Spectroscopy and Imaging

Silver nanoparticles were synthesized by an enzymatic induced growth process onto solid substrates. In order to customize the enzymatically grown nanoparticles (EGNP) to analytical applications in bio-molecular research a detailed study was carried out on the time evolution of the formation of the silver nanoparticles, their morphology and their chemical composition. Therefore, silver nanoparticle films of different densities were investigated using scanning as well as transmission electron microscopy in order to examine their structure. Cross sections of silver nanoparticles prepared for transmission electron microscopy analysis were additionally studied by energy dispersive X-ray spectroscopy in order to probe their chemical composition. The surface coverage of substrates with silver nanoparticles and the maximum particle height were determined using Rutherford backscattering spectroscopy. A variety of silver nanoparticle films depending on the conditions during synthesis was observed. After an initial growth state the silver nanoparticles exhibit the so-called desert rose or nanoflowers-like structure. The complex nanoparticle structure is in clear contrast to the auto-catalytically grown spherical particles, which maintain their overall geometrical appearance during the increase of their diameter. It is shown, that the desert rose like silver nanoparticles consist of single crystalline silver plates containing only pure silver. The surface enhanced Raman spectroscopic (SERS) activity of the EGNP structures looks promising due to the specific rough surface structure of the nanoflowers. SERS measurements of the vitamin riboflavin incubated on silver the nanoparticles are shown as an exemplary application for quantitative analysis.