Synthesis and In-Depth Study of the Mechanism of Silver Nanoplate and Nanodecahedra Growth by LED Irradiation for SERS Application

Silver nanodecahedra and nanoplates were successfully fabricated using a simple solution method, where silver nitrate (AgNO3) was reduced with sodium borohydride (NaBH4) at melting ice temperature. Green light-emitting diode (green LED, wavelength λG = 520 nm) was irradiated into the reaction system to control the morphology of the product. The synthetic procedure was a combination of two processes including the formation of silver seeds and subsequent photomediated crystal growth. This article also presents a mechanism study of the photomediated growth of silver nanoplates and nanodecahedra. In these processes, citrate ions were used as a morphology-controlled reagent and polyvinyl pyrrolidone as a capping agent. The growth process was evaluated by dynamic light scattering and ultraviolet/visible spectra measurements. The obtained silver nanoparticles (AgNPs) possessed various shapes, including triangular, truncated triangular, hexagonal and decahedron depending on the time duration of LED irradiation. Triangular nanoplates or decahedral nanoparticles (80–100 nm) were obtained when the silver colloid was exposed to green LED irradiation for different times (30 min—76 h). The average width and thickness of such nanoparticles were estimated to be approximately 80 nm and 20 nm, respectively. The technology uniqueness in this work is that we can change the morphology of silver from plate to decahedron via prolonging the LED illumination period from 140 min to 76 h instead of changing the light wavelength or temperature of the reaction solution. The surface-enhanced Raman scattering (SERS) experiment was carried out to measure Rhodamine 6G (R6G) concentrations plated on the silicon substrates. Silver nanodecahedra can detect the low concentration of R6G (10−8 M), while silver nanoplates can detect a higher R6G concentration of 10−6 M. Silver nanodecahedra could be used as an effective SERS substrate for ultrasensitive detection.