Gold nanoparticles decorated 2D-WSe2 as a SERS substrate.

Developing well-defined surface enhanced Raman scattering (SERS)-active substrates with superior performance is potentially attractive for many areas of research such as new generation sensing and analysis. Here, a nanohybrid SERS platform has been developed by decorating two-dimensional (2D) tungsten diselenide (WSe2) flakes with zero-dimensional (0D) plasmonic gold nanoparticles (Au NPs). The morphology studies showed that under optimal conditions densely populated Au NPs were formed on the WSe2 surface. Here, we report the utility of the Au NPs/WSe2 nanohybrid structure as an efficient SERS substrate by performing concentration-dependent SERS measurements of a highly fluorescent molecule (Rhodamine 6G, R6G). The hybrid substrate displays promising SERS activity with the detection limit as low as 1 × 10-9 M, which is several orders of magnitude higher than the bare WSe2 on its own (10-3 M). The substrate also exhibits reliable signal stability and reproducibility. These results indicate that the nanohybrid structure has great potential in SERS applications.

Anodic Oxidation of Butan-1-ol on Reduced Graphene Oxide-Supported Pd-Ag Nanoalloy for Fuel Cell Application.

Reduced graphene oxide (RGO)-supported bimetallic Pd x Ag y alloy nanoparticles of various compositions were synthesized by one-pot coreduction of respective precursors with hydrazine for use in the anode catalysis of oxidation of butan-1-ol in alkali. The as-synthesized catalyst materials were characterized by microscopic, spectroscopic, and diffraction techniques. Cyclic voltammetry (CV), chronoamperometry, and polarization studies infer that a few Pd x Ag y materials exhibit an enhanced and synergistic catalytic activity in reference to Pd and Ag nanomaterials. Among the various RGO composites of Pd x Ag y alloy on graphite support, the one containing the Pd70Ag30@RGO composite is the best in catalytic activity. The cycle life of the catalyst is found to be very high, and PdO and Ag2O are found to be generated in the catalyst material with little change in the catalytic capability during the 100th cycle of CV operation. The addition of Ag upto 30 atom % in the Pd x Ag y alloy causes greater formation of butyraldehyde and butyl butanoate among the various products. Larger atom % of Pd helps to form sodium butyrate and sodium carbonate, as evident from the ex situ Fourier transform infrared and high-performance liquid chromatography study of the product mixtures and the separate CV studies of the intermediate products. A suitable mechanism is also proposed to fit the findings.

Engineering of Gadolinium-Decorated Graphene Oxide Nanosheets for Multimodal Bioimaging and Drug Delivery.

Engineering of water-dispersible Gd3+ ions-decorated reduced graphene oxide (Gd-rGO) nanosheets (NSs) has been performed. The multifunctional capability of the sample was studied as a novel contrast agent for swept source optical coherence tomography and magnetic resonance imaging, and also as an efficient drug-delivery nanovehicle. The synthesized samples were fabricated in a chemically stable condition, and efforts have been put toward improving its biocompatibility by functionalizing with carbohydrates molecules. Gd incorporation in rGO matrix enhanced the fluorouracil (5-FU) drug loading capacity by 34%. The release of the drug was ∼92% within 72 h. Gd-rGO nanosheets showed significant contrast in comparison to optically responsive bare GO for swept source optical coherence tomography. The longitudinal relaxivity rate (r 1) of 16.85 mM-1 s-1 for Gd-rGO was recorded, which was 4 times larger than that of the commercially used clinical contrast agent Magnevist (4 mM-1 s-1) at a magnetic field strength of 1.5 T.

Magnetic, Pseudocapacitive, and H2O2-Electrosensing Properties of Self-Assembled Superparamagnetic Co0.3Zn0.7Fe2O4 with Enhanced Saturation Magnetization.

