In recent years, semiconductor nanocrystal quantum dots have garnered the spotlight as an important new class of biological labeling tool. With optical properties superior to conventional organic fluorophores from many aspects, such as high photostability and multiplexing capability, quantum dots have been applied in a variety of advanced imaging applications. This dissertation research goes along with large amount of research efforts in this field, while focusing on the design and development of new nanoprobes from semiconductor nanocrystals that are aimed for useful imaging or sensing applications not possible with quantum dots alone. Specifically speaking, two strategies have been applied. In one, we have taken advantage of the increasing capability of manipulating the shape of semiconductor nanocrystals by developing semiconductor quantum rods as fluorescent biological labels. In the other, we have assembled quantum dots and gold nanocrystals into discrete nanostructures using DNA. The background information and synthesis, surface manipulation, property characterization and applications of these new nanoprobes in a few biological experiments are detailed in the dissertation.