Colloidal hybrid nanoparticles contain multiple nanoscale domains fused together by solid-state interfaces. They represent an emerging class of multifunctional lab-on-a-particle architectures that underpin future advances in solar energy conversion, fuel-cell catalysis, medical imaging and therapy, and electronics. The complexity of these ‘artificial molecules’ is limited ultimately by the lack of a mechanism-driven design framework. Here, we show that known chemical reactions can be applied in a predictable and stepwise manner to build complex hybrid nanoparticle architectures that include M–Pt–Fe3O4 (M = Au, Ag, Ni, Pd) heterotrimers, MxS–Au–Pt–Fe3O4 (M = Pb, Cu) heterotetramers and higher-order oligomers based on the heterotrimeric Au–Pt–Fe3O4 building block. This synthetic framework conceptually mimics the total-synthesis approach used by chemists to construct complex organic molecules. The reaction toolkit applies solid-state nanoparticle analogues of chemoselective reactions, regiospecificity, coupling reactions and molecular substituent effects to the construction of exceptionally complex hybrid nanoparticle oligomers.
Figures at a glance
Figure 1: Stepwise construction of M–Pt–Fe3O4 heterotrimers (M = Ag, Au, Ni, Pd). 
a, Schematic showing the multistep synthesis of M–Pt–Fe3O4 heterotrimers, along with the most significant possible products and their observed frequencies (expressed as the percentage of observed heterotrimers, not total yield). Representative TEM images show Pt nanoparticle seeds (b), Pt–Fe3O4 heterodimers (c) and Au–Pt–Fe3O4 (d), Ag–Pt–Fe3O4 (e), Ni–Pt–Fe3O4 (f) and Pd–Pt–Fe3O4 (g) heterotrimers. All scale bars are 25 nm. h, Photographs of a vial that contains Au–Pt–Fe3O4 heterotrimers in hexane (left), which responds to an external Nd–Fe–B magnet, the same vial with Au–Pt–Fe3O4 heterotrimers in a larger volume of hexanes (middle) and the same vial after precipitation of the heterotrimers with ethanol (right). The precipitated heterotrimers collect next to the external magnet.
Figure 2: Characterization data for M–Pt–Fe3O4 heterotrimers (M = Au, Ag, Ni, Pd). 
a, Powder XRD data for all of the M–Pt–Fe3O4 heterotrimers and of the Pt–Fe3O4 heterodimer for comparison. b, EDS spectra for all of the M–Pt–Fe3O4 heterotrimers. For the Au–Pt–Fe3O4 and Ag–Pt–Fe3O4 samples, a Ni TEM grid was used and the Ni and Cu signals originated from this grid. For the Ni–Pt–Fe3O4 and Pd–Pt–Fe3O4 samples, a Cu TEM grid was used and the Cu signal originated from this grid. c, SAED patterns for all of the M–Pt–Fe3O4 heterotrimers show distinct diffraction spots or rings for each of the components. d, UV-vis absorption spectra for the Au–Pt–Fe3O4 and Ag–Pt–Fe3O4 heterotrimers, and also reference spectra for Au and Ag nanoparticles and the Pt–Fe3O4 heterodimers. a.u. = arbitrary units.
Figure 3: Chemoselective nucleation in the Ag–Pt–Fe3O4 heterotrimer system. 
a–d, TEM images and corresponding schematics showing a series of control experiments, all carried out under the same reaction conditions and designed to probe the chemoselectivity of heterogeneous nucleation in the prototype Ag–Pt–Fe3O4 system: nucleation of Ag on Fe3O4 nanoparticles (a), nucleation of Ag on Pt nanoparticles (b), nucleation of Ag on both Fe3O4 and Pt nanoparticles that are present as a physical mixture (c) and nucleation of Ag exclusively on the Pt domain of Pt–Fe3O4 nanoparticles that are present as interconnected dimers with a solid-state interface (d). The insets in (b) and (c) show enlarged views of the regions indicated by boxes to highlight the lower-contrast Ag regions that nucleate on the higher-contrast Pt particles. The scale bars in the main panels correspond to 20 nm and those in the insets correspond to 5 nm. e, Pt4f XPS spectra for Pt–Fe3O4 heterodimers and the corresponding Pt seeds, which indicate a decreased binding energy in the heterodimers.
Figure 4: Stepwise construction of MxSy–Au–Pt–Fe3O4 heterotetramers (M = Cu, Pb). 
a, Schematic showing the stepwise construction of MxSy–Au–Pt–Fe3O4 heterotetramers, along with the most significant possible products and their observed frequencies (expressed as the percentage of observed heterotetramers, not total yield). b,c, Representative TEM images of Cu9S5–Au–Pt–Fe3O4 heterotetramers, with enlarged regions in (c) showing lattice fringes that correspond to the Fe3O4 (311), Cu9S5 (200), Cu9S5 (111), Au (111) and Pt (111) planes. d,e, Powder XRD data for the Cu9S5–Au–Pt–Fe3O4 (d) and PbS–Au–Pt–Fe3O4 (e) heterotetramers, along with a pattern for Cu9S5–Au heterodimers in (d) for comparison. f, A representative TEM image of the PbS–Au–Pt–Fe3O4 heterotetramers. g, The composite EDS element map for a single PbS–Au–Pt–Fe3O4 heterotetramer particle includes an overlay of Fe (red), Pt (green), Au (blue) and Pb (orange). h–m, A STEM image of a single Cu9S5–Au–Pt–Fe3O4 heterotetramer (h), along with the corresponding EDS element maps for Fe (i), Pt (j), Au (k), Cu (l) and superimposed Fe, Pt, Au and Cu (m). The scale bars correspond to 25 nm (b), 5 nm (c,h) and 10 nm (f).
Figure 5: Higher-order hetero-oligomers based on the Au–Pt–Fe3O4 heterotrimer building block. 
