Surface charge as activity descriptors for electrochemical CO2 reduction to multi-carbon products on organic-functionalised Cu.

Intensive research in electrochemical CO2 reduction reaction has resulted in the discovery of numerous high-performance catalysts selective to multi-carbon products, with most of these catalysts still being purely transition metal based. Herein, we present high and stable multi-carbon products selectivity of up to 76.6% across a wide potential range of 1 V on histidine-functionalised Cu. In-situ Raman and density functional theory calculations revealed alternative reaction pathways that involve direct interactions between adsorbed histidine and CO2 reduction intermediates at more cathodic potentials. Strikingly, we found that the yield of multi-carbon products is closely correlated to the surface charge on the catalyst surface, quantified by a pulsed voltammetry-based technique which proved reliable even at very cathodic potentials. We ascribe the surface charge to the population density of adsorbed species on the catalyst surface, which may be exploited as a powerful tool to explain CO2 reduction activity and as a proxy for future catalyst discovery, including organic-inorganic hybrids.

Protein Induces Layer-by-Layer Exfoliation of Transition Metal Dichalcogenides.

Here, we report a general and facile method for effective layer-by-layer exfoliation of transition metal dichalcogenides (TMDs) and graphite in water by using protein, bovine serum albumin (BSA) to produce single-layer nanosheets, which cannot be achieved using other commonly used bio- and synthetic polymers. Besides serving as an effective exfoliating agent, BSA can also function as a strong stabilizing agent against reaggregation of single-layer nanosheets for greatly improving their biocompatibility in biomedical applications. With significantly increased surface area, single-layer MoS2 nanosheets also exhibit a much higher binding capacity to pesticides and a much larger specific capacitance. The protein exfoliation process is carefully investigated with various control experiments and density functional theory simulations. It is interesting to find that the nonpolar groups of protein can firmly bind to TMD layers or graphene to expose polar groups in water, facilitating the effective exfoliation of single-layer nanosheets in aqueous solution. The present work will enable to optimize the fabrication of various 2D materials at high yield and large scale, and bring more opportunities to investigate the unique properties of 2D materials and exploit their novel applications.

Colloidal synthesis and photocatalytic properties of orthorhombic AgGaS2 nanocrystals.

AgGaS2 (AGS) nanocrystals that exist in the orthorhombic phase were successfully prepared for the first time through a one-pot colloidal synthetic strategy using suitable coordinating solvents. These orthorhombic AGS nanocrystals were found to display great potential in visible-light-driven photocatalysis.

Convenient purification of gold clusters by co-precipitation for improved sensing of hydrogen peroxide, mercury ions and pesticides.

An effective separation process is developed to remove free protein from the protein-protected gold clusters via co-precipitation with zinc hydroxide on their surface. After dialysis, the purified clusters exhibit an enhanced fluorescence for improved sensitive detection and selective visualization.

Glucosamine-conjugated nanoparticles for the separation of insulin-secreting beta cells.

A small molecule, glucosamine, is used as targeting moiety for insulin-secreting beta cell separation in artificial cell mixtures and tissue samples. The specificity of glucosamine allows it to be used in cell sorting applications. In addition, a thrombin-specific cleavable peptide was used as an intermediary to release nanoparticles from cell surfaces to facilitate cell attachment and proliferation.

Surface-functionalized nanoparticles for biosensing and imaging-guided therapeutics.

In this article, the very recent progress of various functional inorganic nanomaterials is reviewed including their unique properties, surface functionalization strategies, and applications in biosensing and imaging-guided therapeutics. The proper surface functionalization renders them with stability, biocompatibility and functionality in physiological environments, and further enables their targeted use in bioapplications after bioconjugation via selective and specific recognition. The surface-functionalized nanoprobes using the most actively studied nanoparticles (i.e., gold nanoparticles, quantum dots, upconversion nanoparticles, and magnetic nanoparticles) make them an excellent platform for a wide range of bioapplications. With more efforts in recent years, they have been widely developed as labeling probes to detect various biological species such as proteins, nucleic acids and ions, and extensively employed as imaging probes to guide therapeutics such as drug/gene delivery and photothermal/photodynamic therapy.

Quantum dot coating of baculoviral vectors enables visualization of transduced cells and tissues.

