Mercaptosuccinic acid-coated NIR-emitting gold nanoparticles for the sensitive and selective detection of Hg²

A sensitive fluorescent detection platform for Hg²⁺ was constructed based on mercaptosuccinic acid (MSA) coated near-infrared (NIR)-emitting gold nanoparticles (AuNPs). The thiolated mercaptosuccinic acid was employed as both reducing agent and surface coating ligand in a one-step synthesis of NIR-emitting AuNPs (MSA-AuNPs), which exhibited stable fluorescence with the maximum wavelength at 800nm and a wide range of excitation (220-650nm) with the maxima at 413nm. The MSA coated NIR-emitting AuNPs showed a rapid fluorescence quenching toward Hg²⁺ over other metal ions with a limit of detection (LOD, 3δ) as low as 4.8nM. The sensing mechanism investigation revealed that the AuNPs formed aggregation due to the "recognition" of Hg²⁺ from the MSA, and the resultant strong coupling interaction between Hg²⁺ and Au (I) to further quench the fluorescence of the AuNPs, which synergistically resulted in a highly sensitive and selective fluorescence response toward Hg²⁺. This proposed strategy was also demonstrated the possibility to be used for Hg²⁺ detection in water samples.