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No description available.

Polydiacetylenes (PDAs) exhibit a chromatic response to solvents, temperature, strain and other environmental perturbations. When formed in a solid-state polymerization, the backbone of the polymer is planar which provides extended conjugation polymer backbone. However, when an external force is exerted on the backbone, the extended conjugation is interrupted and an optical shift from blue to red is observed. A system using conjugated PDA Nano structures has been developed as a model to study the reversibility in the fluorescence resonance energy transfer (FRET) and electronic absorption of the PDA liposome particles. In the first study, a reversible system composed of PDA and Sulforrhodamine-101 was utilized where PDA and SR -101 act as acceptor and donor respectively. Colorimetric transition from blue to red in PDA liposomes was achieved through heating the conjugated liposomes. In this work, the FRET mechanism was evaluated without violating the role of nature that energy flows "down" hill and that the role of donor and acceptor in FRET are fixed. Reversible interchanging roles of donor and acceptor over many thermo-chromatic cycles in a modified-PDA-SR101 liposomal system were also evaluated. The nanotubes synthesized are thus unique and robust. The characterization studies showed that the nanotubes are both in Nano and micro scale. Thus the self-assembled chemistry using this material would find wide applications in such areas such as sensors, actuators, and computational devices at both micro and nano scale and further studies might offer them as an encapsulation drug delivery vehicle. Both these studies offer a new insight to the unique properties of polymerized PDA liposomes.

J E. coli On-Off &ldquo, &rdquo, °, &ndash The specific objectives of the work presented in this dissertation are to design novel molecular sensors based on fluorescence resonance energy transfer (FRET) between fluorophore (donor) and polydiacetylene (PDA, acceptor) for selective detection of biomolecules in solution. The work described in this dissertation is divided into three sections. In the first section, we report here two novel systems where the rate of energy transfer is based on changes in the spectral overlap between the emission of the donor and the absorption of the acceptor (J) as well as changes in the quantum yield of the acceptor. In the second section, we discuss modified these high sensitive molecular sensors based on FRET by using different receptors for selective detection of biomolecules such as proteins or bacteria in solution. The third section develops reversibility studies on FRET based sensors in solution or solid state. In the Chapters two and three, conjugated polydiacetylene (PDA) possessing stimuli-responsive properties have been intensively investigated for developing efficient sensors. Sensors based on FRET between conjugated polymers and fluorophores can be more sensitive than colorimetric based sensors. We use the fluorophore dansyl as the donor and polydiacetylene (PDA) as the acceptor to demonstrate the modulation of FRET efficiency through conformationally induced changes in the PDA absorption spectrum following thermal treatment that converts the PDA backbone of the liposome from the blue form to the red form. We have used steady-state electronic absorption, emission and fluorescence anisotropy (FA) analysis to characterize the thermal-induced FRET between dansyl fluorophores (donor) and PDA (acceptor). Energy transfer was found to be significantly more efficient from dansyl to the red-form PDA. This is due to large increase in the J values between dansyl emission and absorption red-form of PDA. We also have found that the monomer ratio of acceptor to donor (Rad) and length of linkers (functional part that connects dansyl fluorophores to the diacetylene group in the monomer) strongly affected FRET. A decrease in Rad resulted in diminished acceptor emission amplification. This was primarily attributed to lower FRET efficiency between donors and acceptors and a higher background signal. Increase in Rad led to increase probability of FRET from donor to acceptor as larger number of acceptors are present around a given donor. The competition between donor for energy transfer increases with decrease in Rad that contributed to lower FRET efficiency between donors and acceptors. We also found that the FRET amplification of PDA emissions after heating the solution was much higher when dansyl was linked to diacetylene through longer and flexible linkers than through shorter linkers. We attributed this to the insertion of dansyl in the bilayer of the liposomes which led to an increased dansyl quantum yield and a higher interaction of multiple acceptors with limited available donors. This was not the case for shorter and more rigid linkers where PDA amplification was much smaller. Much larger emission amplification for FRET was observed as compared to direct-excitation of PDA. The present studies aim at enhancing our understanding of FRET between fluorophores and PDA-based conjugated liposomes. These findings support the basis of a new sensing platform that utilizes J-modulated FRET as an actuating mechanism. A FRET based protein sensor by using sulforhodamine 101 as donor and PDA as acceptors was developed. This