Colloidal quantum dots. From scaling laws to biological applications

Over a twenty-year period, condensed matter physicists and physical chemist s have elucidated a series of scaling laws which successfully describe the size dependence of solid state properties [1,2]. Often the experiments were performed under somewhat exotic conditions, for instance on mass-selected clusters isolated in molecular beams or on quantum dots grown by molecular beam epitaxy and interrogated at low temperatures and in high magnetic fiel ds. As a result, we now have an understanding of how thermodynamic, optical , electrical, and magnetic properties evolve from the atomic to the solid s tate limit. This area of research is presently undergoing a remarkable tran sformation. The scaling laws, previously the direct subject of research, no w provide a tool for the design of advanced new materials. In the case of c olloidal quantum dots, or semiconductor nanocrystals, these new insights ar e poised to have impact in disciplines remote from solid state physics [3].