NP Surface Research Articles

(Invited) Ligand-Directed CO2 Conversion at Bimetallic Au/Cu Nanocatalysts

The electrochemical CO2 reduction reaction (CO2RR) is a promising approach for converting waste CO2 emissions into value-added chemicals and fuels. Product selectivity will be a key requirement because down-stream chemical separation steps will introduce cost barriers and reduce the efficiency of large-scale systems. Gold electrocatalysts selectively convert CO2 into CO, which can be further processed into a wide range of other commodity chemicals, industrial precursors, and fuel additives. Copper is another popular material because it is less expensive and can directly produce hydrocarbons, but it typically demonstrates a wider product distribution than gold. Bimetallic gold-copper electrocatalysts have emerged as promising candidates for selective CO2 conversion with lower precious metal loadings, but most Au/Cu systems reported to date demonstrate lower product selectivity than pure gold. Here, we’ve combined experiment and theory to describe the CO2RR performance of monodisperse (~1.5 nm), thiol-capped, gold-copper nanoparticles (Au/Cu NPs) containing between 0-64% copper. NPs containing 49% Cu demonstrated the best performance with 94±5% CO Faradaic efficiency between -0.5V to -1.0V vs. RHE and turnover frequencies reaching 60 molecules site-1 s-1. This activity represents a 4-8 fold improvement in catalytic activity and improved product selectivity compared with identically sized, thiol capped Au NPs. X-ray absorption spectroscopy and extended x-ray absorption fine structure (EXAFS) analysis characterized the Au/Cu NP electronic structure and identified unique copper-thiol structures at the NP surface. Complementary density functional theory modeling with realistic, thiol-capped Au/Cu NP structures identified key relationships between NP composition and electrocatalytic performance. Our results show that unique copper-thiol surface structures on the Au/Cu NPs influenced CO2RR performance by stabilizing bound *CO reaction intermediates and preventing H2 evolution. Experiment and theory both indicated less-selective CO2RR at ligand-free NPs, and ligand-free Au/Cu NPs produced H2 with approximately 95% selectivity. Our combination of experiment and theory demonstrate that ligand-directed surface structuring can influence NP chemistry, improve CO2RR product selectivity, and produce highly active electrocatalysts with reduced precious metal loadings.

Relationship between the Degree of Dealloying of Ptpb Ordered Intermetallic Nanoparticle Deposited on TiO2/ Cup-Stacked Carbon Nanotube and ORR Activity in Acidic Aqueous Media for Polymer Electrolyte Fuel Cells