The present work explores the structural, microstructural, optical, magnetic, and hyperfine properties of Co0.3Zn0.7Fe2O4 microspheres, which have been synthesized by a novel template-free solvothermal method. Powder X-ray diffraction, electron microscopic, and Fourier transform infrared spectroscopic techniques were employed to thoroughly investigate the structural and microstructural properties of Co0.3Zn0.7Fe2O4 microspheres. The results revealed that the microspheres (average diameter ∼121 nm) have been formed by self-assembly of nanoparticles with an average particle size of ∼12 nm. UV-vis diffuse reflectance spectroscopic and photoluminescence studies have been performed to study the optical properties of the sample. The studies indicate that Co0.3Zn0.7Fe2O4 microspheres exhibit a lower band gap value and enhanced PL intensity compared to their nanoparticle counterpart. The outcomes of dc magnetic measurement and Mössbauer spectroscopic study confirm that the sample is ferrimagnetic in nature. The values of saturation magnetization are 76 and 116 emu g-1 at 300 and 5 K, respectively, which are substantially larger than its nanosized counterpart. The infield Mössbauer spectroscopic study and Rietveld analysis of the PXRD pattern reveal that Fe3+ ions have migrated from [B] to (A) sites resulting in the cation distribution: (Zn2+ 0.46Fe3+ 0.54)A[Zn2+ 0.24Co2+ 0.3Fe3+ 1.46]BO4. Comparison of electrochemical performance of the Co0.3Zn0.7Fe2O4 microspheres to that of the Co0.3Zn0.7Fe2O4 nanoparticles reveals that the former displays greater specific capacitance (149.13 F g-1) than the latter (80.06 F g-1) due to its self-assembled porous structure. Moreover, it was found that Co0.3Zn0.7Fe2O4 microspheres possess a better electrochemical response toward H2O2 sensing than Co0.3Zn0.7Fe2O4 nanoparticles in a wide linear range.

Non-equilibrium induction of tin in germanium: towards direct bandgap Ge(1-x)Sn(x) nanowires.

The development of non-equilibrium group IV nanoscale alloys is critical to achieving new functionalities, such as the formation of a direct bandgap in a conventional indirect bandgap elemental semiconductor. Here, we describe the fabrication of uniform diameter, direct bandgap Ge(1-x)Sn(x) alloy nanowires, with a Sn incorporation up to 9.2 at.%, far in excess of the equilibrium solubility of Sn in bulk Ge, through a conventional catalytic bottom-up growth paradigm using noble metal and metal alloy catalysts. Metal alloy catalysts permitted a greater inclusion of Sn in Ge nanowires compared with conventional Au catalysts, when used during vapour-liquid-solid growth. The addition of an annealing step close to the Ge-Sn eutectic temperature (230 °C) during cool-down, further facilitated the excessive dissolution of Sn in the nanowires. Sn was distributed throughout the Ge nanowire lattice with no metallic Sn segregation or precipitation at the surface or within the bulk of the nanowires. The non-equilibrium incorporation of Sn into the Ge nanowires can be understood in terms of a kinetic trapping model for impurity incorporation at the triple-phase boundary during growth.

Peanut proteins in periodate specific anion sensing: An ensuing reduction in allergic response.

Peanut proteins conarachin II, conarachin I and arachin were found to behave as highly selective fluorescence sensors for periodate amongst a set of different anions. The interactions of the proteins with periodate were also confirmed by other spectral methods and enzyme linked immunosorbent assay (ELISA). The results indicate a selective interaction of peanut proteins with periodate amongst chloride, sulphate, iodide, phosphate, nitrate, nitrite, bromide, fluoride, persulphate, acetate, thiosulphate, arsenite, arsenate, sulphite, and iodide. Periodate sensing using different synthesized organic molecules are already reported in the literature. In this article we report the efficiency of peanut proteins as anion sensor which are bioactive and inexpensive too. The protein periodate interactions have also resulted in a simultaneous reduction in allergenicity of the peanut proteins. A change in the secondary structure of the protein was found responsible for this change which was further established with the help of circular dichroism and Raman spectroscopy.

