Gas sensing using porous materials for automotive applications.

Improvements in the efficiency of combustion within a vehicle can lead to reductions in the emission of harmful pollutants and increased fuel efficiency. Gas sensors have a role to play in this process, since they can provide real time feedback to vehicular fuel and emissions management systems as well as reducing the discrepancy between emissions observed in factory tests and 'real world' scenarios. In this review we survey the current state-of-the-art in using porous materials for sensing the gases relevant to automotive emissions. Two broad classes of porous material - zeolites and metal-organic frameworks (MOFs) - are introduced, and their potential for gas sensing is discussed. The adsorptive, spectroscopic and electronic techniques for sensing gases using porous materials are summarised. Examples of the use of zeolites and MOFs in the sensing of water vapour, oxygen, NOx, carbon monoxide and carbon dioxide, hydrocarbons and volatile organic compounds, ammonia, hydrogen sulfide, sulfur dioxide and hydrogen are then detailed. Both types of porous material (zeolites and MOFs) reveal great promise for the fabrication of sensors for exhaust gases and vapours due to high selectivity and sensitivity. The size and shape selectivity of the zeolite and MOF materials are controlled by variation of pore dimensions, chemical composition (hydrophilicity/hydrophobicity), crystal size and orientation, thus enabling detection and differentiation between different gases and vapours.

Monolayer detection of ion binding at a crown ether-functionalised supramolecular surface via an integrated optical Bragg grating.

There have been significant recent developments in the field of integrated optical Bragg grating sensors for use in the biological domain, where changes in the thickness of a surface layer upon specific binding of biological targets allows quantitative detection. However in the chemical domain less work has been reported. We present here an integrated optical Bragg grating sensor, capable of evanescently detecting small changes in refractive index down to 10(-6) RIU at infrared wavelengths, within a microfluidic system. The high spectral fidelity of the Bragg gratings combined with precise thermal compensation enables direct monitoring of the surface throughout the experiment. This allows the sensor to probe surface changes in situ and in real-time, from preparation through to chemical modification of the surface, so that the progress of dynamic surface-localized interactions can be followed. Here we describe confirmatory studies to validate this approach, including a comparison with the modelled optical system, before assessing the ability to detect binding of Group I cations at a crown ether-functionalised supramolecular surface. Unlike larger biological entities, for these small chemical species, simple additive changes in film-thickness no longer prevail.

3D Printability Assessment of Poly(octamethylene maleate (anhydride) citrate) and Poly(ethylene glycol) Diacrylate Copolymers for Biomedical Applications.

Herein, we present the first example of 3D printing with poly(octamethylene maleate (anhydride) citrate) (POMaC), a bio-adhesive material which has shown particular promise for implantable biomedical devices. The current methods to fabricate such devices made from POMaC are hindered by the imposed constraints of designing complex molds. We demonstrate the feasibility of exploiting additive manufacturing to 3D print structural functional materials consisting of POMaC. We present 3D printing of biomaterial copolymers consisting of mixtures of poly(ethylene glycol) diacrylate (PEGDA) and POMaC at different ratios. The required parameters were optimized, and characterization of the printing fidelity and physical properties was performed. We have also demonstrated that a range of mechanical properties can be achieved by tuning the POMaC/PEGDA ratio. The biocompatibility of the copolymers was ascertained via a cell viability assay. Such tunable 3D printed biomaterials consisting of POMaC and PEGDA will have significant potential application in the development of functional biomaterial tissue scaffolds and biomedical devices for the future of personalized medicine.

Decoupling manufacturing from application in additive manufactured antimicrobial materials.

3D printable materials based on polymeric ionic liquids (PILs) capable of controlling the synthesis and stabilisation of silver nanoparticles (AgNPs) and their synergistic antimicrobial activity are reported. The interaction of the ionic liquid moieties with the silver precursor enabled the controlled in situ formation and stabilisation of AgNPs via extended UV photoreduction after the printing process, thus demonstrating an effective decoupling of the device manufacturing from the on-demand generation of nanomaterials, which avoids the potential aging of the nanomaterials through oxidation. The printed devices showed a multi-functional and tuneable microbicidal activity against Gram positive (B. subtilis) and Gram negative (E. coli) bacteria and against the mould Aspergillus niger. While the polymeric material alone was found to be bacteriostatic, the AgNPs conferred bactericidal properties to the material. Combining PIL-based materials with functionalities, such as in situ and photoactivated on-demand fabricated antimicrobial AgNPs, provides a synergistic functionality that could be harnessed for a variety of applications, especially when coupled to the freedom of design inherent to additive manufacturing techniques.

