Microfluidic Sensor System for Initial Growth Rate Determination of Small Bacteria Samples

The observation of a cell culture and its growth is a very important part of diagnostics in medical applications as well as biological applications. Especially medical applications benefit from a fast knowledge of the existence of bacteria growth. It can be used for the development of antibiotics as well as for the diagnostics of diseases.The recovered time can be vital for the success of a treatment. We present an approach and device to monitor on-chip bacteria growth based on the absorption measurement with a low limit of detection. A low limit of detection, high sensitivity and a small sample size define the capability of sensing the initial growth rate of small bacteria samples within a few hours. 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 compared to an out-of-plane approach by performing an in-plane optical density measurement so that the sensitivity is improved and thereby the limit of detection is lowered. 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 photo diode. The relation between the absorbed light and the bacteria concentration agrees well with the theory and a growth curve can be recorded. A particular focus is laid on a reproducible setup based on 3D-printed holders where external disturbances such as ambient light are minimized. Because of the increased sensitivity, the limit of detection is only 1.5×10
⁶
bac/ml. By applying the method of this contribution, additional standard laboratory operations can be integrated into chips.