Porous Wood Members-Based Amplified Colorimetric Sensor for Hg2+ Detection through Hg2+-Triggered Methylene Blue Reduction Reactions

Wood has attracted increasing scientific interest in the field of green electronics, biological devices, bioenergy, and energy storage because of its abundance, low cost, biocompatibility, and natural vessel structure. However, its potential application in the important area of environmental monitoring has not yet been effectively explored. In this work, gold nanoparticles (NPs) encapsulated in porous wood (denoted as Au@wood) for high-performance colorimetric detection of Hg2+ in aqueous solution have been constructed. The detection mechanism is based on Hg2+-triggered methylene blue (MB) reduction-assisted signal amplification. In such a detection system, Au NPs can be used as a specific identification element for the binding of Hg2+ due to the formation of gold amalgam to initiate catalytic activity of gold. The low-cost natural wood is introduced to prevent the aggregation of Au NPs and increase the contact area between MB and Au NPs in three-dimensional space. MB, as a tracer molecule, enables the output signals to be directly observed by the naked eye. Such a detection system exhibited an ultralow detection limit of 32 pM for Hg2+, which is greatly lower than the threshold levels (10 nM) for drinking water and other colorimetric methods. The proposed detection system also exhibits high selectivity against other metal ions and works well for environmental water and blood samples. The resultant Au@wood sensor is low cost, easy handling, and convenient, making it an attractive material for point-of-use monitoring of Hg2+ in environmental and biological samples.