1,721,574 research outputs found
Design and development of a novel electronic sensor for detecting mastitis based on conductance
Full text linkMastitis, inflammation of the mammary glands of dairy cows, remains one of the costliest diseases in cattle and its early detection remains a major goal of the dairy industry. It has been established that mastitis causes changes in the conductivity of milk, by damaging the mammary membrane leading to alteration of the balance of sodium, potassium and chloride ions. Previous studies have demonstrated that these changes in milk conductivity can be used as a direct indicator o f the presence and degree of mastitis infection but currently available commercial devices do not appear to be sensitive enough to detect mastitis accurately on-line.
The objective of this project is to design a novel electrochemical sensor to diagnose mastitis on-line in milking systems for cow herds. The study includes some preliminary experiments to assess the feasibility of developing such a sensor, the fabrication of the sensing system including the probe, the instrumentation and related software and the investigation of integrating the system into milking equipment.
A number of primary experiments were carried out in order to investigate what parameters can be used to develop the sensor based on conductivity or impedance measurement. Milk properties such as dielectric properties, conductivity and oxidation behaviour have been investigated using various electrochemical techniques. Cyclic voltammetry was used to characterise the milk initially, electrochemical impedance spectroscopy was carried out to establish the specific electrical properties of milk and basic conductivity measurements were done to calculate the overall conductivity of milk. These methods were cross-referenced against Somatic Cell Count (SCC) measurements which were determined using a bench top instrument in Teagasc National Centre Research laboratories.
Electrochemical impedance measurements showed that measurements should be taken above an operating threshold frequency to avoid polarisation effects and to improve the sensitivity o f the conductivity sensor. Above this frequency, a good correlation between Somatic Cell Count (SCC) and impedance in milk has been found
Calixarenes: molecular modelling of and potentiometric studies on cation complexes
Full text linkChapter 1: The three-dimensional nature of calixarenes and their applications in sensors are reviewed.
Chapter 2: Molecular mechanics was used to model the geometry of a sodium calixarene complex formed with a 1,3-alternate conformation. Partial charges were assigned to the calixarene ligands by a variety of methods. These included various semi-empirical methods (AMI, PM3 and MNDO) arbitrarily assigning formal charges to the ions and carrying out semi-empirical calculations on the full ligand:complex. An investigation into the effect of placing the cation in different starting positions was undertaken in the case of this complex also. The effect of using ligand partial charges calculated with the PM3 and MNDO semi-empirical methods is commented upon.
Chapters 3 and 4: A series of calixarene phosphine oxides were used to construct
ion-selective electrodes, (i.e., potentiometric sensors) and were found to be selective for calcium in the presence of a range of Group 1 and Group 2 interfering ions. Estimations of the characteristics of these electrodes (the cell constant, the Nemstian Slope Factor and potentiometric selectivity coefficients) were obtained by simple but rigorous procedure, developed for a potassium-selective valinomycin ionselective electrode. The procedure involved fitting the experimental data to a mathematical model by non-linear analysis. In this method, the interfering ion concentration is kept constant and the primary ion concentration is varied by means of a series of small volume ‘spikes’, added to a single solution, with the electrodes continually in contact, and measuring the cell potential after each addition.
