S. Sriman Narayanan

Synthesis and in vivo antidiabetic activity of novel dispiropyrrolidines through [3+2] cycloaddition reactions with thiazolidinedione and rhodanine derivatives.

The synthesis of a series of novel dispiropyrrolidines has been accomplished by 1,3-dipolar cycloaddition reaction with 5-arylidene-1,3-thiazolidine-2,4-dione and 5-arylidene-4-thioxo-1,3-thiazolidine-2-one derivatives as dipolarophiles. The structure and stereochemistry of the cycloadduct have been established by single crystal X-ray structure and spectroscopic techniques. Molecular docking studies were performed on 1FM9 protein. The synthesized compounds were screened for their antidiabetic activity on male Wistar rats.

A novel nanobiocomposite based glucose biosensor using neutral red functionalized carbon nanotubes

The performance of a new glucose biosensor based on the combination of biocatalytic activity of glucose oxidase (GOx) with the electrocatalytic properties of CNTs and neutral red (NR) for the determination of glucose is described. This sensor is comprised of a multiwalled carbon nanotubes (MWNTs) conduit functionalized with NR and Nafion (Nf) as a binder and glucose oxidase as a biocatalyst. Neutral red was covalently immobilized on carboxylic acid groups of the CNTs via carbodiimide reaction. The functionalized MWNTs were characterized by microscopic, spectroscopic and thermal methods. The MWNT-NR-GOx-Nf nanobiocomposite was prepared by mixing the GOx solution with NR functionalized CNTs followed by mixing homogeneously with Nafion. The performance of the MWNT-NR-GOx-Nf nanobiocomposite modified electrode was examined by electrochemical impedance spectroscopy and cyclic voltammetry. The catalytic reduction of hydrogen peroxide liberated from the enzymatic reaction of glucose oxidase upon glucose with NR functionalized CNTs leads to the selective detection of glucose. The excellent electrocatalytic activity and the influence of nanobiocomposite film result in good characteristics such as low potential detection of glucose with a large determination range from 1 x 10(-8) to 1 x 10(-3)M with a detection limit of 3 x 10(-9)M glucose, a short response time (with 4s), good stability and anti-interferent ability. The improved electrocatalytic activity and stability made the MWNT-NR-GOx-Nf nanobiocomposite biosensor system a potential platform to immobilize different enzymes for other bioelectrochemical applications.

Amperometric determination of paracetomol by a surface modified cobalt hexacyanoferrate graphite wax composite electrode.

A stable electro active thin film of cobalt hexacyanoferrate (CoHCF) was deposited on the surface of an amine adsorbed graphite wax composite electrode using a simple method. Cyclic voltammetric experiments showed two pairs of well defined peaks for this CoHCF modified electrode which exhibited excellent electrocatalytic property for the oxidation of paracetomol at a reduced overpotential of 100 mV and over a concentration range of 3.33x10(-6) to 1.0x10(-3)M with a slope of 0.208 microA/microM with good sensitivity. The influence of the supporting electrolyte on peak current and peak potential were also obtained in addition with effects of common interference (e.g., ascorbic acid) on the response of the modified electrode. Various parameters that influence the electrochemical behavior of the modified electrode were optimized by varying scan rates and pH. Electrochemical impedance spectroscopy studies suggested that the electrode reaction of the CoHCF film is mainly controlled by transport of counter ion. The immobilized CoHCF maintained its redox activity showing a surface controlled electrode reaction with the electron transfer rate constant (K(s)) of 0.94 s(-1) and charge transfer coefficient of 0.42. Hydrodynamic and chronoamperometric studies were done to explore the utility of the modified electrode in dynamic systems. The results of the differential pulse voltammetry (DPV) using the modified electrode was applied for the determination of paracetomol in commercially available tablets. The results obtained reveal that the electrode under study could be used as an effective sensor for online monitoring of paracetomol.

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.

Chemically modified sensor for amperometric determination of sulphur dioxide

Abstract Copper hexacyanoferrate (CuHCF) modified graphite electrode prepared by mechanical immobilisation method has been used for the amperometric determination of sulphite, which can be extended for the determination of SO 2 in air after absorbing the pollutant in sodium hydroxide solution. This method is based upon the electrocatalytic oxidation of sulphite by the modified electrode. The pH of the medium for oxidation should be in the range of 3.5–8.0. The range of determination of SO 2 is from 5.1 to 30.7 ppm. The presence of H 2 S with SO 2 will interfere in the determination. This can be eliminated by precipitating H 2 S as CuS.

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.

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.

Biomimetic composites and stem cells interaction for bone and cartilage tissue regeneration

Development of bone and cartilage are emerging as prominent techniques in the field of tissue engineering because of the abundance of problems caused by disease, injury and trauma. Bone is the main supporting system of the body, a biocomposite of elements and tissues which is responsible for the excellent tensile and loading strength. Cartilage is an avascular, aneural and alymphatic tissue and does not have regenerative capabilities, so a great amount of assistance is required from outside to repair the defect site. Autografts and allografts are useful in the case of bone defects, but still they require a second surgery from the donor, and transmission of diseases are also possible. The objective of this review is to discuss the approaches that have been taken in bone and cartilage tissue engineering with an emphasis on the cell sources such as embryonic stem cells, adipose derived stem cells, mesenchymal stem cells and progenitor stem cells. A potential scaffold is also important for the mechanical and cellular functions for bone and cartilage regeneration. Awareness will be spanned over different types of scaffolds such as biomaterial scaffolds, nanofibrous scaffolds and hydrogels. The ultimate aim is to focus on the basic aspects and the importance of various signaling and growth factors for tissue engineering, used for tissues that have a poor self healing capacity, such as cartilage, or when defects are too big for the bodys capacity to heal itself, such as large bone defects.

Covalent modification of multiwalled carbon nanotubes with neutral red for the fabrication of an amperometric hydrogen peroxide sensor

The nanoscale dimensions, graphitic surface chemistry and electronic properties of multiwalled carbon nanotubes (MWNTs) make them an ideal candidate for chemical and biochemical sensing. In this paper we explore a covalent chemical strategy for functionalization of MWNTs with neutral red through carbodiimide coupling between the primary amine of neutral red and carboxyl groups of the carbon nanotubes. The construction of an amperometric sensor was achieved by abrasive immobilization of the functionalized MWNTs on a paraffin impregnated graphite electrode followed by a coating of a thin film of nafion. The neutral red functionalized MWNTs were characterized by spectroscopic and electroanalytical methods. From the voltammetric studies, MWNTs were found to exhibit a higher accessible surface area in electrochemical reactions. The modified electrode exhibited stable electrocatalytic activity toward hydrogen peroxide reduction in a wide potential range. A significant decrease in overvoltage for the reduction of hydrogen peroxide, as well as a dramatic increase in the peak currents in comparison with a bare graphite electrode were observed. Such an ability of neutral red functionalized carbon nanotubes to promote the hydrogen peroxide electron transfer reaction with a short response time (<4 s) and long-term stability, a low detection limit, an extended linear concentration range and a high sensitivity suggest great promise for dehydrogenase and oxidase based amperometric biosensors.

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.