Nanomaterials, Volume 6, Issue 9 (September 2016) – 22 articles

Surface-enhanced Raman scattering or surface-enhanced Raman spectroscopy (SERS) is a promising detection technology, and has captured increasing attention. Silver nanowires were synthesized using a rapid polyol method and optimized through adjustment of the molar ratio of poly(vinyl pyrrolidone) and silver nitrate in a glycerol system. Ultraviolet-visible spectrometry, X-ray diffraction, and transmission electron microscopy were used to characterize the silver nanowires. The optimal silver nanowires were used as a SERS substrate to detect prohibited fish drugs, including malachite green, crystal violet, furazolidone, and chloramphenicol. The SERS spectra of crystal violet could be clearly identified at concentrations as low as 0.01 ng/mL. The minimum detectable concentration for malachite green was 0.05 ng/mL, and for both furazolidone and chloramphenicol were 0.1 μg/mL. The results showed that the as-prepared Ag nanowires SERS substrate exhibits high sensitivity and activity. Full article

The inferior hydrophilicity of graphene is an adverse factor to the performance of the graphene modified anodes (G anodes) in microbial fuel cells (MFCs). In this paper, different amounts of hydrophilic graphene oxide (GO) were doped into the modification layers to elevate the hydrophilicity of the G anodes so as to further improve their performance. Increasing the GO doped ratio from 0.15 mg·mg⁻¹ to 0.2 mg·mg⁻¹ and 0.25 mg·mg⁻¹, the static water contact angle (θ_c) of the G-GO anodes decreased from 74.2 ± 0.52° to 64.6 ± 2.75° and 41.7 ± 3.69°, respectively. The G-GO_0.2 anode with GO doped ratio of 0.2 mg·mg⁻¹ exhibited the optimal performance and the maximum power density (P_max) of the corresponding MFC was 1100.18 mW·m⁻², 1.51 times higher than that of the MFC with the G anode. Full article

Graphitic-C₃N₄ nanosheets (CN)/ZnO photocatalysts (CN/ZnO) with different CN loadings were successfully prepared via a simple precipitation-calcination in the presence of exfoliated C₃N₄ nanosheets. Their morphology and structure were thoroughly characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectra (PL). The results showed that hexagonal wurzite-phase ZnO nanoparticles were randomly distributed onto the CN nanosheets with a well-bonded interface between the two components in the CN/ZnO composites. The performance of the photocatalytic Cr(VI) reduction indicated that CN/ZnO exhibited better photocatalytic activity than pure ZnO under visible-light irradiation and the photocatalyst composite with a lower loading of CN sheets eventually displayed higher activity. The enhanced performance of CN/ZnO photocatalysts could be ascribed to the increased absorption of the visible light and the effective transfer and separation of the photogenerated charge carriers. Full article

Magnetic cores of passive components are required to have low hysteresis loss, which is dependent on the coercive force. Since it is well known that the coercive force becomes zero at the superparamagnetic regime below a certain critical size, we attempted to synthesize Ni nanoparticles in a size-controlled fashion and investigated the effect of particle size on the magnetic properties. Ni nanoparticles were synthesized by the reduction of Ni acetylacetonate in oleylamine at 220 °C with trioctylphosphine (TOP) as the capping agent. An increase in the TOP/Ni ratio resulted in the size decrease. We succeeded in synthesizing superparamagnetic Ni nanoparticles with almost zero coercive force at particle size below 20 nm by the TOP/Ni ratio of 0.8. However, the saturation magnetization values became smaller with decrease in the size. The saturation magnetizations of the Ni nanoparticles without capping layers were calculated based on the assumption that the interior atoms of the nanoparticles were magnetic, whereas the surface-oxidized atoms were non-magnetic. The measured and calculated saturation magnetization values decreased in approximately the same fashion as the TOP/Ni ratio increased, indicating that the decrease could be mainly attributed to increases in the amounts of capping layer and oxidized surface atoms. Full article

