Dye-free, simultaneous and multianalyte optical recognition using ionic liquid-based polymeric membrane

The vast majority of chemical sensors are based on a ligand that selectively bind ion of interest. The ligand is typically incorporated within a polymer matrix. In addition to ligand, polymer membrane-based chemical sensors normally require an ion-exchanger and if detection is performed using optical spectroscopy, an additional dye. Such membrane can therefore contain up to five components (polymer, plasticizer, ligand, ion-exchanger and dye). In today’s trend of drastic miniaturization, cross-contamination of sensors and leaching of active components becomes serious issue and there are many examples of the works trying to reduce/stop the leaching. In this work we explore the potential for utilization of more universal components that can take several roles thereby reducing the actual number of active components while retaining the functionality. An interesting consequence of such approach is their generalization hence introduction of the capability for simultaneous multianalyte detection – a concept departing from traditional view of chemical sensors: "one sensor for one ion". In our work we use ionic liquids – a remarkable class of compounds that have so far find application in many application areas. We demonstrate their universality by showing that they can behave as ligands, ion-exchangers and plasticizers, all in the same time. This allows significant simplification of chemical sensors. Moreover, we demonstrate that a system containing only polymer (PVC) and ionic liquid (behaving as ligand, ion exchanger and plasticizer) is capable of simultaneous recognition of two ions in the same time. Due to the relative ease of ionic liquid synthesis, we envision design of ionic liquids whose functionality can approach today’s best ionophore-based sensors

Stimuli responsive polymer gels for sensing applications

This chapter (3) is based on simplifying the design template of an optical sensor through the multifunctionality imparted on it by an IL. The IL simplified polymer gel is termed an optode within this chapter as (a) it is prepared the same manner as optodes, (b) the IL performs many of the same functions as previous materials used in optode design and (c) the analyte or ion movement between the aqueous and organic phases follows the same convention for optodes. The 2-component optode membrane is capable of generating three distinct colours in the presence of Cu2+ and Co2+ ions. It has been found that the IL [P6,6,6,14][DCA] can act as plasticizer, ligand and transducer dye when used in PVC membranes, which significantly simplifies the optode membrane cocktail. Upon exposure to an aqueous Cu2+ solution, a yellow colour is generated within the membrane, while exposure to aqueous Co2+ solution generates a blue colour. Exposure to a solution containing both ions produces a green colour. Vibrational spectroscopy has been used to investigate the molecular basis of the ILmetal ion binding mechanism. Analytical characteristics of the membranes including the effect of interfering ions, binding constants and the limit of detection for both ions have been estimated. A case of simultaneous dual-analyte recognition is presented based on two distinct absorption maxima. The inherent conducting properties of the IL membranes are then investigated as a possible detection channel using WRF. WRF is a novel detection technique, which monitors the conductivity of a given sample wirelessly, allowing non-contact detection and measurement of IL-PVC membranes. The various co-ordinated membranes produce a discriminatory drop in the resulting signal, which is a direct function of the specific metal ion (Cu2+, Co2+ or a mixture) co-ordinated to the IL. The results of the novel WRF technique have been validated principally by EIS; whilst XRF is used to elucidate both WRF and EIS trends. The focus of this chapter (4) is built upon the ideology explored in chapter 3, which is to use an IL as an agent that performs multiple roles within a device. However in this case a synthetic route is employed that yields an IL as a key component in an electrochromic device. A device based on two individual components is achieved through the synthesis of an electrochromic IL that also acts as the supporting electrolyte between two electrodes. This work therefore describes the synthesis and characteristics of a novel electrochromic IL based on a phosphonium core tethered to a viologen moiety. When integrated into a solid-state electrochromic device, the viologen modified IL behaved as both the electrolyte and the electrochromic material. Device fabrication was achieved through in situ photo-polymerisation and encapsulation of this novel IL within a hybrid sol-gel. Important parameters of the device performance, including its coloration efficiency, switching kinetics and optical properties were characterised using UV/Vis spectroscopy. Despite the rather viscous nature of the material, the device exhibited approximately two orders of magnitude faster switching kinetics (221 seconds to reach 95 % absorbance) when compared to previously reported electrochromic ILs (18,000 seconds). This chapter describes the synthesis and characterisation of hybrid sol-gel materials co-polymerised with a monomer based on the light responsive chromophore Spiropyran (SP). The hybrid materials contain a silane centre chemically tethered to an acrylate monomer via a propyl linker which are co-polymerised with a varying metal propoxide/methacrylate complex. These hybrid materials are of the optimum mechanical stability for patterning under incident light. This chapter (5) therefore provides the reader with an in-depth discussion of the chemistries required for sol-gel preparation and the area of photopatterning of sub-micron 3 D structures.This chapter describes the synthesis and characterisation of hybrid sol-gel materials co-polymerised with a monomer based on the light responsive chromophore Spiropyran (SP). The hybrid materials contain a silane centre chemically tethered to an acrylate monomer via a propyl linker which are co-polymerised with a varying metal propoxide/methacrylate complex. These hybrid materials are of the optimum mechanical stability for patterning under incident light. This chapter therefore provides the reader with an in-depth discussion of the chemistries required for sol-gel preparation and the area of photopatterning of sub-micron 3 D structures. This chapter (6) is focused on the photopatterning of electro-active hybrid sol-gels that are based on the chemical composition (MAPTMS,ZrPO,MAAH) as introduced in chapter 4. For these studies however, the hybrid materials are based solely on Zr metallate complexes. The electroactive species that become encapsulated within the polymer matrix are both phosphonium and imidazolium based IL’s, dispersed graphene sheets and the electrochromic dye EV

