Polydiacetylene-Functionalized Noble Metal Nanocages

Stable chitosan-protected noble metal nanocages of relatively small size (50 nm) were successfully synthesized by the galvanic replacement reaction between the corresponding silver nanoparticles and HAuCl4 in aqueous suspension. A broad surface plasmon band peaked around 700 nm and extended to the near-infrared was observed by properly changing the experimental conditions. To test the performance, the nanocages were functionalized with 10,12-pentacosadiynoic acid (PCDA) chains and then irradiated with UV light to induce monomer polymerization. A very high polymer conversion was observed. The time evolution of the electronic absorption and Raman spectra showed a variety of polydiacetylenic forms, including the unusual highly delocalized bluish-green phase. The nanocages act as surface-enhanced Raman scattering (SERS) active substrates with all our available excitation lines and show improved Raman activity in comparison with data from both silver and gold colloids. The shift of the plasmonic band to the NIR is expected to magnify the nonlinear response of polydiacetylene in this region.