μfluidic Sensor for Optical Monitoring of Bacteria Growth with Improved Limit of Detection

We present an approach and device to monitor on-chip bacteria growth based on the absorption measurement with a low limit of detection. Because of the small height of microfluidic channels, a standard optical density method is not applicable. In our approach, the optical path is 20 times longer by performing an in-plane optical density measurement compared to an out-of-plane approach so that the sensitivity is improved. An LED (580 nm center wavelength) is used to propagate light through a sample in the measurement channel. The passing light intensity is measured at the outlet by a photodiode. The relation between the absorbed light and the bacteria concentration agrees well with the theory. A particular focus is laid on reproducible setup based on 3D-printed holders where external disturbances such as ambient light are minimized. In combination with the increased sensitivity, the limit of detection is only 1.5. 106bac/mL. By applying the method of this contribution, additional standard laboratory operations can be integrated into chips.