Layer-by-layer growth of superparamagnetic, fluorescent barcode nanospheres

We report a novel stepwise layer-by-layer synthesis strategy to achieve multi-component barcode nanospheres that contain magnetic nanoparticles (MNPs) as the core and quantum dots (QDs) of different emission colors in spatially separated silica layers as the shells, with QD-free silica layers as the insulation layers. This strategy offers the following unique features: (1) the location of the MNPs and the QDs in the silica spheres are separated spatially, so that no interference of the QD photoluminescence (PL) by the magnetic particles is observed; (2) the PL spectra of barcode nanospheres can be easily tuned through the ratio of different QDs loaded in each layer; (3) the size of the silica nanospheres can range from submicron (∼100 nm) to micrometers depending on the number of layers and the thickness of each layer; (4) QD stability is preserved by embedding the QDs covalently in the silica matrix; (5) fluorescence resonance energy transfer (FRET) between different colored QDs is avoided by isolating them into separated layers with a silica spacer layer.