Raman spectroscopy shows difference in drugs at ultrahigh dilution prepared with stepwise mechanical agitation

OBJECTIVE: The present study aims at deciphering the nature of the water structure of two ultrahigh diluted (UHD) homeopathic drugs by Laser Raman Spectroscopy. METHOD: Two homeopathic drugs Sulphur and Natrum mur in three UHD 30cH, 200cH and 1000cH were selected for the study. Raman spectra of the drugs and their medium (90% ethanol) were obtained in the wave number region of 2600-3800 cm-1. The intensity ratio at vibration frequencies between 3200 and 3420 (R1) and that between 3620 and 3420 (R2) was calculated for each UHD as well as the control. RESULTS: Raman spectra shows differences in intensities in different UHDs and their control in the stretching vibrations of CH and OH groups. The three UHDs of each drug show an inverse relationship with respect to the R1 values. However, for R2 the relationship of UHD for each drug is positive. CONCLUSION: R1 provides information about the relative number of OH groups with strong and weak hydrogen bonds. R2 suggests the relative number of OH groups with broken and weak hydrogen bonds. Judged from R1 values the lower is the rank of UHD, the stronger is the H-bond of the OH groups. In the light of R2 values, the higher is the UHD rank the more abundant is the free OH groups. So, hydrogen bond strength and free OH groups together make an effective UHD rank relating to Sulphur and Natrum mur.

Raman spectroscopy reveals variation in free OH groups and hydrogen bond strength in ultrahigh dilutions

OBJECTIVE: To decipher the nature of water structure in two ultrahigh diluted (UHD) homeopathic drugs by Laser Raman Spectroscopy. METHOD: Two homeopathic drugs Calcarea carbonica (Calc.) and Sepia officinalis (Sep.) in 8cH, 202cH, and 1002cH and their diluent medium 90% ethanol in 8cH and 202cH were used in the present study. Laser Raman spectra of all the samples were obtained in the wave number region of 2400 – 4200 cm-1. The intensity ratio at vibration frequencies between 3200 and 3420 (R1) and that between 3620 and 3420 (R2) were calculated for each UHD of the samples. RESULTS: The spectra show a marked difference in intensities in the stretching vibrations of CH and OH groups of all the samples. R1 values for three UHDs of Calc. and Sep. show negative and positive relationships, respectively. In the case of R2 values, the relationship in three UHDs is 81002 for Calc., and 8> 202 < 1002 for Sep. In the case of control (ethanol UHDs) both R1 and R2 show a negative relationship. CONCLUSION: R1 denotes a relative number of OH groups with strong and weak hydrogen bonds. R2 indicates the relative number of OH groups with broken and weak H-bonds. Therefore, the UHDs of the two drugs and the control are different from each other with respect to hydrogen bond strength of OH groups and the number of free OH groups or non-hydrogen bonded water molecules.

Raman spectroscopy shows difference in drugs at ultrahigh dilution prepared with stepwise mechanical agitation

Abstract Objective: The present study aims at deciphering the nature of the water structure of two ultrahigh diluted (UHD) homeopathic drugs by Laser Raman Spectroscopy. Method: Two homeopathic drugs Sulphur and Natrum mur in three UHD 30cH, 200cH and 1000cH were selected for the study. Raman spectra of the drugs and their medium (90% ethanol) were obtained in the wave number region of 2600-3800 cm-1. The intensity ratio at vibration frequencies between 3200 and 3420 (R1) and that between 3620 and 3420 (R2) was calculated for each UHD as well as the control. Results: Raman spectra shows differences in intensities in different UHDs and their control in the stretching vibrations of CH and OH groups. The three UHDs of each drug show an inverse relationship with respect to the R1 values. However, for R2 the relationship of UHD for each drug is positive. Conclusion: R1 provides information about the relative number of OH groups with strong and weak hydrogen bonds. R2 suggests the relative number of OH groups with broken and weak hydrogen bonds. Judged from R1 values the lower is the rank of UHD, the stronger is the H-bond of the OH groups. In the light of R2 values, the higher is the UHD rank the more abundant is the free OH groups. So, hydrogen bond strength and free OH groups together make an effective UHD rank relating to Sulphur and Natrum mur. (AU)

Raman spectroscopy reveals variation in free OH groups and hydrogen bond strength in ultrahigh dilutions

