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

Abstract

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[triple bond, length as m-dash]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 Förster radius, R0, 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[triple bond, length as m-dash]CC6H4CH2NMe3-4)](OTf)2 (1), which has a smaller association constant with PPE-SO3− and R0 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.