The determination of bacterial identity at the strain level is still a complex and time-consuming endeavor. In this study, visible wavelength spontaneous Raman spectroscopy has been used for the discrimination of four closely related Escherichia coli strains: pathogenic enterohemorrhagic E. coli O157:H7 and non-pathogenic E. coli C, E. coli Hfr K-12, and E. coli HF4714. Raman spectra from 600 to 2000 cm⁻¹ were analyzed with two multivariate chemometric techniques, principal component-discriminant function analysis and partial least squares-discriminant analysis, to determine optimal parameters for the discrimination of pathogenic E. coli from the non-pathogenic strains. Spectral preprocessing techniques such as smoothing with windows of various sizes and differentiation were investigated. The sensitivity and specificity of both techniques was in excess of 95%, determined by external testing of the chemometric models. This study suggests that spontaneous Raman spectroscopy with visible wavelength excitation is potentially useful for the rapid identification and classification of clinically-relevant bacteria at the strain level.

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The present study is concerned with the fabrication and characterization of Me₂Y substituted hexaferrites, Ba₂Me₂Fe_12-xT_xO₂₂(Me = Co²⁺, Mg²⁺, and Cr²⁺, and T = Fe³⁺, and Ga³⁺). The samples were prepared by the conventional ball milling technique and sintering at 1200° C. The effect of the choices of Me and T ions on the structural and magnetic properties of the hexaferrites were investigated. XRD patterns, magnetic parameters, and Mössbauer spectra of the Co₂Y were consistent with a single phase Y-type hexaferrite. However, the CoCr-Y sample was found to be dominated by the Y-type hexaferrite, and M-type and BaCrO₄minority phases were observed in the XRD pattern of the sample. The small increase in saturation magnetization from about 34 emu/g up to 37.5 emu/g was therefore attributed to the development of the M-type phase. On the other hand, XRD pattern of the Cr₂Y sample indicated the dominance of the M-type phase in this sample. The high coercivity (1445 Oe) of this sample is evidence of the transformation of the material from a typically soft magnetic material (Y-type) to a hard magnet (M-type). The Ga-substitution for Fe in Co₂Y did not affect the saturation magnetization significantly, but the coercivity was reduced. However, the sample Ba₂CoMgFe₁₁GaO₂₂exhibited a significant reduction of the saturation magnetization down to a value 26.6 emu/g, which could be due to the attenuation of the super-exchange interactions induced by the Mg²⁺substitution.

In this paper, Y₃Al_xFe_5-xO₁₂ powders with x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 were prepared via solid state reaction method. X-ray diffraction, Vibrating Sample Magnetometry, and Mössbauer Spectroscopy were used to study their structural and magnetic properties. The XRD patterns of the samples show single phase structure with decreasing lattice constant when increasing Al concentration. The saturation magnetization decreases from 28.0 to 10.1 emu/g with increasing Al³⁺ from 0.0 to 1.0 due to the reduction of the superexchange interactions between iron ions in the a and d sublattices. Room temperature Mössbauer spectra for the samples were collected and analyzed. The hyperfine field values for octahedral and tetrahedral sites of the samples decreased with increasing Al concentration. Moreover, Mössbauer results have shown that Al³⁺ ions prefer to replace Fe⁺³ at the octahedral sites.