Search

The ability to control and vary the atomic compositions of two-dimensional (2D) layered semiconductors is of considerable importance for tailoring their electronic and optoelectronic properties. The current methods to tailor chemical composition of 2D layered semiconductors is largely limited to vapor phase chemistry, and solution phase chemistry is insufficiently explored to date. Here, we report a general approach to prepare 2D layered transition metal dichalcogenides (TMDs) by ion exchange reactions in solution phase. By choosing four typical layered metal dichalcogenides including MoS2, MoSe2, WS2 and SnS2 as representative cases, the feasibility and versatility of both cation and anion exchange reactions in layered metal dichalcogenides are confirmed. Transient absorption results indicate that exciton lifetime of these samples as excitation energy is increased. The optoelectronic properties of these TMD nanosheets after the ion exchange exhibit potential for future devices. Our strategy can be employed not only to modulate the atomic composition and electronic structures of layered TMDs, but also open up a new pathway for the fabrication of various hybrid heterostructures. [ABSTRACT FROM AUTHOR]

Cycloaliphatic epoxy resin (3-4-epoxycyclohexane) methyl 3-4-epoxycyclohexyl-carboxylate (ECC) was formulated with flexible hydrogenated bisphenol A diglycidyl ether (HBADGE) to inspect the influence of chain flexibility on the performance and reliability of epoxy packaged Light-emitting Diode (LED). The properties of epoxy encapsulants were characterized by using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analyses (TGA), ultraviolet visible (UV-vis) spectrophotometer, thermomechanical analyzer (TMA), scanning acoustic microscopy (SAM), and scanning electron microscopy (SEM). With the incorporation of flexible HBADGE, favorable properties were obtained, such as decreased thermal expansion coefficient (CTE), lowered storage modulus at reflow temperature, and depressed equilibrium water uptake for the epoxy packaging materials. The light transmittance of encapsulants differed after thermal and UV aging. Compared with Neat ECC and Neat HBADGE, the HBADGE-modified encapsulants endowed LED devices with good performance and high reliability. [ABSTRACT FROM AUTHOR]

SpnF, an enzyme involved in the biosynthesis of spinosyn A, catalyzes a transannular Diels–Alder reaction. Quantum mechanical computations and dynamic simulations now show that this cycloaddition is not well described as either a concerted or stepwise process, and dynamical effects influence the identity and timing of bond formation. The transition state for the reaction is ambimodal and leads directly to both the observed Diels–Alder and an unobserved [6+4] cycloadduct. The potential energy surface bifurcates and the cycloadditions occur by dynamically stepwise modes featuring an "entropic intermediate". A rapid Cope rearrangement converts the [6+4] adduct into the observed [4+2] adduct. Control of nonstatistical dynamical effects may serve as another way by which enzymes control reactions. [ABSTRACT FROM AUTHOR]

Light harvesting and triplet energytransport is investigated inchromophore-functionalized polystyrene polymers featuring light harvestingand energy acceptor chromophores (traps) at varying loading. The seriesof precision polymers was constructed via reversible addition–fragmentationtransfer polymerization and functionalized with platinum acetylidetriplet chromophores by using an azide–alkyne “click”reaction. The polymers have narrow polydispersity and degree of polymerization∼60. The chromophores have the general structure, trans-[−R–C6H4–CC–Pt(PBu3)2–CC–Ar], where R is theattachment point to the polystyrene backbone and Ar is either –C6H4–CC–Ph or –pyrenyl(PE2-Pt and Py-Pt, respectively, with triplet energies of 2.35 and1.88 eV). The polychromophores contain mainly the high-energy PE2-Ptunits (light absorber and energy donor), with randomly distributedPy-Pt units (3–20% loading, energy acceptor). Photophysicalmethods are used to study the dynamics and efficiency of energy transportfrom the PE2-Pt to Py-Pt units in the polychromophores. The energytransfer efficiency is >90% for copolymers that contain 5% of thePy-Pt acceptor units. Time-resolved phosphorescence measurements combinedwith Monte Carlo exciton dynamics simulations suggest that the mechanismof exciton transport is exchange energy transfer hopping between PE2-Ptunits. [ABSTRACT FROM AUTHOR]

