Development of a Multi-Enzymatic Biocatalytic System through Immobilization on High Quality Few-Layer bio-Graphene

In this work, we report the green production of few-layer bio-Graphene (bG) through liquid exfoliation of graphite in the presence of bovine serum albumin. Microscopic characterization evaluated the quality of the produced nanomaterial, showing the presence of 3-4-layer graphene. Moreover, spectroscopic techniques also confirmed the quality of the resulted bG, as well as the presence of bovine serum albumin on the graphene sheets. Next, for the first time, bG was used as support for the simultaneous covalent co-immobilization of three enzymes, namely β-glucosidase, glucose oxidase, and horseradish peroxidase. The three enzymes were efficiently co-immobilized on bG, demonstrating high immobilization yields and activity recoveries (up to 98.5 and 90%, respectively). Co-immobilization on bG led to an increase of apparent K_M values and a decrease of apparent V_max values, while the stability of the nanobiocatalysts prevailed compared to the free forms of the enzymes. Co-immobilized enzymes exhibited high reusability, preserving a significant part of their activity (up to 72%) after four successive catalytic cycles at 30 °C. Finally, the tri-enzymatic nanobiocatalytic system was applied in three-step cascade reactions, involving, as the first step, the hydrolysis of p-Nitrophenyl-β-D-Glucopyranoside and cellobiose.

Development of 3D Printed Enzymatic Microreactors for Lipase-Catalyzed Reactions in Deep Eutectic Solvent-Based Media

In this study, 3D printing technology was exploited for the development of immobilized enzyme microreactors that could be used for biocatalytic processes in Deep Eutectic Solvent (DES)-based media. 3D-printed polylactic acid (PLA) microwell plates or tubular microfluidic reactors were modified with polyethylenimine (PEI) and lipase from Candida antarctica (CALB) was covalently immobilized in the interior of each structure. DESs were found to have a negligible effect on the activity and stability of CALB, and the system proved highly stable and reusable in the presence of DESs for the hydrolysis of p-nitrophenyl butyrate (p-NPB). A kinetic study under flow conditions revealed an enhancement of substrate accessibility in the presence of Betaine: Glycerol (Bet:Gly) DES, while the system was not severely affected by diffusion limitations. Incubation of microreactors in 100% Bet:Gly preserved the enzyme activity by 53% for 30 days of storage at 60 °C, while the buffer-stored sample had already been deactivated. The microfluidic enzyme reactor was efficiently used for the trans-esterification of ethyl ferulate (EF) with glycerol towards the production of glyceryl ferulate (GF), known for its antioxidant potential. The biocatalytic process under continuous flow conditions exhibited 23 times higher productivity than the batch reaction system. This study featured an effective and robust biocatalytic system with immobilized lipase that can be used both in hydrolytic and synthetic applications, while further optimization is expected to upgrade the microreactor system performance.

Green Synthesis and Characterization of Silver Nanoparticles with High Antibacterial Activity Using Cell Extracts of Cyanobacterium Pseudanabaena/Limnothrix sp

In this work, we demonstrated the ability of the cyanobacterium Pseudanabaena/Limnothrix sp. to produce ultra-small silver nanoparticlesin the forms of metallic silver (Ag⁰) and silver oxides (Ag_xO_y) via a facile green synthetic process. The biological compounds in the cyanobacterial cellular extract acted both as reducing agents for silver ions and functional stabilizing agents for the silver nanoparticles. Furthermore, the antibacterical activity of the as-synthesized nanoparticles against Gram-negative Escherichia coli and Gram-positive Corynebacterium glutamicum bacterial cells was evaluated. The experimental results revealed a remarkable bactericidal activity of the nanoparticles that was both time-dependent and dose-dependent. In addition to their excellent bactericidal properties, the developed nanoparticles can be used as nanosupports in various environmental, biological, and medical applications.

Graphene Oxide-Cytochrome c Multilayered Structures for Biocatalytic Applications: Decrypting the Role of Surfactant in Langmuir-Schaefer Layer Deposition

Graphene, a two-dimensional single-layer carbon allotrope, has attracted tremendous scientific interest due to its outstanding physicochemical properties. Its monatomic thickness, high specific surface area, and chemical stability render it an ideal building block for the development of well-ordered layered nanostructures with tailored properties. Herein, biohybrid graphene-based layer-by-layer structures are prepared by means of conventional and surfactant-assisted Langmuir-Schaefer layer deposition techniques, whereby cytochrome c molecules are accommodated within ordered layers of graphene oxide. The biocatalytic activity of the as-developed nanobio-architectures toward the enzymatic oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt and decolorization of pinacyanol chloride is tested. The results show that the multilayer structures exhibit high biocatalytic activity and stability in the absence of surfactant molecules during the deposition of the monolayers.

