Dans les prochaines années, les traitements des maladies graves (cancer, pathologies du cerveau, etc) pourraient fortement bénéficier des progrès en science des matériaux et des nanotechnologies. Du point de vue médical, il est bien connu que les cellules cancéreuses ont tendance à développer des résistances aux chimiothérapies dont les effets secondaires limitent considérablement l'efficacité des traitements. Pour ces raisons, la recherche de thérapies alternatives ciblant les cellules cancéreuses sans affecter les tissus sains est actuellement l'un des domaines les plus actifs de recherche sur le cancer. Dans ce contexte, les nanoparticules magnétiques reçoivent un intérêt croissant pour diverses applications biomédicales allant du diagnostic au traitement ciblé. En effet, grâce à leur possibilité d'actionnement contrôlé à distance par des champs magnétiques externes, les particules magnétiques ont la capacité d'exercer des forces ou couples localisés sur des espèces biologiques ciblées.Ce travail de thèse décrit une approche basée sur l'action mécanique de particules magnétiques bio-fonctionnalisées sur des cellules cancéreuses. Lorsque ces particules sont liées aux cellules cancéreuses, l'application d'un champ magnétique alternatif externe induit l'oscillation des particules, qui transmet alors une force mécanique aux cellules cancéreuses.Les particules magnétiques utilisées pour cette application ont fait l'objet d'un long développement. Contrairement aux particules magnétiques conventionnelles synthétisées par des voies chimiques (« bottom-up »), les particules étudiées dans cette thèse ont été spécialement conçues par des techniques développées pour la micro/nanoélectronique (« top-down »). Ainsi, deux types de particules magnétiques ont été comparés ; des particules antiferromagnétiques synthétiques (SAF) constituées d'empilements de couches magnétiques et des microparticules constituées d'une couche magnétique unique avec une configuration de vortex magnétique.Une fois ces particules mises en solution, les phénomènes d'auto-polarisation qui contribuent à l'agglomération / dispersion de ces particules par les interactions magnétostatiques ont été comparés, ainsi que les couples mécaniques que ces deux types de particules magnétiques peuvent générer sur les cellules cancéreuses lorsqu'elles sont soumises à un champ magnétique externe.Bien que les particules SAF génèrent de plus grands couples, remplacer les constituants de l'empilement magnétique par des matériaux biocompatibles reste délicat, ce qui n'est pas le cas de leurs homologues en vortex magnétique, facilement réalisables avec des oxydes de fer.En exploitant les propriétés des vortex magnétiques en NiFe, nous avons développé une approche pour la destruction ciblée des cellules cancéreuses du carcinome rénal humain. Les tests menés in-vitro montrent que ce stimulus magnéto-mécanique créé deux effets dramatiques : une diminution significative du taux de cellules cancéreuses vivantes, et l'initiation du processus d'apoptose (ou mort cellulaire programmée) et ce, en appliquant de faibles valeurs de champs (~100 Oe c'est-à-dire 10mT) à de très faibles fréquences (~ 20 Hz). Des études pour la quantification de la mort cellulaire par cytométrie en flux ont été menées. Les résultats déjà obtenus bien qu'au stade « preuve de concept » sont très encourageants pour le futur des nouvelles thérapies du cancer. / In the coming years, the treatment of serious diseases (cancer, brain diseases, etc.) could benefit more intensely from advances in materials science and nanotechnology. From the medical point of view, it is well known that cancer cells tend to develop resistance to chemotherapy, and the side effects encountered seriously limit the effectiveness of treatments. For these reasons, the search for alternative therapies that target cancer cells without affecting healthy tissues is currently one of the most active areas of research on cancer. In this context, magnetic nanoparticles are receiving an increasing interest in a variety of applications ranging from biomedical diagnostic to targeted treatments. Indeed, due to their remote actuation by external magnetic fields, the magnetic particles have the ability to locally perform actuations on targeted biological species.This thesis describes an approach based on interfacing cancer cells with bio-functionalized magnetic particles. When these particles are bound to the cancer cells, applying an external alternating magnetic field induces the particles oscillations, which then transmits a mechanical stress to the cancer cells.For this application, specific magnetic particles were prepared. Unlike conventional magnetic particles made by chemical routes ("bottom-up"), the particles studied in this thesis have been specially designed by techniques used in micro / nanoelectronics ("top-down"). Thus, two types of magnetic particles were compared; synthetic antiferromagnetic particles (SAF) consisting of magnetic multilayer stacks and microparticles consisting of a single magnetic layer with a magnetic vortex configuration.Once these particles released in a solution, the self-polarization phenomenon that contributes to the agglomeration / dispersion of these particles by magnetostatic interactions were compared for both types of particles as well as the mechanical torques that they can exert on cancer cells when subjected to an external magnetic field.Although SAF particles generate higher torques, finding biocompatible materials that may replace the constituents of the magnetic stack remains difficult, while vortex-particles would be easier to make in magnetic iron oxides.By exploiting the properties of NiFe magnetic vortices, we have developed an approach for the targeted destruction of the human renal carcinoma cells. The tests launched in vitro show that the magneto-mechanical stimulus creates two dramatic effects: a significant decrease in the rate of alive cancer cells, and the initiation of the apoptosis (programmed cell death). These results were achieved by applying low field values (~ 100 Oe i.e.10mT) at low frequencies (~ 20 Hz). Studies for the quantification of cell death by flow cytometry were conducted. The results already obtained even at the stage of "proof of Concept" are very encouraging for new perspectives of cancer therapies.