We describe the synthesis of nanocomposites, based on nanofibers of silicon carbide, silver nanoparticles, and cellulose. Silver nanoparticle synthesis was achieved with chemical reduction using hydrazine by adding two different surfactants to obtain a nanocomposite with silver nanoparticles of different diameters. Determination of antibacterial activity was based on respiration tests. Enzymatic analysis indicates oxidative stress, and viability testing was conducted using an epifluorescence microscope. Strong bactericidal activity of nanocomposites was found against bacteria Escherichia coli and Bacillus cereus, which were used in the study as typical Gram-negative and Gram-positive bacteria, respectively. It is assumed that reactive oxygen species generation was responsible for the observed antibacterial effect of the investigated materials. Due to the properties of silicon carbide nanofiber, the obtained nanocomposite may have potential use in technology related to water and air purification. Cellulose addition prevented silver nanoparticle release and probably enhanced bacterial adsorption onto aggregates of the nanocomposite material. Full article

The dependence of magnetic relaxation on particle parameters, such as the size and anisotropy, has been conventionally discussed. In addition, the influences of external conditions, such as the intensity and frequency of the applied field, the surrounding viscosity, and the temperature on the magnetic relaxation have been researched. According to one of the basic theories regarding magnetic relaxation, the faster type of relaxation dominates the process. However, in this study, we reveal that Brownian and Néel relaxations coexist and that Brownian relaxation can occur after Néel relaxation despite having a longer relaxation time. To understand the mechanisms of Brownian rotation, alternating current (AC) hysteresis loops were measured in magnetic fluids of different viscosities. These loops conveyed the amplitude and phase delay of the magnetization. In addition, the intrinsic loss power (ILP) was calculated using the area of the AC hysteresis loops. The ILP also showed the magnetization response regarding the magnetic relaxation over a wide frequency range. To develop biomedical applications of magnetic nanoparticles, such as hyperthermia and magnetic particle imaging, it is necessary to understand the mechanisms of magnetic relaxation. Full article

In this work, we report the potential use of novel carbon nanofibers (CNFs), dispersed during fabrication of glass fiber composites to monitor damage propagation under static loading. The use of CNFs enables a transformation of the typically non-conductive glass fiber composites into new fiber composites with appreciable electrical conductivity. The percolation limit of CNFs/epoxy nanocomposites was first quantified. The electromechanical responses of glass fiber composites fabricated using CNFs/epoxy nanocomposite were examined under static tension loads. The experimental observations showed a nonlinear change of electrical conductivity of glass fiber composites incorporating CNFs versus the stress level under static load. Microstructural investigations proved the ability of CNFs to alter the polymer matrix and to produce a new polymer nanocomposite with a connected nanofiber network with improved electrical properties and different mechanical properties compared with the neat epoxy. It is concluded that incorporating CNFs during fabrication of glass fiber composites can provide an innovative means of self-sensing that will allow damage propagation to be monitored in glass fiber composites. Full article

Stretchable large area electronics conform to arbitrarily-shaped 3D surfaces and enables comfortable contact to the human skin and other biological tissue. There are approaches allowing for large area thin films to be stretched by tens of percent without cracking. The approach presented here does not prevent cracking, rather it aims to precisely control the crack positions and their orientation. For this purpose, the polydimethylsiloxane (PDMS) is hardened by exposure to ultraviolet radiation (172 nm) through an exposure mask. Only well-defined patterns are kept untreated. With these soft islands cracks at the hardened surface can be controlled in terms of starting position, direction and end position. This approach is first investigated at the hardened PDMS surface itself. It is then applied to conductive silver films deposited from the liquid phase. It is found that statistical (uncontrolled) cracking of the silver films can be avoided at strain below 35%. This enables metal interconnects to be integrated into stretchable networks. The combination of controlled cracks with wrinkling enables interconnects that are stretchable in arbitrary and changing directions. The deposition and patterning does not involve vacuum processing, photolithography, or solvents. Full article

In this paper, one-dimensional (1D) and two-dimensional (2D) graphene-based plasmonic photonic crystals (PhCs) are proposed. The band structures and density of states (DOS) have been numerically investigated. Photonic band gaps (PBGs) are found in both 1D and 2D PhCs. Meanwhile, graphene-based plasmonic PhC nanocavity with resonant frequency around 175 THz, is realized by introducing point defect, where the chemical potential is from 0.085 to 0.25 eV, in a 2D PhC. Also, the bending wvaguide and the beam splitter are realized by introducing the line defect into the 2D PhC. Full article

