Table 1 Modified SELEX techniques and their advantages

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]