Poly(vinylpyrrolidone)‐Free Multistep Synthesis of Silver Nanoplates with Plasmon Resonance in the Near Infrared Range

Herein, a poly(vinylpyrrolidone) (PVP)‐free method is described for synthesizing Ag nanoplates that have localized surface plasmon resonance in the near‐infrared (NIR) range. Citrate‐capped Ag spherical nanoparticles are first grown into small Ag nanoplates that resonate in the range of 500–800 nm. The small Ag nanoplates are used as seeds to further grow into large Ag nanoplates with a lateral dimension of 100–600 nm and a plasmon resonance wavelength of 800–1660 nm and above. The number of growth steps can be increased as desired. Without introducing additional citrate into the solutions of small Ag nanoplate seeds, large Ag nanoplates can be synthesized within minutes. The entire synthesis is completely PVP free, which promotes the nanoparticle growth along the lateral direction to form large Ag nanoplates. The multistep growth and the minimum usage of citrate are essential for the fast growth of high‐aspect‐ratio Ag nanoplates resonating in the NIR range. Poly(vinylpyrrolidone) (PVP)‐free multistep growth is used to synthesize high‐aspect‐ratio Ag nanoplates with plasmon resonance in the near‐infrared region. Citrate‐capped Ag spherical seeds, instead of the PVP‐capped ones, are used to expedite the synthesis and avoid any polymer coating around the Ag nanoplates.