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

Abstract

Changes in oxygen sensitivity of an poly(o‐phenylenediamine) (PoPD) coated gold electrode was determined by constructing calibration curves in vitro. 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±0.03 μA/ppm, 0.68±0.01 μA/ppm, and 0.48±0.01 μA/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 in vitro 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 in vitro; the error from postcalibration after rinsing resulted in 25 % error.

In vitro development and in vivo application of a platinum-based electrochemical device for continuous measurements of peripheral tissue oxygen

“…This assumption was supported further by unpaired t-tests performed between individual exposure days. A significant decrease in sensitivity (p = 0.03) was recorded initially between Day 0 vs. Day 1, which corroborates previous reports using implantable brain sensors [36,37]. However, there were no further significant differences between Day 1 vs. Day 3 (p = 0.54), Day 1 vs. Day 7 (p = 0.95), or Day 1 vs. Day 14 (p = 0.69).…”

“…Many microelectrode types have been used for the electrochemical reduction of molecular O 2 [28,33,37,38]. Platinum has particularly excellent electrocatalytic properties that make it an ideal candidate for O 2 reduction [21], which consists of a four-electron reduction to H 2 O:…”

“…Sensocompatibility is a term coined by Wisniewski and colleagues to describe the effect the body has on an electrochemical sensor [50], and has been reported previously for different sensors [28,51]. The in vivo environment presents a complex chemical milieu that includes electrode contaminations, such as lipids, proteins, and a tissue matrix that restricts mass transport to the electrode surface and physiologically reacts to a sensor's presence [36,37,52]. The effect of brain homogenate on Pt electrodes has been reported previously whereby bare Pt electrodes demonstrated a decrease in sensitivity after three days of exposure, though no significant difference was noted when compared against non-treated electrodes [28].…”

“…In our case, a drop in sensitivity after 24 h of exposure was noted, which illustrated a negligible deviation over the subsequent 14 days. This initial compromise in sensitivity is to be expected following tissue homogenate contact [37]. The adhesion and proliferation of fouling agents such as proteins and lipids on all Pt electrodes serve to briefly degrade the device's functionality.…”

Real-Time Amperometric Recording of Extracellular H2O2 in the Brain of Immunocompromised Mice: An In Vitro, Ex Vivo and In Vivo Characterisation Study

“…Furthermore, the tissue matrix surrounding the biosensor surface both restricts mass transport of the target analyte to the electrode surface and reacts physiologically to the presence of the sensor. This is a well-documented phenomenon for in vivo electrochemical measurements [ 26 , 29 , 30 ] that warrants considerable attention. Although not an exact representation of the physiological environment, exposing an electrochemical sensor to brain tissue homogenate serves as a good indication of the effect of in vivo conditions on the biosensors performance.…”