Noble metals, especially gold, have been widely used in plasmon resonance applications. Although silver has a larger optical cross section and lower cost than gold, it has attracted much less attention because of its easy corrosion, thereby degrading plasmonic signals and limiting its applications. To circumvent this problem, we report the facile synthesis of superstable AgCu@graphene (ACG) nanoparticles (NPs). The growth of several layers of graphene onto the surface of AgCu alloy NPs effectively protects the Ag surface from contamination, even in the presence of hydrogen peroxide, hydrogen sulfide, and nitric acid. The ACG NPs have been utilized to enhance the unique Raman signals from the graphitic shell, making ACG an ideal candidate for cell labeling, rapid Raman imaging, and SERS detection. ACG is further functionalized with alkyne-polyethylene glycol, which has strong Raman vibrations in the Raman-silent region of the cell, leading to more accurate colocalization inside cells. In sum, this work provides a simple approach to fabricate corrosion-resistant, water-soluble, and graphene-protected AgCu NPs having a strong surface plasmon resonance effect suitable for sensing and imaging. [ABSTRACT FROM AUTHOR]

The mechanism of the Wittig reaction of anisaldehyde with a stabilized ylide was studied by a combination of 13C kinetic isotope effects, conventional calculations, and molecular dynamics calculations in a cluster of 53 THF molecules. The isotope effects support a cycloaddition mechanism involving two sequential transition states associated with separate C—C and P—O bond formations. However, the betaine structure in between the two transition states is bypassed as an equilibrated intermediate in most trajectories. The role of the dynamics of solvent equilibration in the nature of mechanistic intermediates is discussed. [ABSTRACT FROM AUTHOR]

Energy transfer along a nonconjugatedpolymer chain is studiedwith a polystyrene-based copolymer of oligo(phenylene-ethynylene)(OPE) donor and thiophene-benzothiadiazole (TBT) acceptor pendants.The graft copolymers are prepared from reversible addition–fragmentationtransfer polymerization (RAFT) and copper(I)-catalyzed azide–alkyne“click” reaction. The singlet energy transfer from donorto accept is studied via fluorescence emission and ultrafast transientabsorption spectroscopy. Near unity quenching of the OPE excited stateby the TBT moiety occurs on multiple time scales (2–50 ps)dependent on where the initial exciton is formed on the polymer. [ABSTRACT FROM AUTHOR]

Large-scale cubic InN nanocrystals were synthesized by a combined solution- and vapor-phase method under silica confinement. Nearly monodisperse cubic InN nanocrystals with uniform spherical shape were dispersed stably in various organic solvents after removal of the silica shells. The average size of InN nanocrystals is 5.7 ± 0.6 nm. Powder X-ray diffraction results indicate that the InN nanocrystals are of high crystallinity with a cubic phase. X-ray photoelectron spectroscopy and energy-dispersive spectroscopy confirm that the nanocrystals are composed of In and N elements. The InN nanocrystals exhibit infrared photoluminescence at room temperature, with a peak energy of ∼0.62 eV, which is smaller than that of high-quality wurtzite InN (∼0.65-0.7 eV) and is in agreement with theoretical calculations. The small emission peak energy of InN nanocrystals, as compared to other low-cost solution or vapor methods, reveals the superior crystalline quality of our samples, with low or negligible defect density. This work will significantly promote InN-based applications in IR optoelectronic device and biology. [ABSTRACT FROM AUTHOR]

Well-aligned GaN nanocolumns on silicon substrate were fabricated by simple and low-cost chemical vapor deposition without any catalyst. The structure and morphology of the as-synthesized GaN nanocolumns were characterized by X-ray diffraction and scanning and transmission electron microscopies. The aligned GaN nanocolumn arrays exhibited excellent field emission properties with a low turn-on field of 2.6 V/μm (0.01 mA/cm2) and high stability at room temperature, which is sufficient for applications of field emission displays and vacuum nanoelectronic devices. The room-temperature photoluminescence emission with a strong peak at 369 nm indicates that the well-aligned GaN nanocolumns have potential application in light-emitting nanodevices. [ABSTRACT FROM AUTHOR]

