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Arun Chattopadhyay

Publications and source records attributed to Arun Chattopadhyay.

13 recordsLinked to original sources
PubMed2006

Electrochemical actuation of growing copper dendrimers in water.

We report the observation of electrochemical actuation in growing dendritic fibers made of self-assembled copper nanostructures (of 100 nm or less in diameter), on the metallic cathode of an ordinary aqueous electrochemical cell. This could be achieved when a copper anode and another metal cathode is placed in aqueous solution of either dilute HCl or CuSO(4), or CuCl(2), or H(2)O, and upon application of a DC voltage in the range of 1.5-12.0 V. The actuation could be observed with an on-off cycle of the applied voltage in the above range. The phenomenon was also observed with the growth of bimetallic structures using a number of electrolytes such as Ag(NO(3)), Pb(NO(3))(2), CoCl(2), NiCl(2), CdCl(2), ZnCl(2), and HAuCl(4). The fibrous structures remained stretched as they grew longer with time in the presence of an applied voltage. The extent of actuation was dependent on the applied voltage, the concentration of Cu(2+) ions in the solution, and also on ions such as Na(+), which did not get deposited at the cathode. The observed phenomena under different conditions have been explained on the basis of electrocapillarity.

Journal Article↗
PubMed2006

Green fluorescent protein-expressing Escherichia coli as a model system for investigating the antimicrobial activities of silver nanoparticles.

Recombinant Escherichia coli (E. coli) bacteria expressing green fluorescent protein (GFP) was used as a model system to investigate the antimicrobial activities of Ag nanoparticles (NPs). A convenient in situ method of Ag NP synthesis using sodium borohydride, in the bacterial growth medium, was developed to produce preformed NPs for the study. Fluorescence spectroscopic and microscopic techniques allowed rapid detection of time-dependent changes in bacterial growth as well as fluorescence characteristics in the presence of Ag NPs. In addition, X-ray diffraction, UV-vis spectroscopic, and transmission electron microscopic measurements were carried out to understand the effect of Ag NPs on the bacteria. Our observations indicated that Ag NPs, above a certain concentration, not only were bactericidal but also were found to reduce the sizes of treated bacteria in comparison to untreated ones. Cell lysis of Ag NP-treated bacteria was suggested by the increased GFP fluorescence obtained in the medium. In vitro DNA-Ag NP interaction was detected by spectrophotometric analysis. However, electrophoresis studies indicated no direct effect of Ag NPs on DNA or protein profiles.

Anti-Bacterial Agents↗
PubMed2006

Lithography for imprinting colored patterns with quantum dots.

In this article, we report a new form of lithography that involves a reaction between a gas and an ion embedded in a polymer film. The principle is based on a combination of top-down and bottom-up approaches in which a transmission electron microscope grid is placed on a poly(vinylpyrrolidone) film containing Cd2+ ions, which is then exposed to H2S gas. This leads to the generation of a fluorescent yellow pattern due to the formation of CdS nanoparticles on exposed parts of the film. Also, we have used the same method to generate patterns in two colors by starting with a green fluorescent dye incorporated into the film and following the same procedure in which patterned yellow-orange CdS nanoaparticles are distributed over the background fluorescence of the dye. We have used fluorescence microscopy, UV-vis and fluorescence spectroscopy, transmission electron microscopy, atomic force microscopy, and X-ray diffraction methods for the characterization of the products and patterns. This method could possibly be a fairly general method of generating patterned materials on 2D and 3D substrates.

Journal Article↗
PubMed2005

Solid-state storage of Ag nanoparticles in anion exchange resin beads and their recovery.

This paper reports the idea and describes a method of reversible storage and recovery of silver nanoparticles (NPs) in anion exchange resin beads based on the principle of ion exchange. We also report that similar exchange of NPs was not possible with cation exchange resins. The Ag NPs were stored by simple exchange of anions of the resins, which were activated with OH- and NO3- ions. FTIR spectroscopic measurements support that the Ag NPs were exchanged with NO3- ions in the resins. The so-stored NPs could be regenerated by addition of NaBH4 solution to the resins. These NPs were recovered and subsequently utilized for catalytic reduction of an organic dye (eosin). Powder X-ray diffraction (XRD) pattern indicated storage of the NPs in the form of various oxides of silver in the resin, with the peak value of intensity corresponding to XRD of the NPs not changing with time. Scanning electron microscopic measurements show that the NPs in the beads were stable for over a month without the formation of any apparent agglomeration.

