Influencing the Electron Density of Nanosized Au Colloids via Immobilization on MgO to Stimulate Surface Reaction Activities.

Heterogenization of colloidal gold on MgO is demonstrated to facilitate its catalytic surface reactivity. We show that the electron density on Au influenced by its immobilization on MgO along with the ensued metal-support interaction is one of the key parameters to obtain high activity. As elucidated by X-ray absorption spectroscopic (X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and extended X-ray absorption fine structure) studies, the presence of well-dispersed nanosized Au on MgO is observed to result in an enhancement in the electron density of Au. The consequence of this electron-rich gold on the catalytic activity is then investigated using the nitroarene reduction as a model reaction with a detailed kinetic study. The kinetic study is an attempt to use a true heterogeneous system rather than the usually studied quasi-homogeneous systems. The results obtained reveal that the Au/MgO catalyst has a surface rate constant of ∼1.39 × 10-3 mol m-2 s-1, which is significantly higher than those of the reported catalysts. While it validates the higher catalytic activity with a TOF of 9456 h-1 observed for Au/MgO, the increased adsorption constant for 4-nitrophenol on Au/MgO further reflects the efficacy of MgO as the support. This not only allows effective heterogenization of the Au nanoparticles keeping the catalyst stable under the reaction conditions and being reused several times but also renders a capability in reduction of other nitro group-containing substrates. Therefore, the results are believed to be of importance in designing heterogeneous catalysts utilizing the distinctive properties of the nanosized colloids and tuning their surface reactivity as well.

Tunable Surface Wrinkling by a Bio-Inspired Polyamine Anion Coacervation Process that Mediates the Assembly of Polyoxometalate Nanoclusters.

A bio-inspired method is used to render controlled wrinkling surface patterns on supramolecular architectures assembled from polyoxometalate (POM) clusters. It involves a polyamine-multivalent anion interaction generating positively charged coacervates, which while dictating the assembly of POM into spherical structures further facilitate an interesting surface morphogenesis with wrinkling patterns. This spontaneous surface wrinkling depends on the type of multivalent anion and the pH. As the polyamine-anion interaction becomes stronger, the wrinkles turn denser with lesser depth, which eventually undergoes post-buckling to engender a complex surface pattern. Interestingly, the order of influence exerted by different anions on the morphology follows the Hofmeister series. Moreover, the mild synthesis conditions keep the functional POM units dispersed in the sphere with a structural transformability to their lacunary form.

Designing Microreactors Resembling Cellular Microenvironment via Polyamine-Mediated Nanoparticle-Assembly for Tuning Glucose Oxidase Kinetics.

Spatial confinement of glucose oxidase (GOx) in the hollow interior of a bioinspired matrix via polyamine mediated silica nanoparticle assembly under environmentally benign conditions is demonstrated herein. In a similarity to the biosilicification processes in diatoms, we use poly(allylamine hydrochloride) (PAH) to direct the assembly of silica nanoparticles on CaCO3 spheres as the removable core. When this assembly process is performed on the CaCO3 spheres, which are preloaded with GOx in a postsynthesis method, microspheres encapsulating GOx are formed. Interestingly, the encapsulated GOx in these microreactors exhibits activity with a Michaelis-Menten constant ( KM) that is 2- to 3-fold less compared with the free enzyme in the solution. While the microenvironment of the organic (PAH)-inorganic (silica) hybrid system can be advantageous for the substrate to interact with enzyme, the effective pH in the vicinity of the entrapped enzyme may also be accountable for the improved activity, resulting in the lower apparent KM and enhanced specificity constant ( kcat/ KM). A 2-fold higher thermal stability of the encapsulated GOx compared with free GOx in solution further demonstrates the efficacy of the integrated architecture. Additionally, the PAH by virtue of its buffering capability allows the microspheres in imparting pH stability to the encapsulated GOx. Therefore, the method is not only a greener process for performing enzyme immobilization but also anticipated to aid in designing microreactors for enhanced enzyme activity.

l-Cysteine-Conjugated Ruthenium Hydrous Oxide Nanomaterials with Anticancer Active Application.

