Carbon‐Dot‐Decorated Nanodiamonds

The synthesis of a new class of fluorescent carbon nanomaterials, carbon‐dot‐decorated nanodiamonds (CDD‐ND), is reported. These CDD‐NDs are produced by specific acid treatment of detonation soot, forming tiny rounded sp² carbon species (carbon dots), 1–2 atomic layers thick and 1–2 nm in size, covalently attached to the surface of the detonation diamond nanoparticles. A combination of nanodiamonds bonded with a graphitic phase as a starting material and the application of graphite intercalated acids for oxidation of the graphitic carbon is necessary for the successful production of CDD‐ND. The CDD‐ND photoluminescence (PL) is stable, 20 times more intense than the intrinsic PL of well‐purified NDs and can be tailored by changing the oxidation process parameters. Carbon‐dot‐decorated DNDs are shown to be excellent probes for bioimaging applications and inexpensive additives for PL nanocomposites.     

Photoswitchable Fluorescent Liquid Crystal Nanoparticles and Their Inkjet‐Printed Patterns for Information Encrypting and Anti‐Counterfeiting

Liquid crystal nanoparticles (LCNPs) with desirable multifunctionality are catching increasing attention due to their promising applications in various fields. However, reversible photoswitchable fluorescent LCNPs are not reported until now. Here, the first example of water‐dispersible, reversibly phototunable fluorescent LCNPs prepared through a miniemulsion polymerization technique is presented. The LCNPs mainly consist of an aggregation‐induced emission enhancement (AIEE)‐active dicyanodistyrylbenzene‐based monomer, a LC cross‐linking monomer, and a dithienylethene (DAE) derivative as a photochromic molecular switch. The fluorescence of the resultant LCNPs can be switched reversibly between bright (ON) and dark (OFF) states with a high contrast and excellent repeatability upon alternating irradiation of 365 nm UV light and visible light (λ > 450 nm). This observation could be attributed to ring‐opening/ring‐closing photoisomerization of the DAE structure on the basis of an intraparticle fluorescence resonance energy transfer process between the AIEE‐active monomer and DAE derivative. More importantly, the potential for aqueous dispersion of the photoswitchable fluorescent LCNPs as a security ink for information encryption and anti‐counterfeiting is further demonstrated. The results demonstrate that the reversible photoswitchable fluorescent LCNPs as multifunctional nanomaterials exhibit promising applications in photonic fields.     

Isolation and characterization of conformational isomers of N,N′‐bis(3,5‐dichlorosalicylidene)‐2,2′‐ethylenedianiline: crystal structure,photoluminescence, and density functional theory calculation

We have isolated two isomeric solids 1 and 2 of N,N′‐bis(3,5‐dichlorosalicylidene)‐2,2′‐ethylenedianiline and characterized by IR, UV/Vis, X‐ray powder diffraction, thermogravimetric analysis/differential thermal analysis, and X‐ray crystallography. Although the solids are same formulas, each shows different colors and crystal structures. Orange solid ( 1 ) shows endo conformation while yellow solid ( 2 ) exhibits exo form depending on packing modes. UV/Vis spectra of 1 and 2 appear very similar patterns in the solid state; however, the bands of 1 are slightly red‐shifted compared with those of 2 . 1 displays a strong fluorescent emission band at ~582 nm while 2 shows an intense fluorescent signal at ~563 nm. The charge density populations of 1 and 2 have been studied by computational simulations using density functional theory at pbe1pbe/6‐311G** level. The calculated highest occupied molecular orbital and lowest unoccupied molecular orbital energies of 1 and 2 confirm that charge transfer occurs within the organic molecules. The energy difference of HOMO‐LUMO in 1 is smaller slightly than that of 2 about 0.05 eV (~17 nm). Copyright © 2014 John Wiley & Sons, Ltd.     