Imaging of transduced cells and tissues is valuable in developing gene transfer vectors and evaluating gene therapy efficacy. We report here a simple method to use bright and photostable quantum dots to label baculovirus, an emerging gene therapy vector. The labeling was achieved through the non-covalent interaction of glutathione-capped CdTe quantum dots with the virus envelope, without the use of chemical conjugation. The quantum dot labeling was nondestructive to viral transduction function and enabled the identification of baculoviral vector-transduced, living cells based on red fluorescence. When the labeled baculoviral vectors were injected intravenously or intraventricularly for in vivo delivery of a transgene into mice, quantum dot fluorescence signals allow us monitor whether or not the injected tissues were transduced. More importantly, using a dual-color whole-body imaging technology, we demonstrated that in vivo viral transduction could be evaluated in a real-time manner in living mice. Thus, our method of labeling a read-to-use gene delivery vector with quantum dots could be useful towards the improvement of vector design and will have the potential to assess baculovirus-based gene therapy protocols in future.

Aqueous synthesis of highly luminescent AgInS2-ZnS quantum dots and their biological applications.

Highly emissive and air-stable AgInS2-ZnS quantum dots (ZAIS QDs) with quantum yields of up to 20% have been successfully synthesized directly in aqueous media in the presence of polyacrylic acid (PAA) and mercaptoacetic acid (MAA) as stabilizing and reactivity-controlling agents. The as-prepared water-dispersible ZAIS QDs are around 3 nm in size, possess the tetragonal chalcopyrite crystal structure, and exhibit long fluorescence lifetimes (>100 ns). In addition, these ZAIS QDs are found to exhibit excellent optical and colloidal stability in physiologically relevant pH values as well as very low cytotoxicity, which render them particularly suitable for biological applications. Their potential use in biological labelling of baculoviral vectors is demonstrated.

Multicomponent fibers by multi-interfacial polyelectrolyte complexation.

In multi-interfacial polyelectrolyte complexation (MIPC), fusion of nascent fibers from multiple interfaces brings the interfaces to a point from which a composite fiber is drawn. MIPC applied to two, three, and four polyelectrolyte complex interfaces leads to various patterned multicomponent fibers. Cells encapsulated in these fibers exhibit migration, aggregation and spreading in relation to the initial cell or matrix pattern.

Effects of quantum dots on different renal proximal tubule cell models and on gel-free renal tubules generated in vitro.

We investigated the interactions of different types of human and porcine renal proximal tubule-derived cells with core-shell CdSe@ZnS quantum dots (QDs) coated with polymerized histidine-formaldehyde (pHF). The results revealed that porcine and human proximal tubule cells showed a markedly different uptake behavior. This applied to flat epithelial monolayers, as well as to proximal tubules formed on two-dimensional (2D) surfaces in vitro. Primary human cells were most sensitive to the cytotoxic effects of QDs, but displayed inter-donor variability, which appeared to depend on the state of differentiation. The results suggested that human proximal tubule-derived cells were more appropriate than porcine cells for in vitro nanotoxicology. Primary human cells might be suitable when their state of differentiation and inter-donor variability were well-controlled. Furthermore, the results suggested that gel-free proximal tubules formed in vitro could be used as test system to address uptake and transport of nanometer-sized particles in human renal structures.

Synthesis of highly fluorescent metal (Ag, Au, Pt, and Cu) nanoclusters by electrostatically induced reversible phase transfer.

This paper reports a simple and scalable method for the synthesis of highly fluorescent Ag, Au, Pt, and Cu nanoclusters (NCs) based on a mild etching environment made possible by phase transfer via electrostatic interactions. Using Ag as a model metal, a simple and fast (total synthesis time < 3 h) phase transfer cycle (aqueous → organic (2 h incubation) → aqueous) has been developed to process originally polydisperse, nonfluorescent, and unstable Ag NCs into monodisperse, highly fluorescent, and extremely stable Ag NCs in the same phase (aqueous) and protected by the same thiol ligand. The synthetic protocol was successfully extended to fabricate highly fluorescent Ag NCs protected by custom-designed peptides with desired functionalities (e.g., carboxyl, hydroxyl, and amine). The facile synthetic method developed in this study should largely contribute to the practical applications of this new class of fluorescence probes.

Mesoscopic organic nanosheets peeled from stacked 2D covalent frameworks.

Novel mesoscopic organic nanosheets were developed by functionalizing bulk 2D organic covalent framework polymers with small molecules. The water-soluble fluorescent nanosheets are promising as nanocarriers for biological applications.

Highly selective and ultrasensitive detection of Hg(2+) based on fluorescence quenching of Au nanoclusters by Hg(2+)-Au(+) interactions.

A simple label-free method for the detection of Hg(2+) ions with high selectivity and sensitivity has been developed by using fluorescent Au NCs in aqueous media. The sensing mechanism was based on the high-affinity metallophilic Hg(2+)-Au(+) interactions, which effectively quenched the fluorescence of Au NCs.

Protein-directed synthesis of highly fluorescent gold nanoclusters.

A simple, one-pot, "green" synthetic route, based on the "biomineralization" capability of a common commercially available protein, bovine serum albumin (BSA), has been developed for the preparation of highly stable Au nanocrystals (NCs) with red emission and high quantum yield.

