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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.

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...

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.