Molecularly imprinted polymers for detection of volatile organics associated with fuel combustion

Magister Scientiae - MSc (Chemistry)Pollutants such as polycyclic aromatic hydrocarbons (PAHs) are known for their toxic effects which may lead to the cause of degenerative diseases in both humans and animals. PAHs are widespread in the environment, and may be found in water, food, automotive industry and petrochemical industries to name but a few sources. Literature reports have highlighted industrial workplace exposure to PAHs as a leading cause for development of cancer in workers. Particularly, workers in the petrochemical industry are adversely affected and the incidence of skin and lung cancer in this population group is high. The United States of America in its guidelines developed by environmental protection agency (EPA) has identified 18 PAHs as priority pollutants. Among these are anthracene, benzo[a]pyrene and pyrene which have been selected as the focal point of this study due to their significance in the petrochemical industry. Due to the carcinogenic and mutagenic properties reported in literature for certain PAHs, there have been monitoring procedures taken in most countries around the world. The commonly used analytical methods for the detection of PAHs from industrial samples are high performance liquid chromatography (HPLC) coupled to fluorescence detection, membrane filtration, ozonation and reverse osmosis. Analysis of PAHs from the petrochemical industry is typically performed by HPLC method as well as sono-degredation in the presence of oxygen and hydrogen peroxide

Molecular imprinting of polypyrrole for electrochemical sensing of clofibric acid

