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′-[G₃T]₅-3′) as an antenna ligand, in which [G₃T]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 [G₃T]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 ₃T]₅ (Tb³⁺/[G₃T]₅); however, biothiols are readily applicable to selectively grab Hg²⁺ for restoration of the luminescence of Tb³⁺/[G₃T] ₅ initially quenched by Hg²⁺, which can be used for turn on detection of biothiols. With the use of cytosine (C)-rich oligonucleotide c[G₃T]₅ complementary to [G₃T]₅, the formed [G₃T]₅/c[G₃T]₅ duplex cannot sensitize the luminescence of Tb³⁺. However, in the presence of Ag⁺, Ag⁺ can combine the C base of c[G₃T] ₅ to form C-Ag⁺-C complexes, leading to the split of the [G₃T]₅/c[G₃T]₅ duplex and then release of [G₃T]₅. The released [G₃T] ₅ acts as an antenna ligand for sensitizing the luminescence of Tb³⁺. Therefore, the Tb³⁺/[G₃T] ₅/c[G₃T]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-[G₃T] ₅) can unfold the MB-[G₃T]₅ to release the [G₃T]₅ for sensitizing the luminescence of Tb ³⁺, 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 Tb ³⁺. 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.