Long-term Drifts in Sensitivity Caused by Biofouling of an Amperometric Oxygen Sensor

Changes in oxygen sensitivity of an poly(o-phenylenediamine) (PoPD) coated gold electrode was determined by constructing calibration curves invitro. Oxygen sensitivities recorded in the presence of biofoulants were significantly different from those recorded in buffer; however, PoPD demonstrated its effectiveness in providing some resistance to changes in oxygen sensitivity over time compared to a bare electrode. Three sets of PoPD-coated electrodes were calibrated in simple electrolyte of phosphate buffered saline; each set yielding an average oxygen sensitivity of 0.58 +/- 0.03A/ppm, 0.68 +/- 0.01A/ppm, and 0.48 +/- 0.01A/ppm (n=4), which shows the electrode to electrode variation in the PoPD-coating/electrode. These sets were correspondingly exposed to bovine serum albumin, fibrinogen, rat brain homogenate. Exposure to these biofoulants resulted in decreases in sensitivity ranging from 26-35% after immediate exposure. Furthermore, long-term exposure to some biofoulants causes significant decreases in sensitivity over a time period of 14 days. We also estimated through invitro exposure to rat brain homogenate the errors that might be associated with current methods of calibration. Sensitivities to oxygen determined by precalibration resulted in a 50% error from the sensitivity found invitro; the error from postcalibration after rinsing resulted in 25% error.