Adhesion Enhancements and Surface-Enhanced Raman Scattering Activity of Ag and Ag@SiO₂ Nanoparticle Decorated Ragweed Pollen Microparticle Sensor

A simple solution processed layer-by-layer approach was used to immobilize metal nanoparticles (NPs) on the surface of ragweed pollen exine to obtain multifunctional particles with significant surface-enhanced Raman scattering (SERS), two-photon excited fluorescence, and enhanced adhesion properties. The rugged pollen exine was functionalized with an amine terminated silane and then treated with Ag or Ag@SiO 2 NPs that were electrostatically attached to the exterior of the pollen by incubation in an NP solution of the appropriate pH. Nanoparticle agglomeration on the pollen gives rise to broadband near infrared (NIR) (785–1064 nm) plasmonic activity, and strong SERS signals from benzenedithiol deposited on NP–pollen composite particles were observed. In addition to SERS activity, the AgNP coating provides a twofold increase in the adhesive properties of the RW pollen exine on a silicon substrate, leading to a robust, adhesive, broadband NIR excitable SERS microparticle.