Functional Nucleic Acids for DNA Nanotechnology - DNA Nanotechnology: From Structure to Function - page 8

Fig. 2.1 Scheme of systematic evolution of ligands by exponential enrichment (SELEX). The
evolution for FNAs from initial random DNA library is achieved by several rounds of selections
including incubation with target molecules, separation of the active from inactive oligonucleotides,
negative target selection to remove inactive oligonucleotides, amplification to form a new pool for
the next round, and sequencing the oligonucleotides until the activity reaches a constant (Reprinted
from Ref. [ 60 ], copyright 2009, with permission from Elsevier)

N40-N80 are typical [ 50 ]. Shorter may cause the less abundance of the initial pool,
while longer offers more possibilities for forming stable inter- or intra-secondary
structures that would inhibit the binding to target. SELEX is mainly composed
of five general steps: incubating initial pool with target, separating the active
oligonucleotides by certain method, negative selection to get rid of the nonspecific
binding oligonucleotides, amplifying the obtained oligonucleotides to form a new
pool for the next round of selection, and finally sequencing the oligonucleotides
until the activity reaches a constant. Typically, 5-15 rounds are required until
no further enrichment occurs. To accelerate the process, much work has been
focused on the creation of new methods, for example, capillary electrophoresis-
SELEX [ 51 - 53 ], microfluidic SELEX [ 54 , 55 ], and automated SELEX [ 56 - 59 ]
(Fig. 2.1 ).

2.3 The Application of Functional Nucleic Acids in DNA

Nanotechnology

DNA follows restrictive Watson-Crick rule for hybridization to be a highly
predictable assembling unit to form addressable nanostructures. FNAs with
remarkable recognition and catalytic properties make the DNA nanostructures