Magnetic photocatalysts were synthesised by coating a magnetic core with a layer of photoactive titanium dioxide. This magnetic photocatalyst is for use in slurry-type reactors in which the catalyst can be easily recovered by the application of an external magnetic field. The first attempt at producing this magnetic photocatalyst involved the direct deposition of titanium dioxide onto the surface of magnetic iron oxide particles. The photoactivity of these Fe3O4/TiO2 was lower than that of single-phase TiO2 and was found to decrease with an increase in the heat treatment. These observations were explained in terms of an unfavourable heterojunction between the titanium dioxide and the iron oxide core. Fe ion diffusion from the iron oxide core into the titanium dioxide matrix upon heat treatment, leading to a highly doped TiO2 lattice, was also contributing to the observed low activities of these samples. These Fe3O4/TiO2 particles were found to be unstable, with photodissolution of the iron oxide phase being encountered. This photodissolution was dependent on the heat treatment applied, the greater the extent of the heat treatment, the lower the incidence of photodissolution. This was explained in terms of the stability of the iron oxide phases present, as well as the lower photoactivity of the titanium dioxide matrix. In fact, the observed photodissolution was found to be induced-photodissolution. That is, the photogenerated electrons in the titanium dioxide phase were being injected into the lower lying conduction band of the iron oxide core, leading to its reduction and then dissolution. Thus, the approach of directly depositing TiO2 onto the surface of a magnetic iron oxide core proved ineffective in producing a stable magnetic photocatalyst. The introduction of an intermediate passive SiO2 layer between the titanium dioxide phase and the iron oxide phase inhibited the direct electrical contact and hence prevented the photodissolution of the iron oxide phase. Improvements in the photoactivity were seen to be due to the inhibition of both the electronic and chemical interactions between the iron oxide and titanium dioxide phases. Preliminary optimisation experiments revealed that a thin SiO2 layer is sufficient for inhibiting the photodissolution. The thickness of the TiO2 coating was found not to have a significant effect on the photocatalytic performance of the coated particles. Finally, heat treating for 20 minutes at 450??C was sufficient for converting the titanium dioxide into a photoactive phase, longer heating times had no beneficial effect on the photoactivity.

