Suwarna Datar

Curcumin Conjugated Silica Nanoparticles for Improving Bioavailability and Its Anticancer Applications

Curcumin, a yellow bioactive component of Indian spice turmeric, is known to have a wide spectrum of biological applications. In spite of various astounding therapeutic properties, it lacks in bioavailability mainly due to its poor solubility in water. In this work, we have conjugated curcumin with silica nanoparticles to improve its aqueous solubility and hence to make it more bioavailable. Conjugation and loading of curcumin with silica nanoparticles was further examined with transmission electron microscope (TEM) and thermogravimetric analyzer. Cytotoxicity analysis of synthesized silica:curcumin conjugate was studied against HeLa cell lines as well as normal fibroblast cell lines. This study shows that silica:curcumin conjugate has great potential for anticancer application.

Graphene nanoribbon–PVA composite as EMI shielding material in the X band

A very thin graphene nanoribbon/polyvinyl alcohol (GNR/PVA) composite film has been developed which is light weight and requires a very low concentration of filler to achieve electromagnetic interference (EMI) shielding as high as 60 dB in the X band. Atomic force microscope studies show very well conjugated filler concentration in the PVA matrix for varying concentrations of GNR supported by Raman spectroscopy data. The films show 14 orders of increase in conductivity with a GNR concentration of 0.75% [corrected] in PVA. This is possible because of the interconnected GNR network providing a very low percolation threshold as observed from the electrical measurements. Local density of states study of GNR using scanning tunnelling spectroscopy shows the presence of localized states near the Fermi energy. There are multiple advantages of GNR as an EMI shielding material in a polymer matrix. It has good dispersion in water, the conductive network in the composite shows very high electrical conductivity for a very low concentration of GNR and the presence of localized density of states near Fermi energy provides the spin states required for the absorbance of radiation energy in the X band.

Dielectric investigation of a conducting fibrous nonwoven porous mat fabricated by a one-step facile electrospinning process

Currently, there is a considerable demand for materials with inter-balanced dielectric properties to replace the existing traditional insulators in variegated electronic appliances over the range of audio and radio frequency. In the current work, a one-step facile electrospun (E-spun) technique is adopted to fabricate a non woven mat consisting of nano-scale conducting fibers of polyaniline (PANI) and gold nanoparticles (AuNPs) using polyvinyl alcohol (PVA) as a binder. The influence of different amounts of the AuNP solution on the size and distribution of fibers was investigated using high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM). The dielectric constant, losses, AC conductivity and modulus of nanofibers were investigated over a wide frequency and temperature range of 0.1 Hz to 10 MHz and −40 °C to 60 °C respectively by means of Broadband Dielectric Spectroscopy (BDS). AC conductivity varies as a function of frequency, according to Jonschers power law (JPL), and the behavior of the temperature dependent frequency exponent using JPL suggests that the Correlated Barrier Hopping (CBH) is the dominant charge transport mechanism for conducting nanofibrous nonwoven mats. By using the CBH model the maximum barrier height, hopping distance and density of state (DOS) were calculated for the whole temperature range. The incremental increase from 1.6 × 10−6 S cm−1 to 2.5 × 10−6 S cm−1 with increasing amounts of AuNP solution was noticed and is ascribed to the corresponding increased conducting network and reduced trapping centers in the mat. Dielectric constant increases with both increased loading of nanoparticle solution in the mat and the increased temperature, which may be attributed to enhanced interfacial polarization. Shifting and broadening of well-defined peaks were observed in the imaginary part of the dielectric modulus spectrum, indicating Maxwell–Wargner–Sillars (MWS) interfacial polarization. Effective electro-magnetic (EM) shielding was also evaluated for all compositions and a sharp peak of 22.99 dB (>99%) at 11.18 GHz was noticed for a 0.5 mm thick mat of the composite. This was observed to be dependent on the concentration of AuNPs and the thickness of the mat.