NDMA is a recently recognized disinfection byproduct that can be formed by a reaction of monochloramine with natural organic matter (NOM). This study was undertaken to examine the influence of various preoxidation strategies (including prechlorination) on the subsequent formation of NDMA and to determine how this is correlated to the subsequent loss in specific UV absorbance (SUVA) that preoxidation causes. Batch experiments were conducted using surface-water-derived NOM exposed to various oxidants that included free chlorine, permanganate, hydrogen peroxide, and ozone. Photochemical oxidation was also studied by exposing the water to simulated sunlight The amount of NDMA formed after monochloramine was added or formed in situ, in the case when free chlorine was the preoxidant, was significantly reduced by these treatments. The reduction was proportional to the reduction in SUVA that also occurred as a consequence of these treatments indicating that SUVA may be a good surrogate for NDMA precursor content Furthermore, the change in NOMA formation per unit change in SUVA was a constant that did not depend on the nature of the oxidant. [ABSTRACT FROM AUTHOR]

N-nitrosodimethylamine (NDMA)formation in chloraminated Iowa River water (IRW) is primarily attributed to reactions with natural organic matter (NOM) generally classified as humic substances. Experiments were conducted to determine the contribution of various NOM humic fractions to the NOMA formation potential (NDMA FP) in this drinking water source. NOM was concentrated by reverse osmosis (RO) and humic fractions were obtained by a series of resin elution procedures. Mass balances showed that nearly 90% of the NDMA formation potential could be recovered in the NOM concentrate and in water reconstituted using additions of the various humic fractions. Generally, the hydrophilic fractions tended to form more NOMA than hydrophobic fractions, and basic fractions tend to form more NOMA than acid fractions when normalized to a carbon basis. Overall, the hydrophobic acid fraction was the dominant source of NDMA when both formation efficiency and water composition were considered. The amount of NDMA formed in a sample was found to correlate linearly with an oxidation-induced decrease in specific UV absorbance (SUVA) value at 272 nm. This is consistent with a mechanism in which precursors are formed as the direct consequence of the oxidation of NOM. The NOMA FP estimated using the slope of this relationship and the initial SUVA value compared closely to the value obtained by measuring the NDMA formed in solutions dosed with excess concentrations of monochloramine that presumably exhaust all potential precursor sources. However, the NDMA FP could not be correlated to the SUVA value of the individual humic fractions indicating that the relationship of the NDMA FP to SUVA value is probably a water-specific parameter dependent on the exact composition of humic fractions. It is hypothesized that either specific NOMA precursors are distributed among the various humic fractions or that the humic material itself represents a "generic" nonspecific precursor source that requires some degree of oxidation to eventually produce NOMA. The non-monotonic behavior of NOM fluorescence spectra during chloramination and lack of correlation between NOM fluorescence characteristics and NDMA formation limited the usage of fluorescence spectra into probing NDMA formation. [ABSTRACT FROM AUTHOR]

By using the specifically designed multigap nanoelectrodes, we demonstrated an effective approach for the simultaneous dielectrophoretic separation and assembly of metallic and semiconducting single-walled carbon nanotubes (SWNTs). An approximate metallic—semiconductingߞmetallic multiarray structure was created by an inward-propagative sequential assembly of SWNTs under ac electric field. Such kinds of SWNT multiarray structures exhibited ultra-low-power consumption and excellent thermal sensing performances with the sensitivity being dependent on the number of gaps: the more gaps, the higher sensitivity. The effective separation of metallic and semiconducting tubes in different gaps is believed to be responsible for the improved sensitivity to temperature. [ABSTRACT FROM AUTHOR]

This paper presents mechanistic studies on the formation of NDMA, a newly identified chloramination disinfection byproduct, from reactions of monochloramine with natural organic matter. A kinetic model was developed to validate proposed reactions and to predict NDMA formation in chloraminated water during the time frame of 1–5 days. This involved incorporating NDMA formation reactions into an established comprehensive model describing the oxidation of humic-type natural organic matter by monochloramine. A rate-limiting step involving the oxidation of NOM is theorized to control the rate of NDMA formation which is assumed to be proportional to the rate of NOM oxidized by monochloramine. The applicability of the model to describe NDMA formation in the presence of three NOM sources over a wide range in water quality (i.e., pH, DOC, and ammonia concentrations) was evaluated. Results show that with accurate measurement of monochloramine demand for a specific supply, NDMA formation could be modeled over an extended range of experimental conditions by considering a single NOM source- specific value of ONDMA, a stoichiometric coefficient relating the amount of NDMA produced to the amount of NOM oxidized, and several kinetic parameters describing NOM oxidation. Furthermore, the oxidation of NOM is the rate-limiting step governing NDMA formation. This suggests that NDMA formation over a 1–5 day time frame may be estimated from information on the chloramine or free chlorine demand of the NOM and the source-specific linear relationship between this demand and NDMA formation. Although the proposed model has not yet been validated for shorter time periods that may better characterize the residence time in some distribution systems, the improved understanding of the important reactions governing NDMA formation and the resulting model should benefit the water treatment industry as a tool in developing strategies that minimize NOMA formation. [ABSTRACT FROM AUTHOR]

