Achieving Ultrasensitive Point-of-Care Assay for Mercury Ions with a Triple-Mode Strategy Based on the Mercury-Triggered Dual-Enzyme Mimetic Activities of Au/WO3 Hierarchical Hollow Nanoflowers

The exploration of new strategies for portable detection of mercury ions with high sensitivity and selectivity is of great value for biochemical and environmental analyses. Herein, a straightforward, convenient, label-free, and portable sensing platform based on a Au nanoparticle (NP)-decorated WO₃ hollow nanoflower was constructed for the sensitive and selective detection of Hg(II) with a pressure, temperature, and colorimetric triple-signal readout. The resulting Au/WO₃ hollow nanoflowers (Au/WO₃ HNFs) could efficaciously impede the aggregation of Au NPs, thus significantly improving their catalytic activity and stability. The sensing mechanism of this new strategy using pressure as a signal readout was based on the mercury-triggered catalase mimetic activity of Au/WO₃ HNFs. In the presence of the model analyte Hg(II), H₂O₂ in the detection system was decomposed to O₂ fleetly, resulting in a detectable pressure signal. Accordingly, the quantification of Hg(II) was facilely realized based on the pressure changes, and the detection limit could reach as low as 0.224 nM. In addition, colorimetric and photothermal detection of Hg(II) using the Au/WO₃ HNFs based on their mercury-stimulated peroxidase mimetic activity was also investigated, and the detection limits were calculated to be 78 nM and 0.22 μM for colorimetric and photothermal methods, respectively. Hence, this nanosensor can even achieve multimode determination of Hg(II) with the concept of point-of-care testing (POCT). Furthermore, the proposed multimode sensing platform also displayed satisfactory sensing performance for the Hg(II) assay in actual water samples. This promising strategy may provide novel insights on the fabrication of a multimode POCT platform for sensitive, selective, and accurate detection of heavy metal ions.