Label free and high specific detection of mercury ions based on silver nano-liposome

Herein, we report an eco-friendly, mild and one-pot approach for synthesis of silver nanoparticles via a lipopeptide biosurfactant - CHBS. The biosurfactant forms liposome vesicles when dispersed in an aqueous medium. The amino acid groups of the biosurfactant assists in the reduction of Ag(+) ions leading to the production of homogeneous silver nanoparticles, encapsulated within the liposome vesicle, as confirmed from TEM analysis. Rate of synthesis and size of particle were greatly dependent on pH and reaction temperature. Kinetic analysis suggests the involvement of an autocatalytic reaction and the observed rate constant (kobs) was found to decrease with temperature, suggesting faster reaction with increasing temperature. Furthermore, the silver nanoparticles served as excellent probes for highly selective and sensitive recognition of Hg(2+) ions. Interaction with Hg(2+) ions results in an immediate change in colour of nanoparticle solution form brownish red to milky white. With increasing Hg(2+) ions concentration, a gradual disappearance of SPR peak was observed. A linear relationship (A420/660) with an R(2) value of 0.97 was observed in the range of 20 to 100ppm Hg(2+) concentration. Hg(2+) ions are reduced to their elemental forms which thereby interact with the vesicles, leading to aggregation and precipitation of particles. The detection method avoids the need of functionalizing ligands and favours Hg(2+) detection in aqueous samples by visible range spectrophotometry and hence can be used for simple and rapid analysis.