Rajesh Gangwar | Defence Institute of Advanced Technology (DU), Pune, India. (original) (raw)

Papers by Rajesh Gangwar

Journal of Experimental Nanoscience, Oct 25, 2023

AIP Conference Proceedings, 2011

This work presents an optical fiber based relative humidity sensor. Highly mono-dispersed and sta... more This work presents an optical fiber based relative humidity sensor. Highly mono-dispersed and stable silica nanoparticles were synthesized by colloidal route. Layer by layer technique has been utilized to create ultrathin films of silica nanoparticles on the optical fiber end. This fabrication technique is a simple method based on the alternative immersion in oppositely charged colloidal solutions. The coated thin

Physica Scripta, 2022

Heterojunction diodes of ZnS/p-Si have been fabricated using the chemical bath deposition (CBD) t... more Heterojunction diodes of ZnS/p-Si have been fabricated using the chemical bath deposition (CBD) technique at two different deposition durations under both stirring and non-stirring conditions. The x-ray diffraction (XRD) patterns indicate the deposited ZnS films exhibit good crystallinity with the growth direction along the (111) planes of a cubic zinc blend structure. The crystallite size of all the deposited ZnS thin films have been calculated using the Scherer formula and found to be in the range of 2.2–2.7 nm which is very close (∼4 nm) to the size estimated using transmission electron microscopy (TEM). The surface morphology of the deposited ZnS thin films were studied by scanning electron microscopy (SEM) and it was observed that spherical nanoparticles agglomerated with the increase in deposition time. Furthermore, the optical properties of the deposited ZnS thin films were studied using UV-visible (UV-VIS) and photoluminescence (PL) spectroscopy. The effective calculated ban...

Journal of Agricultural and Food Chemistry, 2013

Curcumin, a yellow bioactive component of Indian spice turmeric, is known to have a wide spectrum... more 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.

Materials Research Innovations

ABSTRACT In the last few decades gold nanoparticles have become an intense topic of research due ... more ABSTRACT In the last few decades gold nanoparticles have become an intense topic of research due to it's eminent size and morphology dependent optical, chemical, physical and electrical properties. Gold nanoparticles show useful technological applications in the province of nanoelectronics, optoelectronics, chemical and biological sensors. Due to the size- and shape-dependent properties, synthesis of gold nanoparticles with various methods is still an important area of research. Recent literature reports indicate that gold nanoparticles have vast biomedical applications such as biosensors, bio-imaging, targeted drug delivery and controlled drug release. Other than size and shape, the inter-particle distance dependent optical properties of gold nanoparticles have very interesting applications in the field of sensors. Gold nanoparticles show good selectivity and sensitivity for colorimetric identification of heavy toxic metal ions such as Hg2+, Cd2+, As3+, Pb2+ etc and various biomolecules. The concentration of such toxic metal ions in water can be identified by naked eye also.

Materials Research Express, 2016

Thin multiwall carbon nanotubes (MWCNTs) have been decorated with gold nanoparticles (Au NPs) wit... more 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.

Journal of Experimental Nanoscience, 2014

ABSTRACT Indigenously available natural dyes have been used as natural sensitisers for dye-sensit... more ABSTRACT Indigenously available natural dyes have been used as natural sensitisers for dye-sensitised solar cells (DSSCs) in this study. The chlorophyll extract from Azadirachta indica (Neem) leaves and anthocyanin extract from poinsettia bracts were obtained using ethanol. Nanoparticles of TiO2 having an average size of 80 nm were deposited on fluorine-doped tin oxide (FTO) coated glass using the electrophoretic deposition method. Counter electrode was prepared by spraying conductive graphite over FTO glass substrates. A sandwich-type cell was assembled, and the fill factor and the power conversion efficiency were measured under a light source simulating AM 1.5 with an intensity of 100 mW/cm2. DSSCs containing chlorophyll and anthocyanin exhibited open circuit voltages of 404 and 406 mV with fill factors of 40.1% and 45.8%, respectively. The mixture of the two natural dyes as sensitiser for DSSCs gave the best photovoltaic conversion efficiency of approximately 1%.

