A capillary-based SERS sensor for ultrasensitive and selective detection of Hg2+ by amalgamation with Au@4-MBA@Ag core–shell nanoparticles

A capillary-based SERS sensor was fabricated for ultrasensitive and selective detection of Hg2+ in water. Au@Ag core–shell NPs embedded with 4-mercaptobenzoic acid (4-MBA) (Au@4-MBA@Ag) were prepared by a seed growth method and fixed on the inner wall of the glass capillary to obtain the sensor. Owing to the amalgamation between Ag and Hg, the capillary-based SERS sensor can specifically recognize the reduced Hg2+ without any recognition element, and the resulted Ag/Hg amalgam can weaken the SERS activity of Ag shell; thus, the SERS intensity of the embedded 4-MBA at 1075 cm−1 gradually decreased with the increase of Hg2+ concentration. Under the optimum condition, the fabricated sensor can sensitively determine Hg2+ in water with a limit of detection (LOD) as low as 0.03 nM. The capillary-based SERS sensor offers the advantages of simple preparation, superior stability, and high selectivity, which is promising for rapid and on-site detection of Hg2+ in water combined with a portable Raman device.