Simple construction of a two-component fluorescent sensor for turn-on detection of Hg²⁺ in human serum

The simply constructed fluorescent sensor with inexpensive reagents and low toxicity has attracted increasing attention contributing to its practical application. However, the common construction methods usually required a few building blocks and complex procedures, which is inconvenient for their further application. Herein, a simply constructed fluorescent Hg²⁺ sensor has been developed based on the intrinsic fluorescence quenching power of G-quadruplex. Two components, AGRO 100 and AMT, were used to construct the sensor. AMT was selected as the fluorescent probe because of its distinct merits. The free AMT emits strongly. However, the fluorescence of AMT could be quenched by G-quadruplex DNA. Additionally, AMT is less toxic and inexpensive. AGRO 100 acts as both the quencher and the capture sequence because it consists of G-rich sequences and T-T mismatched base pairs. The fluorescence of AMT could be quenched by the formed G-quadruplex structure of AGRO 100 in the presence of K⁺. In the presence of Hg²⁺, G-quadruplex structure of AGRO 100 was switched to hairpin DNA structure because T-T mismatched base pairs in AGRO 100 could specifically recognize and capture Hg²⁺ with high affinity. Thus, AMT was released and the fluorescence of AMT was recovered. The developed sensing system was successfully applied to detect Hg²⁺ in human serum with good recovery and reproducibility.