An Elegant Biosensor Molecular Beacon Probe: Challenges and Recent Solutions

Table 1

Variations of 5′-X- and 3′-Y-terminal attachments to increase signal-to-noise (S/N) ratio of an MB probe.*

	X	Y	Comments	S/N	LOD	Ref.
1	FAM*	Gold nanoparticle (GNP)	1.4 nm GNP	76–100	N/D	[74]; [75]
2	DABCYL	FAM		14	N/D	[75]
3	2 DABCYL	FAM		~80	N/D	[75]
4	3 DABCYL	FAM	Multiple DABCYL groups increase stem melting temperature by ~5°C	320	N/D	[75]
5	Poly(phenylene ethynylene)s (PPEs)	DABCYL		N/D	N/D	[76]
6	FAM	Coumarin	Dynamic range was found to be 1–100 nM	4 (𝐼coumarin/𝐼FAM)	0.17 nM	[77]
7	Metallophthalocyanine (PC)	Metallo-phthalocyanine (PC)	Two PCs form nonfluorescent H-dimers in the closed MB conformation	≤59	N/D	[78]
8	Lanthanide-based luminescent; complex	BHQ2	Time-resolved acquisition of the luminescent signal	>400	<1 pM	[79]
9	Eu^3+ complex of chlorosulfonylated tetradentate; 𝛽-diketone	BHQ-2	LOD was determined in a cell medium.; Time-resolved acquisition of the luminescent signal.	>200	0.5 nM	[80]
10	Pyrene	Pyrene	Detection based on the excimer formation	~100; 𝐼382nm/𝐼498nm	1 nM	[81]
11	1 to 4 pyrene residues	DABCYL	MB containing two pyrene residues MB demonstrated the best performance	1–29	<1 nM	[82]; [83]

∗N/D: not determined; FAM: fluorescein; DABCYL: 4-((4-(dimethylamino)phenyl)azo)benzoic acid; BHQ2: blackhole quencher 2; LOD: limit of detection; S/N: signal-to-noise ratio.