Facile synthesis of surfactant-free Au cluster/graphene hybrids for high-performance oxygen reduction reaction

Development of a Nanostructured α-MnO2/Carbon Paper Composite for Removal of Ni2+/Mn2+ Ions by Electrosorption

Toxic metal ions, such as Ni²⁺ and Mn²⁺, in industrial waste streams are nonbiodegradable and can cause damage to the human body. Electrochemical cleaning techniques are attractive as they offer more control and produce less sludge than do chemical/biological approaches without the high pressures needed for membranes. Here, nanoneedle-structured α-MnO₂/carbon fiber paper (CFP) composites were synthesized by a hydrothermal approach and used as electrodes for combined electroadsorption and capacitive deionization removal of nickel and manganese ions from pseudoindustrial waste streams. The specific performance of α-MnO₂/CFP (16.4 mg Ni²⁺ per g of active material) not only shows a great improvement in comparison with its original CFP substrate (0.034 Ni²⁺ mg per g), but also is over 6 times that of activated carbon (2.5 mg Ni²⁺ per g). The high performance of α-MnO₂/CFP composites is attributed to their high surface area, desirable mesoporosity, pore-size distribution that permits the further access of ions, and their property as a pseudocapacitor, which contributes to a more efficient electron/charge transfer in the faradic process. Unfortunately, it was also found that some Mn²⁺ ions are released due to the partial reduction of MnO₂ when operated as a negative electrode. For the removal of Mn²⁺ ions, an asymmetric arrangement, consisting of a MnO₂/CFP positive electrode and an activated carbon negative electrode, was employed. This arrangement reduced the Mn²⁺ concentration from 100 ppm to less than 2 ppm, a vast improvement over the systematical two-activated carbon electrode system that could only reach 42 ppm under the same conditions. It was also observed that as long as the MnO₂/CFP composite was maintained as a positive electrode, it was completely stable. The technique was able to reduce both Ni²⁺ and Mn²⁺ ions to well below the 10 ppm requirement for discharge into public sewers in Singapore.

Dispersibility of carbon dots in aqueous and/or organic solvents

Carbon dots have a wide range of applications in biological and medical fields as an alternative to quantum dots because of their low toxicity and excellent luminescence properties. To date, a large number of carbon dots have been prepared and they were consequently reviewed according to their synthetic method, luminescence properties and related applications. The dispersibility of carbon dots in aqueous and/or organic solvents could actually play a significant role in the properties and various application fields, however, such a perspective is ignored by most of the reviewed literature studies. Thus in this minireview, we focus on the surfactant groups of carbon dots which could be classified as hydrophilic, hydrophobic and amphiphilic types. They have accordingly a marked impact on the dispersibility of carbon dots in different solvents as well as the further advantage in those imaging studies in vitro and in vivo.

Low-frequency polarization in molecular-scale noble-metal/metal-oxide nanocomposites

Materials with high dielectric permittivity are highly desirable in the electronics industry. One avenue for enhancing the permittivity of standard metal oxide and ceramic dielectrics is to incorporate nanoscale Ag and Au inclusions in the material. Given the small scale of modern day devices, these inclusions will necessarily be up to a few nanometers in size. We develop methodology by which polarization in nanocomposites with molecular-scale inclusions can be obtained from first-principles calculations, and partitioned into inclusion and matrix contributions. The methodology is applied to a model Ag8/MgO nanocomposite. A 4% volume loading of Ag8 nanoparticles leads to a 30% enhancement of the dielectric permittivity. The enhancement arises from both the electronic polarization of the nanoparticle and the additional polarization of matrix ions in the interfacial region.

