Biomedical Engineering Reference
In-Depth Information
Use of fabricated electrode arrays in microchambers, along with novel sensing
methodologies, has opened up new possibilities in the detection of chemicals and
neurotransmitters. Modified cyclodextrin-based microelectrode arrays have been
demonstrated to simultaneously detect catecholamine neurotransmitters.
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Indi-
vidual concentrations of multiple neurotransmitters are known to have critical
effects on various human behaviors and diseases, and their parallel detection
would provide substantial benefit. In the application illustrated in Figure 3.18,
individual surface modification of microelectrode arrays was performed with
various types of cyclodextrins known to recognize diverse targets through
size matching. This approach can enable microelectrode arrays to precisely
detect subtle differences in multiple neurotransmitters at the same time.
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3.10 Biosensors for Neuroscience Applications
3.10.1 In Vitro Microelectronic Interfaces
Interfacing molecular electronics with neurons is facilitated by the fact that the
cell inherently possesses specific receptors that respond to external stimuli. As
such, the cell intrinsically behaves as a 'sensing' component. In addition, the
transduction cascades that are instigated by the initial receptor-ligand binding
act as signal amplifiers of the binding event. These signaling pathways are
extremely specific and sensitive, allowing the possibility of discerning the
particular interactions taking place at the membrane level.
Neurons have a great potential for cell-based biosensing because of their
intrinsic electrophysiological characteristics. Neuronal cells bind specifically
with neuroactive compounds, drugs and toxins. With the binding of those
substances, they generate electric signals in a substance-specific and
concentration-dependent manner and the response profiles can be directly
monitored by microelectrodes. The neural receptors can bind directly with the
specific substance, or a differential approach can be employed by genetically
knocking out receptors and then watching the generation of the signal in wild-
type cells but not in the knockout cells. Comparing the two responses leads to
the detection of the target agents.
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The neural cells or neuronal networks can
be cultured and maintained on microelectrode arrays for long periods of time.
Long-term neuron and glial co-cultures can be maintained in vitro using the
natural ability of glial cells to support and nourish the neuron cells. It was
observed that spinal monolayers survive for more than nine months in culture
provided that sterility, temperature, pH, osmolarity, oxygenation, and proper
nutrients and growth factors are guaranteed.
Three strategies have been widely investigated to study changes in action
potential patterns using In Vitro Microelectronic Interfaces.
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The first is the
use of compounds that cause major changes in native oscillations, including
synaptically active agents (e.g., glutamine, strychnine, N-methyl
D
-aspartic
acid) and metabolic poisons. Second category includes compounds that cause
changes in network oscillations via disinhibition. The compounds in the second
category include synaptically and metabolically active substances, ion channel
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