Yusran Sulaiman

Simultaneous Electrochemical Detection of Dopamine and Ascorbic Acid Using an Iron Oxide/Reduced Graphene Oxide Modified Glassy Carbon Electrode

The fabrication of an electrochemical sensor based on an iron oxide/graphene modified glassy carbon electrode (Fe3O4/rGO/GCE) and its simultaneous detection of dopamine (DA) and ascorbic acid (AA) is described here. The Fe3O4/rGO nanocomposite was synthesized via a simple, one step in-situ wet chemical method and characterized by different techniques. The presence of Fe3O4 nanoparticles on the surface of rGO sheets was confirmed by FESEM and TEM images. The electrochemical behavior of Fe3O4/rGO/GCE towards electrocatalytic oxidation of DA was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) analysis. The electrochemical studies revealed that the Fe3O4/rGO/GCE dramatically increased the current response against the DA, due to the synergistic effect emerged between Fe3O4 and rGO. This implies that Fe3O4/rGO/GCE could exhibit excellent electrocatalytic activity and remarkable electron transfer kinetics towards the oxidation of DA. Moreover, the modified sensor electrode portrayed sensitivity and selectivity for simultaneous determination of AA and DA. The observed DPVs response linearly depends on AA and DA concentration in the range of 1–9 mM and 0.5–100 μM, with correlation coefficients of 0.995 and 0.996, respectively. The detection limit of (S/N = 3) was found to be 0.42 and 0.12 μM for AA and DA, respectively.

Electrochemical sensor based on gold nanoparticles/ethylenediamine-reduced graphene oxide for trace determination of fenitrothion in water

In this work, a new procedure was investigated for the production of a reduced graphene oxide/gold nanoparticle (rGO/AuNP) nanocomposite for use as an ideally polarizable modifier in electrochemical sensors. Ethylenediamine (en) was used for reducing the active functional groups (epoxy and carboxylic) of graphene oxide (GO) and as a cross linker for the formation of AuNPs during chemical reduction with sodium citrate. The constructed nanocomposite (AuNP/en-rGO) was easily homogenized in dimethylformamide (DMF) and characterized using different techniques. AuNP/en-rGO was drop-cast on a screen-printed electrode (SPE) as an efficient electrochemical sensor for the highly sensitive determination of fenitrothion. The differential pulse voltammetry (DPV) response of the AuNP/en-rGO-modified SPE under optimized conditions was linear in the range of 0.1–6.25 ng mL−1 with a limit of detection of 0.036 ng mL−1 (S/N = 3). The AuNP/en-rGO-modified SPE showed a selective amperometry response toward fenitrothion among other interfering pesticides. In addition, the sensor was successfully employed for determining the fenitrothion residue in some water samples, including tap and lake waters, and the results were in agreement with those using gas chromatography as the standard test method.

Polyaniline-modified nanocellulose prepared from Semantan bamboo by chemical polymerization: preparation and characterization

Crystalline nanocellulose was prepared from Semantan bamboo (Gigantochloa scortechinii) via acid hydrolysis and was used to synthesize a nanocomposite of polyaniline/crystalline nanocellulose (PANi/CNC) via in situ oxidative polymerization of aniline in the presence of crystalline nanocellulose. The electrochemical properties of the nanocomposite were studied using a modified PANi/CNC electrode via cyclic voltammetry, and higher current response was observed for the PANi/CNC-modified electrode compared to that for the modified electrode with PANi. The results obtained from EIS displayed lower value of Rct for the PANi/CNC-modified electrode, indicating that the incorporation of CNC into the PANi structure could enhance the electron transfer rate. The characteristic peaks of PANi and CNC were observed in the FTIR spectra of the nanocomposite, indicating the incorporation of CNC inside the nanocomposite structure. Moreover, in the XRD diffractogram, lower crystallinity was observed at the 2 theta values of 22.6 and 16.1 for PANi/CNC compared to that for pure CNC. The FESEM images showed high porosity of the nanostructure with no phase separation, revealing the homogenous polymerization of the monomer on the surface of the crystalline cellulose. Aggregation of PANi particles was observed with the increasing aniline concentration.

