Sakthivel Gandhi

Superparamagnetic nanosystems based on iron oxide nanoparticles & mesoporous silica: synthesis & evaluation of their magnetic, relaxometric and biocompatability properties

Mesoporous silica has attracted attention in recent years due to its high surface area, tunable ordered narrow pores and easily modifiable functional groups. In the present work, iron oxide nanoparticles (Fe2O3) were incorporated into the pores and surface of mesoporous SBA–15 (Santa Barbara Amorphous) via a thermal pre-synthesis method. The textural and surface properties were characterized using electron microscopy, X-ray diffraction and nitrogen adsorption–desorption analysis. Due to a reduction in thermal pressure during the synthesis, the textural property of the magnetic silica remained highly ordered. The superparamagnetic property of the synthesized material was confirmed using SQUID–VSM. Cell viability studies were carried out with MC3T3 fibroblast cell lines in the presence and absence of magnetic silica and our results showed no significant change in the cell viability between the concentration range of 31.3 μg mL−1 and 250 μg mL−1. The magnetic resonance properties of the iron oxide doped mesoporous silica was determined using MRI and showed excellent longitudinal (R1) and transverse relaxivities (R2) with an R2/R1 ratio close to 1, indicating the potential of this material as a magnetic contrast agent.

Hierarchical mesoporous silica nanofibers as multifunctional scaffolds for bone tissue regeneration

Mesoporous materials with pore sizes between 2 and 50 nm have elicited widespread interest in catalysis, separation, adsorption, sensors, and drug delivery applications due to its highly ordered pore size along with high hydrothermal stability and easily modifiable surface functionalities. Fabricating these mesoporous materials as continuous fibers offers exciting vistas for biomedical applications especially in tissue engineering. The aim of the present study was to fabricate, characterize, and evaluate the cellular and gene expression of mesoporous silica with a long ordered fibrous morphology to support regeneration of bone tissue. Tetraethyl orthosilicate, polyvinyl pyrrolidone, and the tri-block copolymer P-123 were subjected to electrospinning to fabricate continuous ordered mesoporous silica nanofibers by optimizing solution and operation parameters. Mesoporous silica fibers with an average diameter of 470 nm and mesopores of dimension 5.97 nm were obtained. The combination of micropores, mesopores, macropores, and the nanofibrous morphology imparted excellent bioactivity to the mesoporous silica fibrous scaffolds as demonstrated by the proliferation of human osteoblast-like cells (MG63) and by the maintenance of its phenotype. The upregulation of collagen I, alkaline phosphatase, osteocalcin, osteopontin, and bone sialoprotein signifies the maturation of MG63 cells on the silica scaffold. Hence, these novel scaffolds are promising new biomaterials for orthopaedic applications.

A novel nanostructured iron oxide–gold bioelectrode for hydrogen peroxide sensing

Fe(3)O(4) nanoparticles covalently linked to a gold electrode have been used for immobilizing catalase (CAT) enzyme to sense the presence of various concentrations of H(2)O(2). These nanoparticles ranging from 20 to 30 nm were synthesized by thermal co-precipitation of ferric and ferrous chlorides. SEM and XRD have been used for morphological and structural characterization of Fe(3)O(4) nanoparticles. CAT enzyme was linked covalently to the surface of iron oxide using carbodiimide in phosphate buffer (pH 7.4) at 4 °C. The enzyme-iron oxide link was confirmed by FT-IR spectroscopy. Sensing studies carried out using cyclic voltammetry showed a linear response of the CAT/nano Fe(3)O(4)/Au bioelectrode towards H(2)O(2) between 1.5 and 13.5 µM with a very sharp response time of 2 s.

A highly efficient warm white light-emitting Eu2+-activated silicate host: another striking application of mesoporous silica

This study outlines a novel approach to the synthesis of an efficient yellow-emitting Sr0.975Ca0.975Eu0.05SiO4 phosphor with the adequate red spectral components. This was achieved by the use of a well-known silicate source, mesoporous silica. The findings showed that the synthesized phosphor gave a broad emission from blue to red, along with a stable emission color till 450 K and an emission decay time of 1 μs. When the phosphor was fabricated using UV (400 nm) and blue LED (450 nm) chips, it promisingly generated warm white light at a color temperature 80.

Development and evaluation of a highly sensitive rapid response enzymatic nanointerfaced biosensor for detection of putrescine

Putrescine (1,4-diaminobutane) a biologically active diamine has been found to be a valuable analyte for several clinical and analytical purposes. The present work deals with diamine oxidase immobilized on iron oxide nanoparticles for quantifying the amount of putrescine produced, by the decarboxylation of ornithine, which is converted into hydrogen peroxide by the enzyme diamine oxidase (DAO). This reaction can be quantified using electrochemical techniques, which forms the basis of this work. Iron oxide (Fe(3)O(4)) nanoparticles, synthesized using thermal co-precipitation, were chosen for immobilization of DAO due to its simple preparation procedure, high surface area and cost-effectiveness. The size of the particles was in the range of 25-35 nm and the enzyme was linked covalently by carbodiimide activation and confirmed using FT-IR. For detecting the hydrogen peroxide released in the reaction, a glassy carbon-working electrode coated with enzyme linked iron oxide nanoparticles was poised at +0.4 V versus an Ag/AgCl reference electrode and a platinum wire was used as the counter electrode. A step-wise increase in current was observed and linearity was obtained in the range of 2-8 nM, with 0.65 nM as the minimum detection limit and the response time was found to be 0.3 seconds. Ascorbic acid, a common interfering molecule in biological samples, did not interfere with the measurements indicating the high degree of specificity of the diamine oxidase-based nano-interfaced biosensor.

