Microplates with small well-surface area prevent adverse effects on cells caused by DMSO dispensed by Echo Acoustic Liquid Handlers.

Small molecules used in high-throughput screening are typically dissolved in DMSO. For cell-based small molecule screening, in some assays like short-term treatment, cells need to be seeded in microplates first before dispensing small molecules on the cells. Echo Acoustic Liquid Handlers are popular instruments for small molecule dispensing because of the flexibility of dispense protocols and the low risk of cross-contamination. However, we observed that dispensing DMSO in one assay with our Echo induced a change in cellular phenotypes in random wells. We found this effect was confined to two 384-well plate brands and occured within 5 minutes of dispensing DMSO or compounds in DMSO on cells. When loading plates into the Echo, the destination plate is inverted.  We suspected that the inversion of the destination plates with cells causes culture medium to flow to one side and hang on the side-wall of the wells. This leaves less culture medium on the bottom of the wells, and in this condition, DMSO dispensed by the Echo will cause a local surge in DMSO concentration. Most plates designed for imaging have large well surface areas so a large area can be imaged; however we found that smaller well-surface area reduces the ability of the culture medium to flow when flipped and was preferable in this instance. We have validated two 384-well plates from different brands with smaller well-surface area and one 1536-well plate that do not show such cellular phenotypic changes following DMSO dispensed with our Echo.