Mesoporous Three-Dimensional Graphene Networks for Highly Efficient Solar Desalination under 1 sun Illumination

Solar desalination via thermal evaporation of seawater is one of the most promising technologies for addressing the serious problem of global water scarcity because it does not require additional supporting energy other than infinite solar energy for generating clean water. However, low efficiency and a large amount of heat loss are considered critical limitations of solar desalination technology. The combination of mesoporous three-dimensional graphene networks (3DGNs) with a high solar absorption property and water-transporting wood pieces with a thermal insulation property has exhibited greatly enhanced solar-to-vapor conversion efficiency. 3DGN deposited on a wood piece provides an outstanding value of solar-to-vapor conversion efficiency, about 91.8%, under 1 sun illumination and excellent desalination efficiency of 5 orders salinity decrement. The mass-producible 3DGN enriched with many mesopores efficiently releases the vapors from an enormous area of the surface by heat localization on the top surface of the wood piece. Because the efficient solar desalination device made by 3DGN on the wood piece is highly scalable and inexpensive, it could serve as one of the main sources for the worldwide supply of purified water achieved via earth-abundant materials without an extra supporting energy source.

Gold-Copper Aerogels with Intriguing Surface Electronic Modulation as Highly Active and Stable Electrocatalysts for Oxygen Reduction and Borohydride Oxidation

We, for the first time, report the successful synthesis of self-assembled AuCu aerogels by a one-pot kinetically controlled approach. A startling electronic modulation effect of Cu on Au was observed across the entire alloy composition range, for which the optimal upshift of the d-band center for the highest activities was 0.24 eV. Owing to the combination of a nanoporous architecture and a robust electronic effect, the Au₅₂ Cu₄₈ aerogels exhibited better catalytic performance for the oxygen reduction reaction (ORR) and the direct borohydride oxidation reaction (BOR) than commercial Pt/C catalysts. The specific and mass ORR activities were 4.5 and 6.3 times higher, respectively, on the Au₅₂ Cu₄₈ aerogels than on Pt/C with negligible activity decay even after 10 000 cycles and a duration of 40 000 s. For the BOR, the Au₅₂ Cu₄₈ aerogels also exhibited far better selectivity and activity than Pt/C. The new AuCu aerogels show great potential as a promising alternative for Pt-based catalysts in fuel cells.

Platinized spherical supramolecular nanoassemblies of a porphyrin: facile synthesis and excellent catalytic recyclability

Porphyrin-based supramolecular nanoassemblies of a spherical morphology have been attracting broad interest owing to their wide application possibilities in numerous fields of paramount significance. Most of the existing assembly protocols, however, either suffer from the requirement of elaborately-designed yet tediously-synthesized ad hoc porphyrins, the use of surfactant templates, or accurate consideration of the experimental parameters etc. The initiation of a facile surfactant-free fabrication protocol performable under ambient conditions using commercial porphyrins as building blocks is strongly desired. We herein report that a commercial metal-free porphyrins, 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TPPNH2), could be facilely organized to form well-defined discrete spherical nanoassemblies at room temperature by means of a simple reprecipitation method. We further find that the as-manufactured TPPNH2 nanospheres could work as photocatalysts towards the reduction of potassium tetrachloroplatinate(ii), leading to their self-platinization and the production of platinum/porphyrin nanosphere nanocomposites, wherein ultrathin Pt nanoparticles of a size of ca. 3 nm are immobilized on the porphyrin nanospheres. Significantly, by taking the advantage of their easy sedimentation from aqueous suspensions, we show that the as-produced composites could serve as qualified heterogeneous nanocatalysts in terms of their excellent catalytic stability and recyclability towards the reduction of 4-nitrophenol, where the catalytic reactivity exhibits only trivial changes even after the reactions have been repeated 8 times continuously. Taking into account the general concerns of porphyrins- and Pt-based nanostructures, this might provide a facile method for the construction of spherical porphyrin nanostructures with self-platinization capability. Meanwhile, considering the high cost and scarcity of Pt, our nanocomposites with excellent stability and recyclability likely have a bright future of potential uses.

