Preparation of silver particles and its application for surface enhanced Raman scattering with near-infrared excitation

The preparation of silver nanoparticles through the reduction of silver ammonia complex by glucose is reported. The average of the as-prepared particle sizes varied from approx. 35 nm to 120 nm in a dependence of ammonia concentration. The mechanism of silver particle formation is dependent on the ammonia concentration. At low ammonia to silver ions ratios (1:1 and 2:1), the silver oxide particles are formed at first and subsequently are reduced by glucose. Higher ammonia concentrations are able to bind silver ions sufficiently without forming silver oxide as an intermediate and in these cases are silver particles generated through direct reduction of [Ag(NH3)2]+ by glucose. The obtained silver particles were tested in surface enhanced Raman scattering experiments with infrared laser excitation (1064 nm). The adenine was used as a model analyt for evaluation of the surface enhancement efficiency. Before surface enhanced Raman measurements, sodium chloride of a resulting concentration equals to 0.1 mol L−1 was used for treatment of silver particles, leading to a partial etching and coalescence of silver particles. It was found out that the enhancement efficiency of Raman signal is considerably dependent on silver particle size. The highest enhancement factors after addition of concentrated sodium chloride solution were achieved using particles with sizes about 60 nm.