Facile Colorimetric Detection of Silver Ions with Picomolar Sensitivity

Although various colorimetric methods have been actively developed for the detection of Ag⁺ ions because of their simplicity and reliability, the limits of detection of these methods are confined to the nanomolar (nM) level. Here, we demonstrate a novel strategy for colorimetric Ag⁺ detection with picomolar (pM) sensitivity. This strategy involves the use of poly(vinylpyrrolidone)- (PVP-) capped Pt nanocubes as artificial peroxidases that can effectively generate a colored signal by catalyzing the oxidation of peroxidase substrates. In the presence of Ag⁺ ions, the colored signal generated by these Pt cubes is greatly diminished because of the specific and efficient inhibition of Ag⁺ toward the peroxidase-like activity of the Pt cubes. This colorimetric method can achieve an ultralow detection limit of 80 pM and a wide dynamic range of 10^-2-10⁴ nM. To the best of our knowledge, the method presented in this work shows the highest sensitivity for Ag⁺ detection among all reported colorimetric methods. Moreover, this method also features simplicity and rapidness as it can be conducted at room temperature, in aqueous solution, and requires only ∼6 min.