(269a) Droplet Sorting for Generation of Single Heterotypic Cell Pairs

Co-culture of heterotypic cells are fundamental for examining cell-cell interactions. Conventional studies of cell-cell interactions are conducted at the population level and do not reveal details at the single cell resolution. Recent advances in micromanipulation technology, such as hydrodynamic trapping, dielectrophoresis, optical tweezers and magnetic force enable scientists to probe cell-cell interaction at the single cell level. However, cell-pairs created by these methods lack isolated environment to avoid cross contamination between different cell pairs. Additionally, most of the current methods can only create and interrogate a low number of cell-pairs, limited by their use for population description.  

To address these problems, we develop a sophisticated droplet sorter that enriches droplets containing single heterotypic cell-pair from a mixture of all configurations. Our platform includes a solenoid-valve-based droplet sorter and a fluorescence signal processing system with a microcontroller as the core.  The fluorescence intensity between different groups (e.g.: type A and type B) of cells is rendered significantly different, as a result of different labeling concentration of florescent dye. Taking advantage of this labeling strategy, only single laser with single PMT detector is required for the detection and differentiation of multiple groups of cells. A line-focused laser beam, shaped by cylindrical lens, is able to induce fluorescence of encapsulated cells individually. A typical fluorescence spectrum indicates the cell type and cell number in each droplet at single cell resolution. The fluorescence data was processed by a comparator and an analogy-to-digital (AD) converter and finally analyzed by a programmed microcontroller, which determines both the types and numbers of encapsulated cells in each droplet and making the sorting decision in real time.  Accordingly, droplets encapsulating single heterotypic cell-pair can be successfully isolated and enriched as a homogeneous droplet population.