C. Sekar

Synthesis of polyethylene glycol (PEG) assisted tungsten oxide (WO3) nanoparticles for l-dopa bio-sensing applications

Nanocrystalline tungsten oxides (WO(3-δ)) are currently receiving a lot of attention because of their interesting electrical, magnetic, optical and mechanical properties. In this report, we present the synthesis of PEG assisted tungsten oxide (WO(3)) nanoparticles by simple household microwave irradiation (2.45 GHz) method. The samples were characterized using powder X-ray diffraction (XRD), thermal analysis (TG/DTA), transmission electron microscopy (TEM), UV-visible diffusion reflectance spectroscopy (UV-VIS-DRS), cyclic voltammetry and electrochemical impedance spectroscopy. Powder XRD results revealed that both the samples prepared with and without surfactant crystallize in the orthorhombic structure corresponding to WO(3) · H(2)O phase. Subsequent annealing under identical conditions (600°C/air/6h) led to significantly different products i.e. monoclinic W(17)O(47) from surfactant free sample and orthorhombic WO(3) from PEG assisted sample. Blue emission was observed through UV-VIS-DRS with blue shift and the band gap energy was estimated as 2.7 and 3.28 eV for PEG assisted as prepared (WO(3) · H(2)O) and annealed samples (WO(3)) respectively. Electrochemical measurements have been performed on all the samples deposited on the surface of glassy carbon (GC) electrode which showed high sensitivity and good selectivity for PEG assisted sample (WO(3) · H(2)O) for the direct detection of L-dopa.

Fabrication of hydrogen peroxide biosensor based on Ni doped SnO2 nanoparticles

Ni doped SnO(2) nanoparticles (0-5 wt%) have been prepared by a simple microwave irradiation (2.45 GHz) method. Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies confirmed the formation of rutile structure with space group (P(42)/mnm) and nanocrystalline nature of the products with spherical morphology. Direct electrochemistry of horseradish peroxidase (HRP)/nano-SnO(2) composite has been studied. The immobilized enzyme retained its bioactivity, exhibited a surface confined, reversible one-proton and one-electron transfer reaction, and had good stability, activity and a fast heterogeneous electron transfer rate. A significant enzyme loading (3.374×10(-10) mol cm(-2)) has been obtained on nano-Ni doped SnO(2) as compared to the bare glassy carbon (GC) and nano-SnO(2) modified surfaces. This HRP/nano-Ni-SnO(2) film has been used for sensitive detection of H(2)O(2) by differential pulse voltammetry (DPV), which exhibited a wider linearity range from 1.0×10(-7) to 3.0×10(-4)M (R=0.9897) with a detection limit of 43 nM. The apparent Michaelis-Menten constant (K(M)(app)) of HRP on the nano-Ni-SnO(2) was estimated as 0.221 mM. This excellent performance of the fabricated biosensor is attributed to large surface-to-volume ratio and Ni doping into SnO(2) which facilitate the direct electron transfer between the redox enzyme and the surface of electrode.

Development of amperometric l-tyrosine sensor based on Fe-doped hydroxyapatite nanoparticles

A novel biosensor based on Fe-doped hydroxyapatite (Fe-HA) nanoparticles and tyrosinase has been developed for the detection of L-tyrosine. Nanostructured Fe-HA was synthesized by a simple microwave irradiation method, and its phase formation, morphology and magnetic property were examined by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). Electrochemical performance of the nano Fe-HA/tyrosinase modified glassy carbon electrode (GCE) for detection of L-tyrosine was investigated by cyclic voltammetry (CV) and amperometric methods. The fabricated biosensor exhibited a linear response to L-tyrosine over a wide concentration range of 1.0×10(-7) to 1.0×10(-5) M with a detection limit of 245 nM at pH 7.0. In addition, the fabricated sensor showed an excellent selectivity, good reproducibility, long-term stability and anti-interference towards the determination of L-tyrosine.