Bimetallic gold-platinum nanoparticles as a drug delivery system coated with a new drug to target glioblastoma

A drug delivery nanosystem of noble bimetallic nanoparticles (NPs) which consists of Au NPs capped with Pt NPs (Au@Pt NPs) is constructed and functionalised with a quinazoline based small molecule (Au@Pt@Q NPs), acting as a theranostic agent against glioblastoma. Two different hydrothermal synthetic procedures for bimetallic Au@Pt NPs are presented and the resulting nanostructures are fully characterised by means of spectroscopic and microscopic methods. The imaging and targeting capacity of the new drug delivery system is assessed through fluorescent optical microscopy and cytotoxicity evaluations. The constructed Au@Pt NPs consist a monodispersed colloidal solution of 25 nm with photoluminescent, fluorescent and X-Ray absorption properties that confirm their diagnostic potential. Haemolysis testing demonstrated that Au@Pt NPs are biocompatible and fluorescent microscopy confirmed their entering the cells. Cytological evaluation of the NPs through MTT assay showed that they do not inhibit the proliferation of control cell line HEK293, whereas they are toxic in U87MG, U251 and D54 glioblastoma cell lines; rendering them selective targeting agents for treating glioblastoma.

Synthesis, characterization and evaluation of aqueous Zn-based quantum dots for bioapplications

Semiconducting nanoparticles called quantum dots (Qds) present unique optoelectronic properties based on their extremely small size, composition, and spherical shape, which make them suitable for use as diagnostic and theranostic agents in biological samples. The main scope of the fabrication of Qds is real-time diagnosis, therapy, drug delivery, and in vitro and in vivo tracking, presenting strong resistance to photobleaching. In this work, quantum dots such as ZnO, ZnSe, ZnS, and doped ZnS : Mn and ZnS : Cd were developed via a simple sol-gel synthesis in an aqueous solution. Morphological, structural, and optical characterizations were investigated. Moreover, an in vitro biological evaluation of Qds was performed. The results indicate that the photoluminescence is enhanced after doping ZnS Qds with Mn²⁺ and Cd²⁺. Qds have been synthesized for use as fluorescent agents for real-time monitoring in bio-applications.

A Four-enzyme Nanoassembly Consisting of Hydrolases and Oxidoreductases for Multi-step Cascade Reactions

Cascade reactions catalyzed by multi-enzymatic systems have attracted enormous scientific interest over the last decade. They are an emerging technology that significantly expands the applicability of biocatalysts in several biotechnological processes, such as the synthesis of high value-added products. Immobilization of enzymes on a solid carrier is a commonly used strategy to improve the stability and reuse of multiple enzyme systems. Magnetic nanoparticles have been applied as promising nanocarriers for either the immobilization of one enzyme or the co-immobilization of multiple enzymes. In this chapter, we describe the preparation of magnetic iron oxide nanoparticles γ-Fe₂O₃ modified with 3-(aminopropyl)-triethoxysilane (APTES), for the simultaneous covalent co-immobilization of oxidoreductases and hydrolytic enzymes, such as cellulase, β-glucosidase (bgl), glucose oxidase (GOx), and horseradish peroxidase (HRP). Several spectroscopic techniques that are used to characterize the structure and the catalytic performance of such systems are also described.

Germanane Monolayer Films as Antibacterial Coatings

Germanane (GeH), a graphane analogue, has attracted significant interest because of its optoelectronic properties; however, the environmental and biological effects of GeH have scarcely been investigated so far. Here we report a facile approach based on the Langmuir-Schaefer deposition to produce homogeneous and dense GeH monolayer films on various substrates. In view of possible applications and to extend the use of GeH to unexplored fields, we investigated its antibacterial activity for the first time and found that this promising 2D structure exhibits remarkable antibacterial activity against both Gram-negative and Gram-positive bacterial strains.

Green Synthesized Magnetic Nanoparticles as Effective Nanosupport for the Immobilization of Lipase: Application for the Synthesis of Lipophenols

In this work, hybrid zinc oxide-iron oxide (ZnOFe) magnetic nanoparticles were synthesized employing Olea europaea leaf aqueous extract as a reducing/chelating and capping medium. The resulting magnetic nanoparticles were characterized by basic spectroscopic and microscopic techniques, namely, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), fourier-transform infrared (FTIR) and atomic force microscopy (AFM), exhibiting a spherical shape, average size of 15-17 nm, and a functionalized surface. Lipase from Thermomyces lanuginosus (TLL) was efficiently immobilized on the surface of ZnOFe nanoparticles through physical absorption. The activity of immobilized lipase was found to directly depend on the enzyme to support the mass ratio, and also demonstrated improved pH and temperature activity range compared to free lipase. Furthermore, the novel magnetic nanobiocatalyst (ZnOFe-TLL) was applied to the preparation of hydroxytyrosyl fatty acid esters, including derivatives with omega-3 fatty acids, in non-aqueous media. Conversion yields up to 90% were observed in non-polar solvents, including hydrophobic ionic liquids. Different factors affecting the biocatalyst performance were studied. ZnOFe-TLL was reutilized for eight subsequent cycles, exhibiting 90% remaining esterification activity (720 h of total operation at 50 °C). The green synthesized magnetic nanoparticles, reported here for the first time, are excellent candidates as nanosupports for the immobilization of enzymes with industrial interest, giving rise to nanobiocatalysts with elevated features.

