Ashish Aphale

Graphene Oxide as a Quencher for Fluorescent Assay of Amino Acids, Peptides, and Proteins

Understanding the interaction between graphene oxide (GO) and the biomolecules is fundamentally essential, especially for disease- and drug-related peptides and proteins. In this study, GO was found to strongly interact with amino acids (tryptophan and tyrosine), peptides (Alzheimers disease related amyloid beta 1-40 and type 2 diabetes related human islet amyloid polypeptide), and proteins (drug-related bovine and human serum albumin) by fluorescence quenching, indicating GO was a universal quencher for tryptophan or tyrosine related peptides and proteins. The quenching mechanism between GO and tryptophan (Trp) or tyrosine (Tyr) was determined as mainly static quenching, combined with dynamic quenching (Förster resonance energy transfer). Different quenching efficiency between GO and Trp or Tyr at different pHs indicated the importance of electrostatic interaction during quenching. Hydrophobic interaction also participated in quenching, which was proved by the presence of nonionic amphiphilic copolymer Pluronic F127 (PF127) in GO dispersion. The strong hydrophobic interaction between GO and PF127 efficiently blocked the hydrophobic interaction between GO and Trp or Tyr, lowering the quenching efficiency.

Hybrid Electrodes by In-Situ Integration of Graphene and Carbon-Nanotubes in Polypyrrole for Supercapacitors.

Supercapacitors also known as electrochemical capacitors, that store energy via either Faradaic or non-Faradaic processes, have recently grown popularity mainly because they complement, and can even replace, conventional energy storage systems in variety of applications. Supercapacitor performance can be improved significantly by developing new nanocomposite electrodes which utilizes both the energy storage processes simultaneously. Here we report, fabrication of the freestanding hybrid electrodes, by incorporating graphene and carbon nanotubes (CNT) in pyrrole monomer via its in-situ polymerization. At the scan rate of 5 mV s−1, the specific capacitance of the polypyrrole-CNT-graphene (PCG) electrode film was 453 F g−1 with ultrahigh energy and power density of 62.96 W h kg−1 and 566.66 W kg−1 respectively, as shown in the Ragone plot. A nanofibrous membrane was electrospun and effectively used as a separator in the supercapacitor. Four supercapacitors were assembled in series to demonstrate the device performance by lighting a 2.2 V LED.

Structural and band alignment properties of Al2O3 on epitaxial Ge grown on (100), (110), and (111)A GaAs substrates by molecular beam epitaxy

Structural and band alignment properties of atomic layer Al2O3 oxide film deposited on crystallographically oriented epitaxial Ge grown in-situ on (100), (110), and (111)A GaAs substrates using two separate molecular beam epitaxy chambers were investigated using cross-sectional transmission microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). High-resolution triple axis x-ray measurement demonstrated pseudomorphic and high-quality Ge epitaxial layer on crystallographically oriented GaAs substrates. The cross-sectional TEM exhibited a sharp interface between the Ge epilayer and each orientation of the GaAs substrate as well as the Al2O3 film and the Ge epilayer. The extracted valence band offset, ΔEv, values of Al2O3 relative to (100), (110), and (111) Ge orientations using XPS measurement were 3.17 eV, 3.34 eV, and 3.10 eV, respectively. Using XPS data, variations in ΔEv related to the crystallographic orientation were ΔEV(110)Ge>ΔEV(100)Ge≥ΔEV(111)Ge and the conduction band offset, ΔEc, related t...

Interactions between avidin and graphene for development of a biosensing platform

Fundamental understanding of interactions at the interface of biological molecules, such as proteins, and nanomaterials is crucial for developing various biocompatible hybrid materials and biosensing platforms. Biosensors comprising of graphene-based conductive nanomaterials offer the advantage of higher sensitivity and reliable diagnosis mainly due to their superior specific surface area and ballistic conductivity. Furthermore, conductive nanocomposite structures that immobilize proteins can synergize the properties of both transducers and molecular recognition elements improving the performance of the biosensing device. Here we report for the first time, using a combined molecular dynamics simulations and experimental approach, the interactions between avidin and graphene for the development of a sensing platform that can be used for the detection of biological macromolecules such as mismatch repair proteins through biotinylated DNA substrates. We find that the interactive forces between avidin and graphene are mainly hydrophobic, along with some van der Waals, electrostatic and hydrogen bonding interactions. Notably, the structure and function of the avidin molecule are largely preserved after its adsorption on the graphene surface. The MD results agree well with scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) analysis of avidin immobilized on a graphenated polypyrrole (G-PPy) conductive nanocomposite confirming the adsorption of avidin on graphene nanoplatelets as observed from the Fourier-transform infrared spectroscopy (FTIR).

