Understanding and optimising the packing density of perylene bisimide layers on CVD-grown graphene

The non-covalent functionalisation of graphene is an attractive strategy to alter the surface chemistry of graphene without damaging its superior electrical and mechanical properties. Using the facile method of aqueous-phase functionalisation on large-scale CVD-grown graphene, we investigated the formation of different packing densities in self-assembled monolayers (SAMs) of perylene bisimide derivatives and related this to the amount of substrate contamination. We were able to directly observe wet-chemically deposited SAMs in scanning tunnelling microscopy (STM) on transferred CVD graphene and revealed that the densely packed perylene ad-layers adsorb with the conjugated {\pi}-system of the core perpendicular to the graphene substrate. This elucidation of the non-covalent functionalisation of graphene has major implications on controlling its surface chemistry and opens new pathways for adaptable functionalisation in ambient conditions and on the large scale.Comment: 27 pages (including SI), 10 figure

Fabrication of viable cyborg cells with cyclodextrin functionality

We describe two alternative methods for surface functionalisation of Saccharomyces cerevisiae cells with cyclodextrin molecules without affecting the cell viability. The first strategy involved using epichlorohydrin as a cross-linking agent which binds covalently the cyclodextrin to the glycoproteins on the cell wall. The second strategy of interfacing of the cells with CD involved polyelectrolyte mediated deposition of cyclodextrin sulphate on the cell surface. We used the formation of host-guest inclusion complexes of a dye with the grafted cyclodextrins to estimate the average number of CD molecules grafted per cell which can reach up to hundreds of millions of CD molecules. This indicates more than one monolayer of CDs on the cell surface within the surface layer surrounding the yeast cell membrane. Fluorescein diacetate was used to check the viability of the cells after functionalisation. Living cells functionalised with CDs may find many potential applications as they can be loaded with drugs, immunosuppressants and other molecules forming inclusion complexes with their cyclodextrin interface. Therefore, we foresee such cells being used as novel selective biosorbents in polluted waters, whole cell biosensors, drug delivery, cell therapy and cell implant applications

Characterisation and functionalisation of mechanically fractured graphene nanoribbons : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nanoscience at Massey University, Manawatū, New Zealand

Graphene has been heralded as the supermaterial of the future, boasting incredibly high electron mobility, thermal conductivity, and physical strength – all contained within the world’s first true 2D material, only a single atom thick. Graphene nanoribbons (GNRs) broaden this potential further by demonstrating width-dependent band gaps due to confinement effects. In addition, the ability to define the edge geometry and dimensions of GNRs allows control over self-assembly of these novel carbon nanostructures. GNR synthesis has been broadly explored in literature, demonstrating both relatively high yields and atomic-scale precision. Rarely, however, are these two criteria achieved in the same technique. Longitudinal unzipping of carbon nanotubes (CNTs) generates large quantities of nanoribbon material at the expense of quality, while techniques such as chemical vapor deposition (CVD) and bottom up synthesis achieve truly astounding quality, but lack scalability. Recently, the synthesis of highly ordered GNRs with tunable dimensions and unique geometries has been demonstrated using mechanical fracturing of a block of graphite via simple microtomy techniques. This method offers a top-down approach to GNR synthesis providing highly ordered structure on a much larger scale than efforts to date. In this work, this technique has been altered to use a dry-cut method, and the structural and chemical properties of the material obtained therein have been extensively characterised, demonstrating increased quality, structural order, and quantities obtainable. Further, this work has demonstrated the functionalisation of these dry-cut materials both chemically via simple organic chemistries, and non-covalently utilising filamentous bacteriophage as a route towards biofunctionalisation

Synthesis and characterisation of controllably functionalised polyaniline nanofibres

