Nanocrystals are ceramics, metals and metal oxide nanoparticles. In other words, materials assembled of nanometer-sized building blocks are microstructurally heterogeneous, consisting of the building blocks (e.g. crystallites) and the regions between adjacent building blocks (e.g. grain boundaries). It is this inherently heterogeneous structure on a nanometer scale that is crucial for many of their properties and distinguishes them from glasses, gels, etc. that are microstructurally homogeneous. Nanocrystallites of bulk inorganic solids have been shown to exhibit size dependent properties, such as lower melting points, higher energy gaps, and nonthermodynamic structures. In comparison to macro-scale powders, increased ductility has been observed in nanopowders of metal alloys. In addition, quantum effects from boundary values become significant leading to such phenomena as quantum dots lasers. Nanocrystals of various metals have been shown to be harder than the same materials in bulk form. Because wear resistance often is dictated by the hardness of a metal, parts made from nanocrystals might last significantly longer than conventional parts. Nanocrystals absorb and then re-emit the light in a different color and the size of the nanocrystal (in the Angstrom scale) determines the color. Antimicrobial dressing covered with nanocrystalline silver rapidly kills a broad spectrum of bacteria in as little as 30 minutes. Nanocrystal are an ideal light harvester in photovoltaic devices where it absorbs sunlight more strongly than dye molecules or bulk semiconductor materials. Due to this high optical densities can be achieved while maintaining the requirement of thin films. Fluorescent nanocrystals have several advantages over organic dye molecules as fluorescent markers in biology. They are incredibly bright and do not photodegrade. Drug-conjugated nanocrystals attach to the protein in an extracellular fashion, enabling movies of protein trafficking and thus form the basis of a high-throughput fluorescence assay for drug discovery. Cutting tools made of nanocrystalline materials, such as tungsten carbide, tantalum carbide and titanium carbide are more wear and erosion-resistant, and last longer than their conventional (large-grained) counterparts. They are finding applications in the drills used to bore holes in circuit boards.