ELECTROCHEMICAL CHIRAL BIOSENSORS

Recognition of chiral molecules in biological assemblies has been a subject of extensive research. The aim of this work was to fabricate and characterise biocompatible composite materials suitable for chiral recognition. Collagen, the most abundant chiral, extracellular protein, was chosen as a possible matrix. The chiral recognition properties were evaluated by a comparative study in collagen, collagen incorporated in tetramethyl orthosilicate (TMOS) and TMOS. In electrochemical studies, ferrocene was incorporated to facilitate electron transfer. The recognition characteristics of two chiral enzymes, L-lactate oxidase and D-glucose oxidase were tested using circular dichroism (CD), Fourier Transform Infra-Red (FTIR) spectroscopy and electrochemical methods. A surprising result revealed an inversion of chiral selectivity. The effect of various parameters such as immobilisation, temperature, chemical modification, solvent systems, on enantioselectivity is well known. Stereoinversions caused by the ‘sergeants and soldiers’ effect in gel-forming p-conjugated molecules caused by co-assembly has been reported by several groups. The inversion of stereoselectivity observed in this study is probably due to a combination of the microenvironment and electrostatic interactions of the enzyme, mediator and substrate with the chiral collagen matrix. The results may have important implications for biosensing, asymmetric syntheses and understanding the nature of chiral interactions in biological systems

Carbon-based nanomaterials for drugs sensing: a review

Carbon-based nanomaterials such as graphene, carbon nanotubes, carbon nanofibers and nanodiamonds have been fascinated considerable attention as promising materials for drug sensing. These materials have tremendous amount of attraction due to some extraordinary features such as excellent electrical and thermal conductivities as well as high mechanical strength. Hence, these nanomaterials have been used extensively in sensor technology in order to achieved desired sensitivities. To date, carbon based nanomaterials have been exploit in the development of various drug sensing due to their simple preparation methods, and cost effectiveness. The aim of this review is to focus upon carbon based nanomaterials predominantly on drugs sensing applications. This review has been written in summary form including properties, fabrication method, and analytical performances.Abbreviation:Au, Gold; CNFs, Carbon Nanofibers; CNTs, Carbon Nanotubes; CVD, Chemical Vapour Deposition; D-, Dextrorotatory enantiomer; D, Dimensional; DNase, deoxyribonuclease; ESD, Electrospinning deposition; GCE, Glassy Carbon Electrode; Gr, Graphene; GrO, Graphene Oxide; ILs, ionic liquids; L-, Levorotatory enantiomer; LOD, Limit of Detection; MTase, Methyltransferases; MW, Microwave; MWCNTs, Multi-walled Carbon nanotubes; NDs, Nanodiamonds; NPs, Nanoparticles; PECVD, Plasma Enhanced Chemical Vapour Deposition; RGO, Reduced Graphene Oxide; SPE, Screen-Printed Electrode; SPR, Surface Plasmon resonance; ssDNA, single-stranded DNA; SWCNTs, Single-walled Carbon nanotubes

Voltammetric studies and characterizations of biocompatible graphene/collagen nanocomposite-modified glassy carbon electrode towards enantio-recognition of chiral molecules

Chiral recognition has continuously attracted the attention among researchers due to its significance in the field of biomedical, as well as pharmaceutical sciences. Thus, graphene has been found surprisingly unfamiliar for incorporation with collagen, whereby it is fundamentally capable of enhancing the chiral recognition properties in chiral molecules. Hence, pertaining to the promising prospective of this composite, electro-analysis studies had been carried out on graphene/collagen nanocomposites on glassy carbon electrode. On top of that, cyclic voltammetry studies were conducted with various parameters, such as scan rates, temperatures, pH, concentrations, multiple cycles, as well as different graphene conditions to evaluate the potential of graphene/collagen as a promising aspirant in chiral recognition. Apart from that, the properties of nanocomposites were looked into via electrochemical impedance spectroscopy, microscopic, as well as spectroscopic method, involving Fourier transform infrared spectroscopy, UV–visible spectroscopy, Raman spectroscopy, Field-emission scanning electron microscopy, and Transmission electron microscopy. Finally, the optimised nanocomposites were applied in simple chiral recognition of chiral molecules involving Mandelic Acid and Tyrosine

