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The heterogeneous nucleation is expected to be the key mechanism for the nucleation of the CQDs in the hydrothermal reactor.

Dopamine (DA) deficiency has been linked to several psychiatric disorders. Electrochemical determination of the level of DA suffers from abundant ascorbic acid (AA) and uric acid (UA) in body fluids. In this work, a facile argon (Ar) plasma treatment was utilized to enhance the electrocatalytic reactivity of screen-printed carbon electrodes (SPCEs) for selective DA detection. Surface characterization of the Ar-treated SCPEs verified that the carbon paste binders were successfully removed and single-bonded oxygenated moieties (-OH and C-O-C) were generated. Interestingly, the sharper D* and D'' Raman interbands were new key evidence of a higher exposure of carbon defect sites. Electrochemical studies further revealed that the Ar-treated SPCEs possessed faster heterogeneous electron-transfer rates, larger electroactive surface areas, and much higher conductivity when compared with untreated electrodes. As a result, the oxidation potentials of AA, DA, and UA in the mixture could be well-resolved and the current responses were significantly increased. The selective determination of DA in the presence of AA and UA by differential pulse voltammetry gave two linear responses with the limit of detection of 0.27 μM (0.15-10 μM range). Moreover, this Ar-treated SPCE had high reproducibility and good storage stability. These results suggest that Ar-plasma treatment could be a promising method to enhance the electrocatalytic properties of SPCEs for the detection of biomolecules.

In this work, hydroxyapatite/graphene oxide modified screen-printed electrode (SP-HAp/GO) were investigated for L -tryptophan (Trp) detection using linear sweep voltammetry (LSV) technique. HAp/GO composite was prepared by growth of HAp on GO in the simulated body fluid. Surface wettability, surface morphology and chemical functional group of the modified electrodes were determined by contact angle measurement, scanning electron microscope and Fourier transform infrared spectrometer, respectively. Contact angle of the electrode modified with HAp/GO composite is about two- and three-times larger than those of GO-modified electrode (SP-GO) and bare electrode (SP), respectively. SP-HAp/GO and SP show rough surface with cracks and pore-like structures, whereas SP-GO forms dense and smooth surface. After electrochemical determination of Trp, the linear range (7–1,000 µM) and limit of detection (LOD ∼ 5.5 µM) obtained from HAp/GO-modified electrode are better than those of bare (25–1000 µM, LOD ∼ 17.5 µM) and GO-modified (10–1000 µM, LOD ∼ 7.0 µM) electrodes. The information from this study may be useful for rapid Trp determination and for development of electrode materials used in bio-molecule sensors.

The selectivity in the simultaneous detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA) has been an open problem in the biosensing field. Many surface modification methods were carried out for glassy carbon electrodes (GCE), including the use of graphene oxide and amino acids as a selective layer. In this work, molecular dynamics (MD) simulations were performed to investigate the role of serine oligomers on the selectivity of the AA, DA, and UA analytes. Our models consisted of a graphene oxide (GO) sheet under a solvent environment. Serine tetramers were added into the simulation box and were adsorbed on the GO surface. Then, the adsorption of each analyte on the mixed surface was monitored from MD trajectories. It was found that the adsorption of AA was preferred by serine oligomers due to the largest number of hydrogen-bond forming functional groups of AA, causing a 10-fold increase of hydrogen bonds by the tetraserine adsorption layer. UA was the least preferred due to its highest aromaticity. Finally, the role of hydrogen bonds on the electron transfer selectivity of biosensors was discussed with some previous studies. AA radicals received electrons from serine through hydrogen bonds that promoted oxidation reaction and caused the negative shifts and separation of the oxidation potential in experiments, as DA and UA were less affected by serine. Agreement of the in vitro and in silico results could lead to other in silico designs of selective layers to detect other types of analyte molecules.

