Interference elimination in glutamate monitoring with chip integrated enzyme microreactors

On-chip enzyme reactors are often used in medical/pharmaceutical analysis due to their inherent advantages, such as high sample throughput, low reagent consumption, stability, reproducibility and low cost. The present work describes a different application of such microreactors, namely, elimination of interfering ascorbate signals in glutamate monitoring using ascorbate oxidase modified silicon chip microreactors of different sizes (5.3 and 0.95 muL). Glutamate was monitored with a previously developed redox hydrogel integrated bienzyme electrode, based on coupled glutamate oxidase and horseradish peroxidase, inserted in a miniaturized flow cell operated at -50 mV (vs. Ag/AgCl). The developed on-line analysis system was characterized with regard to dilution effects, detection limit, response time and interference ability using model solutions and real samples. Off-line in vivo glutamate measurements could be made by injecting rat brain microdialysate samples collected before and after KCl stimulation without any interference of ascorbate, I Within the studied flow rate range (2-25 muL/min), 1 mM and 200 muM ascorbate could he totally eliminated using the larger and the mailer microreactor, respectively.