Sachin V. Otari

Non-aqueous to aqueous phase transfer of oleic acid coated iron oxide nanoparticles for hyperthermia application

Iron oxide magnetic nanoparticles (MNPs) alone are suitable for a broad spectrum of applications, but the low stability and heterogeneous size distribution in aqueous medium represent major setbacks. These setbacks can however be reduced or diminished through functionalization of MNPs with various biocompatible surfactants. In this study, magnetite (Fe3O4) nanoparticles were modified using oleic acid (OA) to reduce their agglomeration. To render hydrophilicity and to increase the colloidal stability of the MNPs, they were further functionalized with betaine-HCl (BTH). The physiochemical properties were well characterized using X-ray diffraction, Fourier transform infrared, thermogravimetric analysis, transmission electron microscopy and superconducting quantum interference device of the OA-BTH coated Fe3O4 MNPs in order to use them for hyperthermia application. Zeta potential study and size distribution of nanoparticles showed increased stability of the nanoparticles. The coated MNPs show increase in specific absorption rate value of 91.03 W g−1 at 335.2 Oe, making them more suitable for hyperthermia application. Cytotoxicity study was performed by MTT assay on L929 cell line for 24 h incubation period.

Protein–inorganic hybrid system for efficient his-tagged enzymes immobilization and its application in L-xylulose production

The facile synthesis of protein–inorganic hybrid nanoflowers was evaluated for the efficient immobilization of recombinant his-tagged enzymes, which have a broad range of potential applications. In this study, we report the preparation of a metal–protein hybrid nanoflower system for efficient immobilization of the recombinant enzymes L-arabinitol 4-dehydrogenase from Hypocrea jecorina (HjLAD) and NADH oxidase from Streptococcus pyogenes (SpNox). Compared with free enzymes, synthesized hybrid nanoflowers exhibited enhanced enzymatic activities of 246 and 144% for HjLAD and SpNox, respectively. We have demonstrated that immobilized enzymes retained high catalytic activity and improved the tolerance towards pH and temperature changes. Synthesized nanoflowers also retained high storage stability and reusability. In addition, the immobilized enzymes exhibited significantly enhanced L-xylulose production under co-factor regeneration conditions than the free enzyme combination. These results demonstrate that variations in the concentration of metals and synthesis conditions of nanoflowers can be extended to efficiently immobilize recombinant his-tagged enzymes.

In vitro hyperthermia with improved colloidal stability and enhanced SAR of magnetic core/shell nanostructures

Magnetic core/shell nanostructures of Fe3O4 nanoparticles coated with oleic acid and betaine-HCl were studied for their possible use in magnetic fluid hyperthermia (MFH). Their colloidal stability and heat induction ability were studied in different media viz. phosphate buffer solution (PBS), saline solution and glucose solution with different physiological conditions and in human serum. The results showed enhanced colloidal stability in these media owing to their high zeta potential values. Heat induction studies showed that specific absorption rates (SAR) of core/shells were 82-94W/g at different pH of PBS and concentrations of NaCl and glucose. Interestingly, core/shells showed 78.45±3.90W/g SAR in human serum. The cytotoxicity of core/shells done on L929 and HeLa cell lines using 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide and trypan blue dye exclusion assays showed >89% and >80% cell viability for 24 and 48h respectively. Core/shell structures were also found to be very efficient for in vitro MFH on cancer cell line. About 95% cell death was occurred in 90min after hyperthermia treatment. The mechanism of cell death was found to be elevated ROS generation in cells after exposure to core/shells in external magnetic field. This study showed that these core/shells have a great potential to be used in in vivo MFH.

A green chemistry approach for synthesizing thermostable antimicrobial peptide-coated gold nanoparticles immobilized in an alginate biohydrogel

Developing rapid, green, and cost effective approaches for synthesizing metal nanoparticles with biochemical and biomedical applications is currently a top priority. Here, we report a rapid synthesis of gold nanoparticles (AuNPs) in an alginate polymer using thermostable antimicrobial peptides. At a high temperature, these antimicrobial peptides acted as reducing agents and converted Au3+ to Au0 in 15 min while retaining their antimicrobial activity. The alginate polymer acted as a stabilizing agent for this reaction. The resulting Au–peptide–alginate biohydrogel was characterized by UV-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). TEM analysis showed AuNPs of less than 25 nm in diameter, with peptides present on their surfaces. The Au–peptide–alginate biohydrogel showed effective catalytic activity in reducing 4-nitrophenol and hexacyanoferrate(III) in the presence of sodium borohydride with durable reusability. The Au–peptide–alginate biohydrogel was also demonstrated to have antimicrobial activity against pathogenic bacteria. The method presented here for the synthesis of a metal–polymer conjugate is eco-friendly and robust. Large-scale production of the Au–alginate polymer would be possible in a very short time using this method, which makes it potentially useful for biomedical and industrial applications.