The ability to topographically structure and fast controllably actuate hydrogel in two and three dimensions is the key for their promising applications in soft robots, microfluidic valves, cell and drug delivery, and artificial muscles. Inspired by evaporation-induced concentration differentiation phenomenon in the production process of beancurd sheet, we introduce a facile one-step evaporation process to create laminated layer/porous layer heterogeneous structure within graphene oxide-clay-poly(N-isopropylacrylamide) hydrogel in vertical direction and pattern the heterogeneous structure in lateral direction to form tunable, fast, and robust hydrogel actuators. The laminated layer/porous layer architecture is highly stable and robust without possibility of delamination. The evaporation-programmed heterogeneous structures tune thermoresponsive actuations from global bending/unbending for global heterogeneous structure to local bending/unbending and site-specific folding/unfolding for segment-patterned heterogeneous structure, then to directional bending/unbending and chiral twisting/untwisting for stripe-patterned heterogeneous structure. These actuations are instant and reversible without detectable fatigue after many cycles. [ABSTRACT FROM AUTHOR]

Technologicallycontrolling nanostructures is essential to tailoring the functionalitiesand properties of nanomaterials. Various methods free from lithography-basedtechniques have been employed to fabricate 2D nanostructures; howeverit is still hard to achieve a well interconnected 2D regular nanostructure.Here, we demonstrate a facile chemical solution method to self-assemblea regular and interconnected VO2nanonet on the wafer scale.The nanonet shows a well-defined 2D truss network constructed by VO2nanorods with twinning relationships. The growth directionand crystallographic orientation of nanorods are synchronously controlled,leading to horizontally epitaxial growth of nanorods along three symmetricdirections of the (001) single-crystal sapphire substrate. The uniquenanonets enable the acquisition of excellent resistance switchingproperties and dramatic fatigue endurance. A large resistance changeof near 5 orders with a 1.7 °C width of the hysteresis loop ischaracterized comparably to the properties of single crystals withoutdetectable degradation after 500 cycles over the metal-to-insulatortransition. It indicates that the nanonet can serve as an exceptionalcandidate for practical application in switching functional devices.Our findings offer a novel pathway for self-assembly of 2D orderednanostructures, which would provide new opportunities for the bottom-upintegration of nanodevices. [ABSTRACT FROM AUTHOR]

Fluorescence catalytic beacons have emerged as a general platform for sensing applications. However, almost all such sensing systems need covalent modification of the DNAzymes with fluorophore-quencher pairs, which may require elaborate design of the synthetic routes and many heavy and complicated synthetic steps and result in increased cost and lower synthesis yield. Here we report the construction of fluorescent cascadic catalytic beacons. With separation of the molecular recognition module from the signal reporter, this new design both avoids DNAzyme modifications and improves sensitivity through an endonuclease-based cascadic enzymatic signal amplification. This allows detection of l-histidine with high sensitivity (LOD = 200 nM) and excellent specificity. The proposed sensing system has also been used for detection of l-histidine in cellular homogenate with satisfactory results. [ABSTRACT FROM AUTHOR]

A series of MII−LnIIIazido-containing complexes: [LnNi2(IN)5(N3)2(H2O)3]·2H2O (Ln = NdIII(2), EuIII(3), SmIII(4), LaIII(5)) and [GdCu2(IN)5(N3)2(H2O)3]·2H2O (6) have been prepared hydrothermally by using isonicotinate (IN) and azide as bridging ligands with the strategy of synergistic coordination. Their structures have been determined by single-crystal X-ray diffraction analyses and their magnetic properties have been probed by changing the LnIIImetal ions and the 3d ions. All of them crystallize in the monoclinic space group P2(1)/n. The structural analyses revealed that alternating EE/EO azido−M chain and RCOO−/Ln chain are presented in these compounds due to coordination synergy. The variable temperature magnetic susceptibility studies demonstrate that the magnetic properties of the complexes are dominated by the 3d metal ions. [ABSTRACT FROM AUTHOR]

