Marshal Dhayal

Chitosan/polyaniline hybrid conducting biopolymer base impedimetric immunosensor to detect Ochratoxin-A

Chitosan (CS)-polyaniline (PANI) hybrid conducting biopolymer film was obtained on indium-tin-oxide (ITO) electrode using electrochemical polymerization process. Fourier transform infrared (FT-IR) spectra of PANI-CS had showed covalent and hydrogen binding between PANI and CS molecules. Electrochemical impedance spectroscopy (EIS) measurements had showed low charge transfer resistance (R(CT)) of PANI-CS and PANI. Successive rabbit antibody (IgGs) immobilization on PANI-CS, CS and PANI matrixes surface were confirmed with FT-IR and EIS measurements. Ochratoxin-A (OTA) interaction with IgGs had increased R(CT) values and showed linear response up to 10 ng/mL OTA concentration in electrolyte. Relative change in R(CT) was higher in PANI-CS due to higher proportion of carboxylic and hydroxyl functionalities at PANI-CS matrix surfaces. The absolute sensitivity of PANI, CS, and PANI-CS were 16+/-6, 22+/-9 and 53+/-8 Omega mL/ng, respectively derived from slope of linear response up to 10 ng/mL with 1 ng/mL minimum detection limit.

XPS and SPR Analysis of Glycoarray Surface Density

Despite the fact that the carbohydrate microarray has seen increasing use within the field of glycobiology, the surface chemistry of the glycoarray remains largely unexplored. Motivated by the need to develop surface analytical techniques to characterize carbohydrate-modified surfaces, we developed a quantitative X-ray photoelectron spectroscopy (XPS) and surface plasmon resonance imaging (SPR imaging) method to study glycan biosensors. We performed a comparative analysis on the relative coverage of mixed self-assembled monolayers (SAMs) on gold, consisting of a thiol-functionalized trimannoside (Manalpha1,2Manalpha1,2Manalpha-OEG-SH) at varying concentrations (0-100%) mixed separately with two thiol-containing polyethylene glycol oligomers. XPS C1s core level analysis was used to identify the O-C-O functionality unique to the carbohydrate acetal moiety and to separate and quantify the relative coverage of sugar in carbohydrate/OEG mixed SAMs. XPS spectra of the mixed SAMs demonstrated a proportional increase in the acetal signature of the glycan with increasing sugar concentration. To relate surface glycan density with biological function, we carried out a kinetic analysis of Concanavalin A (ConA) binding to SAMs of varying densities of carbohydrate using SPR imaging. We observed protein binding that was highly dependent on both glycan density and the nature of the OEG-thiol used in the mixed self-assembly. These results illustrate the utility of surface analytical techniques such as XPS and SPR in carbohydrate biosensor characterization and optimization.

Using Nano-Arrayed Structures in Sol-Gel Derived Mn2+ Doped Tio2 for High Sensitivity Urea Biosensor

Ordered and self-organized nano-array structures have been developed by Mn 2+ doping in TiO 2 thin fi lms deposition on conducting substrates by dip coating technique. Mn doped TiO 2 thin fi lms exhibits better bioactivity for enzyme immobilization and cyclic voltammetry measurement has been used for qualitative characterization of electrochemical induction of oxidation-reduction process in TiO 2 and Mn doped TiO 2 fi lms. Due to presence of Mn 2+ ions at fi lm surface, current voltage characteristic of Mn doped TiO 2 matrix was enhanced by a factor of ten and it had also reduced the crystallite size and promoted transformation of anatase to rutile phase of TiO 2 . Urea concentration in the electrolyte was determined by observing chronoamperometry response on urease immobilized working electrodes. The urea detection sensitivity of the Mn doped TiO 2 thin fi lms base platform was 2.3 μ A mM − 1 cm − 2 which is about 15 times higher from only TiO 2 base platforms. Such kind of enzyme–TiO 2 /Mn nano-array electrode could contribute a potential prospect in low cost biomedical diagnosis.