Trends of nanotechnology in type 2 diabetes mellitus treatment

There are several therapeutic approaches in type 2 diabetes mellitus (T2DM). When diet and exercise fail to control hyperglycemia, patients are forced to start therapy with antidiabetic agents. However, these drugs present several drawbacks that can affect the course of treatment. The major disadvantages of current oral modalities for the treatment of T2DM are mainly depicted in the low bioavailability and the immediate release of the drug, generating the need for an increase in frequency of dosing. In conjugation with the manifestation of adverse side effects, patient compliance to therapy is reduced. Over the past few years nanotechnology has found fertile ground in the development of novel delivery modalities that can potentially enhance anti-diabetic regimes efficacy. All efforts have been targeted towards two main vital steps: (a) to protect the drug by encapsulating it into a nano-carrier system and (b) efficiently release the drug in a gradual as well as controllable manner. However, only a limited number of studies published in the literature used in vivo techniques in order to support findings. Here we discuss the current disadvantages of modern T2DM marketed drugs, and the nanotechnology advances supported by in vivo in mouse/rat models of glucose homeostasis. The generation of drug nanocarriers may increase bioavailability, prolong release and therefore reduce dosing and thus, improve patient compliance. This novel approach might substantially improve quality of life for diabetics. Application of metal nanoformulations as indirect hypoglycemic agents is also discussed.

A diamino-functionalized silsesquioxane pillared graphene oxide for CO2 capture

In the race for viable solutions that could slow down carbon emissions and help in meeting the climate change targets a lot of effort is being made towards the development of suitable CO₂ adsorbents with high surface area, tunable pore size and surface functionalities that could enhance selective adsorption. Here, we explored the use of silsesquioxane pillared graphene oxide for CO₂ capture; we modified silsesquioxane loading and processing parameters in order to obtain pillared structures with nanopores of the tailored size and surface properties to maximize the CO₂ sorption capacity. Powder X-ray diffraction, XPS and FTIR spectroscopies, thermal analysis (DTA/TGA), surface area measurements and CO₂ adsorption measurements were employed to characterize the materials and evaluate their performance. Through this optimisation process, materials with good CO₂ storage capacities of up to 1.7/1.5 mmol g⁻¹ at 273 K/298 K in atmospheric pressure, were achieved.

Study of the CO₂ uptake performance of silsesquioxane pillared graphene oxide prepared with different pillar loading and way of drying.

Nanocarbon from Rocket Fuel Waste: The Case of Furfuryl Alcohol-Fuming Nitric Acid Hypergolic Pair

In hypergolics two substances ignite spontaneously upon contact without external aid. Although the concept mostly applies to rocket fuels and propellants, it is only recently that hypergolics has been recognized from our group as a radically new methodology towards carbon materials synthesis. Comparatively to other preparative methods, hypergolics allows the rapid and spontaneous formation of carbon at ambient conditions in an exothermic manner (e.g., the method releases both carbon and energy at room temperature and atmospheric pressure). In an effort to further build upon the idea of hypergolic synthesis, herein we exploit a classic liquid rocket bipropellant composed of furfuryl alcohol and fuming nitric acid to prepare carbon nanosheets by simply mixing the two reagents at ambient conditions. Furfuryl alcohol served as the carbon source while fuming nitric acid as a strong oxidizer. On ignition the temperature is raised high enough to induce carbonization in a sort of in-situ pyrolytic process. Simultaneously, the released energy was directly converted into useful work, such as heating a liquid to boiling or placing Crookes radiometer into motion. Apart from its value as a new synthesis approach in materials science, carbon from rocket fuel additionally provides a practical way in processing rocket fuel waste or disposed rocket fuels.

Synthesis of 2D Germanane (GeH): a New, Fast, and Facile Approach

Germanane (GeH), a germanium analogue of graphane, has recently attracted considerable interest because its remarkable combination of properties makes it an extremely suitable candidate to be used as 2D material for field effect devices, photovoltaics, and photocatalysis. Up to now, the synthesis of GeH has been conducted by substituting Ca by H in a β-CaGe₂ layered Zintl phase through topochemical deintercalation in aqueous HCl. This reaction is generally slow and takes place over 6 to 14 days. The new and facile protocol presented here allows to synthesize GeH at room temperature in a significantly shorter time (a few minutes), which renders this method highly attractive for technological applications. The GeH produced with this method is highly pure and has a band gap (E_g ) close to 1.4 eV, a lower value than that reported for germanane synthesized using HCl, which is promising for incorporation of GeH in solar cells.

