A highly selective and colorimetric assay of lysine by molecular-driven gold nanorods assembly

In this contribution, a simple, rapid, colorimeteric and selective assay for lysine was achieved by a controllable end-to-end assembly of gold nanorods (AuNRs) in the presence of Eu3+ and lysine. This one-pot end-to-end assembly of 11-mercaptoundecanoic acid (MUA) modified AuNRs was occurred in Britton-Robinson buffer of pH 6.0, which involves the coordination binding between Eu3+ and COO- groups as well as the electrostatic interaction of the COO- groups of MUA with the -NH3+ group of lysine. As monitored by absorption spectra, scanning electron microscopic (SEM) images and dynamic light scattering (DLS) measurement, the end-to-end chain assembly results in large red-shift in the longitudinal plasmon resonance absorption (LPRA), giving red-to-blue color change of AuNRs. Importantly, it was found that the red-shift of LPRA is linearly proportional to the concentrations of lysine in the range of 5.0 x 10(-6)-1.0 x 10(-3) M with the limit of detection (LOD) being 1.6 x 10(-6) M (3 sigma/k). This red-shift of LPRA is highly selective, making it possible to develop a rapid, selective and visual assay for lysine in food samples. (c) 2012 Elsevier B.V. All rights reserved.