The development of fuel cells that covert chemical energy to electric energy with high efficiency are one of key factor to solve energy issues. In order to widespread the fuel cells to our daily life, various technologies for the fuel cells have been developed with much effort of researchers and engineers. Now, electric cars (EV) powered by electricity which is produced by fuel cells are put on the market. However, it will take a long time before it becomes widespread because from the viewpoints of performance, durability and cost, many unsolved problems are still piled. One of the unsolved problems is sluggish kinetics of oxygen reduction reaction (ORR) even on the surface of platinum (Pt). Although, theoretically, the onset potential of ORR is 1.23 V vs. NHE, due to large overpotential for ORR, the onset potential can be seen around 1 V even on Pt surface which is the best ORR catalyst in acidic aqueous solutions among catalysts composed of single elements. Pt-based alloys, core-shell structures and Pt on metal oxide have been proposed as promising catalysts in many papers. Many results on the enhancement of ORR have been reported. The important principle at the bottom of the ORR enhancements is modification of the electric state of Pt atoms on the catalyst surfaces where oxygen molecules adsorb to start the ORR. In the discussion on the enhancement of ORR and electronic modification of Pt atoms, d-band center theory is often used. The theory has become a popular language in the community of electrocatalysis, especially ORR. The principle of this theory is that in the heterogeneous reaction, adsorption of reactants starts the catalytic reactions, and the binding energy of adsorbates to the catalysis surface is largely dependent on the catalytic activity. Moreover, the binding energy can be related to the electronic structure of the surface atoms of catalysis. For example, in the ORR, the interaction of the molecular oxygen (O2) 2p state with the platinum atom 5d state produces a filled, low-lying bonding and empty, high-lying antibonding molecular orbitals. The more the electrons are filled in the antibonding state, the weaker the Pt-O2 interaction become, resulting in lower catalytic activity because O2 cannot adsorb on the Pt surfaces. On the other hand, the less the electrons are filled in the antibonding state, the stronger the Pt-O2 interaction become, resulting in lower catalytic activity because oxygen intermediate species (or products) cannot desorb from the Pt surface. Therefore, the filling level of electrons in 5d state where adsorption of O2 and desorption of intermediate species (or products) moderately occur produce the highest activity for ORR on the catalyst surfaces. Because Pt bond O2 a little strongly, as mentioned above, the filling level of electron on 5d state is tuned by Pt-based alloys, core-shell structures and Pt on metal oxide. Many papers have reported excellent volcano plots between d-band center and ORR activity, indicating the importance of moderate binding energy between O2 and catalyst surfaces. However, there are several papers suggesting that the d-band center theory cannot predict perfectly the electrocatalytic activity. In order to confirm the value of the d-band theory, more and more experimental results and careful comparison of the data with the theory are needed. In this study, in each PtPb nanopartile coated electrodes treated by the potential cycling, ORR activity was measured with rotating ring-disk electrode method and change of the surface structure and the composition of Pb atoms on the PtPb NP surface treated by the potential cycling was analyzed with transmission electron microscope (TEM). In addition, the d-band center of the Pt atoms on the treated PtPb NPs was evaluated with X-ray photoelectron spectroscopy (XPS). The volcano plot mentioned above for ORR was tried to make with the ORR activities and d-band center obtained with the electrochemically treated PtPb NPs. It was made clear that the NP surfaces prepared by gradual electrochemical dissolution of Pb atoms exhibited the shift of d-band center and that the shift of d-band center controlled the ORR activity on the dealloyed Pt-Pb NP surfaces.

Enhancing Analytical Potential of Electrochemiluminescence By the Silica Nanoparticle Approach

Electrochemiluminescence (ECL) is a leading technique in bioanalysis.1 Since the excited species are produced with an electrochemical stimulus rather than with a light excitation source, ECL displays improved signal-to-noise ratio compared to photoluminescence, with minimized effects due to light scattering and luminescence background.2 In the quest for ever-increasing sensitivities, ECL can ideally be coupled to nanotechnology and supramolecular chemistry to develop new systems and strategies for analyte determination also in very complex matrices. For instance, we have recently shown a supramolecular approach to detect sarcosine, a potential prostate cancer biomarker, in urines, with good sensitivity and very high selectivity.3 Dye-doped silica nanoparticles (DDSNs), semiconductor nanocrystals, or polymer dots were also advantageously used as ECL-active systems.4,5 In particular, DDSNs present many advantages: they can be obtained with accessible synthetic schemes, are intrinsically hydrophilic, and, thanks to silica chemistry, are prone to bioconjugation. Very bright systems can be obtained with this approach since silica is inert from the photophysical point of view, and DDSNs assume the photophysical properties of the dye(s) molecules accumulated within the nanoparticle.5 In DDSNs, light emission is influenced by the combination of several factors that make DDSNs complex multichromophoric structures, such as the coexistence of dye populations experimenting with slightly different environments and the occurrence of intraparticle energy transfer processes (mainly resonance energy transfer or quenching). When ECL comes into play, the scenario is even more complicated by the presence of the coreactant−NP interactions, since the coreactant needs to approach the NP surface and to react with the dyes buried within the silica at different extent. A scenario of such a complexity was then approached at the theoretical level by developing suitable mechanistic models for ECL generation6 while, at the same time, the influence of doping level and particle charging on ECL efficiency was evaluated. The results showed that the ECL intensity of a nanosized system cannot be merely incremented acting on doping, since other parameters come into play.7 These studies provide valuable indications for the design of more efficient ECL nano- and microsized labels for ultrasensitive bioanalysis. (1) http://www.cobas.com/home/product/clinical-and-immunochemistry-testing/technology-elecsys-ecl.html (2) Hesari, M.; Ding, Z. J. Electrochem. Soc. 2016, 163 (4), H3116 (3) Valenti, G.; Rampazzo, E.; Biavardi, E.; Villani, E.; Fracasso, G.; Marcaccio, M.; Bertani, F.; Ramarli, D.; Dalcanale, E.; Paolucci, F.; Prodi, L. Faraday Discuss. 2015, 185, 299 (4) Wusimanjiang, Y.; Meyer, A.; Lu, L.; Miao, W. Anal. Bioanal. Chem. 2016, 408, 7049; Qi, H.; Zhang, C.; Huang, Z.; Wang, L.; Wang, W.; Bard, A. J. J. Am. Chem. Soc. 2016, 138, 1947−1954; Li, H.; Daniel, J.; Verlhac, J.-B.; Blanchard-Desce, M.; Sojic, N. Chem. - Eur. J. 2016, 22, 12702 (5) Zanarini, S.; Rampazzo, E.; Bonacchi, S.; Juris, R.; Marcaccio, M.; Montalti, M.; Paolucci, F.; Prodi, L. J. Am. Chem. Soc. 2009, 131, 14208−14209; Valenti, G.; Rampazzo, E.; Bonacchi, S.; Petrizza, L.; Marcaccio, M.; Montalti, M.; Prodi, L.; Paolucci F. J. Am. Chem. Soc. 2016, 138, 15935 (6) Imai, K.; Valenti, G.; Villani, E.; Rapino, S.; Rampazzo, E.; Marcaccio, M.; Prodi, L.; Paolucci, F. J. Phys. Chem. C 2015, 119, 26111; Daviddi, E.; Oleinick, A.; Svir, I.; Valenti, G.; Paolucci, F.; Amatore, C. ChemElectroChem 2017, 4, 1719 (7) Kesarkar, S.; Rampazzo, E.; Valenti, G.; Marcaccio, M.; Bossi, A.; Prodi, L.; Paolucci, F. ChemElectroChem 2017, 4, 1690

