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 O₂), 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.