Transfection efficiency can be measured by transfecting GFP plasmids into the cells then analyzing the level of GFP expression in the cells using either qualitative or quantitative methods. The GFP plasmids can be co-transfected with RNPs to help locate cells that have a high likelihood of containing RNPs and therefore a higher likelihood of exhibiting the desired genome edits.
Using this approach, it is important to optimize transfection efficiency for each cell type as high transfection is essential for high editing rates. With high transfection efficiencies (80-90%) and high editing rates (as with chemically modified sgRNAs, 70%-90%), it is less critical to identify or isolate the transfected cells.
(Additionally, it is possible to use reporter systems other than GFP to asses transfection efficiency)