Advances in Natural Sciences: Nanoscience and Nanotechnology, 2013

A simple and eco-friendly method has been developed for the synthesis of gold nanoparticles using... more A simple and eco-friendly method has been developed for the synthesis of gold nanoparticles using allamanda flower extract. In this green synthesis method, chloroauric acid (HAuCl 4) solution was reduced with the help of allamanda flower extract. The synthesized gold nanoparticles were characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM) and x-ray diffraction technique for their morphological and structural analysis. The size of the spherical and triangular gold nanoparticles was found to be in the range of 5-40 and 20-70 nm, respectively. The x-ray diffraction analysis revealed that the crystallite size of face-centered cubic (FCC) gold nanoparticles was ∼11 nm. These synthesized gold nanoparticles exhibit good catalytic activity towards the reduction of H 2 O 2. The fabricated sensor exhibits good sensitivity of 21.33 µA mM −1 cm −2 with linear relationship (R 2 = 0.996) in the range from 2 to 10 mM of H 2 O 2 concentration. This work can be extended further for potential applications such as antimicrobial studies, bio-imaging and drug-delivery owing to the known properties of the allamanda flower extract.

Physical Review A, 2009

ABSTRACT

Journal of Molecular Liquids

Journal of Agricultural and Food Chemistry, 2013

Curcumin, a yellow bioactive component of Indian spice turmeric is known to have a 10 wide spectr... more Curcumin, a yellow bioactive component of Indian spice turmeric is known to have a 10 wide spectrum of biological applications. In spite of various astounding therapeutic 11 properties, it lacks in bioavailability mainly due to its poor solubility in water. In this work, 12 we have conjugated curcumin with silica nanoparticles to improve its aqueous solubility and 13 hence to make it more bioavailable. Conjugation and loading of curcumin with silica 14 nanoparticles was further examined with Transmission Electron Microscope (TEM) and 15 Thermogravimetric Analyser. Cytotoxicity analysis of synthesized silica:curcumin conjugate 16 was studied against HeLa cell lines as well as normal fibroblast cell lines. This study shows 17 that silica:curcumin conjugate has great potential for anticancer application. 18 ACS Paragon Plus Environment Journal of Agricultural and Food Chemistry 65 porosity. 30,31 These have been projected to be one of the safest (non-toxic) candidates for 66 DNA-conjugation, drug-delivery and many other applications. 32,33 ACS Paragon Plus Environment Journal of Agricultural and Food Chemistry 108 coated on the silica nanoparticles also evident from the TEM data. Figure 2(a, b) shows TEM 109 images of synthesized silica:curcumin conjugate at two different scales. It is observed from 110 this figure that silica nanoparticles are spherical in shape having diameter of 50±5 nm. It can 111 be seen from this figure that silica nanoparticles are completely surrounded by curcumin as a 112

Advanced Science, …, 2013

A simple colorimetric approach has been utilized for ppb level detection of toxic cadmium ions (C... more A simple colorimetric approach has been utilized for ppb level detection of toxic cadmium ions (Cd 2+ ) in aqueous medium. For this purpose Poly Vinyl Pyrrolidone (PVP) capped spherical gold (Au) nanoparticles (NPs) have been synthesized via wet chemical method. The Au NPs in an aqueous solution of optimal pH 1.0 were found to be highly sensitive to detect the presence of Cd 2+ ions at ppb level through colorimetric response.

… of Sensors (ISPTS), …, 2012

Gold-graphene (Au-G) nanocomposite has been synthesized by wet chemical method. Synthesized Au-G ... more Gold-graphene (Au-G) nanocomposite has been synthesized by wet chemical method. Synthesized Au-G nanocomposite was examined under the UV-vis spectroscopy and transmission electron microscopy (TEM). Further Au-G nanocomposite was drop casted onto the glassy carbon electrode (GCE) by immobilizing glucose oxidase (GOx) into it for the electrochemical detection of glucose. Fabricated sensor demonstrates good linear response to glucose in the range 3 to 18 mM with linearity coefficient 0.964.

