sentences:  Recently, SELEX reactions have been developed where the target is whole cells, which are expanded near complete confluence and incubated with the oligonucleotide library on culture plates.Incubation buffer conditions are altered based on the intended target and desired function of the selected aptamer.For example, in the case of negatively charged small molecules and proteins, high salt buffers are used for charge screening to allow nucleotides to approach the target and increase the chance of a specific binding event.