Surface Capping Research Articles

Investigation of the surface chemical and electronic states of pyridine-capped CdSe nanocrystal films after plasma treatments using H2, O2, and Ar gases

Surface chemical bonding and the electronic states of pyridine-capped CdSe nanocrystal films were evaluated using x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy before and after plasma treatments using H2, O2, and Ar gases from the viewpoint of studying the effects of surface capping organic molecules and surface oxidation. Surface capping organic molecules could be removed during the plasma treatment due to the chemical reactivity, ion energy transfer, and vacuum UV (VUV) of the plasma gases. With O2 plasma treatment, surface capping organic molecules were effectively removed but substantial oxidation of CdSe occurred during the plasma treatment. The valence band maximum energy (EVBM) of CdSe nanocrystal films mainly depends on the apparent size of pyridine-capped CdSe nanocrystals, which controls the interparticle distance, and also on the oxidation of CdSe nanocrystals. Cd-rich surface in O2 and H2 plasma treatments partially would compensate for the decrease in EVBM. After Ar plasma treatment, the smallest value of EVBM resulted from high VUV photon flux, short wavelength, and ion energy transfer. The surface bonding states of CdSe had a strong influence on the electronic structure with the efficient strip of capping molecules as well as different surface oxidations and surface capping molecule contents.

ChemInform Abstract: Optical Properties of Amorphous ZnO, CdO, and PbO Nanoclusters in Solution.

The authors prepared ZnO, CdO, and PbO rock salt-coordinated and ZnO quartzite-coordinated nanoclusters with a microemulsion method in the AOT reverse micelle. X-ray and electron beam diffraction techniques indicate that all have amorphous structures. The similarity of the UV-visible absorption and photoluminescence spectra at room temperature for ZnO, CdO, and PbO rock salt-coordinated nanoclusters indicates that they are all similar in electronic structure. All prepared nanosystems show strong emission in the visible region, and the emission features depend on the wavelength of the excitation. This phenomenon is considered as a result of localization of the electronic state due to the amorphous structure of nanocluster and surface capping. Time-resolved photoluminescence studies on ZnO, CdO, and PbO nanoclusters were performed. The carrier lifetimes near the band-tail are in the sub-and nanosecond time ranges with different characteristics from that of bulk amorphous semiconductors and nanocrystals. The observed properties can be explained in terms of quantum confinement, structural disorder, and surface polarization.

A novel method for synthesis of colloidal silver nanoparticles by arc discharge in liquid

This paper presents a novel, inexpensive and one-step approach for synthesis of silver nanoparticles (Ag NPs) using arc discharge between titanium electrodes in AgNO 3 solution. The resulting nanoparticles were characterized using UV–Vis spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Silver nanoparticles of 18 nm diameter were formed during reduction of AgNO 3 in plasma discharge zone. Optical absorption spectroscopy of as prepared samples at 15 A arc current in AgNO 3 solution shows a surface plasmon resonance around 410 nm. It was found that sodium citrate acts as a stabilizer and surface capping agent of the colloidal nanoparticles. SEM images exhibit the increase of reduced nanoparticles in 6 min arc duration compared with 1 min arc duration. TEM image of the sample prepared at 6 min arc duration shows narrow size distribution with 18 nm mean particle size. Antibacterial activities of silver nanoparticles were investigated at the presence of Escherichia coli (E-coli) bacteria.

Role of anti‐idiotypic antibodies in immune tolerance induction

Replacement therapy using factor VIII (FVIII) elicits FVIII-specific antibodies (abs) in about 25% of the patients. A majority of such abs are directed towards specific FVIII regions in which major epitopes have been identified (C-terminal end of the C2 domain, the N-terminal end of the A2 domain and C1 domain in cases of mild/moderate haemophilia A). We derived five human monoclonal abs (mabs) that react with high affinity to the FVIII C1, C2 or A2 domains respectively and are representative of most of the specific inhibitors observed in haemophilia A patients. We generated mouse anti-idiotypic mabs (anti-Ids) against the paratope of each of the inhibitors. We demonstrated that a combination of these anti-Ids (anti-anti-A2, -C1, -C2) had the ability to neutralize the inhibitory properties of human polyclonal abs in plasma. In 16 of the 18 plasmas tested, the inhibiting FVIII activity was neutralized up to 100% by the anti-Ids mixture with restoration of full FVIII activity. These data allow us to conclude that polyclonal high-affinity FVIII inhibitors could be neutralized with an anti-Ids mixture and that only a limited number of anti-Ids were required for inhibitor neutralization in 90% of the patients. We also demonstrated that anti-Id Abs bound to anti-FVIII human B cell line produced the corresponding anti-FVIII Ab and that this binding was followed by surface capping of complexes. Data obtained in vitro at monoclonal and polyclonal level, confirmed by in vivo assays, and the preliminary results obtained at BCR level, indicate that anti-id mixture made of only a limited number of anti-Ids could be useful in the restoration of haemostasis in haemophilia patients with inhibitor.