Rapid synthesis and characterization of ultra‐thin shell Au@SiO2 nanorods with tunable SPR for shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS)

The recently reported shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) is considered as the next generation of advanced spectroscopy for its surface and molecular generality. With the aim to utilize the virtues of shell‐isolated strategy and advance the SHINERS technique, we introduce a silane‐based rapid synthesis method of silica‐coating Au nanorods (Au@SiO₂ NRs) with manoeuvrable ultra‐thin shell and tunable SPR. The results demonstrate that the SPR of Au NRs could be optimized to obtain large Raman enhancement using either 633 nm or 785 nm laser. Differing from previously reported Au@SiO₂ NRs synthesis method, we can tune the silica shell thickness within several nanometers to maximize the Raman signal while effectively eliminating the exterior interference. And this advanced synthesis method has also significantly reduced the silica‐coating time from one day to ca. 1 h. This method as a new development of SHINERS technique has successfully got enhanced signal in solution Raman tests of malachite green, giving a great potential to be extended to in‐situ measurement for daily life detection. Copyright © 2013 John Wiley & Sons, Ltd.     

Preparation and Characterization of the Fluorescent Carbon Dots Derived from the Lithium‐Intercalated Graphite used for Cell Imaging

Zero‐dimensional fluorescent carbon dots (CDs) that are used as a cell‐imaging reagent are prepared by using a simple and effective route employing lithium‐intercalated graphite from lithium‐ion batteries as a carbon source. Under ultrasonic exfoliation, the interlayer space increases, while the layer distortion and remaining lithium of the lithium‐intercalated graphite are utilized to disrupt the graphitic structure and produce the CD suspension. Subsequently, after concentration and purification, the obtained colloidal CD suspension has a fluorescent yield of up to 1.2% and is therefore comparable to the CDs prepared in previous reports. These CD products are water‐soluble, nanosized (approximately 3.5 nm), and biocompatible and can easily enter into HeLa cells to act as a cell‐imaging reagent without any further functionalization. In addition, these CDs do not impose toxicity against HeLa cells and have high photostability with low photobleaching and demonstrate potential applications for bio‐labeling as well as solution state optoelectronics.     

The distributions of enhancement factors in close‐packed and nonclose‐packed surface‐enhanced Raman substrates

A method employing photochemical hole burning, previously developed to measure the distribution of Raman enhancement factors on a nanostructured substrate for surface‐enhanced Raman scattering, is used to compare the enhancement distributions of benzenethiol adsorbed on substrates optimized for 532 nm laser excitation consisting of close‐packed (CP) or nonclose‐packed (NCP) nanospheres. The ensemble‐averaged Raman enhancement factor was 2.8 times smaller for the NCP substrate. The measured distributions revealed additional information. For instance, 92% of the molecules on the CP substrate and 93.6% of the molecules on the NCP substrate had Raman enhancements below average. The minimum enhancements on both substrates were ~10⁴, but on the NCP substrate the maximum enhancement was 1.2 × 10⁸, whereas on the CP substrate the maximum was 2 × 10¹⁰. The Ag‐coated nanospheres form hemisphere‐on‐cylinder mushroom‐like structures on both lattices, but on the NCP lattice, one third of the molecules are on the flat regions between the mushrooms. The flats on the NCP lattice have enhancements of ~10⁴, showing they are part of a resonant plasmonic structure. The highest NCP enhancements of ~10⁸ are tentatively associated with regions at the bases of the mushrooms, whereas the highest CP enhancements of 2 × 10¹⁰ are tentatively associated with gaps between nanospheres where 0.0025% of the molecules reside. Copyright © 2011 John Wiley & Sons, Ltd.     

Polarization‐resolved high‐resolution Raman spectroscopy with a light‐emitting diode

We demonstrate the use of a light‐emitting diode (LED) based experimental setup for collecting polarization‐resolved Raman spectra with good spectral resolution. The combination of a commercial red LED (630 nm), a 1‐nm bandwidth laser‐line filter, and a polarizing prism is used as a light source. Polarization‐resolved spectra in dimethyl sulfoxide are recorded and compared with the corresponding laser‐Raman spectra. The LED‐excited spectra exhibit a resolution slightly lower than those in the laser case but still close to the resolution of the spectrometer. All relevant spectral features of dimethyl sulfoxide including the symmetric and antisymmetric stretching modes of the CSC moiety are resolved with the experimental setup providing a spectral resolution of approximately 20 cm⁻¹. Copyright © 2013 John Wiley & Sons, Ltd.     

A novel fabrication method of CNT‐CP composite single nanowires self‐templated by dielectrophoresis and electropolymerization

A new method for fabricating carbon nanotube‐conducting polymer (CNT‐CP) composite single nanowires is reported. The method developed is highly efficient, reliable, and economical because it obviates the time consuming process of template fabrication and the post‐synthesis task of positioning nanowires. Single nanowires with diameters of 50‐500 nm are fabricated between electrodes, self‐templated by dielectrophoresis and electropolymerization. Fabrication of an individually addressed nanowire array with cantilever electrodes on a microchip is demonstrated.