This thesis examines the mechanisms of magnetic particle deposition and retention in human airways for magnetically targeted drug delivery. As this is a novel application, fundamental studies were performed to establish the necessary background knowledge for further development. Magnetic particle deposition from an aerosol in simulated airway conditions was studied using numerical and experimental models. The model results showed qualitative agreement; discrepancies were due to particle aggregation, which enhances deposition. Aerosol flow rate had a limited effect; the main factor in effective deposition was the proximity of the particle trajectories to the magnets. This spatial bias shows the importance of particle distribution in the flow as well as magnetic field geometry. These studies demonstrated the feasibility of capturing magnet particles from aerosol in airway conditions. For retention, clearance of particles due to motion of the mucus lining of the airways must be overcome. Particle retention was studied in vitro using various liquids to simulate mucus and identify relevant parameters. An ex vivo animal tissue model was used to demonstrate feasibility. Retention of 3-5 m diameter iron particles was achieved at reduced liquid/mucus viscosities. Larger (~100 m) particles were retained at normal mucus viscosities. The size dependence shows that particle aggregation after deposition is crucial for effective retention. In vitro retention experiments showed aggregate size is correlated with liquid viscosity, i.e. formation of aggregates is limited by forces opposing particle motion along the mucus layer interface. To determine these forces, particle motion on various air-liquid interfaces, chosen to simulate different mucus properties in isolation, was studied. When surfactants are present, as in the mucus layer, particle motion is limited by a velocity-dependent surface tension gradient as well as viscous drag. Pulling particles through the mucus layer into the tissue beneath was also considered as a potential retention strategy. The force required to pull particles through the mucus layer was also studied using various liquids to simulate mucus properties. In addition to the surface tension force holding the particles at the interface, hydrodynamic forces must be overcome to pull particles into or out of a liquid film such as the mucus layer.

No description available.

No description available.

Magnetic photocatalysts were synthesised by coating a magnetic core with a layer of photoactive titanium dioxide. This magnetic photocatalyst is for use in slurry-type reactors in which the catalyst can be easily recovered by the application of an external magnetic field. The first attempt at producing this magnetic photocatalyst involved the direct deposition of titanium dioxide onto the surface of magnetic iron oxide particles. The photoactivity of these Fe3O4/TiO2 was lower than that of single-phase TiO2 and was found to decrease with an increase in the heat treatment. These observations were explained in terms of an unfavourable heterojunction between the titanium dioxide and the iron oxide core. Fe ion diffusion from the iron oxide core into the titanium dioxide matrix upon heat treatment, leading to a highly doped TiO2 lattice, was also contributing to the observed low activities of these samples. These Fe3O4/TiO2 particles were found to be unstable, with photodissolution of the iron oxide phase being encountered. This photodissolution was dependent on the heat treatment applied, the greater the extent of the heat treatment, the lower the incidence of photodissolution. This was explained in terms of the stability of the iron oxide phases present, as well as the lower photoactivity of the titanium dioxide matrix. In fact, the observed photodissolution was found to be induced-photodissolution. That is, the photogenerated electrons in the titanium dioxide phase were being injected into the lower lying conduction band of the iron oxide core, leading to its reduction and then dissolution. Thus, the approach of directly depositing TiO2 onto the surface of a magnetic iron oxide core proved ineffective in producing a stable magnetic photocatalyst. The introduction of an intermediate passive SiO2 layer between the titanium dioxide phase and the iron oxide phase inhibited the direct electrical contact and hence prevented the photodissolution of the iron oxide phase. Improvements in the photoactivity were seen to be due to the inhibition of both the electronic and chemical interactions between the iron oxide and titanium dioxide phases. Preliminary optimisation experiments revealed that a thin SiO2 layer is sufficient for inhibiting the photodissolution. The thickness of the TiO2 coating was found not to have a significant effect on the photocatalytic performance of the coated particles. Finally, heat treating for 20 minutes at 450??C was sufficient for converting the titanium dioxide into a photoactive phase, longer heating times had no beneficial effect on the photoactivity.