Conformational properties of intrinsically disordered proteins bound to the surface of silica nanoparticles

BackgroundProtein-nanoparticle (NP) interactions dictate properties of nanoconjugates relevant to bionanotechnology. Non-covalent adsorption generates a protein corona (PC) formed by an inner and an outer layer, the hard and soft corona (HC, SC). Intrinsically disordered proteins (IDPs) exist in solution as conformational ensembles, whose response to the presence of NPs is not known. MethodsThree IDPs (α-casein, Sic1 and α-synuclein) and lysozyme are compared, describing conformational properties inside HC on silica NPs by circular dichroism (CD) and Fourier-transform infrared (FTIR) spectroscopy. ResultsIDPs inside HC are largely unstructured, but display small, protein-specific conformational changes. A minor increase in helical content is observed for α-casein and α-synuclein, reminiscent of membrane effects on α-synuclein. Frozen in their largely disordered conformation, bound proteins do not undergo folding induced by dehydration, as they do in their free forms. While HC thickness approaches the hydrodynamic diameter of the protein in solution for lysozyme, it is much below the respective values for IDPs. NPs boost α-synuclein aggregation kinetics in a dose-dependent manner. ConclusionsIDPs maintain structural disorder inside HC, experiencing minor, protein-specific, induced folding and stabilization against further conformational transitions, such as formation of intermolecular beta-sheets upon dehydration. The HC is formed by a single layer of protein molecules. SC likely plays a key role stabilizing amyloidogenic α-synuclein conformers. General significanceProtein-NP interactions can mimic those with macromolecular partners, allowing dissection of contributing factors by rational design of NP surfaces. Application of NPs in vivo should be carefully tested for amyloidogenic potential.