Dilute Au-Containing Ag Nanosponges as a Highly Active and Durable Electrocatalyst for Oxygen Reduction and Alcohol Oxidation Reactions

Zero-dimensional nanoparticles (NPs) have been demonstrated as the promising class of catalysts for various chemical and electrochemical reactions. However, the emerging Au-Ag NP catalysts suffer from single functionality, limited activity enhancement, and unsatisfactory stability problems. Here, we report a facile kinetically controlled solution method to prepare a new class of Au-Ag nanoporous sponges (NSs) composed of three-dimensional networks without using additional stabilizing agents at room temperature. The unexpected shift of the d-band center in our Au-Ag NSs was observed for the first time in Au-Ag bimetallic systems, which effectively activates the Au-Ag NSs for electrochemical reactions. The robust electronic effect coupled with abundant accessible active sites from the hierarchically porous architecture make the bare Au-Ag NSs a superior multifunctional catalyst for oxygen reduction, ethylene glycol (EG) oxidation, and glucose oxidation reactions compared to the commercial Pt/C electrocatalyst in alkaline medium. The optimized AuAg_3.2 NSs deliver a mass activity of 1.26 A mg_Au^-1 toward oxygen reduction reaction, which is ∼8.2 times as high as that of the Pt/C electrocatalyst, simultaneously showing outstanding stability with negligible activity decay after 10 000 cycles. For the anodic reactions, these AuAg_3.2 NSs show extremely high activity and stability toward both EG and glucose catalytic oxidation reactions with a higher mass activity of 7.58 and 1.48 A mg_Au^-1, about 3- and 18.5-fold enhancement than Pt/C, respectively. This work provides important insights into the structural design, performance optimization, and cost reduction to promote the practical applications of liquid fuel cells.

A novel electrocatalytic nanocomposite of reduced graphene oxide/silver nanocube hybrid decorated imprinted polymer for ultra-trace sensing of temozolomide

A new nanocomposite of reduced graphene oxide/silver nanocube hybrid decorated molecularly imprinted polymer at the surface of a screen-printed carbon electrode was developed for the electroanalysis of an anticancerous drug, temozolomide, at the ultra-trace level.

Ligand-regulated ORR activity of Au nanoparticles in alkaline medium: the importance of surface coverage of ligands

The surface coverage of ligands instead of their diverse chemical nature dominates the ORR activity and selectivity of AuNPs.

Highly-effective palladium nanoclusters supported on para-sulfonated calix[8]arene-functionalized carbon nanohorns for ethylene glycol and glycerol oxidation reactions

Non-Pt noble metal clusters like Pd clusters are considered as promising electrocatalysts for fuel cells, but they suffer from problems such as easy aggregation during the catalysis reactions.

Naked Au nanoparticles monodispersed onto multifunctional cellulose nanocrystal–graphene hybrid sheets: towards efficient and sustainable heterogeneous catalysts

A synthesis method has been developed for deposition of ∼3 nm monodisperse gold nanoparticles onto cellulose nanocrystal–graphene hybrid sheets.

A Microribbon Hybrid Structure of CoOx-MoC Encapsulated in N-Doped Carbon Nanowire Derived from MOF as Efficient Oxygen Evolution Electrocatalysts

Developing highly efficient electrocatalysts for oxygen evolution is vital for renewable and sustainable energy production and storage. Herein, nitrogen-doped carbon encapsulated CoOx-MoC heterostructures are reported for the first time as high performance oxygen evolution electrocatalysts. The composition can be tuned by the addition of a Mo source to form a nanowire-assembled hierarchically porous microstructure, which can enlarge the specific surface area, thus exposing more active sites, facilitating mass transport and charge transfer. Moreover, it is demonstrated that the formation of CoOx-MoC heterostructures and the resulting synergistic effect between MoC and Co facilitate the reaction kinetics, leading to significantly improved oxygen evolution reaction (OER) activity with an onset overpotential of merely 290 mV, and a low overpotential of 330 mV to afford a current density of 10 mA cm^-2 . The well-constructed microarchitecture contributes to superior long term stability electrochemical behaviors. This work provides a facile strategy via composition tuning and structure optimization for the development of next-generation nonprecious metal-based OER electrocatalysts.