Cathode Degradation From Airborne Contaminants in Solid Oxide Fuel Cells: A Review

Abstract Fundamental understanding of the degradation processes pertinent to solid oxide fuel cell (SOFC) cathodes remains important in order to apply innovative approaches to achieve long-term electrical performance stability and establish long-term systems reliability for mass commercialization. Several processes leading to an increase in the cathode polarization including Nernst and ohmic losses have been identified. The processes include solid-solid and solid-gas interactions among electrochemically active and inactive components of the cell, stack and systems. The cathodic degradation in SOFCs remains most prominent, and the present review focuses on the effects of contaminants present in “real world” air such as H2O, CO2, and trace amounts of SOx on cathode performance. This review also studies the interactions of the cathode with chromium vapor evaporated from high-temperature alloys used in balance of plant components and the interconnect in direct contact with the air flow. Structural and electrochemical degradation mechanisms of the cathode have been discussed, along with novel approaches to mitigate the cathode poisoning.

An experimental modeling of trinomial bioengineering- crp, rDNA, and transporter engineering within single cell factory for maximizing two-phase bioreduction

A carbonyl reductase (cr) gene from Candida glabrata CBS138 has been heterologously expressed in cofactor regenerating E. coli host to convert Ethyl-4-chloro-3-oxobutanoate (COBE) into Ethyl-4-chloro-3-hydroxybutanoate (CHBE). The CR enzyme exhibited marked velocity at substrate concentration as high as 363mM with highest turnover number (112.77±3.95s-1). Solitary recombineering of such catalytic cell reproduced CHBE 161.04g/L per g of dry cell weight (DCW). Introduction of combinatorially engineered crp (crp*, F136I) into this heterologous E. coli host yielded CHBE 477.54g/L/gDCW. Furthermore, using nerolidol as exogenous cell transporter, the CHBE productivity has been towered to 710.88g/L/gDCW. The CHBE production has thus been upscaled to 8-12 times than those reported so far. qRT-PCR studies revealed that both membrane efflux channels such as acrAB as well as ROS scavenger genes such as ahpCF have been activated by engineering crp. Moreover, membrane protecting genes such as manXYZ together with solvent extrusion associated genes such as glpC have been upregulated inside mutant host. Although numerous proteins have been investigated to convert COBE to CHBE; this is the first approach to use engineering triad involving crp engineering, recombinant DNA engineering and transporter engineering together for improving cell performance during two-phase biocatalysis.

Computer assisted detection of liver neoplasm (CADLN)

To date, radiologists evaluate neoplasm images manually. Currently there is wide spread attention for developing image processing modules to detect and measure early stage neoplasm growth in liver. We report the fundamentals associated with the development of a multifunctional image processing algorithm useful to measure early growth of neoplasm and the volume of liver. Using CADLN, a radiologist will be able to compare computer generated volumetric data in serial imaging of the patients over time, that eventually will enable assessing progression or regression of neoplasm growth and help in treatment planning.

Electroactive graphene composite scaffolds for cardiac tissue engineering: Electroactive graphene composite scaffolds for cardiac tissue engineering

Contractile behavior of cardiomyocytes relies on directed signal propagation through the electroconductive networks that exist within the native myocardium. Due to their unique electrical properties, electroactive materials, such as graphene, have recently emerged as promising candidate materials for cardiac tissue engineering applications. In this work, the potential of three-dimensional (3D) nanofibrous graphene and poly(caprolactone) (PCL + G) composite scaffold for cardiac tissue engineering has been explored for the first time. The addition of graphene into PCL led to an increased volume conductivity of scaffolds with an even distribution of graphene particles throughout the matrix. Graphene particles provided local conductive sites within the PCL matrix, which enabled application of external electrical stimulation throughout the scaffold using a custom point stimulation device. When mouse embryonic stem cell derived cardiomyocytes (mES-CM) were seeded on PCL + G scaffolds, cells adhered well, contracted spontaneously, and exhibited classical cardiomyocyte phenotype confirming the biocompatibility of electroactive PCL + G scaffolds. Further functional characterization demonstrated that graphene especially affected Ca2+ handling properties of mES-CM compared to that of cardiomyocytes cultured in 2D culture, highlighting the potential of PCL + G for in vitro cardiac tissue engineering.

Polycaprolactone nanofibrous materials as an efficient dry eye test strip

Dry eye symptoms are moderately common in the general population and are often chronic particularly amongst the older adults above age 65. Dry eye can occur from conditions such as aging, dehydration, corneal ulcers and associated infections, vitamin A deficiency or as a temporary or permanent side effect of laser treatment. Some of the tests available to identify a tear deficient eye are Schirmer strip test, strip Meniscometry and phenol red thread test, the most popular being the Schirmers test, where a patient is tested positive for a dry eye if the test strip is wet for less than 5mm of length over a period of 5 minutes and negative for wetting of at least 10mm within 5minutes. Here we report a simple design and fabrication of an efficient dry eye test strip using a laboratory developed metal rotating collector for electrospinning setup that aligns nanofibers of Polycaprolactone (PCL), a biosafe and biodegradable polymer. Electrospun PCL nanofibers have diameters in the range of 70 - 150nm depending upon the protocol creating either aligned or randomly oriented nanofibers. It was found that both random and aligned PCL nanofibers test strips show fast wetting time of 5 seconds for covering the same distance of 10mm that a conventional test strip covers in 5 minutes making our product approximately sixty times faster and exhibiting high throughput. We believe that this is because of higher capillary transport and better wetting of the nanofibers. It is further demonstrated that the concentration of PCL plays a crucial role in the formation of the nanofibers and hence the wetting phenomena.