Green synthesis of curcumin-silver nanoparticle and its modified electrode assisted amperometric sensor for the determination of paracetamol.

Contamination of paracetamol, a primary analgesic was wide spread in the water system that affects the eco-system. High-dosage of paracetamol to humans cause organ damages and showed adverse effect. It is important to monitor the paracetamol concentration in environmental and human samples periodically. Conventional methods associated with chromatography is found to be high-cost, time consuming and requires high-end instrumentation, Herein, we investigated the role of curcumin during bio-synthesis of silver nanoparticles. The curcumin functionalized silver nanoparticles were further chemically modifying on the electrode surface and the resulting modified electrode was applied for electrocatalytic oxidation of paracetamol. The experimental finding proved that the modified electrode is capable of sensing paracetamol by applying oxidation potential 0.4 V. Both the synthesised material and modified electrode surface were characterized for its physic-chemical properties using spectroscopy and microscopy techniques. The HR-TEM, FESEM and AFM results showed that the distribution of nanoparticle with the size range from 25 to 70 nm and the UV-Vis and Raman spectrophotometer characterization confirms the coordination between SNP and curcumin. Under optimized condition, in 0.1 M NH4Cl (pH 7) at the scan rate of 50 mVs-1. The modified electrode enhanced the sensitivity towards the detection of paracetamol in trace level. The modified electrode is capable of sensing paracetamol in a linear range between 0.59 × 10-6 and 342.1 × 10-6 M, with LOD of 0.29 µM, and linear regression equation of y = 0.092x+502.6 with a correlation coefficient of R2 = 0.996.

Electrochemical sensor for determination of butylated hydroxyanisole (BHA) in food products using poly O-cresolphthalein complexone coated multiwalledcarbon nanotubes electrode.

In this study, we have reported an electrochemical sensor for the determination of butylated hydroxyanisole (BHA) by electropolymerization of O-cresolphthalein complexone (OC) over the multiwalled carbon nanotubes (MWCNTs). In order to confirm the surface morphology, oxidation states, functional groups and charge transfer property of POC/MWCNTs electrode, the resulting POC film with MWCNTs electrode was characterized by spectroscopy, microscopy, and electrochemical techniques. The fabricated electrode was evaluated for its electrochemical performance in oxidation of BHA and the study showed that at POC/MWCNTs electrodes BHA oxidation occurred at 0.27 V. POC/MWCNTs electrode has shown a linear range for the detection of BHA from 0.33 µM to 110 µM with the detection limit of 0.11 µM (S/N = 3). Amperometric determination of BHA was also done using chronoamperometric techniques and the result was found to be linear. The real time analysis of sensors is also validated by analysing the packed potato chips samples.

Fabrication of poly o-cresophthalein complexone film modified electrode and its application to simultaneous determination of purine bases in denatured DNA.

A novel poly o-cresophthalein complexone film (POCF) modified electrode was fabricated and used as a sensor for the simultaneous detection of adenine and guanine. By comparing with the bare paraffin wax impregnated graphite electrode (PIGE), POCF modified electrode showed remarkable increase in the oxidation peak currents of adenine and guanine. The surface morphology of the POC polymer film and its nature on the PIGE were characterized by field emission scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry. The POCF modified electrode exhibited a linear range of 0.08 µM-200 µM with a low detection limit of 0.02 µM (S/N) for adenine and guanine, respectively. Further, the proposed POCF modified electrode was used for simultaneous detection of adenine and guanine in denatured CT-DNA and moth DNA with satisfactory results. The value of (G + C)/(A + T) for CT-DNA and moth DNA was calculated to be 0.79 and 0.78 respectively. The prepared POCF modified electrode showed high reproducibility and excellent stability.

Horseradish peroxidase and toluidine blue covalently immobilized leak-free sol-gel composite biosensor for hydrogen peroxide.