Poly(3,4-ethylenedioxythiophene) Doped with Carbon Materials for High-Performance Supercapacitor: A Comparison Study

A comparative study of multiwalled carbon nanotube (MWCNT), graphene oxide (GO), and nanocrystalline cellulose (NCC) as a dopant in the preparation of poly(3,4-ethylenedioxythiophene)- (PEDOT-) based hybrid nanocomposites was presented here. The hybrid nanocomposites were prepared via the electrochemical method in aqueous solution. The FTIR and Raman spectra confirmed the successful incorporation of dopants (MWCNT, GO, and NCC) into PEDOT matrix in the process of formation of the hybrid nanocomposites. It was observed that the choice of the carbon material affected the morphologies and supercapacitive properties of the hybrid nanocomposites. Incorporation of GO with PEDOT produces a paper-like sheet nanocomposite in which the wrinkled surface results in larger surface area compared to the network-like and rod-like structures of PEDOT/MWCNT and PEDOT/NCC, respectively. Owing to larger surface area, PEDOT/GO exhibits the highest specific capacitance (120.13 F/g), low equivalent series resistance (34.44 Ω), and retaining 87.99% of the initial specific capacitance after 1000 cycles, signifying a long-term cycling stability. Furthermore, the high performance of PEDOT/GO is also demonstrated by its high specific energy and specific power.

Electrochemical properties of PVA–GO/PEDOT nanofibers prepared using electrospinning and electropolymerization techniques

Conducting nanofibers composed of poly(vinyl alcohol) (PVA), graphene oxide (GO) and poly(3,4-ethylenedioxythiophene) (PEDOT) were fabricated via a combined method using electrospinning and electropolymerization techniques. A small amount of GO was dispersed into PVA as the precursor solution for electrospinning, resulting in free-bead nanofiber structures with a diameter range less than 200 nm. SEM images of the obtained nanofiber revealed that PEDOT grew well on the surface of the electrospun nanofibers during the potentiostatic mode of the electropolymerization process. The presence of GO and PEDOT was confirmed by FTIR and Raman spectroscopy analyses. Comparing with the PVA/PEDOT nanofiber, the experimental results indicate that the addition of GO improved the electrochemical performance of the nanofibers. The electrochemical measurements demonstrated that the PVA–GO/PEDOT composite nanofiber could enhance the current response and reduce the charge transfer resistance of the nanofiber.

Development of a PrGO-Modified Electrode for Uric Acid Determination in the Presence of Ascorbic Acid by an Electrochemical Technique

An attractive electrochemical sensor of poly(3,4-ethylenedioxythiophene)/reduced graphene oxide electrode (PrGO) was developed for an electrochemical technique for uric acid (UA) detection in the presence of ascorbic acid (AA). PrGO composite film showed an improved electrocatalytic activity towards UA oxidation in pH 6.0 (0.1 M PBS). The PrGO composite exhibited a high current signal and low charge transfer resistance (Rct) compared to a reduced graphene oxide (rGO) electrode or a bare glassy carbon electrode (GCE). The limit of detection and sensitivity of PrGO for the detection of UA are 0.19 μM (S/N = 3) and 0.01 μA/μM, respectively, in the range of 1–300 μM of UA.

Optimization of peak current of poly(3,4-ethylenedioxythiophene)/multi-walled carbon nanotube using response surface methodology/central composite design

Modification of electrode surface with poly(3,4-ethylenedioxythiophene)/multi-walled carbon nanotube (PEDOT/MWCNT) composite prepared by electrodeposition technique was reported in this study. The optimization of peak current response of PEDOT/MWCNT was performed by utilizing the combination of response surface methodology and central composite design (RSM/CCD). The effect of each variable and the interaction between three variables i.e. the concentration of MWCNT, electrodeposition potential and deposition time were studied and modeled. The statistical analysis showed that the concentration of MWCNT and deposition time have significantly affected the peak current response. A reduced cubic model equation with the coefficient of determination (R2) value of 0.9973 was developed. The optimized condition predicted by the software was compared with the experiment and resulting in less than 2% error, indicating that this model was reliable and able to predict the peak current response accurately. Additionally, the electrochemical properties, chemical properties and morphology of the optimized modified electrode were characterized by cyclic voltammetry (CV), Fourier transform infrared (FTIR), Raman spectroscopy and field emission scanning electron microscopy (FESEM). The peak current of the optimized PEDOT/MWCNT modified electrode was higher than electrode without MWCNT and the FESEM study demonstrated that the tubular structure of MWCNT was uniformly wrapped by PEDOT. The FTIR and Raman spectra proved that MWCNT was successfully incorporated into PEDOT.

