Controlled synthesis of hollow Ag@Au nano-urchins with unique synergistic effects for ultrasensitive surface-enhanced Raman spectroscopy

Ideally, taking advantage of synergistic effects, coinage-metallic nanocomposites combining obvious inner hollow structures and exterior unique dendritic shell architectures have a promising potential to provide unprecedented opportunity for ultrasensitive surface-enhanced Raman scattering spectroscopy (SERS) application. Herein, we report a convenient and robust synthesis of hollow Ag@Au nano-urchins with both obvious inner voids and exterior multi-antennas by employing galvanic replacement reaction between Au3+ ions and Ag nanospheres and then concomitant reduction of Au3+ ions onto precursors. The stable Ag nanospheres play an important role in the seed-mediated growth process, which were fabricated by pulsed laser ablation of Ag target in liquid. Superior to traditional chemical synthesis, the distinctive advantage is that ultra-rapid laser sintering/quenching of Ag nanoseeds enable the Ag outside surfaces to become more stable than those of core regions. The fascinating hollow Ag@Au nano-urchins obtained by adding 6 mL, 0.5 mM HAuCl4 exhibit excellent chemical stability in ionic or oxidative condition. More importantly, the obtained products provide enhanced SERS activity by using 4-Aminothiophenol (4-ATP) as the probe molecules. The obvious inner hollow structure and exterior immense antennas as well as pronounced inter-metallic synergies are integrated to provide ultrasensitive SERS signals with an enhancement factor (EF) up to ~1012. Interestingly, the SERS signals are also clearly distinguishable even the concentration of 4-ATP was decreased to ~10−13 M. The pronounced features are better than many previous works, especially those of smooth-shaped nanocomposites, monometallic nanodendrites or single-phase hollow structures. The superiorities of the hollow Ag@Au nano-urchins will make them become a prominent SERS-based substrate for ultra-trace detection of biomolecules in pathological cell diagnostics, environmental surveillance, and food safety supervision.