Table 2.

Representative DNA response reaction mechanisms

Mechanism	Stimulus signal	Target DNA seq.	Response type	Example ref
Chemical	pH	G‐rich sequences	G‐quadruplex formation	38
Chemical	pH	C‐rich sequences	I‐switch formation	39
Chemical	Na, K ions	G‐rich sequences	G‐quadruplex formation	[[qv: 38a,40]]
Chemical	Hg ions	T‐rich sequences	Duplex formation	41
Chemical	Ions, water	Branched DNA structure network	DNA hydrogel shape change	42
Chemical	ATPb)	A‐rich sequences	ssDNA to ATP aptamer	43
Chemical	Thiol reducing agent such as TCEPa)	Disulphide links	Cleavage of S‐S bond; separation of ssDNA domains	44
Physical	Light	Caging group coated ssDNA	ssDNA to dsDNA	40, 45
Physical	Heat	Complementary ssDNA	ssDNA to dsDNA	46
Molecular	Toehold‐bearing ssDNA	DNA duplex with partial complementarity	Displace existing duplex, release ssDNA	47
Molecular	Cellular peptides, ligands, membrane receptors	DNA aptamers	Linear DNA to well‐defined secondary structure	48
Molecular	Short ssDNA	Hybridization chain reaction (HCR)	Small DNA units to higher‐order structures	49
Molecular	Restriction enzymes	Enzyme‐specific DNA sequences	Cleavage of dsDNA to ssDNA	50
Molecular	Polymerases	Enzyme‐specific DNA primers	Increase in DNA size by amplification	51
Molecular	DNAzymes	Enzyme‐specific DNA sequences	Cleavage of DNA	52

^a) TCEP, tris(2‐carboxyethyl)phosphine

^b) ATP, adenosine triphosphate.