Influence of Monomer Concentration on the Morphologies and Electrochemical Properties of PEDOT, PANI, and PPy Prepared from Aqueous Solution

Poly(3,4-ethylenedioxyhiophene) (PEDOT), polyaniline (PANI), and polypyrrole (PPy) were prepared on indium tin oxide (ITO) substrate via potentiostatic from aqueous solutions containing monomer and lithium perchlorate. The concentration of monomers was varied between 1 and 10 mM. The effects of monomer concentration on the polymers formation were investigated and compared by using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) measurements. FTIR and Raman spectra showed no changes in the peaks upon the increment of the concentration. Based on the SEM images, the increment in monomer concentration gives significant effect on morphologies and eventually affects the electrochemical properties. PEDOT electrodeposited from 10 mM solution showed excellent electrochemical properties with the highest specific capacitance value of 12.8 mF/cm2.

Enhancement of Capacitive Performance in Titania Nanotubes Modified by an Electrochemical Reduction Method

Highly ordered titania nanotubes (TNTs) were synthesised by an electrochemical anodization method for supercapacitor applications. However, the capacitive performance of the TNTs was relatively low and comparable to the conventional capacitor. Therefore, in order to improve the capacitive performance of the TNTs, a fast and facile electrochemical reduction method was applied to modify the TNTs (R-TNTs) by introducing oxygen vacancies into the lattice. X-ray photoelectron spectroscopy (XPS) data confirmed the presence of oxygen vacancies in the R-TNTs lattice upon the reduction of Ti4+ to Ti3+. Electrochemical reduction parameters such as applied voltage and reduction time were varied to optimize the best conditions for the modification process. The electrochemical performance of the samples was analyzed in a three-electrode configuration cell. The cyclic voltammogram recorded at 200 mV s−1 showed a perfect square-shaped voltammogram indicating the excellent electrochemical performance of R-TNTs prepared at 5 V for 30 s. The total area of the R-TNTs voltammogram was 3 times larger than the unmodified TNTs. A specific capacitance of 11.12 mF cm−2 at a current density of 20 μA cm−2 was obtained from constant current charge-discharge measurements, which was approximately 57 times higher than that of unmodified TNTs. R-TNTs also displayed outstanding cycle stability with 99% capacity retention after 1000 cycles.

Synthesis and Characterization of Polyaniline/Graphene Composite Nanofiber and Its Application as an Electrochemical DNA Biosensor for the Detection of Mycobacterium tuberculosis

This article describes chemically modified polyaniline and graphene (PANI/GP) composite nanofibers prepared by self-assembly process using oxidative polymerization of aniline monomer and graphene in the presence of a solution containing poly(methyl vinyl ether-alt-maleic acid) (PMVEA). Characterization of the composite nanofibers was carried out by Fourier transform infrared (FTIR) and Raman spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). SEM images revealed the size of the PANI nanofibers ranged from 90 to 360 nm in diameter and was greatly influenced by the proportion of PMVEA and graphene. The composite nanofibers with an immobilized DNA probe were used for the detection of Mycobacterium tuberculosis by using an electrochemical technique. A photochemical indicator, methylene blue (MB) was used to monitor the hybridization of target DNA by using differential pulse voltammetry (DPV) method. The detection range of DNA biosensor was obtained from of 10−6–10−9 M with the detection limit of 7.853 × 10−7 M under optimum conditions. The results show that the composite nanofibers have a great potential in a range of applications for DNA sensors.