Tuning Localized Surface Plasmon Resonance Wavelengths of Silver Nanoparticles by Mechanical Deformation

We describe a simple technique to alter the shape of silver nanoparticles (AgNPs) by rolling a glass tube over them to mechanically compress them. The resulting shape change in turn induces a red-shift in the localized surface plasmon resonance scattering spectrum and exposes new surface area. The flattened particles were characterized by optical and electron microscopy, single-nanoparticle scattering spectroscopy, and surface-enhanced Raman spectroscopy (SERS). Atomic force microscopy and scanning electron microscopy images show that the AgNPs deform into discs; increasing the applied load from 0 to 100 N increases the AgNP diameter and decreases the height. This deformation caused a dramatic red shift in the nanoparticle scattering spectrum and also generated new surface area to which thiolated molecules could attach, as evident from SERS measurements. The simple technique employed here requires no lithographic templates and has potential for rapid, reproducible, inexpensive, and scalable tuning of nanoparticle shape, surface area, and resonance while preserving particle volume.