Materials Science and …, 2012

Curcumin, a natural polyphenolic compound, has astounding therapeutic applications but lacks in b... more Curcumin, a natural polyphenolic compound, has astounding therapeutic applications but lacks in bioavailability mainly due to its poor solubility in water. Polyvinyl pyrrolidone (PVP) which is a proven drug carrier has been used to facilitate the conjugation of curcumin with gold nanoparticles and to improve the solubility of curcumin in water. In this conjugate diaryl heptanoid chromophore group of curcumin which is a much needed group in biomedical applications remains intact as observed from FTIR and UV-vis spectroscopy analysis. The work shows good promise for such conjugates as therapeutic-cum-imaging materials in biomedical field.

Materials …, 2012

A simple procedure has been developed for aggregation of polyvinylpyrrolidone (PVP) capped gold n... more A simple procedure has been developed for aggregation of polyvinylpyrrolidone (PVP) capped gold nanoparticles by controlling the pH of the solution. PVP-capped gold nanoparticles were synthesized via wet chemical method. Transmission electron microscopy (TEM) and UV-vis spectroscopy techniques were employed for determining the morphological features and surface plasmon resonance (SPR) of the gold nanoparticles. When the pH of the solution containing PVP-capped gold nanoparticles was changed from 6.7 to 1.0, the color of the solution changed from deep red to blue due to SPR weakening by particle aggregate formation. The color of the solution returned to its original red when the pH of the solution was brought back to 6.7. Furthermore, citrate protection of the gold nanoparticles was found to inhibit the reverse action. This reversible/irreversible-selectable structural control of gold nanoparticles with drastic changes in their optical absorption characteristics may find various nanophotonic applications including contactless pH detection.

Advanced Science, …, 2013

A simple approach has been used for the development of antireflective (AR) coating on glass subst... more A simple approach has been used for the development of antireflective (AR) coating on glass substrate. Highly monodispersed and stable silica nanoparticles were synthesized by colloidal route at different concentrations of precursor. The morphology of silica nanoparticles was observed by field emission scanning electron microscopy (FE-SEM). In separate preparations the sizes of the spherical silica nanoparticles was found to be ∼ 100 nm and ∼ 80 nm. Layer-by-Layer (LbL) and time-dependent-deposition (TDD) techniques were used for the formation of antireflection coatings. The antireflection property of the silica nanoparticles coating depends upon number of layers coated and also on deposition time. Such antireflective coatings have useful applications in making windshields, glasses, lenses and solar cells.

This work presents an optical fiber based relative humidity sensor. Highly mono-dispersed and sta... more This work presents an optical fiber based relative humidity sensor. Highly mono-dispersed and stable silica nanoparticles were synthesized by colloidal route. Layer by layer technique has been utilized to create ultrathin films of silica nanoparticles on the optical fiber end. This fabrication technique is a simple method based on the alternative immersion in oppositely charged colloidal solutions. The coated thin film of silica nanoparticles acts as nanometer-scale interferometric cavity. Sensor shows a high sensitivity and fast response towards relative humidity change.

Materials Letters, 2011

The needle-like gold nanostructures were synthesized by using chloroauric acid (HAuCl4) as a meta... more The needle-like gold nanostructures were synthesized by using chloroauric acid (HAuCl4) as a metal precursor and sodium borohydride (NaBH4) as the reducing agent. These needle-like nanostructures of gold were irradiated with high energy electrons (E ~ 6 MeV, ϕ ~ 1012 e cm−2 s−1). The pre- and post-irradiated gold nanostructures were characterized by Scanning Electron Microscopy (SEM), UV–vis spectroscopy, X-ray Diffraction (XRD) and contact angle measurement (GBX-Model Digidrop) techniques. The results of the SEM revealed that after electron irradiation, the needle-like gold structures got fragmented into identical cube-shaped gold nanostructures, though of different sizes. The XRD analysis indicated that the average crystallite size of the gold nanostructures remained unchanged even after irradiation with high energy electrons. A glass surface showed hydrophilic behavior when coated with needle-like nanostructures and became ultra hydrophilic when coated with cube-shaped gold nanostructures.