Nano-carbon: preparation, assessment, and applications for NH3 gas sensor and electromagnetic interference shielding

We report on the preparation and characterization of nano-carbon for applications in NH3 sensing and electromagnetic interference shielding (EMI, X-band, 8–12 GHz). Nano-carbon was synthesized by combustion of 1,7,7-trimethyl-bi-cycloheptan (camphor, C10H16O) deposited at 77 K. Morphological analysis showed nano-carbon was spherically concentric shells (40–50 nm); interconnected spatially. In Raman, vibration modes observed at 1390 (D) and 1580 (G) cm−1, indicated presence of sp3 within sp2 shells. UV-visible and photoluminescence spectroscopic analysis revealed that, band gap of nano-carbon was 4.5 eV with midgap of 2.7 eV and two flouro-excited states; making it useful for Fabry–Perot interferometer optical fibre gas sensor. Details of sensor system, its mechanism and transfer function analysis is presented. The system sensitivity was 3 ppm with response and recovery time, respectively, 5 and 8 s. The molecular imprint of NH3 on nano-carbon (1–5 ppb C-loss/10 cycles; 2 : 1, sp3 : sp2 rupture) was obtained that set life time of sensor probe. In EMI, % reflection of nano-carbon was comparable with copper. The losses due to hopping and migration current were large in nano-carbon and attributed to in-plane σ-bond and tetrahedral sites in nano-carbon that interacted with radiation at higher skin depth, around four times more than that of copper. Details of EMI shielding mechanism is presented.

Microwave absorption properties of reduced graphene oxide strontium hexaferrite/poly(methyl methacrylate) composites

The key factors to consider when designing microwave absorber materials for eradication of electromagnetic (EM) pollution are absorption of incident EM waves and good impedance matching. By keeping these things in mind, flexible microwave absorber composite films can be fabricated by simple gel casting techniques using reduced graphene oxide (RGO) and strontium ferrite (SF) in a poly(methyl methacrylate) (PMMA) matrix. SF nanoparticles are synthesized by the well known sol-gel method. Subsequently, reduced graphene oxide (RGO) and SF nanocomposite (RGOSF) are prepared through a chemical reduction method using hydrazine. The structure, morphology, chemical composition, thermal stability and magnetic properties of the nanocomposite are characterized in detail by various techniques. The SF particles are found to be nearly 500 nm and decorated on RGO sheets as revealed by field emission scanning electron microscopy and transmission electron microscopy analysis. Fourier transform infrared and and Raman spectroscopy clearly show the presence of SF in the graphene sheet by the lower peak positions. Finally, ternary polymer composites of RGO/SF/PMMA are prepared by an in situ polymerization method. Magnetic and dielectric studies of the composite reveal that the presence of RGO/SF/PMMA lead to polarization effects contributing to dielectric loss. Also, RGO surrounding SF provides a conductive network in the polymer matrix which is in turn responsible for the magnetic loss in the composite. Thus, the permittivity as well as the permeability of the composite can be controlled by an appropriate combination of RGO and SF in PMMA. More than 99% absorption efficiency is achieved by a suitable combination of magneto-dielectric coupling in the X-band frequency range by incorporating 9 wt% of RGO and 1 wt% of SF in the polymer matrix.

Corrigendum: Graphene nanoribbon–PVA composite as EMI shielding material in the X band (2013 Nanotechnology 24 455705)

There was an error in calculating the weight percentage of the graphene nanoribbon (GNR) in PVA. There were three films made with different concentrations of GNR. The correct weight percentage of GNR in PVA in three films should be 0.75%, 1.5% and 2.5% instead of 0.0075 wt%, 0.015 wt%, and 0.025 wt% respectively. Reference to the weight percentage has been made in the abstract, line 5; page 3, paragraph 5, second line; page 4, paragraph 1; page 6, paragraph 2, line 6; figure caption 4; figure caption 10 and figures 9 and 10, the corrected versions of which are shown below.

Photon assisted conducting atomic force microscopy study of nanostructured additives in P3HT:PCBM

One of the ways of improving the efficiency of polymer solar cells is to increase the conductive paths in the photoactive layer. The present work focuses on the study of the effect of additives (silver nanoparticles (Ag NPs) and graphene (Gr)) in photoactive poly-3-hexyl thiophene:phenyl-C61-butyric acid methyl ester (P3HT:PCBM). The morphology and localised photocurrent obtained using Photon Assisted Conducting Atomic Force Microscopy reflect the role of these additives in the photocurrent produced by the active layer. The study depicts that the morphology of a P3HT:PCBM film changes completely with Gr additives, whereas a very small change occurs with the addition of Ag NPs. A localised photocurrent measurement exhibits that the space charge limited conduction (SCLC) phenomenon could be the dominant process of charge conduction in the P3HT:PCBM film with additives. The study also demonstrates that the carrier mobility is enhanced by more than an order of magnitude with Gr as the additive. This is a significant change for achieving efficient charge separation and transportation in polymer solar cell application.

