Lalit M. Bharadwaj

Comparative study of carbon nanotube dispersion using surfactants.

Dispersion of carbon nanotubes (CNTs) is a challenging task for their utilization in nanoscale device applications. This account reports a comparative analysis on dispersion of multiwalled carbon nanotubes (MWNTs) with four surfactants-Triton X-100, Tween 20, Tween 80, and sodium dodecyl sulfate (SDS). Among the four surfactants, Triton X-100 and SDS provide maximum and minimum dispersion, respectively. Dispersion of MWNTs has been characterized with UV-vis spectroscopy and transmission electron microscopy (TEM). TEM results are in agreement with the UV-vis measurements. The experimentally observed trend of dispersing power of surfactants is consistent with their chemical structures. An optimum CNT-to-surfactant ratio has been determined for each surfactant. This parameter is shown to affect the nanotube dispersion significantly. Surfactant concentration above or below this ratio is shown to deteriorate the quality of nanotube dispersion. TEM analysis of a high-surfactant-concentration sample enables us to construct a plausible mechanism for decrease in CNT dispersion at high surfactant concentration, consistent with the UV-vis observations. Temperature stability of the surfactant is another important factor affecting the quality of CNT dispersion.

Damaged carbon nanotubes get healed by ion irradiation

Carbon nanotubes (CNTs) are being used for varied applications. It is therefore important to study their stability under extreme conditions of temperature and irradiation. In this work, we report the stability of CNTs [both single-wall CNTs (SWCNTs) and multiwalled CNTs (MWCNTs)] under irradiation of a carbon ion beam of energy 55 MeV. The irradiated samples were analyzed using Raman spectroscopy. The Raman results indicate the interesting phenomenon of healing or annealing of CNTs under ion beam irradiation. The annealing process appears to begin at the lowest value of fluences and persists for quite a good range of fluence values. As the irradiation dose increases (≈1×1014 ions/cm2) the MWCNTs begin to amorphize whereas the SWCNTs system continues to heal.

Immobilization of enzyme on long period grating fibers for sensitive glucose detection.

Glucose oxidase (GOD) immobilized long period grating (LPG) fibers have been proposed for the specific and sensitive detection of glucose. The treatment of LPG fibers with aminopropyl triethoxysilane has induced biding sites for the subsequent GOD immobilization. Field emission scanning electron microscopy, confocal laser scanning microscopy, infrared spectroscopy and Raman spectroscopy have provided detailed evidences about the effectiveness of the adopted biofunctionalization methodology. The enzyme activity is conserved during the immobilization step. Fabricated LPG sensor was tested on different glucose solutions to record the transmission spectra on an optical spectrum analyzer. The wavelength shifts in the transmission spectra are linearly correlated with the glucose concentration in the range of 10-300 mg dL(-1). The fabricated sensor gives fast response and is demonstrated to be of practical utility by determining glucose contents in blood samples. Proposed technique can further be extended to develop LPG fiber based novel, sensitive and label free nanosensors for disease diagnosis and clinical analysis.

Synthesis and conjugation of ZnO nanoparticles with bovine serum albumin for biological applications

Semiconductor nanomaterials tagged with biomarkers may be used for an early fluorescence-based detection of breast cancer. ZnO nanoparticles are water-soluble, non-toxic, photo-chemically stable with highly fluorescence applicability and are regarded for their possible biocompatibility. As a long-term research planning, we are aiming to use QDs conjugated with serum-biomarker for the diagnosis of breast cancer. The present work is a part in the said direction and reports preliminary observations on the synthesis and conjugation of ZnO nanoparticles with a representative protein marker.

Recovery of Pure ZnO Nanoparticles from Spent Zn-Mno2 Alkaline Batteries

The recovery of pure ZnO (zinc oxide) nanoparticles from spent Zn-Mn dry alkaline batteries is reported. Spent batteries were dismantled to separate the contained valuable metals of the cell electrodes in the form of black powder. Treatment of this black powder with 5 mol L(-1) HCl produced leach liquor, primarily containing 2.90 g L(-1) Zn and 2.02 g L(-1) Mn. Selective and quantitative liquid-liquid extraction of Zn(II) was then carried out in three counter current steps by using Cyanex 923 (0.10 mol L(-1) in n-hexane). Zn(II) distributed in the organic phase as complex ZnCl(2)·2R (R = Cyanex 923 molecule). The metal loaded organic phase was subjected to combust at 600 °C to yield pure ZnO nanoparticles (40-50 nm). Important characteristics of the synthesized nanoparticles were investigated by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction spectroscopy (XRD), and atomic force microscopy (AFM).

