Self-Assembly of “Patchy” Nanoparticles: a Versatile Approach to Functional Hierarchical Materials Cite This: Chem

Chemical Science PERSPECTIVE View Article Online View Journal | View Issue Self-assembly of “patchy” nanoparticles: a versatile approach to functional hierarchical materials Cite this: Chem. Sci.,2015,6, 3663 David J. Lunn, John R. Finnegan and Ian Manners* The solution-phase self-assembly or “polymerization” of discrete colloidal building blocks, such as “patchy” nanoparticles and multicompartment micelles, is attracting growing attention with respect to the creation of complex hierarchical materials. This approach represents a versatile method with which to transfer functionality at the molecular level to the nano- and microscale, and is often accompanied by the emergence of new material properties. In this perspective we highlight selected recent examples of the self-assembly of anisotropic nanoparticles which exploit directional interactions introduced through their Received 30th March 2015 shape or surface chemistry to afford a variety of hierarchical materials. We focus in particular on the Accepted 13th April 2015 solution self-assembly of block copolymers as a means to prepare multicompartment or “patchy” DOI: 10.1039/c5sc01141h micelles. Due to their potential for synthetic modification, these constructs represent highly tuneable www.rsc.org/chemicalscience building blocks for the fabrication of a wide variety of functional assemblies. Creative Commons Attribution 3.0 Unported Licence. 1 Introduction deconstruction of a virus and isolation of its capsid for biomedical applications, and the template directed reactive-ion- “Top-down” and “bottom-up” are two well-known, comple- etching of bulk silicon to prepare microchips bearing nano- mentary, and all-encompassing design strategies for the prep- metre-scale features. Bottom-up approaches focus on the aration of functional nanomaterials. Top-down approaches assembly of subunits or ‘building blocks’ to prepare increas- focus either on the breaking down of a pre-existing hierarchical ingly complex and hierarchical systems, categorized as either system into its constituent parts, or on the guided transfer of directed assembly or self-assembly. In directed assembly, the This article is licensed under a 1 order during material preparation. Examples include the formation of subunits is guided by external stimuli, for example by magnetic elds2 or optical tweezers.3 In contrast, self-assembly exploits the predened interactions of discrete Open Access Article. Published on 12 May 2015. Downloaded 9/27/2021 8:33:15 PM. School of Chemistry, University of Bristol, Bristol BS8 1TS, UK. E-mail: ian.manners@ subunits to prepare organized structures.4,5 To maintain order bristol.ac.uk David Lunn grew up in Ber- John Finnegan grew up in the khamsted, a small town just Scottish capital, Edinburgh, north of London. He graduated before completing his under- in 2009 with an MSci in Chem- graduate degree at the Univer- istry from the University of sity of Durham in 2012. John has Bristol, gaining industrial expe- gone on to graduate with a MRes rience in 2008 working in the from the University of Bristol Netherlands for DSM Biomed- under the supervision Prof. Ian ical. David stayed at the Manners. Now continuing his University of Bristol to complete work in Manners group, John is his PhD as one of the rst cohort working towards a PhD thesis on of the Bristol Chemical the subject of functional nano- Synthesis Center for Doctoral materials via crystallization- Training (BST CDT), graduating in 2014. His PhD project focussed driven self-assembly. on the synthesis and self-assembly of functional block copolymers under the supervision of Prof. Ian Manners and Prof. Paul Pringle. For his next step, David has been awarded a Marie Curie Global Fellowship to work for Prof. Craig J. Hawker at UCSB and Prof. Hagan Bayley at the University of Oxford. This journal is © The Royal Society of Chemistry 2015 Chem. Sci.,2015,6, 3663–3673 | 3663 View Article Online Chemical Science Perspective throughout hierarchical assemblies, which span length scales self-assembled structures have the ability to error-check and orders of magnitude greater than the feature sizes of the self-repair.7,10,11 building blocks from which they are constructed, each subunit Through the self-assembly of well-dened subunits, the must be well-dened and able to combine with others in a information required to encode hierarchical systems is mini- controlled manner. mized. The tobacco mosaic virus (TMV), the rst to be discov- Despite the bewildering complexity achieved in Nature ered and considered the herald of modern virology, is through bottom-up self-assembly, the actual pool of molecular comprised of 2130 identical protein subunits each containing building blocks used is relatively