Journal of Experimental Nanoscience, Oct 25, 2023

AIP Conference Proceedings, 2011

This work presents an optical fiber based relative humidity sensor. Highly mono-dispersed and sta... more This work presents an optical fiber based relative humidity sensor. Highly mono-dispersed and stable silica nanoparticles were synthesized by colloidal route. Layer by layer technique has been utilized to create ultrathin films of silica nanoparticles on the optical fiber end. This fabrication technique is a simple method based on the alternative immersion in oppositely charged colloidal solutions. The coated thin

Physica Scripta, 2022

Heterojunction diodes of ZnS/p-Si have been fabricated using the chemical bath deposition (CBD) t... more Heterojunction diodes of ZnS/p-Si have been fabricated using the chemical bath deposition (CBD) technique at two different deposition durations under both stirring and non-stirring conditions. The x-ray diffraction (XRD) patterns indicate the deposited ZnS films exhibit good crystallinity with the growth direction along the (111) planes of a cubic zinc blend structure. The crystallite size of all the deposited ZnS thin films have been calculated using the Scherer formula and found to be in the range of 2.2–2.7 nm which is very close (∼4 nm) to the size estimated using transmission electron microscopy (TEM). The surface morphology of the deposited ZnS thin films were studied by scanning electron microscopy (SEM) and it was observed that spherical nanoparticles agglomerated with the increase in deposition time. Furthermore, the optical properties of the deposited ZnS thin films were studied using UV-visible (UV-VIS) and photoluminescence (PL) spectroscopy. The effective calculated ban...

Journal of Agricultural and Food Chemistry, 2013

Curcumin, a yellow bioactive component of Indian spice turmeric, is known to have a wide spectrum... more 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.

Materials Research Innovations

ABSTRACT In the last few decades gold nanoparticles have become an intense topic of research due ... more ABSTRACT In the last few decades gold nanoparticles have become an intense topic of research due to it's eminent size and morphology dependent optical, chemical, physical and electrical properties. Gold nanoparticles show useful technological applications in the province of nanoelectronics, optoelectronics, chemical and biological sensors. Due to the size- and shape-dependent properties, synthesis of gold nanoparticles with various methods is still an important area of research. Recent literature reports indicate that gold nanoparticles have vast biomedical applications such as biosensors, bio-imaging, targeted drug delivery and controlled drug release. Other than size and shape, the inter-particle distance dependent optical properties of gold nanoparticles have very interesting applications in the field of sensors. Gold nanoparticles show good selectivity and sensitivity for colorimetric identification of heavy toxic metal ions such as Hg2+, Cd2+, As3+, Pb2+ etc and various biomolecules. The concentration of such toxic metal ions in water can be identified by naked eye also.

Materials Research Express, 2016

Thin multiwall carbon nanotubes (MWCNTs) have been decorated with gold nanoparticles (Au NPs) wit... more 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.

Journal of Experimental Nanoscience, 2014

ABSTRACT Indigenously available natural dyes have been used as natural sensitisers for dye-sensit... more ABSTRACT Indigenously available natural dyes have been used as natural sensitisers for dye-sensitised solar cells (DSSCs) in this study. The chlorophyll extract from Azadirachta indica (Neem) leaves and anthocyanin extract from poinsettia bracts were obtained using ethanol. Nanoparticles of TiO2 having an average size of 80 nm were deposited on fluorine-doped tin oxide (FTO) coated glass using the electrophoretic deposition method. Counter electrode was prepared by spraying conductive graphite over FTO glass substrates. A sandwich-type cell was assembled, and the fill factor and the power conversion efficiency were measured under a light source simulating AM 1.5 with an intensity of 100 mW/cm2. DSSCs containing chlorophyll and anthocyanin exhibited open circuit voltages of 404 and 406 mV with fill factors of 40.1% and 45.8%, respectively. The mixture of the two natural dyes as sensitiser for DSSCs gave the best photovoltaic conversion efficiency of approximately 1%.

