Dendrigraft polymer-based synthesis of silver nanoparticles showing bright blue fluorescence

A novel method is reported here for the synthesis of optically clear and stable colloidal solutions of silver nanoparticles. According to size they show different colours depending upon their plasmonic absorption frequencies. The materials have been synthesized at room temperature by chemical reduction of silver ions (silver nitrate) coordinated with dendrigraft polymer, polyethyleneimine (PEI) using formaldehyde in aqueous medium. UV–vis absorption and transmission electron microscopy (TEM) studies show single-band absorption with peak maximum at 354 nm for ∼3 nm sized particles, whereas a side band at ∼400 nm was observed when the particle size increased to ∼20 nm. Highly narrow particle size distribution was observed in case of samples having ∼3 nm size silver particles and also the process of reduction could be completed within minutes. More interestingly, the 3-nm sized particles showed strong blue (474 nm) fluorescence under UV excitation. Thin films of all synthesized samples were prepared on silica substrate by fine spray coating technique.