Covalent attachment of actin filaments to Tween 80 coated polystyrene beads for cargo transportation

In this manuscript, a new strategy has been reported for circumscribed covalent attachment of barbed and pointed ends of actin filaments to polystyrene beads. A comparative study of attachment of actin filaments to polystyrene beads was performed by blocking functionally active sites on polystyrene beads with nonionic detergents such as Tween 20, Tween 80 and polyethylene glycol (PEG). Effective blocking of active sites was obtained with Tween 80 at 0.1% concentration. Attachment of single bundle of actin filament to bead was assessed by rotational motion of bead tailed actin in front and lateral view. Velocity of actin filaments attached to different size of beads in in-vitro motility assay was calculated to ascertain their attachments. Velocity of actin attached to 1.0 and 3.0 microm polystyrene beads was reduced to 3.0-4.0 and 0.0-1.0 microm/s, respectively as compared to free actin velocity of 4.0-6.0 microm/s. Single point attachment of actin filaments to different size of beads was assessed by decrease in sliding velocity. Present study provides insight into the actin-myosin based molecular motor systems for drug delivery and biosensors applications.

Controlling the density and site of attachment of gold nanoparticles onto the surface of carbon nanotubes

A facile method for controlling the density and site of attachment of gold nanoparticles onto the surface of carbon nanotubes is demonstrated. Nitric acid based oxidation was carried out to create carboxylic groups exclusively at the ends of carbon nanotubes, whereas oxidation using a mixture of nitric and sulfuric acid with varied reaction time was carried out to control the population of carboxylic groups on the side walls of nanotubes. In turn, 4-aminothiophenol modified gold nanoparticles were covalently interfaced to these carboxylated multi-walled carbon nanotubes in the presence of a zero length cross-linker, 1-ethylene-3-(3-dimethylaminopropyl) carbodiimide. Raman spectroscopic results showed increase in height of disorder band with each of these successive steps, indicating the increase in degree of functionalization of the carbon nanotubes. Fourier transformed infrared spectroscopic analysis affirmed the functionalization of nanostructures and the formation of nanohybrid. Transmission electron and field emission scanning electron microscopic analysis ascertained the attachment of gold nanoparticles to the ends and side walls of the multi-walled carbon nanotubes. The new hybrid nanostructures may find applications in electronic, optoelectronic, and sensing devices.

Bioconjugation of InGaP quantum dots for molecular sensing.

Fluorescence-based molecular sensing and cellular imaging are commonly carried out with the application of organic dyes. Quantum dots (QDs) are now recognized as better tools because they are brighter, size tunable, and more photostable than dyes. Most of the proposed QD-based biosensing systems involve elements of known toxicity. The present work reports the functionalization of biocompatible InGaP/ZnS core-shell QDs with anti-bovine serum albumin (anti-BSA) to exploit them as fluorescent probes for antigen detection. Successful bioconjugation was characterized with the absorption and emission spectra showing blue shifts of around 40 and 30 nm, respectively. Gel electrophoresis and particle size distribution studies further confirmed the mass increment of QDs after their functionalization with anti-BSA. Surface plasmon resonance spectrometry has been used to study the affinity of QD-(anti-BSA) probes for bovine serum albumin (BSA). Photoluminescence quenching of the developed probe is observed in the presence of BSA.

Doped Zinc-Organic Framework for Sensing of Pesticide

Basolite Z-1200 is one of the most popular commercially available MOF for the gas storage applications. Pristine Basolite Z-1200 is an electrically non-conducting material. This research focuses to tap the potential of Basolite Z-1200’s unique porous structure for the adsorption and sensing of a pesticide. For this, the above said MOF has been treated with mineral acids (HCl) to make it electrically active. The protonated MOF solutions have been used to form conducting thin films on glass slides. Electrical measurements have indicated that the proton doping reduces the overall resistance of the MOF. Prepared thin films have been used to sense Mecoprop some in sample solutions. Conducting MOF thin films may find applications in environmental sensors, pre-concentration, solid phase extraction, electronic devices etc.

Magnetic field-guided orientation of carbon nanotubes through their conjugation with magnetic nanoparticles

Low intensity magnetic fields (22mT) rendered by a pair of bar magnets have been used to achieve in situ precise orientation of multiwalled carbon nanotubes (MWCNTs) and their directional deposition on solid substrates. The nanotubes were imparted magnetic characteristics through Fe3O4 (magnetite) nanoparticles covalently attached to their surface. The side walls of nanotubes were first acid oxidized with H2SO4/HNO3 (3:1 v/v) mixture and amine-functionalized magnetic nanoparticles were then interfaced to ends and side walls of the nanotubes through covalent linkages in the presence of a zero length cross linker, 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide. Fourier transformed infrared spectroscopic investigations affirmed the functionalization of nanostructures and formation of a magnetic nanohybrid. Transmission electron microscopy results revealed the attachment of nanoparticles along the side walls of MWCNTs. A flow cell was utilized to orient magnetic nanohybrid in the desired direction and also to create thin films of aligned MWCNTs. Further, directional assembly of magnetic MWCNTs at different orientation angles on solid substrates was studied by field emission scanning electron microscopy and optical microscopy. The procedure can be scaled to align CNTs on large surface areas for numerous applications, e.g., nanosensors, field emitters, and composites.