Self-indicating, simultaneous multianalyte recognition using an ionic liquid

Ionic Liquids (ILs) are the subject of increased diverse research worldwide due to many attractive inherent characteristics such as high thermal stability, negligible vapour pressure and physical and chemical diversity due to the many permutations possible1. We have studied the IL [P6,6,6,14][DCA] as a self-indicating, simultaneous, multianalyte recognition system for heavy metal ions such as Cu2+ and Co2+. When incorporated into a polymer membrane, this system maintains all these attractive features with the added bonus of the IL now being self-plasticizing. The optical response is obtained via co-ordination of the heavy metal to the anion [DCA]-.2 A system like this can be viewed as a building block for future chemical sensing platforms; where the system itself is responsive toward an analyte, thereby eliminating the need for a reactive chromophore. The resulting system can also be viewed as an optode containing only two components (polymer and plasticizer) as opposed to a classical 5-component optode (polymer, plasticizer, ionophore, ion-exchanger, dye). This simplification of components shows potential for further studies in electrochemical-based sensors (ISE’s). Our aim will be to present the results obtained thus far from both optical and structural characterization studies. 1. Wilkes, J. S., Green Chemistry, 2002, 4, (2), 73-80. 2. Vangdal, B.; Carranza, J.; Lloret, F.; Julve, M.; Sletten, J., Journal of the Chemical Society-Dalton Transactions 2002, (4), 566-574

A two-component polymeric optode membrane based on a multifunctional ionic liquid

This work details the use of a 2-component optode membrane which is capable of generating three distinct colours in the presence of Cu2+ and Co2+ ions. It has been found that the ionic liquid (IL) trihexyltetradecylphosphonium dicyanamide [P6,6,6,14][DCA] can act as plasticizer, ligand and transducer dye when used in poly(vinylchloride) (PVC) membranes, which significantly simplifies the optode membrane platform. Upon exposure to an aqueous Cu2+ solution, a yellow colour is generated within the membrane, while exposure to aqueous Co2+ solution generates a blue colour. Exposure to a solution containing both ions produces a green colour. Vibrational spectroscopy has been used to investigate molecular basis of the IL-metal binding mechanism. Analytical characteristics of the membranes including the effect of interfering ions, binding constants and the limit of detection for both ions have been estimated. Finally the case of simultaneous dual-analyte recognition is presented based on two distinct absorption maxima