Here we described the preparation and characterization by atomic force microscopy of dumbbell-shaped conjugates between 450 bp double-stranded DNA polymer, poly(dG)-poly(dC), and 5 nm gold nanoparticles (GNPs). We have demonstrated that the size of the nanoparticles in the conjugates can be increased in a controlled fashion. Application of the conjugates for measuring the electrical conductivity of DNA is discussed. Full article

To search for nano-drug preparations with high efficiency in tumor treatment, we evaluated the drug-loading capacity and cell-uptake toxicity of three kinds of nanoparticles (NPs). Pullulan was grafted with ethylenediamine and hydrophobic groups to form hydrophobic cholesterol-modified amino-pullulan (CHAP) conjugates. Fourier transform infrared spectroscopy and nuclear magnetic resonance were used to identify the CHAP structure and calculate the degree of substitution of the cholesterol group. We compared three types of NPs with close cholesterol hydrophobic properties: CHAP, cholesterol-modified pullulan (CHP), and cholesterol-modified carboxylethylpullulan (CHCP), with the degree of substitution of cholesterol of 2.92%, 3.11%, and 3.46%, respectively. As compared with the two other NPs, CHAP NPs were larger, 263.9 nm, and had a positive surface charge of 7.22 mV by dynamic light-scattering measurement. CHAP NPs showed low drug-loading capacity, 12.3%, and encapsulation efficiency of 70.8%, which depended on NP hydrophobicity and was affected by surface charge. The drug release amounts of all NPs increased in the acid media, with CHAP NPs showing drug-release sensitivity with acid change. Cytotoxicity of HeLa cells was highest with mitoxantrone-loaded CHAP NPs on MTT assay. CHAP NPs may have potential as a high-efficiency drug carrier for tumor treatment. Full article

The preparation of fluorescent nanocomposite materials with tunable emission wavelengths by combining cellulose nanofibrils (CNFs) with inorganic nanoparticles is important for promoting CNFs applications. A CNF/CdS nanocomposite was prepared via in situ compositing at room temperature on oxidized CNFs with CdS quantum dots. By controlling the –COOH/Cd²⁺ ratio on the CNF, the feeding time of Na₂S and the ultrasonic maturing time, the size of the CdS quantum dots on the CNF surface could be adjusted so that to obtain the CNF/CdS nanocomposite material with different fluorescent colors. The results indicated that the CdS particles quantized were evenly distributed on the CNF. The maximum average size of the CdS nanoparticles glowed red under the excitation of UV light was 5.34 nm, which could be obtained with a –COOH/Cd²⁺ ratio of 1.0, a Na₂S feeding time of 20 min, and an ultrasonic maturing time of 60 min. A series of CNF/CdS nanocomposite materials were obtained with CdS nanoparticle sizes varying from 3.44 nm to 5.34 nm, the emission wavelength of which varied from 546 nm to 655 nm, and their fluorescence color changed from green to yellow to red. This is the first time the fluorescence-tunable effect of the CNF/CdS nanocomposite has been realized. Full article

Comprehensive imaging of a biological individual can be achieved by utilizing the variation in spatial resolution, the scale of cathodoluminescence (CL), and near-infrared (NIR), as favored by imaging probe Gd₂O₃ co-doped lanthanide nanophosphors (NPPs). A series of Gd₂O₃:Ln³⁺/Yb³⁺ (Ln³⁺: Tm³⁺, Ho³⁺, Er³⁺) NPPs with multispectral emission are prepared by the sol-gel method. The NPPs show a wide range of emissions spanning from the visible to the NIR region under 980 nm excitation. The dependence of the upconverting (UC)/downconverting (DC) emission intensity on the dopant ratio is investigated. The optimum ratios of dopants obtained for emissions in the NIR regions at 810 nm, 1200 nm, and 1530 nm are applied to produce nanoparticles by the homogeneous precipitation (HP) method. The nanoparticles produced from the HP method are used to investigate the dual NIR and CL imaging modalities. The results indicate the possibility of using Gd₂O₃ co-doped Ln³⁺/Yb³⁺ (Ln³⁺: Tm³⁺, Ho³⁺, Er³⁺) in correlation with NIR and CL imaging. The use of Gd₂O₃ promises an extension of the object dimension to the whole-body level by employing magnetic resonance imaging (MRI). Full article

