Advances in engineering nanostructures with exquisite control of size and shape, their unique properties and broad applications (e.g., probes in ultrasensitive molecular sensing and diagnostic imaging, agents for photodynamic therapy and actuators for drug delivery, triggers for photothermal treatment, and precursors for building solar cells, electronics and light emitting diodes) have made nanotechnology an exciting research area. As the field moves from academic findings to industrial products, concerns have surfaced on the subject of the toxicity of nanostructures.