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

Structural integrity of a wind loaded cylindrical steel shell structure

The structural integrity and life assessment can be considered as a mandatory request in the civil engineering designing and manufacturing process. The paper is presenting the procedure for determination of crack acceptability based on fracture toughness with failure assessment methods (FAD-1 and FAD-2) which is applied to a cylindrical steel shell structure with welded joints which is having the wind as a main load. The assessment is using BS7910/2013. Thus were assessed common types of flaws met at steel shell cylindrical structure elements using failure assessment diagrams - level 1 - FAD-1. The results are presenting the acceptability level for each type of flaw with comparative graphs, determining also the critical dimension of the flaw. For each flaw was calculated the failure assessment diagram (FAD-2). Different comparisons between group of flaws were done, revealing the critical crack like flaw. Also the critical value of flaw dimensions were calculated for each flaw type. The methodology establishes clear rules for assessment of structural elements with cracks, determining the initial flaws, assessed flaws and critical values of the cracks. Based on the detailed procedures described in the paper, on conclusions to the assessment done on each type of flaw, the assessment methods can be applied very easy in current design practice with different material characteristic

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

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

Ion-selective electrodes in real-life applications: can we reduce or even eliminate the need for calibration?

The recent success in lowering of the low detection limit of ion-selective electrodes (ISEs) has opened up new application areas (most notably environmental analysis). The new possibilities have intensified issues that weren’t critical in other application fields. In particular, the potential of ISEs to be integrated as detector systems in autonomous, deployable devices for environmental analysis have opened the question of the measure of uncertainty in prediction of unknown concentration based on calibration as well as the necessity of reduction or even elimination of calibration itself. Here we point out the need for the maximal efficiency of using obtained results based on utilization of solid-contact ISEs for heavy metal analysis in soil. We advocate altering the current definition of detection limit and using signal-to-noise ratio as suggested earlier by Bakker and Pretsch.[1] We also suggest new method for jointly estimating the calibration curve and the unknown concentrations using all the data. This method is in statistical analysis called Bayesian analysis. It allows more accurate prediction of unknown concentration, especially near and even below the detection limit. Furthermore, it allows using of multiple sensors (without disregarding poor performing sensors) which will allow further tightening of the prediction intervals. Finally, we will present initial work on developing “calibrationless” chemical sensors where we use ISEs as model system. We are developing tests that will enable us to understand whether the surface or the bulk of the membrane has been altered (i.e. due to biofouling or poisoning of the electrode surface) thus avoiding the need to re-calibrate the sensors. [1] Bakker E. Pretsch E; Trends Anal. Chem.; 2005, 24, (3), 19

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

Schizophrenic molecules and materials with multiple personalities - how materials science could revolutionise how we do chemical sensing

Molecular photoswitches like spiropyrans derivatives offer exciting possibilities for the development of analytical platforms incorporating photo-responsive materials for functions such as light-activated guest uptake and release and optical reporting on status (passive form, free active form, guest bound to active form). In particular, these switchable materials hold tremendous promise for microflow-systems, in view of the fact that their behaviour can be controlled and interrogated remotely using light from LEDs, without the need for direct physical contact. We demonstrate the immobilisation of these materials on microbeads which can be incorporated into a microflow system to facilitate photoswitchable guest uptake and release. We also introduce novel hybrid materials based on spiropyrans derivatives grafted onto a polymer backbone which, in the presence of an ionic liquid, produces a gel-like material capable of significant photoactuation behaviour. We demonstrate how this material can be incorporated into microfluidic platforms to produce valve-like structures capable of controlling liquid movement using light

Miniature, all-solid-state ion-selective sensor as a detector in autonomous, deployable sensing device

Lowering of the detection limit of ion-selective electrodes (ISEs) as well as their simple construction, low production cost and low power requirements make ISEs an ideal candidate for detector systems that can be integrated into autonomous, deployable sensing devices. Routine analysis and early warning systems are applications that first spring to mind, however great added value can be obtained by integration of many such devices into a wireless sensing network. In this work we describe our work towards the miniaturization of ISEs and their integration of with all-solid-state reference electrode into an all-solid-state sensor with a view of integration in autonomous, deployable sensing device. This work has two avenues: 1) development of a platform that can house all-solid-state ISEs and reference electrodes and 2) development of electronic circuitry for data acquisition and wireless transmission of the data. The latter utilizes novel, in-house made motes (a node in a wireless sensor network that is capable of performing some processing, gathering sensory information and communicating with other connected nodes in the network) that operate at lower frequency and therefore consume lower power then other, commercially available ones. In addition, they are easier to program which bridges the gap of communication between chemists and computer scientists. Intensification of the work in producing all-solid-state reference electrodes has enabled us to work on development of a platform that houses all-solid-state ISEs and reference electrode. We will here describe our progress in this avenue of our research

Integration of miniature, ultrasensitive chemical sensors in microfluidic devices

Simple construction, good detection limit1, very low power demand, and simple experimental setup coupled with miniaturization opportunities arising from solid-state format makes ISEs an excellent prospect for integration in autonomous sensing devices and ultimately their integration in large wireless chemo-sensing networks.2,3 Microfluidics, also known as “lab-on-a-chip” is an emerging technology that is changing the future of instrument design. Microfluidics enables small scale fluid control and analysis, allowing developing smaller, more cost-effective, and more powerful systems.4,5,6 We are working on development of miniature devices featuring sensitive yet simple sensors that could enable rapid access to important environmental information from in-situ deployed sensors, and thereby facilitate timely action to minimize the adverse impact of emerging incidents. Our work involves integration of ultra-sensitive yet simple chemical sensors into a microfluidic device that has integrated wireless communications capabilities. Our ultimate objective is to develop a microfluidic chip that will incorporate polymer-based lead-selective solid-state electrodes. We will test the series of developed chips for the best design to accommodate these sensors. Initially, we are targeting lead-selective sensors and their application to the monitoring of drinking and natural water quality. Our ultimate vision is the development of a microfluidic-based platform with fully integrated screen-printed solid-state ISEs, and the associated reference electrode, which will be suitable for use as a chemo-sensing component in a widely distributed wireless sensor network (WSN) for monitoring the quality of a fresh water system. A key challenge in the realization of this vision is to build in advanced system diagnostics, and particular, sensor status tests using simple electronic signals, in a manner similar to those used in physical transducers.7 In this way, it may be possible to assist in distinguishing sensor malfunction or signal artifacts from real events, even in relatively simple, low cost platforms

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