Molecularly imprinted polymers (MIPs) are artificial biomimetic receptors with applications in separation ranging from small molecules to whole cells. The combination of the MIP principle with conducting polymers allows the fabrication of specific and selective layers for sensing purposes. Not only the robustness of MIPs against environmental conditions and their low cost compared with natural receptors are advantages of MIPs, but also the possibility to prepare them for compounds which have no natural receptors. In this work, piezoelectric quartz crystals and analogous gold substrates were electrochemically coated with molecularly imprinted conducting polypyrrole films for pulsed amperometric detection (PAD) of clofibric acid, a metabolite of the blood lipid regulator clofibrate. Usually clofibric acid is detected by using reversed-phase HPLC with spectrophotometric detection. This requires large instrumentation, ultrapure solvents, and suitable sample preparation. An electrochemical sensing method would be advantageous due to the simple setup and low cost, and the use of organic solvents for the detection could be avoided. The films were prepared by cyclic voltammetry of an aqueous solution containing pyrrole as monomer, clofibric acid or, for feasibility studies, caffeine as template, and potassium chloride, potassium nitrate, or phosphate buffer solution as conducting salt. Non-imprinted polymers (NIPs) were prepared without template under the same conditions. The electrodeposition was monitored by a quartz crystal microbalance combined with an electrochemical cell. The deposition was influenced by the number of cycles and the applied potential, by the monomer concentration and the type of conducting salt, and also by the presence of the template. Cyclic voltammetry data obtained during polymerization and deposited weight estimations revealed a decrease of the polymerization rate with increasing clofibric acid concentration. Template entrapment and template removal were studied with X-ray photoelectron spectroscopy. The results indicated that clofibric acid could be removed after imprinting with an aqueous ethanol solution. Binding of caffeine and clofibric acid was studied with PAD. The results showed that optimizations of the washing procedure were needed. Washing procedures under stirring with frequent solvent change were tested with methanol, ethanol, and variation of the washing time, and were compared with washing by PAD measurements. In binding experiments, the highest sensor response to clofibric acid was obtained with sensors treated by PAD washing although the sensor response decreased gradually with repeated washing/measurement cycles. MIP and NIP surfaces were studied with atomic force microscopy (AFM), ellipsometry, contact angle measurements, and zeta potential measurements. AFM measurements revealed smooth surfaces with roughnesses of 6–8 nm for imprinted and non-imprinted layers. Differences between MIP and NIP layers were revealed by contact angle and zeta potential measurements. The results showed that contact angles were higher for MIPs than for NIPs and that the isoelectric point was lower for MIPs than for NIPs. Binding experiments with clofibric acid and other substances showed a pronounced selectivity of the MIP for clofibric acid vs. carbamazepine, but the response of MIP and NIP to the structurally related molecule 2,4-dichlorophenoxyacetic acid was higher than the response to clofibric acid. The smooth surface might be a reason for an excessively low density of specific binding sites for clofibric acid. Additionally to cyclic voltammetry, the application of potential pulses during polymerization was tested. Compared with cyclic voltammetry, the use of potential pulses resulted in more adherent films, which allowed testing the application of a negative potential as washing method. To introduce functional groups into the polymer, which could build more non-covalent bonds with the template during polymerization, pyrrole propionic acid and 2-(1H-pyrrole-1-yl)ethanamine were tested as monomers. Successful polymerization was obtained by copolymerization with pyrrole. The feasibility of sensor fabrication with a combination of molecular imprinting and electrochemical deposition of polypyrrole for the detection of clofibric acid could be demonstrated, but the specificity (response for MIP vs. NIP) and selectivity were strongly dependent on preparation and washing conditions.Molekular geprägte Polymere (molecularly imprinted polymers, MIPs) sind künstliche biomimetische Rezeptoren, die zu Trennungszwecken für verschiedene Substanzen, von kleinen Molekülen bis hin zu ganzen Zellen, entwickelt werden können. Die Kombination des MIP-Prinzips mit leitfähigen Polymeren erlaubt die Entwicklung spezifischer und selektiver Schichten zu Messzwecken. Nicht nur die Widerstandsfähigkeit der MIPs gegen Umwelteinflüsse und ihre niedrigen Herstellungskosten im Vergleich zu natürlichen Rezeptoren gehören zu ihren Vorteilen, sondern auch die Möglichkeit, MIPs für Substanzen herzustellen, für die es keine natürlichen Rezeptoren gibt. In dieser Arbeit wurden goldbeschichtete piezoelektrische Quarzkristalle und Glassubstrate elektrochemisch mit molekular geprägten leitfähigen Polypyrrolfilmen für die amperometrische Detektion von Clofibrinsäure, einem Metaboliten des Blutfettsenkers Clofibrat, beschichtet. Gewöhnlich wird Clofibrinsäure spektrophotometrisch mittels reversed-phase HPLC detektiert. Dies erfordert aufwändige Instrumentierung, hochreine Lösungsmittel und eine geeignete Probenvorbereitung. Der Vorteil einer elektrochemischen Methode wäre der mit niedrigen Kosten verbundene einfache Aufbau der Messanordnung und die Möglichkeit, den Einsatz organischer Lösungsmittel vermeiden zu können. Die Filme wurden mittels Zyklovoltammetrie in wässriger Lösung bestehend aus Pyrrol als Monomer, Clofibrinsäure oder, für erste Machbarkeitsstudien, Koffein als Templat und Kaliumchlorid, Kaliumnitrat oder Phosphatpufferlösung als Leitsalz hergestellt. Nicht-geprägte Polymere (non-imprinted polymers, NIPs) wurden ohne Templatzusatz unter ansonsten gleichen Bedingungen hergestellt. Die elektrochemische Beschichtung der Sensoroberfläche wurde durch die Kombination der elektrochemischen Zelle mit einer Quarzkristallmikrowaage beobachtet. Die Abscheidung des Polymers wurde durch die Anzahl der Zyklen und das verwendete Potential, die Konzentration des Monomers und der Art des Leitsalzes sowie durch das Templat beeinflusst. Zyklovoltammetrische Messwerte, die während der Polymerisation erhalten wurden, und Abschätzungen der Polymermasse zeigten, dass mit steigender Konzentration an Clofibrinsäure die Polymerisationsrate sinkt. Der Einschluss und die Entfernung der Templatmoleküle wurden mit Röntgenphotonenspektroskopie untersucht. Die Ergebnisse deuteten darauf hin, dass Clofibrinsäure mit ethanolischer Lösung aus dem Polymer entfernt werden konnte. Bindungsversuche mit Koffein und Clofibrinsäure wurden mit gepulster amperometrischer Detektion (pulsed amperometric detection, PAD) durchgeführt. Die Ergebnisse zeigten, dass das Vorgehen zur Templatentfernung optimiert werden sollte. Waschmethoden unter Rühren mit regelmäßigem Wechsel des Lösungsmittels wurden mit Methanol, Ethanol und Veränderung der Waschzeit getestet und mit Waschen durch PAD verglichen. Die höchste Sensorantwort auf Clofibrinsäure in Bindungsversuchen wurde mit Sensoren, die mittels PAD gewaschen worden waren, erreicht, doch die Sensorantwort nahm mit zunehmender Zahl an Wasch- und Bindungsversuchen ab. Die Oberflächen der MIPs und NIPs wurden mit Rasterkraftmikroskopie (atomic force microscopy, AFM), Ellipsometrie, Kontaktwinkelmessungen und Zeta-Potentialmessungen untersucht. AMF-Messungen ergaben mit 6–8 nm eine geringe Rauigkeit der Oberflächen von MIPs und NIPs. Unterschiede zwischen MIPs und NIPs zeigten sich bei Kontaktwinkel- und Zeta-Potentialmessungen. Für MIPs wurden höhere Kontaktwinkel als für NIPs festgestellt. Weiterhin lag der isoelektrische Punkt von MIPs niedriger als der von NIPs. Bindungsversuche mit Clofibrinsäure und anderen Substanzen zeigten eine höhere Selektivität der MIPs für Clofibrinsäure im Vergleich zu Carbamazepin, aber die Sensorantwort von MIPs und NIPs auf das strukturell ähnliche Molekül 2,4-Dichlorphenoxyessigsäure war höher als die Sensorantwort auf Clofibrinsäure. Zusätzlich zur Zyklovoltammetrie wurde die Verwendung von Potentialpulsen als Polymerisationsmethode getestet. Im Vergleich zur Zyklovoltammetrie ergab die Verwendung von Potentialpulsen Filme, die stärker an der Goldoberfläche der Sensoren hafteten, was die Verwendung eines negativen Potentials als Waschmethode zur Entfernung des Templats erlaubte. Zur Einführung funktioneller Gruppen in das Polymer, welche die Anzahl nicht-kovalenter Bindungen zwischen Templat und Polymer erhöhen könnten, wurden Pyrrolpropionsäure und 2-(1H-Pyrrol-1-yl)ethanamin als Monomere getestet. Eine Polymerisation wurde durch Copolymerisation mit Pyrrol erreicht. Die Machbarkeit der Sensorherstellung mit einer Kombination aus molekularer Prägung und elektrochemischer Polymerisation von Polypyrrol zur Detektion von Clofibrinsäure konnte gezeigt werden, aber Spezifität und Selektivität hingen stark von den Herstellungs- und Waschbedingungen ab