Journal Article↗
PubMed2005

Photocatalytic polypyrrole-TiO2-nanoparticles composite thin film generated at the air-water interface.

Herein, we report a new method of generation of TiO(2) nanoparticles (NPs) incorporated thin films of polypyrrole (PPy) at the air-water interface. Aqueous TiO(2) NPs when treated with H(2)O(2) and left in a chamber of pyrrole vapor resulted in the formation of a film at the interface, in addition to bulk precipitate. Spectroscopic, X-ray diffraction, and electron microscopic measurements establish the formation of a thin film of PPy with the incorporation of TiO(2) NPs. The TiO(2)-containing PPy films when transferred onto glass substrates were able to photo catalyze the decomposition of aqueous organic dyes: methyl orange and methylene blue. Further, these films could also photo catalyze the oxidation of iodide to triiodide ions in aqueous potassium iodide solution. We find that the PPy-TiO(2) composite films catalyze the reactions in the presence of light more efficiently than a suspension of TiO(2) NPs.

Journal Article↗
PubMed2005

A polyaniline-containing filter paper that acts as a sensor, acid, base, and endpoint indicator and also filters acids and bases.

In this paper we report a new idea for synthesizing polyaniline in an ordinary filter paper. The synthesis was carried out by a process in which aqueous acidic aniline solution and the oxidizing agent H(2)O(2) was added to the paper drop by drop and in sequence. Uniform polymerization could be obtained with the addition of reagents in either sequence. The polymer formation led to a green coloration of the paper. Formation of the emeraldine salt of polyaniline was confirmed by UV-vis and FTIR spectroscopy. Scanning electron microscopic measurements were made for surface characterization of the polymer formed in the paper. The same paper was used as a sensor for ammonia in vapor and in solution, for acid and base as well as endpoint indication, and also to filter acids and bases. We found that, using the polymer-containing paper, ammonia concentrations in a solution as low as 14 ppm could be measured.

Journal Article↗
PubMed2005

Au nanoparticles and polyaniline coated resin beads for simultaneous catalytic oxidation of glucose and colorimetric detection of the product.

In this letter, we report the synthesis of Au nanoparticles (NPs) and polyaniline (PANI) on the same cation-exchange resin beads and demonstrate their use in catalyzing the oxidation of glucose to gluconic acid by Au NPs and simultaneously in detecting the formation of the acid by the color change of PANI. The synthesis was carried out by exchanging the cations of the resins with HAuCl4 and anilinuium chloride and then reducing the metal ions by NaBH4 to produce Au NPs followed by polymerization of aniline using H2O2. The green emeraldine salt form of PANI thus obtained was treated with NaOH to be converted to blue emeraldine base before use. The deposition of Au NPs was confirmed by a change in color of the bead, visible spectroscopy, X-ray diffraction, and scanning electron microscopic measurements. On the other hand, the presence of PANI was confirmed by Fourier transform infrared (FTIR) and ultraviolet-visible (UV-vis) spectroscopy. The formation of gluconic acid from glucose was confirmed by FTIR spectroscopy. We could detect the presence of glucose of a minimum 1.0 mM concentration in water, using the present method. Our experimental observations demonstrate the possibility of the incorporation of multifunctional components on the surfaces of resins for carrying out a chemical reaction as well as detection of the product.

Aniline Compounds↗
PubMed2004

Reversible encapsulation of nanometer-size polyaniline and polyaniline-Au-nanoparticle composite in starch.

In this paper we report a new method of solubilization of polyaniline and polyaniline-Au-nanoparticle composite by encapsulating nanometer-size particles in starch. The solubilization was carried out in the presence of ultrasonic waves. We also report that the encapsulation was completely reversible and the dissolved polyaniline as well as the composite could be recovered by replacement with molecular iodine. In addition, the polymer particles could also replace molecular iodine from starch-iodine complex. UV-Visible and Fourier transform infrared (FTIR) spectroscopic measurements established the reversible nature of encapsulation. Transmission electron microscopic measurements showed that the sizes of the particles encapsulated in starch were on the order of 10-20 nm for both polyaniline and Au-nanoparticle-polyaniline composite particles. X-ray diffraction evidenced the presence ofAu-nanoparticles in the starch-polyaniline-Au-nanoparticle composite. Finally, we also mention here that the dissolved polyaniline could also be recovered as a precipitate by enzyme (diastage) hydrolysis of the polyaniline encapsulating starch.

