Mercury^II-mediated construction of DNA capsules for turn-on fluorescence detection of melamine

Researchers have shown significant interest in three-dimensional DNA building blocks due to their potential applications in biomedicine and biosensing. This study focuses on the synthesis of an Hg^II ion-stabilized DNA capsule with T-Hg^II-T pairs for the purpose of detecting melamine (MA). MA reacts with Hg^II to form a MA-Hg^II-MA complex, which causes Hg^II to leave the capsule shell, ultimately leading to capsule collapse and release of fluorescent cargo as output signal. Density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS) were used to demonstrate the ability of MA to extract Hg^II from the T-Hg^II-T adducts. The DNA capsules were characterized using TEM, SEM, DLS, zeta-potential, and melting curve analysis, which indicated the successful construction of the Hg^II-intercalated DNA shell. The MA-triggered destruction of the DNA capsules was visualized by confocal microscopy, and the dynamics of decapsulation were evaluated through fluorescent cargo release. The Hg^II-stabilized DNA capsules enable MA detection with a detection limit of 0.037 µM and are insensitive to potential interfering ions and amino acids. The tests conducted using MA spiked milk solution resulted in recoveries ranging from 109 to 113% (0.1 µM) and 94.5 to 96% (0.5 µM). These results suggest that the system is promising for highly accurate and reproducible monitoring of MA adulteration.