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For atomic force microscopy (AFM), fast scanning usually results in low imaging resolution, which leads to inaccurate sample topography reconstruction. Based on the analysis for the experimental step-response of AFM, a practical dynamic imaging method is proposed in this article to enhance measurement performance under fast scanning speed. Specifically, the experimental step-response is employed to obtain the transient displacement of the piezo-actuator in the Z-axis, which is then utilized, together with the control error, to calculate the topography of the detected sample surface. As no model is required to enable this algorithm, it presents such advantages as easy implementation and reliable imaging results. Some experimental results are included to demonstrate the superior performance of the proposed imaging method. [ABSTRACT FROM AUTHOR]

Both antibiotics and surfactants commonly exist in natural environment and have generated great concerns due to their biological influence on the ecosystem. A major concern lies in the capacity of antibiotics to induce bacterial filaments formation, which has potential health risks. However, their joint effect is not clear so far. Here, we studied the joint effect of cephalexin (Cex), a typical antibiotic, and differently charged surfactants on the formation of E. coli filaments. Three kinds of surfactants characterized by different charges were used: cationic surfactant (CTAB), anionic surfactant (SDS) and nonionic surfactant (Tween). Data showed that Cex alone caused the formation of E. coli filaments, elongating their maximum profile from ca. 2 μm (a single E. coli cell) to tens of micrometers (an E. coli filament). A joint use of surfactants with Cex could produce even longer E. coli filaments, elongating the maximum length of the bacteria to larger than 100 μm. The capacity order of different surfactants under their optimum concentrations to produce elongated E. coli filaments was Tween > SDS > CTAB. The E. coli filaments were characterized with a normal DNA distribution and a good cell membrane integrity. We measured the stiffness of bacterial cell wall by atomic force microscopy and correlated the elongation capacity of the E. coli filaments to the stiffness of cell wall. Zeta potential measurement indicated that inserting into or being bound to the cell surface in a large quantity was tested not to be the major way that surfactants interacted with bacteria. Image 1 • Cex alone causes formation of E. coli filaments, which has potential health risk. • A combination use of surfactants with Cex produces even longer E. coli filament. • The capacity order of surfactants to produce E. coli filaments is Tween > SDS > CTAB. • The stiffness of cell wall is correlated with the elongation of E. coli filaments. [ABSTRACT FROM AUTHOR]

Coating of polydimethylsiloxane (PDMS) surface with a traditional Chinese herb extract chlorogenic acid (CA) solves the contemporary problem of sterilization of PDMS surface. The E. coli grows slower and has a higher death rate on the CA-coated PDMS surfaces. A smoother morphology of these E. coli cell wall is observed by atomic force microscopy (AFM). Unlike the reported mechanism, where CA inhibits bacterial growth by damaging the cell membrane in the bulk solution, we find the CA-coated PDMS surface also decreases the stiffness of the cell wall. A decrease in the Young's modulus of the cell wall from 3 to 0.8 MPa is reported. Unexpectedly, the CA effect on the swarming ability and the biofilm stability of the bacteria can be still observed, even after they have been removed from the CA environment, indicating a decrease in their resistance to antibiotics for a prolonged time. The CA-coated PDMS surface shows better antibiotic effect against three types of both Gram-positive and Gran-negative bacteria than the gentamicin-coated PDMS surface. Coating of CA on PDMS surface not only solves the problem of sterilization of PDMS surface, but also shines light on the application of Chinese traditional herbs in scientific research. [ABSTRACT FROM AUTHOR]

Abstract: Fabrication of porous polymer films is important for its potential applications in industry and everyday life. In this study, a thermoresponsive polymer poly(N-isopropylacrylamide-co-butylmethacrylate) (PNIBMA) was introduced to fabricate porous films on the glass surface. PNIBMA can alter its structure with temperature and has a lower critical solution temperature (LCST) of about 20°C. The porous film of PNIBMA was prepared by drying a drop of PNIBMA solution (in CHCl3) on a glass surface under a moist air flow. Atomic force microscope (AFM) images showed that the porous polymer film contained many layers of vacant spheres with diameters of about 1μm. This unique surface characteristic endowed the porous film with higher hydrophobicity than a flat PNIBMA film made by direct coating. This study expanded the materials for porous films fabrication in the field of thermoreponsive polymers and should be of great potential in scientific researches and industry applications. [Copyright &y& Elsevier]

Abstract: We synthesized a cationic polymer, poly(PEGMA)-4N, which has brush-like chains and four positively charged amino groups at the end of the molecules. DNA condensation induced by poly(PEGMA)-4N was investigated through electrophoresis assay by its ability to retard DNA mobility and to inhibit HindIII enzyme cleavage. The detailed structures of DNA condensates induced by poly(PEGMA)-4N were observed through atomic force microscopy (AFM). Interactions between polymers and DNA are mainly attributed into depletion effect and electrostatic interaction. Positively charged amino groups in poly(PEGMA)-4N interact with DNA through electrostatic interaction, and depletion effect also takes effect because poly(PEGMA)-4N is a flexible polymer. Comparing the contributions that the two interactions gave in DNA condensation process, we found that depletion effect played a major role compared with electrostatic interaction. [Copyright &y& Elsevier]