Table 1.

Types of SELEX development processes.

S. No.	Type	Description	Reference
1.	Negative SELEX	For removal of non-specific aptamers	Ellington and Szostak, 1992
2.	Counter SELEX	For removal of cross-reactive aptamers by incubating them targets obtained from related species	Jenison, 1994
3.	Genomic SELEX	For the identification of binding motif present in the genome of an organism	Singer et al., 1997
4.	In vivo SELEX	Aptamers are generated in vivo, inside the cell and then characterized	Coulter et al., 1997
5.	Chimeric SELEX	In this method, well- characterized aptamers are fused together so that the resulting aptamer can bind to different targets (one aptamer can recognise two or more different targets)	Burke and Willis, 1998
6.	Cell-SELEX	For the development of aptamers which recognise markers present in whole cell	Homann and Goringer, 1999
7.	Indirect SELEX	In this SELEX method, the binding of aptamers with their targets are metal-ion dependent	Kawakami et al., 2000
8.	Photo- SELEX	In this method, nucleotides are light-sensitive and irradiation with UV rays is employed to select the specific aptamer-target from the pool	Golden et al., 2000
9.	Toggle SELEX	For identification of cross- reactive aptamers by using toggled targets	Bianchini et al., 2001
10.	Tailored SELEX	Aptamers often contain primer- hybridization site. Introduction of cleavable primer hybridization site in aptamers will select for primer-free-aptamers.	Vater et al., 2003
11.	CE (Capillary electrophoresis)- SELEX	This process selects high affinity aptamers in a few cycles (2-4) thus shortens the aptamer selection process	Mendonsa and Bowser, 2004; Mosing and Bowser, 2009
12.	FluMag SELEX	Targets are tagged with fluorophores	Stoltenburg et al., 2005
13.	Target expressed on cell surface- SELEX (TECS- SELEX)	In this method, a cell is engineered to express a recombinant protein which will be used as target protein for aptamer development	Ohuchi et al., 2006
14.	Nanoselection based SELEX	One step method to isolate aptamers using fluorescence and atomic force microscopy	Peng et al., 2007
15.	MonoLEX	Column chromatography and pyrosequencing is used to select specific aptamer sequences	Nitsche et al., 2007
16.	Microfluidic SELEX	Selection of aptamers are performed on a microfluidic chip	Cho et al., 2010.
17.	High- throughput SELEX	In this method, high-throughput DNA sequencing and advanced bioinformatic analysis is coupled for aptamers selection	Hoon et al., 2011
18.	Particle display SELEX	Flow cytometry based method for aptamer selection	Wang et al., 2014
19.	Hi-fidelity SELEX	Digital-PCR is used to intensify the SELEX selection and development	Ouellet et al., 2015
20.	Isogenic cell SELEX	Aptamers are first selected against targets overexpressed on isogenic cell line, then counter- selected against microRNA mediated silencing of targets	Takahashi et al., 2016