Synthesis of Ultrafine and Highly Dispersed Metal Nanoparticles Confined in a Thioether-Containing Covalent Organic Framework and Their Catalytic Applications

Covalent organic frameworks (COFs) with well-defined and customizable pore structures are promising templates for the synthesis of nanomaterials with controllable sizes and dispersity. Herein, a thioether-containing COF has been rationally designed and used for the confined growth of ultrafine metal nanoparticles (NPs). Pt or Pd nanoparticles (Pt NPs and Pd NPs) immobilized inside the cavity of the COF material have been successfully prepared at a high loading with a narrow size distribution (1.7 ± 0.2 nm). We found the crystallinity of the COF support and the presence of thioether groups inside the cavities are critical for the size-controlled synthesis of ultrafine NPs. The as-prepared COF-supported ultrafine Pt NPs and Pd NPs show excellent catalytic activity respectively in nitrophenol reduction and Suzuki-Miyaura coupling reaction under mild conditions and low catalyst loading. More importantly, they are highly stable and easily recycled and reused without loss of their catalytic activities. Such COF-supported size-controlled synthesis of nanoparticles will open a new frontier on design and preparation of metal NP@COF composite materials for various potential applications, such as catalysis and development of optical and electronic materials.

Self-template synthesis of biomass-derived 3D hierarchical N-doped porous carbon for simultaneous determination of dihydroxybenzene isomers

Nitrogen doped hierarchical porous carbon materials (HPCs) was achieved by the successful carbonization, using pig lung as biomass precursor. Three-dimensional HPCs constituted with sheets and lines were synergistically inherited from original pig lung. Such structure provided a large specific surface area (958.5 g-1 m2) and rich porous, effectively supported a large number of electro-active species, and greatly enhanced the mass and electron transfer. High graphitization degree of HPCs resulted in good electrical conductivity. Furthermore, the different electronegativity between nitrogen and carbon atoms in HPCs could affect the electron cloud distribution, polarity and then the electrochemical oxidation kinetics of dihydroxybenzene isomers. Based on these characteristics of HPCs, the electrochemical sensor for dihydroxybenzene isomers exhibited high sensitivity, excellent specificity and stability. Quantitative analysis assays by differential pulse voltammetry (DPV) technology showed that the sensor has wide linear ranges (0.5-320, 0.5-340 and 1-360 μmol L-1) and low detection limits (0.078, 0.057 and 0.371 μmol L-1) for the catechol, resorcinol and hydroquinone, respectively. This proposed method was successfully applied for simultaneous detection of dihydroxybenzene isomers in river water.

A Chiral-Nanoassemblies-Enabled Strategy for Simultaneously Profiling Surface Glycoprotein and MicroRNA in Living Cells

Assemblies of nanomaterials for biological applications in living cells have attracted much attention. Herein, graphene oxide (GO)-gold nanoparticle (Au NP) assemblies are driven by a splint DNA strand, which is designed with two regions at both ends that are complementary with the DNA sequence anchored on the surface of the GO and the Au NPs. In the presence of microRNA (miR)-21 and epithelial cell-adhesion molecule (EpCAM), the hybridization of miR-21 with a molecular probe leads to the separation of 6-fluorescein-phosphoramidite-modified Au NPs from GO, resulting in a decrease in the Raman signal, while EpCAM recognition reduces circular dichroism (CD) signals. The CD signals reverse from negative in original assemblies into positive when reacted with cells, which correlates with two enantiomer geometries. The EpCAM detection has a good linear range of 8.47-74.78 pg mL^-1 and a limit of detection (LOD) of 3.63 pg mL^-1 , whereas miR-21 detection displays an outstanding linear range of 0.07-13.68 amol ng^-1_RNA and LOD of 0.03 amol ng^-1_RNA . All the results are in good agreement with those of the Raman and confocal bioimaging. The strategy opens up an avenue to allow the highly accurate and reliable diagnosis (dual targets) of clinic diseases.

Nitrogen and Fluorine-Codoped Porous Carbons as Efficient Metal-Free Electrocatalysts for Oxygen Reduction Reaction in Fuel Cells

The severe dependence of oxygen reduction reaction (ORR) in fuel cells on platinum (Pt)-based catalysts greatly limits the process of their commercialization. Therefore, developing cost-reasonable non-precious-metal catalysts to replace Pt-based catalysts for ORR is an urgent task. Here, we use the composite of inexpensive polyaniline and superfine polytetrafluoroethylene powder as precursor to synthesize a metal-free N,F-codoped porous carbon catalyst (N,F-Carbon). Results indicate that the N,F-Carbon catalyst obtained at the optimized temperature 1000 °C exhibits almost the same onset (0.97 V vs RHE) and half-wave potential (0.84 V vs RHE) and better durability and higher crossover resistance in alkaline medium compared to commercial 20% Pt/C, which is attributed to the good dispersion of fluorine and nitrogen atoms in the carbon matrix, high specific surface area, and the synergistic effects of fluorine and nitrogen on the polarization of adjacent carbon atoms. This work provides a new strategy for in situ synthesis of N,F-codoped porous carbon as highly efficient metal-free electrocatalyst for ORR in fuel cells.