Aggregation of unfolded or misfolded proteins into amyloid fibrils can cause various diseases in humans. However, the fibrils synthesized in vitro can be developed toward useful biomaterials under some physicochemical conditions. In this study, atomistic molecular dynamics simulations were performed to address the mechanism of beta-sheet formation of the unfolded hen egg-white lysozyme (HEWL) under a high temperature and low pH. Simulations of the protonated HEWL at pH 2 and the non-protonated HEWL at pH 7 were performed at the highly elevated temperature of 450 K to accelerate the unfolding, followed by the 333 K temperature to emulate some previous in vitro studies. The simulations showed that HEWL unfolded faster, and higher beta-strand contents were observed at pH 2. In addition, one of the simulation replicas at pH 2 showed that the beta-strand forming sequence was consistent with the ‘K-peptide’, proposed as the core region for amyloidosis in previous experimental studies. Beta-strand formation mechanisms at the earlier stage of amyloidosis were explained in terms of the radial distribution of the amino acids. The separation between groups of positively charged sidechains from the hydrophobic core corresponded to the clustering of the hydrophobic residues and beta-strand formation.

Thin anatase TiO2 films with preferential (004) orientation were successfully fabricated via multilayering technique, growth and stop repeatedly, using DC-magnetron sputtering and annealed at a relatively low temperature. The multilayering deposition technique suppressed the number of oxygen vacancy defects in TiO2 films without interrupting the columnar growth. The main columnar structure oriented along (101) plane and along (004) plane. Confirmed by the texture coefficient, the preferential (004) orientation of TiO2 films increased with increasing number of compact layers and the highest value was observed for post-annealed films at 200 °C. The surface morphology analysis indicated that the increase of surface roughness with increasing number of compact layers was related to the promotion of crystallization. The optical properties of multilayer films revealed that high number of compact layers greatly enhanced their absorption in the entire visible region, expanded energy band gap and increased refractive index.

The 100-nm titanium dioxide (TiO2) thin film and its composites with copper (Cu) underlayers of various thicknesses, 4 nm–16 nm, were fabricated on glass substrates by a DC-magnetron sputtering technique. Optical properties of the pristine and the composite films revealed that increasing Cu underlayer thickness greatly increased their absorption in the entire visible region, leading to a decrease in the band gap energy. This should significantly enhance the solar-driven catalytic activity. However, it was found that the photocatalytic activity under the UV radiation determined from photo-degradation of methyl orange (MO) of thick Cu underlayer films exhibited the reduction in degradation rate. The photoluminescence indicated that Cu nanoparticles at TiO2/Cu interface layer not only generated shallow level defects in TiO2 band gap but also acted as recombination centers for photo-generated carriers. This phenomenon was the result of the presence of Cu surface roughness as well as the presence of large aggregates in thick Cu layers. Therefore, the life time and the number of free carriers transported to the TiO2 surface decreased causing the reduction in photodegradation activity of TiO2 composite films.

Developing capacitor with high capacitance and power capacity has received much attention in the scientific research. This research aimed to study the effect of polyaniline (PANI) content on the capacitance of the capacitor fabricated from PANI/carbon powder composites. Wasted-sweet potato was used as the source of carbon for synthesizing carbon powder (CP). Two types of CP were considered in the study, including with and without sulfuric acid pre-treatment. For CP without acid treatment, the sweet potato was heated at 900 °C for 2 h in argon atmosphere. For CP with acid treatment, the sweet potato was reacted with concentrated sulfuric acid for 2 h and then heated at 900 °C for 2 h in argon atmosphere. Both samples were ground before use. PANI contents of 0-5 %wt were used to combine with the CP samples. SEM, FTIR and potentiostat/galvanostat, respectively, investigated the physical, chemical and electrochemical properties of the composites. The electrochemical results showed that 5 %wt PANI composited with acid-treated CP provided the highest specific capacitance of 304.87 F/g. This composite also showed high stability under charge-discharge investigation. This study confirms that carbon powder synthesized from wasted-sweet potato composited with PANI can be useful for developing supercapacitor.

