Oxygen sensor based on the fluorescence quenching of a ruthenium complex immobilized in a biocompatible poly(ethylene glycol) hydrogel

An optically based system has been developed for use as an oxygen sensor for a cell culture bioreactor. Electrochemical sensors based on the Clark oxygen electrode are typically used With cell-culture bioreactors. These sensors, however, are subject to long-term drift, due in part to biofouling, and require penetrating the bioreactor with the probe in order to perform a measurement. We report an implantable sensor that, when used with an external fiber-optic probe, takes advantage of the oxygen stimulated fluorescence quenching of dichloro(tris-1,10-phenanthroline) ruthenium (II) hydrate. This fluorophore was immobilized in a photopolymerized hydrogel made from poly(ethylene glycol) diacrylate (PEG-DA), a polymer known to minimize protein and cell adhesion. A low-average molecular weight PEG-DA (MW = 575) was employed to hinder the fluorophore from leaching. The PEG-DA precursor solution contained 40 % H2O such that, upon polymerization, the gel was already in the hydrated state. Sensor hydrogels stored in H2O for several months retained their physical shape and sensitivity to oxygen. The sensor showed a high degree of reproducibility across a range of oxygen concentrations that are typical for cell culture experiments (0-9.1 ppm O-2), and a linear model produced a strong correlation (R-2 = 0.995) compared with a commercial electrochemical probe. No drift or hysteresis was identified in the sensor across cycles of varying oxygen concentrations in this range.