Wan Jefrey Basirun

Recent advances in DNA-based electrochemical biosensors for heavy metal ion detection: A review

The presence of heavy metal in food chains due to the rapid industrialization poses a serious threat on the environment. Therefore, detection and monitoring of heavy metals contamination are gaining more attention nowadays. However, the current analytical methods (based on spectroscopy) for the detection of heavy metal contamination are often very expensive, tedious and can only be handled by trained personnel. DNA biosensors, which are based on electrochemical transduction, is a sensitive but inexpensive method of detection. The principles, sensitivity, selectivity and challenges of electrochemical biosensors are discussed in this review. This review also highlights the major advances of DNA-based electrochemical biosensors for the detection of heavy metal ions such as Hg2+, Ag+, Cu2+ and Pb2+.

Influence of particle size on performance of a nickel oxide nanoparticle-based supercapacitor

The influence of the particle size of an active material on its performance as a supercapacitor electrode was reported. Nickel oxide nanoparticles (NiO NPs) with a uniform particle size were synthesized via a facile sol–gel method, and various sizes of NiO NPs (8, 12, and 22 nm) were achieved by calcination at various temperatures (300, 400, and 500 °C). TEM observations and XRD analysis were used to determine the particle size of the NiO NPs. The field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images showed flake-like morphologies, which consisted of interconnected nanoparticles with a porous channel to facilitate the diffusion of the electrolyte. The NiO NPs with an average particle size of 8 nm gave the highest specific capacitance value of 549 F g−1 at a scan rate of 1 mV s−1 compared to the NiO NPs with average particle sizes of 12 and 22 nm. These results suggest that the particle size of the NiO nanostructure plays an important role because of the presence of a higher number of active sites for a faradaic reaction.

Graphene–Gold Nanoparticles Hybrid—Synthesis, Functionalization, and Application in a Electrochemical and Surface-Enhanced Raman Scattering Biosensor

Graphene is a single-atom-thick two-dimensional carbon nanosheet with outstanding chemical, electrical, material, optical, and physical properties due to its large surface area, high electron mobility, thermal conductivity, and stability. These extraordinary features of graphene make it a key component for different applications in the biosensing and imaging arena. However, the use of graphene alone is correlated with certain limitations, such as irreversible self-agglomerations, less colloidal stability, poor reliability/repeatability, and non-specificity. The addition of gold nanostructures (AuNS) with graphene produces the graphene–AuNS hybrid nanocomposite which minimizes the limitations as well as providing additional synergistic properties, that is, higher effective surface area, catalytic activity, electrical conductivity, water solubility, and biocompatibility. This review focuses on the fundamental features of graphene, the multidimensional synthesis, and multipurpose applications of graphene–Au nanocomposites. The paper highlights the graphene–gold nanoparticle (AuNP) as the platform substrate for the fabrication of electrochemical and surface-enhanced Raman scattering (SERS)-based biosensors in diverse applications as well as SERS-directed bio-imaging, which is considered as an emerging sector for monitoring stem cell differentiation, and detection and treatment of cancer.

Characterization of nickel-doped biphasic calcium phosphate/graphene nanoplatelet composites for biomedical application

The effect of the addition of an ionic dopant to calcium phosphates for biomedical applications requires specific research due to the essential roles played in such processes. In the present study, the mechanical and biological properties of Ni-doped hydroxyapatite (HA) and Ni-doped HA mixed with graphene nanoplatelets (GNPs) were evaluated. Ni (3wt.% and 6wt.%)-doped HA was synthesized using a continuous precipitation method and calcined at 900°C for 1h. The GNP (0.5-2wt.%)-reinforced 6% Ni-doped HA (Ni6) composite was prepared using rotary ball milling for 15h. The sintering process was performed using hot isostatic pressing at processing conditions of 1150°C and 160MPa with a 1-h holding time. The results indicated that the phase compositions and structural features of the products were noticeably affected by the Ni and GNPs. The mechanical properties of Ni6 and 1.5Ni6 were increased by 55% and 75% in hardness, 59% and 163% in fracture toughness and 120% and 85% in elastic modulus compared with monolithic HA, respectively. The in-vitro biological behavior was investigated using h-FOB osteoblast cells in 1, 3 and 5days of culture. Based on the osteoblast results, the cytotoxicity of the products was indeed affected by the Ni doping. In addition, the effect of GNPs on the growth and proliferation of osteoblast cells was investigated in Ni6 composites containing different ratios of GNPs, where 1.5wt.% was the optimum value.

Spongy nitrogen-doped activated carbonaceous hybrid derived from biomass material/graphene oxide for supercapacitor electrodes

Carbon derived from low cost agricultural waste material was used as a precursor for the preparation of a spongy-like nitrogen doped activated composite from carbon/graphene oxide via a one-step thermal treatment. N-doping and activation of the carbon/graphene oxide mixture were achieved simultaneously by the treatment of urea and potassium hydroxide at 800 °C. The nitrogen content and ratio between the nitrogen species was controlled by the mass ratio of KOH : carbon. The composite was prepared with a KOH : carbon ratio of 1 which resulted in a moderate surface area (1712.4 m2 g−1) and a high nitrogen content (14.51%). The hybrid material gave high specific capacitance (267 F g−1 at 5 mV s−1) and good cycling stability (92.3% capacitance retention after 5000 cycles) in 6 M KOH electrolyte. Hence, the new composite presented in this work can be used as an advanced material for supercapacitor applications.