Ionic liquids - inherent sensing and transduction of metal ion complexation

Ionic Liquids (IL’s) - being organic salts that are liquid at room temperature, display inherent ionic conductivity and a wide electrochemical window. This has led to their inevitable incorporation into electrochemical sensing techniques1. Radio Frequency (RF) detection provides a technique which can monitor conductivity wirelessly, but also has the required sensitivity and is non-invasive on the sample. We have used the IL trihexyltetradecylphosphonium dicyanamide[P6,6,6,14][DCA] which can easily be incorporated and solidified into a polymeric membrane. The resulting clear, homogenous membrane shows an optical response upon co-ordination to the metal ions Cu2+(yellow)and Co2+ (blue), and both ions simultaneously (green). RF can not only discriminate between the coordinated and noncoordinated membranes, but also between the individual co-ordinated membranes. The resultant downward trend in conductivity has been validated by Electrochemical Impedance Spectroscopy (EIS) and by X-Ray Flourescence (XRF). XRF shows that the results obtained from RF and EIS are directly related to the binding selectivity of the ligand [DCA]-. IL’s can bind to a variety of heavy metal ions and other important target analytes such as CO2.2 If a drop in conductivity can be presumed upon binding to an analyte, then the inherent conductivity properties of IL’s could be exploited in future electrochemical sensing. 1 . D. Wei., Anal. Chim. Acta. 2008, 607, 126-135 2 . E. Bates., J. Am. Chem. Soc,200

Mesospheric winds measured by MF radar with full correlation analysis: error properties and impacts on studies of wind variance

The mesosphere is one of the most difficult parts of the atmosphere to sample; it is too high for balloon measurements and too low for in situ satellites. Consequently, there is a reliance on remote sensing (either from the ground or from space) to diagnose this region. Ground-based radars have been used since the second half of the 20th century to probe the dynamics of the mesosphere; medium-frequency (MF) radars provide estimates of the horizontal wind fields and are still used to analyse tidal structures and planetary waves that modulate the meridional and zonal winds. The variance of the winds has traditionally been linked qualitatively to the occurrence of gravity waves. In this paper, the method of wind retrieval (full correlation analysis) employed by MF radars is considered with reference to two systems in Antarctica at different latitude (Halley at 76∘ S and Rothera at 67∘ S). It is shown that the width of the velocity distribution and occurrence of “outliers” is related to the measured levels of anisotropy in the received signal pattern. The magnitude of the error distribution, as represented by the wind variance, varies with both insolation levels and geomagnetic activity. Thus, it is demonstrated that for these two radars the influence of gravity waves may not be the primary mechanism that controls the overall variance

Combined EISCAT radar and optical multispectral and tomographic observations of black aurora

Black auroras are recognized as spatially well-defined regions within a uniform diffuse auroral background where the optical emission is significantly reduced. Black auroras typically appear post-magnetic midnight and during the substorm recovery phase, but not exclusively so. We report on the first combined multimonochromatic optical imaging, bistatic white-light TV recordings and incoherent scatter radar observations of black aurora by EISCAT of the phenomenon. From the relatively larger reduction in luminosity at 4278 Å than at 8446 Å we show that nonsheared black auroras are most probably not caused by downward directed electrical fields at low altitude. From the observations, we determine this by relating the height and intensity of the black aurora to precipitating particle energy within the surrounding background diffuse aurora. The observations are more consistent with an energy selective loss cone. Hence the mechanism causing black aurora is most probably active in the magnetosphere rather than close to Earth

Light-modulated ion binding: towards calibrationless sensors

Emerging technologies create new application fields but few of them require that we completely rethink our approach in preparation and characterization of sensors. The vision of internet scale wireless sensor networks (WSNs) requires the deployment of enormous numbers of sensors. This necessarily means that the cost of each sensor must be brought down significantly if this vision is to be realized. An ideal solution for this problem would be a sensor that does not interact with its environment in any way until there is a need for measurement. Upon the measurement, the sensor’s surface is completely regenerated and returned into the state as before the measurement. This step is critical as it ensures that the measurement did not any effect on the sensor hence no calibration is necessary. In our work, we use compounds that indeed can be switched between the active and passive state using light. Most commonly used compounds are so called spiropyrans (SP) and spirooxazines (SO). Here we show the recent advance in preparation of reversible, light-modulated sensors using surface immobilised SP/SO derivatives. A further attractive property of these materials is that they are inherently self-indicating through striking colour changes that enable the state to be easily determined (active vs. passive), and the presence of a bound guest to be detected. These spectral changes enable a range of self-diagnostic tests to be incorporated that enable binding events to be controlled at the surface interface, and for real binding events to be distinguished from artefacts arsing from changes in light intensity, or photobleaching of the active component. We have identified most notable problems for utilization of these compounds in “calibrationless” sensors such as relatively weak binding constants, photodegradation, and unfavourable kinetics of switching between the active and passive state and we demonstrate our approach in solving these problems