Method for the accurate preparation of cell-spiking standards

Preparation of calibration standards for cell enumeration is critical in characterizing the performance of any method or apparatus intended for recovering rare cells. Diluting a cell suspension serially is prone to statistical sampling errors as the cell suspension becomes more dilute, whereas transferring and injecting cells individually into a diluent with a micromanipulator is time-consuming. We developed a simple and robust method using a surface-modified glass capillary to siphon and eject cells. One-dimensional confinement of cells offered by the capillary made cell enumeration by visual counting simple and rapid, and cell ejection from the capillary was near 100% when the appropriate surface coating and cell solution was used. The residence time of cells in the capillary, however, could affect the percentage of cells that was ejected from the capillary. To characterize the performance of this method, we enumerated the ejected cell using both visual counting under a microscope and automated detection using a chip-based flow cytometer.