Kwok Feng Chong

Impedimetric graphene-based biosensor for the detection of Escherichia coli DNA

A label-free impedimetric DNA biosensor based on graphene nanosheets has been developed for the detection of Escherichia coli O157:H7 strain GZ-021210. Probe DNA (pDNA) of E. coli was immobilized onto graphene nanosheets by the surface functionalization of graphene with 1-pyrenebutyric acid (PyBA) followed by carbodiimide linkage. The hybridization of complementary DNA (cDNA) of E. coli with the immobilized pDNA increased the electron transfer resistance of the graphene nanosheets, as observed by electrochemical impedance spectroscopy (EIS). The E. coli DNA biosensor displayed a wide range of linear response (1.0 × 10−10 M to 1.0 × 10−14 M), low detection limit (0.7 × 10−15 M), single-base mismatch selectivity, high robustness and good reproducibility. The current work demonstrates an important advancement in the development of a sensitive biosensor for E. coli detection.

Aminopyrene functionalized reduced graphene oxide as a supercapacitor electrode

In this work, we report on the structural and electrochemical properties of aminopyrene functionalized reduced graphene oxide (Ap-rGO) for its suitability as a supercapacitor electrode. The Ap-rGO is prepared by sonicating a suspension of rGO with aminopyrene and the filtered sediment is subjected to spectroscopy studies and electrochemical studies. Spectroscopy studies reveal the successful functionalization of aminopyrene onto Ap-rGO through π–π interactions. Electrochemical analyses of Ap-rGO show a substantial increase in the specific capacitance for Ap-rGO (160 F g−1 at 5 mV s−1) compared to the non-functionalized rGO (118 F g−1 at 5 mV s−1). The enhancement is shown to be the pseudocapacitance arising from the electron donating effect of the amine group and the electron accepting effect of rGO, which enable facile electron transfer between the surface-bound amine group and rGO. The Ap-rGO has desirable charge storage properties such as low series resistance (0.4 Ω) and superior cycling stability (85% after 5000 cycles). Furthermore, the Ap-rGO has 1.5 fold higher energy density than the non-functionalized rGO electrode, thereby making it suitable as a deployable supercapacitor electrode.

High performance supercapacitor using catalysis free porous carbon nanoparticles

Very high supercapacitance values are obtained using catalyst free porous carbon nanoparticles (PCNs). The obtained PCNs have a porous structure with fine particles 35 nm in size. The specific capacitance of PCNs is 343 F g −1 and 309 F g −1 at 5 mV s −1 and 0.06 A g −1 , respectively. PCNs shows a high cyclic stability of about 90% and high columbic efficiency of 95% over 2500 cycles at 1 A g −1 . Impedance spectra show low resistance of PCNs, supporting their suitability for supercapacitor electrode application.

Bio-waste Corn-cob Cellulose Supported Poly(hydroxamic acid) Copper Complex for Huisgen Reaction: Waste to Wealth Approach

Corn-cob cellulose supported poly(hydroxamic acid) Cu(II) complex was prepared by the surface modification of waste corn-cob cellulose through graft copolymerization and subsequent hydroximation. The complex was characterized by IR, UV, FESEM, TEM, XPS, EDX and ICP-AES analyses. The complex has been found to be an efficient catalyst for 1,3-dipolar Huisgen cycloaddition (CuAAC) of aryl/alkyl azides with a variety of alkynes as well as one-pot three-components reaction in the presence of sodium ascorbate to give the corresponding cycloaddition products in up to 96% yield and high turn over number (TON 18,600) and turn over frequency (TOF 930h-1) were achieved. The complex was easy to recover from the reaction mixture and reused six times without significant loss of its catalytic activity.

Colchicine prodrugs and codrugs: Chemistry and bioactivities

Antimitotic colchicine possesses low therapeutic index due to high toxicity effects in non-target cell. However, diverse colchicine analogs have been derivatized as intentions for toxicity reduction and structure-activity relationship (SAR) studying. Hybrid system of colchicine structure with nontoxic biofunctional compounds modified further affords a new entity in chemical structure with enhanced activity and selectivity. Moreover, nanocarrier formulation strategies have been used for colchicine delivery. This review paper focuses on colchicine nanoformulation, chemical synthesis of colchicine prodrugs and codrugs with different linkers, highlights linker chemical nature and biological activity of synthesized compounds. Additionally, classification of colchicine prodrugs based on type of conjugates is discussed, as biopolymers prodrugs, fluorescent prodrug, metal complexes prodrug, metal-labile prodrug and bioconjugate prodrug. Finally, we briefly summarized the biological importance of colchicine nanoformulation, colchicine prodrugs and codrugs.

Electrospun nanofiber membranes as ultrathin flexible supercapacitors

A highly flexible electrochemical supercapacitor electrode was developed with a novel metal oxide-reinforced nanofiber electrode by utilizing a solution-based electrospinning technique. The facile fabrication steps involved the introduction of metal precursors into a polymeric solution, which was subjected to an in situ electrospinning process. The electrospun polymeric web with metallic ingredients was then subjected to an oxidative stabilization process that induced the formation of metal oxide nanoparticles within the polymer structure. Finally, the metal oxide nanoparticles incorporated with nanofibers were obtained using a carbonization process, thus converting the polymer backbones into a carbon-rich conductive nanofiber structure. The fabricated nanofibers were decorated and implanted with metal oxide nanoparticles that had a surface-decorated structure morphology due to the solubility of the precursors in the reaction solution. The electrochemical performance of the fabricated metal oxide reinforced with nanofiber electrodes was investigated as an electrochemical system, and the novel morphology significantly improved the specific capacitance compared to a pristine carbon nanofiber membrane. As a result of the uniform dispersion of metal oxide nanoparticles throughout the surface of the nanofibers, the overall capacitive behavior of the membrane was enhanced. Furthermore, a fabricated free-standing flexible device that utilized the optimized nanofiber electrode demonstrated high stability even after it was subjected to various bending operations and curvatures. These promising results showed the potential applications of these lightweight, conductive nanofiber electrodes in flexible and versatile electronic devices.

