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′}(CCC₆H₅)](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)(CCC₆H₄CH₂NMe₃-4)](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.