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Interaction of native ovalbumin (OVA) with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) Langmuir-Blodgett monolayer has been studied at the air-water interface. A compressibility study shows the positive association with DPPC. Adsorption kinetics shows that the protein adsorption is a one-step process and the amount of protein adsorbed depends on the concentration of protein at the water subphase. Incorporation of protein into the DPPC layer is surface-pressure dependent. The compressibility study indicates that the DPPC-OVA interaction is hydrophobic in nature and structural reorganization is eminent to adjust the hydrophobic mismatch between DPPC acyl chains and OVA hydrophobic moieties. At higher pressure, OVA tends to squeeze out from the DPPC monolayer. A nanometer scale FE-SEM image confirms this observation. Globular aggregates of protein of dimension 60-80 nm were observed in DPPC-OVA supported film. Steady-state fluorescence spectroscopy suggests that the tryptophan residues of OVA are main emitting species. The blue shift of tryptophan fluorescence in supported film may be due to the tryptophan molecule of protein exposed to the hydrophobic air phase.

In this article, we report the results of the extent of interaction as well as the formation of a bioconjugate of human hemoglobin (Hb) with silver (Ag). The complexation process and conformational changes are characterized using different spectroscopic and microscopic techniques. The UV-vis study demonstrates the perturbation of the soret/heme band and generates conformational heterogeneity within the heme group in the presence of silver. A fluorescence study suggests that the Tryptophan (Trp) residues of Hb are in a more polar environment after conjugation. Initial fluorescence enhancement with addition of silver is due to metal-enhanced fluorescence. Moreover, the fluorescence quenching after the formation of the Hb-Ag bioconjugate follows the modified Stern-Volmer (S-V) plot. The S-V plot along with the time-resolved fluorescence study indicates the presence of both static and dynamic types of quenching. In addition, the reduction potential values of the entities (Hb-heme, Ag(+), and Trp) indicate the possible electron transfer. The secondary structure calculation from CD and FTIR spectra indicate alpha-helix to beta-sheet conversion, and unfolding of Hb is also responsible for the bioconjugate formation. In addition, FE-SEM, phase contrast inverted microscopy (PCIM) images demonstrate the formation of the silver-protein bioconjugate. The overall data show that there is a change in the secondary as well as the tertiary structure of Hb after conjugation with silver.

A simple and effective stepwise-method has been developed to remove defects from the top graphene layers of highly orientated pyrolytic graphite. Using a combination of ozone exposure and moderately high temperature we have shown that a defect-rich graphite surface can be modified to generate a graphene-like surface containing a negligible amount of oxygen, hydrogen and sp 3 carbon. We report definitive x-ray photoelectron and x-ray absorption spectroscopy analysis after each stage of the process, suggest a mechanism by which the modification occurs and propose it as a route towards the preparation or manipulation of pristine graphene samples.

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The synthesis of some bromine-substituted rhodamine derivatives viz., 4,5-dibromorhodamine methyl ester (dye 2) and 4,5-dibromorhodamine n-butyl ester (dye 3) are reported. These dyes were synthesized to promote a more efficient cancer cell photosensitizer for potential use in in vitro bone marrow purging in preparation for autologous bone marrow transplantation. Spectroscopic and photophysical characterization of these dyes together with rhodamine 123 (dye 1) are reported in water, methanol, ethanol and also in a microheterogeneous system, sodium dodecyl sulfate. The possible mechanism of photosensitization is characterized in terms of singlet oxygen efficiency of these dyes. Singlet oxygen quantum yields for bromine-substituted dyes are in the range of 0.3-0.5 depending on the solvent. For dye 1 no singlet oxygen production is found. The photodynamic actions of these dyes in different cell lines are tested. It was found that dye 2 and dye 3 are efficient photosensitizers and mediate eradication of K562, EM2, myeloid cell lines (CML) and the SMF-AI rhabdomyosarcoma line.

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A simplistic design of a self-powered UV-photodetector device based on hybrid r-GO/GaN is demonstrated.Under zero bias, the fabricated hybrid photodetector shows a photosensivity of ∼ 85% while ohmic contact GaN photodetector with identical device structure exhibits only ∼5.3% photosensivity at 350 nm illumination (18 µW/cm 2 ). The responsivity and detectivity of the hybrid device were found to be 1.54 mA/W and 1.45×10 10 Jones (cm Hz ½ W −1 ), respectively at zero bias with fast response (60 ms), recovery time (267 ms) and excellent repeatability. Power density-dependent responsivity & detectivity revealed ultrasensitive behaviour under low light conditions. The source of observed self-powered effect in hybrid photodetector is attributed to the depletion region formed at the r-GO and GaN quasi-ohmic interface.The tremendous progress in gallium nitride (GaN) based light emitting diodes (LEDs), 1 laser diodes 2 , and other GaN based devices, namely, UV photodetector (PD) has attracted a great deal of interest from research community. 3 Being chemically inert and thermally stable, they are the most suitable for applications such as flame detection, secure space communication and ozone layer monitoring. 4,5 To match the requirements for such applications in remote and extreme environment, it is highly desirable for the UV devices to be ultrasensitive, with fast response and operate in self-powered mode. However, inherent high defect density associated with as-grown epitaxial GaN films limits its performance. 6The various schemes of metal-semiconductor (M-S) interfaces have been used to improve the UV-PDs device performance. The use of two different metal electrodes on n-GaN with modulating Schottky barrier height leads to a fast response speed but limited reverse saturation current density. 7 Earlier study has shown Schottky contact photodiode of Ni/GaN/Au with asymmetric interdigitated finger electrodes having a responsivity of 5 mA/W in self-powered mode at UV illumination. 8 Recently, Sun et al. have reported a high responsivity of 104 mA/W at zero bias voltage of interdigitated Schottky contact photodiode of Ni (80 nm) /GaN/Ti (20 nm) /Al (60 nm) device. 9 On the other hand, the use of highly transparent conductive electrodes (TCE) such as indium-tin-19 W. S. Hummers and R. E. Offeman, J. Am. Chem. Soc. 80, 1339 (1958).