Measurements on the fly– Introducing mobile micro-sensors for biotechnological applications

Abstract The application of standard sensor electrodes is often limited to stirred tank reactors due to their wired nature and their large space requirement. For other cultivation systems, sensors require a great technical effort to be implemented. Here we propose a new concept of sensors: miniaturized, mobile, wireless, and self-contained spherical sensors with diameters of only 7.9 mm. The micro-probes send their data wirelessly at a frequency band of about 433 MHz to a base station during the process run and are easily deployable for many biotechnological applications and reactor types, without any need to modify the cultivation system, as the probes are nearly non-invasive due to their small size. The system consists of a platform that can accommodate various sensor types, e.g., temperature as shown in this work. The sensor spheres are reusable and can be charged by induction before being deployed in a biotechnological application. Furthermore, redundancy can easily be realized by adding several sensors into a single reactor, since each base station can coordinate up to 24 spheres. From computational fluid dynamics (CFD) simulations we could infer the maximum allowable density of spheres that would still enable them to be homogeneously distributed within a reactor as 1.1 g/cm 3 . We could demonstrate the practical applicability of our concept by deploying the spheres in shaking flasks, lab-scale stirred tank reactors, and tube reactors in typical lab environments. In all cases, the spheres showed reliable data transmission despite the potentially shielding technical environment.