Robert Byrne

Organic electrochemical transistor incorporating an ionogel as a solid state electrolyte for lactate sensing

Room temperature Ionic liquids (RTILs) have evolved as a new type of solvent for biocatalysis, mainly due to their unique and tunable physical properties.[1] In addition, within the family of organic semiconductor-based sensors, organic electrochemical transistors (OECTs) have attracted particular interest.[2] Here, we present a simple and robust biosensor, based on a OECT, capable of measuring lactic acid using a gel-like polymeric materials that endow RTIL (ionogel)[3] as solid-state electrolyte both to immobilise the enzyme and to serve as a supporting electrolyte.[4] This represents the first step towards the achievement of a fast, flexible, miniaturised and cheap way of measuring lactate concentration in sweat.

Photo-regenerable surface with potential for optical sensing

Photochromic spiropyran was covalently immobilized using alkyldiamine couplers with varying chain length (2, 4, 6, 8 methylene groups) onto an optically transparent polymeric surface. The relatively nonpolar and colourless spiropyran form can be reversibly switched to a charged, highly coloured, zwitterionic merocyanine isomer using UV and visible light, respectively. The merocyanine form complexes with metal ions, and this results in a shift in the absorbance spectrum, and a corresponding colour change is observed. Upon irradiation of the complex with visible light, the cation is released and the merocyanine (active) isomer reverts back to the spiropyran (passive) form. Optical switching and complexation behaviour of the polymer-bound spiropyran–merocyanine system is highly dependent on the tether length of the spiropyran from the polymeric surface. The effect is demonstrated using cobalt(II) chloride in solution.

An Electrochromic Ionic Liquid: Design, Characterization, and Performance in a Solid-State Platform

This work describes the synthesis and characteristics of a novel electrochromic ionic liquid (IL) based on a phosphonium core tethered to a viologen moiety. When integrated into a solid-state electrochromic platform, the viologen modified IL behaved as both the electrolyte and the electrochromic material. Platform fabrication was achieved through in situ photo-polymerization and encapsulation of this novel IL within a hybrid sol–gel. Important parameters of the platform performance, including its coloration efficiency, switching kinetics, and optical properties were characterised using UV–vis spectroscopy and cyclic voltammetry in tandem. The electrochromic platform exhibits a coloration efficiency of 10.72 cm2 C–1 and a varied optical output as a function of the incident current. Despite the rather viscous nature of the material, the platform exhibited approximately 2 orders of magnitude faster switching kinetics (221 s to reach 95 % absorbance) when compared to previously reported electrochromic ILs (18 000 s).

Materials science and the sensor revolution

For the past decade, we have been investigating strategies to develop ways to provide chemical sensing platforms capable of long-term deployment in remote locations 1 , 2 , 3 . This key objective has been driven by the emergence of ubiquitous digital communications and the associated potential for widely deployed wireless sensor networks (WSNs). Understandably, in these early days of WSNs, deployments have been based on very reliable sensors, such as thermistors, accelerometers, flow meters, photodetectors, and digital cameras. Biosensors and chemical sensors (bio/chemo-sensors) are largely missing from this rapidly developing field, despite the obvious value offered by an ability to measure molecular targets at multiple locations in real-time. Interestingly, while this paper is focused on the issues with respect to wide area sensing of the environment, the core challenge is essentially the same for long-term implantable bio/chemo-sensors 4 , i.e.; how to maintain the integrity of the analytical method at a remote, inaccessible location?

Investigating Nanostructuring within Imidazolium Ionic Liquids: A Thermodynamic Study Using Photochromic Molecular Probes

