Somdev Tyagi

One of the most widely used methods for surface-enhanced Raman scattering (SERS) employs silver or gold nanoparticles either in colloidal suspension or in the dry-drop form. In such substrates the SERS amplification factors depend critically on the interparticle distances. Here, we report that microwave absorption as a function of temperature in dry-drop substrates can be used as a probe to demarcate temperature regions for thermal annealing to produce SERS substrates with very high amplification factors. Copyright (c) 2011 John Wiley & Sons, Ltd.

Changes of optical properties of wound tissue in hairless rats were quantified by diffuse photon density wave methodology at near-infrared frequencies. The diffusion equation for semi-infinite media was used to calculate the absorption and scattering coefficients based on measurements of phase and amplitude with a frequency domain device. There was an increase in the absorption and scattering coefficients and a decrease in blood saturation of the wounds compared with the nonwounded sites. The changes correlated with the healing stage of the wound. The data obtained were supported by immunohistochemical analysis of wound tissue. These results verified now by two independent animal studies could suggest a noninvasive method to detect the progress of wound healing.

Objective and Design: Myeloperoxidase (MPO) and proinflammatory cytokines play an important role in the development of inflammation. These markers are generally measured using tedious ELISA procedures. In this study, a novel technique utilizing antibody conjugated quantum dot nanoparticles was developed to detect myeloperoxidase, IL-1 α and TNF-α in vivo in the dextran sodium sulfate (DSS) model of experimental colitis. Materials and Methods: Colitis was induced in animals (n=8 animals/ group) by feeding 4% DSS solution ad libitum for seven to eight days. Quantum Dots exhibiting fluorescence at various wavelengths were conjugated to MPO, IL-1 α and TNF-α polyclonal antibodies and tested in vivo at various stages of colitis. Tissue sections obtained were imaged with confocal microscope. The image intensity obtained from the tissue specimen was correlated with clinical activity measured as Disease Activity Index (DAI). Results: Myeloperoxidase, IL-1α and TNF-α were visualized with quantum dots on various days of disease. The intensity of quantum dots increased with increase in inflammation. The increase in intensity showed an excellent correlation with the DAI based on the clinical parameters. Conclusion: The study demonstrated that multiple biomarkers can be detected simultaneously and their quantitative expression correlated well with clinical disease severity. This novel technology should facilitate design of a novel optical platform for imaging various biomarkers of inflammation, early detection of acute and chronic disease markers and inflammation-mediated cancer markers. This detection may also facilitate determination of therapeutic success.

We have used the near-field scanning microwave microscopy (NSMM) technique in the 1-10 GHz range to monitor the free water content of skin. The water content is interpreted from the measured dielectric properties of the epidermis. The finger skin was first hydrated by soaking in water at 37 degrees C for 30 min followed by monitoring of water content as the free water evaporated under ambient conditions. The same technique has also been employed to image a 1 cm x 1 cm sample of chicken skin. It has been shown that variations exist in the resonant frequencies and quality factors of tissue under varying physical parameters. The samples analysed were as-received and thermally dehydrated or damaged chicken tissue samples. We contrast between the dielectric properties with the optical images. We also discuss possible application of our imaging technique in clinical monitoring of the wound healing process.

A frequency domain diffuse optical tomography instrument operating in the Near Infrared region (680-830nm) has been designed and used to monitor healing in diabetic wounds in a rat animal model. Instrument design and calibration are described and preliminary data of the in vivo experiment are reported. Excellent discrimination capability between the control and the diabetic population is possible, while the time course of impaired healing in diabetic animals appears to have different optical coefficients from the normal healing in the control group.

Synthesis, structure and electronic properties are reported on single crystals of Sm 4Mo 18O 32 and Nd 4Mo 18O 32. The triclinic crystal structure has three distinctly different Mo metal atom clusters (Mo 2, Mo 4 and Mo 6), which extend in complex chains. The temperature dependence of the electrical resistivity displays a broad minimum around 150–200 K with a pronounced increase in the 30–50 K range. However, unlike the related monoclinic reduced Mo oxides, A 4Mo 18O 32 (A = Y, Gd–Yb), there is no true metal–insulator transition in the Sm and Nd analogs. We discuss these observations in terms of correlations among the Mo clusters.

Diffuse photon density wave (DPDW) methodology at Near Infrared frequencies has been used to calculate absorption and scattering from wounds of healthy and diabetic rats. The diffusion equation for semi-infinite media is being used for calculating the absorption and scattering coefficients based on measurements of phase and amplitude with a frequency domain device. Differences observed during the course of healing in the two populations can be correlated to the delayed healing observed in diabetics. These results are encouraging and further work will focus on the implementation of this device to the clinical setting as a monitoring tool in chronic diabetic wounds.

We have fabricated Fe / Sm - Co bilayers with gradient Fe thicknesses in order to systematically study the dependence of exchange coupling on the thickness of the Fe layer. The Fe layer was deposited at two different temperatures (150 and 300 C⁠) to study the effect of deposition temperature on the exchange coupling. Magneto-optical Kerr effect and x-ray magnetic circular dichroism (XMCD) have been employed as nondestructive rapid characterization tools to map the magnetic properties of the gradient samples. Systematic enhancement in exchange coupling between the soft layer and the hard layer is observed as the soft layer thickness is decreased. Separate exchange couplings of the Fe layer with Co and Sm in the hard layer are revealed through measuring the element-specific hysteresis curves using XMCD. The single-phase-like magnetization reversal critical thickness increases from 12 nm for Fe deposited at 150 C to 24 nm for Fe deposited at 300 C⁠, indicating an important role of the state of the interface in the exchange coupling.

Multilevel Monte Carlo simulations of a Bi2Sr2CaCu2O8+delta (BSCCO) system are carried out including both Josephson and electromagnetic couplings for a range of anisotropies. A first-order melting transition of the flux lattice is seen on increasing the temperature and/or the magnetic field. The phase diagram for BSCCO is obtained for different values of the anisotropy parameter gamma. The best fit to the experimental results of Majer [Phys. Rev. Lett. 75, 1166 (1995) ] is obtained for gammaapproximate to250 provided one assumes a temperature dependence lambda(2)(0)/lambda(2)(T)=1-t of the penetration depth with t=T/T-c. Assuming a dependence lambda(2)(0)/lambda(2)(T)=1-t(2) the best fit is obtained for gammaapproximate to450. For finite anisotropy the data are shown to collapse on a straight line when plotted in dimensionless units which shows that the melting transition can be satisfied with a single Lindemann parameter whose value is about 0.3. A different scaling applies to the gamma=infinity case. The energy jump is measured across the transition and for large values of gamma it is found to increase with increasing anisotropy and to decrease with increasing magnetic field. For infinite anisotropy we see a two-dimensional behavior of flux droplets with a transition taking place at a temperature independent of the magnetic field. We also show that for smaller values of anisotropy it is reasonable to replace the electromagnetic coupling with an in-plane interaction represented by a Bessel function of the second kind (K-0), thus justifying our claim in a previous paper.