novel FRET based system primarily utilizes changes in J values (the spectral overlap between the emission of the donor and absorption of the acceptor) for the modulation of FRET efficiency between donors and acceptors. These FRET based sensors can be modified by tagged receptors (for proteins, viruses, and bactria) onto PDA liposomes which can interact with ligands present on proteins or bacteria. The biotin-streptavidin interactions were used as a sensing model system to test our FRET sensor response. In chapter 4, four different biotin-tagged lipids were used as receptors to investigate the effect of interactions between ligand-receptors on the FRET efficiency. The biotin was covalently linked to the liposome surface when using biotin-tagged diacetylene; whereas the biotin-tagged lipids with hydrophobic chains but without diacetylene functionalities provided non-covalently inserted lipids in liposomes. These studies were used to elucidate the effect of molecular interactions on FRET sensor response. The conjugated polymerized liposomes consisted of sulforhodamine-tagged-diacetylene and receptors linked lipids in different molar ratios. The characterization of the liposomes and sensing mechanism was investigated using UV-Vis and steady-state emission spectroscopy. The liposome solution yielded a weak donor emission (sulforhodamine 101) from after photo-polymerization of diacetylene monomers. This is due to energy transfer from the donor to PDA backbone chains (acceptors). The addition of streptavidin which interacted with biotin receptors resulted in increase in the sulforhodamine 101 emissions. The stress, due to interactions between biotin and streptavidin, induced the chromatic shift in the absorption spectrum of PDA which led to a decrease in the spectral overlap (J) between the emission spectra of donor and the absorption spectra of acceptor, leading to a decrease in the FRET efficiency from sulforhodamine 101 to PDA. These sensors, thus, show an "On-Off" type optical mechanism based on FRET between fluorophores and PDA where the donor emission was highly quenched in the "Off" state but was turned "On" due to receptor-ligand interactions. Large electronic absorbance and emission intensity differences between covalently and non-covalently bound biotin liposome systems were observed which indicated that the molecular interactions between biotin and PDA backbone play a crucial role in the FRET sensor response. In Chapter 5, we also developed FRET sensor for the detection of E. coli in aqueous media. Two glucose-based receptors were used in this study: (1) glucose-tagged lipid which can be inserted non-covalently in the bilayer of liposome, and (2) glucose-tagged diacetylene monomer in which the receptors were covalently bound to the backbone of the PDA liposome. The steady-state UV/Vis absorbance and fluorescence emission spectroscopy, and the fluorescence microscopy analysis of the receptors-containing liposomes were investigated for the detection of E. coli. The blue shift in the absorption spectrum of the conjugated PDA backbone induced through the interactions between receptors and bacteria resulted in decrease in the spectral overlap between the emission of SR-101 (donor) and the absorption of PDA (acceptor). This, ultimately, led to change in FRET efficiency between SR-101 and PDA after glucose - E. coli binding and caused increase in the emission intensity of SR-101. Polydiacetylenes have been exploited because of their sensitivity to external stimuli, such as temperature, pH, ions, and ligands. Unfortunately, the majorities of the sensors developed are not reversible but used as a one-time use. Here we report our preliminary results of a benzoic acid monomer of polydiacetylene (PDA-mBzA) to investigate reversible FRET characteristics between fluorophore and PDA. The LS films containing dansyl-tagged-diacetylene monomers and m-aminobenzoic acid derivatized- diacetylene monomers in different molar ratios were self-assembled and polymerized. The UV/Vis and steady-state fluorescence emission analysis of these LS films were investigated. These systems have shown partial reversible FRET over many "on-off" cycles. We believe that this incomplete FRET reversibility is due to liposomes preparation conditions used for liposomes which decreased PDA-mBzA amount in liposomes. We also reported reversible FRET studies on the liposome solutions, made from the monomer of m-aminobenzoic acid derivatized-10,12-pentacosadiynoic acid (PDA-mBzA) monomers and 11-((5-dimethylaminonaphthalene-1-sulfonyl)amino)undecanoic acid (DAUDA) or dansyl-tagged diacetylene. After photo-polymerization, the solution appeared blue in color at room temperature. Heating and cooling cycles (between 25 ºC and 95 ºC temperature range), illustrated a visible color change from blue to red and a complete return to blue over many thermal cycles. Our preliminary reversible absorption and emission measurements showed that there exist opportunities for reversibility in FRET response. We are now performing more experiments to increase the FRET reversibility in these experiments. Although our system does not display full reversibility, the preliminary absorption and emission measurements strongly suggest that there exist opportunities for fully reversible selective and sensitive FRET-based sensors after further optimization of the system.