Cytotoxicity Effects of Water-Soluble Multi-Walled Carbon Nanotubes Decorated with Quaternized Hyperbranched Poly(ethyleneimine) Derivatives on Autotrophic and Heterotrophic Gram-Negative Bacteria

Oxidized multi-walled carbon nanotubes (oxCNTs) were functionalized by a simple non-covalent modification procedure using quaternized hyperbranched poly(ethyleneimine) derivatives (QPEIs), with various quaternization degrees. Structural characterization of these hybrids using a variety of techniques, revealed the successful and homogenous anchoring of QPEIs on the oxCNTs' surface. Moreover, these hybrids efficiently dispersed in aqueous media, forming dispersions with excellent aqueous stability for over 12 months. Their cytotoxicity effect was investigated on two types of gram(-) bacteria, an autotrophic (cyanobacterium Synechococcus sp. PCC 7942) and a heterotrophic (bacterium Escherichia coli). An enhanced, dose-dependent antibacterial and anti-cyanobacterial activity against both tested organisms was observed, increasing with the quaternization degree. Remarkably, in the photosynthetic bacteria it was shown that the hybrid materials affect their photosynthetic apparatus by selective inhibition of the Photosystem-I electron transport activity. Cytotoxicity studies on a human prostate carcinoma DU145 cell line and 3T3 mouse fibroblasts revealed that all hybrids exhibit high cytocompatibility in the concentration range, in which they also exhibit both high antibacterial and anti-cyanobacterial activity. Thus, QPEI-functionalized oxCNTs can be very attractive candidates as antibacterial and anti-cyanobacterial agents that can be used for potential applications in the disinfection industry, as well as for the control of harmful cyanobacterial blooms.

New Porous Heterostructures Based on Organo-Modified Graphene Oxide for CO2 Capture

In this work, we report on a facile and rapid synthetic procedure to create highly porous heterostructures with tailored properties through the silylation of organically modified graphene oxide. Three silica precursors with various structural characteristics (comprising alkyl or phenyl groups) were employed to create high-yield silica networks as pillars between the organo-modified graphene oxide layers. The removal of organic molecules through the thermal decomposition generates porous heterostructures with very high surface areas (≥ 500 m²/g), which are very attractive for potential use in diverse applications such as catalysis, adsorption and as fillers in polymer nanocomposites. The final hybrid products were characterized by X-ray diffraction, Fourier transform infrared and X-ray photoelectron spectroscopies, thermogravimetric analysis, scanning electron microscopy and porosity measurements. As proof of principle, the porous heterostructure with the maximum surface area was chosen for investigating its CO₂ adsorption properties.

Titanium Dioxide Grafted on Graphene Oxide: Hybrid Nanofiller for Effective and Low-Cost Proton Exchange Membranes

A nanostructured hybrid material consisting of TiO2 nanoparticles grown and stabilized on graphene oxide (GO) platelets, was synthesized and tested as nanofiller in a polymeric matrix of sulfonated polysulfone (sPSU) for the preparation of new and low-cost nanocomposite electrolytes for proton exchange membrane fuel cell (PEMFC) applications. GO-TiO2 hybrid material combines the nanoscale structure, large interfacial area, and mechanical features of a 2D, layered material, and the hygroscopicity properties of ceramic oxides, able to maintain a suitable hydration of the membrane under harsh fuel cell operative conditions. GO-TiO2 was synthetized through a new, simple, one-pot hydrothermal procedure, while nanocomposite membranes were prepared by casting using different filler loadings. Both material and membranes were investigated by a combination of XRD, Raman, FTIR, thermo-mechanical analysis (TGA and Dynamic Mechanical Analysis) and SEM microscopy, while extensive studies on the proton transport properties were carried out by Electrochemical Impedance Spectroscopy (EIS) measurements and pulse field gradient (PFG) NMR spectroscopy. The addition of GO-TiO2 to the sPSU produced a highly stable network, with an increasing of the storage modulus three-fold higher than the filler-free sPSU membrane. Moreover, the composite membrane with 3 wt.% of filler content demonstrated very high water-retention capacity at high temperatures as well as a remarkable proton mobility, especially in very low relative humidity conditions, marking a step ahead of the state of the art in PEMs. This suggests that an architecture between polymer and filler was created with interconnected routes for an efficient proton transport.

Rapid Carbon Formation from Spontaneous Reaction of Ferrocene and Liquid Bromine at Ambient Conditions

Herein, we present an interesting route to carbon derived from ferrocene without pyrolysis. Specifically, the direct contact of the metallocene with liquid bromine at ambient conditions released rapidly and spontaneously carbon soot, the latter containing dense spheres, nanosheets, and hollow spheres. The derived carbon carried surface C-Br bonds that permitted postfunctionalization of the solid through nucleophilic substitution. For instance, treatment with diglycolamine led to covalent attachment of the amine onto the carbon surface, thus conferring aqueous dispersability to t he solid. The dispersed solid exhibited visible photoluminescence under UV irradiation as a result of surface passivation by the amine. Hence, the present method not only allowed a rapid and spontaneous carbon formation at ambient conditions, but also surface engineering of the particles to impart new properties (e.g., photoluminescence).

