The
ability to monitor the chemical composition of brain interstitial
fluid remains an important challenge in the field of bioanalytical
chemistry. In particular, microelectrode biosensors are a promising
resource for the detection of neurochemicals in interstitial fluid
in both animals and humans. These biosensors can provide second-by-second
temporal resolution and enzymatic recognition of virtually any redox
or nonredox molecule. However, despite miniaturization of these sensors
to 50–250 μm in diameter to avoid vascular and cellular
injury, inflammation and foreign-body reactions still occur following
their implantation. Here, we fabricated microelectrodes with platinized
carbon fibers to create biosensors that have an external diameter
that is less than 15 μm. Platinization was achieved with physical
vapor deposition, and increased sensitivity to hydrogen peroxide and
improved enzymatic detection were observed for these carbon fiber
microelectrodes. When these devices were implanted in the brains of
rats, no injuries to the parenchyma or brain blood vessels were detected.
In addition, these microelectrodes provided different estimates of
basal glucose, lactate, and oxygen concentrations compared to conventional
biosensors. Induction of spreading depolarization in the cerebral
cortex further demonstrated the greater sensitivity of our microelectrodes
to dynamic neurochemical changes. Thus, these minimally invasive devices
represent a major advance in our ability to analyze brain interstitial
fluid.
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