     

Bifunctional Pancharatnam‐Berry Metasurface with High‐Efficiency Helicity‐Dependent Transmissions and Reflections

Manipulating circularly‐polarized (CP) waves in desired multi‐prescribed manners, especially in both transmission and reflection schemes, in a single flat device is of particular importance in photonic integration, imaging processing and communication systems. However, available approaches suffer from large thickness, low efficiencies as well as limited wavefront control spaces. Here, we propose a general strategy by using specially tailored Pancharatnam‐Berry (PB) meta‐atoms with helicity‐dependent transmissions and reflections to design high‐efficiency CP bifunctional metasurfaces. As a proof of the strategy, two metadevices are designed and characterized at microwave frequencies: the former one achieving focusing/diverging lenses at transmission/reflection side of the metasurface; the latter one realizing CP beam separation under illuminations of CP waves with different chirality, respectively. Both numerical and experimental results demonstrate the predicted EM functionalities, and all these functionalities exhibit very high efficiencies (88%～94%). Our findings afford a new route to design high‐performance CP bi‐functional metasurfaces operating in other frequency domains or with other functionalities.     

Imaging the Hydrated Microbe‐Metal Interface Using Nanoscale Spectrum Imaging

PdAu nanocrystals are synthesised by Geobacter sulfurreducens, a dissimilatory metal‐reducing bacterium, and the resulting bimetallic nanocrystal‐decorated microbes are imaged using a range of advanced electron microscopy techniques. Specifically, the first example of elemental mapping of fully hydrated biological nanostructures using scanning transmission electron microscope (STEM) energy dispersive X‐ray (EDX) spectrum imaging within an environmental liquid‐cell is reported. These results are combined with cryo‐TEM and ex situ STEM imaging and EDX analysis with the aim of better understanding microbial synthesis of bimetallic nanoparticles. It is demonstrated that although Au and Pd are colocalized across the cells, the population of nanoparticles produced is bimodal, containing ultrasmall alloyed nanocrystals with diameters <3 nm and significantly larger core‐shell structures (>200 nm in diameter) which show higher Pd contents and exhibit a Pd enriched shell only a few nanometers thick. The application of high‐resolution imaging techniques described here offers the potential to visualize the microbe‐metal interface during the bioproduction of a range of functional materials by microbial “green” synthesis routes, and also key interfaces underpinning globally relevant environmental processes (e.g., metal cycling).     

Full‐field X‐ray reflection microscopy of epitaxial thin‐films

Novel X‐ray imaging of structural domains in a ferroelectric epitaxial thin film using diffraction contrast is presented. The full‐field hard X‐ray microscope uses the surface scattering signal, in a reflectivity or diffraction experiment, to spatially resolve the local structure with 70 nm lateral spatial resolution and sub‐nanometer height sensitivity. Sub‐second X‐ray exposures can be used to acquire a 14 µm × 14 µm image with an effective pixel size of 20 nm on the sample. The optical configuration and various engineering considerations that are necessary to achieve optimal imaging resolution and contrast in this type of microscopy are discussed.     

Chip‐Free Microscale‐Incubator‐Based Synthesis of Chitosan‐Based Gene Silencing Nanoparticles

The development of polymer‐based nanoparticles to ferry siRNA continues to evolve. It is becoming increasingly apparent that gene silencing nanoparticles produced by conventional bulk manufacturing techniques often exhibit physicochemical heterogeneity within and between batches that can affect the biological performance. Here a new facile and robust “chip‐free” method is presented, termed chip‐free agitation‐generated droplets (CAD) preparation, using chitosan‐based gene silencing nanoparticles as an example. The CAD‐prepared silencing particles, in comparison to the particles prepared by the conventional bulk protocol, exhibit lower surface charge (9 mV vs 21 mV at N/P = 5), higher stability (≈40% higher binding affinity and up to 30% less morphological deformation), and are less prone to aggregation measured by nanoparticle tracking analysis over a period of one month. Furthermore, these physical attributes contribute up to 19% higher in cell viability at N/P = 5, while the gene silencing of enhanced green fluorescent protein remains constant in a human cell line. Control of particle properties is necessary to advance siRNA‐based delivery; the CAD preparation represents a physical complement to chemical design modifications, which can be readily transferred among research labs and utilized for alternative polymer systems.     

