Fabrication and characterization of rhombic silver nanoparticles array being used as a localized surface plasmon resonance (LSPR)-based nano-biosensor were reported in this paper. The sensor consists of a rhombic Ag nanoparticles array with single particle dimension of similar to 140 nm in-plane width and 47 nm out-of-plane height. Characteristics of the nanoparticles such as extinction spectroscopy properties, refractive index sensitivity, and concentration of the target molecules were analyzed. The LSPR-based extinction spectra of the antigen or antibody with lower concentration were detected. The detection results from 100 nM target molecule indicate a larger peak wavelength shift for the rhombic nanoparticles-based nano-biosensor than that of the reported triangular particles-based biosensor. Using a discrete dipole approximation (DDA) algorithm aided design approach we demonstrated that the refractive index sensitivity is 330 nm per refractive index unit for the fabricated rhombic Ag nanoparticles array. (C) 2008 Elsevier B.V. All rights reserved.