SiO2@12,17-tetramethyl-3-dihydro-(2s-trans)-thyl-7(Ce6), was developed for PEF by virtue of multiple "hot spots" of AuNPRs. Fluorescence enhancement of fluorophores can be realized owing to the larger and stronger electromagnetic fields located at the sharp tips of AuNPRs than those on spherical particles and nanorods. A silica shell was employed as a rigid spacer to precisely adjust the distance between the AuNPR and Ce6 for optimal PEF. Owing to the improved fluorescence signal, core-shell PEF-based AuNPRs can be applied as a turn-on probe for highly selective and sensitive detection of pyrophosphate (PPi) with a desirable detection limit of 0.2 µM using a displacement approach. Meanwhile, we demonstrated that these nanomaterials have great potential for real-time monitoring of polymerase chain reaction (PCR) products, successfully revealing an approximately 240 times higher detectable fluorescence response than that of traditional gel electrophoresis. Furthermore, cell imaging indicates the potential applications of PEF-based probes in living cells.

Dual-emission fluorescent sensor based on AIE organic nanoparticles and Au nanoclusters for the detection of mercury and melamine.

A novel dual-emission ratiometric fluorescence probe is designed and developed by linking two parts, positively charged aggregation-induced emission (AIE) organic fluorescence nanoparticles (OFNs) as the reference and negatively charged Au nanoclusters (Au NCs) as the response, by electrostatic attraction for the first time. This probe can be used for not only visual but quantitative determination of Hg(2+) as well as melamine, because red fluorescence of Au NCs can be quenched by mercury ions and recovered by melamine, due to the strong affinity metallophilic Hg(2+)-Au interaction and stronger affinity Hg(2+)-N. During this process, the green fluorescence of AIE-OFNs remains constant owing to the protection of ε-polylysine (ε-Ply). In addition, the prepared dual-emission ratiometric fluorescence probe has good biocompatibility, indicating the potential of the probe in applications of biological imaging and detection. The results revealed that this dual-emission ratiometric fluorescence probe broadens the application of AIE-based organic fluorescent nanoparticles, and presents a new method to prepare more sensitive, biocompatible, and visual ratiometric fluorescent probes.

Aggregation-induced emission compounds as new assisted matrices for laser desorption/ionization time-of-flight mass spectrometry.

Here, N,N'-bis(4-hydroxylsalicylidene)-p-phenylenediamine (BSPD-OH), N,N'-bis(4-methoxylsalicylidene)-p-phenylenediamine (BSPD-OMe) and N,N'-bis(salicylidene)-p-phenylenediamine (BSPD), which belong to the same category of aggregation-induced emission (AIE) compounds based on Schiff base reactions, were synthesized and applied as new matrices in the analysis of small molecules by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). This type of AIE compounds can be good MALDI matrices. Conventional organic matrices often produce large amounts of matrix ions, hindering the analysis of low molecular weight (LMW) compounds. However, these AIE compounds generate few matrix ions and less background interference because their presence as aggregates decreases the generation of matrix interference. The sensitivity of the AIE matrix is high because the aggregates can improve the absorption of the applied laser emissions. We can regulate the ionization efficiency of the AIE matrix by changing its aggregation state. During this study, BSPD-OH exhibited better ionization efficiency than the other two AIE matrices because it has more phenolic hydroxyl groups. BSPD-OH was successfully applied to the analysis of various LMW compounds including amino acids, organic amine compounds, isoquinoline compounds and fluoroquinolones compounds. This material also can be employed during the qualitative and quantitative analysis of LMW metabolites in human urine without requiring complicated separation processes.

Distinguish cancer cells based on targeting turn-on fluorescence imaging by folate functionalized green emitting carbon dots.

Developing efficient methods for visual detection of cancer cells has the potential to contribute greatly to basic biological research and early diagnosis of cancer. Here, we report facile and one-step synthesis of green fluorescence carbon dots (CDs) with the help of a new passivating agent--poly(acrylate sodium) (PAAS). Based on the as-prepared CDs, a novel turn-on fluorescence probe was designed for targeting imaging of cancer cells via hydrogen-bond interaction between folic acid and CDs (FA-CDs). Intracellular experiments indicated that FA-CDs probe could accurately distinguish folate receptor (FR)-positive cancer cells in different cell mixtures with turn-on mode. In particular, combining the targeting of FA-CDs probe with the excellent photostability of CDs has inestimable meaning for fluorescence-assisted surgical resection and acquisition real-time information about tumor cells. Obviously, the as-prepared FA-CDs probe may have great potential as a high-performance platform for accurately recognizing special cancer cells, which may provide new tools for cancer prognosis and therapy.

Multifunctional core-shell upconversion nanoparticles for targeted tumor cells induced by near-infrared light.

Here we synthesize silica-coated NaYF4:Yb/Er nanocomposites with a photosensitizer hypericin covalently bound to silica shells (UCNPs@SiO2@hypericin) successfully, exhibiting precise size-control, good water dispersity and excellent biocompatibility. Under near-infrared light (NIR) irradiation, UCNPs convert NIR light to strong green light which agrees well with the absorbance peak of the photosensitizer hypericin, and triggers hypericin to generate singlet oxygen effectively. The cell apoptosis studies by flow cytometry, fluorescence microscope imaging with Annexin V-FITC/PI and caspase-3 western blotting demonstrate that UCNPs@SiO2@hypericin-FA displays outstanding performance in the induction of apoptosis of Hela cells and HepG2 cells under NIR light irradiation for a short time. At the same time, UCNPs@SiO2@hypericin-FA nanocomposites are proved to exhibit little cytotoxicity by cell viability experiments. By the use of confocal microscopy, cell uptake results show that folate receptor FR(+) cell lines such as Hela cells could internalize more UCNPs@SiO2@hypericin-FA than FR(-) cell lines, such as 293T cells, with highly selective cellular uptake. All the results indicate that UCNPs@SiO2@hypericin-FA nanocomposites have a promising potential in the application of PDT and other diseases in deep tissues.

[Effects of two kinds of allelochemicals on photosynthesis and chlorophyll fluorescence parameters of Solanum melongena L. seedlings].

In a culture experiment, the effects of different concentration 2,6-bis (1, 1-dimethylethyl) phenol and 1,2-benzodicarboxylic dimethyl ester on the photosynthesis and chlorophyll fluorescence characteristics of eggplant seedlings were studied, and the results showed that these two allelochemicals were the barriers of chlorophyll content, net photosynthetic rate (Pn), and stomatal conductance (Gs). The intercellular CO2 concentration (Ci) decreased in the former period, and then increased. The allelochemicals increased initial fluorescence (Fo), but decreased maximum photochemical efficiency of PS II (Fv/Fm), quantum efficiency of non-cyclic electron transport of PS II (phi(PSII)), photochemical quenching ((qP) and antenna conversion efficiency (Fv'/Fm' ). 2,6-bis (1,1-dimethylethyl) phenol made non-photochemical quenching (qN) increase first and decrease then, while 1,2-benzodicarboxylic dimethyl ester decreased qN, which was harmful to the photosynthesis structure.