α-Si3N4 whiskers with novel saw-toothed and riblike structures have been synthesized in a high yield by a carbothermal reduction and nitridation route. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and selected-area electron diffraction (SAED). The results show that the saw-toothed whiskers with one smooth surface and another toothlike surface have lengths about several tens of microns and widths in the range of 600−1200 nm. The riblike whiskers are composed of Si3N4 rod-arrays, which grow closely packed perpendicular to the central axial whiskers with uniform diameter and length. The growth mechanism of the products can be considered as a combination of VS mechanism and secondary epitaxial nucleation process. The photoluminescence (PL) spectrum of the whiskers shows a strong blue light emission peak at 406 nm and a weak peak at 485 nm, suggesting their potential applications in light and electron emission devices. [ABSTRACT FROM AUTHOR]

The bromodomain and extra-terminal (BET) family proteins, consisting of BRD2, BRD3, BRD4, and testis-specific BRDT members, are epigenetic "readers" and play a key role in the regulation of gene transcription. BET proteins are considered to be attractive therapeutic targets for cancer and other human diseases. Recently, heterobifunctional small-molecule BET degraders have been designed based upon the proteolysis targeting chimera (PROTAC) concept to induce BET protein degradation. Herein, we present our design, synthesis, and evaluation of a new class of PROTAC BET degraders. One of the most promising compounds, 23, effectively degrades BRD4 protein at concentrations as low as 30 pM in the RS4;11 leukemia cell line, achieves an IC50 value of 51 pM in inhibition of RS4;11 cell growth and induces rapid tumor regression in vivo against RS4;11 xenograft tumors. These data establish that compound 23 (BETd-260/ZBC260) is a highly potent and efficacious BET degrader. [ABSTRACT FROM AUTHOR]

Controllable self-assembly of ordered and regularly patterned semiconductor nanoarchitectures is of great interest in achieving fantastic functionalities and properties of nanomaterials in nanodevices. Here we demonstrate a symmetric confined growth methodology for fabricating a geometrically patterned and well-oriented two-dimensional nanonet by a solution growth. A uniform orthogonal VO2 nanonet composed of single-crystalline nanowalls is self-assembled in a one-step process and exhibits single-crystal-like crystallographic characteristics. It is revealed that the 4-fold symmetric structure of (001) TiO2 determines the orthogonal geometrical pattern of the nanonet; in addition, the interfacial mismatch energy controls the horizontal growth direction and morphology of one-dimensional nanocrystals competing with the surface energy. The unique VO2 nanonet exhibits excellent thermochromic performances due to its self-generated porosity and sluggish phase transition. The initial optical modulation temperature is near room temperature. The solar modulating ability (ΔTsol) is up to 11.82% with the maximum visible light transmittance (Tvis-max) more than 70%. The proposed growth strategy could be adopted in more systems to perform self-assembly of regularly patterned nanoarchitectures with well interconnectivity and preferred orientation, which offers promising opportunities for exploiting potential nanodevices in various applications. [ABSTRACT FROM AUTHOR]

Here, we report photodynamic oncotherapies mediated by gonadotropin-releasing hormone (GnRH) receptors. We synthesized conjugates 1 and 2 by coupling zinc phthalocyanine (ZnPc) to GnRH analogues. Compared to unmodified ZnPc, conjugates 1 and 2 exhibited higher and more specific phototoxicities to breast cancer cells. Furthermore, the two conjugates demonstrated excellent antitumor efficacies in a breast cancer-grafted animal model. Biodistribution study suggested the high biosafety of conjugate 2 because of the low retention in brain and skin. [ABSTRACT FROM AUTHOR]

