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.