"The aim of the present project is to explore different synthesis strategies to obtain silicon nanocrystals and carbon nanodots with luminescent properties as alternative to conventional fluorescent biomarkers or other light-emitting semiconductor nanoparticles containing heavy metals known as quantum dots. Nanostructured silicon can provide appealing properties such as size and wavelength-dependent luminescence emission in the red/near infrared window, resistance to photobleaching, and robust surface chemistry for grafting of bio-molecules without incurring the burden of intrinsic toxicity or elemental scarcity of quantum dots. Carbon-based nanostructures with fluorescent properties remain relatively unexplored but similar behaviour and properties can be envisaged.The production of silicon nanocrystals will be approached by means of two different methods: i) thermal processing of silesquioxanes to produce an encapsulating oxide matrix for the silicon nanocrystals and ii) laser pyrolysis of silicon precursors either in gas phase or in the form of aerosols containing organometallic precursors. Both methods are quite novel and offer great possibilities for scaling up the batch production of silicon nanocrystals offered by current methodologies. Likewise, the synthesis of carbon nanodots will be explored by both thermal decomposition and laser ablation of carbon-containing precursors.To stabilize the nanoparticles and render them biocompatible for in vitro and in vivo diagnostic imaging experiments, different passivating and encapsulating agents like alkyl or alkoxy-groups and micelle-forming polymers and phospholipids will be evaluated. Finally, fluorescent labelling of cells, evaluation of cytotoxicity, drug-loading, circulation and degradation of selected samples will be carried out."