In this paper, we are interested in the detection of biological molecules. This detection relies on the use of nanosensors based on localized surface-plasmon resonance (LSPR). We discuss the sensitivity of these nanosensors by studying the influence of the concentration of Biotin on the shift of the LSPR wavelength. Moreover, to study the selectivity of these sensors, the systems Biotin/Anti-Biotin (AB) and Biotin/Streptavidin (SA) are used to detect very weak concentration of AB or SA. We found respectively 7 pM and 3 nM for the limits of detection of SA and AB. (C) 2008 Elsevier B.V. All rights reserved.