We present a simple in situ method to fabricate silver (Ag) nanciparticle arrays in a layer-by-layer (LBL) assembled hyaluronan (HA)/poly(dimethyldiallylammonium chloride) (PDDA) multilayer structure, in which the LBL multilayered film is constructed by electrostatic attraction between positively charged PDDA and negatively charged HA, followed by in situ synthesis of embedded Ag nanoparticle arrays in the LBL "nanoreactors," where the abundant negatively charged carboxyl groups of HA bind and further reduce Ag+ ions under UV-irradiating. The arrays morphology is highly dependent on the number of bilayers, and the surface density of nanoparticles in the arrays can be simply tailored by the number of irradiation/drying cycles during fabrication. The embedded Ag nanciparticle arrays possess good stability for localized surface plasmon resonance (SPR) absorption spectrum-based biosensors and superior antimicrobial capability. These render great potentials for the films in both biosensing and antimicrobial applications. (C) 2008 Elsevier Inc. All rights reserved.