Ronan Daly

Europium-Directed Self-Assembly of a Luminescent Supramolecular Gel from a Tripodal Terpyridine-Based Ligand†

Eu(III), the last piece in the puzzle: Europium-induced self-assembly of ligands having a C(3)-symmetrical benzene-1,3,5-tricarboxamide core results in the formation of luminescent gels. Supramolecular polymers are formed through hydrogen bonding between the ligands. The polymers are then brought together into the gel assembly through the coordination of terpyridine ends by Eu(III) ions (blue dashed arrow: distance between two ligands in the strand direction).

Inkjet printing for pharmaceutics – A review of research and manufacturing

Global regulatory, manufacturing and consumer trends are driving a need for change in current pharmaceutical sector business models, with a specific focus on the inherently expensive research costs, high-risk capital-intensive scale-up and the traditional centralised batch manufacturing paradigm. New technologies, such as inkjet printing, are being explored to radically transform pharmaceutical production processing and the end-to-end supply chain. This review provides a brief summary of inkjet printing technologies and their current applications in manufacturing before examining the business context driving the exploration of inkjet printing in the pharmaceutical sector. We then examine the trends reported in the literature for pharmaceutical printing, followed by the scientific considerations and challenges facing the adoption of this technology. We demonstrate that research activities are highly diverse, targeting a broad range of pharmaceutical types and printing systems. To mitigate this complexity we show that by categorising findings in terms of targeted business models and Active Pharmaceutical Ingredient (API) chemistry we have a more coherent approach to comparing research findings and can drive efficient translation of a chosen drug to inkjet manufacturing.

Chemical Nano-Gardens: Growth of Salt Nanowires from Supramolecular Self-Assembly Gels

In this article, we examine the phenomenon of single-crystal halide salt wire growth at the surface of porous materials. We report the use of a single-step casting technique with a supramolecular self-assembly gel matrix that upon drying leads to the growth of single-crystal halide (e.g., NaCl, KCl, and KI) nanowires with diameters ~130-200 nm. We demonstrate their formation using electron microscopy and electron-dispersive X-ray spectroscopy, showing that the supramolecular gel stabilizes the growth of these wires by facilitating a diffusion-driven base growth mechanism. Critically, we show that standard non-supramolecular gels are unable to facilitate nanowire growth. We further show that these nanowires can be grown by seeding, forming nanocrystal gardens. This study helps understand the possible prefunctionalization of membranes to stimulate ion-specific filters or salt efflorescence suppressors, while also providing a novel route to nanomaterial growth.

Cross-Linking the Fibers of Supramolecular Gels Formed from a Tripodal Terpyridine Derived Ligand with d-Block Metal Ions

The tripodal terpyridine ligand, L, forms 1D helical supramolecular polymers/gels in H2O-CH3OH solution mediated through hydrogen bonding and π-π interactions. These gels further cross-link into 3D supramolecular metallogels with a range of metal ions (M) such as Fe(II), Ni(II), Cu(II), Zn(II), and Ru(III); the cross-linking resulting in the formation of colored or colorless gels. The fibrous morphology of these gels was confirmed using scanning electron microscopy (SEM); while the self-assembly processes between L and M were investigated by absorbance and emission spectroscopy from which their binding constants were determined by using a nonlinear regression analysis.

Applications of Paper-Based Diagnostics

Paper has been used for applications in analytical and bioanalytical devices for more than a century, owing to its low cost due to its ubiquitous nature. Paper, a cellulosic material, presents several attractive attributes that render it useful in the construction of devices including: biodegradability, biocompatibility, worldwide abundance, chemical stability, three-dimensional fibrous structure, inertness to commonly-used reagents, ease of production and modification. Due to these characteristics, paper is one of the most widely researched substrates for the construction of low-cost disposable devices and sensing platforms. This chapter reviews the changing economic landscape, including the demand for low-cost diagnostics and a price comparison with other inexpensive substrates. The properties of paper, manufacturing challenges, labelling chemistries are also discussed along with the historical trends in marketed, paper-based devices.

