The present invention relates to analyte detection devices and methods of using such devices to detect minute quantities of a target analyte in a sample. In particular, the invention provides a method of detecting a target analyte in a sample comprising mixing the sample with a first detection conjugate and a second detection conjugate in solution, wherein the first and second detection conjugates comprise metallic nanostructures coupled to binding partners that are capable of specifically binding to the target analyte if present in the sample to form a complex between the first detection conjugate, the analyte, and the second detection conjugate, wherein a change in an optical signal upon complex formation indicates the presence of the target analyte in the sample. Methods of preparing nanostructures and nanoalloys, as well as nanostructures and nanoalloys conjugated to binding partners, are also described.