Abstract: A method for preparing nanoparticles includes preparing a mixture containing an organic solvent, surfactant and water; adding a first quantity of a first silica precursor and ammonia to the mixture; adding a second quantity of the first silica precursor and a second silica precursor to the mixture; adding acetone to the mixture; removing silica nanoparticles from the mixture; and drying the silica nanoparticles.

Abstract: Surfaces coated with a target-induced fluorescent compound are used to detect target elements, especially trace elements. The target-induced fluorescent compound does not fluoresce when excited at a specific wavelength until it has bound a target element. The use of these coated surfaces provides several benefits including reduced background for greater sensitivity and eliminating the need to separate target-induced fluorescent compound that has not bound target element from target-induced fluorescent compound that has bound target element. Coated nanoparticles are especially useful for detection of target elements.