SeCaT-meter 600: Prism-based dual channel optical density meter with self-calibration.

Accurate and real-time monitoring of optical density (OD) is one of the key requirements for control of microbial fermentations. It provides insight into current cell concentration and growth dynamics of microbial cell cultures by measuring optical density at 600 nm (OD600). In combination with additional chemical (e.g. pH, dissolved oxygen), and physical (e.g. temperature) parameters, adjustments of culture conditions can be made during cultivation. Optical density is determined through either in-line, on-line or off-line measurements, although on a laboratory scale manual sampling (off-line) is typically performed due to the high acquisition costs of on-line devices. UV/Vis spectrometers or photometers are generally used for this purpose, but these are not suitable in resource-limited settings or for small-scale laboratories or field applications due to their acquisition costs and the limited possibility of self-performed repairs and modifications. Using widely available electronic components and 3D printing, we designed a self-calibrating photometer capable of precise OD600 measurements for bioprocess monitoring. This device is intended to offer an affordable and robust solution for both laboratory-scale experiments and field applications, where portability and ease of use are paramount.