1-Pyrenebutyric Acid Functionalized Reduced Graphene Oxide (1-Pb-Rgo) Energy Storage

Supercapacitors are a class of energy storage device which has high energy density and high power density. As a material with unique 2D structure as well as outstanding physical properties such as high electrical conductivity and large surface area, graphene demonstrates great potential to be the electrode material for supercapacitors. Despite graphene showing theoretical surface area as high as 2630 m2/g, results acquired showed that not all the surface area were utilized. This could be due to the tendency of the graphene layers to restack. In this work, 1-pyrenebutyric acid (1-PB) was anchored to graphene with the pyrenyl group via π-π stacking to prevent the restacking of graphene layers. The successful functionalization of 1-PB on the hydrophobic surface of rGO was characterized with UV-Vis Spectroscopy and Fourier Transformed Infrared Spectroscopy (FTIR). The electrochemical performance of 1-PB-rGO was studied through cyclic voltammetry (CV), galvanostatic charge-discharge (CD) and electrochemical impedance spectroscopy (EIS). Using 6 M KOH as the electrolyte, we obtained an enhanced specific capacitance for 1-PB-rGO. These findings indicates that the non-covalent functionalization of 1-PB on rGO enhances the capacitive storage ability and it show potential as an electrode material in the energy storage application.

Electrochemical Biosensor for Nitrite Based on Polyacrylic-Graphene Composite Film with Covalently Immobilized Hemoglobin

A new biosensor for the analysis of nitrite in food was developed based on hemoglobin (Hb) covalently immobilized on the succinimide functionalized poly(n-butyl acrylate)-graphene [poly(nBA)-rGO] composite film deposited on a carbon-paste screen-printed electrode (SPE). The immobilized Hb on the poly(nBA)-rGO conducting matrix exhibited electrocatalytic ability for the reduction of nitrite with significant enhancement in the reduction peak at −0.6 V versus Ag/AgCl reference electrode. Thus, direct determination of nitrite can be achieved by monitoring the cathodic peak current signal of the proposed polyacrylic-graphene hybrid film-based voltammetric nitrite biosensor. The nitrite biosensor exhibited a reproducible dynamic linear response range from 0.05–5 mg L−1 nitrite and a detection limit of 0.03 mg L−1. No significant interference was observed by potential interfering ions such as Ca2+, Na+, K+, NH4+, Mg2+, and NO3− ions. Analysis of nitrite in both raw and processed edible bird’s nest (EBN) samples demonstrated recovery of close to 100%. The covalent immobilization of Hb on poly(nBA)-rGO composite film has improved the performance of the electrochemical nitrite biosensor in terms of broader detection range, lower detection limit, and prolonged biosensor stability.

Flakes Size-Dependent Optical and Electrochemical Properties of MoS2

Background: Molybdenum disulfide (MoS2) is a transition metal dichalcogenides and has some interesting and promising properties. MoS2 has direct and indirect band gaps depending on its crystalline structure. In addition, its sheets morphology makes it a good candidate for supercapacitor applications. Objective: The aim of this work is to study the effect of MoS2 flakes size on its optical and electrochemical properties. Method: MoS2 with different flakes sizes were prepared by exfoliation method. The exfoliation was performed by sonication of MoS2 powder in N,N-Dimethylformamide followed by different centrifugation speeds. UV-Vis spectra illustrated the optical energy gap was inversely proportional to the MoS2 flakes size. Results: Absorption coefficient values indicated that the exfoliation reduced the number of layers. Symmetric supercapacitor was made from two MoS2 electrodes and tested in 6 M KOH electrolyte. The specific capacitance was found to be dramatically increased with decreasing flakes size (9.5 and 4.5 mF/cm2 for 0.26 and 0.98 µm flakes size, respectively). Conclusion: These findings recommend that MoS2 can be the excellent electrode material for supercapacitor.

Reflectometric Optosensor for Visual Detection of Ammonia Based on Silica Pellet Sensing Material

Ammonia (NH3) has been widely used in the manufacture of fertilizers that applied to soil, but the high consumption of fertilizers will end up with water pollution. Owing to the deleterious effects of NH3 to human and environment, a new optosensor for NH3 has been fabricated based on silica pellet sensing material. Microsilica was synthesized by sol-gel method in the presence of cobalt(II) chloride hexahydrate (CoCl2·6H2O), followed by manual grinding process to obtain micro-sized silica particles. Due to the non-transparent pellet material used for NH3 sensing, a fiber optic reflectance spectrophotometer was employed for monitoring of reflectance signal transduction event as the pellet colour changed from pink to blue hue upon reaction with NH3 at optimum pH 13. Due to the high porosity and surface area of silica microparticles were used as immobilization matrix, the immobilized Co2+ ion demonstrated broad dynamic linear range from 18 to 100 ppm NH3 with a fast response time of 3 min. The reflectometric sensing protocol involves a single-step NH3 assay which merely requires dispensing small aliquots of NH3 onto the reaction surface of the pellet sensor. This makes on-site NH3 detection more user-friendly and convenient when compared to traditional electrochemical-, infrared- and gas chromatography-based methods.