Bacterial infections are a serious problem for patients with burns and other wounds. Such burn wound infection accounts for the pathogenic bacteria by colonising onto burned areas. Therefore, the need for detection and inhibition of such bacterial colonisation requires a methodology for sensing/killing pathogenic bacteria. This research project aims to design a ‗smart‘ wound dressing system which can respond to the microbiological environment of the wound via a simple colour change and will release antimicrobials only when required. Two strains of pathogenic bacteria Staphylococcus aureus (MSSA 476) and Pseudomonas aeruginosa (PAO1) were used in the study. The non-pathogenic bacterium E.coli (DH5α) was used as a control organism as it does not secrete virulence factors and therefore does not lyse membranes of vesicles. The key contributions of this thesis are outlined below. Firstly, an initial responsive nanocapsule system was studied. The fundamental work with giant unilamellar vesicles proved such a responsive system can provide antimicrobial properties when antimicrobial agents were encapsulated within the vesicles. Secondly, partially polymerised vesicles—polydiacetylene/phospholipid vesicles were then developed to improve vesicle stability. The vesicle system was optimised by varying molar concentration of diacetylene monomers (TCDA) in order to obtain relatively stable vesicles as well as sensitivity to the toxins secreted by the pathogenic strains. Measurements proved that the polydiacetylene/phospholipid vesicles can respond to pathogenic bacteria when fluorescent dye/antimcirobials were encapsulated in the vesicles. Finally, a simple prototype dressing was constructed. Plasma polymerised maleic anhydride (pp-MA) deposited onto non-woven polypropylene was shown to be a good method to stabilise vesicles via covalent bonding. Vesicle adhered to pp-MA non-woven polypropylene showed the ability to inhibit/kill the pathogenic strains, quantified by the Japanese Industry Standard assay and also gave a fluorimetric colour response in the presence of pathogenic bacteria when a fluorescent dye is encapsulated within vesicles. Other simple prototypes were also attempted by using hydrogels (gelatine and collagen) to maintain vesicle stability as well as promote tissue healing.

Point-of-care testing (POCT) devices have received increasing attention because of their potential to address the urgent need for quick and accurate diagnostic tools, especially in areas of personal care and clinical medicine. They offer several benefits over current diagnostic systems, including rapid diagnostic results in comparison to microbial cultures, simple interpretation of results, portability, and requiring no specialised laboratory equipment or technical training to operate. These are essential for diagnosing critical illnesses, such as sepsis, in areas of poor healthcare infrastructure. Sepsis, an innate physiological response to infection, is a growing problem worldwide with high associated costs and mortality rates, and affects a wide range of patients including neonates, infants, the elderly, and immunocompromised individuals. A literature review of the biomarkers of sepsis and the currently available diagnostic systems indicates the need for a biosensor capable of meeting the requirements of designing POCT systems and achieving detection of low concentrations of biomarkers. To meet these demands, two significant contributions to developing POCT platforms have been achieved and described in this thesis, including: 1) development of a colorimetric, magnetically separable biosensor that can be easily fabricated and demonstrates an easily identifiable colour response upon analyte detection, as well as the ability to capture and detection target biomarkers at low concentrations from complex solutions; and 2) tuning of the biosensor’s colorimetric response to achieve low detection limits, as well as demonstration of the versatility of the biosensor for sensing different target analytes. The developed biosensor in this work combines colour responsive polydiacetylenes and superparamagnetic iron oxide for the first time to achieve a biosensor capable of meeting these demands. The sensors exhibit identifiable colour responses to biomolecule detection, capture of a target analyte from complex solutions, sensing of different target analytes, a lower detection limit of 0.01 mg/mL, and rapid separation from solution with a common magnet. This work has been a significant demonstration of the capabilities of this biosensor as a new platform for POCT systems to diagnosis sepsis, and potentially other sensing applications.