Modification of poly(benzimidazole‐amide) nanocomposites by the incorporation of amine‐functionalized ZnO nanoparticles: Thermal and morphological characterization

Fabrication, characterization, and properties of novel poly(benzimidazole‐amide)/functionalized ZnO nanocomposites (PBIA/APS‐ZnO NCs) were investigated. At first, an aromatic PBA containing 3 imidazole units per repeat unit was synthesized by direct polycondensation of 1,3‐bis(5‐carboxylic acid‐2‐benzimidazole)benzene (BCAB) with 5‐(2‐benzimidazole)‐1,3‐phenylenediamine (DAMI) with good yield as a polymeric matrix. The periphery of zinc oxide nanoparticles (ZnO NPs) was modified with 3‐aminopropyltriethoxysilane (APS) to have a better dispersion NPs and enhancing interactions between nanoparticles and PBIA matrix. Different percentages of functionalized NPs (0, 4, 8, and 12 wt.%) were then embedded in PBA matrix through ultrasonic irradiation technique. Fourier transform infrared and thermo‐gravimetric analysis (TGA) confirmed that APS was successfully attached on the ZnO NP surface. The obtained NCs were characterized by means of Fourier transform infrared, X‐ray diffraction, scanning electron microscopy, and TGA. The TGA of the PBIA/APS‐ZnO NCs showed the enhancement in the thermal stability in comparison with the neat PBIA and that this increase is higher when the NP content increases. Scanning electron microscopy analyses of NCs revealed that the dispersion of APS‐ZnO NPs was uniformly done in the PBIA matrix.

Enhanced and Facet-specific Electrocatalytic Properties of Ag/Bi2Fe4O9 Composite Nanoparticles.

Ag/Bi2Fe4O9 nanoparticles (BFO NPs) have been synthesized using a two-step approach involving glycine combustion and visible light irradiation. Their structures were characterized in detail using X-ray diffraction, transmission electron microscope, scanning electron microscopy, and scanning transmission electron microscopy techniques. Their electrocatalytic properties were studied through enzymatic glucose detection with an amperometric biosensor. The Ag deposited on selective crystal facets of BFO NPs significantly enhanced their electrocatalytic activity. To gain insights into the origin of the enhanced electrocatalytic activities, we have carried out studies of Ag+ reduction and Mn2+ oxidation reaction at the {200} and {001} facets, respectively. The results suggest effective charge separation on the BFO NP surfaces, which is likely responsible for the enhanced electrocatalytic properties. Furthermore, enhanced ferromagnetism was observed after the Ag deposition on BFO NPs, which may be related to the improved electrocatalytic properties through spin-dependent charge transport. The facet-specific electrocatalytic properties are highly interesting and desired for chemical reactions. This study demonstrates that Ag/BFO NPs are potentially useful for electrocatalytic applications including biosensing and chemical synthesis with high product selectivity.

Internal standard-based SERS aptasensor for ultrasensitive quantitative detection of Ag+ ion

A ratiometric surface-enhanced Raman scattering (SERS) aptasensor based on internal standard (IS) methods was proposed for the ultrasensitive and reproducible quantitative detection of silver ion (Ag+) with Au@Ag core-shell nanoparticle (Au@Ag NP) substrate. In principle, the thiolated 5′-Rox C-containing labeled aptamer probe (Rox-aptamer) is firstly immobilized on the SERS substrate surface and then hybridizes with the complementary DNA (cDNA) to form a rigid double-stranded DNA (dsDNA), in which the Rox Raman labels is used to produce the Raman signal. Furthermore, the pyridine is employed as an IS element to provide the ratiometric determination of target. In the presence of Ag+, the Rox-aptamer is turned into the cytosine (C)-Ag+-C mediated hairpin structure, which remarkably reduces the distance between the Rox labels and the Au@Ag NP surface responsible for a measurable ‘turn-on’ signal change of Rox. This IS-based ratiometric SERS aptasensor exhibits a limit of detection of 50 pM for Ag+ with a linear detection range from 0.1 to 100 nM and the shortcoming of irreproducibility of SERS signal could be overcome. The proposed method provides a simple, robust, and rapid approach for the sensitive and reproducible quantitative detection of Ag+, and it could also be used for the detection of other metal ions which exhibits specific interactions with natural or synthetic bases.

Copper Metal-Organic Framework Nanoparticles Stabilized with Folic Acid Improve Wound Healing in Diabetes.

