1.2 Nanoscale Actors and Their Properties

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Figure 1.5: The scale of small things, nanoscale and microscale.

with. Thus the surface atoms are higher in energy and more reactive. This makes a large,

bulk material generally unreactive, and nanoscale material highly reactive. This is also

true for possible reactions on the surface of a material as well as interactions of the

surface with its environment.

This principle leads to some interesting phenomena. To give an example on a still

more human scale, a human will break through the surface of water when stepping on

it, but a water strider cannot, since the strider cannot break the intermolecular forces

on the surface of water that make up its surface tension [2]. The smaller the surface, the

larger the effect that surface tension has. That also changes the flow properties through

small-diameter channels, which will become important for microfluidic devices, since

the intermolecular forces, i. e., viscosity, will become predominant.

Keeping nanoscale properties in mind, let us look at the structure of the molecules

that become important in the body and in nanotechnology. The most important materi-

als in a cell are made from either lipids, nucleotides, sugars, or amino acids. We’ll look

at all of these materials in more detail, starting with lipids.

Structure and function of molecules – lipids and lipid membranes. The most common

lipids are made from fatty acids that are attached to a head group (Figure 1.6). The fatty

acid is by itself amphiphilic, i. e. it has a hydrophilic head and a long, hydrophobic tail.

In water, therefore, fatty acids will aggregate in such a way that they form a phase where

the hydrophilic heads face the water and the hydrophobic tails face away from it. This

phase, though, is not a solid phase like a salt crystal, but a liquid crystal phase. A liquid