An ultrasensitive electrochemical sensor for simultaneous determination of xanthine, hypoxanthine and uric acid based on Co doped CeO2 nanoparticles

A novel electrochemical sensor has been fabricated using Co doped CeO2 nanoparticles for selective and simultaneous determination of xanthine (XA), hypoxanthine (HXA) and uric acid (UA) in a phosphate buffer solution (PBS, pH5.0) for the first time. The Co-CeO2 NPs have been prepared by microwave irradiation method and characterized by Powder XRD, Raman spectroscopy, HRTEM and VSM measurements. The electrochemical behaviours of XA, HXA and UA at the Co-CeO2 NPs modified glassy carbon electrode (GCE) were studied by cyclic voltammetry and square wave voltammetry methods. The modified electrode exhibited remarkably well-separated anodic peaks corresponding to the oxidation of XA, HXA and UA over the concentration range of 0.1-1000, 1-600 and 1-2200μM with detection limits of 0.096, 0.36, and 0.12μM (S/N=3), respectively. For simultaneous detection by synchronous change of the concentrations of XA, HXA and UA, the linear responses were in the range of 1-400μM each with the detection limits of 0.47, 0.26, and 0.43μM (S/N=3), respectively. The fabricated sensor was further applied to the detection of XA, HXA and UA in human urine samples with good selectivity and high reproducibility.

A novel disposable electrochemical sensor for determination of carbamazepine based on Fe doped SnO2 nanoparticles modified screen-printed carbon electrode.

An effective strategy to fabricate a novel disposable screen printing carbon electrode modified by iron doped tin dioxide nanoparticles for carbamazepine (CBZ) detection has been developed. Fe-SnO2 (Fe=0 to 5 wt.%) NPs were synthesized by a simple microwave irradiation method and assessed for their structural and morphological changes due to Fe doping into SnO2 matrix by X-ray diffraction and scanning and transmission electron microscopy. The electrochemical behaviour of carbamazepine at the Fe-SnO2 modified screen printed carbon electrode (SPCE) was investigated by cyclic voltammetry and square wave voltammetry. Electron transfer coefficient α (0.63) and electron transfer rate constant ks (0.69 s(-1)) values of the 5 wt.% Fe-SnO2 modified SPCE indicate that the diffusion controlled process takes place on the electrode surface. The fabricated sensor displayed a good electrooxidation response towards the detection of CBZ at a lower oxidation potential of 0.8 V in phosphate buffer solution at pH7.0. Under the optimal conditions, the sensor showed fast and sensitive current response to CBZ over a wide linear range of 0.5-100 μM with a low detection limit of 92 nM. Furthermore, the practical application of the modified electrode has been investigated by the determination of CBZ in pharmaceutical products using standard addition method.

A new strategy for simultaneous determination of 4-aminophenol, uric acid and nitrite based on a graphene/hydroxyapatite composite modified glassy carbon electrode

A novel electrochemical sensor has been fabricated based on a graphene/hydroxyapatite nanocomposite modified glassy carbon electrode (GCE) for the selective and simultaneous detection of 4-aminophenol (4-AP), uric acid (UA) and nitrite ions (NO2−) in a phosphate buffer solution (PBS, pH 7.0) for the first time. The modified electrode exhibited improved electrocatalytic activity towards the oxidation of 4-AP, UA and NO2− in the form of three strong peaks in both the cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques. Under optimum conditions, the ternary system comprising 4-AP, UA and NO2− exhibited linear calibration plots over a wide range of 0.1–425 μM, 1–1000 μM and 3–950 μM with detection limits of 0.29 μM, 0.03 μM and 0.025 μM for 4-AP, UA and NO2− respectively. The developed sensor displayed high sensitivity and low detection limits coupled with good stability and reproducibility which were attributed to the synergistic effect of graphene and HAP in the nanocomposite. In addition, the fabricated sensor was applied to the determination of UA, 4-AP and NO2− in urine and tap water samples with satisfactory results.

Highly sensitive electrochemical sensor for simultaneous determination of dihydroxybenzene isomers based on Co doped SnO2 nanoparticles

We have fabricated an electrochemical sensor for the simultaneous determination of two dihydroxybenzene isomers of phenolic compounds, hydroquinone (HQ) and catechol (CC) using Co doped SnO2 nanoparticles (Co-SnO2 NPs) for the first time. Cobalt doped SnO2 NPs were synthesized by a microwave irradiation method and characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Square wave voltammetry (SWV) studies yielded two well resolved strong peaks at the 3 wt% Co-SnO2 NP modified glassy carbon electrode (GCE) corresponding to the reduction of HQ and CC at −0.091 V and +0.041 V respectively. Under the optimum conditions, an adequate voltammetric peak to peak separation of 132 mV was found between the two isomeric species owing to the excellent catalytic activity of SnO2 NPs due to cobalt doping. For individual detection, the linear responses of HQ and CC were in the concentration ranges of 0.5–600 and 0.1–600 μM with the detection limits of 0.45 and 0.094 μM respectively. For simultaneous detection by synchronous change of the concentrations of HQ and CC, the linear response ranges were in the order of 1–150 μM each with the detection limits of 0.137 and 0.116 μM for HQ and CC respectively. With good selectivity and sensitivity, the practical application of the modified electrode has been investigated by the simultaneous determination of HQ and CC in tap water samples using the standard addition method with satisfactory results.