Optical properties of ZnTe nanorods synthesized via a facile low-temperature solvothermal route

ZnTe nanorods have been synthesized in hydrazine hydrate solution at a low temperature of 80 °C and subsequent thermal treatment in N2. The advantages of this method are of simplicity, easy to scale-up, low cost, and without using any organic dispersant or surface capping agent. Scanning electron microscopy images indicate the nanorod shape of as-prepared ZnTe with a diameter of 150-300 nm and length up to several micrometres. X-ray diffraction pattern confirms that the ZnTe nanorods have the cubic structure of zinc blende type with lattice parameter a = 6.111 Å. Thermo-gravimetric analysis and differential scanning calorimetry investigations reveal that neutral hydrazine and excess tellurium are directly intercalated into the ZnTe precursor framework and are decomposed during the thermal treatment. Absorption spectrum shows that as-synthesized ZnTe nanorods have an interband absorption at 543 nm (2.28 eV). Photoluminescence spectrum and fluorescent imaging of the products exhibit a visible light emission (at 558 nm).

Molecular modeling of proteinlike inclusions in lipid bilayers: Lipid-mediated interactions

We investigated the insertion of transmembrane structures in a lipid bilayer and their interactions using self-consistent field theory. The lipids are coarse-grained on a united-atom level and consist of a phosphatidylcholinelike headgroup and two hydrophobic tails. The inclusions, acting as simple models for proteins that span biological membranes, are rigid rods (radius R ) with a hydrophobic surface and hydrophilic end caps. The insertion free energy Omega of an individual rod is strongly regulated by the affinity between its hydrophobic surface and the lipid tails. This affinity also controls the best match of the hydrophobic length of the rod with that of the bilayer. The line tension tau(=Omega/2piR) is practically independent of R . The perturbations in the bilayer as a function of distance from the inclusion, have the shape of a damped oscillation. The wavelength and decay length are related to the elastic properties of the bilayer and do not depend on R . These results are used to analyze how the lipid matrix affects the interaction between transmembrane objects, for computational reasons considering the limit of R-->infinity . Contributions on different length scales can be distinguished: (i) a long-range elastic interaction, which is an exponentially decaying oscillation; (ii) an exponentially decaying repulsion on an intermediate length scale, resulting from the loss of conformational entropy of the lipid tails; and (iii) a short-range interaction due to the finite compressibility of the lipid tails, which manifests either as a depletion attraction if there is no affinity between the tails and the inclusions' surface or, otherwise, as an oscillatory structural force.

MARCI and MOC observations of the atmosphere and surface cap in the north polar region of Mars

We used MGS–MOC and MRO–MARCI daily mapping images of the North Polar Region of Mars from 16 August 2005 ( L s = 270°) to 21 May 2009 ( L s = 270°), covering portions of three consecutive martian years (MY 27–MY 29), to observe the seasonal behavior of the polar ice cap and atmospheric phenomena. The rate of cap regression was similar in MY 28 and MY 29, but was advanced by 3.5° of L s (∼7–8 sols) in MY 29. The spatial and temporal behaviors of dust and condensate clouds were similar in the two years and generally in accord with prior years. Dust storms (>100 km 2) were observed in all seasons, with peak activity occurring at L s = 10–20° from 50°N to 70°N and at L s = 135–140° from 70°N to 90°N. The most active quadrant was 0–90°W in MY 28, shifting to 180–270°W in MY 29. The majority of regional storms in both years developed in longitudes from 10°W to 60°W. During late summer the larger storms obscure the North Polar Region in a cloud of dust that transitions to north polar hood condensate clouds around autumnal equinox. Changes in the distribution of perennial ice deposits, especially in Olympia Planum, were observed between the 2 years, with the MY 29 ice distribution being the most extensive observed to date. Modeling suggests that the small, bright ice patches on the residual cap are not the result of slope or elevation effects. Rather we suggest that they are the result of local meteorological effects on ice deposition. The annual darkening and brightening of peripheral areas of the residual cap around summer solstice can be explained by the sublimation of a brighter frost layer revealing an underlying darker, ice rich layer that itself either sublimes to reveal brighter material below or acts as a cold trap, attracting condensation of water vapor that brightens the surface. An alternative explanation invokes transport and deposition of dust on the surface from the cap interior, and later removal of that dust. The decrease in cap albedo and accompanying increase in near surface atmospheric stability may be related to the annual minimum of polar storm activity near northern summer solstice.

