FRET based ultra sensor for detection of Hg (II) in water: A comparative study using citrate and marcapto propanoic acid as stabilizer of AuNPs

Rhodamin 6G (Rh6G) functionalized Au nanoparticles (AuNPs) are being used as efficient fluorescence probe for selective sensing of heavy metal ions. It has been observed that the quenching of fluorescence of Rh6G in presence of AuNPs takes place through fluorescence resonance energy transfer (FRET). Recovery of fluorescence of Rh6G emission in presence of Hg (II) in AuNPs–Rh6G coupled system has been explained as the increasing affinity of heavy metal ions to form shell and thereby reduced the FRET rate. In presence of heavy metal ions such as Hg (II), Rh6G molecules are released from the AuNPs surface and the fluorescence of Rh6G is restored. The modulation of photoluminescence quenching efficiency of Rh6G–AuNPs in the presence of Hg (II) ions can achieve a large turn on fluorescence enhancement. Our experiment using marcapto propanoic acid (MPA) caped AuNPs show much less fluorescence enhancement in presence of Hg2+ compares to tri sodium citrate (TSC) stabilized AuNPs.