Development of electrochemical biosensor with nano-interface for xanthine sensing--a novel approach for fish freshness estimation.

Highly sensitive, selective and mediator-free electrochemical biosensor with nano-interface for sensing xanthine using xanthine oxidase (XOx) has been developed. Towards the preparation of nano-interface, Fe3O4 nanoparticles were synthesized by thermal co-precipitation method and structural, morphological characterizations were carried out using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and field emission transmission electron microscope (FE-TEM) respectively. The modified electrode with the covalently linked XOx was confirmed by FT-IR. With the modified electrode as working electrode, electrochemical studies were carried out. The linear range was found to be from 0.4 to 2.4 nM. The biosensor exhibited an optimum response in less than 2 s and was not prone to interferences from ascorbic acid, urea and sucrose. The Michaelis-Menten constant (Km) was found to be 1.3 nM. The limit of detection is found to be 2.5 pM and limit of quantification as 8.3 pM. The developed biosensor was used for the real time measurement of fish freshness.

Mesoporous silica: a highly promising and compatible candidate for optical and biomedical applications

A simple post-co-precipitation strategy is adopted for the construction of a mesoporous silica framework in which the rare earth gadolinium oxide (Gd2O3:Eu3+& Gd2O3:Sm3+, Eu3+) is incorporated as an emissive probe for optical and bio-medical applications. The samples show good emission along with the required theranostic properties. In the blue region, a better red emissive behavior is observed in the case of Eu3+ doped sample while the Sm3+ and Eu3+ co-doped sample exhibit the same in the near ultra-violet region. Moreover, the structural and textural properties of mesoporous silica are preserved even in the presence of rare earth doped Gd2O3 and this can very well be utilized for theranostic applications. A clear confocal microscopy image shows a red spot, and thus its potential towards trackability is confirmed. In addition to this, other admirable properties are also associated with it namely, an excellent drug loading ability, bio-compatibility, easy surface modification by the targeting moiety and excellent longitudinal relaxivity (T1) under magnetic resonance imaging (MRI), which stands par for it to be utilized in the field of theranostics too. This material shows good luminescence properties along with the desired internal–external morphology, and a narrowly ordered porosity can validate the application of these materials in multi-faceted fields such as phosphors for LEDs, bio-imaging, theranostics etc.

ETHANOL AND TRIMETHYL AMINE SENSING BY ZnO-BASED NANOSTRUCTURED THIN FILMS

Undoped and fluorine (F)-doped nanostructured zinc oxide (ZnO) thin films were deposited over glass substrates by spray pyrolysis technique using zinc acetate dihydrate with and without ammonium fluoride as dopant in precursor solution respectively. The deposition conditions and the concentration of the dopant were optimized to obtain nanostructured ZnO thin films. The film obtained from 0.05 M of zinc acetate aqueous solution and 20% F sprayed at the rate of 3 ml/min on preheated substrate kept at 503 K yielded spherical shape well-connected grains, which has large surface to volume ratio. The structural and morphological studies of the films were investigated by using X-ray diffraction (XRD) and scanning electron microscope (SEM) respectively. The diffraction peak positions in XRD confirmed the formation of highly crystalline ZnO film with hexagonal wurtzite phase. Further sensing behavior of the films towards various concentrations of volatile organic compounds (VOCs) such as ethanol and trimethyl amine (TMA) has been investigated at an optimized operating temperature of 373 K and reported.

Synthesis of a novel hierarchical mesoporous organic-inorganic nanohybrid using polyhedral oligomericsilsesquioxane bricks

A successful method has been demonstrated for the synthesis of a mesoporous organic–inorganic nanohybrid using amine functionalized polyhedral oligomericsilsesquioxane (POSS) and pluronic polymer as a silica precursor and structure directing agent, respectively. The results confirmed the presence of porous structure, along with the high surface area and uniform pore size distribution which can be utilized for various applications namely catalysis, drug-delivery, etc.

A novel efficient mesoporous silica assisted green emitting phosphors-an exotic remote phosphor with high quantum yield

A novel attempt towards the development of Eu2+ doped barium silicate and strontium barium silicate has been put forth using a versatile material, namely mesoporous silica through a convenient wet-solid phase reaction. The developed phosphor can be efficiently excited in a broad spectral range of 200–500 nm, and gets emitted strongly in the green region. On introduction of strontium to Eu2+ doped barium silicate phosphor, a clear red shift has been recorded in the photoluminescence spectra. These mesoporous silica assisted synthesis of Ba1.95Eu0.05SiO4 and Ba0.975Sr0.975Eu0.05SiO4 phosphors showed a good thermal luminescence stability and high quantum efficiency of about 85%. It has been successfully used for the fabrication of a flexible and translucent remote phosphor. The fabricated remote phosphor attached proto-type LED exhibits a very strong green emission and this can be utilized as an efficient green component for various applications apart from the white LED productions.