An innovative concept of floating nanoarrays (FNAs) as promising new-generation surface-enhanced Raman scattering (SERS) sensors was proposed for the first time and has been successfully realized via a facile triblock-copolymer-assisted chemical route. At least two categories of the complicated highly uniform Pt–Pd FNAs with a fairly small assembled diameter of less than 100 nm respectively consisted of quasi-orderly assembled spherical and petal-like nanocrystals with unique radially distributed compositions were evidently classified and reproducibly fabricated. The synthesized Pt–Pd FNAs were found to exhibit unusually strong surface plasmon resonance bands in the visible region and have been successfully demonstrated as practical SERS sensors with remarkably low analytical limits of detection.