Composition-Dependent Formation of Platinum Silver Nanowires

The understanding of shape control of colloidal nanoparticles is still rather limited even after well over a decade of intensive research efforts. While surface capping agents can greatly influence the growth habit of nanocrystals in solution, the formation of certain morphology can hardly be understood based on both experimental data and simulations. Without a good understanding of the origins for shape formation, deterministic approaches to the synthesis of nanostructures can be hard to realize. In this paper, we describe the synthesis and formation of PtAg alloy nanowires in the presence of oleylamine and oleic acid through the oriented attachment. Transmission electron microscopy study shows the formation of wormlike nanowires occurs largely at the composition around Pt(50)Ag(50). Both Pt and Ag rich alloy nanostructures form sphere-like or faceted nanoparticles under the same reaction conditions. Density functional theory calculation is used to understand the interactions between the functional groups of capping agents and low index planes of PtAg alloys. The structural order of interfaces after collision between primary particles is obtained by molecular dynamic simulation. The results indicate that the formation of alloy nanowires is mostly driven by the interplay between the binding energy of capping agents on alloy surfaces and the diffusion of atoms at the interface upon the collision of primary nanoparticles.

Photocatalytic study of two-dimensional ZnO nanopellets in the decomposition of methylene blue

We report several significant photodecomposition rates of methylene blue (MB) obtained before and after the refluxing process of own-synthesized two-dimensional (2D) zinc oxide (ZnO) nanopellets. Each photodecomposition rate of MB was found highly dependent on the weight of photocatalyst. The existing photodecomposition rate has been successfully improved to a factor of 22.0 times through refluxing process in excessive pyridine where the surface capping ligand (oleic acid) is removed from the 2D ZnO nanopellets. On the other hand, the refluxed photocatalyst (0.04 g) in this study was found to exhibit excellent recyclability up to three cycles. Furthermore, X-ray powder diffraction spectrums for the refluxed photocatatalyst, respectively, before and after three cycles of photocatalytic reactions, has generated the same patterns showing that the photocatalyst is stable and feasible to be used as an efficient photocatalyst material. Hence, these 2D ZnO nanopellets would provide a new alternative route as a highly efficient photocatalyst for wastewater treatment.

Gold nanoparticles delivery in mammalian live cells: a critical review.

Functional nanomaterials have recently attracted strong interest from the biology community, not only as potential drug delivery vehicles or diagnostic tools, but also as optical nanomaterials. This is illustrated by the explosion of publications in the field with more than 2,000 publications in the last 2 years (4,000 papers since 2000; from ISI Web of Knowledge, ‘nanoparticle and cell’ hit). Such a publication boom in this novel interdisciplinary field has resulted in papers of unequal standard, partly because it is challenging to assemble the required expertise in chemistry, physics, and biology in a single team. As an extreme example, several papers published in physical chemistry journals claim intracellular delivery of nanoparticles, but show pictures of cells that are, to the expert biologist, evidently dead (and therefore permeable). To attain proper cellular applications using nanomaterials, it is critical not only to achieve efficient delivery in healthy cells, but also to control the intracellular availability and the fate of the nanomaterial. This is still an open challenge that will only be met by innovative delivery methods combined with rigorous and quantitative characterization of the uptake and the fate of the nanoparticles. This review mainly focuses on gold nanoparticles and discusses the various approaches to nanoparticle delivery, including surface chemical modifications and several methods used to facilitate cellular uptake and endosomal escape. We will also review the main detection methods and how their optimum use can inform about intracellular localization, efficiency of delivery, and integrity of the surface capping.

Synthesis and characterization of perovskite PbTiO3 nanoparticles with solution processability

Ferroelectrics with perovskite structure (ABO3), for example, lead titanate (PbTiO3), are the most studied ferroelectric oxides because of their versatile properties for use in thin film capacitors, electronic transducers, actuators, high-k dielectrics, pyroelectric sensors, and nonlinear optics. The studies on nanostructured PbTiO3 are limited, mainly due to the lack of facile synthetic techniques to prepare nano-sized PbTiO3, i.e., colloidal PbTiO3 nanoparticles. Herein, we presented a novel nonaqueous, relatively low temperature, and highly scalable route to PbTiO3 nanoparticles. The use of oleic acid as surface capping ligand provides nanoparticles with good solubility in organic solvents, thereby enabling the low-cost solution based processing. Rather than the use of expensive bimetallic alkoxide precursors, common chemicals were utilized in this non-hydrolytic thermal decomposition approach; moreover, there is no need for extremely high temperature and long reaction time, making it possible for the large scale synthesis.