Induced neural stem cell differentiation on a drawn fiber scaffold-toward peripheral nerve regeneration.

To achieve regeneration of long sections of damaged nerves, restoration methods such as direct suturing or autologous grafting can be inefficient. Solutions involving biohybrid implants, where neural stem cells are grown in vitro on an active support before implantation, have attracted attention. Using such an approach, combined with recent advancements in microfabrication technology, the chemical and physical environment of cells can be tailored in order to control their behaviors. Herein, a neural stem cell polycarbonate fiber scaffold, fabricated by 3D printing and thermal drawing, is presented. The combined effect of surface microstructure and chemical functionalization using poly-L-ornithine (PLO) and double-walled carbon nanotubes (DWCNTs) on the biocompatibility of the scaffold, induced differentiation of the neural stem cells (NSCs) and channeling of the neural cells was investigated. Upon treatment of the fiber scaffold with a suspension of DWCNTs in PLO (0.039 g l-1) and without recombinants a high degree of differentiation of NSCs into neuronal cells was confirmed by using nestin, galactocerebroside and doublecortin immunoassays. These findings illuminate the potential use of this biohybrid approach for the realization of future nerve regenerative implants.

Shining a light on the photo-sensitisation of organic-inorganic hybrid polyoxometalates.

Finding new ways of using visible light (or, more specifically, solar irradiation) to drive commercially significant and/or challenging chemical processes is an ongoing research goal. Polyoxometalates (POMs) are discrete, metal-oxide clusters which are cheap, robust and easily synthesised but can also act as versatile molecular building blocks, allowing for astonishing variety in their structures and properties. In particular, the rich redox chemistry and inherent photo-activity of POMs makes them attractive for use in a variety of photochemical applications, however POMs characteristically only absorb strongly in the UV region. In this perspective, we discuss the various strategies which have been employed in order to sensitise POMs to visible light, with a particular focus on hybrid inorganic-organic POM species. We will discuss the two clear photo-activation mechanisms which have been developed to date and provide an outlook on some of the possible future directions of the field.

3D-Printable Photochromic Molecular Materials for Reversible Information Storage.

The formulation of advanced molecular materials with bespoke polymeric ionic-liquid matrices that stabilize and solubilize hybrid organic-inorganic polyoxometalates and allow their processing by additive manufacturing, is effectively demonstrated. The unique photo and redox properties of nanostructured polyoxometalates are translated across the scales (from molecular design to functional materials) to yield macroscopic functional devices with reversible photochromism. These properties open a range of potential applications including reversible information storage based on controlled topological and temporal reduction/oxidation of pre-formed printed devices. This approach pushes the boundaries of 3D printing to the molecular limits, allowing the freedom of design enabled by 3D printing to be coupled with the molecular tuneability of polymerizable ionic liquids and the photoactivity and orbital engineering possible with hybrid polyoxometalates.

Surface-based molecular self-assembly: Langmuir-Blodgett films of amphiphilic Ln(III) complexes.

The unique photophysical properties of the Ln(III) series has led to significant research efforts being directed towards their application in sensors. However, for "real-life" applications, these sensors should ideally be immobilised onto surfaces without loss of function. The Langmuir-Blodgett (LB) technique offers a promising method in which to achieve such immobilisation. This mini-review focuses on synthetic strategies for film formation, the effect that film formation has on the physical properties of the Ln(III) amphiphile, and concludes with examples of Ln(III) LB films being used as sensors.

An investigation into dispersion upon switching between solvents within a microfluidic system using a chemically resistant integrated optical refractive index sensor.

A planar Bragg grating device has been developed that is capable of detecting changes in the refractive index of a wide range of fluids including solvents, acids and bases. The integration of this high precision refractive index sensor within a chemically resistant microfluidic flow system has enabled the investigation of diverse fluid interactions. By cycling between different solvents, both miscible and immiscible, within the microfluidic system it is shown that the previous solvent determines the nature of the refractive index profile across the transition in composition. This solvent dispersion effect is investigated with particular attention to the methanol-water transition, where transients in refractive index are observed that are an order of magnitude larger in amplitude than the difference between the bulk fluids. The potential complications of such phenomenon are discussed together with an example of a device that exploits this effect for the unambiguous composition measurement of a binary solvent system.