In situ controllable growth of Ag particles on paper for smartphone optical sensing of Hg2+based on nanozyme activity stimulation

Given the huge threat of Hg2+ to human health, it is always significant to develop Hg2+ monitoring tools. Utilizing its impacts on nanozyme catalysis is a promising strategy to realize Hg2+ detection. However, nearly all the assays fabricated based on the principle should be performed in solution and in laboratory and require bulky signal reading instruments, hindering their wider applications. It is highly desired to develop portable, efficient, and practical Hg2+ sensors. Herein, we proposed the in situ controllable growth of Ag nanoparticles (AgNPs) on paper to fabricate a smartphone optical nanosensor for highly sensitive Hg2+ detection based on enzyme-mimetic activity stimulation. The ultrasmall AgNPs were directly grown on paper wafers to obtain test strips, which further integrated a 3D-printed holder and an APP built-in smartphone to fabricate the sample-to-answer sensor. The AgNPs-based test strips exhibited a target-stimulated peroxidase-like activity to catalyze the oxidation of 3,3 ',5,5 '-tetramethylbenzidine, and the chromogenic information was captured and processed by the smartphone to rapidly report the level of Hg2+. With the portable nanosensor, highly sensitive and specific detection of Hg2+ was achieved, with a detection limit down to 0.44 nM. The sensor gathers the features of easy construction, simple operation, excellent capability, and robust performance together, promising great potential for rapid onsite analysis.