The successful treatment of chronic nonhealing wounds requires strategies that promote angiogenesis, collagen deposition, and re-epithelialization of the wound. Copper ions have been reported to stimulate angiogenesis; however, several applications of copper salts or oxides to the wound bed are required, leading to variable outcomes and raising toxicity concerns. We hypothesized that copper-based metal-organic framework nanoparticles (Cu-MOF NPs), referred to as HKUST-1, which are rapidly degraded in protein solutions, can be modified to slowly release Cu2+, resulting in reduced toxicity and improved wound healing rates. Folic acid was added during HKUST-1 synthesis to generate folic-acid-modified HKUST-1 (F-HKUST-1). The effect of folic acid incorporation on NP stability, size, hydrophobicity, surface area, and copper ion release profile was measured. In addition, cytotoxicity and in vitro cell migration processes due to F-HKUST-1 and HKUST-1 were evaluated. Wound closure rates were assessed using the splinted excisional dermal wound model in diabetic mice. The incorporation of folic acid into HKUST-1 enabled the slow release of copper ions, which reduced cytotoxicity and enhanced cell migration in vitro. In vivo, F-HKUST-1 induced angiogenesis, promoted collagen deposition and re-epithelialization, and increased wound closure rates. These results demonstrate that folic acid incorporation into HKUST-1 NPs is a simple, safe, and promising approach to control Cu2+ release, thus enabling the direct application of Cu-MOF NPs to wounds.

Roles of Textural and Surface Properties of Nanoparticles in Ultrasound-Responsive Systems.

Acoustic inertial cavitation (IC) is a crucial phenomenon for many ultrasound (US)-related applications. This study aimed to investigate the roles of textural and surface properties of NPs in IC generation by combining typical IC detection methods with various types of silica model NPs. Acoustic passive cavitation detection, optical high-speed photography, and US imaging have been used to quantify IC activities (referred to as the IC dose, ICD) and describe the physical characteristics of IC activities from NPs. The results showed that the ICDs from NPs were positively correlated to their surface hydrophobicity and that their external surface hydrophobicity plays a much more crucial role than do the textural properties. The high-speed photography revealed that the sizes of IC-generated bubbles from superhydrophobic NPs ranged from 20-40 μm at 4-6 MPa and collapsed in several microseconds. Bubble clouds monitored with US imaging showed that IC from NPs was consistent with the surface hydrophobicity. The simulation results based on the crevice model of cavitation nuclei correlated well with the experimental results. This study has demonstrated that the surface property, instead of the textural property, of NPs dominated the IC generation, and surface nanobubbles adsorbed on the NP surface have been proposed to be cavitation nuclei.

A comparative toxicity study of TiO2 nanoparticles in suspension and adherent culture under the dark condition

The present study focused on the different acute toxicity of TiO2 nanoparticles(TiO2 NPs) towards the bacteria in suspension culture and adherent culture under the dark conditions. The study investigated the bacteria toxicity with TiO2 NPs at different concentrations(1—2000 mg/L), sizes(10 nm, 35 nm) and specific surface areas in unit volume solution(0—224 m2/L) characterized by the cell viability, extracellular polymeric substances(EPS) release and biofilm formation. The bacteria in adherent culture was found to be more resistant against the toxicity of TiO2 NPs compared to that in suspension culture. An NP dose and surface area dependent(rather than the size) bacterial viability was observed in suspension culture, specifically the surface area positively correlated with the toxicity of TiO2 NPs. The size of TiO2 NPs, however, played a more critical role in toxicity of TiO2 NPs in adherent culture. Therefore, the surface area dependent toxicity of TiO2 NPs is a comprehensive parameter describing the dose and size dependent toxicity of TiO2 NPs. The electron microscopic(SEM, TEM, EDX) observations suggested the EPS release and biofilm formation, during aggregation of TiO2 NPs on the bacteria after 12 h cultivation in adherent culture under the dark condition. A possible toxic mechanism could be that “effective surface areas” that directly contact with the bacterial membrane greatly contributed to the toxicity of TiO2 NPs in both suspension culture and adherent culture. Therefore, as for the possible resistance mechanism, EPS secretion and subsequent biofilm formation may protect the bacteria against the toxicity of TiO2 NPs.