Bioactive nanomaterials, namely: ruthenium hydrous oxide (or ruthenium oxy-hydroxide), RuOx(OH)y and also a surface-conjugated novel material of the same within the template of an amino acid molecule, l-cysteine, have been studied. These compounds have been prepared through a simple wet chemical route, under physiological conditions, such that they could be suitably used in anticancer applications. Several physical methods were used for the nanomaterial characterization, e.g.: thermal analysis of the as prepared ruthenium hydrous oxide by differential scanning calorimetry (DSC) followed by thermal gravimetric analysis (TGA). This confirms that the material is a precursor for anhydrous nanocrystalline ruthenium oxide (RuO2), as is affirmed by powder X-ray diffraction pattern. Also, optical spectroscopic absorption (UV-vis and FT-IR) study of these nanoparticles (NPs) to ascertain their surface conjugation with l-cysteine have been performed. Besides these, surface morphology of the NPs were studied by field emission scanning electron microscopy (FE-SEM) along with their elemental purity check through energy dispersive X-ray analysis (EDX). Their surface chemical microenvironments were examined by X-ray photo electron spectroscopy (XPS). The hydrodynamic size of the prepared NPs were measured through dynamic light scattering (DLS) studies. Further, biological consequences of these NPs on cancerous HeLa cells and their cytotoxicity effects have been reported with MTT assay, such an application has not been reported so far.

A bio-inspired strategy for the interfacial assembly of graphene oxide with in situ generated Ag/AgCl: designing sustainable hybrid photocatalysts.

Herein, we report a polyamine-mediated assembly to integrate graphene oxide (GO) sheets with Ag/AgCl to fabricate a hybrid nanocomposite (GO-Ag/AgCl) at nearly neutral pH and ambient temperature. Inspired by the role of polyamines in the excellent integration of components to generate hierarchical nanostructures in biominerals such as diatoms, we showed that our strategy enabled the fabrication of GO-semiconductor composites with a well-integrated structure. The polyamines not only facilitated the in situ generation of Ag/AgCl, but also simultaneously allowed their interaction with GO suitable for visible light active photocatalysis, as revealed by the detailed characterization of the synthesized materials. Consequently, the GO-Ag/AgCl exhibited nearly 5 times higher photocatalytic activity and better photostability than Ag/AgCl under visible light irradiation. The nanocomposite reached its highest activity at the graphene content of 4.16 wt%. Thus, the assembly process represented an effective way to design hybrid composites. Moreover, as a sustainable photocatalyst, it facilitates effective separation of the photogenerated charge carriers at the interface, thereby improving activity and stability.

Assembly of multiple components in a hybrid microcapsule: designing a magnetically separable Pd catalyst for selective hydrogenation.

In analogy to the role of long-chain polyamines in biosilicification, poly-L-lysine facilitates the assembly of nanocomponents to design multifunctional microcapsule structures. The method is demonstrated by the fabrication of a magnetically separable catalyst that accommodates Pd nanoparticles (NPs) as active catalyst, Fe3O4 NPs as magnetic component for easy recovery of the catalyst, and silica NPs to impart stability and selectivity to the catalyst. In addition, polyamines embedded inside the microcapsule prevent the agglomeration of Pd NPs and thus result in efficient catalytic activity in hydrogenation reactions, and the hydrophilic silica surface results in selectivity in reactions depending on the polarity of substrates.

Confinement of CuII -phthalocyanine in a bioinspired hybrid nanoparticle-assembled structure yields selective and stable epoxidation catalysts.

Herein, we demonstrate that a bioinspired assembly of silica nanoparticles with polyamines as structure-directing agents similar to that known for the biosilicification of diatoms can pave the way for the efficient encapsulation of sulfonated copper-phthalocyanine in a hybrid microcapsule structure, in which the organic component provides a capable environment for its catalytic activity in epoxidation reactions and the nanoassembled structure imparts stability.

N-acetylglucosamine biofunctionalized CdSeTe quantum dots as fluorescence probe for specific protein recognition.

Hsp70 proteins are implicated in resistance to chemotherapy in cancers, the detection of which is important for cancer treatment and prognosis. In this work, we report the study on the detection of specific intracellular target protein in fixed cells using GlcNAc-conjugated CdSeTe QDs. The QDs were coupled with Con A via a carbodiimide reaction and then were further assembled with GlcNAc by lectin-carbohydrate interaction between Con A and GlcNAc. The obtained QDs-Con A-GlcNAc conjugates have an emission wavelength at 650 nm that is close to the near-infrared (NIR) regions and a specific recognition for Hsp70. These results show that the QDs-Con A-GlcNAc probe can be a promising tool for direct localization of the Hsp70 protein.

Sonochemical fabrication of twinned ZnO hollow ellipses for electrochemical biosensing.

Twinned ZnO hollow ellipses (ZnO HEs) have been successfully fabricated by a one-step template-free sonochemical route. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the ZnO HEs had a hexagonal wurtzite structure, the wall of which was composed of ZnO nanorods. A possible growth mechanism for the formation of ZnO HEs was proposed, in which sonication played a crucial role. The highly efficient H2O2 electrochemical biosensor was fabricated using the film immobilized with hemoglobin, ZnO HEs and chitosan on glassy carbon electrode. The biosensor showed high stability and excellent electrocatalytic activity toward H2O2 with a linear range from 0.5 to 250 microM and a detection limit of 0.15 microM.