Diamond-like carbon/amorphous silicon bilayer films were deposited on SiO2, Ge, and Ta2O5 substrates using a pulsed filtered cathodic arc (PFCA) system. Amorphous silicon (a-Si) layer was firstly deposited on three substrates using DC magnetron sputtering, then diamond-like carbon (DLC) film was deposited on a-Si layer via pulsed filtered cathodic arc. The thicknesses of a-Si layer and DLC film as monitored by in-situ ellipsometry during the film deposition were 7 and 10 nm, respectively. The surface energy of SiO2, Ge, and Ta2O5 substrates was determined by measuring the contact angle of water on these substrates. It was found that the contact angles of water on SiO2, Ge, and Ta2O5 substrates were 53°, 63°, and 75°, respectively. This result indicates that SiO2 has the highest surface energy while Ta2O5 has the lowest surface energy. The thickness of the a-Si layer and DLC film was determined from the cross-section transmission electron microscopy (TEM) images. The thinnest a-Si layer of 5.64 nm was obta...

Carbon-based photoluminescent nanodot has currently been one of the promising materials for various applications. The remaining challenges are the carbon sources and the simple synthetic processes that enhance the quantum yield, photostability and biocompatibility of the nanodots. In this work, the synthesis of blue photoluminescent carbon nanodots from limeade via a single-step hydrothermal carbonization process is presented. Lime carbon nanodot (L-CnD), whose the quantum yield exceeding 50% for the 490 nm emission in gram-scale amounts, has the structure of graphene core functionalized with the oxygen functional groups. The micron-sized flake of the as-prepared L-CnD powder exhibits multicolor emission depending on an excitation wavelength. The L-CnDs are demonstrated for rapidly ferric-ion (Fe3 +) detection in water compared to Fe2 +, Cu2 +, Co2 +, Zn2 +, Mn2 + and Ni2 + ions. The photoluminescence quenching of L-CnD solution under UV light is used to distinguish the Fe3 + ions from others by naked eyes as low concentration as 100 μM. Additionally, L-CnDs provide exceptional photostability and biocompatibility for imaging yeast cell morphology. Changes in morphology of living yeast cells, i.e. cell shape variation, and budding, can be observed in a minute-period until more than an hour without the photoluminescent intensity loss.

Crystal of hydroxyapatite (HAp) was grown on silk fibers using simulated body fluid (SBF) at a temperature of 37 °C. Effect of SBF concentrations and sericin protein on the growth of HAp crystals on the silk fiber was discussed. The results showed that sericin protein was an important parameter to induce HAp crystals. Furthermore, the crystal was grown perfectly for both 1.0 and 1.5  standard SBF concentrations but difference in HAp crystal size. Sericin protein may lower nucleation barrier and high surface area to absorb SBF for HAp nucleation. These results may be a new research topic on HAp crystallization using protein as a seed. It may lead to further improvement and applied for many HAp-based biomaterial applications.

DLC/a-Si films were deposited on germanium substrates. a-Si film was initially deposited as a seed layer on the substrate using DC magnetron sputtering. DLC film was then deposited on the a-Si layer via a pulsed filtered cathodic arc (PFCA) system. In situ ellipsometry was used to monitor the thicknesses of the growth films, allowing a precise control over the a-Si and DLC thicknesses of 6 and 9 nm, respectively. It was found that carbon atoms implanting on a-Si layer act not only as a carbon source for DLC formation, but also as a source for SiC formation. The Raman peak positions at 796 cm−1 and 972 cm−1 corresponded to the LO and TO phonon modes of SiC, respectively, were observed. The results were also confirmed using TEM, XPS binding energy and XPS depth profile analysis.

A lens based on liquid in the confined volume of a volumetric flask was presented as a potential projector to observe microscopic floating organisms or materials. In this experiment, a mosquito larva from a natural pond was selected as a demonstration sample. By shining a light beam from a laser pointer of any visible wavelength through the volumetric flask filled with liquid, the movements of floating objects were clearly observed on a screen. The magnification was simply controlled by changing either the volume of the flask or the distance of the screen from the flask.

