Detection of urinary spermine by using silver-gold/silver chloride nanozymes

In this paper, we report a simple one-step synthesis method for silver-gold bimetallic nanoparticles deposition on silver chloride nanosheets to form Ag-Au/AgCl nanohybrid with oxidase-like and peroxidase-like catalytic activity. We used these nanohybrid in the detection of spermine. First, 13 nm-sized Au NPs were synthesized by citrate reduction of HAuCl₄ solution, and then, Ag⁺ ions were added to the solution without any purification. The added Ag⁺ reacted with the Cl^- ions in the dispersion, thus immediately forming AgCl nanosheets through a precipitation reaction, and the aurophilic interactions with the Au NPs resulted in the formation and in situ self-deposition of Ag-Au NPs on the AgCl nanosheets at room temperature. We investigated the enzyme-mimicking activity of the Ag-Au/AgCl nanohybrid in detail via the O₂- or H₂O₂-Amplex Red (AR) redox system. The Ag-Au/AgCl nanohybrid exhibited at least 150-fold higher catalytic activity than that of Ag-Au NPs or AgCl nanosheets, due to synergistic effect. Spermine inhibited the enzyme-mimic activity of the Ag-Au/AgCl nanohybrid, thereby allowing for the construction of a probe for detecting nanomolar concentrations of spermine in urine samples. This cost-effective sensing system was used to easily and rapidly detect the concentrations of spermine in complex urine samples.