Table 1.

Modified SELEX techniques and their advantages

Modified SELEX techniques	Principle	Advantages	References
Negative SELEX	Removing the nucleic acid sequences that bind to the matrix, on which the targets are attached	Increased affinity of the selected aptamers	[7]
Counter SELEX	Removing non-specific nucleic acid sequences from the target by performing negative selection on a molecule that is structurally close to the target	More specific aptamers	[7]
CE-SELEX	Selection on capillary electrophoresis, therefore more efficient separation of linked sequences from unbound sequences, in solution	Use of non-immobilized targets, fewer cycles required (therefore less expensive because less sample and less solvent required)	[5, 7, 8]
MonoLEX	A single selection step by affinity chromatography	Only one step, therefore much faster	[9]
Mag-SELEX	With oligonucleotides and/or targets attached to metal beads, separation of bound and unbound sequences by a magnetic field	Use of smaller targets, easier and faster separation step	[5, 7]
Microfluidic SELEX	Use of a microfluidic system	Selection can be automated, association with Mag-SELEX or CE-SELEX possible	[5, 7]
HTS-SELEX	Addition of high-throughput sequencing to each round	Early identification of sequence enrichment, leading to a gain in efficiency and a decrease in the number of cycles required	[5, 7, 10]
Cell-SELEX	Cells used as targets, with a negative selection step using healthy cells	The target is a transmembrane protein or an unidentified protein specific to a cell type	[5, 7, 8, 11]
In vivo SELEX	Selection in living organisms by injection of nuclease-resistant nucleic acids	Selection of aptamers that target a tissue and can penetrate or identify it in a living organism, identification of protein markers in a tissue	[5, 7]
Spiegelmer	For chiral targets, SELEX process performed on the enantiomeric form of the target, then synthesis of the selected aptamer with l-nucleotides	More stable and nuclease-resistant aptamers	[5, 8]
Chimeric SELEX	Selection of two aptamers specific of two targets, and combination in a single molecule	Aptamer that can bind to two separate targets	[5]
Toggle-SELEX	Use of homologous targets, from different species, every other round	Aptamer with significant affinity for its target even when changing species	[5]
Crossover-SELEX	Use of purified protein or tissue/cell as targets every other round	The selected aptamer has more chance to recognize its target in vivo	[5]
Truncation SELEX	All probable nucleotide truncations of the selected aptamer are used to perform a new screening	The size of the final aptamer is reduced while being as much or more efficient than the initial one	[5]
Modified SELEX	Use of modified nucleotides	Modification of aptamer properties	[5]