Promoting the Electrochemical Performances by Chemical Depositing of Gold Nanoparticles Inside Pores of 3D Nitrogen-Doped Carbon Nanocages

Carbon Nanomaterials are excellent electrode materials due to their extraordinary conductivity, prolific structures, and morphologies. Herein, a novel nanocarbon-based material (Au@NCNC) was synthesized by embedding gold nanoparticles (AuNPs) inside the pores of three-dimensional hierarchical nitrogen-doped carbon nanocages (NCNC) through an in situ chemical deposition method. The resultant Au@NCNC was employed as an electrochemical catalyst for the oxygen reduction reaction (ORR) and as an electrode material for supercapacitors. The conductivity and hydrophilicity of Au@NCNC were much more improved than those of pristine NCNC. Meanwhile, the bubble adhesive force on the Au@NCNC film was much lower underwater than that of NCNC, which provided easy accessibility to the active sites of reactants, such as hydrated O₂. Therefore, the deposition of AuNPs inside pores of NCNC facilitated the transfer of electrons and diffusion of ions, promoting the electrocatalytic performance of Au@NCNC. As a result, Au@NCNC exhibited high performance toward ORR, which manifested in high numbers of electron transfer (3.7-3.9), high kinetic current density, enhanced electrocatalytic stability, and remarkable methanol durability. Moreover, Au@NCNC displayed high specific capacitance, good rate capability, and cycling stability with ∼97% of its initial capacitance retained at the high current density of 10 A g^-1 after 5000 cycles. This could be attributed to the synergetic effect of ultrafine gold nanoparticles, the hierarchical porous structure, and the hydrophilic surface of NCNC as well. This work offers an excellent alternative for Pt-based catalysts in fuel cells, ORR, and supercapacitive electrode materials by enhancing the conductivity and surface hydrophilicity of electrocatalysts.

In Situ Growth of Clean Pd Nanoparticles on Polystyrene Microspheres Assisted by Functional Reduced Graphene Oxide and Their Excellent Catalytic Properties

Herein an in situ growth of clean palladium nanoparticles (Pd NPs) on functional reduced graphene oxide (RGO)-coated polystyrene (PS) microspheres is achieved by a simple two-step process. On the basis of the hydrophobic interaction and π-electron interaction, the PS/RGO composite particles are first prepared by the reduction of graphene oxide in the presence of PS microspheres. Second, without using any additional reducing agent or stabilizer, the clean Pd NPs grow in situ on the surface of PS/RGO composite particles in water through a spontaneous redox reaction between Pd²⁺ and RGO. Significantly, owing to the stabilizer-free surface of Pd NPs and the synergistic effect of RGO and Pd NPs, the resultant PS/RGO@Pd composite particles feature pronounced catalytic activity toward the reduction of p-nitrophenol and Suzuki coupling reactions. Moreover, the catalyst particles can be easily recovered by centrifugation because of the large size of support microspheres and recycled consecutively.

Selective Bromination of Graphene Oxide by the Hunsdiecker Reaction

Halogenated graphenes have been attracting great attention in the recent years. The currently used methods are usually non-specific, and halogen groups are randomly distributed over the graphene. Here we demonstrate a selective graphene functionalization based on a well known reaction mechanism-Hunsdiecker reaction-applied on selective bromination of graphene oxide. The chemical analysis using various spectroscopic methods proved a high efficiency of this functionalization method. Bromination can be carried out under mild conditions without any high temperature or high pressure treatment. The chemical modification led to introduction of up to 20 wt.% of bromine covalently bonded to the graphene skeleton. The modified graphene was characterized in detail using a broad range of microscopic and spectroscopic methods and no significant contamination by reaction by-products was detected.