Fabrication and deformation behaviour of multilayer Al2O3/ Ti/TiO2 nanotube arrays

In this study, titanium thin films were deposited on alumina substrates by radio frequency (RF) magnetron sputtering. The mechanical properties of the Ti coatings were evaluated in terms of adhesion strength at various RF powers, temperatures, and substrate bias voltages. The coating conditions of 400W of RF power, 250°C, and a 75V substrate bias voltage produced the strongest coating adhesion, as obtained by the Taguchi optimisation method. TiO2 nanotube arrays were grown as a second layer on the Ti substrates using electrochemical anodisation at a constant potential of 20V and anodisation times of 15min, 45min, and 75min in a NH4F electrolyte solution (75 ethylene glycol: 25 water). The anodised titanium was annealed at 450°C and 650°C in a N2 gas furnace to obtain different phases of titania, anatase and rutile, respectively. The mechanical properties of the anodised layer were investigated by nanoindentation. The results indicate that Youngs modulus and hardness increased with annealing temperature to 650°C.

Synthesis and characterization of Co3O4 ultra-nanosheets and Co3O4 ultra-nanosheet-Ni(OH)2 as non-enzymatic electrochemical sensors for glucose detection.

The present study examines the synthesis of Co3O4 ultra-nanosheets (Co3O4 UNSs) and Co3O4 ultra-nanosheet-Ni(OH)2 (Co3O4 UNS-Ni(OH)2) via solvothermal process and their application as non-enzymatic electrochemical sensors for glucose detection. X-ray diffraction and transmission electron microscopy results confirmed the Co3O4 UNS deposition on Ni(OH)2 surface. The presence of Co3O4 UNSs on Ni (OH) 2 surface improved the sensitivity of glucose detection, from the increase of glucose oxidation peak current at the Co3O4 UNS-Ni(OH)2/glassy carbon electrode (current density: 2000μA·cm(-2)), compared to the Co3O4 UNSs. These results confirmed that Ni(OH)2 on glassy carbon electrode is a sensitive material for glucose detection, moreover the Co3O4 UNSs can increase the interaction and detection of glucose due to their high surface area. The estimated limit of detection (S/N=3) and limit of quantification (S/N=10) of the linear segment (5-40μM) are 1.08μM and 3.60μM respectively. The reproducibility experiments confirmed the feasibility of Co3O4 UNS-Ni(OH)2 for the quantitative detection of certain concentration ranges of glucose.

Solid-phase electrochemical reduction of graphene oxide films in alkaline solution

Graphene oxide (GO) film was evaporated onto graphite and used as an electrode to produce electrochemically reduced graphene oxide (ERGO) films by electrochemical reduction in 6 M KOH solution through voltammetric cycling. Fourier transformed infrared and Raman spectroscopy confirmed the presence of ERGO. Electrochemical impedance spectroscopy characterization of ERGO and GO films in ferrocyanide/ferricyanide redox couple with 0.1 M KCl supporting electrolyte gave results that are in accordance with previous reports. Based on the EIS results, ERGO shows higher capacitance and lower charge transfer resistance compared to GO.

Ga doped RGO–TiO2 composite on an ITO surface electrode for investigation of photoelectrocatalytic activity under visible light irradiation

Gallium (Ga) doped reduced graphene oxide–titania (RGO–TiO2) composites were successfully synthesized by a sol–gel method and deposited on an ITO coated glass substrate via an electrophoretic deposition method. The photocatalyst materials were tested in the CO2 conversion reaction in aqueous media. Prior to this, the catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis reflectance spectroscopy and Fourier transform infrared spectroscopy (FTIR). The synergistic effect of RGO and Ga doping on TiO2 was investigated. Electron–hole recombination on the catalyst surface can be minimized greatly by using RGO with TiO2 while Ga doping assists in reducing the band gap energy. The corresponding expansion of the absorption range towards the visible region was also observed. The results showed that both RGO and Ga enhance CO2 adsorption on the catalyst surface, hence facilitating a high CO2 conversion yield. The photoreduction products were mostly formic acid and trace amounts of methanol. A higher yield of formic acid was produced by the Ga–RGO–TiO2 composite films compared to the RGO–TiO2 composite and pure TiO2 film during a 120 min period of visible light irradiation.

Nanocomposites of nitrogen-doped graphene decorated with a palladium silver bimetallic alloy for use as a biosensor for methotrexate detection

The synthesis and application of composites of N-graphene decorated with a bimetallic palladium–silver alloy (PdAg/NG–GCE) for the detection of methotrexate (MTX) are described. The nanocomposites were synthesized with different ratios of Ag and Pd (3 : 1, 1 : 1 and 2 : 1). Energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) show that the Pd and Ag cations were completely reduced to Pd and Ag, respectively, during the formation of PdAg/NG. Transmission electron microscopy (TEM) showed good loading between the PdAg alloy nanoparticles and the NG nanosheets with a Pd : Ag ratio of 1 : 1. The TEM results also depicted the existence of PdAg alloy nanoparticles with sizes between 3 and 13 nm, decorated on the surface of NG nanosheets. Electrochemical impedance spectroscopy (EIS) data also showed a decrease in the charge transfer resistance of Pd1Ag1/NG–GCE compared with Pd/NG, Ag/NG, NG and GCE, which suggests that the electron-transfer kinetics for MTX oxidation is highly facilitated at the Pd1Ag1/NG interface. The electrocatalytic activity of Pd1Ag1/NG–GCE towards MTX was also explored using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at pH 5.8. The anodic peak currents of MTX on Pd1Ag1/NG–GCE were approximately 8-fold higher than on the non-modified electrodes. A good linear ratio of the oxidation peak currents and MTX concentrations over the range of 0.02–200 μM with a limit of detection of 1.32 nM was achieved.