A facile method for the synthesis of large-size Ag nanoparticles as efficient SERS substrates.

Silver nanoparticles (Ag NPs) enjoy a reputation as an ultrasensitive substrate for surface-enhanced Raman spectroscopy (SERS). However, large-scale synthesis of Ag NPs in a controlled manner is a challenging task for a long period of time. Here, we reported a simple seed-mediated method to synthesize Ag NPs with controllable sizes from 50 to 300 nm, which were characterized by scanning electron microscopy (SEM) and UV-Vis spectroscopy. SERS spectra of Rhodamine 6G (R6G) from the as-prepared Ag NPs substrates indicate that the enhancement capability of Ag NPs varies with different excitation wavelengths. The Ag NPs with average sizes of ~150, ~175, and ~225 nm show the highest SERS activities for 532, 633, and 785-nm excitation, respectively. Significantly, 150-nm Ag NPs exhibit an enhancement factor exceeding 108 for pyridine (Py) molecules in electrochemical SERS (EC-SERS) measurements. Furthermore, finite-difference time-domain (FDTD) calculation is employed to explain the size-dependent SERS activity. Finally, the potential of the as-prepared SERS substrates is demonstrated with the detection of malachite green. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]