Fabrication of highly ordered Cu2+/Fe3+ decorated polyhedral oligomeric silsesquioxane hybrids: How metal coordination influences structure

Incorporation of isolated metal centers into well-organized nanostructures is a promising route in the development of the next generation of chemical, magnetic and electronic devices. In this work, a layer-by-layer protocol to grow highly ordered thin films of metal-decorated organic-inorganic cage-like polyhedral oligomeric silsesquioxane (POSS) is introduced. The key strategy is to use metal ions (Cu²⁺ or Fe³⁺) as linker for the amino-functionalized cage-like POSS, which are self-assembled between arachidic acid layers during Langmuir-Schaefer deposition. The Langmuir-Schaefer films are examined by X-ray photoelectron spectroscopy, X-ray diffraction, grazing incidence wide-angle X-ray scattering and extended X-ray absorption fine structure in order to understand how the coordination of metal ions influences the structure in the course of the layer-by-layer formation of the films.

Hypergolics in Carbon Nanomaterials Synthesis: New Paradigms and Perspectives

Recently we have highlighted the importance of hypergolic reactions in carbon materials synthesis. In an effort to expand this topic with additional new paradigms, herein we present novel preparations of carbon nanomaterials, such-like carbon nanosheets and fullerols (hydroxylated fullerenes), through spontaneous ignition of coffee-sodium peroxide (Na₂O₂) and C₆₀-Na₂O₂ hypergolic mixtures, respectively. In these cases, coffee and fullerenes played the role of the combustible fuel, whereas sodium peroxide the role of the strong oxidizer (e.g., source of highly concentrated H₂O₂). The involved reactions are both thermodynamically and kinetically favoured, thus allowing rapid product formation at ambient conditions. In addition, we provide tips on how to exploit the released energy of such highly exothermic reactions in the generation of useful work.

H-Shaped Copolymer of Polyethylene and Poly(ethylene oxide) under Severe Confinement: Phase State and Dynamics

The self-assembly and the dynamics of an H-shaped copolymer composed of a polyethylene midblock and four poly(ethylene oxide) arms (PE-b-4PEO) are investigated in the bulk and under severe confinement into nanometer-spaced LAPONITE clay particles by means of small- and wide-angle X-ray diffraction (SAXS, WAXS), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), rheology, and dielectric spectroscopy (DS). Because of the H-shaped architecture, the PE midblock is topologically frustrated and thus unable to crystallize. The superstructure formation in the bulk is dictated solely by the PEO arms as inferred by the crystallization/melting temperature relative to the PEO homopolymer. Confinement produced remarkable changes in the interlayer distance and PEO crystallinity but left the local segmental dynamics unaltered. To reconcile all structural, thermodynamic, and dynamic effects, a novel morphological picture is proposed with interest in emulsions. Key parameters that stabilize the final morphology are the severe chain confinement with the associated entropy loss and the presence of interactions (hydrophobic/hydrophilic) between the LAPONITE and the PEO/PE blocks.

Functional Carbon Materials Derived through Hypergolic Reactions at Ambient Conditions

Carbon formation from organic precursors is an energy-consuming process that often requires the heating of a precursor in an oven at elevated temperature. In this paper, we present a conceptually different synthesis pathway for functional carbon materials based on hypergolic mixtures, i.e., mixtures that spontaneously ignite at ambient conditions once its ingredients contact each other. The reactions involved in such mixtures are highly exothermic, giving-off sizeable amounts of energy; hence, no any external heat source is required for carbonization, thus making the whole process more energy-liberating than energy-consuming. The hypergolic mixtures described here contain a combustible organic solid, such as nitrile rubber or a hydrazide derivative, and fuming nitric acid (100% HNO₃) as a strong oxidizer. In the case of the nitrile rubber, carbon nanosheets are obtained, whereas in the case of the hydrazide derivative, photoluminescent carbon dots are formed. We also demonstrate that the energy released from these hypergolic reactions can serve as a heat source for the thermal conversion of certain triazine-based precursors into graphitic carbon nitride. Finally, certain aspects of the derived functional carbons in waste removal are also discussed.

Synthesis of Highly Crystalline Graphite from Spontaneous Ignition of In Situ Derived Acetylene and Chlorine at Ambient Conditions

We exploited a classic chemistry demonstration experiment based on the reaction of acetylene with chlorine to obtain highly crystalline graphite at ambient conditions. Acetylene and chlorine were generated in-situ by the addition of calcium carbide (CaC2) in a concentrated HCl solution, followed by the quick addition of domestic bleach (NaClO). The released gases reacted spontaneously, giving bursts of yellow flame, leaving highly crystalline graphite deposits in the aqueous phase. This was a rather benign alternative towards synthetic graphite, the latter usually being prepared at high temperatures. The synthetic graphite was further utilized to obtain graphene or conductive inks.

