Venkat R. Bhethanabotla

Surface acoustic wave hydrogen sensor

The present invention provides a delay line SAW device fabricated on a lithium niobate substrate and coated with a bilayer of nanocrystalline or other nanomaterials such as nanoparticles or nanowires of palladiumn and metal free pthalocyanine which will respond to hydrogen gas in near real time, at low (room) temperature, without being affected by CO, O2, CH4 and other gases, in air ambient or controlled ambient, providing sensitivity to low ppm levels.

Thermodynamics of mixtures containing alkoxyethanols. Part XV. DISQUAC characterization of systems of alkoxyethanols with n-alkanes or cyclohexane

Binary mixtures of alkoxyethanols, CH3–(CH2)n–O–(CH2CH2O)mOH, and n-alkanes or cyclohexane are characterized in terms of DISQUAC. The corresponding dispersive (DIS) and quasichemical (QUAC) interchange coefficients, Ceh,lDIS/QUAC, for the (e,h) contacts (type e, –O–; type h, –OH) are given. In comparison with the values for 1-alkanol + monooxalkane systems, the proximity effects in CH3–(CH2)n–O–CH2–CH2–OH + n-alkane mixtures lead to an increase in the Ceh,lDIS and Ceh,lQUAC (l = 1,2) coefficients and to a decrease in Ceh,2DIS. For other hydroxyethers (3-methoxypropanol, 4-methoxybutanol), the Ceh,lQUAC (l = 1,2) coefficients approach those of 1-alkanol + monooxalkane mixtures with increasing separation between the –O– and OH– groups. However, the Ceh,2DIS coefficient is still lower than in alcoholic solutions, indicating that proximity effects in the framework of DISQUAC remain. DISQUAC yields a consistent description of the vapor–liquid equilibria, VLE, and of liquid–liquid equilibria, LLE. Good results are obtained for azeotropic data. The coordinates of the critical points are represented over a reasonable range of composition and temperature. Excess molar enthalpies HmE and the excess molar heat capacity at constant pressure, CpmE, are well reproduced. The typical large deviations for properties at infinite dilution, excess molar partial enthalpies, HmE,∞, and natural logarithms of activity coefficients, ln γi∞, of the associated compound are found. Thermodynamic properties of alkoxyethanol + alkane mixtures are determined by the self-association of the polar compound ia both inter- and intramolecular H-bonds, as well as by dipole–dipole interactions between alkoxyethanol molecules. These interactions are analyzed in terms of the effective dipole moments () and are more important than in 1-alkanol + alkane mixtures. The dipole–dipole interactions in systems with alkoxyethanols decrease along a homologous series, and are enhanced by the presence of two ether atoms. Intramolecular H-bonds are more relevant than the intermolecular H-bonds and become weakened with the separation between the –O– and –OH groups of the hydroxyethers.

Removal of Nonspecifically Bound Proteins on Microarrays Using Surface Acoustic Waves

Nonspecific binding of proteins is an ongoing problem that dramatically reduces the sensitivity and selectivity of biosensors. We demonstrate that ultrasonic waves generated by surface acoustic wave (SAW) devices remove nonspecifically bound proteins from the sensing and nonsensing regions of the microarrays. We demonstrate our approach for controllably and nondestructively cleaning the microarray interface. In this work, SAWs were generated using 128 YX lithium niobate, chosen for its high coupling coefficient and efficient power transfer to mechanical motion. These waves propagating along the surface were coupled into specifically bound and nonspecifically bound proteins on a patterned surface of 40 mum feature size. Fluorescence intensity was used to quantify cleaning efficacy of the microarrays. Our results have shown that excess protein layers and aggregates are removed leaving highly uniform films as evidenced by fluorescence intensity profiles. Selected antigen-receptor interactions remained bound during the acoustic cleaning process when subjected to 11.25 mW of power and retained their efficacy for subsequent antigen capture. Results demonstrate near-complete fluorescence signal recovery for both the sensing and nonsensing regions of the microarrays. Of significance is that our approach can be integrated into existing array technologies where sensing and nonsensing regions are extensively fouled. We believe that this technology will be pivotal in the development and advancement of microsensors and their biological applications.

A comparison of hard-body models for axially-symmetric molecules

Values of the second to the fifth virial coefficient are reported for the gaussian overlap model for hard molecules of spheroidal symmetry. Where possible, these results are compared with those for the corresponding hard ellipsoids. It is found that the two models give nearly identical results. It is suggested that the relative simplicity of the hard gaussian overlap model recommends it for future study.

Silver-copper alloy nanoparticles for metal enhanced luminescence

Large metal enhanced luminescence was realized at the vicinity of easily fabricated Ag–Cu alloy nanoparticles upon tuning of their surface plasmon resonance spectra by changing only one experimental variable—the annealing temperature, for maximum spectral overlap with the emission and excitation spectra of the luminophores. We observed strong emission enhancement of luminophores (141.48±19.20 times for Alexa Fluor 488 and 23.91±12.37 times for Alexa Fluor 594) at the vicinity of these Ag–Cu nanoparticles, which is significantly larger than for pure Ag nanoparticles. We present theoretical calculations to provide insights into these experimental findings.

