The use of Ge⁰ nanocrystals (NCs) and nanowires (NWs) for advanced materials applications are of great interest; however, complex synthetic routes have hindered their use and development. We have recently developed a simple route to produce Ge⁰ NCs and NWs from the reduction of Ge⁺² precursors at 300°C and 1 atm Ar without using metal catalysts and without producing salt byproducts. Taking a molecular design approach, we tailor the Ge-ligand bond and the ligand steric hindrances to control Ge⁺² precursors' reactivity. More reactive Ge⁺² precursors yield Ge⁰ NCs, while less reactive alkoxide precursors yield Ge⁰ NWs. X-ray diffraction and transmission electron microscopy show that both NCs and NWs are in cubic phase. The surface of these Ge⁰ NCs and NWs can be further functionalized to prevent spontaneous oxidation, which is useful for both optical and biological applications. The resultant Ge⁰ NCs are optically active, as demonstrated by the presence of photoluminescence in both visible (around 450 nm) and infrared region (around 1300 nm). Ge⁰ NCs also display highly nonlinear optical behavior; the experimentally measured two photon absorption coefficient ranges from 1190 to 1940 cm/GW. We also demonstrate that water-soluble Ge⁰ NCs are stable for months. Preliminary investigations on the use of Ge⁰ NCs as a biological probe reveal that dinitrophenol (DNP)-decorated Ge⁰ nanocrystals readily bind to anti-DNP IgE receptors on mast cells, while maintaining high cell viability comparable to the control cells. The details of synthesis, optical properties, and biofunctionalization will be presented. The authors acknowledge generous support from NSF CAREER (DMR-0094145). Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

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