Table 2.

Key aspects, advantages, and disadvantages of the currently used SELEX methods.

Method	Key Aspects	Advantages	Disadvantages
IP-SELEX	Includes immunoprecipitation.	Selects aptamers against proteins under normal physiological conditions. Increased affinity and specificity.	More time-consuming than standard SELEX.
Capture-SELEX	Oligonucleotide library is immobilized on a support instead of the targets to identify aptamers against small soluble molecules.	Suitable for the selection of aptamers against small molecules. Immobilization of the target not required. Used for the discovery of structure-switching aptamers.	Some oligonucleotides from the library might be not released/selected.
Cell-SELEX	Utilizes whole live cells as targets for selection of aptamers.	Prior knowledge of the target not required. Aptamers are selected against molecules in their native state. Many potential targets available on the cell surface. Protein purification not required.	Suitable for cell surface targets. Requires high level of technical expertise. Costly. Time consuming. Post SELEX identification of the target required.
CE-SELEX	Involves separation of ions based on electrophoretic mobility.	Fast. Only few (1–4) rounds of selection required. Reduced non-specific binding. Target immobilization not required.	Not suitable for small molecules. Expensive equipment.
M-SELEX	Combines SELEX with a microfluidic system.	Rapid. Very efficient (only small amounts of reagents needed). Applicable to small molecules. Automatable.	Low purity/recovery of aptamers. Target immobilization required.
AFM-SELEX	Employs AFM to create three-dimensional image of the sample surface.	Able to isolate high affinity aptamers. Fast (only 3–4 rounds required).	Expensive equipment required. Immobilization of target and aptamers required.
AEGIS-SELEX	Utilizes libraries with the artificially expanded genetic code.	High specificity of the selected aptamers.	Poor recognition of the unnatural bases by natural DNA polymerases.
Animal-SELEX	Aptamers are selected directly within live animal models.	Selected aptamers bind the targets in their natural environment. Prior knowledge of the target not required. Minimal optimization needed.	Time consuming (many rounds required).