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1 Introduction

Sensors always have several elements: the sensing or detection element, the transducer,

possibly an amplifier, and an analysis element. What does that look like?

In humans, the sensing elements, or detectors, are the eyes, nose, ears, and the me-

chanical and temperature sensors in the skin. The transducers are often receptors or

ion channels that change the original signal into an electrical signal, more specifically

a membrane potential. That membrane potential is or initiates an action potential that

is sent to various places in the brain. In the brain, the signal will be analyzed and made

sense of. The brain also initiates actions based on the sensor input, i. e., your hand might

take the rose your lover hands you. And it will often have some memory of the signal

and can learn from it.

In technology, sensors work very much in the same way. The signal is generally

transduced into another signal that can be analyzed more easily. The fuel gauge in your

car is a good example (Figure 1.55): the fluid level is hard to measure, but when trans-

duced to an electrical signal via a resistor it is easy to analyze. The most common am-

plifier in (nano)technology is the bipolar junction transistor. An additional voltage is

adding to the charges of the transistor output, and thus amplifies the signal.

Figure 1.55: Example of a transducer: the fuel level is sensed, then transduced into an electrical signal via a

resistor, which is then analyzed and displayed on the dashboard of your car.

In biomimetic nanotechnology, there are a variety of sensing elements, but in a lot of

cases the original signal is translated into an electrical signal that is transferred into a

computer for analysis and recognition. Nowadays, computers might even remember the

signal or a signal pattern and learn from that “experience”.

When developing and creating a new sensor in the nanoscale, one always has to

prove that one actually made what one wanted to make as well as calibrate the sensor.

Therefore, the new sensors always have to be characterized. There are only few tech-

niques that can characterize materials on such a small scale. For conductive and semi-

conductive materials, the most common technique is the scanning tunneling microscope

(STM) (Figure 1.56). When two conductive surfaces are getting very close to each other,