Sensory measurement of mercury and cadmium ions in water using silicon nanowires-modified screen printed carbon electrode

Modified screen printed carbon electrode (SPCEs) with silicon nanowires (SiNWs) were used as working electrode for the simultaneous detection of Hg(II) and Cd(II) ions in water. Linear sweep with anodic stripping voltammetry with optimum conditions of 0.05 M HCl as the supporting electrolyte, –1.2 V deposition potential and 150 s deposition time were applied. The formed electrode material was thoroughly investigated for the morphology, effects of supporting electrolyte, deposition time and potential were well calibrated for the detection of Hg(II) and Cd(II) ions. The interference studies in the presence of other competitive ions in waste water such as Ni(II), Al(III), SO3–, SO42–, Mg(II), As(III), Zn(II) and Pb(II) indicated no significant interference, which reflects the availability of these species in the sample solution that did not affect the detection and measurement of Hg(II) and Cd(II) ions. However, Cu(II) presence found to affect the detection of Hg(II) or Cd(II) ions to some extent by suppressing the peak current. Further, the efficiency of the prepared electrode investigated by the testing of sea water samples and comparing its results against ICP-MS and AAS indicated that the screen printed carbon electrode can well be suited for the non-destructive measurement of Hg(II) and Cd(II) ions in real-time samples

Top-down fabrication of silicon nanowire sensor using electron beam and optical mixed lithography

The realization of reliable nanobiosensor devices requires the improvement of fabrication techniques to form the nanometer-sized structures and patterns, which were used to attach nano materials such as DNA for the device elements. This study demonstrates the sensitivity of silicon nanowires (SiNWs) as a sensing element in sensor application. Starting with silicon on insulator (SOI) material, the SiNWs with <100nm in width were fabricated using electron beam lithography combined with conventional CMOS process. Different numbers of SiNWs which are single, 10 arrays of nanowires and 20 arrays of nanowires were developed. Subsequently, the two metal electrodes which are designated as source (S) and drain (D) were fabricated on top of individual SiNWs using optical lithography process. Optical and electrical characteristic have been proposed to verify the outcome of the fabricated structures. One major part is to observe the SiNWs optically in order to meet the nano-scale variation by using High Power Microscope (HPM) inspection and Field Emission Scanning Electron Microscope (FESEM) imaging. Finally, the samples will be tested electrically using I-V measurement system. The results show that device with single SiNW with 60nm in width give the highest resistivity value due to surface to volume ratio

Voltammetric determination of dopamine mediated by nanoparticle WO3/MWCNT modified glassy carbon electrode

Chemically-modified electrode fabricated by mechanical attachment of multi-walled carbon nanotubes/tungsten oxide (MWCNTs/WO3) in the electrocatalytic study of dopamine was investigated. The MWCNTs/WO3 nanocomposite has been characterized using voltammetric techniques of cyclic voltammetry, chronoamperometry and chronocoulometry. The CNT/WO3/GCE induces a 2.9 enhancement oxidative peak with peak separation of approximately 200 mV, shifting towards a lower potential in the electrochemical oxidation of 0.4 mM dopamine at pH 7.0, in comparison with the WO3/GCE, MWCNTs/GCE and bare GCE. The lowering positive potential and enhancement current are evident of electrocatalysis process. From the calibration plot, the high sensitivity response of 57.00 μA/μM for the anodic peak with the detection limit of 0.018 μM (100 mV/s scan rate) of dopamine at the CNT/WO3/GCE were obtained. Based on the chronocoulometric study on 0.4 mM dopamine in 0.1 M KCl, the diffusion coefficient was found to be 5.43 x 10-8 cm2/s with the surface charge of 6.86 x 10-4 C/cm2. The easily prepared nanocomposite-modified electrode showed to have high sensitivity, selectivity and good reproducibility