small. Starting with a simple 158 amino acids. These subunits self-assemble around a single collection of just over 20 amino acids, 5 nucleotides, a handful strand of RNA to form a stable structure 300 nm long (Fig. 1). If of sugars and a series of abundant metal ions, structures such genetic information were required to encode the entire struc- as polypeptides, nucleic acids, polysaccharides and hybrid ture, the genome would be larger than the virus itself. However, organic–inorganic materials (e.g. bone, with many levels of to encode the identical subunits that undergo dened self- structural hierarchy) can be prepared.6 Complexity arises from assembly requires only a small percentage of the total RNA.12 the self-assembly of these building blocks using a variety of TMV illustrates how Nature achieves hierarchical self- molecular interactions, for example electrostatic, hydrogen assembly so elegantly to create functional materials with many bonding, metal–ligand and p-donor/acceptor, as well as many levels of substructure.6,9,10 Considerable effort is still focussed other covalent and non-covalent linkages.7 Polypeptides on understanding natural self-assembly processes based on the prepared by the chain growth polymerization of amino acid idea that new knowledge and insight can be harnessed for the subunits by the translation of messenger ribonucleic acid creation of synthetic routes to novel structures with reduced (mRNA), or within pre-existing enzymes, undergo intra- defects and enhanced properties. As methods for the prepara- molecular chain folding through non-covalent interactions tion of “patchy” particles have improved, a large variety of new determined by the sequence of amino acids. This chain folding building blocks has become widely accessible. In this Perspec- ff a b Creative Commons Attribution 3.0 Unported Licence. a ords secondary structures such as -helices, -sheets and tive we have sought to highlight a selection of recent examples, b-turns, which drive the further self-assembly of the polypeptide wherein the relatively weak but directional interactions between into more complex tertiary structures. These tertiary structures “patchy” particles are exploited to prepare hierarchical assem- can constitute the highest level of structural order for a single blies. First, we discuss supramolecular polymerizations, which protein, or alternatively, can function as subunits for the further provide a conceptual foundation for the self-assembly processes growth of hierarchical assemblies. For example, the globular described in later discussions. multifunctional protein actin can undergo controlled self- assembly or “polymerization” to form quaternary structures in 2 Supramolecular polymerizations via the form of laments, which are responsible for a variety of This article is licensed under a crucial structural functions in the cell.8 As disorder in the directional non-covalent interactions resulting assemblies may lead to biomaterial failure or cell Supramolecular polymerization under thermodynamic control ffi death, Nature maximizes the e ciency of self-assembly by refers to the self-assembly of molecular monomers by “moder- 7,9 Open Access Article. Published on 12 May 2015. Downloaded 9/27/2021 8:33:15 PM. preparing low energy structures. Using dynamic molecular ately strong, reversible non-covalent, but highly directional interactions that have some degree of reversibility, the resulting forces that result in high molecular weight linear polymers under dilute conditions”.13 Whereas a conventional covalent polymer is considered to be in a “static” state due to the non- reversibility of the covalent bonds between monomeric units, a Ian Manners was born in London supramolecular polymer formed by a process of this type will (UK) in 1961, and completed his remain in a state of dynamic equilibrium. Nevertheless, despite PhD at the University of Bristol. Aer postdoctoral work in Ger- many and the USA, he joined the University of Toronto (Canada) as an assistant professor in 1990; he become full professor in 1995 and received a Research Chair in 2001. In 2006 he returned to his Alma Mater to take up a Chair in Inorganic, Macromolecular, and Materials Chemistry. His awards include on Alfred P.Sloan Fellowship (1994), a Corday-Morgan Fig. 1 Schematic representation and TEM image of the tobacco Medal (1997), the Steacie Prize (2001), a Marie Curie Chair from mosaic virus. One molecule of single strand RNA (1) surrounded by 2130 coat proteins (2) that make up the virus capsid (3). Transmission the European Union (2005), and a Humboldt Research Award electron microscopy (TEM) image©1994 Rothamsted Experimental (2011). He is an elected member of the National Academies of Station. Tobacco mosaic schematic by Thomas Splettstoesser (http:// Science of Canada

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