Automation of Cell Viability Assays Utilizing Microfluidic Dispensing Technology

Cellular viability assays are widely used to investigate the potency or toxicity of biologically active molecules. One of the most widespread techniques to measure cellular viability is a luminescent CellTiter-Glo® (CTG) Assay, a homogeneous method based on quantitation of the ATP present, an indicator of metabolically active cells. The "add-mix-measure" format generates a luminescent signal proportional to the amount of ATP and, thus, proportional to the number of metabolically active cells present in the culture. It is designed for use with multiwell formats, making it ideal for automated high-throughput screening, cell proliferation, and cytotoxicity assays. However, in our hands, CTG has limitations for use on automatic platforms because the reliability of dispense degrades over extended run times, primarily due to liquid dispensers becoming clogged.

Multidrop combi TEMPEST (1)

Assessment of cell viability after long period of inactivity 1 µl of CTG was added to 5 µl of media-containing cells (after 72 hours of incubation in 5% CO2 at 37°C). CTG was left in the system for 16 hours (overnight). Data could not be generated with Multidrop Combi because the reagent clogs the cartridge lines after a long period of inactivity. Using TEMPEST in an automated setting with recirculation turned on allowed us to avoid clogging issue and generate data after overnight incubation with a viscous reagent.

We have tested the use of CTG in two liquid dispensers: Multidrop® Combi Liquid Dispenser (ThermoFisher) and TEMPEST® (FORMULATRIX). The Multidrop consistently provided accurate and precise dispenses data during daily operations where many plates were dispensed in rapid succession. However, when runs had periods of inactivity (such as overnight or longer pace times), CTG would frequently clog the cartridge lines. Data obtained with TEMPEST has been found to be more reliable in extended run scenarios. Using the TEMPEST in a fully automated setting with recirculation turned on allows experiments to be performed in multiple time-based formats, including overnight runs and longer pace times. We have also demonstrated that the TEMPEST provides better precision in the 1536-well plate format.