We designed and fabricated multilayer assemblies of biodegradable poly(lactic acid) (PLA) nanoparticles based on hydrogen-bonding or electrostatic interactions. The PLA nanoparticles were prepared by precipitation method and their surface charge was switched by modified precipitation in the presence of poly(ethylene imine) (PEI). Moreover, gold nanoparticles were grown within the PLA nanoparticle assemblies either through UV-irradiation or under mild reducing conditions to create biodegradable nanocomposites with distinct optical response which allows monitoring biodegradation of the films. The nanocomposite coatings of PLA nanoparticles were enzymatically degraded by α-chymotrypsin. We demonstrated that the biodegradation process can be colorimetrically monitored with UV-vis spectroscopy thus opening the way for facile and real-time monitoring useful for biotechnology applications. © 2010 Elsevier Ltd.