The use of agrochemicals has increased considerably in recent years, and consequently, there has been increased exposure of ecosystems and human populations to these highly toxic compounds. The study ...and development of methodologies to detect these substances with greater sensitivity has become extremely relevant. This article describes, for the first time, the use of atomic force spectroscopy (AFS) in the detection of enzyme-inhibiting herbicides. A nanobiosensor based on an atomic force microscopy (AFM) tip functionalised with the acetolactate synthase (ALS) enzyme was developed and characterised. The herbicide metsulfuron-methyl, an ALS inhibitor, was successfully detected through the acquisition of force curves using this biosensor. The adhesion force values were considerably higher when the biosensor was used. An increase of ~250% was achieved relative to the adhesion force using an unfunctionalised AFM tip. This considerable increase was the result of a specific interaction between the enzyme and the herbicide, which was primarily responsible for the efficiency of the nanobiosensor. These results indicate that this methodology is promising for the detection of herbicides, pesticides, and other environmental contaminants.
We recently reported a noncovalent chemistry bead-based method that can sort single-walled carbon nanotubes (SWNTs) to ultrahigh purity. The method is based on the higher affinity of functionalized ...agarose beads for M(etallic) carbon nanotubes in acidic pH versus S(emiconducting) SWNTs based on the selective charge reversal of metallic carbon nanotubes. However, fundamental understanding of the relative selective affinity of various functional groups for certain electronic type nanotubes remains somewhat lacking. We show that the chemical force microscopy (CFM) technique can measure the subtle differences between various common functional groups (such as −NH2, −OH, −SO3H/–SO3 –Na+, −NO2, etc.) and the different electronic types of SWNTs. We show that the amine-functionalized alkane has significantly higher interaction forces with S SWNTs. On the other hand, SO3 –Na+- and NO2-functionalized naphthalene show significantly higher interaction forces with M SWNTs compared with S SWNTs; the −SO3H substitution on an alkane, however, shows no significant selectivity for any single electronic type of SWNTs. We discovered two novel molecules (sodium 4-amino-1-naphthalenesulfonate and 1-amino-4-nitronaphthalene) that are able to have significantly higher interaction force with M SWNTs and provide complete electronic type discrimination over the entire nanotube diameter range. We also show that the CFM platform can be applied to distinguish between M or S tubes from an as-grown SWNTs mixture in air. The platform can also be applied for studying the effect of solvent (water) on the selectivity. It is anticipated that our new CFM method using functionalized tips will be able to accelerate the development of noncovalent separation strategies for improved nanotube electronic type separation.
Atomic force microscopy (AFM) is capable of solid surface characterization at the microscopic and submicroscopic scales. It can also be used for the determination of surface tension of solids (
γ) ...from pull-off force (
F) measurements, followed by analysis of the measured
F values using contact mechanics theoretical models. Although a majority of the literature
γ results was obtained using either Johnson–Kendall–Roberts (JKR) or Derjaguin–Muller–Toporov (DMT) models, re-analysis of the published experimental data presented in this paper indicates that these models are regularly misused. Additional complication in determination of
γ values using the AFM technique is that the measured pull-off forces have poor reproducibility. Reproducible and meaningful
F values can be obtained with strict control over AFM experimental conditions during the pull-off force measurements (low humidity level, controlled and known loads) for high quality substrates and probes (surfaces should be free of heterogeneity, roughness, and contamination). Any probe or substrate imperfections complicate the interpretation of experimental results and often reduce the quality of the generated data. In this review, surface imperfection in terms of roughness and heterogeneity that influence the pull-off force are analyzed based upon the contact mechanics models. Simple correlations are proposed that could guide in selection and preparation of AFM probes and substrates for
γ determination and selection of loading conditions during the pull-off force measurements. Finally, the possibility of AFM measurements of solid surface tension using materials with rough surfaces is discussed.
The biosynthesis of the
Mycobacterium tuberculosis
cell wall is targeted by some of the most powerful antituberculous drugs. To date, the molecular mechanisms by which these antibiotics affect the ...cell wall characteristics are not well understood. Here, we used atomic force microscopy – in three different modes – to probe the nanoscale surface properties of live mycobacteria and their modifications upon incubation with four antimycobacterial drugs: isoniazid, ethionamide, ethambutol, and streptomycine. Topographic imaging, combined with quantitative surface roughness analysis, demonstrated that all drugs induce a substantial increase of surface roughness to an extent that correlates with the localization of the target (i.e., synthesis of mycolic acids, arabinogalactans, or proteins). Chemical force microscopy with hydrophobic tips revealed that the structural alterations induced by isoniazid and ethambutol were correlated with a dramatic decrease of cell surface hydrophobicity, reflecting the removal of the outermost mycolic acid layer. Consistent with this finding, tapping mode imaging, combined with immunogold labeling, showed that the two drugs lead to the massive exposure of hydrophilic lipoarabinomannans at the surface. Taken together, these structural, chemical, and immunological data provide novel insight into the action mode of antimycobacterial drugs, as well as into the spatial organization of the mycobacterial cell wall.