Molecular photoswitches have been used to investigate the possibility of nanostructured polar and nonpolar domains in ionic liquids (ILs). Two photochromic compounds, spiropyran (BSP) and spirooxazine (SO) were added to imidazolium based ionic liquids containing the anion [NTf2](-), and their photochromic behavior was monitored with increasing side chain length (C(2)-C(12)) of the imidazolium cation. Increasing side chain length was found to have only minor effects on the rate of thermal relaxation of the merocyanine form of spiropyran (MC(BSP)) and spirooxazine (MC(SO)) to BSP and SO, respectively. BSP was found to be a suitable optical probe, as linear correlations in parameters were observed for this compound. This is believed to be because BSP-IL interactions are based on hydrogen bonding between the MC(BSP) and the ionic liquid cations, compared to MC(SO), which is limited to electrostatic interactions. Hence, the sensitivity of MC(BSP) is enhanced in the charged polar regions of the IL. Increasing the side chain of the cation results in slight increases in MC(BSP) to BSP relaxation activation energy from 96.93 kJ x mol(-1) in [C(4)mIm][NTf(2)] to 105.27 kJ x mol(-1) in [C(12)mIm][NTf(2)]. MC(BSP) to BSP relaxation DeltaS(double dagger) and DeltaH(double dagger) values also increase with increasing side chain length. The ability for spirocyclic compounds to switch between polar and nonpolar forms appears to allow polar and nonpolar regions in ILs to be probed dynamically using a single probe dye. It appears that the value of the ground state equilibrium constant, K(e), is dominated by the nonpolar regions of the IL while the equilibrium constant of activation, K(double dagger), is dominated by the polar regions. A correlation of side chain length to equilibrium constant of activation is believed to be because polar regions are possibly expanding due to increasing influence of nonpolar side chain interactions and compound insertion upon the overall solvent structure. The result of such reordering and dispersion of polar regions reduces solvent-solute interactions which increases the rate of MC(BSP) to BSP relaxation.

Characterisation and analytical potential of a photo-responsive polymeric material based on spiropyran

In this paper we consider the critical issues inhibiting the widespread deployment of bio/chemo-sensors in wireless sensor networks. Primary among these is the problem of performing calibration at remote locations, and the consequent need for integrated fluidic systems for performing tasks like sampling, calibration and detection. Our conclusion is that low-cost, bio/chemo-sensing platforms that provide reliable information over long periods of use will only be realised through the use of microfluidic platforms that are much more biomimetic in nature than technologies employed in current devices. Central to driving down costs will be the development of fluidic platforms with integrated soft polymer actuators that will replace existing pumps and valves. A particularly attractive approach is to employ photo-controlled polymer actuators, wherein the status of the material can be effectively switched using light, as this allows physical separation of the control layer from the fluidic platform layer in a planar system. This, in principle, should greatly simplify manufacturing and therefore drive down costs. In this paper, we describe a polymeric gel and a linear polymer modified with a photochromic moiety and show that it is possible to utilize photochromic molecules for performing sensing and actuating functions.

Photo-patternable hybrid ionogels for electrochromic applications

This work describes the development of photopatternable ionogels based on a hybrid organic/inorganic sol–gel material and both phosphonium (trihexyltetradecylphosphonium dicyanamide [P6,6,6,14][dca], trihexyltetradecylphosphonium bis(trifluoromethanesulfonyl)-amide [P6,6,6,14][NTf2]) and imidazolium (1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate [emIm][FAP]) room temperature ionic liquids (RTILs). Ionogels were prepared via a two step process with the RTIL content varied between 40 and 80 w/w%, and characterised via Raman and Electrochemical Impedance Spectroscopy. 1 and 2 photon polymerisation was performed on the hybrid ionogels using photolithography, resulting in three dimensional structures that were characterised using scanning electron microscopy. Electrochromic ionogels were prepared by addition of ethyl viologen dibromide (EV) to an ionogel containing [emIm][FAP] and hybrid sol–gel material. This composition was photo-polymerised on ITO electrodes by UV irradiation and subsequentially characterised viaUV/Vis spectroelectrochemistry. It was also possible to fabricate a solid state electrochromic device based on EV and switch between the colourless (oxidised) and blue (reduced) forms using a perturbation signal of 1 V.

