Capillary-immobilized Ag@UiO-66-NH₂ nanocomposite sensor for ultrasensitive mercury (II) detection

Mercury ions (Hg 2+ ) are extremely toxic, posing severe risks to human health and ecosystems even at trace concentrations. Their prevalence necessitates the development of rapid, selective, and portable methods for on-site Hg 2+ detection in environmental monitoring. Here we report a surface-enhanced Raman scattering (SERS) sensor that employs a capillary-immobilized Ag@UiO-66-NH 2 nanocomposite as the substrate for the indirect detection of Hg 2+ . The inner wall of a glass capillary was amino-functionalized and sequentially decorated with silver nanoparticles (AgNPs) and a zirconium-based metal–organic framework (UiO-66-NH 2 ). After that, Dithizone (DTZ) was immobilized onto the resulting Ag@UiO-66-NH 2 composite to form stable Raman-active complexes. In the presence of Hg 2+ , the strong chelation between DTZ and Hg 2+ induces distinct SERS signal changes, enabling highly sensitive and selective detection of Hg 2+ . A key advantage of this sensor is the ability to directly load microliter-scale samples into a pretreated capillary for on-site analysis using a portable Raman spectrometer. The sensor exhibits a linear response between the DTZ signal intensity and Hg 2+ concentration over a broad range (10 −12 –10 −5  mol·L −1 ), with excellent linearity (R 2  = 0.9900), uniformity, reproducibility, and selectivity against common interfering ions. This method was validated in environmental water samples, demonstrating good agreement with ICP-MS while simplifying sample handling and minimizing pretreatment. These findings underscore the sensor's considerable potential for practical, on-site monitoring of Hg 2+ in both environmental and industrial contexts.