Time-Resolved Probes Based on Guanine/Thymine-Rich DNA-Sensitized Luminescence of Terbium(III)

In this study, we have developed a novel strategy to highly sensitize the luminescence of terbium(III) (Tb3+) using a designed guanine/thymine-rich DNA (5'-[G(3)T](5)-3') as an antenna ligand, in which [G(3)T](5) improved the luminescence of Tb3+ by 3 orders of magnitude due to energy transfer from nucleic acids to Tb3+ (i.e., antenna effect). Furthermore, label-free probes for the luminescent detection of biothiols, Ag+, and sequence-specific DNA in an inexpensive, simple, and mix-and-read format are presented based on the [G(3)T](5)-sensitized luminescence of Tb3+ (GTSLT). The long luminescence lifetime of the probes readily enables time-resolved luminescence (TRL) experiments. Hg2+ can efficiently quench the luminescence of Tb3+ sensitized by [G(3)T](5) (Tb3+/[G(3)T](5)); however, biothiols are readily applicable to selectively grab Hg2+ for restoration of the luminescence of Tb3+[G(3)T](5) initially quenched by Hg2+, which can be used for turn on detection of biothiols. With the use of cytosine (C)-rich oligonucleotide c[G(3)T](5) complementary to [G(3)T](5), the formed [G(3)T](5)/c[G(3)T](5) duplex cannot sensitize the luminescence of Tb3+. However, in the presence of Ag+, Ag+ can combine the C base of c[G(3)T](5) to form C-Ag+-C complexes, leading to the split of the [G(3)T](5)/c[G(3)T](5) duplex and then release of [G(3)T](5). The released [G(3)T](5) acts as an antenna ligand for sensitizing the luminescence of Tb3+. Therefore, the Tb3+[G(3)T](5)/c[G(3)T](5) probe can be applied to detect Ag+ in a turn on format. Moreover, recognition of target DNA via hybridization to a molecular beacon (MB)-like probe (MB-[G(3)T](5)) can unfold the MB-[G(3)T](5) to release the [G(3)T](5) for sensitizing the luminescence of Tb3+, producing a detectable signal directly proportional to the amount of target DNA of interest. This allows the development of a fascinating label-free MB probe for DNA sensing based on the luminescence of Tb3+. Results and methods reported here suggest that a guanine/thymine-rich DNA-sensitized luminescence probe of Tb3+ represents a new opportunity for versatile background-free biosensing applications.