This work demonstrated the design and synthesis of multiple dye-doped silica cross-linked micellar nanoparticles (MD-SCMNPs) by encapsulating three organic dyes (fluorescein derivative (FCD), coumarin derivative (HCE) and Rhodamine b (RhB)) in SCMNPs cores for colour-tuneable sensing of cysteine (Cys) in aqueous media and in living cells. In the presence of Cys, HCE exhibited blue emission, and RhB exhibited purple emission, while FCD reacted with Cys and exhibited green fluorescence "turn-on" in the core of MD-SCMNPs. This green-light-emitting sensing product may cause "step by step" fluorescent resonance energy transfer (FRET) from HCE to the sensing product and then to RhB. Based on the FRET process in the core, MD-SCMNPs can quantitatively detect Cys by a colour change with a low limit of detection (LOD) of 0.3 mu M in living cells. Furthermore, MD-SCMNPs exhibited ultrasmall size (similar to 12 nm) and excellent dispersity and biocompatibility, which could potentially be used as a visualized Cys sensor for health monitoring and disease prediction in the human body. (C) 2018 Published by Elsevier Inc.