Soft materials are finding applications in areas ranging from microfluidic device technology to nanofabrication. We review recent work in these areas, discuss the motivation for device fabrication with soft materials, and describe applications of soft materials. In particular, we discuss active microfluidic devices for cell sorting and biochemical assays, replication-molded optics with subdiffraction limit features, and nanometer-scale resonators and wires formed from single-molecule DNA templates as examples of how the special properties of soft materials address outstanding problems in device fabrication.

https://science.sciencemag.org/content/sci/290/5496/1536.full.pdf

From Micro- to Nanofabrication with Soft Materials

The factors which determine image contrast in optical and electron micrographs are discussed in relation to a new metal shadow‐casting technique whereby the contrast of images is greatly increased by depositing obliquely a thin film of metal on the microscope preparations Further advantages of the use of shadow‐casting are described, and an estimate is made of the lower limit of size of objects which should be observable by shadow‐casting Examples are given and illustrations are shown of the applications of this technique to the electron micrography of particles of macromolecular dimensions, of replicas of such particles, and of surface replicas prepared in several ways

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Applications of Metallic Shadow‐Casting to Microscopy

On the development of the goss texture in iron-3% silicon

Colorimetric Microdetermination of Formic Acid Based on Reduction to Formaldehyde

We examined relationships among cell wall feruloylation, diferulate cross-linking, p-coumarate deposition, and apoplastic peroxidase (EC 1.11.1.7) activity with changes in the elongation rate of leaf blades of slow and rapid elongating genotypes of tall fescue (Festuca arundinacea Schreb.). Growth was not directly influenced by ferulic acid deposition but leaf elongation decelerated as 8–5-, 8–O–4-, 8–8-, and 5–5-coupled diferulic acids accumulated in cell walls. Growth rapidly slowed and stopped with the deposition of p-coumarate, which is primarily associated with lignification in grass cell walls. Accretion of ferulate, diferulates and p-coumarate continued after growth ended, into the later stages of secondary wall formation. The concentration of 8-coupled diferulates dwarfed that of the more commonly measured 5–5-coupled isomer, suggesting that the latter dimer is a poor indicator of diferulate cross-linking in cell walls. Further work is required to clearly demonstrate the role of diferulate cross-linking and p-coumaroylated lignins in the cessation of leaf growth in grasses.

Relationship of growth cessation with the formation of diferulate cross-links and p-coumaroylated lignins in tall fescue leaf blades.

A simple method is described for making replicas of surfaces for study in the electron microscope. The surface to be studied is cleaned and then coated with a very thin slightly wedge‐shaped film of polyvinyl formal having a range in thickness from about 500 to 750A in 2.5 cm. This film is formed by dipping the prepared surface into a 0.5‐percent solution of the resin dissolved in dioxane or ethylene dichloride and permitting the solvent to evaporate while the surface is held in a vertical position. The replica film is removed by placing the coated surface under water and peeling the film from it. A description of this technique is given in detail. A graph is presented which shows the thickness of resin films obtainable from various concentrations of resin in dioxane, and a table gives the interference effects which may be used for determining approximate thicknesses of thin resin films. Several easy procedures are described for checking the thickness of such films. A technique is described for preparing strong films having a thickness of 100A and an area of 3 cm2 when mounted in air. Such films are very useful when working with the electron microscope and several methods are described for mounting specimens on them, including a conditioning treatment—useful in mounting water suspensions—which makes one surface very hydrophilic. Five micrographs show the results obtainable with the techniques described.

Surface Replicas for Use in the Electron Microscope

An investigation of the effects of rolling and annealing on the orientation of individual grains in silicon ferrite strip yielded results which led to the formulation of a theory for the appearance of the ``magnetic'' orientation in the final processed strip. It is proposed that, in a fine‐grained strip of silicon ferrite, those grains which are already in the ``magnetic'' orientation before rolling will keep that mean orientation during rolling but become more highly strained than other grains, and therefore, they will become the portions of the cold‐rolled strip with highest free energy. In the annealing process these highest energy regions will recrystallize first, becoming lowest energy regions which will be able to consume the now higher energy regions surrounding them. Since these nuclei have the ``magnetic'' orientation, the final product also attains the ``magnetic'' orientation.

David Harker

Papers

Surface Replicas for Use in the Electron Microscope

Relations between Initial and Final Orientations in Rolling and Annealing of Silicon Ferrite