Single-, bi-, and multilayer graphenes were successfully prepared by sonicating bulk graphite in distilled water. Effect of different sonication times, including 3, 6, 12, 36, and 72 hours, on thickness of graphene layer were reported. Sonication time strongly affected the homogeneity and sedimentation of the graphene suspensions. Longer time of sonication enhanced the suspension homogeneity as well as increased the concentration of exfoliated graphene. The stably dispersed suspensions were obtained from 36 and 72 hours of sonication time, representing a clear gray suspension for more than 3 months. Thickness of the resulted graphenes was measured by scanning electron microscopy (SEM). UV-visible spectroscopy and Raman spectroscopy were used to investigate the graphitic characteristics of the exfoliated graphenes.

Carbon particles were synthesized via laser ablation of a bulk graphite in ethanol medium using Nd:YAG laser with a wavelength of 1064 nm. The target was irradiated by the laser beam with a pulse energy of 3 J, a pulse repetition rate of 2 Hz, and a pulse duration of 5 ms. Effect of using ethanol as a liquid medium for laser ablation on physical, chemical, and optical properties of resulted carbon particles was reported. SEM images presented that a flake-like morphology of graphite in the target has been transformed into a flower-like cluster after the ablation. Raman measurement showed that G peak position of the graphite flakes and that of the synthesized carbon particles were similar, about 1582 cm-1, whereas D peak position and its shape of the synthesized particles was different from those of graphite flakes. UV-visible and fluorescent spectrometers were used to investigate absorption and emission characteristics of the particles, respectively. The carbon particles can absorb a light in the UV range and emit a photoluminescence of bright blue-green color.

DLC/a-Si bilayer film was deposited on germanium substrate. The a-Si layer, a seed layer, was firstly deposited on the substrate using DC magnetron sputtering and DLC layer was then deposited on the a-Si layer using pulsed filtered cathodic arc method. The bilayer films were deposited with different DLC/a-Si thickness ratios, including 2/2, 2/6, 4/4, 6/2, and 9/6. The effect of DLC/a-Si thickness ratios on the sp3content of DLC was analyzed by Raman spectroscopy. The results show that a-Si layer has no effect on the structure of DLC film. Furthermore, the upper shift inGwavenumber and the decrease inID/IGinform that sp3content of the film is directly proportional to DLC thickness. The plot modified from the three-stage model informed that the structural characteristics of DLC/a-Si bilayer films are located close to the tetrahedral amorphous carbon. This information may be important for analyzing and developing bilayer protective films for future hard disk drive.

This study is to evaluate a color variation of the zirconium nitride thin film, prepared from deposition technique of different N2 flow rates, ranging from 0.0 to 3.0 sccm, whereas the Ar flow rate is fixed at 3 sccm. The thin film was deposited on an unheated silicon wafer (100) via a reactive DC magnetron sputtering. The deposition current and deposition time were 0.6 A and 15 minutes, respectively. In the study, colors of film were changed from silver, gold, dark brown, brown, purple, pink to blue, when N2 flow rate further increase. Interestingly, the results indicate that gold color occurs in a very small interval of N2 flow rate.

Carbon nanoparticles were synthesized via laser ablation of graphite target in distilled water. The particle sizes of carbon nanoparticles were investigated as a function of laser energy: 1, 1.5, and 2 J/pulse. Using water as a matrix during synthesis is another potential way to control the particle size. The mean size increases when increasing the laser energy. The particle morphology is a globular shape. The sizes of the nanoparticle were evaluated from both SEM image analysis and Scherrer’s equation. The sizes from the equation are smaller than those obtained from SEM, which indicates that the particles are polycrystallines.

Heterogeneous nucleation of hydroxyapatite (HAp) can be facilitated by physical and chemical properties of material surface. In this article, we reported how effective surface porosity and roughness are for inducing nucleation of HAp crystal in simulated body fluid. Two types of micrographite film (MGF) prepared from assembly of micrographite flakes were used as seeds to induce HAp crystal: uncompressed (high surface porosity) and compressed (low surface porosity) MGFs. Compressed MGF was prepared by applying mechanical compression to the uncompressed MGF. Uncompressed and compressed MGFs have similar surface wettability with the water contact angles (θ) of 113° and 107°, respectively. The number density of HAp crystals on the uncompressed MGF was higher than that of the compressed MGF by a factor of 6. This result implied that surface porosity and roughness were more effective parameters for inducing HAp crystal than surface wettability. Uncompressed MGF also induced HAp nucleation better than a cover glass although the glass had high wettability (θ = 64°). The effectiveness of uncompressed MGF on inducing HAp crystals was as high as that of the SiO2 -coated Si substrate. Our finding suggests that we do not require to functionalize material surface to be an effective seed; a surface with pores or roughness of the right scale is enough.