Aniline Compounds↗
PubMed2004

Starch-mediated shape-selective synthesis of Au nanoparticles with tunable longitudinal plasmon resonance.

We report the synthesis ofAu nanoparticles, with tunable longitudinal plasmon band and shape selectivity, mediated by starch in the presence of ultrasonic waves. The synthesis was carried out by reduction of HAuCl4, at various concentrations, using H2O2 as the reducing agent. When the reactions were carried out in the absence of ultrasonic waves, there was no occurrence of the longitudinal resonance band, while the transverse plasmon resonance band shifted toward a higher wavelength. Transmission electron microscopic measurements revealed an increase in particle sizes with increasing higher initial HAuCl4 concentration. On the other hand, in the presence of ultrasonic waves, as the initial concentration of HAuCl4 was increased, while the transverse plasmon resonance band remained the same, the longitudinal plasmon resonance band increasingly shifted toward a higher wavelength. Transmission electron microscopic measurements revealed the change in shape from spherical to triangular to hexagonal particles with increasing initial HAuC14 concentration. We also report that the starch-stabilized nanoparticles could be precipitated from the solution by a starch digesting enzyme which also binds with the particles resulting in its precipitation.

Chemical Precipitation↗
PubMed2004

Spreading and recoil of a surfactant-containing water drop on glass-supported alcohol films.

In this paper we report the experimental observation of spreading and recoil of surfactant-containing water drops on various alcohol films supported on glass slides. The time evolution of spreading and recoil behavior was recorded by placing a web camera above the drop. We observed that the drop spread the fastest on CH3OH, followed by C2H5OH, and the slowest on i-PrOH. On the other hand, the recoil behavior was just the opposite. The drop recoiled the slowest on CH3OH and fastest on i-PrOH, while it recoiled in an intermediate time on C2H5OH. In addition, concentration of surfactant in the drop played a prominent role in the spreading and recoil time of the drop, with higher surfactant concentration making the drop spread and recoil faster. The time evolution of spreading velocity of the drop on different alcohol films at various surfactant concentrations occurred with a Gaussian distribution and the peak velocity was reached earliest on CH3OH followed by C2H5OH, while on i-PrOH it took the longest time. The recoil behavior was similar. The variation of velocity as a function of radius exhibited oscillatory behavior, indicating the existence of an interfacial phenomenon. We also report the observation that spreading of the drop occurred without observable fingering instability. Further, we observed by Fourier transform infrared (FTIR) spectroscopic measurements that the drop had mixed with the alcohol films as it spread. Miscibility of the alcohol in the film with the drop, alcohol evaporation cooling-induced temperature gradient, and Marangoni effect probably play important roles in the spreading and recoil behavior of the drop.

Journal Article↗
PubMed2003

Macroscopic and mesoscopic patterns observed in thin films formed due to polymerization of aniline at the air-water interface.

We report two-dimensional mesoscopic and macroscopic patterns observed in thin films formed due to polymerization of aniline at the air-water interface. The polymerization at the interface was coupled to a reaction in the bulk medium that was either an iron (ferroin)-catalyzed Belousov-Zhabotinsky (BZ) reaction or another reaction condition where the ferroin component of BZ reaction was replaced by FeSO(4) or Mohr's salt [(NH(4))(2)SO(4).FeSO(4).6H(2)O]. Also, a simple mixture of KBrO(3) and KBr in aqueous acidic solution produced patterned polymers at the interface, observed with aniline introduced from both the vapor phase and the bulk phase (by dissolving in H(2)SO(4)). Observation under an optical microscope revealed that the macroscopic patterns consisted of mesoscopic patterns of various geometrical shapes. In one case, regular circular mesoscopic patterned polymer growth was observed when the reaction was carried out in the presence of 2.02 mM sodium dodecyl sulfate. On the other hand, when the film was grown in an ultrasonicator bath there were no observable mesoscopic or macroscopic patterns in the film.

Journal Article↗
PubMed2003

Fabrication of submicron scale patterned plastic thin film fluidic devices with controllable thickness.

We present a soft-lithography based method to fabricate plastic thin film fluidic devices on glass and plastic substrates. Principles of soft-lithography and spin casting were used to generate the films. The thickness of these films is controllable and the patterns we have generated have submicron scale dimensions. By using commercially available compact disc (CD) components as molds, we have been able to generate parallel line and cross patterns on these thin films. These patterned films could be lifted from the substrates and further folded into rolls.

Glass↗