Monitor, categorize and manipulate label-free water-in-oil droplets in microfluidic systems*

A key point of droplet based microfluidics is the availability of powerful but easy-to-implement methods for high throughput real-time analysis and automated manipulation of the droplets. We developed a novel optical device, consisting of a fast camera with integrated data processing for smart and fast algorithms enabling label-free real-time monitoring and active manipulation of passing droplets. The device continuously analyzes up to 3000 particles per second in real-time with respect to bright-field image parameters like size, brightness, granularity, circumference, speed and many more. According to these parameters and combinations thereof, the passing droplets can be sorted. We measure different droplet production parameters and demonstrate label-free detection of cells encapsulated in droplets. Furthermore, we performed label-free sorting of cell laden droplets from empty droplets. The peripheral sorting electronics are controlled by our device. Decision making is based on predefined parameter ranges that are compared to the measurement results of the droplets right before the sorting gate. Similarly, in another experiment we demonstrate efficient sorting of droplets depending on size.