Objective: To decipher the nature of water structure in two ultrahigh diluted (UHD) homeopathic drugs by Laser Raman Spectroscopy. Method: Two homeopathic drugs Calcarea carbonica (Calc.) and Sepia officinalis (Sep.) in 8cH, 202cH, and 1002cH and their diluent medium 90% ethanol in 8cH and 202cH were used in the present study. Laser Raman spectra of all the samples were obtained in the wave number region of 2400 – 4200 cm-1. The intensity ratio at vibration frequencies between 3200 and 3420 (R1) and that between 3620 and 3420 (R2) were calculated for each UHD of the samples. Results: The spectra show a marked difference in intensities in the stretching vibrations of CH and OH groups of all the samples. R1 values for three UHDs of Calc. and Sep. show negative and positive relationships, respectively. In the case of R2 values, the relationship in three UHDs is 8<202>1002 for Calc., and 8> 202 < 1002 for Sep. In the case of control (ethanol UHDs) both R1 and R2 show a negative relationship. Conclusion: R1 denotes a relative number of OH groups with strong and weak hydrogen bonds. R2 indicates the relative number of OH groups with broken and weak H-bonds. Therefore, the UHDs of the two drugs and the control are different from each other with respect to hydrogen bond strength of OH groups and the number of free OH groups or non-hydrogen bonded water molecules.(AU)

Charge Transport in Polypyrrole Nanotubes.

True metallic conductivity in conjugated polymers has been major challenge for the last few years. Heeger and co-workers have reported metallic conductivity in bulk polyaniline film, but the problem of metallic transport in their nanophase still remains unexplored. In the recent past, our group had observed metallic conductivity in single nanotube by studying I-V characteristics using Atomic Force Microscopy. In the present work, Polypyrrole (PPy) nanotubes with variable wall thickness have been synthesized by chemical route. Electrical measurements--current-voltage characteristics as well as variation of resistance over the temperature range from 12 K to 300 K for these nanotubes with variable wall thickness, have also been carried out. The conductivity varies widely from semiconductor to metallic as the wall thickness decreases. Transmission Electron Microscopic study, further, confirms that very aligned and ordered polymer chains are formed due to directional growth in thin walled polypyrrole nanotubes, results in true metallic conductivity with a positive temperature coefficient of resistance over the whole temperature range. To the best of our knowledge, there is no such systematic study reported so far which embraces variation of charge transport characteristics with varying wall thickness of conjugated polymer nanotubes involving both I-V and R-T measurements supplementing each other, which being the main focus of this communication.

Probing Thermal Flux in Twinned Ge Nanowires through Raman Spectroscopy.

We report a noninvasive optical technique based on micro-Raman spectroscopy to study the temperature-dependent phonon behavior of normal (nondefective) and twinned germanium nanowires (Ge-NWs). We studied thermophysical properties of Ge-NWs from Raman spectra, measured by varying excitation laser power at ambient condition. We derived the laser-induced temperature rise during Raman measurements by analyzing the Raman peak position for both the NWs, and for a comparative study we performed the same for bulk Ge. The frequency of the Ge-Ge phonon mode softens for all the samples with the increase in temperature, and the first-order temperature coefficient (χT) for defected NWs is found to be higher than normal NWs and bulk. We demonstrated that apart from the size, the lamellar twinning and polytype phase drastically affect the heat transport properties of NWs.

Peanut protein sensitivity towards trace iron: a novel mode to ebb allergic response.

Peanut is a rich source of plant protein which is inexpensive and abundant in nature. The peanut proteins however cause hypersensitive immunogenic responses in certain individuals. A minute amount of contamination may cause strong allergic reactions and even death. Many chemical pretreatment procedures have been developed and prescribed earlier for removal of this allergenicity. In the present article we have observed trace level Fe(III) and Cu(II) complexation of the protein fractions of peanut at pH 4.8 using different spectral methods. Consequently we studied the allergic response of Fe(III) complex of the protein fractions using competitive enzyme linked immunosorbent assay (ELISA) technique and found that there were considerable losses in allergenicity of conarachin I and arachin fractions upon complexation. Immunoassay of Cu(II) complex was avoided keeping in view the Cu toxicity in living systems. The results bring up a new strategy towards reduction of allergenicity using an inexpensive and simple methodology.

Antibacterial effect of silver nanoparticles and the modeling of bacterial growth kinetics using a modified Gompertz model.

