Exotic Monoliths

This thesis is entitled 'Exotic Monoliths', which has been defined, in the context of this thesis, as monoliths; (1) synthesised by methods not previously described in the literature, (2) synthesised from commonly used silica or organic polymer materials but whose surface has been modified with a novel material such as dyes, nano-particles and biologically active compounds, and (3) synthesised from materials which are not based on silica or organic polymers, such as zirconia or titania. The first two of these definitions have been the main focus for this thesis. The thesis itself comprises five chapters. Chapter 1 presents an introduction to polymer monolith stationary phases and a detailed summary of the many different methods of synthesis. The surface modification of the monoliths and their applications in separation science, along with a short comparison with particle packed columns and introduction to some more novel inorganic monoliths is also presented. Following on from this, Chapter 2 shows the preliminary work carried out on synthesising monoliths in capillary. Presented in this chapter is an investigation of thermally initiated polymerisation in standard 100 μm i.d. capillary and in larger diameter fused silica and PEEK capillary moulds. Photo-initiated polymerisation using both conventional UV lamps and light emitting diodes is also investigated, along with a novel application of LED synthesised monoliths, i.e. using short plugs of monoliths as retaining frits for column packing. Finally a short study of the ability to reproduce literature methods of surface modification by successfully grafting a layer of methacrylic acid and 2-aminoethyl methacrylate on the surface of a monolithic scaffold is shown. Chapter 3 presents the research carried out on the modification of organic polymer monoliths with photochromic dyes and the synthesis of monoliths directly from modified photochromic dyes with a polymerisable double bond. A novel application of these photochromic monoliths is their use as photo-switchable electroosmotic pumps allowing eluent flow to be controlled by light in micro-fluidic devices, which is also presented in this chapter. It is shown that by switching the wavelength of irradiation from visible to ultraviolet an increase or decrease, respectively, in the flow rate can be observed. The final two chapters, 4 and 5, present novel methods of monolith synthesis using light emitting diodes in the visible region. Chapter 4 looks at the polymerisation of methacrylate monomers within polyimide coated moulds using red light while Chapter 5 looks at the polymerisation of styrenic monomers in poly(tetrafluoroethylene) coated capillaries using blue light emitting diode arrays. In both cases the characterisation and application of the synthesised monoliths is presented showing that they are suited to use in separation science. The suitability of this method to polymerise monoliths in chips moulds was also shown, as was the ability of the initiation system activated by red light to be used for the photo-initiated grafting of chromophoric monomers. A final section entitled 'General Conclusions and Outlook' provides a summary of the thesis and areas for further work

Spiropyran modified microfluidic chip channels for photonically controlled sensor array detection of metal ions

Microfluidic chips are particularly attractive for analytical purposes because they provide a convenient small platform for rapid analysis and detection.1 Furthermore, spiropyrans dyes can be used as photonically controlled, self-indicating molecular recognition agents for the fabrication of sensors.2 Here, we show how through integrating the beneficial characteristics of microfluidic devices and spiropyrans dyes, a simple and very innovative chip for on-line metal ion sensor array can be realised. The chip (4x3cm) consists of four independent 180m depth, polydimethylsiloxane (PDMS) channels. 1’-(3-Carboxypropyl)-3,3’-dimethyl-6-nitrospiro-[2H-1]-benzopyran-2,2’-indoline is covalently immobilised on the ozone plasma activated PDMS microchannel surfaces. Upon exposure to UV light, the transparent PDMS channels change to light purple colour because the spiropyran molecules of the surface undergo a heterocyclic ring cleavage that result in the formation of the highly conjugated merocyanine form. When stock solutions of several ion metals (Ca2+,Zn2+,Hg2+,Cu2+) are pumped independently through the four channels, different optical responses were observed for each metal. 1-L.Basabe-Desmonts et al. Anal.Bioanal.Chem.(2008)390:307–315. 2-R.J.Byrne et al. J.Mat.Chem.(2006)16:1332-1337

Spiropyran modified PDMS micro-fluidic chip device for photonically controlled sensor array detection of metal ions

