Effect of structure: A new insight into nanoparticle assemblies from inanimate to animate

Abstract

Nanoparticle (NP) assemblies are among the foremost achievements of nanoscience and nanotechnology because their interparticle interactions overcome the weaknesses displayed by individual NPs. However, previous studies have considered NP assemblies as inanimate, which had led to their dynamic properties being overlooked. Animate properties, i.e., those mimicking biological properties, endow NP ensembles with unique and unexpected functionalities for practical applications. In this critical review, we highlight recent advances in our understanding of the properties of NP assemblies, particularly their animate properties. Key examples are used to illustrate critical concepts, and special emphasis is placed on animate property-dependent applications. Last, we discuss the barriers to further advances in this field.

Fig. 1. Schematic diagrams of NP assemblies having inanimate and animate properties.

NP assemblies have novel optical, electronic, magnetic, optothermal, and mechanical properties. Reproduced with permission from the American Association for the Advancement of Science (56). Emerging animate properties are expected to inspire a new era of NP assemblies.

Fig. 2. Comparison between bulk materials and NPs.

Compared with bulk materials, NPs can have very different shape, optical, electronic, magnetic, and mechanical properties (left to right). Reproduced with permission from John Wiley and Sons (108). Reproduced with permission from the American Chemical Society (109). Reproduced with permission from the American Association for the Advancement of Science (110).

Fig. 3. Covalent bond-type coupling between assembled NPs.

(A) Covalent bonding between atoms in molecules. (B) Energy states of coupled and uncoupled quantum dots (QD). (C) Electromagnetic coupling between adjacent NPs in ordered arrays (top) and NP assemblies (bottom). (B) and (C) are reproduced with permission from John Wiley and Sons (44). (D) Schematic diagrams of plasmon hybridization of the dipoles. Reproduced with permission from John Wiley and Sons (45). (E) Schematic diagrams of dipole-dipole interactions. (F) Schematic diagrams of dipolar interactions between magnetic NPs.

Fig. 4. Ionic bond–type interactions in assemblies.

(A) Ionic bonding between atoms in crystals and the assembly of hard NPs with soft organic ligands. (B to D) Schematic diagrams, scanning electron microscopy (SEM) images, and transmission electron microscopy (TEM) images of native bone, respectively. (E to G) Schematic diagrams, SEM images, and TEM images, respectively, of hierarchical intrafibrillarly mineralized collagen synthesized by a polyacrylic acid–calcium intermediate. (B) to (G) are reproduced with permission from John Wiley and Sons (49). (H) Atomic force microscopy property maps (top) and sectional Young’s modulus analyses (bottom) of hierarchical intrafibrillarly mineralized collagen. Reproduced with permission from John Wiley and Sons (50). (I and J) Surface SEM images of Anodonta woodiana nacre and synthetic nacre, respectively. (K) Mechanical performance of different materials. (I) to (K) are reproduced with permission from the American Association for the Advancement of Science (52).

Fig. 5. General physicochemical properties of NP assemblies.

(A to C) Schematic diagrams of intraparticle electronic energy transfer in ordered superparticles (SPs), random SPs, and ordered arrays, respectively. (D) Simulated relative intraparticle transfer efficiency. (E) Calculated average enhanced electrostatic field intensity. (F) TEM image of needle-like CdSe-CdS superlattices. (A) to (E) are reproduced with permission from John Wiley and Sons (44). (G and H) Schematic diagrams and SEM image of unidirectionally aligned needle-like SPs, respectively. (I) Dependence of photoluminescence intensity on polarization angle. (F) to (I) are reproduced with permission from the American Association for the Advancement of Science (56). (J) TEM image of binary Fe₃O₄ nanocrystal superlattices. Insets: Magnified image, corresponding selected area electron diffraction patterns, and structural model. (K) SEM image of binary Fe₃O₄ nanochain superlattices. (L) Zero field–cooled and field-cooled magnetization curves for the 7.2-nm Fe₃O₄ nanocrystals (red), 14.3-nm Fe₃O₄ nanocrystals (olive), and binary Fe₃O₄ nanocrystal superlattices (blue). (J) to (L) are reproduced with permission from the American Chemical Society (46). (M) SEM image of the nanosheet assemblies. (N) Nanosheet assembly model and its calculated displacement distribution profile. (O) TEM image of the nanosheets. (P) Nanosheet model and its calculated displacement distribution profile. (M) to (P) are reproduced with permission from the Nature Publishing Group (3). a.u., arbitrary units.

Fig. 6. Animate properties of NP assemblies.

(A) Schematic diagrams of NP assembly motion under an applied external magnetic field. (B) Synthesis and (C) TEM image of nano-sized stirring bars. (D) Schematic representation of the parallel stirring of droplets on a magnetic stir plate. (B) to (D) are reproduced with permission from John Wiley and Sons (72). (E) Schematic diagrams of self-healing properties. (F) Schematic diagram of the self-assembly of metal liquid–like 3D gold nanorod arrays. Reproduced with permission from the Nature Publishing Group (77).

Fig. 7. Self-replication properties of NP assemblies.

(A) Schematic diagrams of self-replication properties. (B) Dark-field images showing the formation of several Ag dimer chains. Reproduced with permission from John Wiley and Sons (82). (C) Time-lapse images of the self-replication process of assemblies. Reproduced with permission from the Nature Publishing Group (83).

Fig. 8. Applications of animate NP assemblies.

(A) Schematic diagram of the reversible trapping of molecules. (B) Schematic diagram of the interaction between proteins and a nanocoil. Reproduced with permission from the American Chemical Society (7). (C) Bacterial capture by 3D nanoclaws at high flow velocity. (D) SEM image of polycrystalline nanowires during bacterial capture. (E) Bacterial capturing efficiencies of different dialyzers. (C) to (E) are reproduced with permission from the Nature Publishing Group (89). (F) Schematic diagram of the actuation mechanisms of graphene paper. (G) Bending angle as a function of irradiation intensity. (F) and (G) are reproduced with permission from the American Association for the Advancement of Science (93). UV, ultraviolet; Vis, visible.