Propylene glycol stabilizes the linear response of glutamate biosensor: potential implications for in-vivo neurochemical monitoring

L-glutamate is one the most important excitatory neurotransmitter at central nervous system level
and it is implicated in several pathologies. So, it is very important to monitor its variations, in real
time in animal models’ brain. The present study aimed to develop and characterize a new
amperometric glutamate biosensor design that exploits the selectivity of Glutamate Oxidase
(GluOx) for l-glutamate, and the capability of a small molecule as propylene glycol (PG), never
used before, to influence and extend the stability and the activity of enzyme. Different designs were
evaluated by modifying the main components in their concentrations to find the most suitable
design. Moreover, enzyme concentrations from 100 U/ml up to 200 U/ml were verified and
different PG concentrations (1%, 0.1% and 0.05%) were tested. The most suitable selected design
was Ptc/PPD/PEI(1%)2/GlutOx5/PG(0.1%) and it was compared to the same already described
design loading PEDGE, instead of PG, in terms of over-time performances. PG has proved to be
capable of determining an over-time stability of the glutamate biosensor in particular in terms of
linear region slope (LRS) up to 21 days.