The enzyme horseradish peroxidase and the water-soluble mediator toluidine blue were covalently immobilized to 3-aminopropyl trimethoxy silane precursor through glutaraldehyde crosslinker. A rigid ceramic composite electrode was fabricated from this modified silane along with graphite powder, which resulted in an amperometric biosensor for H2O2. The electrochemical behaviour of the modified biosensor was monitored using cyclic voltammetry in the potential range of 0.2V to -0.4V vs SCE. The biosensor exhibited a stable voltammogram with cathodic peak at -0.234V and anodic peak at -0.172V, with a formal potential of -0.203V. Various factors influencing the performance of the biosensor such as buffer solution, pH, temperature and potential were examined for optimizing the working conditions. The modified biosensor exhibited a good catalytic behaviour for the reduction of H2O2 at a lower potential of -0.25V without any barrier from possible interferents. The analytical working range was found to be 0.429µM to 0.455mM of H2O2 with a detection limit of 0.171µM. The fabricated biosensor is robust for long-term usage in addition to the high sensitivity, rapid response and having an advantage of surface renewability by simple mechanical polishing.

A novel bimediator amperometric sensor for electrocatalytic oxidation of gallic acid and reduction of hydrogen peroxide.

A novel bimediator amperometric sensor is fabricated for the first time by surface modification of graphite electrode with thionine (TH) and nickel hexacyanoferrate (NiHCF). The electrochemical behavior of the TH/NiHCF bimediator modified electrode was characterized by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The TH/NiHCF bimediator modified electrode exhibited a pair of distinct redox peaks for NiHCF and TH with formal potentials of 0.33V and -0.27V vs. SCE at a scan rate of 50mV s(-1) in 0.1M NaNO3 and 0.1M NH4NO3 respectively. The electrocatalytic activity of the bimediator modified electrode towards oxidation of gallic acid with NiHCF and reduction of hydrogen peroxide with TH was evaluated and it was observed that the modified electrode showed an electrocatalytic activity towards the oxidation of gallic acid in the concentration range of 4.99×10(-6)-1.20×10(-3)M with a detection limit of 1.66×10(-6)M (S/N=3) and reduction of H2O2 in the concentration range of 1.67×10(-6)-1.11×10(-3)M with a detection limit of 5.57×10(-7)M (S/N=3). The bimediator modified electrode was found to exhibit good stability and reproducibility.

Electrochemical behavior of Azure A/gold nanoclusters modified electrode and its application as non-enzymatic hydrogen peroxide sensor.

A novel non-enzymatic hydrogen peroxide sensor was developed using Azure A/gold nanoclusters modified graphite electrode. The method of preparation of Azure A/gold nanoclusters was simple and it was characterized by UV-visible spectroscopy, field emission scanning electron microscopy (FESEM) and confocal Raman microscopy. The electrochemical properties of Azure A/gold nanoclusters modified graphite electrode was characterized by cyclic voltammetry. In 0.1M H(2)SO(4) the modified electrode showed redox peaks which correspond to the redox behavior of gold nanoparticle. In 0.1M PBS the modified electrode exhibited well defined redox peaks with the formal potential of -0.253 V which is analogous to the redox reaction of Azure A. The results have shown that the gold nanoclusters has reduced the formal potential of Azure A and enhanced the current due to the fast charge transfer kinetics. Also the modified electrode showed an enhanced electrocatalytic activity towards the reduction of H(2)O(2) in the concentration range of 3.26×10(-6)M to 3.2×10(-3)M with a detection limit of 1.08×10(-6)M (S/N=3). The proposed electrode exhibited good stability and reproducibility, and it has the potential application as a sensor for other biologically significant compounds.

Selective electrooxidation of uric acid in presence of ascorbic acid at a room temperature ionic liquid/nickel hexacyanoferarrate nanoparticles composite electrode.

A novel amperometric sensor for the determination of uric acid was fabricated using room temperature ionic liquid and nickel hexacyanoferrate nanoparticle composite which was immobilized on paraffin wax impregnated graphite electrode. The nickel hexacyanoferrate nanoparticle was characterized by UV-vis, X-ray diffraction and field emission scanning electron microscopy. The electrochemical behavior of the modified electrode was investigated in detail by electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry. Various experimental parameters influencing the electrochemical behavior of the modified electrode were optimized by varying the supporting electrolyte, scan rate and pH. The apparent electron transfer rate constant (K(s)) and charge transfer coefficient (α) of the modified electrode were found to be 1.358(± 0.02)cm/s and 0.65, respectively from cyclic voltammetry. The sensor exhibited an excellent electrocatalytic activity towards the oxidation of uric acid. The interference from ascorbic acid was easily overcome by coating the modified electrode with PEDOT layer. Under optimal condition, the determination range for uric acid is from 1.0 × 10(-6)M to 2.6 × 10(-3)M and the detection limit was 3.3 × 10(-7)M (3σ). The proposed method has been used for the determination of uric acid in human urine samples.