Engineering a Localized Surface Plasmon Resonance Platform for Molecular Biosensing

In this work, we introduce a new perspective on the development of Localized Surface Plasmon Resonance (LSPR) optical biosensors. Computational simulations, focused on the assessment of the LSPR spectrum and spatial distribution of the electromagnetic field enhancement near a metallic nanoparticle, elucidated the behavior of crucial parameters, as figure of merit, bulk and molecular sensitivity, which governs a LSPR sensor performance. Gold and silver nanospheres were explored as starting point to assess plasmonic optical characteristics of the nanostructured sensor platform. Here, for the first time in the literature, Campbell’s model was evaluated exploiting a NP size-dependence approach. The theoretical analyses indicate a nonlinear behavior of the bulk and molecular sensitivity as function of the NP size. Substantial LSPR peak shifts due to the adsorption of molecules layer on a NP surface were observed for nanoparticles with ~5 nm and ~40 nm radius. Moreover, on molecular sensing, LSPR peak shift is also determined by the thickness of adsorbed molecular shell layers. We observed that for 40 nm radius gold and silver nanospheres, significant LSPR peak shift could be induced by small (few nm) thickness change of the adsorbate shell layer. Moreover, this work provides insights on the LSPR behavior due to adsorption of molecular layer on a NP surface, establishing a new paradigm on engineering LSPR biosensor. Furthermore, the proposed approach can be extended to engineer an efficiently use of different nanostructures on molecular sensing.

Probing fibronectin conformation on a protein corona layer around nanoparticles.

Protein unfolding induced by nanoparticles (NPs) can lead to exposure of cryptic epitopes that might dictate biological identity and affect NP biological fate (e.g., blood circulation time, biodistribution, and tumor accumulation). Here, we monitor the conformation of fluorescence resonance energy transfer (FRET)-labelled fibronectin (FN) on corona-coated gold NPs. We found that the labelled FN proteins, which directly accessed the gold NP surface, underwent more pronounced conformational changes than those associated with the protein corona via protein-protein interactions. FRET and liquid chromatography-mass spectrometry analyses demonstrated that NP size/concentration, pH change, and the level of surface coverage by the corona can tune the accessibility of labelled FN to the gold NP surface. Although some subsequently adsorbing proteins accessed the NP surface thanks to incomplete surface coverage and protein exchange (the Vroman effect), most outer-layer proteins could not directly bind to the NP surface, blocked by pre-adsorbed corona layers. This finding was also partially confirmed by isothermal titration calorimetry (ITC) analysis. These results suggest the proof-of-concept that outermost-layer proteins with modestly changed conformation rather than unfolded proteins at the gold NP surface effectively create the NPs' biological identity, which might have important implications on biological fates of gold NPs.

Tuning the surface of Au nanoparticles using poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol): enzyme free and label free sugar sensing in serum samples using resonance Rayleigh scattering spectroscopy.

Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (F-108) functionalized gold nanoparticles (Au NPs) have been successfully synthesized. During synthesis it is found that an increase in the F-108 concentration contributes to agglomeration in the media, increasing the size of the Au particles, and boosting the curcumin concentration leads to a higher density of functional groups, resulting in smaller Au NPs. FT-IR analysis reveals that the hydroxyl and phenolic groups of curcumin and F-108 are involved during the functionalization of Au surfaces. Enhancement in the fluorescence/RRS intensity is due to the combination of the influence of the shape/size of the Au NPs as well as the extent of curcumin conjugation at the interface of the Au NP surface and F-108. The presence of sugar molecules remarkably boosts the RRS intensity without significantly affecting the fluorescence and surface plasmon absorbance of the Au NPs; in contrast, the RRS intensity of standard CTAB functionalized Au NPs is unaffected by glucose molecules indicating that the functionalization of F-108 at Au surfaces is crucial. Interestingly, no interference from other potential interferents and antioxidant substances like ascorbic acid, creatinine and acetaminophen is observed. This method is simple and fast, and offers a wider linear dynamic range, 0-10 mM, that is applicable under physiological conditions and in serum samples. It is stable and provides an excellent recovery for serum samples, thus, potentially it can be useful in this field due to its low energy consumption, enzyme free assay, fast response time, better selectivity and sensitivity.