Rational structure design of microwave absorption material (MAM) is of fundamental significance in terms of enhancing the electromagnetic microwave absorption performance and deeply understanding the specific correlation between the material structure and its electromagnetic microwave absorption (EMA) performance. Here, bowl-like carbon nanoparticles (BLCNs) as novel MAM have been successfully fabricated via calcination of bowl-like polydopamine. Interestingly, BLCNs have exhibited dramatically enhanced EMA performance with a minimum reflection loss of -45.3 dB and an effective bandwidth of below -10 dB in the wide range of 4.2 GHz, implying the unique critical role of the microstructure in adjusting the EMA performance. Our work not only paves an attractive way for the design of advanced and lightweight MAM, but also provides valuable insights into the relationships between the material structure and its EMA performance. [ABSTRACT FROM AUTHOR]

Various interferences from measurement conditions and substrate inhomogeneity are well-known confounding factors for poor reproducibility, which is a challenge in surface-enhanced Raman scattering (SERS) quantification. To address these issues, novel substrates and versatile internal standards have been designed and the repeatability is improved to some degree. However, these internal standards are either complex or unstable enough to resist harsh environments such as acid and oxidation. Graphene-isolated-Au-nanocrystal (GLAN) has unique properties and been applied for cell multimodal imaging and chemotherapy but not for SERS quantification analysis yet. Herein, we chose GLANs to improve the accuracy of SERS analysis. GIAN integrates the SERS effect and internal standard into a simple nanoparticle and is proved to be an ideal platform for SERS analysis given its superior properties: (l) chemical stability, it remains stable in strong acid and oxidation, even mimic bioenvironment; (2) a simple core--shell structure, with a thin graphitic shell which is not only a protector that avoiding inner Au catalysis unnecessary reaction but also an internal standard to eliminate the interference during the Raman detections; (3) the big-IT structure can absorb target molecule thus achieve an enrichment effect and quench background fluorescence. Laser power, focus, and substrate fluctuations as well as coexist substance interferences were investigated and the accuracy was improved greatly with the introduction of 2D band internal standard in Raman silent region with less background. Moreover, GIAN was applied for crystal violet determination directly on fish muscle and scale, which was rapid and convenient without complex extraction process. All these results indicate GIAN is an optimum choice for SERS analysis in complex systems. [ABSTRACT FROM AUTHOR]

FLT3 has been validated as a therapeutic target for the treatment of acute myeloid leukemia (AML). In this paper, we describe for the first time, pteridin-7(8H)-one as a scaffold for potent FLT3 inhibitors derived from structural optimizations on irreversible EGFR inhibitors. The representative inhibitor (31) demonstrates single-digit nanomolar inhibition against FLT3 and subnanomolar KD for drug-resistance FLT3 mutants. In profiling of the in vitro tumor cell lines, it shows good selectivity against AML cells harboring FLT3-ITD mutations over other leukemia and solid tumor cell lines. The mechanism of action study illustrates that pteridin-7(8H)-one derivatives suppress the phosphorylation of FLT3 and its downstream pathways, thereby inducing G0/G1 cell cycle arrest and apoptosis in AML cells. In in vivo studies, 31 significantly suppresses the tumor growth in MV4-11 xenograft model. Overall, we provide a structurally distinct chemical scaffold with which to develop FLT3 mutants-selective inhibitors for AML treatment. [ABSTRACT FROM AUTHOR]

With their unique optical properties and distinct Raman signatures, graphitic nanomaterials can serve as substrates for surface-enhanced Raman spectroscopy (SERS) or provide signal amplification for bioanalysis and detection. However, a relatively weak Raman signal has limited further biomedical applications. This has been addressed by encapsulating gold nanorods (AuNRs) in a thin graphitic shell to form gold graphitic nanocapsules. This step improves plasmon resonance, which enhances Raman intensity, and has the potential for integrating two-photon luminescence (TPL) imaging capability. However, changing the morphology of gold graphitic nanocapsules such that high quality and stability are achieved remains a challenge. To address this task, we herein report a confinement chemical vapor deposition (CVD) method to prepare the construction of AuNR-encapsulated graphitic nanocapsules with these properties. Specifically, through morphological modulation, we (1) achieved higher plasmon resonance with near-IR incident light, thus achieving greater Raman intensity, and (2) successfully integrated two-photon luminescence dual-modal (Raman/TPL) bioimaging capabilities. Cancer-cell-specific aptamers were further modified on the AuNR@G graphitic surface through simple, but strong, π-π interactions to achieve imaging selectivity through differential cancer cell recognition. [ABSTRACT FROM AUTHOR]