Monte Carlo conformational searches with molecular mechanics geometry optimisation gave very clear and positive explanations for the selectivity several calixarenes for several Group 1 and Group 2 ion, while NMR spectroscopic studies supported the conclusions drawn from the modelling studies about changes in conformation upon complexation with metal ions
Development of novel gas sensors
Full text linkOf all human senses our ability to detect odours may be the least appreciated and certainly the least understood [1], and yet is one o f the most powerful. Humans can only see a narrow region o f the light spectrum (300-700 ran), hear a small range in the frequency spectrum (20-20KHz), touch objects that are close. The smell and taste o f substances however can give us much more information about an objects nature. However quantifying these senses is difficult. The taste o f substances has been provisionally classed as being Sour, Bitter, Sweet or Salty. Smells have been classed as being camphoraceous, ethereal, floral, minty, musky, pungent or putrid [2], but this has been described as being over simplistic [3], Therefore to mimic the nose it is necessary to understand how the nose function
Smaller, smarter, faster: the development and application of microfluidic devices to the determination of phosphorus in natural waters
Full text linkThe development of a miniaturised microfluidic instrument for monitoring phosphorus in natural waters from the optimisation of the chemistry through to the fabrication of the microfluidic manifold in polymeric materials is presented. The research initially was concerned with optimising the yellow colorimetric method for a phosphate determination and its transferral to a Si-etched microfluidic chip configuration. Th is simple method employs one reagent mixed in a 1:1 ratio with an orthophosphate-containing sample to produce a yellow colour absorbing strongly below 400nm.
A stopped flow approach is used which, together with the very rapid kinetics and simple reagent stream, enables a very uncomplicated microfluidic manifold design to be adopted. The working wavelength wa s 380nm, which coincided with the peak output of a recently developed U V -L E D narrow bandwidth light source. The limit of detection for the yellow method is 0.2 mgL'1 P O ^ - P with a linear range from 0 - 5 0 mgL*1 P O 43“ - P possible. T h e reaction time at room temperature is less than 3 minutes, which m ean s up to 20 sam ple s / hour can be analysed.
The next stage in the research involved applying the results obtained in the Sietched microfluidic chips to the design and fabrication of a microfluidic manifold in polymer materials. Chips were made by a combination of microfabrication techniques including a C 0 2 laser ablation, hot embossing and micromilling. Transferring the technology to a polymeric platform required a whole new set of experiments to be undertaken. The key is su e s add ressed were multiple layer alignment, optical detection, bonding of polymeric materials; the provision of leakfree fluidic interconnects to external tubing and reproducible analytical measurements
Novel potentiometric sensors based on calixarenes
Full text linkThis thesis represents a study of the performance of potentiometnc ion sensors incorporating modified calixarene compounds as the lonophores. Three different groups of modified calixarenes were studied, namely tetramenc, hexamenc and oxa calixarenes and formed the basis of Na+, Cs+ and K+ sensors respectively.
Tetramenc calix[4]arenes containing ketone functionalities methyl ketone (If), tbutyl ketone (Ig) and adamantyl ketone (Ih) and ester functionalities methyl ester (Ic), ethyl ester (Id) and «-butyl ester (Ie) were incorporated into mini electrode and macro electrode sensors with a conventional liquid filling solution. A further two denvatives containing the monoacid tnmethylester (Ij) and the monoacid tnethylester (Ik) were also assessed for their lonophonc potential and compared to their tetra methylester and tetra ethylester counterparts. All of the ester compounds and the methyl ketone denvative were found to exhibit excellent selectivities for sodium ions over the alkali and alkaline earth metals. An effort was made throughout the research to identify the functionalities in these new class of complexing ligands which are most likely to induce and enhance selective lonbinding.
The caesium selective electrodes were based on hexamenc calix[6]arenes ligands (Ila) and (lib). Both ligands contained an ethylester moiety in the substituted lower nm position with an unsubstituted (Ha) and p-t-butyl substituted (lib) para position.
The potassium selective electrodes are based on some monooxa and dioxa calix[4]arenes and on the ethylester p-f-butyl calix[5]arene. The oxa calixarenes contain an additional methoxy spacer unit in the macrocyclic nng and hence have cavity sizes intermediate between that of the tetramenc and hexamenc structures. The electrodes based on these ligands showed varying degrees of selectivity and stability but are unlikely to provide viable individual ion sensors for potassium.
