100

౪

5 Hearing

5.2 Vibration Sensors Using Biological Cells, Molecules, and

Methods

Receivers and microphones are a mature technology and have been well miniaturized,

so that the need for nanovibration sensors using biological molecules and cells is small

and only very few examples exist. The majority of these sensors are developed to study

the human ear itself, specifically its hair cells.

One of the problems in studying hair cells is that it is necessary to stimulate and then

monitor the hair cells at specific frequencies to understand their mechano-electrical

transduction. Ideally, the force should be delivered instantaneously by a spring of a very

precise stiffness (spring constant), and the effect of the stimulation should be measured

by a rigid fiber. Such a system has been developed using nanomechanical force probes

[6] (Figure 5.4). These nanomechanical force probes included integrated piezoresistive

sensing and piezoelectric actuation. The spring constant was in the necessary range and

the probe was capable of delivering mechanical stimuli with sub-10 µs rise times in wa-

ter.

Figure 5.4: A nanomechanical force probe is used to measure the mechano-electrical transduction of the

hair cells at specific frequencies [6].

Another approach to controlling the hair bundles of the hair cells is to use magnetic

particles [7] (Figure 5.5). The control is supposed to be remote, reversible, and localized.

This has been achieved by coating specific hair cells with cubic nanoparticles; each cell

could then be stimulated to remotely open and close its MET ion channel at time scales

that varied from a few seconds to 100 µs. The effect could be measured by measuring cal-

cium ion flows via a fluorescent probe. This system was effective for studying individual

hair cells as well as other systems with mechanosensitive ion channels.

In summary, no reports were found in which biological molecules or cells were

used to create a biomimetic sound receiver. But with the research done to study the

mechanosensitive-electrical transduction process of the ear it might be possible in the

future to mimic the wavelength separation and amplification of the membranes, thus

leading to more sensitive receivers on the nanoscale.