Micro‐fluidic chips are particularly attractive in biological and life sciences for analytical purposes because they provide a convenient small platform for rapid analysis and detection [1]. Using micro‐fluidic devices for the determination of ions emerges as a potential solution to some of the challenges not overtaken by conventional techniques e.g. atomic absorption, inductively‐coupled plasma‐optical emission, mass spectrometry and ion‐selective electrodes [2]. For example, these devices can integrate complex sample handling processes, calibration, and detection steps into a compact, portable system. Moreover they require small sample volumes (low μl or nl), consume little power, and are easily constructed for multi‐analyte detection, either through multiple parallel fluidic architectures or by using arrays of detection elements. Organic photochromic compounds like spiropyrans are particularly interesting targets for the development of new approaches to sensing since they offer new routes to multi‐functional materials that take advantage of their photo‐reversible interconversion between two thermodynamically stable states (a spiropyran (SP) form, and a merocyanine (MC) form), which have dramatically different charge, polarity and molecular conformations. Furthermore, they can be easily incorporated into membranes for improved robustness and ease of handling [3], but from our perspective, most interesting of all, they have metal ion‐binding and molecular recognition properties which are only manifested by the MC form. Based on the coordinationinduced photochromism characteristic of the MC form, spiropyrans have been employed as molecular probes for metal ions and organic molecules [4]. In this abstract, we show how through integrating the beneficial characteristics of micro‐fluidic devices and spiropyrans photoswitches, a simple and very innovative chip configured as an on‐line metal ion sensor array can be realised (Figure 1). The micro‐fluidic device consists of five independent 94 μm depth, 150 μm width channels fabricated in polydimethylsiloxane. The spiropyran 1’‐(3‐carboxypropyl)‐3,3’‐dimethyl‐6‐nitrospiro‐1‐benzopyran‐2,2’‐indoline (SP‐COOH) is immobilised by physical adsorption directly on ozone plasma activated PDMS micro‐channel walls. When the colourless, inactive, spiropyran coating absorbs UV light it switches to the highly coloured merocyanine form (MC‐COOH), which also has an active binding site for certain metal ions. Therefore metal ion uptake can be triggered using UV light and subsequently reversed on demand by shining white light on the coloured complex, which regenerates the inactive spiropyran form, and releases the metal ion. When stock solutions of several metal ions (Ca2+, Zn2+, Hg2+, Cu2+, Co2+) are pumped independently through the five channels, different optical responses were observed for each metal (Figure 2), (i.e. complex formation with metal ions is associated with characteristic shifts in the visible spectrum), and the platform can therefore be regarded as a micro‐structured device for online multi‐component monitoring of metal cations

The use of scanning contactless conductivity detection for the characterisation of stationary phases in micro-fluidic chips

The use of scanning capacitively coupled contactless conductivity detection for the evaluation of the structural homogeneity and density of both packed and monolithic stationary phases in microfluidic chips is presented here for the first time

Simple fluorinated moiety insertion on Aβ 16-23 peptide for stain-free TEM imaging.

Peptide aggregation and fibre formation are one of the major underlying causes of several neurodegenerative disorders such as Alzheimer's disease. During the past decades the characterisation of these fibres has been widely studied in an attempt to further understand the nature of the related diseases and in an effort to develop treatments. Transmission electron microscopy (TEM) is one of the most commonly used techniques to identify these fibres, but requires the use of a radioactive staining agent. The procedure we report overcomes this drawback through simple addition of a fluorinated moiety to a short Amyloid β sequence via solid phase peptide synthesis (SPPS). This method is synthetically straightforward, widely applicable to different aggregation-prone sequences and, above all, allows for stain-free TEM imaging with improved quality compared to standard imaging procedures. The presence of the fluorinated moiety does not cause major changes in the fibre structure or aggregation, but rather serves to dissipate the microscope's electron beam, thus allowing for high contrast and straightforward imaging by TEM.The authors are grateful for funding from the ERC Starting Investigator grant ASPiRe (no. 240629). The authors are also grateful to Dr Marco Di Antonio for assistance with HPLC purification.This is the final published version of the article. It was originally published in Analyst (Sonzini S, Jones ST, Walsh Z, Scherman OA, Analyst, 2015, 140, 2735, doi:10.1039/c4an02278e) http://dx.doi.org/10.1039/c4an02278

Photochromic spiropyran monolithic polymers: Molecular photo-controllable electroosmotic pumps for micro-fluidic devices

