A Concave Nanogap for Ultrasensitive Aptamer-Based SERS Detection and <i>In Situ</i> Imaging of Heavy Metal Ions

Heavy metal pollution can lead to irreversible damage to human health. Surface-enhanced Raman scattering (SERS) platforms are versatile for toxicity monitoring and <i>in situ</i> imaging, but they are often limited by false positives. In this study, we proposed the use of concave-facet nanocubes (CF NCs) to create sufficiently large nanogaps, which can be used for the deposition of probes such as aptamers. Aptamers adopt an extended configuration within these nanogaps, effectively preventing compression-induced false signals. By utilizing the robust electromagnetic field present within the nanogaps, the developed SERS platform has demonstrated a broad detection range of 0.1 to 1000 nM for Hg²⁺ and a limit of detection as low as 0.1 nM. This platform was further applied to the analysis of Pb²⁺ and Cd²⁺. Furthermore, this system was applied to visualize the distribution of Hg²⁺ ions in zebrafish larvae, providing detailed insights into Hg²⁺ bioaccumulation. This work presents a universal strategy for concave-shaped nanoparticle-assisted SERS detection of analytes with weak or no Raman signatures, such as heavy metal ions, while reducing false-positive results in analysis. It also underscores the promising potential for targeted <i>in situ</i> imaging in biological samples, serving as a tool for investigating the mechanisms of toxicity in various substances.