An attempt to correlate surface physics with chemical properties: molecular beam and Kelvin probe investigations of Ce1−xZrxO2 thin films

What is the correlation between physical properties of the surfaces (such as surface potential, electronic nature of the surface), and chemical and catalysis properties (such as chemisorption, sticking probability of surface)? An attempt has been made to explore any correlation that might exist between the physical and chemical properties of thin film surfaces. Kelvin probe microscopy (KPM) and the molecular beam (MB) methods were employed to carry out the surface potential, and oxygen adsorption and oxygen storage capacity (OSC) measurements on Ce1-xZrxO2 thin films. A sol-gel synthesis procedure and spin-coating deposition method have been applied to make continuous nanocrystalline Ce1-xZrxO2 (x = 0-1) (CZ) thin films with uniform thickness (35-50 nm); however, surface roughness and porosity inherently changes with CZ composition. MB studies of O2 adsorption on CZ reveal high OSC for Ce0.9Zr0.1O2, which also exhibits highly porous and significantly rough surface characteristics. The surface potential observed from KPM studies varied between 30 and 80 mV, with Ce-rich compositions exhibiting the highest surface potential. Surface potential shows large changes after reduction or oxidation of the CZ film demonstrating the influence of Ce3+/Ce4+ on surface potential, which is also a key to catalytic activity for ceria-based catalysts. The surface potential measured from KPM and the OSC measured from MB vary linearly and they depend on the Ce3+/Ce4+ ratio. More and detailed studies are suggested to arrive at a correlation between the physical and chemical properties of the surfaces.

Temperature Dependent Electron Transport Properties of Gold Nanoparticles and Composites: Scanning Tunneling Spectroscopy Investigations

Scanning tunneling spectroscopy (STS) is used for investigating variations in electronic properties of gold nanoparticles (AuNPs) and its composite with urethane-methacrylate comb polymer (UMCP) as function of temperature. Films are prepared by drop casting AuNPs and UMCP in desired manner on silicon substrates. Samples are further analyzed for morphology under scanning electron microscopy (SEM) and atomic force microscopy (AFM). STS measurements performed in temperature range of 33 °C to 142 °C show systematic variation in current versus voltage (I-V) curves, exhibiting semiconducting to metallic transition/Schottky behavior for different samples, depending upon preparation method and as function of temperature. During current versus time (I-t) measurement for AuNPs, random telegraphic noise is observed at room temperature. Random switching of tunneling current between two discrete levels is observed for this sample. Power spectra derived from I-t show 1/f2 dependence. Statistical analysis of fluctuations shows exponential behavior with time width τ ≈ 7 ms. Local density of states (LDOS) plots derived from I-V curves of each sample show systematic shift in valance/conduction band edge towards/away from Fermi level, with respect to increase in temperature. Schottky emission is best fitted electron emission mechanism for all samples over certain range of bias voltage. Schottky plots are used to calculate barrier heights and temperature dependent measurements helped in measuring activation energies for electron transport in all samples.

Decoration of gold nanoparticles on thin multiwall carbon nanotubes and their use as a glucose sensor

Thin multiwall carbon nanotubes (MWCNTs) have been decorated with gold nanoparticles (Au NPs) with polyaniline (PANI) as an inter-linker by a simple wet chemical method. The synthesized AuNPs:MWCNT:PANI composite was studied with UV–vis, FTIR, Raman spectroscopy, x-ray diffractometer, transmission electron microscopy (TEM) and atomic force microscopy (AFM). Conducting AFM (C-AFM) images of the composite reveal the role played by the two components in electrochemical reactions. The size of the Au NPs was found to be 13 ± 2 nm in the composite as observed from TEM. The synthesized AuNPs:MWCNT:PANI composite was further drop casted onto a glassy carbon electrode (GCE) for electrocatalytic study. The resulting composite exhibits good electrocatalytic activity towards reduction of H2O2 and O2. A glucose biosensor was developed by immobilizing glucose oxidase into AuNPs:MWCNT:PANI composite film on GCE. The fabricated sensor demonstrates good linear response to glucose (i.e. R = 0.9975) in the range of 2 to 12 mM.