Highly sensitive surface-enhanced Raman scattering detection of hexavalent chromium based on hollow sea urchin-like TiO2@Ag nanoparticle substrate

• A simple method for ultrasensitive detection of Cr(VI) was developed.
• A hollow sea urchin-like TiO2@Ag NPs was prepared with high SERS enhancement.
• The method has a linearity in the range from 10 nM to 2 μM with a LOD of ~1.45 nM.
• The method excellent selectivity and good application in water samples.

As one of the most toxic heavy metals, hexavalent chromium (Cr(VI)) has long been a concern due to its threats to human health and the environment. In this work, we develop a sensitive surface-enhanced Raman scattering (SERS) sensor for highly specific detection of Cr(VI) using hollow sea urchin-like TiO2@Ag nanoparticles (NPs). The TiO2@Ag NPs are functionalized with glutathione (GSH) and used as substrates with 2-mercaptopyridine (2-MPy) as a Raman reporter for a recyclable SERS-active sensor, enabling ultrasensitive detection of Cr(VI). Excellent SERS signals of 2-MPy reporters are detected when GSH complexation with Cr(VI) causes aggregation of the TiO2@Ag NPs. The developed sensor exhibits good linearity in the range from 10 nM to 2 μM for Cr(VI) with a detection limit of ca. 1.45 nM. It features excellent selectivity to Cr(VI) over other interfering metal ions, and good application for quantitative analysis of Cr(VI) in water samples. Moreover, the proposed SERS sensor can be fully regenerated when exposed to UV light as a result of the self-cleaning ability of the substrates. In contrast to the traditional SERS detection, the present work shed new light on the design and synthesis of hierarchically self-assembled 3D substrate for SERS, catalysis and biosensor development.