In the food industry, it is very important to take care of the quality, safety and organoleptic properties of the products supplied. For this reason, food must be checked. However, not all information can be found using conventional techniques such as immunoassays, chromatographic techniques, etc. DNA-based techniques can be used for these cases where traditional procedures are insufficient. Among them, the best known technique is PCR. The aim of the thesis was to isolate DNA from vegetable samples (broccoli, beetroot, carrot and pepper). DNA was isolated using the magnetic particle method and the traditional CTAB method. Both methods were able to isolate the DNA from the vegetable samples in quality and at a concentration suitable for PCR, where the 35S rDNA gene region was amplified (more precisely about 700 bp of the 18S-ITS1-5,8S region). After amplification, the PCR products were subjected to restriction reactions and the results compared to bioinformatic analysis. These steps have succeeded in finding suitable enzymes for diferentiation of PCR products from the tested vegetable species.

Identification of bacterial DNA consists from several steps: cell lysis, isolation and purification of DNA, precipitation by ethanol, identification of bacterial strain by PCR or other molecular biology methods. Each step must be optimised. Nucleic acids can be isolated from cells using magnetic particles. The molecules of DNA are bound to the surface of magnetic carriers by electrostatic interaction, and then they are eluted into buffer. The aim of the work will be to optimize individual steps of identification of bacterial DNA: cell lysis, DNA isolation, characterization of solid magnetic carriers functionalized by amino groups for nucleic acids isolation. The presence of DNA will be verified using agarose gel electrophoresis and the amount of eluted DNA will be determined spectrophotometrically. The quality of isolated DNA will be proved by their amplification using polymerase chain reaction (PCR). Furthermore, the thesis focuses on the study of secondary structures of nucleic acids – cruciforms structures and quadruplexes. These structures are involved in the regulation of cellular processes and their appearance is associated with cancer development and neurodegenerative diseases. In silico genome analysis was performed on important food industry microorganisms. The microorganisms genomic sequences were obtained from the NCBI (National Center for Biotechnology) database. The Palindrome Analyzer and G4 Hunter software were used for the analysis.

The effectiveness of magnetic microparticles in isolation of DNA from Lactobacillus rhamnosus CCM 1825T and DNA from chicken erythrocytes were studied in diploma thesis. Magnetic HEMA based microparticles coated by carboxylic groups and hyperbranched styrene-divinylbenzene particles (IMC AS ČR, Prague, Czech Republic) were used for DNA isolation. Magnetic microparticles Dynabeads® DNA DIRECT™ Universal (Dynal, Norway) based on polystyrene and MPG® Uncoated (PureBiotech, USA) based on magnetic glass were used as a control. The dependence of amount of eluted DNA on concentration of DNA in the base solution and the dependence of amount of eluted DNA on concentration of magnetic microparticles were studied. The affinity of magnetic microparticles to RNA for various concentrations of RNA solution was studied, too. The ability of tested particles to isolate DNA from real samples was validated using milk product Actimel. The quality of isolated DNA of Lactobacillus genus was proved using genus specific PCR.

Master’s thesis contains information about the enzymes, biosensors, enzyme biosensors and magnetic particles. Cholinesterasa (ChE) is the generally name for the two related enzymes, mutually differing appearance and biological functions. Acetylcholinesterasa (AChE) is necessary for the transmission of nervous excitement. AChE is located at cholinergic synapses, where is the hydrolysis of the neurotransmitter acetylcholine and this termination by the nervous excitement. Butyrylcholinesterasa (BChE) is related to AChE and it is present in serum. Experimental part was focused on electrochemical biosensors with cholinesterase enzyme using magnetic particles for reversible reconstruction layer. Cholinesterase immobilization was carried out on the magnetic particles by covalent binding after glutaraldehyde activated. The measurement of activity take place with acetylthiocholin as a substrate in a flow system, magnetic particles were captured before the platinum electrode and produced by thiocholin is detected amperometric. The aim was to measure inhibition of AChE. Significant inhibition ChE is caused by certain drugs and pesticides based on organophosphates. There was tested by inhibition of AChE pesticide dichlorvos. Emphasis was on finding possible experimental conditions for the creation of the automated procedure to measure the AChE activity, which was based on auto-injector and pumps of Gilson, together with a 735 programme for the definition of the working configuration, preparation of measurement scripts and implementation of application methods.