Hg(II) immobilized MWCNT graphite electrode for the anodic stripping voltammetric determination of lead and cadmium.

The preparation of Hg(II)-modified multi walled carbon nanotube (MWCNT) by reaction of oxidized MWCNT with aqueous HgCl(2) was carried out. The Hg(II)-modified multi walled carbon nanotube (Hg(II)/MWCNT) dispersed in Nafion solution was used to coat the polished graphite electrode surface. The Hg(II)/MWCNT modified graphite electrode was held at a cathodic potential (-1.0 V) to reduce the coordinated Hg(II) to Hg forming nanodroplets of Hg. The modified electrode was characterized by FESEM/EDAX which provided useful insights on the morphology of the electrode. The SEM images showed droplets of Hg in the size of around 260 nm uniformly distributed on the MWCNT. Differential pulse anodic stripping voltammetry (DPASV) and electrochemical impedance spectroscopy were used to study the Hg(II) binding with MWCNT. Differential pulse anodic stripping voltammetry of ppb levels of cadmium and lead using the modified electrode yielded well-defined peaks with low background current under a short deposition time. Detection limit of 0.94 and 1.8 ng L(-1) were obtained following a 3 min deposition for Pb(II) and Cd(II), respectively. Various experimental parameters were characterized and optimized. High reproducibility was observed from the RSD values for 20 repetitive measurements of Pb(II) and Cd(II) (1.7 and 1.9%, respectively). The determination of Pb(II) and Cd(II) in tap water and Pb(II) in human hair samples was carried out. The above method of fabrication of Hg(II)/MWCNT modified graphite electrode clearly suggests a safe route for preparing Hg immobilized electrode for stripping analysis.

Electrocatalytic oxidation of L-tryptophan using copper hexacyanoferrate film modified gold nanoparticle graphite-wax electrode.

A novel copper hexacyanoferrate (CuHCF) film modification on cysteamine (Cys)-gold nanoparticle (AuNp) graphite-wax (GW) composite electrode was achieved for the quantitative determination of L-Tryptophan (L-Trp) at a reduced overpotential of 400mV in comparison with the bare Cys-AuNp-GW composite electrode. This modified electrode exhibited a well resolved pair of redox peaks corresponding to the hexacyanoferrate (II/III) reactions of CuHCF film at a formal potential of 0.65 V at a scan rate of 20 mV s(-1). Electrochemical impedance spectroscopy (EIS) studies with the modified electrode showed a very low charge transfer resistance to the electron transfer kinetics of Fe(II)/Fe(III) reactions. A linear range of 8.5×10(-7) M to 1.2×10(-4) M with a detection limit of 1.85×10(-8) M was achieved for the determination of L-Trp with a sensitivity of 0.1198 µA/µM. The influence of ultrasonication on the stability of the CuHCF film modified electrode was investigated. In addition, the CuHCF film modified electrode displayed an excellent reproducibility towards the real time analysis of L-Trp in commercial milk samples.

Bienzyme based biosensing platform using functionalized carbon nanotubes.

This work presents a novel approach to design an amperometric transducer capable of detecting glucose and hydrogen peroxide. The biosensor is based on a bienzyme-channelling configuration, employing the enzymes glucose oxidase and horseradish peroxidase, which were immobilized with Toluidine blue (TB) functionalized multiwalled carbon nanotubes (MWNTs). TB was covalently immobilized with carboxylic acid groups of the carbon nanotubes via carbodiimide reaction. The MWNT/TB/GOD/HRP/Nf nanobiocomposite was prepared by mixing the GOx and HRP solution with TB functionalized CNTs followed by mixing homogeneously with Nafion. The MWNTiTB/GOD/HRP/Nf nanobiocomposite was characterized by scanning electron microscopy. The performance of the MWNT/TB/GOD/HRP/Nf nanobiocomposite modified electrode was examined by electrochemical impedance spectroscopy and cyclic voltammetry. Linear calibrations were achieved upto 1.4 x 10(-7)-1.6 x 10(-3) M for glucose and 6.8 x 10(-8)-1.7 x 10(-3) M for H2O2. A remarkable feature of this bienzyme electrode is the possibility to detect glucose and H2O2 at very low applied potentials where the noise level and interferences from other electro-active compounds are minimal.