Silver (Ag) nanoparticles are of great interest for many applications. However, their fabrications have been limited by the synthesis methods in which size, shape, and aggregation are still difficult to control. Here, we reported on using direct current (DC) magnetron sputtering for growing Ag nanoparticles on unheated substrates. Effects of sputtering condition on grain size of Ag nanoparticle were discussed. At constant sputtering current and deposition time, the average sizes of Ag nanoparticles were 5.9 ± 1.8, 5.4 ± 1.3, and 3.8 ± 0.7 nm for the target-substrate distances of 10, 15, and 20 cm, respectively. The morphology evolution from nanoparticles to wormlike networks was also reported. High-resolution transmission electron microscopy image represented clear lattice fringes of Ag nanoparticles with a d-spacing of 0.203 nm, corresponding to the (200) plane. The technique could be applied for growth of nanoparticles that were previously difficult to control over size and size uniformity.

Al2O3nanoparticles were synthesized using laser ablation of an aluminum (Al) target in deionized water. Nd:YAG laser, emitted the light at a wavelength of 1064 nm, was used as a light source. The laser ablation was carried out at different energies of 1, 3, and 5 J. The structure of ablated Al particles suspended in deionized water was investigated using X-ray diffraction (XRD). The XRD patterns revealed that the ablated Al particles transformed intoγ-Al2O3. The morphology of nanoparticles was investigated by field emission scanning electron microscopy (FE-SEM). The FE-SEM images showed that most of the nanoparticles obtained from all the ablated laser energies have spherical shape with a particle size of less than 100 nm. Furthermore, it was observed that the particle size increased with increasing the laser energy. The absorption spectra of Al2O3nanoparticles suspended in deionized water were recorded at room temperature using UV-visible spectroscopy. The absorption spectra show a strong peak at 210 nmarising from the presence of Al2O3nanoparticles. The results on absorption spectra are in good agreement with those investigated by XRD which confirmed the formation of Al2O3nanoparticles during the laser ablation of Al target in deionized water.

We report on the first use OF carbon-nanotube-based films to produce crystals of proteins. The crystals nucleate on the surface of the film. The difficulty of crystallizing proteins is a major bottleneck in. the determination of the structure and function of biological molecules. The crystallization of two model proteins and two medically relevant proteins was studied. Quantitative data on the crystallization times of the model protein lyozyme are also presented. Two types of nanotube films, one made with the surfactant Triton X-100 (TX-100) and one with gelatin, were tested. Both induce nucleation of the crystal phase at supersaturations at which the protein solution would otherwise remain clear: however, the gelatin-based film induced nucleation down to much lower supersaturations for the two model proteins with which it was used. it appears that the interactions of gelatin with the protein molecules are particularly favorable to nucleation. Crystals of the C I domain of the human cardiac myosin-binding protein-C that diffracted to a resolution of 1.6 angstrom were obtained on the TX-100 film. This is far superior to the best crystals obtained using standard techniques, which only diffracted to 3.0 angstrom. Thus, both of our nanotube-based films are very promising candidates for future work on crystallizing difficult-to-crystallize target proteins.

Natural materials, such as bone and spider silk, possess remarkable properties as a result of sophisticated nanoscale structuring. They have inspired the design of synthetic materials whose structure at the nanoscale is carefully engineered or where nanoparticles, such as rods or wires, are self-assembled. Although much work has been done in recent years to create ordered structures using diblock copolymers and template-assisted assembly, no reports describe highly ordered, three-dimensional nanotube arrays within a polymeric material. There are only reports of two-dimensional network structures and structures on micrometer-size scales. Here, we describe an approach that uses plasticized colloidal particles as a template for the self-assembly of carbon nanotubes (CNTs) into ordered, three-dimensional networks. The nanocomposites can be strained by over 200% and still retain high conductivity when relaxed. The method is potentially general and so may find applications in areas such as sensing, photonics, and functional composites.