Sulfhydryl-containing proteins play critical roles in various physiological and biological processes, and the activities of those proteins have been reported to be susceptible to thiol oxidation. Therefore, the development of protein thiol target fluorescent probe is highly desirable. In the present work, a biotinylated coumarin fluorescence "off-on" probe SQ for selectively detecting protein thiols in biotin receptor-positive cancer cells was designed with a 2,4-dinitrobenzenesulfony as the thiol receptor. The probe exhibited dramatic fluorescence responses toward sulfhydryl-containing proteins (ovalbumin (OVA), bovine serum albumin (BSA)): up to 170-fold fluorescence enhancement with 70 nm blue-shift was observed with the addition of OVA. However, low molecular weight thiols (Cys, glutathione (GSH), Hey) caused negligible fluorescence changes of SQ In addition, biotin receptor-positive Hela cells displayed strong red and green fluorescence after incubation of SQfor 1 h; neither red nor green fluorescence signal could be visualized in biotin-negative normal lung Wi38 cells. These results imply that the probe has potential application in fluorescent imaging protein thiols on the surface of Hela cells. [ABSTRACT FROM AUTHOR]

Photoactivatable probe-based fluorescent imaging has become an efficient and attractive technique for spatiotemporal microscopic studies of biological events. However, almost all previously reported photoactivatable organic probes have been based on hydrosoluble precursors, which have produced water-soluble active fluorophores able to readily diffuse away from the photocleavage site, thereby dramatically reducing spatial resolution. Hydroxyphenylquinazolinone (HPQ), a small organic dye known for its classic luminescence mechanism through excited-state intramolecular proton transfer (ESIPT), shows strong light emission in the solid state, but no emission in solution. In this work, HPQ was employed as a precursor to develop a localizable, photoactivatable two-photon probe (PHPQ) for spatiotemporal bioimaging applications. After photocleavage, PHPQ releases a precipitating HPQ fluorophore which shows both one-photon and two-photon excited yellow-green fluorescence, thereby producing a localizable fluorescence signal that affords high spatial resolution for bioimaging, with more than 200-fold one-photon and 150-fold two-photon fluorescence enhancement. [ABSTRACT FROM AUTHOR]

Many one-photon fluorescence-based theranostic nanosystems have been developed for simultaneous therapeutic intervention/monitoring for various types of cancers. However, for early diagnosis of cancer, two-photon fluorescence microscopy (TPFM) can realize deep-tissue imaging with higher spatial resolution. In this study, we first report a multiple functional nanoprobe for contrast-enhanced bimodal cellular imaging and targeted therapy. Components of the nanoprobe include (1) two-photon dye-doped mesoporous silica nanoparticles (TPD-MSNs); (2) MnO2 nanosheets that act as a (i) gatekeeper for TPD-MSNs, (ii) quencher for TP fluorescence, and (iii) contrast agent for MRlj (3) cancer cell-targeting aptamers. Guided by aptamers, TPDMSNs are rapidly internalized into the target cells. Next, intracellular glutathione reduces Mn2 to Mn2+ ions, resulting in contrast-enhanced TP fluorescence and magnetic resonance signal for cellular imaging. Meanwhile, preloaded doxorubicin and Chlorin e6 are released for chemotherapy and photodynamic therapy, respectively, with a synergistic effect and significantly enhanced therapeutic efficacy. [ABSTRACT FROM AUTHOR]

DNA nanotechnology has been extensively explored to assemble various functional nanostructures for versatile applications. Mediated by Watson-Crick base-pairing, these DNA nanostructures have been conventionally assembled through hybridization of many short DNA building blocks. Here we report the noncanonical self-assembly of multifunctional DNA nanostructures, termed as nanoflowers (NFs), and the versatile biomedical applications. These NFs were assembled from long DNA building blocks generated via rolling circle replication (RCR) of a designer template. NF assembly was driven by liquid crystallization and dense packaging of building blocks, without relying on Watson-Crick base-pairing between DNA strands, thereby avoiding the otherwise conventional complicated DNA sequence design. NF sizes were readily tunable in a wide range, by simply adjusting such parameters as assembly time and template sequences. NFs were exceptionally resistant to nuclease degradation, denaturation, or dissociation at extremely low concentration, presumably resulting from the dense DNA packaging in NFs. The exceptional biostability is critical for biomedical applications. By rational design, NFs can be readily incorporated with myriad functional moieties. All these properties make NFs promising for versatile applications. As a proof-of-principle demonstration, in this study, NFs were integrated with aptamers, bioimaging agents, and drug loading sites, and the resultant multifunctional NFs were demonstrated for selective cancer cell recognition, bioimaging, and targeted anticancer drug delivery. [ABSTRACT FROM AUTHOR]

