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A Detailed Model of Electroenzymatic Glutamate Biosensors To Aid in Sensor Optimization and in Applications in Vivo
journal contribution
posted on 2017-10-27, 00:00 authored by Mackenzie Clay, Harold G. MonbouquetteSimulations conducted
with a detailed model of glutamate biosensor
performance describe the observed sensor performance well, illustrate
the limits of sensor performance, and suggest a path toward sensor
optimization. Glutamate is the most important excitatory neurotransmitter
in the brain, and electroenzymatic sensors have emerged as a useful
tool for the monitoring of glutamate signaling in vivo. However, the utility of these sensors currently is limited by their
sensitivity and response time. A mathematical model of a typical glutamate
biosensor consisting of a Pt electrode coated with a permselective
polymer film and a top layer of cross-linked glutamate oxidase has
been constructed in terms of differential material balances on glutamate,
H2O2, and O2 in one spatial dimension.
Simulations suggest that reducing thicknesses of the permselective
polymer and enzyme layers can increase sensitivity ∼6-fold
and reduce response time ∼7-fold, and thereby improve resolution
of transient glutamate signals. At currently employed enzyme layer
thicknesses, both intrinsic enzyme kinetics and enzyme deactivation
likely are masked by mass transfer. However, O2-dependence
studies show essentially no reduction in signal at the lowest anticipated
O2 concentrations for expected glutamate concentrations
in the brain and that O2 transport limitations in vitro are anticipated only at glutamate concentrations
in the mM range. Finally, the limitations of current biosensors in
monitoring glutamate transients is simulated and used to illustrate
the need for optimized biosensors to report glutamate signaling accurately
on a subsecond time scale. This work demonstrates how a detailed model
can be used to guide optimization of electroenzymatic sensors similar
to that for glutamate and to ensure appropriate interpretation of
data gathered using such biosensors.
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Keywords
glutamate biosensor performanceO 2 transport limitationssensor performancedependence studies showO 2 concentrationssubsecond time scaleelectroenzymatic sensorsO 2glutamate concentrationscross-linked glutamate oxidaseH 2 O 2Electroenzymatic Glutamate Biosensorspermselective polymer filmenzyme layer thicknessesmonitoring glutamate transients
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