Polysense proposes to evaluate the feasibility of single fiber optical sensors for continuous invasive monitoring of pH and carbon dioxide. The sensing element is a small drop of a rubbery crosslinked heterogeneous polymer attached to the end of an optical fiber. The polymer contains functional groups, e.g. amines, that react with hydrogen ion. Protonation of the amine groups introduces a fixed charge which causes the polymer to swell due to electrostatic repulsion. Because swelling moves the heterogeneities in the polymer further from the optical fiber surface, it is accompanied by a decrease in the quantity of light diffusely reflected back into the optical fiber at the phase interfaces within the polymer. Reflected intensity serves as a measure of the pH of the medium. The pH sensor can also serve as the internal element in a carbon dioxide sensor. This is accomplished by contacting the pH sensitive polymer with a solution of bicarbonate and coating it with a hydrophobic carbon dioxide permeable membrane. The proposed sensors offer improved ruggedness and stability at reduced cost compared to other pH sensing technologies. They are to be incorporated into systems for continuous invasive blood gas measurements to monitor the respiratory status of patients in critical care. This will replace the current technology which involves intermittent sampling and laboratory or bedside analysis.
| Shakhsher, Z; Seitz, W R; Legg, K D (1994) Single fiber-optic pH sensor based on changes in reflection accompanying polymer swelling. Anal Chem 66:1731-5 |