A novel photo-controllable micro-fluidic electroosmotic pump based on spiropyran monolithic polymers is presented here for the first time. Photochromic monolithic scaffolds have been synthesised within poly(tetrafluoroethylene) coated fused silica capillaries. These monoliths have a photochromic spiropyran monomer incorporated in the bulk by thermally induced copolymerisation with a cross-linking agent (divinylbenzene) and were encased in micro-fluidic devices to function as photo-controllable electroosmotic pumps (EOPs). Due to the presence of the spiropyran the monolith can exist in two forms: a zwitterionic merocyanine (MC) form and an uncharged spiropyran (SP). As both forms bare a net overall zero charge, an acidic electrolyte was used to produce a stable anodic electroosmotic flow (EOF), while still retaining the ability to switch between the SP and the MC forms, which exhibit different charge distributions. It was confirmed that visible light, which produces the SP form, caused an increase in EOF while UV light, which generates the MC form, caused a decrease in EOF. In this way the EOF from the chip was modified by light and not by changing the electric field, temperature or buffer pH, some of the more common methods of altering the EOF

Applications of novel functional materials: from microfluidics to chemical sensing

Novel functional materials offer unique capabilities hitherto inaccessible using conventional materials. In particular, we focus on photo-controlled guest binding and release, inherent signalling of status, photo-actuation and solvent driven motion of small structures as examples of the fascinating behaviour of these exceptional materials. We have shown that by integrating the beneficial characteristics of PDMS micro-fluidic devices and spiropyrans dyes, a micro-chip configured as an on-line photonically controlled selfindicating system for metal ion accumulation and release can be realised. Moreover, spiropyran functionalised micro-beads were incorporated into micro-fluidic flow systems, such as capillary separation columns. In addition, photochromic monolithic scaffolds were synthesised within polytetrafluoroethylene coated fused silica capillaries and used as stationary phases in micro-chips to function as photo-controllable electro-osmotic pumps. Novel multifunctional materials based on ionogels, consisting of a polymeric structure incorporating spiropyran units and phosphonium based ionic liquids, have been used as light-actuated valve structures in micro-fluidic platforms. Through variation of the composition of the ionogels, the micro-valves can be tuned to open at different times under similar illumination conditions. In parallel, the ionogels were soaked in ethanol and then transferred to water, where they moved spontaneously. This movement is driven by the expulsion of the ethanol from the gel and subsequent ethanol spreading at the air-water interface. We have investigated this solvent driven motion for as a driving force for moving small objects in aqueous media. We have also developed an innovative miniaturised system for continuous measurement of the pH of sample solutions and vapour streams during chemical or biological processes. It consists of a simple barcode sensor with several pH dyes doped in an ionogel matrix which is able to generate a characteristic fingerprint-type colour response within a single “snapshot” for different pH solutions and vapours. As the sensor is based on an ionogel polymer, it has extremely long stability, and the sensor dyes show no measureable leaching into aqueous sample solutions. Finally a wearable, robust, flexible and disposable micro-fluidic device which incorporates micro-Light Emitting Diodes (μ-LEDs) as a detection system, for real time monitoring of the pH of sweat generated during an exercise period has been fabricated and assessed. In our approach, the sensors are immobilised within ECG electrodes, as this allows the pH measurements to be gathered without changing the conventional form of ECG monitoring during exercise. This provides immediate feedback regarding sweat composition to an athlete and coach, which can be used to optimise the hydration and performance of the athlete

Stress dissipation in cucurbit[8]uril ternary complex small molecule adhesives.

The ability to control supramolecular and macroscopic self-assembly and disassembly holds great potential for responsive, reversible adhesives that can efficiently broker stresses accumulated between two surfaces. Here, cucurbit[8]uril is used to directly adhere two functionalized mica substrates creating surface-surface interactions that are held together through photo-reversible CB[8] heteroternary complexes. Comparison of single molecule, bulk and macroscopic adhesion behavior give insight into cooperativity and stress dissipation in dynamic adhesive systems

Photoreversible ion-binding using spiropyran modified silica microbeads

In this paper, we report the covalent immobilisation of spiropyran on silica microbeads of 5 μm diameter and subsequent evaluation of the photoswitchable behaviour and light-modulated ion-binding properties of the spiropyran modified silica microbeads towards a range of different metal ions. The beads can be effectively switched using light emitting diodes between a white spiropyran form (by irradiation with a white 430–760 nm light emitting diode) and a pink merocyanine form (upon irradiation with a UV light 375 nm emitting diodes) that undergoes, under exposure to certain metal ions (such as Cu2+ and Zn2+, final concentration of 7.7 × 10–4 M in ethanol solution), a further reversible spectral and colour change due to the formation of merocyanine-metal ion complexes. Furthermore, the accumulated ions can subsequently released from the beads on demand using light emitting diodes to reform the inactive spiro form. Keywords: photoreversible ion binding