We demonstrated a multilayer molybdenum disulfide (MoS₂) nanomechanical resonator by using optical Fabry-Perot (F-P) interferometric excitation and detection. The thin circular MoS₂ nanomembrane with an approximate 8-nm thickness was transferred onto the endface of a ferrule with an inner diameter of 125 μm, which created a low finesse F-P interferometer with a cavity length of 39.92 μm. The effects of temperature and viscous air damping on resonance behavior of the resonator were investigated in the range of −10–80 °C. Along with the optomechanical behavior of the resonator in air, the measured resonance frequencies ranged from 36 kHz to 73 kHz with an extremely low inflection point at 20 °C, which conformed reasonably to those solved by previously obtained thermal expansion coefficients of MoS₂. Further, a maximum quality (Q) factor of 1.35 for the resonator was observed at 0 °C due to viscous dissipation, in relation to the lower Knudsen number of 0.0025~0.0034 in the tested temperature range. Moreover, measurements of Q factor revealed little dependence of Q on resonance frequency and temperature. These measurements shed light on the mechanisms behind viscous air damping in MoS₂, graphene, and other 2D resonators. Full article

We have developed self-assembled copper (Cu) micro-labyrinth (ML) with graphene skin for transparent flexible electrodes of optoelectronic devices. The Cu ML is simply formed by heating a thin Cu film with a 100-nm thickness on a SiO₂/Si substrate at 950 °C under hydrogen ambient to block the oxidation. Moreover, the Cu ML can have graphene skin at the surface by inserting carbo-hydroxyl molecules (C_xH_y) during heating due to the catalytic decomposition of C–H bonds on the Cu surface. The Cu ML with graphene skin (Cu ML-G) has superior sheet resistivity below 5 Ω/sq and mechanical flexibility without cracks at the bending radius of 0.1 cm. Although the transmittance of Cu ML-G is a little lower (70%~80%) than that of conventional metallic nanowires electrodes (such as Ag, ~90% at the visible wavelength), it has good thermal stability in conductivity without any damage at 200 °C due to a micro-sized pattern and graphene skin which prohibits the surface migration of Cu atoms. Full article

Plant constituents could act as chelating/reducing or capping agents for synthesis of silver nanoparticles (AgNPs). The green synthesis of AgNPs has been considered as an environmental friendly and cost-effective alternative to other fabrication methods. The present work described the biosynthesis of AgNPs using callus extracts from Taxus yunnanensis and evaluated their antibacterial activities in vitro and potential cytotoxicity in cancer cells. Callus extracts were able to reduce silver nitrate at 1 mM in 10 min. Transmission electron microscope (TEM) indicated the synthesized AgNPs were spherical with the size range from 6.4 to 27.2 nm. X-ray diffraction (XRD) confirmed the AgNPs were in the form of nanocrystals. Fourier transform infrared spectroscopy (FTIR) suggested phytochemicals in callus extracts were possible reducing and capping agents. The AgNPs exhibited effective inhibitory activity against all tested human pathogen bacteria and the inhibition against Gram-positive bacteria was stronger than that of Gram-negative bacteria. Furthermore, they exhibited stronger cytotoxic activity against human hepatoma SMMC-7721 cells and induced noticeable apoptosis in SMMC-7721 cells, but showed lower cytotoxic against normal human liver cells (HL-7702). Our results suggested that biosynthesized AgNPs could be an alternative measure in the field of antibacterial and anticancer therapeutics. Full article

Copper oxide (CuO)-decorated cerium oxide (CeO₂) nanoparticles were synthesized and used to detect glucose non-enzymatically. The morphological characteristics and structure of the nanoparticles were characterized through transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The sensor responses of electrodes to glucose were investigated via an electrochemical method. The CuO/CeO₂ nanocomposite exhibited a reasonably good sensitivity of 2.77 μA mM⁻¹cm⁻², an estimated detection limit of 10 μA, and a good anti-interference ability. The sensor was also fairly stable under ambient conditions. Full article