Nano‐Ruby: A Promising Fluorescent Probe for Background‐Free Cellular Imaging

Bioprobes based on fluorescent ruby nanoparticles, which are suitable for ultrasensitive imaging, are reported. A stable aqueous/buffer colloid, permitting facile conjugation to proteins, is produced by femtosecond laser ablation of ruby and the nanoparticles (mean size 17 nm) are photostable, with long lifetime (1–4 ms) 694 nm emission. With time‐gating complete (>20 dB) suppression of cell autofluorescence and suppression of exogenous fluorophores is observed. Nanoparticles are imaged in as‐grown cells and those immunolabeled with quantum dots. Immunoassay binding to target biomolecules is also demonstrated.     

Controlling fluorescence emission with split‐ring‐resonator‐based plasmonic metasurfaces

Metasurfaces, which consist of resonant metamaterial elements in the form of two‐dimensional thin planar structures, retain great capabilities in manipulating electromagnetic wave and potential applications in modifying interaction with fluorescent molecules. The metasurfaces with magnetic responses are favorable to weakening fluorescence quenching while less investigated in controlling fluorescence. In this paper, we demonstrate control over fluorescence emission by engineering the magnetic and electric modes in plasmonic metasurfaces consisting of 45‐nm‐thick gold split‐ring‐resonators (SRRs). The fluorescence emission exhibits an enhancement factor of ∼18 and is predominantly x‐polarized with assistance of the magnetic mode excited by oblique incidence with an x‐polarized electric field. The magnetic and electric modes excited by oblique incidence with a y‐polarized electric field contribute to the rotation of emission polarization with respect to the incident polarization. The results demonstrate manipulating the interaction of fluorescent emitters with different resonant modes of the SRR‐based metasurface at the nanoscale by the polarization of incident light, providing potential applications of metasurfaces in a wide variety of areas, including optical nanosources, fluorescence spectroscopy and compact biosensors.

     

Successive,Seed‐Mediated Growth for the Synthesis of Single‐Crystal Gold Nanospheres with Uniform Diameters Controlled in the Range of 5–150 nm

A simple and robust route is described to the synthesis of single‐crystal Au nanospheres with diameters controlled in the range of 5 nm to 150 nm. The success of this synthesis relies on the use of single‐crystal Au spheres with different diameters as the seeds for successive growth and the use of a slow injection rate for the precursor to enable surface diffusion for the atoms added onto the surface of a seed. The diameters could be precisely controlled by varying the size and/or number of the seeds. The products exhibit excellent uniformity in terms of both size and shape and they are expected to find widespread use in a number of applications, including self‐assembly, fabrication of metallodielectric photonic crystals, plasmonics, and biomedical research.     

Assembly‐Induced Emission of Cellulose Nanocrystals for Hiding Information

Fluorescent‐labeled cellulose nanocrystal (CNC) films have been used to record and protect information in paper materials, whereas the fluorescent materials usually suffer photobleaching. Herein, a strategy of solid‐state emission induced by the vertical assembly of CNCs was established. The assembly‐induced emission starts from the structural diffraction of CNC, whose wavelength is adjusted into the ultraviolet (UV) region for hiding information under natural light. The small diameter (≈10 nm) of CNCs then promotes the resonance between the vertically assembled CNCs and the UV light, leading to a strong blue emission with an emitting quantum efficiency as high as 13.90%. By introducing the vertical‐assembly film with a specific pattern into paper materials, an anti‐counterfeiting image is obtained under a UV radiation. Since CNCs are a kind of cellulose with high crystallinity, this material can be a wear‐resistant anti‐counterfeiting material for banknotes or other paper applications.     

