Magnetic sensor macrospheres as easy-to-use, remote-controlled, optical sensors in bioprocess monitoring

Optical sensor patches immobilized in cultivation flasks or tank reactors are nowadays state-of-the-art for monitoring process parameters in real-time. We produced magnetic sensor macrospheres (MagSeMac) as mobile, remote-controlled sensor patches by coating soft-magnetic steel spheres with an indicator dye which is incorporated in a polymer support matrix. Depending on the matrix polymer and the incorporated dyes, the sensors can be utilized for real-time monitoring (oxygen as analyte) or even for delayed readout (pH). The chosen sensor chemistry allows signal readout with the same commercially available fiber phase fluorimeter for both pH and oxygen. The sensor spheres typically have diameters of 1-4 mm and can be trapped in front of an optical fiber by specially designed magnetic separators. The attachment is very firm and can withstand even strong shear forces induced by stirred liquid inside a vessel. This approach makes it possible to measure process parameters in places and cavities otherwise hardly accessible. After usage, these mobile sensor patches can be recovered from the medium and used for a second time or simply be disposed and replaced by a new sphere. Moreover, the sensor sphere can be kept at a constant position relative to the optical fiber even when the flask or vessel is moving.