Oxidative and nitrosative stress markers have been successfully separated within a short time utilizing nL-pL sample volumes using microchip electrophoresis. Although most of the products of reactive oxygen and nitrogen species are either electrochemically reducible and/or oxidizable, the majority of work has been dedicated to the electrochemical detection of oxidizable analytes and only a few applications have addressed the detection of reducible species. This is primarily due to the high electrochemical background resulting from oxygen reduction, even at low negative potentials, that leads to high LODs. Previously our group investigated the coupling of bipolar electrochemistry with fluorescence to obtain better LODs for reducible compounds without a potentiostat. The main challenge that was encountered with that newly developed detection system was insufficient limiting current at the reporting channel. The use of an oxidizable sacrificial electrochemical species in the reporting channel was explored to obviate this problem. In this work the evaluation of sacrificial species to obtain better detection limits is discussed.<br/>The detection system consisted of 5 cm, 40 μm × 15 μm PDMS simple-t microchip aligned at a 15 μm pyrolyzed photoresist film (PPF) carbon electrode using a pseudo-in channel configuration. A 30 μm Au electrode was placed in the in-channel configuration as the reporter channel. The two electrodes were connected using a copper wire to complete bipolar electrode system. The electric field across the reporting channel was adjusted to bias the bipolar electrode for detection in the separation channel. A sacrificial electroactive species was added to the fluorescent probe solution in the reporter channel. LODs were 10-fold lower using this configuration compared to the conventional reductive electrochemical detection Calibration curves were obtained for 3-nitrotyrosine and sodium anthraquinone-2-sulfonate with an R<sup>2</sup> greater than 0.98. Progress on the application of this system for the detection of oxidative and nitrosative stress biomarkers will also be described.

Improvement of the detection limits of bipolar electrode-based fluorescence detector for microchip electrophoresis using a sacrificial electrochemical species

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ACS Fall 2022

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