Advances in Natural Sciences: Nanoscience and Nanotechnology, 2013

A simple and eco-friendly method has been developed for the synthesis of gold nanoparticles using... more A simple and eco-friendly method has been developed for the synthesis of gold nanoparticles using allamanda flower extract. In this green synthesis method, chloroauric acid (HAuCl 4) solution was reduced with the help of allamanda flower extract. The synthesized gold nanoparticles were characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM) and x-ray diffraction technique for their morphological and structural analysis. The size of the spherical and triangular gold nanoparticles was found to be in the range of 5-40 and 20-70 nm, respectively. The x-ray diffraction analysis revealed that the crystallite size of face-centered cubic (FCC) gold nanoparticles was ∼11 nm. These synthesized gold nanoparticles exhibit good catalytic activity towards the reduction of H 2 O 2. The fabricated sensor exhibits good sensitivity of 21.33 µA mM −1 cm −2 with linear relationship (R 2 = 0.996) in the range from 2 to 10 mM of H 2 O 2 concentration. This work can be extended further for potential applications such as antimicrobial studies, bio-imaging and drug-delivery owing to the known properties of the allamanda flower extract.

Physical Review A, 2009

ABSTRACT

Journal of Molecular Liquids

Journal of Agricultural and Food Chemistry, 2013

Curcumin, a yellow bioactive component of Indian spice turmeric is known to have a 10 wide spectr... more Curcumin, a yellow bioactive component of Indian spice turmeric is known to have a 10 wide spectrum of biological applications. In spite of various astounding therapeutic 11 properties, it lacks in bioavailability mainly due to its poor solubility in water. In this work, 12 we have conjugated curcumin with silica nanoparticles to improve its aqueous solubility and 13 hence to make it more bioavailable. Conjugation and loading of curcumin with silica 14 nanoparticles was further examined with Transmission Electron Microscope (TEM) and 15 Thermogravimetric Analyser. Cytotoxicity analysis of synthesized silica:curcumin conjugate 16 was studied against HeLa cell lines as well as normal fibroblast cell lines. This study shows 17 that silica:curcumin conjugate has great potential for anticancer application. 18 ACS Paragon Plus Environment Journal of Agricultural and Food Chemistry 65 porosity. 30,31 These have been projected to be one of the safest (non-toxic) candidates for 66 DNA-conjugation, drug-delivery and many other applications. 32,33 ACS Paragon Plus Environment Journal of Agricultural and Food Chemistry 108 coated on the silica nanoparticles also evident from the TEM data. Figure 2(a, b) shows TEM 109 images of synthesized silica:curcumin conjugate at two different scales. It is observed from 110 this figure that silica nanoparticles are spherical in shape having diameter of 50±5 nm. It can 111 be seen from this figure that silica nanoparticles are completely surrounded by curcumin as a 112

Advanced Science, …, 2013

A simple colorimetric approach has been utilized for ppb level detection of toxic cadmium ions (C... more A simple colorimetric approach has been utilized for ppb level detection of toxic cadmium ions (Cd 2+ ) in aqueous medium. For this purpose Poly Vinyl Pyrrolidone (PVP) capped spherical gold (Au) nanoparticles (NPs) have been synthesized via wet chemical method. The Au NPs in an aqueous solution of optimal pH 1.0 were found to be highly sensitive to detect the presence of Cd 2+ ions at ppb level through colorimetric response.

… of Sensors (ISPTS), …, 2012

Gold-graphene (Au-G) nanocomposite has been synthesized by wet chemical method. Synthesized Au-G ... more Gold-graphene (Au-G) nanocomposite has been synthesized by wet chemical method. Synthesized Au-G nanocomposite was examined under the UV-vis spectroscopy and transmission electron microscopy (TEM). Further Au-G nanocomposite was drop casted onto the glassy carbon electrode (GCE) by immobilizing glucose oxidase (GOx) into it for the electrochemical detection of glucose. Fabricated sensor demonstrates good linear response to glucose in the range 3 to 18 mM with linearity coefficient 0.964.

