An ultra-sensitive fluorescent "Turn On" biosensor for glutathione and its application in living cells.

In this work, an effective controlled-release biosensor based on Au nanocages (AuNCs) capped with disulfide-containing DNA molecular gates was developed for ultra-sensitive and highly selective detection of glutathione (GSH). Oligonucleotides containing the S-S bonds were assembled on the surface of the AuNCs by means of electrostatic interactions in order to inhibit the release of fluorescent molecules such as Rhodamine B (RhB) loaded by AuNCs. In the presence of GSH, due to the specific cleavage of S-S bonds in disulfide-containing single-stranded DNAs (ssDNAs) as well as their subsequent departure from the surface of AuNCs, the pores could be opened, and then the dye molecules would be released from AuNCs. The concentration of GSH ranged from 1.0 × 10 to 6.0 × 10 M could be detected. The developed amplification strategy based on the controlled-release of fluorescent molecules reached an extraordinary sensitivity of GSH. A detection limit of as low as 4.8 × 10 M with an excellent selectivity toward GSH could be achieved. The results of fluorescence microscopy imaging of GSH in living cells indicate that the fabricated system is an efficient controlled-release biosensor in response to intracellular target molecules and predict its potential use for in situ molecular imaging in living systems.