BACKGROUND: An alternative to conventional antibiotics is needed to fight against emerging multiple drug resistant pathogenic bacteria. In this endeavor, the effect of silver nanoparticle (Ag-NP) has been studied quantitatively on two common pathogenic bacteria Escherichia coli and Staphylococcus aureus, and the growth curves were modeled. METHODS: The effect of Ag-NP on bacterial growth kinetics was studied by measuring the optical density, and was fitted by non-linear regression using the Logistic and modified Gompertz models. Scanning Electron Microscopy and fluorescence microscopy were used to study the morphological changes of the bacterial cells. Generation of reactive oxygen species for Ag-NP treated cells were measured by fluorescence emission spectra. RESULTS: The modified Gompertz model, incorporating cell death, fits the observed data better than the Logistic model. With increasing concentration of Ag-NP, the growth kinetics of both bacteria shows a decline in growth rate with simultaneous enhancement of death rate constants. The duration of the lag phase was found to increase with Ag-NP concentration. SEM showed morphological changes, while fluorescence microscopy using DAPI showed compaction of DNA for Ag-NP-treated bacterial cells. CONCLUSIONS: E. coli was found to be more susceptible to Ag-NP as compared to S. aureus. The modified Gompertz model, using a death term, was found to be useful in explaining the non-monotonic nature of the growth curve. GENERAL SIGNIFICANCE: The modified Gompertz model derived here is of general nature and can be used to study any microbial growth kinetics under the influence of antimicrobial agents.

Raman scattering study of InAs nanowires under high pressure.

The pressure-dependent phonon modes of InAs nanowires have been investigated by Raman spectroscopy under high pressure up to ∼58 GPa. X-ray diffraction measurements show that InAs nanowires at 21 GPa exhibit a phase transition from a wurtzite to an orthorhombic crystal structure, with a corresponding drastic change in the first-order Raman spectra. In the low-pressure regime, a linear increase in phonon frequencies is observed, whereas splitting between longitudinal and transversal optical phonon modes decreases as a function of applied pressure. The calculated mode Grüneisen parameters and Born's transverse effective charge indicate that the wurtzite InAs nanowires exhibit a more covalent nature under compression.

DNA-mediated wirelike clusters of silver nanoparticles: an ultrasensitive SERS substrate.

Stable metal nanoclusters (NCs) with uniform interior nanogaps reproducibly offer a highly robust substrate for surface-enhanced Raman scattering (SERS) because of the presence of abundant hot spots on their surface. The synthesis of such an SERS substrate by a simple route is a challenging task. Here, we have synthesized a highly stable wirelike cluster of silver nanoparticles (Ag-NPs) with an interparticle gap of ~1.7 ± 0.2 nm using deoxyribonucleic acid (DNA) as the template by exploiting an easy and inexpensive chemical route. The red shift in the surface plasmon resonance (SPR) band of Ag-NCs compared to SPR of a single Ag-NP confirms the strong interplasmonic interaction. Methylene Blue (MB) is used as a representative Raman probe to study the SERS effect of the NCs. The SERS measurements reveal that uniform, reproducible, and strong Raman signals were observed up to the single-molecule level. The intensity of the Raman signal is not highly dependent on the polarization of the excitation laser. The DNA-based Ag-NCs as a substrate show better isotropic behavior for their SERS intensity compared to the dimer, as confirmed from both the experimental and theoretical simulation results. We believe that in the future the DNA-based Ag-NCs might be useful as a potential SERS substrate for ultrasensitive trace detection, biomolecular assays, NP-based photothermal therapeutics, and a few other technologically important fields.

Epitaxial growth of crystalline polyaniline on reduced graphene oxide.

Due to its unique electronic properties, graphene has already been identified as a promising material for future carbon based electronics. To develop graphene technology, the fabrication of a high quality P-N junction is a great challenge. Here, we describe a general technique to grow single crystalline polyaniline (PANI) films on graphene sheets using in situ polymerization via the oxidation-reduction of aniline monomer and graphene oxide, respectively, to fabricate a high quality P-N junction, which shows diode-like behavior with a remarkably low turn-on voltage (60 mV) and high rectification ratio (1880:1) up to a voltage of 0.2 V. The origin of these superior electronic properties is the preferential growth of a highly crystalline PANI film as well as lattice matching between the d-values [∼2.48 Å] of graphene and {120} planes of PANI.