Two-step process for programmable removal of oxygen functionalities of graphene oxide: functional, structural and electrical characteristics

Here we report a two-step programmable reduction of graphene oxide (GO) which was synthesized by oxidation of graphite. X-Ray photoelectron spectroscopic (XPS) analysis confirmed the synthesis of exfoliated graphene oxide (GO) by introduction of oxygen as carboxylic (–COOH), epoxy (C–O–C) and hydroxyl (–OH) groups. The first step of GO reduction was achieved separately by (i) hydrazine (rGO11) and (ii) sodium borohydride (rGO21). Soda lime was used in the second-stage reduction of (a) hydrazine reduced GO (rGO12) and (b) sodium borohydride reduced GO (rGO22) to remove most of the remaining carboxylic functionalities from the rGO11 and rGO21 surface. XPS spectra of rGO21 showed a decrease (38 to 30%) in the oxygen whereas the further reduction of rGO21 with soda lime can further reduce the oxygen content. Quantitative analysis of C(O)OX in GO shows about 43% of carbon atoms (C 1s signal) as carboxylic functionalities whereas the reduction of the GO with sodium borohydride reduced this signal to about 10%. The use of soda lime for both rGO11 and rGO21 further reduced the amount of carboxylic functionalities. An increase in the proportion of carbon atoms as sp2 and decrease in the oxygen functionalities were controlled in the two-step reduction. A good correlation in the conductivity of reduced GO with the percentage proportion of sp2 carbon was observed.

Mycotoxin detection on antibody-immobilized conducting polymer-supported electrochemically polymerized acacia gum.

Electrochemical polymerization of acacia gum (AG) was initiated by electroactive polyaniline (PANI) monomers by radical cation formation and their coupling reactions with AG molecules. R(CT) values obtained from electrochemical impedance spectroscopy analysis at various AG concentrations with PANI were drastically decreased, confirming formation of conducting AG complexes with PANI. Quantitative analysis of ochratoxin-A (OTA) detection in electrolyte was carried out on rabbit antibody-immobilized PANI and PANI-AG matrices. The observed sensitivities of 50, 150, and 250 mg AG-added PANI matrix-based platforms were 3.3 ± 0.5, 10.0 ± 0.5, and 12.7 ± 0.5 μA/ng/ml, respectively. The sensitivity of only PANI electrodes was 2.6 ± 0.3 μA/ng/ml, which was relatively lower than AG-added PANI. This increase was due to the presence of glycan functional groups in AG molecules that supported the retention of activity of antibodies. In addition, enhanced electron transportation at AG-PANI film surface was observed due to formation of an electroactive polymer film of two different electroactive functions to contribute toward enhancement in the detection sensitivity.

Strategies to prepare TiO2 thin films, doped with transition metal ions, that exhibit specific physicochemical properties to support osteoblast cell adhesion and proliferation.

Metal ion doped titanium oxide (TiO2) thin films, as bioactive coatings on metal or other implantable materials, can be used as surfaces for studying the cell biological properties of osteogenic and other cell types. Bulk crystallite phase distribution and surface carbon-oxygen constitution of thin films, play an important role in determining the biological responses of cells that come in their contact. Here we present a strategy to control the polarity of atomic interactions between the dopant metal and TiO2 molecules and obtain surfaces with smaller crystallite phases and optimal surface carbon-oxygen composition to support the maximum proliferation and adhesion of osteoblast cells. Our results suggest that surfaces, in which atomic interactions between the dopant metals and TiO2 were less polar, could support better adhesion, spreading and proliferation of cells.

