Atomic Force Microscopy

The technique of AFM was introduced by G. Binning6 in 1986 and has been used to visualize biological structures for more than a decade. AFM offers several advantages when viewing biological structures. AFM measurements can be made on samples in vacuum, in air under ambient conditions, and in fluids under near physiological conditions. Samples are not required to be stained, to be conductive, or to be arranged in a highly ordered manner. AFM can be used to scan fields ranging in size from less than 20 nm up to ~150 | m, a)

FIGURE 13.2 SEM images with concomitant EDX analysis of crystals observed in powdered weaponized bacterial spore surrogates. Powders were dusted onto a silicon substrate; no coatings were applied to the samples. (a) A micrograph of a microcrystal found in samples grown in media containing large quantities of magnesium and phosphate. The crystals are ~10 ||m x 10 ||m x 2 ||m. (b) Elemental composition of the same crystal shown in (a), as measured by EDX analysis results in large magnesium and phosphorus peaks. (c) Octahedral protein toxin crystals (indicated by the arrows), generated by Bacillus thuringiensis, are ~1 ||m in length. B. thuringiensis spores are also seen in the micrograph. (d) EDX analysis of the protein toxins seen in (c) shows the particle to be organic, containing only carbon, nitrogen, and oxygen. The silicon peak is due to the substrate.

FIGURE 13.2 SEM images with concomitant EDX analysis of crystals observed in powdered weaponized bacterial spore surrogates. Powders were dusted onto a silicon substrate; no coatings were applied to the samples. (a) A micrograph of a microcrystal found in samples grown in media containing large quantities of magnesium and phosphate. The crystals are ~10 ||m x 10 ||m x 2 ||m. (b) Elemental composition of the same crystal shown in (a), as measured by EDX analysis results in large magnesium and phosphorus peaks. (c) Octahedral protein toxin crystals (indicated by the arrows), generated by Bacillus thuringiensis, are ~1 ||m in length. B. thuringiensis spores are also seen in the micrograph. (d) EDX analysis of the protein toxins seen in (c) shows the particle to be organic, containing only carbon, nitrogen, and oxygen. The silicon peak is due to the substrate.

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