Chapter 9 – Emerging Biophysics Techniques  403

Synthetic biology can operate both from a top-​down or bottom-​up context, for example,

by stripping away components from an existing biological system to reduce it to more basic

components, as exemplified by the artificial cells developed by Craig Venter (see Chapter 2).

These top-​down approaches can also be viewed as a redesign of natural biology or reverse

engineering—​adapting nature, making it more efficient for the specific set of tasks that you

wish the new design to perform. Similarly, a device can be generated into larger systems by

combining smaller length scale components that have been inspired by existing components

in the natural world, but now in an artificial combination not seen in nature. Thus, creating

a totally new artificial device, but inspired by biology, for example, in the use of oil-​stabilized

nanodroplets that utilize soft-​matter nanopores in their outer membranes that can be joined

together to create a complex array with a far greater complexity of function than a single

droplet (see Chapter 6).

Although such synthetic biology devices can span multiple length scales, much current

research is focused at the nanometer length scale. The motivation comes from the glacial

time scales of evolution resulting in a myriad of optimized natural technological solutions to

a range of challenging environmental problems. Life has existed on planet Earth for around

4 billion years in which time the process of genetic mutation combined with selective envir­

onmental pressures has resulted in highly optimized evolutionary solutions to biological

problems at the molecular level. These are examples of established bionanotechnology. Thus,

instead of attempting to design miniaturized devices completely de novo, it makes sense to

try to learn lessons from the natural world, concerning the physical architecture of natural

molecular machines and subcellular structures, and the processing structures of cellular

functions, that have evolved to perform optimized biological roles.

The range of biophysics tools relevant to synthetic biology is large. These include in par­

ticular many fluorescence-​based imaging detection methods and electrical measurements

and control tools. Several synthetic biology methods utilize surface-​based approaches, and so

many surface chemistry biophysics tools are valuable. Similarly, biophysics tools that measure

molecular interactions are useful in characterizing the performance of devices. Also, atomic

force microscopy (AFM) has relevance here, both for imaging characterization of synthetic

constructs on surfaces and also for smart positioning of specific synthetic constructs to

different regions of a surface (see Chapter 6). Many of these devices have potential benefits to

healthcare, and these are discussed in a separate section later in this chapter.

The general area of study of biological processes and structures with a view to gener­

ating newly inspired designs and technologies is called biomicry. Structural coloration, as

exhibited in the well-​known iridescence of the wings of many species of butterfly, is an excel­

lent example but is also found in myriad species including the feathers of several birds, insect

wing cases such as many beetles, bees, dragonflies, moths. It is also observed in fish scales,

plant leaves and fruit, and the shells of several mollusks.

Many examples of this phenomenon arise from single or multilayer thin film interference

and scattering effects. To understand the basic principle, some of the incident light of wave­

length λ propagated in a medium of refraction index n0 will be reflected from the surface of a

thin film at angle θ0, while a proportion will be refracted through the film of thickness d1 and

refractive index n1 at an angle θ1, some of which will then reflect from the opposite boundary

back through the film and into the original medium. Back-​reflected light will then emerge

if the conditions for constructive interference are met between all the multiple reflected

beams. For this single thin film system, the condition for constructive interference is given by

2n1d1cosθ1=​(m –​ 1/​2)λ where m is a positive integer.

This process can occur for an arbitrary number of layers of different thicknesses and

refractive indices (Kinosita et al., 2008), and since the conditions for constructive interference

are dependent on the wavelength of incident light these multilayers can be used to generate

precisely tuned spectral characteristics of emergent light from a broad spectrum incident

light source such as sunlight; for example, the beetle Chrysina resplendens contains ~120

thin layers which produce a bright iridescent gold color (see Worked Case Example 9.3).

Structural coloration has an attraction compared to conventional pigment-​based coloration

technologies in having high brightness which does not fade, plus having iridescence and