Cellular bias on the microscale: probing the effects of digital microfluidic actuation on mammalian cell health, fitness and phenotype

The potential benefits of using new technologies such as microfluidics for life science applications are exciting, but it is critical to understand and document potential biases imposed by these technologies on the observed results. Here, we report the first study of genome-level effects on cells manipulated by digital microfluidics. These effects were evaluated using a broad suite of tools: cell-based stress sensors for heat shock activation, single-cell COMET assays to probe changes in DNA integrity, and DNA microarrays and qPCR to evaluate changes in genetic expression. The results lead to two key observations. First, most DMF operating conditions tested, including those that are commonly used in the literature, result in negligible cell-stress or genome-level effects. Second, for DMF devices operated at high driving frequency (18 kHz) and with large driving electrodes (10 mm x 10 mm), there are significant damage to DNA integrity and differential genomic regulation. We hypothesize that these effects are caused by droplet heating. We recommend that for DMF applications involving mammalian cells that driving frequencies be kept low (<= 10 kHz) and electrode sizes be kept small (<= 5 mm) to avoid detrimental effects.