Breaking through the Poisson Distribution: A compact high-efficiency droplet microfluidic system for single-bead encapsulation and digital immunoassay detection.

Droplet encapsulation of a single cell or bead is widely used in digital detection, single-cell sequencing, and drug screening. However, the encapsulation of particles is totally random restricted by the Poisson distribution. The theoretical possibility of single-particle encapsulation is usually only approximately 10%. In ultra-high multiplexed digital detection or other applications that needing to measure large numbers of particles, the number of the partitions required to be counted is extremely high, further result in great increase of statistical number of invalid droplets and the redundancy of detection data. Here, a bead ordered arrangement droplet (BOAD) system is proposed to break through the Poisson distribution. BOAD system tactfully combines sheath flow, Dean vortex, and compression flow channel to achieve orderly arrangement of particles for the first time, and could achieve the fastest orderly arrangement of particles in the shortest structure. The efficiency of single-bead encapsulation is improved to as high as 86%. Further application to encapsulate encoding beads and IL-10-targeted magnetic beads demonstrates the potential for bead-based ultra-high multiplexed digital detection. Thus, use of the BOAD system is very promising for many applications needing high single-particle encapsulation ratio in limited partitions, such as multiplexed digital bio-detection, single-cell analysis, drug screening, and single exosome detection.