# Optimization of the angle for scattered light measurements in 3D-printed cultivation vessels

## TL;DR

This paper introduces an optical adapter to optimize the angle for measuring scattered light in 3D-printed cultivation vessels, improving biomass monitoring in biotechnology.

## Contribution

The study introduces an optical adapter to rapidly determine the optimal angle for scattered light measurements in 3D-printed vessels.

## Key findings

- An angle of 110° provides higher signal intensity and sensitivity compared to larger angles.
- The 110° angle was validated for various biotechnologically relevant microorganisms.
- The optical adapter can be used to test different vessel sizes and geometries.

## Abstract

Monitoring key parameters during the cultivation of microorganisms—including biomass concentration—is often a crucial prerequisite for attaining reproducible results in the field of biotechnology. In order to overcome the drawbacks associated with conventional methods for assessing biomass concentration (such as cell dry weight or optical density measurements), several devices to facilitate continuous online monitoring have been developed. Yet despite the success of innovative solutions (such as acceleration sensors) in addressing the challenging dynamical behavior of liquids within shaken systems, the performance of these sensors can still be affected by reflections at the liquid–air interface or at the top of the cultivation vessels. In our previous work, a 3D-printed cultivation vessel equipped with modified optical waveguide paths was utilized in an effort to overcome this challenge, allowing for the measurement of scattered light in a lateral direction. In this work, we developed an optical adapter that allows for the rapid assessment of the optimal measurement angle of excitation and detection within these 3D-printed cultivation vessels. The findings of the present study indicate that an angle of 110° yields higher signal intensities and enhanced sensitivity in comparison to larger angles, and this finding was additionally confirmed for a set of biotechnologically relevant microorganisms. While these results suggest that the angle of 110° should be integrated into the cultivation vessels in the future, the optical adapter also holds the potential to further investigate vessels with different sizes or geometries.

The online version contains supplementary material available at 10.1007/s00216-025-06131-4.