The dominant role of the solvent–water interface in water droplet templating of polymers

We investigate the formation of microstructured polymer networks known as Breath Figure templated structures created by the presence of water vapour over evaporating polymer solutions. We use a highly controlled experimental approach to examine this dynamic and non-equilibrium process to uniquely compare pure solvent systems with polymer solutions and demonstrate using a combination of optical microscopy, focused ion-beam milling and SEM analysis that the porous polymer microstructure is completely controlled by the interfacial forces that exist between the water droplet and the solvent until a final drying dilation of the imprints. Water droplet contact angles are the same in the presence or absence of polymer and are independent of size for droplets above 5 μm. The polymer acts a spectator that serves to trap water droplets present at the air interface, and to transfer their shape into the polymer film. For the smallest pores, however, there are unexpected variations in the contact angle with pore size that are consistent with a possible contribution from line tension at these smaller dimensions.

Cell Proliferation Tracking Using Graphene Sensor Arrays

The development of a novel label-free graphene sensor array is presented. Detection is based on modification of graphene FET devices and specifically monitoring the change in composition of the nutritive components in culturing medium. Micro-dispensing of Escherichia coli in medium shows feasibility of accurate positioning over each sensor while still allowing cell proliferation. Graphene FET device fabrication, sample dosing, and initial electrical characterisation have been completed and show a promising approach to reducing the sample size and lead time for diagnostic and drug development protocols through a label-free and reusable sensor array fabricated with standard and scalable microfabrication technologies.

Taming Self-Organization Dynamics to Dramatically Control Porous Architectures

We demonstrate templating of functional materials with unexpected and intricate micro- and nanostructures by controlling the condensation, packing, and evaporation of water droplets on a polymer solution. Spontaneous evaporation of a polymer solution induces cooling of the liquid surface and water microdroplet condensation from the ambient vapor. These droplets pack together and act as a template to imprint an entangled polymer film. This breath figure (BF) phenomenon is an example of self-organization that involves the long-range ordering of droplets. Equilibrium-based analysis provides many insights into contact angles and drop stability of individual drops, but the BF phenomenon remains poorly understood thus far, preventing translation to real applications. Here we investigate the dynamics of this phenomenon to separate out the competing influences and then introduce a modulation scheme to ultimately manipulate the water vapor-liquid equilibrium independently from the solvent evaporation. This approach to BF control provides insights into the mechanism, a rationale for microstructure design, and evidence for the benefits of dynamical control of self-organization systems. We finally present dramatically different porous architectures from this approach reminiscent of microscale Petri dishes, conical flasks, and test tubes.

Existence of Micrometer-Scale Water Droplets at Solvent/Air Interfaces

Standard surface energy balances using literature values for pure liquids predict that water droplets are unstable at the liquid/air interfaces of many common organic solvents. While the behavior of macroscopic drops in the presence of solvents has been studied, the study of droplets in the micrometer size regime and the possible role of line tension are notably absent. In this article, we experimentally investigate the existence and stability of such micrometer-scale droplets formed at air/solvent interfaces and the possible roles played by partial solubility of organic liquids in water and solvent migration in the lowering of the key air/water surface tension. Three solvents are studied: toluene, butyl acetate, and chloroform, using a technique to optically monitor both condensation and manual deposition of water microdroplets onto air/solvent surfaces. This demonstrates both the existence of stable water droplets and allows measurement of the contact angles at the solvent/water/air interface. Contact angles are shown to be independent of droplet size (diameters: 2-30 μm), ruling out a line tension stabilization mechanism for droplets of radii greater than 1 μm. The interfacial tensions of the deposited water droplets are independently measured using an equivalent macroscopic experiment, which yield results consistent with the partial miscibility of toluene and butyl acetate in water. A discrepancy is observed for chloroform, for which possible mechanisms are discussed.

Observations of modal interaction in lateral bulk acoustic resonators

High Q factor resonators, such as micro-electro-mechanical systems based lateral bulk acoustic resonators excited in their primary in-plane modes, are promising candidates for timing and frequency reference applications as well as gravimetric bio-sensing. The excitation and detection of out-of-plane modes is often assumed to be unlikely in such devices. However, we report observations of modal interaction with out-of-plane spurious modes that reduces the Q factor of the in-plane modes by up to a factor 3. We also show that the appearance of the spurious modes is unpredictable, and therefore, we propose statistical metrics to minimize the risk of modal interaction.