Turn-on sensing for Ag+ based on AIE-active fluorescent probe and cytosine-rich DNA.

An aggregation-induced-emission (AIE)-active molecule, 4,4'-(1E,1'E)-2,2'-(anthracene-9,10-diyl) bis (ethene-2,1-diyl) bis (N,N,N-trimethylbenzenaminium iodide) (DSAI), used as a label-free and turn-on fluorescent probe, was developed for Ag(+) sensing. The cytosine-rich DNA (oligo-C) chosen as a base could be induced to form a hairpin structure in the presence of Ag(+). To improve the sensitivity of Ag(+) detection, we selected nuclease S1 to reduce the fluorescence intensity of DSAI via its strong ability to hydrolyze oligo-C. In the solution containing oligo-C, DSAI, and nuclease S1, in the absence of Ag(+), oligo-C was broken into fragments by nuclease S1; this meant DSAI could not aggregate, leading to non-emission of the solution. In the presence of Ag(+), oligo-C was induced to form a hairpin structure via the C-Ag(+)-C base pair and DSAI could aggregate on the surface of the hairpin structure to produce a strong emission. On increasing the amount of Ag(+) in the solution containing oligo-C, DSAI, and nuclease S1, the fluorescence intensity of DSAI gradually increased, and the highest intensity was nearly 16-fold higher than the original intensity. The detection limit at a signal-to-noise ratio (S/N) of 3 was estimated to be 155 nmol L(-1). The new sensing method provides simplicity, easy operation, and good sensitivity and selectivity for Ag(+) detection.