Fabrication of an amperometric bienzyme biosensing system with neutral red functionalized carbon nanotubes.

Novel nanomaterials for biosensor applications represent a rapidly progressing field of nanotechnology. An exploration of functionalized multi-walled carbon nanotubes (MWNTs) as a platform for amperometric determination of glucose employing the enzymes glucose oxidase (GOx) and horseradish peroxidase (HRP), which were immobilized with neutral red (NR) functionalized MWNTs is presented. The fabrication and analytical characterization of the glucose biosensor for the measurement of low concentration of glucose is described. Owing to the electrocatalytic effect of carbon nanotubes, the measurement of faradic responses resulting from enzymatic reactions has been realized at low potential with acceptable sensitivity. Experimental parameters affecting the sensitivity of biosensors, e.g., applied potential, pH, temperature etc., were optimized and potential interferences were examined. The response time for the glucose biosensor was very fast (within 2 seconds) and it showed good storage stability at 4 degrees C over a 5-month period. The proposed biosensor exhibited short response time, high sensitivity, easy operation, and simple sensor assembly. The biosensor was successfully applied to the determination of glucose in human blood samples and acceptable results were obtained.

Mechanically immobilized nickel aquapentacyanoferrate modified electrode as an amperometric sensor for the determination of BHA.

Nickel aquapentacyanoferrate (NAPCF), a novel transition metal complex has been prepared and its ability to act as an electrocatalyst for BHA oxidation has been demonstrated. The cyclic voltammetric behaviour of the NAPCF modified electrode prepared by mechanical immobilization on the graphite electrode was well defined. A pair of redox peaks corresponding to the electrochemical behaviour of the NAPCF was observed at 0.35 V and 0.31 V, corresponding to the anodic and cathodic peaks respectively, with a formal potential of 0.33 V. The NAPCF modified electrode favoured electrocatalytic oxidation of BHA to occur at a greatly minimized overpotential of 0.48 V. Experiments were performed to characterize the electrode as an amperometric sensor for the determination of BHA. The anodic peak current was linearly related to BHA concentration in the range of 6.24x10(-7) M to 2.19x10(-4) M with a detection limit of 2.49x10(-7) M and a correlation coefficient of 0.9979. Amperometry in stirred solution exhibited quick and sensitive response to BHA, showing the possible application of the modified electrode in flow system analysis. The modified electrode retained its initial response for more than 2 months when stored in supporting electrolyte, owing to the chemical and mechanical stability of the NAPCF mediator. This modified electrode was also quite effective in the determination of BHA in commercial samples.

Fabrication of bienzyme nanobiocomposite electrode using functionalized carbon nanotubes for biosensing applications.

Mediated biosensors consisting of an oxidase and peroxidase (POx) have attracted increasing attention because of their wider applicability. This work presents a novel approach to fabricate nanobiocomposite bienzymatic biosensor based on functionalized multiwalled carbon nanotubes (MWNTs) with the aim of evaluating their ability as sensing elements in amperometric transducers. Electrochemical behavior of the bienzymatic nanobiocomposite biosensor is investigated by Faradaic impedance spectroscopy and cyclic voltammetry. The results indicate that glucose oxidase (GOD) and horseradish peroxidase (HRP) are strongly adsorbed on the surface of the thionin (TH) functionalized MWNTs and demonstrate a facile electron transfer between immobilized GOD/HRP and the electrode via the functionalized MWNTs in a Nafion film. The functionalized carbon nanotubes act as molecular wires to allow efficient electron transfer between the underlying electrode and the redox centres of enzymes through TH. Linear ranges for these electrodes are from 10nM to 10mM for glucose and 17nM to 56mM for hydrogen peroxide with the detection limit of 3 and 6nM, respectively. A remarkable feature of the bienzyme electrode is the possibility to determine glucose and hydrogen peroxide at a very low applied potential where the noise level and interferences from other electroactive compounds are minimal. Performance of the biosensor is evaluated with respect to response time, detection limit, selectivity, temperature and pH as well as operating and storage stability.

(1'S)-4-(3,4-Dichlorophenyl)-1'-(3,5-dimethoxyphenyl)-1,2,3,4-tetrahydronaphthalene-2-spiro-2'-pyrrolizidine-3'-spiro-3''-indoline-1,2''-dione.