Oriented morphogenesis of ZnO nanostructures from water-soluble zinc salts under environmentally mild conditions and their optical properties.

Herein, we report a bottom-up, mineralization strategy, which borrows key principles from biomineralization processes, to synthesize nanostructured materials. A long-chain polyamine simultaneously mineralizes and assembles ZnO nanoparticles directly from water-soluble zinc salts under sustainable synthesis conditions. These thus-generated oriented structures undergo interesting morphogenesis that is controlled by changing the ratio of polyamine/Zn(2+) ions. As the ratio increases, the morphology changes from a spherical shape to oval-, dumbbell-, and finally hexagonal-rod-shaped structures that contain unique hollow rod structures. Using XPS, XRD, FT-IR, Raman spectroscopy, DLS, and confocal fluorescence microscopic analysis, we elucidate the mechanism of structural evolution; this mechanism involves the initial formation of a zinc/amine complex that is furnished with polyamine chains. These chains facilitate the condensation process to form ZnO nanoparticles and their assembly in aqueous medium at neutral pH. Further, the presence of defects in the thus-morphogenized ZnO structures leads to blue luminescence and efficient photoinduced activity, assisted by the surface-hole-trapping effect of polyamines.

Controlled orientation in a bio-inspired assembly of Ag/AgCl/ZnO nanostructures enables enhancement in visible-light-induced photocatalytic performance.

In a bio-inspired approach, polyamine-mediated mineralization of ZnO was explored to develop an environmentally benign methodology for synthesizing Ag/AgCl/ZnO nanostructures. The assembling properties displayed by the polyamines to create composite structures was utilized to have the nanocomponents effectively interact with each other in a way that is desirable for the application envisaged. The polyamines, which act as a mineralizing agent for ZnO nanoparticles, also facilitate the formation of Ag/AgCl within ZnO under ambient conditions. Thus synthesized Ag/AgCl/ZnO nanostructures represent a multi-heterojunction system in which the nanocomponents lead in a synergistic way to enhancement in the photocatalytic activity under visible-light irradiation.

Spatial Confinement of Enzyme and Nanozyme in Silica-Based Hollow Microreactors.

Designing a strategy for encasing enzymes and nanozymes in microreactors with spatial confinement in a way to improve the selectivity and activity of nanozymes is an exciting goal. In the present work, we report a facile route to encapsulate glucose oxidase (GOx) and poly(ethylenimine) (PEI)-conjugated magnetite nanoparticles (Fe3O4-PEI) in the hollow interior of hybrid microreactors. The microreactors are prepared by polyallylamine hydrochloride (PAH)-mediated silica (SiO2) nanoparticle assembly on calcium carbonate (CaCO3) particles as a removable core. By tuning both shape and phase (vaterite/calcite and pure calcite) of CaCO3, it allows generation of GOx and Fe3O4-PEI-encapsulated silica hollow microspheres (GOx-Fe3O4@SHS) and microcubes (GOx-Fe3O4@SHC). As observed, in a biomimetic cascade catalysis, the confined GOx in the microreactors is able to catalyze oxidation of glucose to gluconic acid and hydrogen peroxide (H2O2), followed by the activation of H2O2 by Fe3O4-PEI for the oxidation of the chromogenic substrate o-phenylenediamine (oPD) to 2,3-diaminophenazine. Comparison of the peroxidase-like activity of the encapsulated Fe3O4-PEI shows that the hollow microspheres (GOx-Fe3O4@SHS) result in activity 14 times higher than that of the hollow microcubes (GOx-Fe3O4@SHC), which in turn is corroborated to the differential loading capacity of GOx in microspheres and microcubes. The evaluation of kinetic parameters indicates a fivefold increase in the catalytic constant (kcat) of Fe3O4-PEI confined in hollow microspheres (GOx-Fe3O4@SHS) compared to the mixture comprising free GOx and Fe3O4-PEI in solution. It suggests that the confined space in the microreactors allows the tandem reactions of GOx and Fe3O4-PEI to take place in close proximity, leading to an improved overall activity. This indeed is seen in the kcat obtained for Fe3O4@SHS (GOx added externally during the assay), which is 14 times lower than that of GOx-Fe3O4@SHS.

Trapping Pd(0) in nanoparticle-assembled microcapsules: an efficient and reusable catalyst.

Pd nanoparticles dually encased by soft (polyamine) and hard (silica) materials in a microcapsule structure, obtained via a nanoparticle self-assembly method, exhibit excellent catalytic activity, with efficient catalyst recovery and reusability.

Microcapsule Structure with a Tunable Textured Surface via the Assembly of Polyoxomolybdate Clusters: A Bioinspired Strategy and Enhanced Activities in Alkene Oxidation.