Layer-by-Layer Assembly of Clay-Carbon Nanotube Hybrid Superstructures

Much of the research effort concerning layered materials is directed toward their use as building blocks for the development of hybrid nanostructures with well-defined dimensions and behavior. Here, we report the fabrication through layer-by-layer deposition and intercalation chemistry of a new type of clay-based hybrid film, where functionalized carbon nanotubes are sandwiched between nanometer-sized smectite clay platelets. Single-walled carbon nanotubes (SWCNTs) were covalently functionalized in a single step with phenol groups, via 1,3-dipolar cycloaddition, to allow for stable dispersion in polar solvents. For the production of hybrid thin films, a bottom-up approach combining self-assembly with Langmuir-Schaefer deposition was applied. Smectite clay nanoplatelets act as a structure-directing interface and reaction media for grafting functionalized carbon nanotubes in a bidimensional array, allowing for a controllable layer-by-layer growth at a nanoscale. Hybrid clay/SWCNT multilayer films deposited on various substrates were characterized by X-ray reflectivity, Raman, and X-ray photoelectron spectroscopies, as well as atomic force microscopy.

Enzymatic Conversion of Oleuropein to Hydroxytyrosol Using Immobilized β-Glucosidase on Porous Carbon Cuboids

In the present study, we developed novel β-glucosidase-based nano-biocatalysts for the bioconversion of oleuropein to hydroxytyrosol. Using non-covalent or covalent immobilization approaches, β-glucosidases from almonds and Thermotoga maritima were attached for the first time on oxidized and non-oxidized porous carbon cuboids (PCC). Various methods were used for the characterization of the bio-nanoconjugates, such as Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and fluorescence spectroscopy. The oxidation state of the nanο-support and the immobilization procedure play a key role for the immobilization efficiency or the catalytic activity of the immobilized β-glucosidases. The nano-biocatalysts were successfully used for the hydrolysis of oleuropein, which leads to the formation of its bioactive derivative, hydroxytyrosol (up to 2.4 g L-1), which is a phenolic compound with numerous health benefits. The bio-nanoconjugates exhibited high thermal and operational stability (up to 240 hours of repeated use), which indicated that they are efficient tools for various bio-transformations.

Development of Effective Lipase-Hybrid Nanoflowers Enriched with Carbon and Magnetic Nanomaterials for Biocatalytic Transformations

In the present study, hybrid nanoflowers (HNFs) based on copper (II) or manganese (II) ions were prepared by a simple method and used as nanosupports for the development of effective nanobiocatalysts through the immobilization of lipase B from Pseudozyma antarctica. The hybrid nanobiocatalysts were characterized by various techniques including scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). The effect of the addition of carbon-based nanomaterials, namely graphene oxide and carbon nanotubes, as well as magnetic nanoparticles such as maghemite, on the structure, catalytic activity, and operational stability of the hybrid nanobiocatalysts was also investigated. In all cases, the addition of nanomaterials during the preparation of HNFs increased the catalytic activity and the operational stability of the immobilized biocatalyst. Lipase-based magnetic nanoflowers were effectively applied for the synthesis of tyrosol esters in non-aqueous media, such as organic solvents, ionic liquids, and environmental friendly deep eutectic solvents. In such media, the immobilized lipase preserved almost 100% of its initial activity after eight successive catalytic cycles, indicating that these hybrid magnetic nanoflowers can be applied for the development of efficient nanobiocatalytic systems.

Highly Conductive Metallic State and Strong Spin-Orbit Interaction in Annealed Germanane

Similar to carbon, germanium exists in various structures such as three-dimensional crystalline germanium and germanene, a two-dimensional germanium atomic layer. Regarding the electronic properties, they are either semiconductors or Dirac semimetals. Here, we report a highly conductive metallic state in thermally annealed germanane (hydrogen-terminated germanene, GeH), which shows a resistivity of ∼10^-7 Ω·m that is orders of magnitude lower than any other allotrope of germanium. By comparing the resistivity, Raman spectra, and thickness change measured by AFM, we suggest the highly conductive metallic state is associated with the dehydrogenation during heating, which likely transforms germanane thin flakes to multilayer germanene. In addition, weak antilocalization is observed, serving as solid evidence for strong spin-orbit interaction (SOI) in germanane/germanene. Our study opens a possible new route to investigate the electrical transport properties of germanane/germanene, and the large SOI might provide the essential ingredients to access their topological states predicted theoretically.

