A label-free fluorescent biosensor for ultratrace detection of terbium (ш) based on structural conversion of G-quadruplex DNA mediated by ThT and terbium (ш)

In this paper, a novel label-free fluorescent biosensor for terbium (ш) (Tb 3+ ) was proposed based on structural conversion of G-quadruplex DNA mediated by Thioflavin T (ThT) and Tb 3+ . In the presence of K + , ThT could bind to K + -stabilized parallel G-quadruplex, giving rise to high fluorescence intensity . Upon the addition of Tb 3+ , Tb 3+ could competitively bind to parallel G-quadruplex leading to the structural change, which resulted in fluorescence decrease. The change of fluorescence intensity (Δ F = F 0 – F ) showed a good linear response toward the concentration of Tb 3+ over the range from 1.0   pM to 10.0   µM with a limit of detection of 0.55   pM. This proposed biosensor was simple and cost-effective in design and in operation with ultrahigh sensitivity and selectivity . Thus, the proposed biosensor could be a promising candidate for monitoring ultratrace Tb 3+ in environment.