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Luminescent silicon clusters

New high-resolution nanoprobes are required for efficient, accurate, non-toxic, and minimally-perturbing in vivo imaging of cells. Two candidate materials are being studied: Nanocrystalline diamond (NCD), and Silicon passivated nanoclusters (NSi). Both particles are good candidates for biological probes because they are biocompatible and photostable. We are processing NCD particles, making diluted suspensions in cell media and testing their luminescence properties using in vitro studies of the Mosquitofish nervous system to obtain monodispersed particles suitable for imaging cellular transport and to demonstrate that their blue-greenred luminescence is not quenched by the media. This will be followed by in vivo studies of the Mosquitofish nervous system using deconvolution-assisted structured illumination microscopy (dSIM). The nanoparticles to be developed and tested will make possible in vivo monitoring and tracking of spinal motor neuron changes through time and contribute to the understanding of spinal motor neuron development, remodeling, structure, function, aging, and death. NSi and Europium doped-NSi are being synthesized following a top-down protocol used to prepare standing nanoporous silicon. The films are divided into nanoclusters, each of which is made of several silicon nanoparticles. Allowing the nanoclusters to develop a silicon oxide layer improves their photoluminescence efficiency and stability in biological environments. The Eu-doped NSi nanoprobe will emit in a distinct color spectrum. They will be prepared by doping the surface of the silicon nanostructure with Eu ions. We favor the Eu2+ valence state in the oxidized external layer of the nanostructures as it shows larger absorption cross section compared with the 3+ state. We have demonstrated that the presence of the NSi favors the 2+ state. Our preliminary results with in vivo and in vitro samples show that our passivated silicon nanostructures are highly luminescent and stable probes. In vitro biological samples impregnated with NSi showed stable luminescence one year after preparation. This project was initially supported through seed funds from the PR-NSF-EPSCoR Phase V Program.