Bilayer DLC/a-Si films was deposited on germanium substrate. a-Si films was initially deposited as a seed layer on the substrate using DC magnetron sputtering. DLC films was then deposited on the a-Si layer via a pulsed filtered cathodic arc (PFCA) system. In situ ellipsometry was used to monitor growth in thickness of a-Si and DLC films, allowing a good control over growth conditions. The thickness of DLC and a-Si layers were 9 nm and 6 nm, respectively. In this work, the interface of a-Si and DLC layers was investigated by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that the SiC layer was formed at the interface of a-Si and DLC layers.

Here we culture Chinese hamster ovary cells on isotropic, aligned and patterned substrates based on multiwall carbon nanotubes. The nanotubes provide the substrate with nanoscale topography. The cells adhere to and grow on all substrates, and on the aligned substrate, the cells align strongly with the axis of the bundles of the multiwall nanotubes. This control over cell alignment is required for tissue engineering; almost all tissues consist of oriented cells. The aligned substrates are made using straightforward physical chemistry techniques from forests of multiwall nanotubes; no lithography is required to make inexpensive large-scale substrates with highly aligned nanoscale grooves. Interestingly, although the cells strongly align with the nanoscale grooves, only a few also elongate along this axis: alignment of the cells does not require a pronounced change in morphology of the cell. We also pattern the nanotube bundles over length scales comparable to the cell size and show that the cells follow this pattern.

Crystals of hydroxyapatite (HAp) were grown on silk fibers using simulated body fluid (SBF) at a temperature of 37 °C. Two different conditions of silk thread were investigated for efficiency of inducing HAp: i) with sericin protein and ii) without sericin protein. Effect of simulated body fluid (SBF) concentrations at 1.0 × SBF and 1.5 × SBF and sericin protein on HAp growth was discussed. The results showed that HAp was successfully crystallized on silk from both 1.0 × SBF and 1.5 × SBF concentrations. The crystal size obtained from the 1.5 × SBF concentration was larger than that of the 1.0 × SBF concentration. However, it was found that the 1.5 × SBF offered less number of the crystals per unit area than that of the 1.0 × SBF. The physical and chemical compositions of HAp were characterized by XRD, SEM and optical microscopy. This study may be very useful for many applications, especially in biomedical and material science.

Electrical conductivity of bulk graphite was investigated as a function of its volume density and temperature. The bulk graphite was prepared from pressing natural graphite powders obtained from two different conditions: i) without any treatment and ii) with 24 hr of ultrasonic treatment. Powders from each condition were consolidated using an isobaric press of different pressures, including 5, 10, 20, 30, 40 and 50 MPa. Ultrasonic treatment helped to exfoliate graphene from its parent graphite which enhanced the electrical conductivity of the compressed bulk graphite. Scanning electron microscopy (SEM) and UV-Vis spectroscopy confirmed that multilayer graphenes and nanographite were obtained after the sonication. Raman spectroscopy was also used to investigate the graphitic characteristics of sonicated graphite. The bulk graphite of 50 MPa consolidation from the sonicated powders offered the highest electrical conductivity which was due to its highest density as well as a combination of multilayer graphene. Effect of temperature on the electrical conductivity was discussed. The conductivity increases when increasing the temperature.

Alumina nanoparticles were synthesized from a bulk aluminium using laser ablation from Nd:YAG laser with a wavelength of 1064 nm in deionized water. Physical and chemical properties of the nanoparticles were investigated as a function of the laser pulse energies, including 1, 3 and 5 J. 3 J of laser energy offered plenty of spherical nanoparticles with a uniform size distribution of less than 100 nm. UV-visible spectroscopy was used to evaluate the optical property of the obtained suspension, representing a strong peak at 213 nm. XRD analysis showed that plenty of the nanoparticles are κ-Al2O3, which would be very useful for many applications.