Effect of electropolymerization potential on the properties of PEDOT/ZnO thin film composites

The physical, chemical and electrochemical properties of poly(3,4-ethylenedioxythiophene) /zinc oxide (PEDOT/ZnO) thin film electrode that were prepared electrochemically were studied. PEDOT was potentiostatically deposited on the hexagonal flake-like ZnO-covered ITO glass substrate by applying three different potentials (1.0 V, 1.25 V and 1.5 V) where under these circumstances, the effect of varying electropolymerization potentials where studied. The optical bandgap of each of the PEDOT/ZnO composites prepared were noticed to be within the range of 3.40 eV to 3.45 eV which were in between the optical band gap values of sole PEDOT and ZnO. The presence of both materials was asserted from XRD, FTIR and Raman analysis where all of the corresponding peaks for each of the materials in the spectra were assigned. SEM revealed the flake-like hexagonal morphology of ZnO which is in agreement with the XRD analysis. While the PEDOT morphology was discerned with round-shaped granular morphology where the average grain size was decreased with the electropolymerization potentials. The resistance of charge transfer of PEDOT/ZnO thin film was directly proportional to the electropolymerization potential while on the specific capacitance was inversely proportional. The composite exhibit both PEDOT and ZnO unique properties that can be used as a multi-functional material in various potential applications

Green synthesis of silver nanoparticle decorated on reduced graphene oxide nanocomposite using clinacanthus nutans and its applications

A straightforward approach that uses Clinacanthus nutans leaf extract as a bio-reduction agent has been reported to anchor silver nanoparticles onto graphene oxide (rGO-Ag). The nanocomposite was characterized by using ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, and X-ray diffraction. A qualitative colour transition from yellowish to dark brown confirmed the biosynthesis of rGO-Ag nanocomposite and showed a surface plasmon resonance at 263 nm and 425 nm. Utilizing cyclic voltammetry, the electrochemical characteristics of the rGO-Ag nanocomposite modified screen printed carbon electrodes were examined. The rGO-Ag nanocomposite electrode enhanced anodic current approximately 1.29 times greater compared to silver nanoparticles (AgNPs) and 1.34 times greater compared to graphene oxide (GO). Moreover, rGO-Ag nanocomposites exhibited excellent antibacterial activity against typical Gram-positive (S. aureus) (11.99 ± 0.26 mm) and Gram-negative (E. coli) (11.86 ± 0.29 mm) bacteria. Toxicity was assayed using brine shrimp Artemia salina. The results of hatching and mortality assay demonstrates that AgNPs and rGO-Ag nanocomposite is biocompatible with A. salina at a low dosage (0.001 mg/mL). This work offers a guide for the future synthesis of nanocomposites using green reductants. The as- synthesized nanocomposite shows a promising component for the development of biomedical devices applications

Electrochemical detection of a local anesthetic dibucaine at arrays of micro liquid liquid interfaces

Electrochemical characterization and detection of protonated dibucaine (DIC+) at microinterface array across water|1,6-dichlorohexane were performed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Some thermodynamic parameters of dibucaine, such as the standard transfer potential, the Gibbs energy of transfer and the partition coefficient, were estimated by CV. In addition to the analytical parameters, the impact of bovine serum albumin (BSA) on dibucaine detection (in artificial serum matrices) was also investigated. DPV was applied to detect a lower concentration of DIC+, resulting in a detection limit of 0.9 ± 0.06 µM. While the presence of BSA affected CV, demonstrated as reduced current responses, DPV was confirmed to be an efficient method for lowering concentrations of the dibucaine detection in the artificial serum matrix in the presence of BSA, with a limit of detection (LOD) of 1.9 ± 0.12 µM

Introduction to basic concepts of analytical chemistry

Analytical chemistry is an important area, particularly in the industrial sector, agriculture, health and the environment. This book is written with the aim to provide basic concepts in analytical chemistry which involves titration, gravimetry, solvent extraction, chromatography, electrochemical methods, thermal analysis and data analysis. The contents in this book are designed in a simple way with several examples that suitable for students, academicians and researchers