Detection of Acidic Pharmaceutical Compounds Using Virus-Based Molecularly Imprinted Polymers

Molecularly imprinted polymers (MIPs) have proven to be particularly effective chemical probes for the molecular recognition of proteins, DNA, and viruses. Here, we started from a filamentous bacteriophage to synthesize a multi-functionalized MIP for detecting the acidic pharmaceutic clofibric acid (CA) as a chemical pollutant. Adsorption and quartz crystal microbalance with dissipation monitoring experiments showed that the phage-functionalized MIP had a good binding affinity for CA, compared with the non-imprinted polymer and MIP. In addition, the reusability of the phage-functionalized MIP was demonstrated for at least five repeated cycles, without significant loss in the binding activity. The results indicate that the exposed amino acids of the phage, together with the polymer matrix, create functional binding cavities that provide higher affinity to acidic pharmaceutical compounds

Recent Advances in Electrosynthesized Molecularly Imprinted Polymer Sensing Platforms for Bioanalyte Detection

The accurate detection of biological materials has remained at the forefront of scientific research for decades. This includes the detection of molecules, proteins, and bacteria. Biomimetic sensors look to replicate the sensitive and selective mechanisms that are found in biological systems and incorporate these properties into functional sensing platforms. Molecularly imprinted polymers (MIPs) are synthetic receptors that can form high affinity binding sites complementary to the specific analyte of interest. They utilise the shape, size, and functionality to produce sensitive and selective recognition of target analytes. One route of synthesizing MIPs is through electropolymerization, utilising predominantly constant potential methods or cyclic voltammetry. This methodology allows for the formation of a polymer directly onto the surface of a transducer. The thickness, morphology, and topography of the films can be manipulated specifically for each template. Recently, numerous reviews have been published in the production and sensing applications of MIPs; however, there are few reports on the use of electrosynthesized MIPs (eMIPs). The number of publications and citations utilising eMIPs is increasing each year, with a review produced on the topic in 2012. This review will primarily focus on advancements from 2012 in the use of eMIPs in sensing platforms for the detection of biologically relevant materials, including the development of increased polymer layer dimensions for whole bacteria detection and the use of mixed monomer compositions to increase selectivity toward analytes