Materials Science and …, 2012

Curcumin, a natural polyphenolic compound, has astounding therapeutic applications but lacks in b... more Curcumin, a natural polyphenolic compound, has astounding therapeutic applications but lacks in bioavailability mainly due to its poor solubility in water. Polyvinyl pyrrolidone (PVP) which is a proven drug carrier has been used to facilitate the conjugation of curcumin with gold nanoparticles and to improve the solubility of curcumin in water. In this conjugate diaryl heptanoid chromophore group of curcumin which is a much needed group in biomedical applications remains intact as observed from FTIR and UV-vis spectroscopy analysis. The work shows good promise for such conjugates as therapeutic-cum-imaging materials in biomedical field.

Materials …, 2012

A simple procedure has been developed for aggregation of polyvinylpyrrolidone (PVP) capped gold n... more A simple procedure has been developed for aggregation of polyvinylpyrrolidone (PVP) capped gold nanoparticles by controlling the pH of the solution. PVP-capped gold nanoparticles were synthesized via wet chemical method. Transmission electron microscopy (TEM) and UV-vis spectroscopy techniques were employed for determining the morphological features and surface plasmon resonance (SPR) of the gold nanoparticles. When the pH of the solution containing PVP-capped gold nanoparticles was changed from 6.7 to 1.0, the color of the solution changed from deep red to blue due to SPR weakening by particle aggregate formation. The color of the solution returned to its original red when the pH of the solution was brought back to 6.7. Furthermore, citrate protection of the gold nanoparticles was found to inhibit the reverse action. This reversible/irreversible-selectable structural control of gold nanoparticles with drastic changes in their optical absorption characteristics may find various nanophotonic applications including contactless pH detection.

Advanced Science, …, 2013

A simple approach has been used for the development of antireflective (AR) coating on glass subst... more A simple approach has been used for the development of antireflective (AR) coating on glass substrate. Highly monodispersed and stable silica nanoparticles were synthesized by colloidal route at different concentrations of precursor. The morphology of silica nanoparticles was observed by field emission scanning electron microscopy (FE-SEM). In separate preparations the sizes of the spherical silica nanoparticles was found to be ∼ 100 nm and ∼ 80 nm. Layer-by-Layer (LbL) and time-dependent-deposition (TDD) techniques were used for the formation of antireflection coatings. The antireflection property of the silica nanoparticles coating depends upon number of layers coated and also on deposition time. Such antireflective coatings have useful applications in making windshields, glasses, lenses and solar cells.

This work presents an optical fiber based relative humidity sensor. Highly mono-dispersed and sta... more This work presents an optical fiber based relative humidity sensor. Highly mono-dispersed and stable silica nanoparticles were synthesized by colloidal route. Layer by layer technique has been utilized to create ultrathin films of silica nanoparticles on the optical fiber end. This fabrication technique is a simple method based on the alternative immersion in oppositely charged colloidal solutions. The coated thin film of silica nanoparticles acts as nanometer-scale interferometric cavity. Sensor shows a high sensitivity and fast response towards relative humidity change.

Materials Letters, 2011

The needle-like gold nanostructures were synthesized by using chloroauric acid (HAuCl4) as a meta... more The needle-like gold nanostructures were synthesized by using chloroauric acid (HAuCl4) as a metal precursor and sodium borohydride (NaBH4) as the reducing agent. These needle-like nanostructures of gold were irradiated with high energy electrons (E ~ 6 MeV, ϕ ~ 1012 e cm−2 s−1). The pre- and post-irradiated gold nanostructures were characterized by Scanning Electron Microscopy (SEM), UV–vis spectroscopy, X-ray Diffraction (XRD) and contact angle measurement (GBX-Model Digidrop) techniques. The results of the SEM revealed that after electron irradiation, the needle-like gold structures got fragmented into identical cube-shaped gold nanostructures, though of different sizes. The XRD analysis indicated that the average crystallite size of the gold nanostructures remained unchanged even after irradiation with high energy electrons. A glass surface showed hydrophilic behavior when coated with needle-like nanostructures and became ultra hydrophilic when coated with cube-shaped gold nanostructures.