N
H
N
H
G
G
G
G
G
G
G
G
C
C
C
C
C
C
C
C
C
G
A
A
A
A
A
A
A
T
T
T
Bulk and single-molecule characterization of an improved molecular beacon utilizing H-dimer excitonic behavior
Nick Conley, Andrea Kurtz, Hui Wang, Robert J. Twieg, W. E. Moerner
J. Phys. Chem. B Letter; 2007; ASAP Web Release Date: 21-Jun-2007
Unlike conventional molecular beacons (MBs), our self-quenched intramolecular dimer (SQuID) molecular beacon has two fluorophores instead of a fluorophore and a quencher.
In the absence of target, the SQuID MB has a blue shifted absorption and quenched emission.  Addition of target results in a 22-fold increase in fluorescence emission.
Text Box: no target
no target
Text Box: with target
with target
Colors of SQuID MB
Single-molecule (SM) fluorescence emission from surface-immobilized SQuID MBs (a) in the absence of target and (b) in the presence of target. (c) SM time traces illustrating two-step photobleaching of SQuID MB bound to target. (d) Histogram of SM intensities.
Advantages over conventional MBs:
(1)doubled SM emission intensity of the target-bound beacon ensures a higher signal-to-background ratio
(2)single-pot labeling
(3)visible colorimetric detection of target
(4)intrinsic single-molecule two-step photobleaching behavior