The mathematical stability study for the system of the CoO(OH) – overoxidized polypyrrole composite synthesis in the presence of fluor ions

The potentiostatic synthesis of CoO(OH) – Overoxidized polypyrrole composite in the presence of fluor ions has been investigated mathematically. The corresponding mathematical model was described and analyzed by means of linear stability theory and bifurcation analysis. The steady-state stability requirements, like also oscillatory and monotonic instability conditions are derived.Mongolian Journal of Chemistry 16 (42), 2015, 13-1

Molecularly imprinted polypyrrole sensors for the detection of pyrene in aqueous solutions

Recently, electrochemical sensors have emerged as tools for polyaromatic hydrocarbons (PAH) detection that are cost-effective, easy to produce and use, highly selective and sensitive, and with good reproducibility. Polypyrrole may be easily produced from polymerization of pyrrole, by chemical as well as electrochemical methods, to produce dimensionally stable semi-conductive polymer materials, under mild synthesis conditions. In this study, polypyrrole was used as the stable molecular framework within which to create an imprint of the desired polyaromatic hydrocarbon, in situ, at glassy carbon electrodes. The molecularly imprinted polymer (MIP) sensors were washed to remove the imprint and subsequently characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and cyclic voltammetry (CV). The MIP sensors were then applied to the detection of pyrene and non-imprinted polymers (NIP) sensors were also evaluated for comparison with the MIP sensors. Calibration curves obtained for the detection of the pyrene at the MIP sensors in aqueous media reported limits of detection (LOD) of 2.28 × 10−7 M for pyrene and limit of quantification (LOQ) of 6.92 × 10−7 M (n = 3). The sensitivity of the MIP sensors (32.53 A/M) determined from the slopes of the calibration curves reported twice the value measured for NIP sensors (14.48 A/M)

Molecularly imprinted polymer sensor systems for environmental estrogenic endocrine disrupting chemicals

Philosophiae Doctor - PhD (Chemistry)There is growing concern on endocrine disrupting compounds (EDCs). The presence of drugs in water supplies was first realized in Germany in the early 1990s when environmental scientists discovered clofibric acid. Clofibric acid has the ability to lower cholesterol in ground water below a water treatment plant. Endocrine disrupting compounds can be defined as those chemicals with the ability to alter daily functioning of the endocrine system in living organisms. There are numerous molecules that are regarded or referred to as EDCs such as but not limited to organochlorinated pesticides, industrial chemicals, plastics and plasticizers, fuels, estrogens and many other chemicals that are found in the environment or are in widespread use. 17?- estradiol is the principal estrogen found in mammals during reproductive years. Estriol is produced in large quantities during pregnancy. 17?-estradiol is the strongest, estriol the weakest. Estriol is water soluble, estrone and estradiol are not. Although estrogen is produced in women they are also at risk of over exposure to estrogen. Pesticides are extensively used today in agricultural settings to prevent and control pests. Various pesticides, including banned organochlorines (OCs) and modern non-persistent pesticides, have shown the ability to disrupt thyroid activity, disturbing the homeostasis of the thyroid system. Because these EDCs have adverse effects on health of both human and wildlife, it is imperative to develop viable costeffective analytical methods for the detection of these EDCs in complicated samples and at very low concentrations. Very high selectivity towards particular compounds is a very important property for the suitability of a detection method. This is because these compounds mostly coexist in complex matrices which makes the detection of a specific compound very challenging. It is paramount to develop highly sensitive and selective methods for the detection of these estrogens and phosphoric acid-based pesticides at trace levels

Development of a dual sensor polymer-based system for antibiotic detection in water samples

