Droplet-based microfluidics as bioreactors for bacterial community study and patient postoperative monitoring

Droplet-based microfluidics that emerged a decade ago has offered a new route to boost the efficiency of biochemical methods in terms of detection time and sensitivity [Kaminski et al., Chem. Soc. Rev. 46, 2017]. Droplet-based fluidic technology saves materials consumption and reduces experimental wastes, allowing for real-time and individual tracking of each reactor, and has found numerous applications in biology and biotechnology [Baraban et al., Lab. Chip, 11, 2011]. In our lab, we developed a droplet-based microfluidic system to detect the bioreaction (e.g., bacterial growth, antibiotic effect, enzyme reaction dynamic, and so on) in high throughput and sensitivity by detecting fluorescence signals. The system achieves monitoring the bioreaction in the hundred to thousand droplets with the size of 200 nL with multi-channel automatically. Depending on the different purposes, this system can be adjusted to monitor the same batch of analytes over time in the long term (days), or continuously real-time detect analytes level change, as well as to switch between various optical settings.
For example, we used the millifluidic droplets reactor system to study the bacterial coexistence by monitoring two Escherichia coli strains' growth simultaneously in real time [Zhao et al., Lab. Chip, 21, 2021]. Our system offers an environment with high statistical output, unaffected bacteria growth, and long-time measurements in a well-mixed liquid inhabit. By reading fluorescence in two parallel detector channels, we obtained and analyzed the monoculture and co-culture of these two strains E. coli BFP and E. coli YFP and explained the interaction and relationship between them. In another work, we investigated the antibiotic effect on bacterial coexistence. Our automatic nanoliter droplet analyzer is used to study the interactions of the sensitive and resistant strains of E. coli in the presence of antibiotics and to define the criteria leading to the emergence of cross-protection phenomena.
Moreover, due to the quick response and high sensitivity properties, we miniaturized the system to a bedside portable size and introduced it to the clinical field of real-time sensing drain α-amylase activity for postoperative monitoring of patients undergoing pancreatic surgery. Based on the reaction of the starch-FL reagent with amylase to produce a fluorescence intensity that correlates with the concentration of amylase, thus enabling the detection of the patient's amylase level. In this work, our strategy significantly improves the determination time (3 min) and detection limit (7 nmol/s·L) and reduces material requirement (10 μL) and wastes.
In the future, we expect to apply our portable device in more clinical scenarios, e.g., lactate and lipase level monitoring, and septicemia determination, in which case bacteria poisons the blood, and needs urgent and accurate low-concentration detection. Not limited to aqueous phase droplets, our research group also focused on solid and semi-solid environments, such as incubating bacteria or cancer cells in gel beads or capsules. For instance, we encapsulated two bacterial strains in agarose gel beads to study the effect of space on bacterial coexistence [Nguyen Le et al., Micromachines, 14, 2023]. We also cultured cancer cells in capsules and adjusted the core-shell ratio to structure cell growth conditions [Peng et al., Biotechnology Journal, 2023].