The final section of the thesis is devoted to solid state sensors. Electrodes were constructed by contacting the PVC liquid membrane either directly onto a platinum substrate or indirectly where the contact between the PVC and the platinum was provided by a layer of conducting polymer polypyrrole (PPy). The calix[4]arene involved was the tetramenc ethylester denvative (Id). Good functioning electrodes were produced and the PPy layer was found to enhance the stability of the contact
Analytical applications of sensor arrays and virtual instrumentation
Full text linkAn ammonium detection system using Ion-Selective Electrodes (ISEs) in Flow-Injection Analysis (FIA) is described. Because of the low selectivity of the nonactin ammonium selective electrode towards some common ions, different selectivity enhancement techniques have been examined. A Sensor Array Detector (SAD) which comprises ISEs selective for ammonium, sodium, potassium and calcium was used. A modified form of the Nikolskii-Eisenman Equation is proposed in which the charge power function of the interfering ion activity is linearised. Selectivity is quantified for the PVC membrane electrodes (NH4+, Na , K \ Ca ') in terms of constants rather than conventional coefficients. These constants and other electrode parameters such as cell constant and slope are estimated by means of the FIA-SAD approach.
The SAD response was modeled via the Nikolskii-Eisenman equation with SIMPLEX regression model The applicability of the resulting values for these parameters is demonstrated through the determination of unknowns by direct solution of the system of modified Nikolskii-Eisenman equations describing the array response. The results show that the use of an array of ISEs under FIA regimes for the detection of ammonium in the concentration range 10 '4 to 10 '2 mol dm'3 gives a much higher improvement in the determination of ammonium in aqueous samples than the use of a single ammonium electrode in steady-state or kinetic measurements. This approach is suitable for use in real-time monitoring applications where batch calibration techniques cannot easily be implemented.
Computer controlled laboratory instrumentation is of growing importance both in research and in industry. Different hardware and software approaches may be chosen which allow the development of high quality products, Last trends in hardware and software strategies are analyzed and some general guidelines are given for instrumentation development. The graphical compiler Lab VIEW 3.0 for instrumentation from National Instruments is presented and evaluated in terms of flexibility and low cost for the production of virtual instrumentation for research, biomedical applications and industrial environmental monitoring
Development of new adaptive materials based on spiropyran molecular photoswitches
Full text linkSpiropyrans are a family of photochromic compounds that can be reversibly switched between two states: a colourless, non-polar, uncharged spiro form (SP) and a highly coloured, polar, conjugated, zwitterionic merocyanine form (MC), i.e. SP → MC (UV light), MC → SP (green, white light). Furthermore, the MC form possesses a phenolate group that can reversibly bind metal ions and this ion binding is also photo-reversible, as when the MC-ion complex reverts to the passive SP form (upon green/white light exposure), it releases the bound ions. Using molecular-switches based on spiropyran-like molecules, new materials were produced whose properties such as metal-ion uptake/release and polarity can be controlled under external photonic stimulation.
Spiropyran derivatives were immobilised on polystyrene and silica microbeads and evaluated for their reversible photoswitchable metal ion binding behaviour. When in the MC form, in the presence of metal ions such as Cu2+ and Zn2+, further spectral and colour changes occurred that were found to vary according which metal ion was bound. Subsequent irradiation with white light caused reformation of the SP form and release of the metal ion. This process was shown to be repeatable at least several times. The spiropyran functionalised silica microbeads were packed into a capillary column and the new stationary phase demonstrated to form the basis of a photodynamic system for retention, detection and release of metal ions pumped into the capillary.
In parallel other spiropyran derivatives were incorporated into monolithic stationary phases. The spiropyran-functionalised polymer was switched between a protonated MC form and a neutral SP form upon white light irradiation. The monoliths were encased on a microfluidic chip and the system filled with an acid electrolyte. When a voltage was applied at the two ends of the encased monolith, electro-osmotic flow was generated and the flow rate shown to be variable upon white light exposure as a consequence of the formation of the SP form and the formation/disruption of the surface charge necessary for efficient electro-osmotic pumping.