Designer molecular probes for phosphonium ionic liquids

Investigations into the extent of structuring present in phosphonium based ionic liquids (ILs) have been carried out using photochromic molecular probes. Three spiropyran derivatives containing hydroxyl (BSP-1), carboxylic acid (BSP-2) and aliphatic chain (C(14)H(29)) (BSP-3) functional groups have been analysed in a range of phosphonium based ionic liquids and their subsequent physico-chemical interactions were reported. It is believed that the functional groups locate the probe molecules into specific regions based upon the interaction of the functional groups with particular and defined regions of the ionic liquid. This structuring results in thermodynamic, kinetic and solvatochromic parameters that are not predictable from classical solvent models. BSP-1 and BSP-2 exhibit generally negative entropies of activation ranging from -50 J K(-1) mol(-1) to -90 J K(-1) mol(-1) implying relatively low solvent-solute interactions and possible anion interactions with IL polar functional groups. Higher than expected activation energies of 60 kJ mol(-1) to 100 kJ mol(-1) obtained for polar probes maybe be due to IL functional groups competing with the charged sites of the merocyanine (MC) isomer thus reducing MC stabilisation effects. Differences in thermal relaxation rate constants (2.5 x 10(-3) s(-1) in BSP-1 and 3 x 10(-4) s(-1) in BSP-2 in [P(6,6,6,14)][dbsa]) imply that while the polar probe systems are primarily located in polar/charged regions, each probe experiences slightly differing polar domains. BSP-3 entropies of activation are positive and between 30 J K(-1) mol(-1) to 66 J K(-1) mol(-1). The association of the non-polar functional group is believed to locate the spiropyran moiety in the interfacial polar and non-polar regions. The thermal relaxation of the MC form causes solvent reorientation to accommodate the molecule as it reverts to its closed form. Slow thermal relaxation rate constants were obserevd in contrast to high activation energies (5 x 10(-4) s(-1) and 111.91 kJ mol(-1) respectively, for BSP-3 in [P(6,6,6,14)][dbsa]). This may be due to steric effects arising from proposed nano-cavity formation by the alkyl chains in phosphonium based ILs.

Graphene-doped photo-patternable ionogels: tuning of conductivity and mechanical stability of 3D microstructures

This work reports for the first time the development of enhanced-conductivity, graphene-doped photo-patternable hybrid organic-inorganic ionogels and the effect of the subsequent materials condensation on the conductivity and mechanical stability of three-dimensional microstructures fabricated by multi-photon polymerisation (MPP). Ionogels were based on photocurable silicon/zirconium hybrid sol–gel materials and phosphonium (trihexyltetradecylphosphonium dicyanamide) [P6,6,6,14][DCA] ionic liquid (IL). To optimise the dispersion of graphene within the ionogel matrices, aqueous solutions of graphene were prepared, as opposed to the conventional graphene powder approach, and employed as catalysts of hydrolysis and condensation reactions occurring in the sol–gel process. Ionogels were prepared via a two step process by varying the hydrolysis degree from 25 to 50%, IL content between 0–50 w/w%, and the inorganic modifier (zirconate complex) concentration from 30 to 60 mol.% against the photocurable ormosil and they were characterised via Raman, Electrochemical Impedance Spectroscopy and Transmission Electron Microscopy. MPP was performed on the hybrid ionogels, resulting in three-dimensional microstructures that were characterised using scanning electron microscopy. It is clearly demonstrated that the molecular formulation of the ionogels, including the concentration of graphene and the zirconate network modifier, plays a critical role in the conductivity of the ionogels and influences the resulting mechanical stability of the fabricated three-dimensional microstructures. This work aims to establish for the first time the relationship between the molecular design and condensation of materials in the physico-chemistry and dynamic of ionogels.

On-Body Chemical Sensors for Monitoring Sweat

In this paper, we discuss the challenges of performing on-body chemical analysis of body fluids. Wearable chemosensors are a relatively novel implementation, bringing new challenges to the field of wearable sensor technology and body sensor networks. Integration of chemical sensors into a textile substrate is a challenging task, as a chemical reaction must happen for these devices to generate a signal. Furthermore, they often require mixing samples and reagents, which results in waste generation. Therefore a wearable chemosensor must be capable of controlling the movement of these substances for a reaction to occur before generating a signal that can be measured. In this paper, we present the design and development of platforms to collect and analyse sweat in-situ and provide real-time feedback to the wearer. Two approaches are described, the first a textile based approach developed during the EU BIOTEX project. The second improves on this design through miniaturisation of the device by using a micro-fluidic platform. The performance of the developed systems is presented and the relevance of these wearable lab-on-a-chip devices is discussed for personalised healthcare and sports performance.