•We prepared CH3 Self-Assembled Monolayer (SAM) as protective coating on copper.•Temperature stability was analyzed by advanced scanning probe microscopy techniques.•100°C stress leads to a ...significant tunneling current rise and hydrophobicity drop.•At 150°C stress the degradation results in a state of decomposition of the SAM film.•High current spots and local hydrophobic variations can be detected in the nanoscale.
In this study, we used Self-Assembled Monolayer (SAM) with CH3 end-group molecules to protect copper surfaces from oxidation and investigated at nanometer scale the integrity and temperature stability of the protective film. The films were characterized by dynamic Chemical Force Microscopy (dCFM), Torsional Resonance Tunneling Atomic Force Microscopy (TR-TUNA) and Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR).
We observed that temperature stress degraded local properties of our SAM films significantly, when compared to unstressed films. After temperature stress at 100°C, tunneling current increased and hydrophobicity decreased substantially. In combination with the ATR-FTIR results we assigned local high current spots and local hydrophobic variations to cuprous oxide (Cu2O). After temperature stress at 150°C, the measurements indicate a decomposition of the SAM film and a further oxidation of the copper surface. In addition, the results show that dynamic dCFM and TR-TUNA are appropriate tools to characterize SAM films structurally, chemically and electrically. Most important, in contrast to conventional contact mode Atomic Force Microscopy techniques, we did not observe any damage to the SAM film by dCFM and TR-TUNA measurements.
Chemical force microscopy analyzes the interactions between various chemical/biochemical moieties in situ. In this work we examined force-distance curves and lateral force to measure the interaction ...between modified AFM tips and differently functionalized molecular monolayers. Especially for the measurements in gas phase, we investigated the effect of humidity on the analysis of force-distance curves and the images in lateral force mode. Flat chemical patterns composed of different functional groups were made through micro-contact printing and lateral force mode provided more resolved analysis of the chemical patterns. From the images of 1-octadecanethiol/11-mercapto-1-undecanoic acid patterns, the amine group functionalized tip brought out higher contrast of the patterns than an intact silicon nitride tip owing to the additional chemical interaction between carboxyl and amine groups. For more complex chemical interactions, relative chemical affinities toward specific peptides were assessed on the pattern of 1-octadecanethiol/phenyl-terminated alkanethiol. The lateral image of chemical force microscopy reflected specific preference of a peptide to phenyl group as well as the hydrophobic interaction.
Mechanisms contributing to the adsorption of natural organic matter (NOM) on surfactant-modified iron oxide-coated sand (IOCS) were explored by microscopic surface characterization techniques and ...adsorption tests. Electrostatic interactions that were thought to be from the positively charged, surface-coated surfactant, hexadecyltrimethyl ammonium (HDTMA), seemed to be unimportant, likely because the outward-pointing tail groups of the surface-coated HDTMA monolayers hindered the interactions. Improved hydrophobic interactions followed by ligand exchange are believed to be the dominant mechanisms. Atomic force microscopy (AFM) force analysis with chemically modified tips was used to explore the adsorption mechanisms between NOM and IOCS, where an iron oxide-coated mica surface was utilized as a substitute for the IOCS surface. It demonstrates the changes of pull-on forces and the increases in hydrophobic interactions from the modification of IOCS with HDTMA.
The XPS (ESCA) method was employed to quantitatively determine polyelectrolyte adsorption on the mica basal plane from low ionic strength solutions. Particular emphasis was given to the effect of the ...polyelectrolyte charge density. By combining the results obtained from XPS and surface force measurements it was possible to analyze the cation exchange at the surface that occurs as a result of polyelectrolyte adsorption. AFM-imaging was used to obtain information on the structure of the adsorbed layer when the polyelectrolyte coverage was low. Further, the desorption of preadsorbed polyelectrolyte layers by addition of inorganic salt and by addition of an anionic surfactant was investigated by XPS and some complementary surface force measurements. The results demonstrate that the lower the polyelectrolyte charge density is, the easier it is to remove the polyelectrolyte from the surface. The surfactant, which by itself does not adsorb to the mica surface, is more efficient in this respect than the inorganic salt. This observation can be rationalized by considering that the surfactant and polyelectrolyte form complexes with each other. Thus, the surfactant brings negative charges into the adsorbed layer that reduces the affinity to the surface. However, high-charge-density polyelectrolytes are removed to a very limited degree even when the surfactant concentration is above the critical micellar concentration, which is explainable by the poor solubility of the polyelectrolyte−surfactant complexes formed.
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