Ph. D. ThesisIn April 2019, the UN issued a warning that the overuse of antibiotics could lead to 10 million fatalities annually by 2050. It would also be a significant financial burden as there can be losses of €1.6 billion per single strain of antimicrobial resistant (AMR) bacteria, occurring primarily but not limited to the costs of medical care, hospitalisation, and patient care. Infiltration of antibiotics into groundwater arises from multiple sources; agriculture, highly populated residential areas and pharmaceutical effluents. These leached antibiotics journey to river systems cause selective pressure, thereby giving rise to accelerated AMR development. One route for aiding this issue is to slow the growth rate the emergence of AMR by controlling the levels of antibiotics that gain entry to water systems. To monitor this, a low-cost and reliable sensor platform is needed that can rapidly and on-site identify contaminated areas. Molecularly Imprinted Polymers (MIPs) are synthetic receptors that have potential for specific detection of contaminants in complicated matrices but have found limited commercial applications. The work within this thesis will explore the rational design of MIPs, their optimisation for a plethora of targets and the investigation of various applications to exploit their favourable characteristics when deployed as sensor platforms. Looking at how these imprinted polymers have been developed and utilised in recent times (primarily 2010-2020) and assessing any limitations encountered. These limitations have holstered MIP use, giving rise to the need for the critical review, which has been carried out in this thesis, on what development is needed to boost their applications to convert them into a mainstream commercial tool. Most MIP-based sensor systems focus primarily on a single analysis technique. Chapter 3 sees a novel, dual detection system developed which facilitates direct validation of the results and therefore can realise reliable detection of antibiotics in aqueous samples. Fluorescent monomers have been incorporated into the MIP complex allowing for fluorescent analysis as well as thermal, producing a dual sensor platform thus vastly enhancing the reliability of the biosensor. 3 Two applications of MIPs, that have been deployed as sensors, have been experimentally assessed. A focus on mounting these polymers onto Screen Printed Electrodes (SPEs) and the subsequent thermal analysis will be describe in chapter 4. This work comprised of a comparison of two techniques was carried out to determine the most appropriate method for attaching the polymers to the surface of the SPE, direct polymerisation onto the SPE against dropcasting of MIP particles synthesized by free radical polymerisation on the SPE surface. The direct polymerisation proved to afford MIP-modified SPEs to have higher levels of binding affinity. Chapter 5 explores an investigation into the evolution from small molecule targets to large macromolecules including whole bacteria. This proof-of-concept study saw a yeast mixture used as a target for MIP detection since yeast resembles bacteria in size and shape but does not need to be handled in a certified biosafety lab. A full evaluation of the work carried out concludes the thesis with an aim to gauge how the work undertaken will contribute to the development of a new division of quantitative sensor platforms. Secondly, the work produced will construct foundations for what is still needed to push the use of MIPs into commercial use to combat the rise in AMRManchester Metropolitan Universit

New strategies for developing receptors based on molecular imprinting for analytical applications

434 p.La presente tesis se ha basado en la síntesis y aplicación de polímeros de huella molecular (MIP) para elanálisis químico del 4-etilfenol y los compuestos pertenecientes a su ruta metabólica, que son el etil esterde ácido cumárico, el ácido cumárico y el vinilfenol. Los fenoles volátiles como el 4-etilfenol y el 4-vinilfenol afectan a las características organolépticas del vino, siendo perjudiciales en altasconcentraciones. El nivel de 4-etilfenol es proporcional a la concentración y la actividad de la levaduraresponsable de su aparición en vino, y por lo tanto puede ser utilizado como un indicador de su presencia.El trabajo experimental se ha sido divido en dos secciones principales, en función de la técnica analíticaen la que ha sido implementado el material impreso desarrollado. Inicialmente, se presenta unametodología para el desarrollo y aplicación de fases estacionarias basadas en MIP. Los materialesdesarrollados han sido evaluados como fases estacionarias en extracción en fase sólida y cromatografíalíquida.Como segundo apartado del trabajo, se describen distintas técnicas de impresión molecular para suimplementación en sensores voltamperométricos, por un lado, la síntesis de películas MIP sobreelectrodos de oro y por otro, la síntesis de nanopartículas MIP y su posterior inmovilización en lasuperficie de electrodos de oro