Direct Synthesis of Gold Nanoparticle‐Over‐Nanosheet for Sensitive SERS Detection

A simple ethanol sol‐based method for the synthesis of gold nanosheets (AuNSs) and gold nanoparticle‐over‐nanosheet (AuNP/NS) is developed. Gold nanoparticles (AuNPs) with average sizes of ≈8 nm are grown in situ on the surface of the AuNS, which forms a NP/NS structure that obtains strong, significantly improved, surface‐enhanced Raman spectroscopy activity with the magnitude ≈2 and ≈6 orders higher than the simplex AuNP and AuNS, respectively. This performance is mainly attributed to uniform AuNPs that are closely packed over AuNS and coupled with NP–NS and NP–NP interactions. The NP–NS–GP (the gap between NP–NS) is narrower than NP–NP–GP in which much stronger and steadier plasmon resonance is obtained that can significantly enhance the Raman signal. The results show that single‐crystalline AuNS is an ideal substrate, which can be further coated with other metallic NPs to form a new flexible, high‐activity and AuNS‐based nanocomposite for a wide variety of applications.     

Self‐Assembly of Drug–Drug Conjugates as Drug Self‐Delivery System for Tumor‐Specific pH‐Triggered Release

An acid‐labile doxorubicin dimer (D‐DOX) is designed as drug–drug conjugate for tumor intracellular pH‐triggered release, by conjugating doxorubicin (DOX) with adipic acid dihydrazide (ADH). The dimer‐based surfactants modified with polyethylene glycol (PEG), DOX‐ADH‐DOX‐PEG or are synthesized by mono‐PEGylation and bi‐PEGylation, respectively. Then the prodrug nanoparticles are fabricated with different drug contents via dialyzing the mixture solution of D‐DOX and the PEGylated surfactants in dimethyl sulfoxide (DMSO) with different mass ratios against water. It is found that the smaller prodrug nanoparticles (142–163 nm) could be obtained with the mono‐PEGylated surfactant, than those of 157–225 nm with the bi‐PEGylated surfactant. Furthermore, the mono‐PEGylated surfactant results in a higher drug content of 51% due to their lower PEG contents. All prodrug nanoparticles could release DOX completely within 36 h at pH 5.0, with the premature drug leakage of less than 10% at pH 7.4. The 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assays demonstrate the proposed drug self‐delivery system possessed an enhanced anticancer efficacy against HepG2 cells than the free DOX.     

Drop‐cast and dye‐sensitized ZnO nanorod‐based visible‐light photodetectors

We report the facile fabrication of metal–semiconductor–metal (MSM) photodetectors with dye‐sensitized ZnO nanorods (NRs) operating at wavelengths of ～405–638 nm by a simple drop casting method. The ZnO NRs were synthesized by the hydrothermal synthesis method at 75 °C. The droplet of ethanol solution containing ZnO NRs was dropped between two metal electrodes and dried at 65 °C, which allows the ZnO NRs to be adhered and contacted to both metal electrodes. When a violet light of 405 nm was illuminated into the MSM ZnO NRs‐based photodetector, the photocurrent gain was obtained as ～3.9 × 10³ at the applied bias voltage of 5 V. By increasing the bias voltage from 10 V to 15 V, the device exhibited good recovery performance with a largely reduced reset time from 85.68 s to 2.47 s and an increased on–off ratio from 17.9 to 77.4. To extend the photodetection range towards the long visible spectral region, the ZnO NRs were sensitized by the N719 dye and then drop‐cast. The dye‐sensitized ZnO NRs‐based photodetector also exhibited good photocurrent switching under 638 nm of light illumination. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrothermal Preparation of Photoluminescent Graphene Quantum Dots Characterized Excitation‐Independent Emission and its Application as a Bioimaging Reagent

Zero‐dimensional photoluminescent (PL) graphene quantum dots (GQDs) that can be used as the cell‐imaging reagent are prepared by a hydrothermal route using the graphene oxide (GO) as the carbon source. Under the optimized hydrothermal conditions, an initial hydrogen peroxide concentration of 0.5 mg mL^?1 at 180 °C for 120 min, the GO sheets can be cut into nanocrystals with lateral dimensions in the range of 1.5–5.5 nm and an average thickness of around 1.1 nm. The as‐prepared GQDs exhibit an abundance of hydrophilic hydroxy and carboxyl groups and emit bright blue luminescence with up‐conversion properties in a water solution at neutral pH. Most interestingly, they indicate excitation‐independent emission characteristics, and the surface state is demonstrated to have a key role in the PL properties. The fluorescence quantum yield of the GQDs is tested to be around 6.99% using quinine sulfate as a standard. In addition, the as‐prepared GQDs can enter into HeLa cells easily as a fluorescent imaging reagent without any further functionalization, indicating they are aqueous stability, biocompatibility, and promising for potential applications in biolabeling and solution state optoelectronics.