Selective label-free detection of G-quadruplex structure of human telomere by emission spectral changes in visible-and-NIR region under physiological condition through the FRET of a two-component PPE-SO3--Pt(II) complex ensemble with Pt•••Pt, electrostatic and π-π interactions

The formation of polymer-metal complex aggregates and the FRET between PPE-SO3- and several water-soluble cationic alkynylplatinum(II) complexes are revealed from UV-vis, steady-state emission and time-resolved emission decay studies. From the Stern-Volmer plots, [Pt{tpy(C6H4CH2NMe3-4)-4'}(C CC6H5)](OTf)(2) (2) is found to be the most efficient quencher of PPE-SO3- at both low and high concentrations. This has been ascribed to its low steric bulkiness and the stronger interactions with PPE-SO3-, and hence the largest association constant with PPE-SO3-, as well as the largest Forster radius, R-0, among the complexes studied. The PPE-SO3--2 ensemble has been employed in the detection of human telomere in aqueous buffer solution (50 mM KH2PO4, pH 6.8) and found to have better selectivity than the ensemble containing [Pt(tpy)(C CC6H4CH2NMe3-4)](OTf)(2) (1), which has a smaller association constant with PPE-SO3- and R-0 value than 2. By modulation of the aggregation/deaggregation of the polymer-metal complex aggregates and hence the FRET from the PPE-SO3- donor to the aggregated forms of 2 as acceptor, the PPE-SO3--2 ensemble has been demonstrated for the sensitive and selective label-free detection of human telomere via the monitoring of emission spectral changes over the visible-NIR region. Ratiometric emission of PPE-SO3--2 ensemble at 620 and 795 nm has been shown to distinguish the G-quadruplex structure formed by human telomeric DNA from those of other G-quadruplex-forming sequences.