High efficiency and nearly cubic power dependence of below-band-edge photoluminescence in water-soluble, copper-doped ZnSe/ZnS quantum dots.

Three-photon absorption (3PA) and three-photon-excited photoluminescence (3PE-PL) of ZnSe/ZnS and copper-doped ZnSe/ZnS core-shell quantum dots (QDs) in aqueous solutions have been unambiguously determined by Z-scan and 3PE-PL measurements with 200-fs laser pulses at 1000 nm. The 3PA cross-section is as high as 3.5 x 10(-77) cm6 s2 photon(-2) for 4.1 nm-sized, copper-doped ZnSe/ZnS QDs, while their below-band-edge PL is found to be nearly cubic dependent on the excitation intensity, with efficiency enhanced by approximately 20 fold compared to the undoped ZnSe/ZnS QDs.

Ultrasensitive Pb2+ detection by glutathione-capped quantum dots.

Water-soluble and stable quantum dots (QDs), CdTe and CdZnSe, are applied for ultrasensitive Pb(2+) detection. These QDs are capped with glutathione (GSH) shells. GSH and its polymeric form, phytochelatin, are employed by nature to detoxify heavy metal ions. As a result of specific interaction, the fluorescence intensity of GSH-capped QDs is selectively reduced in the presence of heavy metal ions such as Pb(2+). The detection limit of Pb(2+) is found to be 20 nM due to the superior fluorescence properties of QDs. Detailed studies by spectroscopy, microscopy, and dynamic light scattering show that competitive GSH binding of Pb(2+) with the QD core changed both the surface and photophysical properties of the QDs. Fluorescence of QDs is quenched, and QD aggregation occurs. Coupling the GSH-capped QDs with a high-throughput detection system, we have developed a simple scheme for quick and ultrasensitive Pb(2+) detection without the need for additional electronic devices. In the presence of ionic mixtures, our system is still capable of Pb(2+) detection with a detection limit as low as 40 nM. The system only becomes less sensitive when the ionic mixture is present at a very high concentration (i.e., > or =50 microM).

Controlled photostability of luminescent nanocrystalline ZnO solution for selective detection of aldehydes.

Water-soluble, silane-functionalized ZnO nanocrystals were synthesized with improved colloidal stability, and their photostability was controlled for the selective detection of aldehydes.

Substrate binding induces a cooperative conformational change in the 12S subunit of transcarboxylase: Raman crystallographic evidence.

The 12S subunit of transcarboxylase is a 338 000 Da hexamer that transfers carboxlylate from methylmalonyl-CoA (MM-CoA) to biotin; in turn, the biotin transfers the carboxylate to pyruvate on another subunit, the 5S. Here, Raman difference microscopy is used to study the binding of substrate and product, and their analogues, to single crystals of 12S. A single crystal is the medium of choice because it provides Raman data of unprecedented quality. Crystalline ligand-protein complexes were formed by cocrystallization or by the soaking in/soaking out method. Raman difference spectra were obtained by subtracting the spectrum of the apo crystal from that of a crystal with the substrate or product bound. Raman difference spectra from crystals with the substrate bound are dominated by bands from the protein's amide bonds and aromatic side chain residues. In contrast, Raman difference spectra involving the product, propionyl-CoA, are dominated by modes from the ligand. These results show that substrate binding triggers a conformational change in 12S, whereas product binding does not. The conformational change involves an increase in the amount of alpha-helix since markers for this secondary structure are prominent in the difference spectra of the substrate complex. The number of MM-CoA ligands bound per 12S hexamer can be gauged from the intensity of the MM-CoA Raman features and the fact that the protein concentration in the crystals is known from X-ray crystallographic data. Most crystal samples had six MM-CoAs per hexamer although a few, from different soaking experiments, contained only 1-2. However, both sets of crystals showed the same degree of protein conformational change, indicating that the change induced by the substrate is cooperative. This effect allowed us to record the Raman spectrum of bound MM-CoA without interference from protein modes; the Raman spectrum of a 12S crystal containing 2 MM-CoA ligands per hexamer was subtracted from the Raman spectrum of a 12S crystal containing six MM-CoA ligands per hexamer. The conformational change is reversible and can be controlled by soaking out or soaking in the ligand, using either concentrated ammonium sulfate solutions or the solution used in the crystallization trials. Malonyl-CoA also binds to 12S crystals and brings about conformational changes identical to those seen for MM-CoA; in addition, butyryl-CoA binds and behaves in a manner similar to propionyl-CoA. These data implicate the -COO- group on MM-CoA (that is transferred to biotin in the reaction on the intact enzyme) as the agent bringing about the cooperative conformational change in 12S.