Influence of strontium on the synthesis and surface properties of biphasic calcium phosphate (BCP) bioceramics

Purpose Biphasic calcium phosphate (BCP) ceramics are suitable for synthetic bone applications. The strontium substituted calcium phosphate ceramics have potential for use in orthopedic surgeries. Aim of the present work is to introduce strontium into BCP (composed of hydroxyapatite and tricalcium phosphate) ceramics and to study their bioactivity and mechanical properties. Methods BCP ceramics have been synthesized at room temperature under the physiological pH of 7.4 by gel method in the presence of strontium (5, 10 M %). Results The appropriate choice of anhydrous CaCl2 as precursor solution has promoted the formation of BCP instead of pure HA for CaCl2.2H2O. Powder X-ray diffraction analysis confirmed the formation of BCP with different HA and β –TCP ratios depending upon the Sr content. The presence of Sr has reduced the nucleation and growth rate of BCP when compared to pure system. The SEM micrographs showed that the microstructural morphology of BCP changes from fibrous to platelet. Conclusion Nanoindentation studies indicate a significant decrease in the hardness and elastic modulus values of BCP ceramics due to Sr doping. In vitro bioactivity study has revealed the formation of apatite layer on the Sr doped BCP samples and the doping enhanced its bioactivity.

Changes in Caenorhabditis elegans immunity and Staphylococcal virulence factors during their interactions

The nematode Caenorhabditis elegans is used as a model system for the study of host-pathogen interactions. Lipoteichoic acid (LTA) is one of the major virulent and immunostimulatory components found in gram positive bacteria. The current study used LTA isolated from Staphylococcus aureus and pathogenic and non-pathogenic Staphylococcus epidermidis. The overall physiological assays revealed that LTA exposed C. elegans show a significant reduction in the life span, production of eggs and progenies. To understand the involvement of innate immune specific players at the mRNA level, the regulation of few candidate antimicrobial genes was studied during Staphylococcal LTA exposures. qPCR analysis indicated an upregulation of antimicrobial peptides during LTA exposures. To understand the involvement of LTA and other virulent genes during infection, the regulation of LTA synthase and a few virulence genes was monitored during host exposure. The qPCR analyses indicated the upregulation of ltaS and other virulence genes (atoxin, sak, ssaA and fbe) during infection. Ability of the pathogens to modify their internal machinery during host presence was monitored by Fourier transform infrared spectroscopy, electrochemical impedance spectroscopy and cyclic voltametric analyses. The FTIR results indicated distinct alterations of peaks from Staphylococcal LTA composition between control and the host exposed. Further, EIS and CV data displayed clear differences between the host exposed Staphylococcal samples compared to their respective unexposed controls. The pathogenic and non-pathogenic strains showed different types of regulations and interactions during host exposures. The observed modifications clearly suggest that the Gram positive pathogen changes its LTA production and possibly the structure to cause a severe pathogenic effect on an interacting host.

Vitamin Sensors Based on Nanostructured SnO2 for Food and Pharmaceutical Applications

Abstract Vitamins are biologically active organic compounds with a diverse chemical nature and are essential for normal growth and functioning of the body. The deficiency or overdosage of the vitamins causes several diseases such as cardiovascular, scurvy, cancer, depression, anemia, etc. Therefore, it is essential to develop a simple portable diagnostic tool for the quick and precise determination of essential vitamins in human body, food, and pharmaceuticals. In the present chapter, we report the design and development of nanostructured SnO2-based electrochemical sensors for selective determination of the three most important water-soluble vitamins: riboflavin (RF), folic acid (FA), and ascorbic acid (AA). Modification of SnO2 through chemical doping (Cr, Cu, Mn) significantly improved its sensing performance. The fabricated sensors show excellent antiinterference abilities against several other relevant electroactive species and metal ions and proved to be useful to estimate RF, FA, and AA content in milk, fruits, energy drinks, and pharmaceutical products.