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.