Optics in droplet microfluidics

Droplet-based microfluidics facilitates the manipulation of small volumes of liquids of two immiscible phases; e.g., water and oil. Effectively, the technique involves a small reactor in which a chemical reaction or biological process can be performed and observed over time. Microdroplets can be mixed, sorted, incubated, and analyzed. Those operations can be performed in specially designed microfluidic chips, creating small lab-on-a-chip devices. Besides miniaturization, an added advantage is that many replications of one experiment can be performed very quickly.

In our research, we aim to observe the behavior of various clinically relevant bacteria strains. More specifically, we are interested to see how they react to antibiotics. Antimicrobial resistance (AMR) is one of the most urgent threats to global health. It occurs when bacteria, viruses, fungi, or parasites transform over time and are no longer sensitive to medicines. As a result, antibiotics or other antimicrobial drugs become unsuccessful and can no longer treat diseases effectively. The World Health Organization (WHO) has recognized AMR as one of the top 10 threats to global public health.

Monitoring bacterial behavior; i.e., growth, is a challenging and time-consuming task, particularly when we need to monitor thousands or millions of replicate experiments. Optical methods combined with microfluidics enable us to address this problem. Using specially designed chips, we can apply droplets in the path of a laser beam and analyze the light scattered from bacteria cells. The intensity of the scattered light is proportional to bacterial concentration in the droplets, and we can follow it over time. We can monitor more than 1000 droplets per second and analyze them with dedicated software. Additionally, we can also make the system more compact and easier to use by using fiber optics.


Natalia Pacocha, Jakub Bogusławski, Michał Horka, Karol Makuch, Kamil Liżewski, Maciej Wojtkowski, and Piotr Garstecki, “High-Throughput Monitoring of Bacterial Cell Density in Nanoliter Droplets: Label-Free Detection of Unmodified Gram-Positive and Gram-Negative Bacteria,” Analytical Chemistry 93(2), 843-850 (2021).


Text: Jakub Bogusławski, PhD