Point-of-care testing (POCT) devices have received increasing attention because of their potential to address the urgent need for quick and accurate diagnostic tools, especially in areas of personal care and clinical medicine. They offer several benefits over current diagnostic systems, including rapid diagnostic results in comparison to microbial cultures, simple interpretation of results, portability, and requiring no specialised laboratory equipment or technical training to operate. These are essential for diagnosing critical illnesses, such as sepsis, in areas of poor healthcare infrastructure. Sepsis, an innate physiological response to infection, is a growing problem worldwide with high associated costs and mortality rates, and affects a wide range of patients including neonates, infants, the elderly, and immunocompromised individuals. A literature review of the biomarkers of sepsis and the currently available diagnostic systems indicates the need for a biosensor capable of meeting the requirements of designing POCT systems and achieving detection of low concentrations of biomarkers. To meet these demands, two significant contributions to developing POCT platforms have been achieved and described in this thesis, including: 1) development of a colorimetric, magnetically separable biosensor that can be easily fabricated and demonstrates an easily identifiable colour response upon analyte detection, as well as the ability to capture and detection target biomarkers at low concentrations from complex solutions; and 2) tuning of the biosensor’s colorimetric response to achieve low detection limits, as well as demonstration of the versatility of the biosensor for sensing different target analytes. The developed biosensor in this work combines colour responsive polydiacetylenes and superparamagnetic iron oxide for the first time to achieve a biosensor capable of meeting these demands. The sensors exhibit identifiable colour responses to biomolecule detection, capture of a target analyte from complex solutions, sensing of different target analytes, a lower detection limit of 0.01 mg/mL, and rapid separation from solution with a common magnet. This work has been a significant demonstration of the capabilities of this biosensor as a new platform for POCT systems to diagnosis sepsis, and potentially other sensing applications.

Les polydiacétylènes sont des polymères π-conjugués, obtenus par polymérisation topochimique à l'état solide de motifs diacétyléniques, sous l'effet d'un stimulus thermique ou photochimique. Depuis leur découverte en 1969 par Wegner, les polydiacétylènes ont fait l'objet de nombreux travaux de recherche. Ces travaux ont consisté tout d'abord à élucider le mécanisme de polymérisation, puis à étudier les diverses propriétés photophysiques, optiques, et électroniques des polymères. Néanmoins, la plupart des diacétylènes étudiés ne possédaient pas de substituants susceptibles d'être modifiés chimiquement. Le premier chapitre de cette thèse décrit la synthèse de nouvelles molécules diacétyléniques symétriques comportant des groupements azoles, et l'étude de leur polymérisation à l'état solide. La modification de l'organisation des motifs diacétyléniques.par interaction avec des molécules capables de former des liaisons hydrogène, et l'incorporation de ces motifs dans des matériaux hybrides organiques-inorganiques de type,. MOF ont également été examinées.Dans le deuxième chapitre, nous nous sommes intéressés aux composés diacétyléniques dicationiques fonctionnalisés par des groupements triéthylammoniums, imidazoliums et benzimidazoliums. La synthèse de ces composés, leur caractérisation spectroscopique, et cristallographique, ainsi que l'étude de leur réactivité thermique et photochimique ont été réalisées.Dans le troisième chapitre, nous proposons une méthode directe de préparation de carbone dopé à l'azote par pyrolyse des molécules diacétyléniques neutres, ainsi que la synthèse de carbone mésoporeux en présence d'un sel métallique. Un autre aspect de ce chapitre est l'optimisation des teneurs en azote en utilisant comme précurseurs les composés diacétyléniques dicationiques, associés à des anions riches en azote, notamment l'anion dicyanamide [dca] et tricyanométhide [tcm]. / Diacetylenes (DA) are unusual molecules owing to their ability to polymerize in the solid state. Such a polymerization is triggered off thermally or photochemicaly, and leads to the formation of enyne structures. Since their discovery in 1969 by Wegner, polydiacetylenes (PDA) have been the focus of much attention. Initially, many studies were devoted to elucidating the mechanism of polymerization, then assessment of the diverse photophysical, optical, and electronic properties of the polymers became the main goal. Yet, the vast majority of the DA that were studied did not possess substituents that could be modified chemicallyThe first chapter describes the synthesis of new symmetrical diacetylenic molecules functionalized with azole substituents and the study of the polymerization of these compounds in the solid state. Then, we present the modification of the organization of these diacetylenes by the interaction with molecules capable of forming hydrogen bonds, and the use of these molecules as ligands for the synthesis of Metal Organic Frameworks (MOF).The second chapter is devoted to the synthesis, characterization and crystallographic study of ionic diacetylenic compounds bearing triethylammonium, imidazolium and benzimidazolium groups. The photochemical and thermal behaviors of these DA have been tested.In the third chapter, we propose a straightforward route to N-doped graphitic carbon by direct pyrolysis of neutral diacetylenic precursors, and investigate the possibility of forming porous materials by adding a metal salt as a catalyst. Furthermore, another aspect of this chapter was to optimize the nitrogen content of these materials by using dicationic DA with N-rich anions, e.g. dicyanamide [dca] and tricyanomethide [tcm].

