A flow-through mechanical trap for repetitive analysis of individual particles

We describe the construction of a flow-through analyzer with a mechanical fluidic control system that allows individual particles such as beads or cells to be trapped repeatedly for optical analysis. This instrument allows long measurements of particles sampled from rapid flow and can be used to determine contributions to measurement variance and individuate environmental perturbations on single cells. The demonstration system described here includes basic detection channels for forward-scattered light and fluorescence, a pinch-valve based trap, a mechanism for controlling the position of trapped particles, and a holding loop for long-duration studies of single particles. It can operate in a flow-cytometer mode and in modes that resample particles over periods of seconds to minutes. The system is capable of flow rates of 10 ml min-1, making it especially useful for studies of rare particles, and its cost effectiveness could allow for multiple units to operate in parallel to sample higher volumes.