Vapor-liquid equilibrium data for ethanol-n-heptane-1-propanol and ethanol-n-heptane-2-propanol and their interpretation by a simple association model

Abstract Pradhan, A.G., Bhethanabotla, V.R. and Campbell, S.W. 1993. Vapor-liquid equilibrium data for ethanol-n-heptane- 1-propanol and ethanol-n-heptane-2-propanol and their interpretation by a simple association model. Fluid Phase Equilibria, 84: 183-206. Vapor-liquid equilibrium measurements are reported for ethanol-n-heptane-1-propanol and for ethanol-n-heptane-2-propanol at 303.15 K. The data consist of total pressure as a function of liquid phase composition and were measured in a Van Ness apparatus. Theoretical results presented by Nagata and Ohtsubo (Nagata, I. and Ohtsubo, K., 1986. Thermochim. Acta, 102: 185-205) were used to develop a simple association model applicable to ternary systems which contain two alcohols and a hydrocarbon. In addition to an equilibrium constant for each alcohol, the model requires a single physical parameter for each hydrocarbon-alcohol pair and a cross-association constant for each alcohol-alcohol pair. For binary alcohol-hydrocarbon systems, the model reduces to that of Renon and Prausnitz (Renon, H. and Prausnitz, J.M., 1967. Chem. Eng. Sci., 22: 299-307). The model represents the data reported in this paper, as well as data from the literature, with good accuracy.

Acoustic streaming induced elimination of nonspecifically bound proteins from a surface acoustic wave biosensor: Mechanism prediction using fluid-structure interaction models

Biosensors typically operate in liquid media for detection of biomarkers and suffer from fouling resulting from nonspecific binding of protein molecules to the device surface. In the current work, using a coupled field finite element fluid-structure interaction simulation, we have identified that fluid motion induced by high intensity sound waves, such as those propagating in these sensors, can lead to the efficient removal of the nonspecifically bound proteins thereby eliminating sensor fouling. We present a computational analysis of the acoustic-streaming phenomenon induced biofouling elimination by surface acoustic-waves (SAWs) propagating on a lithium niobate piezoelectric crystal. The transient solutions generated from the developed coupled field fluid solid interaction model are utilized to predict trends in acoustic-streaming induced forces for varying design parameters such as voltage intensity, device frequency, fluid viscosity, and density. We utilize these model predictions to compute the vario...

Bisphosphonate-modified gold nanoparticles: a useful vehicle to study the treatment of osteonecrosis of the femoral head

Legg-Calvé-Perthes disease (LCPD) is a juvenile form of osteonecrosis of the femoral head that presents in children aged 2-14 years. To date, there is no effective medical therapy for treating LCPD largely due to an inability to modulate the repair process, including the predominance of bone resorption. This investigation aims to evaluate the feasibility of using gold nanoparticles (GNPs) that are surface modified with a bisphosphonate compound for the treatment of osteonecrosis at the cellular level. Studies have found osteoclast-mediated resorption to be a process that contributes significantly to the pathogenesis of femoral head deformities arising from Perthes disease. Our in vitro model was designed to elucidate the effect of alendronate-(a bisphosphonate) modified GNPs, on osteoclastogenesis and osteoclast function. RAW 264.7 macrophage cells were cultured with recombinant mouse receptor activator of NF-κB ligand (RANKL), which stimulates osteoclastogenesis, and were then treated with alendronate-modified GNPs for 24, 48, and 72 h. Cell proliferation, osteoclast function, and osteoclast morphology were evaluated by trypan blue dye exclusion assay, tartrate-resistant acid phosphatase (TRAP) staining, and transmission electron microscopy (TEM) imaging. Comparative studies were performed with GNPs that were only stabilized with citrate ions and with alendronate alone. Neither osteoclastogenesis nor osteoclast function were adversely affected by the presence of the citrate-GNP. Alendronate-modified GNPs had an enhanced effect on inducing osteoclast apoptosis and impairing osteoclast function when compared to unbound alendronate populations.

Design of efficient focused surface acoustic wave devices for potential microfluidic applications

Focused interdigital transducers (F-IDTs) patterned on surfaces of piezoelectric substrates can be used to generate surface acoustic waves (SAW) with high intensity and high beam-width compression ratio. A three dimensional coupled field finite element model of a focused SAW (F-SAW) device with interdigital transducers shaped as concentric circular arcs based on a YZ LiNbO3 substrate is developed in this study. This model was utilized to investigate the effect of geometric shape of transducers on the focusing properties of F-IDTs to identify the optimal design for potential microfluidic applications. The transducer design parameters investigated in the current study include number of finger pairs, degree of arc, geometric focal length, and wavelength of F-SAW. The transient response of the device on application of impulse and ac electrical inputs at the transmitting FIDT fingers were utilized to deduce the device frequency response and propagation characteristics of F-SAWs, respectively. The influence of ...

Sorption of benzene, toluene and chloroform by poly(styrene) at 298.15 K and 323.15 K using a quartz crystal balance

An isopiestic apparatus using the quartz crystal balance principle has been constructed for vapor sorption measurements on polymers. Isothermal solubilities of benzene, toluene and chloroform in poly(styrene) were measured in the concentrated polymer regime. Benzene results were obtained at 323.15 K. Toluene and chloroform results were obtained at 298.15 K and at 323.15 K. Solvent activities were represented with a modified Flory-Huggins activity model and compared with available literature data with favorable results. Comparisons were also made with predictions of three free volume activity models described in the literature. Details of the applicability and reliability of the quartz crystal balance for these sorption measurements are considered and discussed.