Single-Atomic Ruthenium Catalytic Sites on Nitrogen-Doped Graphene for Oxygen Reduction Reaction in Acidic Medium

The cathodic oxygen reduction reaction (ORR) is essential in the electrochemical energy conversion of fuel cells. Here, through the NH₃ atmosphere annealing of a graphene oxide (GO) precursor containing trace amounts of Ru, we have synthesized atomically dispersed Ru on nitrogen-doped graphene that performs as an electrocatalyst for the ORR in acidic medium. The Ru/nitrogen-doped GO catalyst exhibits excellent four-electron ORR activity, offering onset and half-wave potentials of 0.89 and 0.75 V, respectively, vs a reversible hydrogen electrode (RHE) in 0.1 M HClO₄, together with better durability and tolerance toward methanol and carbon monoxide poisoning than seen in commercial Pt/C catalysts. X-ray adsorption fine structure analysis and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy are performed and indicate that the chemical structure of Ru is predominantly composed of isolated Ru atoms coordinated with nitrogen atoms on the graphene substrate. Furthermore, a density function theory study of the ORR mechanism suggests that a Ru-oxo-N₄ structure appears to be responsible for the ORR catalytic activity in the acidic medium. These findings provide a route for the design of efficient ORR single-atom catalysts.

Graphitic carbon nitride supported platinum nanocomposites for rapid and sensitive colorimetric detection of mercury ions

In this study, graphitic carbon nitride supported platinum nanocomposites (g-C₃N₄/PtNPs) have been synthesized for the first time by an ultrasonic-assisted chemical reduction method. By using g-C₃N₄ as the stabilizer, Pt ions could be reduced to PtNPs by NaBH₄ and uniformly deposited on the surface of g-C₃N₄. The resulting g-C₃N₄/PtNPs exhibited enhanced catalytic activity for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) compared to that of g-C₃N₄ or PtNPs alone. After interaction with Hg²⁺, the catalytic activity of g-C₃N₄/PtNPs was effectively inhibited due to the formation of HgPt amalgam. On the basis of this effect, a novel label free colorimetric sensor has been developed for sensitive detection of Hg²⁺ through the g-C₃N₄/PtNPs mediated catalytic reaction. A detection limit as low as 1.23 nM was achieved. This assay also exhibited excellent selectivity toward Hg²⁺ over other metal ions. In addition, it was successfully applied to the determination of Hg²⁺ in real water samples. In view of the advantages, such as simple operation, cost-effective, rapid response and naked-eye observation, the developed colorimetric sensor hold great potential for the detection of toxic Hg²⁺ in environmental and biological samples.

Ultrasensitive multiplexed immunoassay of autophagic biomarkers based on Au/rGO and Au nanocages amplifying electrochemcial signal

A novel sandwich-assay electrochemical immunosensor for simultaneous determination of autophagic biomarkers was introduced for the first time, the gold-reduced grapheme oxide nanocomposite (Au/r-GO) set as a good conductive platform with super high specific area, and provided more binding sites for the both antibodies of Beclin-1 and LC3B-II. While Au nanocages (AuNCs) served as good conductive platform to encapsulate a large amount of redox probe and secondary antibodies for signal amplification, due to the abundant reactive oxygen functional groups on its surface. Through differential pulse voltammetry (DPV) measurements, two separate signals can be detected directly in a single run, which represent the existence of Belin-1 and LC3B-II. Under optimized conditions, the electrochemical immunosensor exhibited good sensitivity and selectivity for the simultaneous determination of Beclin-1 and LC3B-II with linear ranges of 0.1–100 ng/mL. The detection limit for Beclin-1 and LC3B-II is 0.02 and 0.03 ng/mL respectively. This method was also applied for the analysis of Beclin-1 and LC3B-II levels in experimental cellular protein lysates, and the results were in good agreement with those of enzyme linked immunosorbent assay. This approach gives a promising simple, sensitive and quantitative strategy for the detection of autophagy