Optimization of Silver Nanoparticle Synthesis by Banana Peel Extract Using Statistical Experimental Design, and Testing of their Antibacterial and Antioxidant Properties

BACKGROUND

In this study, silver nanoparticles (AgNPs) were synthesized using Banana Peel Extract (BPE), and characterized using UV- Vis absorbance spectroscopy, X-Ray Powder Diffraction (XRD), Atomic Force Microscopy (AFM), and Fourier Transform Infrared Spectroscopy (FTIR). UV-Vis absorbance spectroscopy showed the characteristic plasmon resonance of AgNPs at 433 nm. The synthesized AgNPs were tested for their antibacterial and antioxidant properties.

METHODS

Nanoparticle size (between 5 and 9 nm) was measured using AFM, whereas their crystallinity was shown by XRD. FTIR identified the ligands that surround the nanoparticle surface. The synthesis conditions were optimised using Central Composite Design (CCD) under Response Surface Methodology (RSM). Silver nitrate (AgNO3) and BPE concentrations (0.25-2.25 mM, 0.2-1.96 % v/v respectively), incubation period (24-120 h) and pH level (2.3-10.1) were chosen as the four independent factors. The fitting parameters (i.e. the wavelength at peak maximum, the peak area, and the peak width) of a Voigt function of the UV- Vis spectra were chosen as the responses. The antibacterial properties of the AgNPs were tested against Escherichia coli and Staphylococcus aureus using the tube dilution test. The synthesized nanoparticles were tested for total phenolic composition (TPC) using the Folin - Ciocalteau method, whereas their radical scavenging activity using the 1,1-diphenyl-2- picrylhydrazyl (DPPH) free radical assay.

RESULTS

An optimum combination of all independent factors was identified (BPE concentration 1.7 % v/v, AgNO3 concentration 1.75 mM, incubation period 48 h, pH level 4.3), giving minimum peak wavelength and peak width. The nanoparticles inhibited the growth of E. coli, whereas S. aureus growth was not affected. However, no superiority of AgNPs compared to AgNO3 used for their fabrication (1.75 mM), with respect to antibacterial action, could be here demonstrated. AgNPs were found to present moderate antioxidant activity (44.71± 3.01%), as measured using DPPH assay, while the BPE (used for their fabrication) presented alone (100%) an antioxidant action equal to 86±1%, something expected due to its higher total phenolic content (TPC) compared to that of nanoparticles.

CONCLUSION

Altogether, the results of this study highlight the potential of an eco-friendly method to synthesize nanoparticles and its promising optimization through statistical experimental design. Future research on the potential influence of other synthesis parameters on nanoparticles yield and properties could further promote their useful biological activities towards their successful application in the food industry and other settings.

Iron-substituted cubic silsesquioxane pillared clays: Synthesis, characterization and acid catalytic activity

Novel pillared structures were developed from the intercalation of iron-substituted cubic silsesquioxanes in a sodium and an acid-activated montmorillonite nanoclay and evaluated as acid catalysts. Octameric cubic oligosiloxanes were formed upon controlled hydrolytic polycondensation of the corresponding monomer (a diamino-alkoxysilane) and reacted with iron cations to form complexes that were intercalated within the layered nanoclay matrices. Upon calcination iron oxide nanoparticles are formed which are located on the silica cubes (pillars) and on the surfaces of the clay platelets. Acid activation of the nanoclay was performed in order to increase the number of acid active sites in the pristine clay and thus increase its catalytic activity. A plethora of analytical techniques including X-ray diffraction, thermal analyses, Fourier transform infrared, electron paramagnetic resonance, Raman, Mössbauer and X-ray photoelectron spectroscopies and porosimetry measurements were used in order to follow the synthesis steps and to fully characterize the final catalysts. The resulting pillared clays exhibit a high specific area and show significant acid catalytic activity that was verified using the catalytic dehydration of isopropanol asa probe reaction.

Synthesis, characterization and assessment of hydrophilic oxidized carbon nanodiscs in bio-related applications

Hydrophilic oxidized carbon nanodiscs able to be used as drug delivery system and as support in nanobiocatalytic applications.

Top-down and bottom-up approaches to transparent, flexible and luminescent nitrogen-doped carbon nanodot-clay hybrid films

Two easy approaches are successfully employed for the preparation of nitrogen-doped carbon nanodot (NCND)-clay hybrids (bulk solids and thin films). Fluorescent and small NCNDs are intercalated within the interlayer space of LAPONITE® clay with a simple ion exchange reaction in bulk or embedded between functionalized LAPONITE® sheets by combining a layer-by-layer approach with a self-assembly process. In both cases, homogeneous hybrids with 2D-ordered NCNDs (accounting for >20 wt%) are produced, with the NCND optoelectronic properties preserved. Drop casting of suspensions or self-assembly on flexible substrates allows the fabrication of luminescent flexible films. The transparency of the films is found to be adjustable either by controlling the concentration of the drop-cast suspensions or by the number of layers in the self-assembly procedure. The prepared films are stable over time: the inert LAPONITE® platelets not only guide the highly ordered 2D assemblies of NCNDs in the interlayer space but also protect them from external agents, which could affect their surfaces and thus alter their optoelectronic properties.