In this thesis the synthesis and the characterisation of these new materials is described and the switchable optical properties evaluated
Chemical sensing using polypyrrole actuators
Full text linkIn the modern age methods for the calibration of sensors have become particularly important. Situations can arise where the deployment of sensors in the field, particularly in bulk, could be augmented to a very useful degree through the application of some form of autonomous monitoring system. This system would ideally be capable of taking a measurement, relaying the data to a central database and then re-setting the sensor to a default form. Inherently conducting polymers (ICPs) are useful in modem research due to their highly conductive properties when doped, and their concurrent mechanical flexibility. The ICP polypyrrole can be prepared as an electromechanical actuator, capable of operation under low applied power.
Through the application of colorimetric dyes to the polypyrrole actuators simple sensors can be developed with the actuator acting as a delivery mechanism of the sensor to the sample of interest. This concept has been developed through the use of LED-based detectors and RGB-analysis of digital images
Novel integrated paired emitter-detector diode flow analysis system
Full text linkMy PhD programme of research at the National Centre of Sensor Research has focussed on the development of a miniaturized detection system based on the concept of a Paired Emitter-Detector Diode (PEDD) LED optical sensor as a generic optical sensor platform for colorimetric analysis as developed within the research group. This research was funded by Science Foundation Ireland (SFI). This novel optical sensor employs two LEDs, operating one as a light source and the other as a light detector. The emitter LED is forward biased and the detector reverse biased. A simple timer circuit measures the time taken for the photocurrent generated by the emitter LED to discharge the detector LED from 5 V (logic I) to 1.7 V (logic 0).
PEDDs of various wavelengths and designs were investigated and initially calibrated using pH indicator dyes.
The PEDD has been applied as an inexpensive detector in a flow-injection system for determining low concentration levels of phosphate employing the malachite green spectrophotometric method. The novel flow detector employed within this manifold is a highly sensitive, low cost, miniaturized light emitting diode (LED) based flow detector, which achieved an improved LOD in comparison to a LED-photdiode sensor.
The PEDD has also been applied as a photometric detector in HPLC. Separation of transition metal ions, manganese (11) and cobalt (11) were carried out using a Nucleosil 100-7 (functionalised with IDA groups) column. The PEDD was calibrated using Mn (11) and Co (11) PAR complexes providing a linear response. Higher sensitivity and improved precision were obtained from the PEDD compared to the commercially available UV-vis variable wavelength detector
Clinical applications of calixarene based sodium-selective electrodes
Full text linkSince their beginnings in the late 1960's ion-selective electrodes have rapidly become one of the most important types of chemical sensor. They are commercially available for a large variety of ions, are widely used and have been characterised thoroughly by many investigators. Having attained this level of sophistication, research in this area today is often directed towards novel applications of such sensors. This thesis represents a study of certain clinical applications of sodium-selective electrodes.
As ion-selective electrodes possess the ability to directly sense analytes, they are well suited to whole blood, plasma and serum critical analyte testing. These critical analytes are major electrolytes, blood gases and some metabolites. Analysers based on ion-selective electrodes can provide fast turn-around time for critical care testing. With this in mind, a flow injection analysis system has been developed for the determination of sodium in blood samples. Here, the advantages of flow injection analysis and potentiometric detection were combined with those of computer control, to produce a blood analyser which has the potential to be user friendly, analytically reliable, portable and applicable to continuous monitoring.
Following this research, our attention turned to solid-state devices. Here, one opens up the possibility of mass fabrication of miniature, disposable, planar electrodes. Our efforts concentrated on the development of a potentiometric device, consisting of a solid-state sodium selective electrode and a solid-state chloride electrode. The device is based on a combination of screen printed Ag/AgCl electrodes and an ion-selective PVC membrane electrode. It was developed for use as a screening tool for Cystic Fibrosis, utilising the raised sodium level in sweat, which is a diagnostic indicator for the condition
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