Using an afterglow plasma to modify polystyrene surfaces in pulsed radio frequency (RF) argon discharges

Abstract A systematic study has been made to characterise a pulsed RF discharge used for the plasma treatment of polymers. Using a time-resolved Langmuir probe and a time-resolved retarding field energy analyser (RFA) the electron temperature and density, plasma potential, ion energy distribution function (IEDF) and electron energy distribution function (EEDF) has been measured. The source was pulsed for a range of frequencies from 100 Hz to 1 KHz at various duty cycles from 20 to 80%. A base pressure less than 10 −5 Torr was achieved to decrease the level of impurities in the chamber. The electron temperature ( T e ) decreases from 5 eV to less than 0.5 eV in afterglow. The cooling rate of T e depends on the pressure, power and duty cycle. By pulsing a biased grid synchronously with the pulsed RF, ions are selected from different time of the plasma and allowed to impinge on a polymer surface. Modified oxygen to carbon (O/C) ratio in the upper layer of polystyrene has been measured by X-ray photon emission spectroscopy (XPS) for different energy and flux of plasma ions. These results show that the treatment is either insensitive to ion energy or dominated by the UV in the discharge.

Ultra-small gold nanoparticles synthesized in aqueous solution and their application in fluorometric collagen estimation using bi-ligand functionalization

An effective, rapid and facile hydrosol approach was developed to synthesize monodisperse ultra-small gold nanoparticles (∼2 nm) using lithium borohydride (LiBH4) as a reducing agent. These lithium borohydride gold nanoparticles (LBH-AuNPs) are highly stable at pHs ranging from 3 to 10.6. We have subjected these LBH-AuNPs to bi-ligand co-functionalization with FITC (fluorescent isothiocyanate) and fluorescent lysine molecules. It was observed that these particles exhibit enhanced tolerance of FITC and lysine bi-ligand functionalization. The fluorescence resonance energy transfers (FRET) from the FITC and lysine to the AuNPs, and the replacement of these fluorophores by collagen as ligands have been exploited for the sensitive fluorometric detection of rat tail collagen. Linearity in the reappearance of FITC and lysine fluorescence was observed at 2 to 10 μg ml−1 of extracted rat collagen, which demonstrated the successful use of these bi-ligand surface functionalised gold nanoparticles as a probe for the sensitive fluorometric estimation of rat tail collagen.

Growth, differentiation, and migration of osteoblasts on transparent Ni doped TiO2 thin films deposited on borosilicate glass†

A simple and cost effective dip coating method was used to deposit thin films of amorphous (AM) or anatase (AN) titanium dioxide (TiO(2)) on borosilicate glass substrates, either with or without prior doping of TiO(2) with nickel (Ni) cations by a specially designed sol gel technique. The objective of the study was to compare the physicochemical and biological properties of these films and assess their use in orthopedic implants or for in vitro cell biological studies. Analytical techniques such as XRD and XPS, in combination with ATR-FTIR and SEM revealed that only AN films, prepared by controlled heating up to 450°C, irrespective of prior doping with Ni, contained significant crystalline structures of variable morphologies. This observation could be linked to the carbon and oxygen contents and the availability of functional groups in the films. Cell biological studies revealed that Ni doping of TiO(2) in both AM and AN films improved the adhesion, spreading, proliferation, differentiation, and migration of MC3T3 cells. Our studies provide a new approach to prepare optically transparent metal surfaces, with tunable physicochemical properties, which could be suitable for eliciting optimal osteoinductive cell responses and permit the detailed in vitro cell biological studies of osteoblasts.

Synthesis of glycopolymers at various pendant spacer lengths of glucose moiety and their effects on adhesion, viability and proliferation of osteoblast cells

Multivalent glycopolymers containing three different glucose pendant spacer lengths in the polymer backbone having various weight percentages of covalently bonded glucose moieties were obtained by the deacetylation of acetylated polymers synthesized via reversible addition-fragmentation chain transfer (RAFT) process. This allowed us to control the packing density of the glucose moieties in one unit of the glycopolymer. The biological responses of these macromolecules in terms of cytotoxicity of glucose moieties at various spacer lengths and concentrations were investigated without perturbing the intrinsic chemical nature of functional moiety by employing in vitro osteoblast cells. Osteoblast cell adhesion, viability and proliferation response with synthesized glycopolymers revealed that the higher glycopolymer concentration tolerance limit was associated with an increase in pendant spacer length of glucose moiety in the glycopolymer.