Sundar Babu

Contactless Tip‐Selective Electrodeposition of Palladium onto Carbon Nanotubes and Nanofibers

Abstract Palladium was electrodeposited onto the tips of isolated carbon nanofibers and carbon nanopipes using an electric field. The amount of Pd deposited on the tips was controlled by varying the field application time. The morphology obtained varied from agglomerate of small particles that just covers the end of the nanotube to large ramified deposits that grow off the tip of the nanotube. The influence of the orientation of the carbon nanostructures with respect to the applied electric field and the quantity of the metal deposited is discussed. Electron microscopy was used to characterize the morphology and location of the deposits.

Pulsed Bipolar Electrodeposition of Palladium onto Graphite Powder

The pulsed bipolar electrodeposition of palladium onto 1-2 μm graphite particles was investigated. The amount of palladium deposited was strongly correlated with field intensity, showing an abrupt increase at 2-3 kV/cm. The electrodeposition was successful for frequencies ranging from 500 Hz to 20 kHz, and the amount of deposited palladium was independent of the frequency used. These results demonstrate that the preparation of bipolar electrodeposited catalysts can be achieved within a very large frequency window. Palladium surface area measurements indicate an increase in dispersion with increasing frequency. Sonication of the graphite prior to deposition leads to significantly greater palladium dispersion. Electron microscopy characterization reveals three types of growth: surface-bound, ramified, and amorphous. The surface-bound growth appears as spherical deposits on the order of 5 nm in both dc and pulsed-field experiments. The ramified deposits consist of interconnected 25-50 nm diam spherical structures extending from the graphite particles and appear in the samples prepared at all studied frequencies.

A study of spatially coupled bipolar electrochemistry on the sub-micrometer scale: colloidal particles on surfaces and cylinders in nuclear-track etched membranes

In the present study we explore the feasibility of applying spatially coupled bipolar electrochemistry to the sub-micrometer regime. This is a technique where electrically isolated objects can be interconnected by the application of electric fields and has previously been demonstrated on the millimeter and micrometer scales. Three experimental designs were explored: annealed Au and Ag films on glass, annealed Ag films on silicon nitride membranes and Ag tubes immobilized within polycarbonate nuclear-track etched membranes. In the evaporated and annealed film part of this study, particles on the order of 20–50 nm were exposed to electric fields up to 2 kV cm − 1 for periods up to 180 s, in a mixture of toluene and acetonitrile. Plasmon resonance measurements and scanning electron microscopy (SEM) were used to characterize the changes following field application. At all field intensities and times studied, the gold particle sub-monolayers did not appear to be discernibly affected. The plasmon resonance absorption of the silver sub-monolayers displayed significant peak broadening after field application. Further experiments using transmission electron microscopy (TEM) analysis of annealed silver films on silicon nitride membranes demonstrated particle agglomeration without evidence for particle interconnection or morphological change. This result suggests that, under these experimental conditions, physical movement of the Ag particles occurs instead of electrochemical processes. In order to prevent particle movement, polycarbonate membranes were used to anchor silver cylinders with diameters of 1 m, 400nm and 200 nm. Results from these experiments demonstrated that for Ag in 1:1 toluene–acetonitrile, spatially coupled bipolar electrochemistry (SCBE) reaches a practical limit for structures between 200 and 400 nm since the width of the deposit approaches the size of the metal particles. At 200 nm the result is electrochemical migration of the particles, where a commensurate amount of Ag is deposited on one side and dissolved on the other. This size limitation is specific only to SCBE, where structures are required to electro-dissolve, not to the application of bipolar electrochemistry to structures below 200 nm.