Biosynthesis of copper nanoparticles supported on manganese dioxide nanoparticles using Centella asiatica L. leaf extract for the efficient catalytic reduction of organic dyes and nitroarenes

In this study we designed a novel, cost-efficient and green method for the synthesis of copper nanoparticles (Cu NPs) supported on manganese dioxide (MnO2) NPs, using Centella asiatica L. leaf extract as a naturally-sourced reducing agent, without stabilizers or surfactants. This synthetic process is environmentally-friendly and avoids the use of toxic reducing agents. Phenolic hydroxyl groups in the leaf extract are believed to reduce Cu2+ in solution to generate Cu NPs that are subsequently stabilized on the MnO2 NP surfaces. The resulting Cu/MnO2 nanocomposite was fully characterized using X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. This material was found to function as a highly active, efficient and recyclable heterogeneous catalyst for the reduction of Congo red, rhodamine B and methylene blue as well as nitro compounds such as 2,4-dinitrophenylhydrazine and 4-nitrophenol in the presence of NaBH4 in aqueous media at ambient temperature. The high stability of the Cu/MnO2 nanocomposite also allows the catalyst to be separated and reused several times without any significant loss of activity.

Surface Modification of Zinc Oxide by 3-aminopropyltiethoxysilane and a Comparative Study of Effect of Corrosion on Carbon Steel With Epoxy Containing Graphene Oxide-Zinc Oxide (GO-ZnO) Hybrids

The use of coupling agent, 3-aminopropyltiethoxysilane (APTES) in the silanization reaction with metal oxides plays an important role to ensure that additional chemical modification can successfully be achieved. Studies have shown that introducing metal oxides onto graphene oxide sheets can improve the dispersion of sheets in a polymeric matrix, contributing to its excellent anti-corrosion properties. Hence, two methods of APTES attachment has been explored, where the first method utilizes a reflux process to introduce siloxane bonds to the ZnO NP surface; the latter usesuse of ultrasonication to stimulate the functionalization of ZnO NPs. Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) were employed to characterize the APTES-Functionalized ZnO and the precipitation on the surface of GO sheets. The effect of GO-ZnO produced by the different types of functionalized ZnO on the corrosion protection and barrier performance of epoxy coating was investigated by electrochemical impedence spectroscopy (EIS). The results revealed that the long duration of reaction time provided by the reflux method managed to increase the number of siloxane bonds on the ZnO surface, allowing more amine groups to be attached onto the GO sheets and thus improve the corrosion resistance of epoxy.

Antibacterial effect of the laser-generated Se nanocoatings on Staphylococcus aureus and Pseudomonas aeruginosa biofilms

The antibacterial properties of selenium nanoparticles (Se NPs) were successfully demonstrated in vitro for Staphylococcus aureus and Pseudomonas aeruginosa biofilms. The possible mechanisms of antibacterial impact included the emergence of reactive oxygen species, induced by free radicals on the NP surface and accompanied by subsequent oxidative stress, as well as mechanical decomposition of the mitochondrial membrane. Se nanocoatings were deposited on bare and silver-coated silica glass substrates via inkjet printing with concentrated nanoinks, prepared by infrared laser-ablative processing of a solid Se target in a 50%-isopropyl solution. The resulted porous nanofilms with high-percentage surface coverage, consisting of spherical Se NPs and Se nanorods, were characterized by means of standard microscopy techniques (optical, scanning electron, transmission), UV–vis–IR and EDX spectroscopy.

Domain Formation and Conformational Changes in Gold Nanoparticle Conjugates Studied Using DPD Simulations.

