Impedance-controlled cell entrapment using microhole-array chips allows the isolation and identification of single, highly productive cells

Highly productive cells are required for the manufacture of biopharmaceutical proteins, but the best-performing cells can be difficult to isolate from a large and heterogeneous background. Although this problem has been addressed by gently positioning individual cells on microhole arrays, such a procedure is typically monitored by microscope which limits the size of the array to the field view of the microscope and also requires the use of direct illumination, which bleaches the sensitive fluorescent reagents needed to identify the most productive cells. We have circumvented these problems by developing an impedance-based method for cell positioning, and by defining a relationship between impedance and occupancy we are also able to monitor the progress of the cell positioning process. We identified cells secreting large amounts of a model antibody by mixing the cells with semi-solid medium and a light-sensitive antibody detection reagent, and then using impedance controlled positioning to capture cells on the microholes in absence of direct light. Following a 1-day incubation, antibody secretion could be determined qualitatively using fluorescence imaging and a simple image processing algorithm. For the first time, we have shown that antibody secretion from individual cells on a microhole array can be classified and used to identify the most productive cells. Because this procedure does not rely on optical analysis it could easily be scaled up to allow the screening of millions of cells at a time.