Biotemplating plasmonic nanoparticles using intact microfluidic vasculature of leaves

Leaves are an abundant natural resource, and consist of a sophisticated microfluidic network of veins that transport nutrients and water, thereby enabling photosynthesis. Here, we simultaneously exploit the microfluidics as well as chemistry of processed leaf vasculature (venation) in order to template the in situ generation of plasmonic metal (gold and silver) nanoparticles under ambient conditions. This biotemplating approach involves capillary flow of metal salts through skeleton leaf vasculature, and does not require additional reducing agents for plasmonic nanoparticle formation. Gold nanoparticles, 30-40 nm in diameter, and silver nanoparticles, approximately 9 nm in diameter, were formed within the intact leaf vasculature using this method. Absorption spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron diffraction analyses were employed to ascertain the formation of nanoparticles in the leaf veins. Fourier transform infrared (FT-IR) spectroscopy was employed in order to obtain insights into functional groups responsible for formation of the plasmonic nanoparticles within the leaves. Gold nanoparticles, templated within leaves, demonstrated excellent catalytic properties, thereby imparting catalytic and plasmonic properties to the leaf itself. Furthermore, nanoparticles can be recovered from the leaves as soluble dispersions by simply combusting the organic leaf matter. Taken together, this is a simple yet powerful biotemplating approach for the generation of plasmonic nanoparticles and formation of biotic-abiotic structures for diverse, low-cost applications in sensing, catalysis, and medicine.