Nano-crystalline diamond electrodes with cap layer decorated by gold particles

We describe the electrochemical characteristics of a nano-crystalline diamond (NCD) electrode with a thin (∼ 60 nm) low-doped cap layer on a highly boron-doped diamond contact layer, where the grain boundary areas of the surface are decorated by gold particles by electroplating. The presence of the surface cap layer leads to a reduced background current compared to the highly doped NCD electrodes. At the same time, the electrical resistance to the gold particles via grain boundary defects of the cap layer does not limit the activity of the particles in 0.1 M H 2SO 4 electrolyte. The equivalent circuit of the decorated cap-layer electrodes is discussed using the results of electrochemical impedance spectroscopy and data on gold–diamond Schottky diodes fabricated on identical NCD layers. This equivalent circuit can be reduced to a low number of key elements, which could be useful for optimizing such electrodes for high sensitivity/low noise applications.

Luminescence and magnetic properties of Co doped ZnO nanocrystals

We report on the optical and magnetic properties of Co doped ZnO nanocrystals (NCs). With surface capping treatment by TOPO, the Co doped ZnO NCs show ferromagnetic ordering even at room temperature, while the NCs without the capping treatment show paramagnetic. We compared the photoluminescence (PL) properties between ferromagnetic and paramagnetic NCs, and found that the PL intensity from Co intra d-d transition increases in ferromagnetic NCs. Our results imply that the ferromagnetic property is related to the reduction of the deep bound states at the NCs surface.

Valine 및 Alanine 분자로 표면 처리된 수용성의 ZnS 나노입자의 합성 및 특성연구

본 논문에서는 구조가 간단하고 생체분야에 응용 가능한 valine, alanine등의 아미노산 분자를 이용하여 수용성 ZnS 나노입자를 합성하였다. 얻어진 고체 생성물들은 XRD, HR-TEM, 및 EDXS분석으로 그 특성을 조사하였다. HR-TEM image 분석의 결과 크기가 대략 3.3에서 3.6 nm 의 입자들이 만들어 졌음을 확인 할 수 있었으며, 나노 입자 표면의 아미노산 분자들은 FT-IR 과 FT-Raman spectrum 을 얻어 결합 모드 등을 분석하였다. Water soluble ZnS nanocrystals were synthesized by capping the surface of the nanocrystals with valine and alanine molecules, which are structurally simple and bio friendly amino acids. The obtained ZnS nanocrystal powders were characterized by XRD, HR-TEM, and EDXS spectroscopies. The measured particle sizes by HR-TEM images were in the range of 3.3 to 3.6 nm. In addition, the surface capping amino acids molecules were characterized by FT-IR and FT-Raman spectroscopies.

Effect of Surface Capping with Poly(vinyl alcohol) on the Photocarrier Relaxation of ZnO Nanowires

The effect of surface capping with poly(vinyl alcohol) (PVA) on the photocarrier relaxation of the aqueous chemically grown ZnO nanowires (NWs) has been investigated. The decay in the photocurrent during steady ultraviolet illumination due to the photocarrier relaxation has been reduced in the capped NWs, as evidenced from a decrease in the photocurrent only by 12% of its maximum value under steady illumination for 15 min and a decrease in the photocurrent by 49% of its maximum value during the same interval of time in the as-grown NWs. The surface modification is confirmed from the FESEM, HRTEM, and FTIR results. The photoluminescence spectrum shows an enhanced ultraviolet emission and a reduced defect-related emission in the capped ZnO NWs compared to bare ZnO.

Optical properties of citrate-stabilized CdS nanoparticles

Citrate-stabilized CdS nanoparticles of size ∼4 nm are obtained by varying the sulfide:citrate ion concentration in a simple aqueous synthesis method. The optical absorption and photoluminescence properties of the nanoparticles are studied. The size of the crystallites is found to be less affected by sulfide:citrate ratio. At lower concentrations of S 2−, trap state emission is favoured and at higher concentrations excitonic transition is predominant as shown by optical absorption and photoluminescence spectra. Effective surface capping and optimum concentration of S 2− leads to the quenching of surface-defect-related emission. Increase in citrate ion concentration is found to increase the intensity of photoluminescence band arising from trap state emission revealing the role of sulfide:citrate ratio on surface modification of CdS nanocrystals. The nanoparticles are hexagonal as shown by the X-ray diffraction and selected area electron diffraction pattern.