A gold nanoparticle (AuNP) conjugate formed with 11-mercaptoundecanoic acid (MUA) and thiolated polyethylene glycol (SH-PEG) is simulated using dissipative particle dynamics (DPD) methods, obtaining an excellent agreement with previous experimental observations. The simulations cover the isolated components (AuNP, MUA, and SH-PEG), as well as pairs of components, and finally the all three components at the same time. In this latter case, changes in the order of addition of MUA and SH-PEG over the AuNP are also considered. The AuNP is formed by independent gold beads and keeps an almost spherical shape throughout the simulation. MUA forms micelles of four to six MUA units when dispersed in water, while SH-PEG stays individually and well solvated. When exposed to AuNP, both molecules show a tendency to form patches on the surface. SH-PEG displays two different conformations (radial and tangential) depending on its relative concentration and the presence of other molecules at the NP surface. When combined at subsaturation concentrations, MUA arrives faster to the AuNP surface than SH-PEG and forms patches while SH-PEG occupies the remaining free surface. In these conditions, the order of addition of the different components partially alters these results. When SH-PEG is added over an already formed MUA/AuNP partial layer, it adopts a radial conformation over the MUA formed patches; on the contrary, if MUA is added over an already formed SH-PEG/AuNP partial layer, much less SH-PEGs adopt a radial conformation and MUA patches are significantly smaller.

Synthesis of Cu Nanoparticles: Stability and Conversion into Cu2S Nanoparticles by Decomposition of Alkanethiolate.

A lean synthesis of copper nanoparticles (Cu NP) from CuCl2 in dodecane via formation of Cu(I)-dodecanethiolate (Cu(I)-DDT) and their decomposition paths including spontaneous C-S bond cleavage of the alkanethiol on the surface of Cu NP is presented. The reduction of Cu(I)-DDT by the tert-butylamine-borane complex (TBAB) in dodecane under N2 at elevated temperatures leads to the formation of thiol-protected Cu NP with narrow size distribution in the size range of 3-10 nm depending on the reaction conditions. The Cu NP in the presence of excess dodecanethiol reacts further to Cu2S NP under decomposition of the ligand on the particle surface. The Cu2S formation occurs after a short time at T > 175 °C or within ∼12 h at room temperature. If excess thiol is removed immediately after the synthesis, the resulting colloid shows irreversible aggregation within days or hours. Our results suggest that alkanethiols are not long-term stable on nanocopper surfaces and that the formation of copper(I) sulfide under the cleavage of the C-S bond occurs even at room temperature.

Silver nanoparticle-human hemoglobin interface: time evolution of the corona formation and interaction phenomenon

In this paper, we have used spectroscopic and electron microscopic analysis to monitor the time evolution of the silver nanoparticles (Ag NP)–human hemoglobin (Hb) corona formation and to characterize the interaction of the Ag NPs with Hb. The time constants for surface plasmon resonance binding and reorganization are found to be 9.51 and 118.48 min, respectively. The drop of surface charge and the increase of the hydrodynamic diameter indicated the corona of Hb on the Ag NP surface. The auto correlation function is found to broaden with the increasing time of the corona formation. Surface zeta potential revealed that positively charged Hb interact electrostatically with negatively charged Ag NP surfaces. The change in α helix and β sheet depends on the corona formation time. The visualization of the Hb corona from HRTEM showed large number of Hb domains aggregate containing essentially Ag NPs and without Ag NPs. Emission study showed the tertiary deformation, energy transfer, nature of interaction and quenching under three different temperatures.

Design, Self-Assembly, and Switchable Wettability in Hydrophobic, Hydrophilic, and Janus Dendritic Ligand–Gold Nanoparticle Hybrid Materials

Controlling nanoparticles’ (NPs) surface polarity, colloidal stability, and self-assembly into well-defined complex architectures is of paramount importance for emergent nano- and biotechnologies, and each depends strongly on the ligand shell composition and chemical nature. In this study, a series of dendritic ligands with hydrophobic, hydrophilic, and Janus surface groups was synthesized, grafted onto Au NPs, and their effects on the self-assembly behavior and surface polarity of the corresponding hybrid materials were investigated. A generalized, flexible strategy was utilized for ligand synthesis that independently introduces dendritic end groups, responsible for the surface polarity and colloidal properties, and specific surface NPs binding groups, reducing the number of synthetic steps. The dendritic ligands obtained were grafted onto NP surfaces through solution phase ligand-exchange, and the resulting NP–dendron hybrids were studied using a variety of techniques such as transmission electron micro...