A novel method for functionalising solution based polyaniline (PAni) nanofibres is reported whereby the degree of side-chain attachment can be controllably altered. The covalent attachment of functional side-groups to the surface of PAni nanostructures is achieved by post-polymerisation reflux in the presence of a nucleophile and the functionalised nanomaterial can be purified by simple centrifugation. The technique is therefore easily scalable. We demonstrate that control over the extent of side-chain attachment can be achieved simply by altering the amount of nucleophile added during reflux. We provide evidence that covalently attached carboxlate side-chains influence the doping mechanism of polyaniline and can be used to introduce self-doping behaviour. Acid functionalised nanofibres remain redox active and retain their optical switching capabilities in response to changes in the local chemical environment, thus making them suitable for adaptive sensing applications

Graphene edge structures: Folding, scrolling, tubing, rippling and twisting

Conventional three-dimensional crystal lattices are terminated by surfaces, which can demonstrate complex rebonding and rehybridisation, localised strain and dislocation formation. Two dimensional crystal lattices, of which graphene is the archetype, are terminated by lines. The additional available dimension at such interfaces opens up a range of new topological interface possibilities. We show that graphene sheet edges can adopt a range of topological distortions depending on their nature. Rehybridisation, local bond reordering, chemical functionalisation with bulky, charged, or multi-functional groups can lead to edge buckling to relieve strain, folding, rolling and even tube formation. We discuss the topological possibilities at a 2D graphene edge, and under what circumstances we expect different edge topologies to occur. Density functional calculations are used to explore in more depth different graphene edge types.Comment: Additional figure in published versio

Functionalisation of colloidal transition metal sulphides nanocrystals: A fascinating and challenging playground for the chemist

Metal sulphides, and in particular transition metal sulphide colloids, are a broad, versatile and exciting class of inorganic compounds which deserve growing interest and attention ascribable to the functional properties that many of them display. With respect to their oxide homologues, however, they are characterised by noticeably different chemical, structural and hence functional features. Their potential applications span several fields, and in many of the foreseen applications (e.g., in bioimaging and related fields), the achievement of stable colloidal suspensions of metal sulphides is highly desirable or either an unavoidable requirement to be met. To this aim, robust functionalisation strategies should be devised, which however are, with respect to metal or metal oxides colloids, much more challenging. This has to be ascribed, inter alia, also to the still limited knowledge of the sulphides surface chemistry, particularly when comparing it to the better established, though multifaceted, oxide surface chemistry. A ground-breaking endeavour in this field is hence the detailed understanding of the nature of the complex surface chemistry of transition metal sulphides, which ideally requires an integrated experimental and modelling approach. In this review, an overview of the state-of-the-art on the existing examples of functionalisation of transition metal sulphides is provided, also by focusing on selected case studies, exemplifying the manifold nature of this class of binary inorganic compounds

Exploiting double exchange Diels-Alder cycloadditions for immobilization of peptide nucleic acids on gold nanoparticles

The generation of PNA-decorated gold nanoparticles (AuNPs) has revealed to be more difficult as compared to the generation of DNA-functionalized ones. The less polar nature of this artificial nucleic acid system and the associated tendency of the neutral poly-amidic backbone to aspecifically adsorb onto the gold surface rather than forming a covalent bond through gold-thiol interaction, combined with the low solubility of PNAs itself, form the main limiting factors in the functionalization of AuNP. Here, we provide a convenient methodology that allows to easily conjugate PNAs to AuNP. Positively charged PNAs containing a masked furan moiety were immobilized via a double exchange Diels-Alder cycloaddition onto masked maleimide-functionalized AuNPs in a one-pot fashion. Conjugated PNA strands retain their ability to selectively hybridize with target DNA strands. Moreover, the duplexes resulting from hybridization can be detached through a retro-Diels-Alder reaction, thus allowing straightforward catch-and-release of specific nucleic acid targets

Functionalised polyanaline nanofibers

Polyaniline (PAni) is a conducting polymer which switches between distinct states exhibiting dramatically different properties. The colour, conductivity and redox state of PAni all depend on the local chemical environment of the material. Consequently PAni has great potential for sensing applications. The nanostructured form of PAni is particularly interesting as it provides a very large surface-to-volume ratio that can lead to dramatic enhancement of sensor sensitivity and response time. In this work, we focus on derivatising polyaniline nanofibres. Using the technique described, carboxylate terminated side-chains can be covalently bound to solution based fibres