The fabrication of nanocapsules starts with the electrodeposition of Au nanowires in nanoporous membranes. In brief, Au nanowires were electrodeposited from commercially available cynide based electrolyte (434 HS RTU; Technic, Inc., Cranston, RI). The diameter of the nanowires can be controlled by the size of the nanopores from tens of nanometers to 400 nm, and the length of the Au nanowires is determined by the amount of electric charge passing through the circuit. After dissolving the membrane, the nanowires were resuspended and sonicated in ethanol and deionized (D.I.) water alternatively twice before redispersed in D.I. water. Billions of nanowires can be fabricated at a time with length of 8.5 μm and diameter of 300 nm as shown in Fig. 1(a). Next, a 180 nm thick SiO2 layer was coated on the surface of the Au nanowires via hydrolysis of tetraethyl orthosilicate (TEOS, 0.8 ml; Alfa Aesar, Ward Hill, MA, 99.999+%) in ammonia (0.2 ml; Fisher Scientific, Certified A.C.S. Plus, Pittsburgh, PA), ethanol (6 ml; Pharmco-aaper, ACS/USP grade, Brookfield, CT), and deionized water (3.6 ml) for 1 hr (Fig. 1(b)). Finally, Ag NPs were synthesized on the surface of silica by mixing Au/SiO2 nanowires with freshly prepared silver nitrate (AgNO3; Acros Organics, Belgium, 99.85%), and ammonia, stirring for 1 hr before adding polyvinylpyrrolidone (PVP, 10 ml of 2.5 × 10−5 M in ethanol; Sigma-Aldrich, St. Louis, MO, Mw = 40,000) to catalyze the growth of Ag NPs at 70 °C. After 7 hrs reaction, dense Ag NPs were obtained on the entire surface of the nanocapsules as shown in Figs. 1(c) and 2.