Synthesis of cross-linked protein-metal hybrid nanoflowers and its application in repeated batch decolorization of synthetic dyes

Herein, we report the preparation of a cross-linked protein-metal hybrid nanoflower (NF) system for laccase immobilization. The immobilized laccase showed effective encapsulation yield and activity recovery of 78.1% and 204%, respectively. The catalytic efficiency (kcatVmax-1) of cross-linked NF (CL-NF) was 2.2-fold more than that of free laccase. The CL-NF also exhibited significantly higher stability towards pH and temperature changes. It exhibited excellent storage stability and tolerance towards solvents and inhibitors as compared with the free enzyme. After 10 cycles of reuses, the NF and CL-NF laccase showed 41.2% and 92.3% residual activity, respectively. The CL-NF showed high oxidation potential, 265% that of the free enzyme, towards phenolic compounds. The CL-NF laccase retained the residual decolorization efficiency of up to 84.6% for synthetic dyes under repeated batch conditions of 10 cycles. These results suggested that the preparation of CL-NF is an effective approach to enhance the enzymatic properties and has great potential in many industrial applications.

SnO2 hollow nanotubes: A novel and efficient support matrix for enzyme immobilization

A major challenge in the industrial use of enzymes is maintaining their stability at elevated temperatures and in harsh organic solvents. In order to address this issue, we investigated the use of nanotubes as a support material for the immobilization and stabilization of enzymes in this work. SnO2 hollow nanotubes with a high surface area were synthesized by electrospinning the SnCl2 precursor and polyvinylpyrrolidone (dissolved in dimethyl formamide and ethanol). The electrospun product was used for the covalent immobilization of enzymes such as lipase, horseradish peroxidase, and glucose oxidase. The use of SnO2 hollow nanotubes as a support was promising for all immobilized enzymes, with lipase having the highest protein loading value of 217 mg/g, immobilization yield of 93%, and immobilization efficiency of 89%. The immobilized enzymes were fully characterized by various analytical methods. The covalently bonded lipase showed a half-life value of 4.5 h at 70 °C and retained ~91% of its original activity even after 10 repetitive cycles of use. Thus, the SnO2 hollow nanotubes with their high surface area are promising as a support material for the immobilization of enzymes, leading to improved thermal stability and a higher residual activity of the immobilized enzyme under harsh solvent conditions, as compared to the free enzyme.

Rapid synthesis and decoration of reduced graphene oxide with gold nanoparticles by thermostable peptides for memory device and photothermal applications

This article presents novel, rapid, and environmentally benign synthesis method for one-step reduction and decoration of graphene oxide with gold nanoparticles (NAuNPs) by using thermostable antimicrobial nisin peptides to form a gold-nanoparticles-reduced graphene oxide (NAu-rGO) nanocomposite. The formed composite material was characterized by UV/Vis spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and high-resolution transmission electron microscopy (HR-TEM). HR-TEM analysis revealed the formation of spherical AuNPs of 5–30 nm in size on reduced graphene oxide (rGO) nanosheets. A non-volatile-memory device was prepared based on a solution-processed ZnO thin-film transistor fabricated by inserting the NAu-rGO nanocomposite in the gate dielectric stack as a charge trapping medium. The transfer characteristic of the ZnO thin-film transistor memory device showed large clockwise hysteresis behaviour because of charge carrier trapping in the NAu-rGO nanocomposite. Under positive and negative bias conditions, clear positive and negative threshold voltage shifts occurred, which were attributed to charge carrier trapping and de-trapping in the ZnO/NAu-rGO/SiO2 structure. Also, the photothermal effect of the NAu-rGO nanocomposites on MCF7 breast cancer cells caused inhibition of ~80% cells after irradiation with infrared light (0.5 W cm−2) for 5 min.

Canna edulis Leaf Extract-Mediated Preparation of Stabilized Silver Nanoparticles: Characterization, Antimicrobial Activity, and Toxicity Studies

A novel approach to synthesize silver nanoparticles (AgNPs) using leaf extract of Canna edulis Ker-Gawl. (CELE) under ambient conditions is reported here. The as-prepared AgNPs were analyzed by UV-visible spectroscopy, transmission emission microscopy, X-ray diffraction, Fourier transform-infrared spectroscopy, energy-dispersive analysis of X-ray spectroscopy, zeta potential, and dynamic light scattering. The AgNPs showed excellent antimicrobial activity against various pathogens, including bacteria and various fungi. The biocompatibility of the AgNPs was analyzed in the L929 cell line using NRU and MTT assays. Acridine orange/ethidium bromide staining was used to determine whether the AgNPs had necrotic or apoptotic effects on L929 cells. The concentration of AgNPs required for 50% inhibition of growth of mammalian cells is far more than that required for inhibition of pathogenic microorganisms. Thus, CELE is a candidate for the eco-friendly, clean, cost-effective, and nontoxic synthesis of AgNPs.