A polyamine-mediated bioinspired strategy to assemble Keggin-type phosphomolybdic acid (PMA) clusters is demonstrated for the fabrication of microcapsule (MC) structures with unique surface textures. It involves supramolecular aggregation of polyamines with multivalent anions, which then allows the assembly of negatively charged PMA into MCs in an aqueous medium under ambient conditions. Resembling the role of polyamines in biosilicification of diatoms, the polyamine-anion interaction is shown to be the key for the assembly process. It not only provides structural stability but also facilitates an interesting transition from a smooth to a wrinkled surface alongside a change in the Keggin form to its lacunary form depending on the pH of the medium. Moreover, the presence of isolated PMA units in the hybrid structure enables them to be active in catalyzing the aerobic oxidation of alkenes under solvent-free conditions with better selectivity and reusability. Hence, the assembly approach represents an effective way for heterogenization of PMA-based materials and is expected to find considerable application in the wider hybrid-cluster field.

In Situ Strategy to Encapsulate Antibiotics in a Bioinspired CaCO3 Structure Enabling pH-Sensitive Drug Release Apt for Therapeutic and Imaging Applications.

Herein we demonstrate a bioinspired method involving macromolecular assembly of anionic polypeptide with cationic peptide-oligomer that allows for in situ encapsulation of antibiotics like tetracycline in CaCO3 microstructure. In a single step one-pot process, the encapsulation of the drug occurs under desirable environmentally benign conditions resulting in drug loaded CaCO3 microspheres. While this tetracycline-loaded sample exhibits pH dependent in vitro drug-release profile and excellent antibacterial activity, the encapsulated drug or the dye-conjugated peptide emits fluorescence suitable for optical imaging and detection, thereby making it a multitasking material. The efficacy of tetracycline loaded calcium carbonate microspheres as pH dependent drug delivery vehicles is further substantiated by performing cell viability experiments using normal and cancer cell lines (in vitro). Interestingly, the pH-dependent drug release enables selective cytotoxicity toward cancer cell lines as compared to the normal cells, thus having the potential for further development of therapeutic applications.

Microfluidic chip integrated with flexible PDMS-based electrochemical cytosensor for dynamic analysis of drug-induced apoptosis on HeLa cells.

A novel microfluidic platform integrated with a flexible PDMS-based electrochemical cytosensor was developed for real-time monitoring of the proliferation and apoptosis of HeLa cells. The PDMS-gold film, which had a conductive smooth surface and was semi-transparent, facilitated electrochemical measurements and optical microscope observations. We observed distinct increases and decreases in peak current intensity, corresponding to cell proliferation in culture medium and apoptosis in the presence of an anticancer drug, respectively. This electrochemical analysis method permitted real-time, label-free monitoring of cell behavior, and the electrochemical results were confirmed with optical microscopy. The flexible microfluidic electrochemical platform presented here is suitable for on-site monitoring of cell behavior in microenvironments.

Synthesis and electrocatalytic activity of haemin-functionalised iron(II, III) oxide nanoparticles.

Haemin-functionalised magnetic iron(II, III) oxide (Fe3O4) nanoparticles (Fe3O4/haemin) were synthesised by changing the acidity of a solution of the two compounds. The nanoparticles were characterised by transmission electron microscopy, UV-vis absorption spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, measurement of magnetisation, and electrochemical techniques. The properties of both haemin and Fe3O4 were retained. Thus, Fe3O4/haemin nanoparticles exhibited pronounced electrocatalytic activity towards trichloroacetic acid (TCA) like haemin itself. Interestingly, electrocatalytic activity towards TCA was affected by detection temperature, which was controlled via electrically heated carbon paste electrodes. The maximal catalytic current was 5.8 times higher at 60°C than at room temperature (25°C). This proposed electrochemical sensor for TCA possessed a linear detection range of 5-80 µM and a detection limit of 0.3 µM at 60°C.

Bio-inspired motifs via tandem assembly of polypeptides for mineralization of stable CaCO3 structures.

A macromolecular-assembly of polypeptides constructs a network of anionic and cationic charges vital for recognizing and coassembling Ca(2+) and CO(3)(2-) ions to mineralize and stabilize different mineral forms of CaCO(3) with core-shell or solid morphologies in an aqueous solution.

Poly(L-Lysine)-pyranine-3 coacervate mediated nanoparticle-assembly: fabrication of dynamic pH-responsive containers.

Counter-ion condensation of Poly(L-Lysine) in the presence of pyranine-3 generates spherical coacervates, which then template the assembly of silica nanoparticles to form microcapsule structures that dynamically control the optical ratiometric sensing of both the change in pH and release of the probe molecule.