In the title compound C(37)H(32)Cl(2)N(2)O(4), the unsubstituted pyrrolidine ring shows a twist conformation whereas the substituted pyrrolidine ring shows an envelope conformation. The dimeth-oxy benzene ring is perpendicular to the tetra-lone ring, making a dihedral angle of 89.94 (5)°. Mol-ecules are linked into centrosymmetric dimers by N-H⋯O hydrogen bonds and the crystal structure is stabilized by C-H⋯π inter-actions and C-H⋯O hydrogen bonds. One meth-oxy group is disordered over two positions with the site occupancy factors of 0.84 (2) and 0.16 (2).

9-Ethyl-2,3-dihydro-9H-carbazol-4(1H)-one.

In the title compound, C(28)H(30)N(2)O(2), the cyclo-hexene ring system adopts a sofa conformation. The crystal structure is stabilized by C-H⋯O inter-actions between methyl H atoms of the ethyl substituents and the O atoms of carbonyl groups of adjacent mol-ecules, and by an inter-molecular carbon-yl-carbonyl inter-actions [3.207 (2) Å].

(4S)-4-(3,4-Dichloro-phen-yl)-1'-methyl-4'-phenyl-3,4-dihydronaphthalene-2-spiro-3'-pyrrolidine-2'-spiro-1''-acenaphthyl-ene-1,2''(2H,1''H)-dione.

In the title compound, C(37)H(27)Cl(2)NO(2), the 3,4-dichloro-phenyl ring makes a dihedral angle of 46.66 (6)° with the phenyl ring. The mol-ecular structure is stabilized by weak intra-molecular C-H⋯O inter-actions and the crystal structure is stabilized by weak inter-molecular C-H⋯O inter-actions. The C-C-C-C-C five-membered ring is planar, while the C-C-C-C-N five-membered ring adopts a half-chair conformation.

Ethyl 4'-ethenyl-2'-oxo-4-phenyl-2-(3,4,5-trimethoxy-phen-yl)spiro-[pyrrolidine-3,3'-indoline]-5-carboxyl-ate monohydrate.

In the title compound, C(31)H(32)N(2)O(6)·H(2)O, the pyrrolidine ring adopts an envelope conformation. The ethyl C atoms of the ethoxy-cabonyl group are disordered over two positions with occupancies of ca 0.80 and 0.20. Intra-molecular N-H⋯O hydrogen bonds form S(5) and S(6) ring motifs. Mol-ecules are linked into a three-dimensional framework by O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds, and by C-H⋯π inter-actions.

Ethyl 3-hydr-oxy-13-methyl-4'-phenyl-2'-(3,4,5-trimethoxy-phen-yl)-6,7,8,9,11,12,13,14,15,16-deca-hydro-spiro-[cyclo-penta-[a]phenanthrene-16,3'-pyrrolidine]-5'-carboxyl-ate.

In the title compound, C(39)H(45)NO(7),the pyrrolidine ring is connected to an estrone group, a trimeth-oxy benzene and a phenyl ring. The pyrrolidine ring exhibits a twist conformation and the other five-membered ring an envelope conformation. Mol-ecules are linked by N-H⋯O hydrogen bonds, C-H⋯π inter-actions and C-H⋯O hydrogen bonds.

Ethyl 2-[4-(benzyloxy)anilino]-4-oxo-4,5-dihydro-furan-3-carboxyl-ate.

In the title compound, C(20)H(19)NO(5), the dihydro-furan ring is almost planar [maximum deviation of 0.021 (2)°] and makes dihedral angles of 28.1 (7) and 54.5 (5)° with the benzyl and phenyl-amino rings, respectively. The mol-ecular packing is stabilized by intra-molecular N-H⋯O hydrogen bonds and inter-molecular C-H⋯O inter-actions.

(E)-3-Hydr-oxy-13-methyl-16-[4-(methyl-sulfan-yl)benzyl-idene]-7,8,9,11,12,13,15,16-octa-hydro-6H-cyclo-penta-[a]phen-an----thren-17(14H)-one.

In the title compound, C(26)H(28)O(2)S, the dihedral angles between the mean plane of the five membered ring and the 4-(methyl-sulfan-yl)benzyl-idine ring in the two crystallographically independent mol-ecules are 34.05 (10) and 40.53 (15)°. The packing is stabilized by inter-molecular O-H⋯O and C-H⋯O inter-actions.