<p>Extracellular matrix (ECM) creates high-resolution chemical patterns, by assembling simple molecules with nm-scale features (e.g., carbohydrates, nucleotides, amino acids) into complex structures up to micrometers and extending to even larger scales across tissues (e.g., glycans, DNA, proteins), capable of carrying out the diverse and complex cellular functions. Mimicking the complexity of such biological systems requires precise control over the chemical patterning on substrates that exhibit physiochemical properties similar to biological systems (such as hydrogels). Although hydrogels provide tunable physiochemical properties suitable for biological applications; it is a porous material where pore sizes can range from 30 nm to greater than 1000 nm. Due to this structural heterogeneity, chemical patterning below the length scale of this heterogeneity is very challenging.</p> <p>Here, we demonstrate a new assembly system for generating a nanostructured presentation of carbohydrates on the hydrogel surface. This approach is based on the striped phases assembly of functional alkanes where 1-nm resolution functional patterns are readily assembled on substrates such as highly ordered pyrolytic graphite (HOPG). In this assembly, molecules are stabilized by noncovalent interactions, including alkyl-pi interactions underlying the HOPG, van der Waals interaction between the adjacent alkyl chains, and hydrogen bonding between polar head groups. Topochemical polymerization converts internal diynes into conjugated polydiacetylenes (PDAs). PDAs can also be utilized to covalently attach the striped pattern to polyacrylamide hydrogels through free radical chemistry.</p> <p>Here, we synthesize new amphiphiles with carbohydrate headgroups (N-acetyl-D-glucosamine (GlcNAc), and D-glucuronic acid (GlcA)), assembled into striped phases on HOPG and covalently transfer to polyacrylamide hydrogels. GlcNAc binds to wheat germ agglutinin (WGA), a lectin that binds specifically in a multivalent fashion (dissociation constant KD in nm range) to GlcNAc. We show that GlcNAc striped phases generate highly selective interactions with wheat germ agglutinin (WGA) but do not induce specific binding with concanavalin A (another lectin molecule that does not target GlcNAc). We further demonstrate that WGA binding affinity can be modulated by shifting the position of diacetylenes that bring the polymer backbone closer to the GlcNAc, increasing the effecting local concentration of carbohydrates.</p> <p>We investigated the possibility of using sPDA for secondary functionalization with complex biological molecules (such as biotin and cRGD) to mimic the ECM composition closely. The unusual reactivity of the sPDA backbones during the covalent transfer of the striped phase monolayer to hydrogels illustrates the potential of sPDA reactivity azides. In this work, we show that the addition of substituted azide molecules to sPDA-functionalized hydrogels produces a decrease in the fluorescence of the sPDA monolayer. Since these reactions are occurring on porous hydrogel surfaces characterization using techniques such as IR or NMR is difficult. We carried out further solution-phase reactions using a soluble PDA where PDA UV-vis absorption spectra red-shift after the reaction between the PDA backbone and azide. These experiments support the hypothesis of sPDA and azide click reaction.</p>