90

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4 Smell and Taste

Figure 4.7: G-protein-coupled receptors (GPCR) are

stabilized inside a membrane and attached to car-

bon nanotube resistors to create an artificial nose.

Odorant-binding is detected via a change in cur-

rent [21]. (a) Schematic of nanodisc sensor. (b) AFM

image showing the attachment of nanodiscs to nan-

otubes. (c) IV curves of the same nanotube device

as-fabricated (red), after functionalization (green),

and after incubation in a solution of receptor protein

micelles (black).

in femtomolar concentrations. It demonstrated one weird effect, though: chamomile en-

hances specifically the sucrose signal, even though chamomile itself does not bind to the

sweet receptor binding domain [22].

So far, actual insect and mammalian cells and receptor molecules were used as the

sensing element and connected to a transducing element, and thus detected. But how

could one mimic the function of smell and taste detection and identification (i. e., the

detection and identification of chemicals in gases and liquids, respectively) with nonbi-

ological sensor molecules?

4.3 Biomimetic Chemical Sensors

To mimic smell and taste, several functions have to be incorporated: The chemical has

to be taken up from water (taste) or air (smell), the molecule has to bind to a sensing

molecule, and then the binding has to effect a change in a signal. The signal is then trans-

duced or transferred to an analysis that makes sense of the signal. Not all of the functions