Rapid and efficient synthesis of colloidal gold nanoparticles by arc discharge method

We report a simple, inexpensive and one-step synthesis route of colloidal gold nanoparticles using arc discharge between titanium electrodes in HAuCl4 solution achieving long-time stability. Gold nanoparticles of 8 nm diameter were formed during reduction of HAuCl4 in the plasma discharge zone. The resulting nanoparticles were characterized using UV–Vis spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Optical absorption spectroscopy of as prepared samples at 15 A arc current in HAuCl4 solution shows a surface plasmon resonance around 550 nm. It was found that sodium citrate acts as a stabilizer and surface capping agent of the colloidal nanoparticles. SEM images exhibit the increase of reduced nanoparticles in 4 minutes arc duration compared with 1 minute arc duration. A TEM image of the sample prepared at 4 minutes arc duration shows a narrow size distribution with 8 nm mean particle size. The plasmonic peak intensity of as prepared gold nanoparticles in 1 minute arc duration gradually increases due to seed mediation up to 6 hours.

Synthesis and thermoelectric properties of PbTe nanorods and microcubes

The pure face-centered cubic lead telluride nanorods and microcubes have been synthesized by the composite-hydroxide-mediated (CHM) approach using hydrazine and NaBH 4 as a reducing agent, respectively. The method is based on reactants in hydroxide melts at a eutectic temperature of 200 °C and normal atmosphere without using an organic dispersant or surface capping agent. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and energy dispersive X-ray spectroscopy are used to characterize the structure, morphology, and composition of the samples. The results show that the diameter of nanorods is 40–70 nm, while the size of microcubes is up to several micrometers. The measurement of thermoelectricity shows that the room temperature Seebeck coefficient value of the nanorods is up to 679.8 μV/K, about 2.56 times larger than that of the lead telluride bulk material, while the Seebeck coefficient value of the microcubes is only 195.5 μV/K.

Effects of Size and Capping Reagents on Biexciton Auger Recombination Dynamics of CdTe Quantum Dots

CdTe quantum dots (QDs) were synthesized using oleic acid (OA) and thioglycolic acid (HS-CH2COOH, TGA) as capping reagents. Biexciton Auger recombination of CdTe QDs was examined by femtosecond transient absorption spectroscopy by changing excitation intensity. The lifetime of biexciton Auger recombination τAuger was analyzed as a function of QD diameter D and capping reagents. It was found that τAuger is proportional to Dα, and that the scaling index α is dependent on capping reagents and/or surface conditions. For TGA capped CdTe QDs, α is determined to be 4.6, whereas it is 7.0 for OA capped CdTe QDs with high luminescence quantum yields Φ of 60−85%. This relationship did not hold for small size OA capped CdTe QDs with rather low Φ of 15−30%, in which τAuger became as short as 2∼3 ps irrespective of the diameter. These results suggest that biexciton Auger recombination of CdTe QDs is strongly dependent on the QD surface trapping and capping reagents.

Doped ZnO Colloids for Cancer Detection - Bio-Imaging and Cytotoxicity Study

AbstractWe report the synthesis and surface modification of bio-friendly ZnO based colloids, which have been used for cancer cell detection providing significant advantages on quantum confinement effects, high emission brightness in UV to blue-violate range, non-toxicity and a unique dual color imaging feature. The ZnO nanoparticles were single crystal nanoparticles having spherical shape in size of 1-2 or 4-5 nm depending on the surface capping agents. All the colloidal solutions were stable for 30-45 days. The surface capping is a more effective technique in controlling the nanoparticle size, while dopants are effective in modifying the bandgap and optical properties. Unique dual colour images with blue colour in nucleus and turquoise colour in cytoplasm were obtained using either pure ZnO or Co doped ZnO colloids on human osteosarcoma (Mg-63) cells. The dual colour function is the combined effects of quantum confinement and the bio-compatible surface capping groups. The cytotoxicity study proved no cell proliferation by the nanoparticles up to the concentration of 1000 μg/mL, which is the highest concentration reported so far. Since a dosage of only 50-100μM is enough for the in vivo detection on rate, these ZnO colloids have high potential for use as the detection media for Lab-on-a-Chip devices.