NOVELTY - Method for making silicon nanorods comprises reacting gold (Au) nanocrystals with a silane in a liquid medium, where each of the nanorods has an average diameter of 1.2-10 nm and has a length of 1-100 nm.    USE - The method is useful for making silicon nanorods, which is useful in a light emitting diode, an integrated circuit, a contrasting agent, a solar cell, and a transistor, where the transistor is a field effect transistor. The silicon nanorods are useful for imaging a biological sample. The method is useful for making nanostructures, preferably nanorods, and nanowires (all claimed).    ADVANTAGE - The method provides silicon nanorods as uniformly dispersed colloid.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a composition comprising many silicon nanorods, where each of the nanorods has an average diameter of 1.2-10 nm, and has a length of 1-100 nm;    (2) a method of imaging a biological sample comprising treating the sample with a contrasting agent comprising the composition, and imaging the treated sample;    (3) a method for making nanostructures of a desired length, comprising determining a desired length for the nanostructures, and reacting a seed material with a precursor in a liquid medium to produce the nanostructures, where the molar ratio of seed material to precursor is selected to achieve the desired nanostructure length;    (4) a method for making silicon nanorods of a desired length, comprising determining a desired length for the silicon nanorods, and reacting Au nanocrystals with a silane in a liquid medium to produce the nanorods, where the molar ratio of silane to Au nanocrystals is selected to achieve the desired nanorod length, and each of the nanorods has an average diameter of 1.2-10 nm and has a length of 1-100 nm; and    (5) a method for forming nanostructures comprising heating a mixture of a group IV metal organometallic precursor and metal nanocrystals in a liquid medium at a temperature, where the precursor decomposes and nanostructures grow from the metal nanocrystals, rapidly cooling the liquid medium, and subjecting the nanostructures to an etch to remove the material of the metal nanocrystals there from.