Graphene/Carbon Dot Hybrid Thin Films Prepared by a Modified Langmuir-Schaefer Method

The special electronic, optical, thermal, and mechanical properties of graphene resulting from its 2D nature, as well as the ease of functionalizing it through a simple acid treatment, make graphene an ideal building block for the development of new hybrid nanostructures with well-defined dimensions and behavior. Such hybrids have great potential as active materials in applications such as gas storage, gas/liquid separation, photocatalysis, bioimaging, optoelectronics, and nanosensing. In this study, luminescent carbon dots (C-dots) were sandwiched between oxidized graphene sheets to form novel hybrid multilayer films. Our thin-film preparation approach combines self-assembly with the Langmuir-Schaefer deposition and uses graphene oxide nanosheets as template for grafting C-dots in a bidimensional array. Repeating the cycle results in a facile and low-cost layer-by-layer procedure for the formation of highly ordered hybrid multilayers, which were characterized by photoluminescence, UV-visible, X-ray photoelectron, and Raman spectroscopies, as well as X-ray diffraction and atomic force microscopy.

The effect of the degree of oxidation on broadband nonlinear absorption and ferromagnetic ordering in graphene oxide

We report on the effect of the degree of oxidation on the broadband non-linear optical response and magnetic behavior of graphene oxide, as well as on a route for obtaining reduced graphene oxide with enhanced optical properties without sacrificing the high dispersibility of the parent graphene oxide. As more sp(3) states evolved with the rise in oxidation degree, it turned out that the sp(2)/sp(3) fraction and sp(2) clustering are crucial parameters for tuning the broadband non-linear optical absorption over a wide range from ps to ns laser pulses for both visible and infrared laser irradiation. This was clearly confirmed by two different approaches, namely by a synthetic route through the gradual oxidation of graphene oxide from 1 to 3 oxidizing cycles, and reversely by in situ reduction of graphene oxide by UV laser irradiation. Furthermore, as the sp(3) states carry localized magnetic moments, ferromagnetic ordering is observed at low temperatures. The magnetization and temperature at which ferromagnetic ordering evolves are found to increase on increasing the oxidation degree. The tuning of non-linear optical and magnetic properties of graphene oxide by oxidation/reduction thus provides an easy way to endow graphene oxide with tunable physical features highly required in both optoelectronics and spintronics applications.

Stabilization of Phenolic Radicals on Graphene Oxide: An XPS and EPR Study

A graphene oxide-gallic acid hybrid material was synthesized by the immobilization of gallic acid (3,4,5-trihydroxobenzoic acid) on graphene oxide. The grafting was achieved via the formation of amide bonds between the amine groups on the organofunctionalized graphite oxide surface and the carboxyl groups of the gallic acid molecules. The EPR signal of the gallic acid radicals in this hybrid material remained almost unaltered over at least 500 days, with less than 3% signal decay over that period, pointing to the truly remarkable stability of these radicals. The produced material was characterized by Fourier transform infrared, X-ray photoelectron, and electron paramagnetic resonance spectroscopies as well as by thermogravimetric analysis and the Kaiser test. The stability of the radicals in the material was studied in powder form and in aqueous solution vs pH. We demonstrate that in the graphene oxide-gallic acid hybrid material a radical is favorably stabilized on the ring-O while the oxidation of the second OH is precluded, and this results in long-term stabilization of the gallic acid radicals in solid hybrid material. Thus, in applications where it will be used under O2-free and humidity-free conditions, the graphene oxide-gallic acid hybrid material is a reliable spintronics scaffold.

In situ growth of capping-free magnetic iron oxide nanoparticles on liquid-phase exfoliated graphene

We report a facile approach for the in situ synthesis of very small iron oxide nanoparticles on the surface of high-quality graphene sheets. Our synthetic strategy involved the direct, liquid-phase exfoliation of highly crystalline graphite (avoiding any oxidation treatment) and the subsequent chemical functionalization of the graphene sheets via the well-established 1,3-dipolar cycloaddition reaction. The resulting graphene derivatives were employed for the immobilization of the nanoparticle precursor (Fe cations) at the introduced organic groups by a modified wet-impregnation method, followed by interaction with acetic acid vapours. The final graphene-iron oxide hybrid material was achieved by heating (calcination) in an inert atmosphere. Characterization by X-ray diffraction, transmission electron and atomic force microscopy, Raman and X-ray photoelectron spectroscopy gave evidence for the formation of rather small (<12 nm), spherical, magnetite-rich nanoparticles which were evenly distributed on the surface of few-layer (<1.2 nm thick) graphene. Due to the presence of the iron oxide nanoparticles, the hybrid material showed a superparamagnetic behaviour at room temperature.