Low contact resistance between graphene and metals is of paramount importance to fabricate high performance graphene-based devices. In this paper, the impact of both defects induced by helium ion (He⁺) bombardment and annealing on the contact resistance between graphene and various metals (Ag, Pd, and Pt) were systematically explored. It is found that the contact resistances between all metals and graphene are remarkably reduced after annealing, indicating that not only chemically adsorbed metal (Pd) but also physically adsorbed metals (Ag and Pt) readily form end-contacts at intrinsic defect locations in graphene. In order to further improve the contact properties between Ag, Pd, and Pt metals and graphene, a novel method in which self-aligned He⁺ bombardment to induce exotic defects in graphene and subsequent thermal annealing to form end-contacts was proposed. By using this method, the contact resistance is reduced significantly by 15.1% and 40.1% for Ag/graphene and Pd/graphene contacts with He⁺ bombardment compared to their counterparts without He⁺ bombardment. For the Pt/graphene contact, the contact resistance is, however, not reduced as anticipated with He⁺ bombardment and this might be ascribed to either inappropriate He⁺ bombardment dose, or inapplicable method of He⁺ bombardment in reducing contact resistance for Pt/graphene contact. The joint efforts of as-formed end-contacts and excess created defects in graphene are discussed as the cause responsible for the reduction of contact resistance. Full article

Graphene and carbon quantum dots have extraordinary optical and electrical features because of their quantum confinement properties. This makes them attractive materials for applications in photovoltaic devices (PV). Their versatility has led to their being used as light harvesting materials or selective contacts, either for holes or electrons, in silicon quantum dot, polymer or dye-sensitized solar cells. In this review, we summarize the most common uses of both types of semiconducting materials and highlight the significant advances made in recent years due to the influence that synthetic materials have on final performance. Full article

The unique parameters of graphene (GN)—notably its considerable electron mobility, high surface area, and electrical conductivity—are bringing extensive attention into the wearable technologies. This work presents a novel graphene-based electrode for acquisition of electrocardiogram (ECG). The proposed electrode was fabricated by coating GN on top of a metallic layer of a Ag/AgCl electrode using a chemical vapour deposition (CVD) technique. To investigate the performance of the fabricated GN-based electrode, two types of electrodes were fabricated with different sizes to conduct the signal qualities and the skin-electrode contact impedance measurements. Performances of the GN-enabled electrodes were compared to the conventional Ag/AgCl electrodes in terms of ECG signal quality, skin–electrode contact impedance, signal-to-noise ratio (SNR), and response time. Experimental results showed the proposed GN-based electrodes produced better ECG signals, higher SNR (improved by 8%), and lower contact impedance (improved by 78%) values than conventional ECG electrodes. Full article

In this paper, anisotropic graphene plasmonic structures are explored for light trapping and absorption enhancement in surrounding media. It is shown that electrically tunable and versatile spectral and polarization selectivity can be realized. Particularly, it is possible to control absorption of the incident light’s polarization component at a specific wavelength by varying the Fermi energy with suitable geometric designs. It may find applications for new types of infrared and THz photodetectors and will promote the research of other novel polarization devices. Full article

Innovative systems exploring the flexibility and the transparency of modern semiconducting materials are being widely researched by the scientific community and by several companies. For a low-cost production and large surface area applications, thin-film transistors (TFTs) are the key elements driving the system currents. In order to maintain a cost efficient integration process, solution based materials are used as they show an outstanding tradeoff between cost and system complexity. In this paper, we discuss the integration process of ZnO nanoparticle TFTs using a high-k resin as gate dielectric. The performance in dependence on the transistor structure has been investigated, and inverted staggered setups depict an improved performance over the coplanar device increasing both the field-effect mobility and the I_ON/I_OFF ratio. Aiming at the evaluation of the TFT characteristics for digital circuit applications, inverter circuits using a load TFT in the pull-up network and an active TFT in the pull-down network were integrated. The inverters show reasonable switching characteristics and V/V gains. Conjointly, the influence of the geometry ratio and the supply voltage on the devices have been analyzed. Moreover, as all integration steps are suitable to polymeric templates, the fabrication process is fully compatible to flexible substrates. Full article