Step‐by‐Step Design and Synthesis of Au@SiO(2)@Phenyl‐azathiacrown for SERS‐Based Specific Quantification of Inorganic Mercury

Direct SERS‐based quantification of inorganic metal species has been a problem, because they have a small Raman cross‐section or even no vibrational mode. Here, we report a new strategy for SERS‐based quantification of such metal species, as exemplified by inorganic mercury (Hg(II)) in waters. Step‐by‐step design and synthesis from azathioethers [3, 9‐dithia‐6‐monoazaundecane (DMA) and 3,6,12,15‐tetrathia‐9‐monoazaheptadecane (TTM)] to an azathiacrown [7‐aza‐1,4,10,13‐tetrathiacyclohexadecane (NS4)] demonstrate an improved S‐pulling effect and size‐fit specificity towards Hg(II) to form Hg−S bonds. Modification of NS4 on the surface of Au@SiO(2) by using a 4‐(bromomethyl)benzoic linker enabled direct SERS‐based specific quantification of Hg(II) for the first time, in which the ultrathin layer (ca. 2 nm) that covered the Au core (55 nm) could be a barrier preventing the Au core from having direct interaction with the Hg(II), and with phenyl serving as an internal standard (IS). The ratio of the Hg−S SERS band intensity at 270 cm(−1) to that of IS [(γCC+γCCC) at 1046 cm(−1)] was practically proportional to the concentration of Hg(II), eliminating the inevitable uncertainties encountered in SERS‐based measurements. Such a methodology is expected to pave a new way for SERS‐based quantification of inorganic metal species when specific complexing substrates and suitable ISs are designed.