CO2/Water Emulsions Stabilized by Partially Reduced Graphene Oxide

Using functional materials to stabilize emulsions of carbon dioxide (CO₂) and water is a promising way to expand the utility of CO₂ and functional materials. Here we demonstrate for the first time that the partially reduced graphene oxide (rGO) can well stabilize the emulsion of CO₂ and water without the aid of any additional emulsifier or surface modification for rGO. More interestingly, such a novel kind of emulsion provides a facile and versatile route for constructing highly porous three-dimensional rGO materials, including rGO, metal/rGO, and metal oxide/rGO networks. The as-synthesized Au/rGO composite is highly active in catalyzing 4-nitrophenol reduction and styrene epoxidation.

Development of a Novel Electrochemical Sensor for Determination of Matrine in Sophora flavescens

A simple and sensitive electrochemical sensor fabricated with graphene nanosheets (GNs) and a hydroxyapatite (HA) nanocomposite-modified glassy carbon electrode (GCE) was developed for the determination of matrine (MT). The as-prepared electrode (GNs/HA/GCE) was verified to outperform bare a GCE and GNs-modified electrode with increased oxidation peak currents and the decreased over-potential in the redox process of MT, indicating the great enhancement of electrocatalytic activity toward the oxidation of MT by the composite of GNs and HA. Under the optimized conditions, the oxidation peak currents were related linearly with the concentration of MT, ranging from 2 μM to 3 mM, and the detection limit (S/N = 3) was 1.2 μM. In addition, the proposed electrochemical sensor can be successfully applied in the quantitative determination of MT in Sophora flavescens extract.

Ultrasensitive electrochemical detection of Dicer1 3'UTR for the fast analysis of alternative cleavage and polyadenylation

Alternative cleavage and polyadenylation (APA) is involved in several important biological processes in animals, e.g. cell growth and development, and cancer progression. The increasing data show that cancer cells are inclined to produce mRNA isoforms with a shortened 3'UTR undergoing APA. For example, the Dicer1 isoform with a shorter 3'untranslated region (3'UTR) was found to be overexpressed in some cancer cells, which may be used as a potential novel prognostic biomarker for cancer. In the present work, a novel electrochemical biosensor for ultrasensitive determination of Dicer1 was designed by using gold nanoparticles and p-sulfonated calix[6]arene functionalized reduced graphene oxide (Au@SCX6-rGO) as nanocarriers. The results showed that the expressions of the shorter 3'UTR (Dicer1-S) both in BT474 and SKBR3 were obviously higher than those of the longer Dicer1 (Dicer1-L) by the constructed biosensor, which agreed well with the result analyzed by the RT-qPCR method. The detection ranges of Dicer1-S and Dicer1-L were 10^-14-10^-9 M and 10^-15-10^-10 M. The LODs were 3.5 and 0.53 fM. The specificity of the proposed biosensor was also very high. For the first time, the expressional analysis of different 3'UTRs caused by APA was studied by an electrochemical method. Moreover, the use of a macrocyclic host for constructing an electrochemical/biosensing platform has rarely been reported. The proposed electrochemical sensing strategy is thus expected to provide a new method for determination of novel biomarkers and a novel method for fast and cheap analysis of APA.

Spectroscopic investigation on porphyrins nano-assemblies onto gold nanorods

The interaction between gold nanorods (Au NRs), synthesized by a conventional seeded growth protocol, and the anionic tetrakis-(4-sulfonatophenyl)porphyrin (TPPS₄) has been investigated through various spectroscopic techniques. At neutral pH, the formation of H-aggregates and the inclusion of porphyrin monomers in CTAB micelles covering the nanorods have been evidenced. Under mild acidic conditions (pH=3) a nano-hybrid assembly of porphyrin J-aggregates and Au NRs has been revealed. For the sake of comparison, Cu(II) and Zn(II) metal porphyrin derivatives as well as a cationic porphyrin have been studied in the same experimental conditions, showing that: i) CuTPPS₄ forms porphyrin H-dimers onto the Au NRs; ii) ZnTPPS₄ undergoes to demetallation, followed by acidification of the central core and eventually aggregation onto Au NRs; iii) cationic porphyrin does not interact with Au NRs.