Ultrasmall inorganic oxide nanoparticles doped with trivalent lanthanide ions (Ln3+), a new and huge family of luminescent bioprobes, remain nearly untouched. Currently it is a challenge to synthesize biocompatible ultrasmall oxide bioprobes. Herein, we report a new inorganic oxide bioprobe based on sub-5 nm amine-functionalized tetragonal ZrO2-Ln3+ nanoparticles synthesized via a facile solvothermal method and ligand exchange. By utilizing the long-lived luminescence of Ln3+, we demonstrate its application as a sensitive time-resolved fluorescence resonance energy transfer (FRET) bioprobe to detect avidin with a record-low detection limit of 3.0 nM. The oxide nanoparticles also exhibit specific recognition of cancer cells overexpressed with urokinase plasminogen activator receptor (uPAR, an important marker of tumor biology and metastasis) and thus may have great potentials in targeted bioimaging. [ABSTRACT FROM AUTHOR]

Amine-functionalized lanthanide-doped KGdF4 nanocrystals, synthesized via a facile one-step solvothermal route by employing polyethylenimine as the surfactant and capping ligand, have been demonstrated to be sensitive time-resolved FRET bioprobes to detect a trace amount of biomolecules such as avidin at a concentration of 5.5 nM and to be potential T1-MRI contrast agents due to a large longitudinal relaxivity of Gd3+ (5.86 S-1mM-1 per Gd ion and 3.99 x 105 S-1mM-1 per nanocrystal). [ABSTRACT FROM AUTHOR]

Nano is one of the hottest topics in current science and technology. Characterizations of nanomaterials by high resolution transmission electron microscopy (TEM) are becoming indispensable today. To gain better performance of TEM, people are expecting a novel TEM grid of which the supporting film should be highly conductive, ultrathin but robust, and preferably nanoholey. Here we report a method of mass producing such a kind of carbon nanotube TEM grids. The supporting films are made by cross stacking ultrathin superaligned carbon nanotube films, resulting in a large number of nanosized holes and numerous effective edges. Together with the robustness, good conductivity, and strong adsorbability inherited from carbon nanotubes, these TEM grids show much better performance than conventional amorphous carbon grids. [ABSTRACT FROM AUTHOR]

The Joule-heating-induced vacuum breakdown of the carbon nanotube (CNT) yarns was studied. Wall-by-wall breakdown and superplastic deformation of CNTs are the main physical processes at the hottest location before breakdown. The two ends at the breaking point are needle-shaped with surfaces rich in tightly compacted conelike CNT bundles with a single CNT at the tips. Both of the ends can provide emission currents of over 150 A within an area 5 m in diameter; the cathode ends start field emission at a lower voltage. Laser irradiation was introduced to control the breaking location making the methodology more practical. Small pixels were constructed with the yarn emitter cathodes, which are potentially building blocks of large outdoor displays. [ABSTRACT FROM AUTHOR]

EGFR-targeted inhibitors (gefitinib and erlotinib) provided an effective strategy for the treatment of non-small-cell lung cancer. However, the EGFR T790M secondary mutation has become a leading cause of clinically acquired resistance to these agents. Herein, on the basis of the previously reported irreversible EGFR inhibitor (compound 9), we present a structure-based design approach, which is rationalized via analyzing its binding model and comparing the differences of gatekeeper pocket between the T790M mutant and wild-type (WT) EGFR kinases. Guided by these results, a novel 6,7-dioxo-6,7-dihydropteridine scaffold was discovered and hydrophobic modifications at N5-position were conducted to strengthen nonpolar contacts and improve mutant selectivity over EGFRWT. Finally, the most representative compound 17d was identified. This work demonstrates the power of structure-based strategy in discovering lead compounds and provides molecular insights into the selectivity of EGFRL858R/T790M over EGFRWT, which may play an important role in designing new classes of mutant-selective EGFR inhibitors. [ABSTRACT FROM AUTHOR]