A PMMA microcapillary quantum dot linked immunosorbent assay (QLISA)

The development of a simple and inexpensive quantum dot based immunoassay for detecting myeloperoxidase (MPO) in stool samples is reported (QLISA). The method developed utilizes readily available polymethylmethacrylate (PMMA) microcapillaries as substrates for performing the sandwich assay. High power (80 mW) and low power (10 mW) UV-LEDs were tested for their efficiency in maximizing detection sensitivity in a waveguide illumination or a side illumination mode. The results obtained indicate that both waveguide and side illumination modes can be employed for detecting MPO down to 15 ng/mL, however the high power LED in a side illumination mode improves sensitivity and simplifies the data acquisition process. The protocol and sensor robustness was evaluated with animal stool samples spiked with MPO and the results indicate that the sensitivity of detection is not compromised when used in stool samples. The effect of the ionic strength of the environment on the fluorescence stability of quantum dots was evaluated and found to affect the assay only if long imaging times are employed. Replacing the buffer with glycerol during imaging increased the fluorescence intensity of quantum dots while significantly minimized the loss in intensity even after 2h.

Effect of size at the nanoscale and bilayer rigidity on skin diffusion of liposomes

This study reports the effect of liposome particle size at the nanoscale and bilayer deformability on the permeation through MatTek human skin equivalents and provides a comparative quantitative measure through calculation of diffusion coefficients. Exploring DOPC and DPPC fluorescent liposomes, our results demonstrate the faster diffusion of 50 nm liposomes compared with 100 and 200 nm liposomes when the lipid bilayer remains the same. Diffusion kinetics of the 50 nm particles appear not to depend on the rigidity of the lipid layer, whereas diffusion of particles larger than 100 nm is significantly affected by the rigidity of the bilayer, and DOPC liposomes diffuse faster than their DDPC equivalents. Our results suggest that liposomes composed of a rigid bilayer can be expected to remain intact after passing through the stratum corneum.

An educational package for environmentally friendly, economic operation of power systems

This paper presents a Windows™-based educational package developed by the authors to provide power systems students with basic training on the environmentally friendly, economic operation of power systems. The suitability of the package has been demonstrated here with the help of a six-generator thermal power system.

Identification of binding interactions between myeloperoxidase and its antibody using SERS

Surface Enhanced Raman Spectroscopy (SERS) is a widely used spectroscopic method that can dramatically increase the sensitivity of Raman spectroscopy and has demonstrated significant benefit in the identification of biological molecules. We report the use of SERS in differentiating the bound immunocomplex of myeloperoxidase (MPO) and its antibody from the unbound complex and its individual components. The SERS signal was enabled by gold nanoparticles attached to MPO, pAb and their immunocomplex at an excitation wavelength of 785 nm. The obtained SERS spectrum of MPO is in agreement with previous literature. Comparative SERS spectrum analysis of MPO, pAb, and their immunocomplex reveals the significant peak shifts and intensity variations caused by the conformational changes due to the immunocomplex formation. Several key areas have been identified which correspond to specific amino acids being shielded from undergoing resonance while new amino acid residues are made visible in the SERS spectrum of the immunocomplex and could be a result of conformational binding. Our work demonstrates the capability of SERS to identify binding events and differentiate an immunocomplex from its unbound components with direct applications in biosensors.

SERS study on myeloperoxidase and its immunocomplex: Identification of binding interactions

Surface Enhanced Raman Spectroscopy (SERS) has demonstrated significant benefit in the identification of biological molecules. In this paper we have examined how to identify and differentiate the 150 kDa protein myeloperoxidase (MPO) from its corresponding antibody (Ab) and their immunocomplex through the use of SERS. The SERS signal of these biological molecules was enabled by 40 nm gold nanoparticles. The SERS spectra for both MPO and the Ab (an IgG molecule) demonstrated results consistent with previous published work on the Raman spectra of MPO and IgG antibodies. The immunocomplex SERS spectra showed peak shifts and intensity variations that could be attributed to conformational changes that occur during immunocomplex formation. Several key spectral areas have been identified which correspond to specific amino acids being shielded from undergoing resonance while new amino acid residues are made visible in the SERS spectrum of the immunocomplex and could be a result of conformational binding. These results indicate that SERS can be used to identify binding events and distinguish an immunocomplex from its individual components.