The molecular composition of mycobacteria and Gram-negative bacteria cell walls is structurally different. In this work, Raman microspectroscopy was applied to discriminate mycobacteria and Gram-negative bacteria by assessing specific characteristic spectral features. Analysis of Raman spectra indicated that mycobacteria and Gram-negative bacteria exhibit different spectral patterns under our experimental conditions due to their different biochemical components. Fourier transform infrared (FTIR) spectroscopy, as a supplementary vibrational spectroscopy, was also applied to analyze the biochemical composition of the representative bacterial strains. As for co-cultured bacterial mixtures, the distribution of individual cell types was obtained by quantitative analysis of Raman and FTIR spectral images and the spectral contribution from each cell type was distinguished by direct classical least squares analysis. Coupled atomic force microscopy (AFM) and Raman microspectroscopy realized simultaneous measurements of topography and spectral images for the same sampled surface. This work demonstrated the feasibility of utilizing a combined Raman microspectroscopy, FTIR, and AFM techniques to effectively characterize spectroscopic fingerprints from bacterial Gram types and mixtures.

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Fundamental understanding of interfacial electron transfer (ET) among electrolyte/DNA/solidsurface will facilitate the design for electrical detection of DNA molecules. In this report, the electron transfer characteristics of synthetic DNA (sequence from pathogenic Cryptosporidium parvum) selfassembled on a gold surface was electrochemically studied. The effects of immobilization order on the interface ET related parameters such as diffusion coefficient (D 0 ), surface coverage (θ R ), and monolayer thickness (d i ) were determined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). DNA surface density (Γ DNA ) was determined by the integration of the charge of the electro-oxidation current peaks during the initial cyclic voltammetry scans. It was found that the DNA surface density at different modifications followed the order: Γ DNA (dsS-DNA/ Au) > Γ DNA (MCH/dsS-DNA/Au) > Γ DNA (dsS-DNA/MCH/Au). It was also revealed that the electro-oxidation of the DNA modified gold surface would involve the oxidation of nucleotides (guanine and adenine) with a 5.51 electron transfer mechanism and the oxidative desorption of DNA and MCH molecules by a 3 electron transfer mechanism. STM topography and current image analysis indicated that the surface conductivity after each surface modification followed the order: dsS-DNA/ Au < MCH/dsS-DNA/Au < oxidized MCH/dsS-DNA/Au < Hoechst/oxidized MCH/dsS-DNA/Au. The results from this study suggested a combination of variations in immobilization order may provide an alternative approach for the optimization of DNA hybridization and the further development for electrical detection of DNA.

The nanostructures and hydrophobic properties of cancer cell membranes are important for membrane fusion and cell adhesion. They are directly related to cancer cell biophysical properties, including aggressive growth and migration. Additionally, chemical component analysis of the cancer cell membrane could potentially be applied in clinical diagnosis of cancer by identification of specific biomarker receptors expressed on cancer cell surfaces. In the present work, a combined Raman microspectroscopy (RM) and atomic force microscopy (AFM) technique was applied to detect the difference in membrane chemical components and nanomechanics of three cancer cell lines: human lung adenocarcinoma epithelial cells (A549), and human breast cancer cells (MDA-MB-435 with and without BRMS1 metastasis suppressor). Raman spectral analysis indicated similar bands between the A549, 435 and 435/BRMS1 including ~720 cm(-1) (guanine band of DNA), 940 cm(-1) (skeletal mode polysaccharide), 1006 cm(-1) (symmetric ring breathing phenylalanine), and 1451 cm(-1) (CH deformation). The membrane surface adhesion forces for these cancer cells were measured by AFM in culture medium: 0.478 ± 0.091 nN for A549 cells, 0.253 ± 0.070 nN for 435 cells, and 1.114 ± 0.281 nN for 435/BRMS1 cells, and the cell spring constant was measured at 2.62 ± 0.682 mN m(-1) for A549 cells, 2.105 ± 0.691 mN m(-1) for 435 cells, and 5.448 ± 1.081 mN m(-1) for 435/BRMS1 cells.

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