Indiana University-Purdue University Indianapolis (IUPUI) / Optical refrigeration in quantum dots was carried out in this research. Zinc-blende crystalline CdSe/CdS (core/shell structure) QDs with complete surface passivation were synthesized and been used as the cooling substance. Phonon-assisted up-conversion photoluminescence driven by sub-band gap laser excitation was utilized as the cooling mechanism in the QD samples. A net cooling efficiency was predicted by a semi-empirical model developed during the research, within a range of the laser excitation energy, even after taking into account possible parasitic heating processes. To observe the cooling effect, the experiment was carried out in a thermally isolated environment, which temperature was also monitored. By using an optical thermometry technique developed for this research, a maximum temperature drop around 0.68 K was observed in the experiment. This development paves the way to use QDs' cooling in new industrial and fundamental research approaches.

Quantum dots (QDs) are semiconductor nanoparticle fluorophores with size tunable emission wavelengths and large absorption cross sections, making QDs ideal optical imaging agents. Optical imaging has seen considerable academic and commercial interest, particularly for preclinical imaging. This interest stems from the capacity to multiplex, i.e., the detection of multiple independent imaging probes simultaneously, the accessibility of optical imaging equipment, and the absence of ionizing radiation. Since multiple in vivo targets can be imaged simultaneously, multiplexing is particularly appealing for targeted molecular imaging. In oncology, where a myriad of receptors can be used as targets for personalized medicine, multiplexed imaging would improve rapid receptor status profiling. Given their flexible design, QDs can be engineered for use as targeted contrast agents. To meet the needs of this application, the QDs must 1) emit in the near or short wavelength infrared (NIR/SWIR) wavelength regime to mitigate absorption of light by tissues, 2) be biocompatible, and 3) enable functionalization with targeting agents, such as antibodies or small molecules. In this thesis, the first requirement was addressed by synthesizing an inverted Type-I ZnSe/InP/ZnS system, which is the first InP based system with tunable emission past 750 nm. Biocompatibility of the InP system was confirmed with in vivo toxicity studies of the ZnSe/InP/ZnS QDs. The third requirement was addressed by the development of bioconjugation and functionalization schemes resulting in active QD targeting to the biologically interesting cellular targets human epidermal growth factor receptor 2 (HER2) and folic acid receptor alpha. In addition to developing the new contrast agent, the imaging approach was also refined to address concerns of non-specific labeling of the tumor. To discern between targeted and untargeted binding in vivo, a dual tracer approach using both an untargeted and targeted imaging probe, paired with a corresponding image processing algorithm, was implemented and validated. Identifying the limitations of this approach in NIR-I imaging, resulting from tissue auto fluorescence and light attenuation, laid the groundwork for future imaging work in the SWIR. In order to explore the utility of SWIR for dual tracer approaches, PbS/CdS QDs emitting throughout the SWIR wavelength regime were synthesized. The PbS/CdS QDs were used to generate pilot in vivo SWIR imaging data in collaboration with the National Research Council of Canada. The pilot data demonstrate that tissue attenuation and autofluorescence will not be an issue in the SWIR wavelength regime. By pairing SWIR emitting QDs with dual tracer imaging principles, future studies may be able to discern tumor biomarker status at tissue depth. Such an approach would allow researchers to determine how tumors respond to targeted therapies, furthering the development of personalized medicine. / 2022-09-27T00:00:00Z

No description available.

Les amines biogènes (AB) sont des substances physiologiquement actives résultant de la décarboxylation enzymatique des acides aminés libres. Elles participent, dans le corps, aux processus de transmissions d'informations et de régulation de fonctions physiologiques mais peuvent aussi, à doses élevées, avoir des effets néfastes pour la santé. De nombreuses AB sont répertoriées dans la littérature, telles que l'histamine, la cadavérine et la putrescine. Mais, seul le contrôle d'histamine dans la chair de certains poissons de la famille des scombridés est actuellement réglementée (CE n° 2073/2005). Du fait de cette réglementation, les techniques d'analyses chimiques de l'histamine sont largement documentées. Elles peuvent être semi-quantitatives (chromatographie sur couche mince) ou encore quantitatives (fluorescence moléculaire) mais, la chromatographie liquide haute-performance reste, à ce jour, l'unique méthode homologuée au niveau des instances de santé européenne. En marge de ces méthodes traditionnelles, l'enjeu d'un dispositif rapide, peu onéreux et permettant un contrôle plus systématique des aliments anime à la fois la communauté scientifique et le monde économique. Dans ce contexte, la pertinence à recourir à des Quantum Dots (QD) fonctionnalisés par un dérivé d'ortho-phthalaldéhyde (OPA) (utilisé en tant qu'agent de dérivation en fluorescence moléculaire pour les AB) a été posée. Lors de ce projet, deux éléments clés d'un tel dispositif ont été réalisés et caractérisés. Les premiers correspondent aux dérivés fonctionnalisés de l'OPA (4-Me-OPA et 4-HO-OPA). Ils ont été obtenus avec succès selon trois voies de synthèse. Les premières correspondent à des optimisations de synthèses référencées du 4-HO-OPA à partir d'alcool furfurylique ou du 3,4-diméthylphénol. Enfin, celle issue de l'acide 3-méthoxybenzoïque est une adaptation d'une synthèse référencée du 4-MeO-OPA. Dans un second temps, les propriétés du 4-MeO-OPA en tant qu'agent de dérivation vis-à-vis de l'histamine ont été évaluées et comparées à celles de l'OPA. Pour cela, les conditions optimales de complexation ont été étudiées par spectroscopies Ultra-Violet (UV) et de fluorescence moléculaire. Les seconds composants du dispositif sont des nanostructures fluorescentes (QD) dont les propriétés d'émission de fluorescence sont modulables. Notre choix s'est porté sur les QD hydrosolubles de cadmium et sélénium stabilisés par de l'acide mercaptosuccinique. Ces derniers ont été synthétisés par trois modes d'activation (thermique, micro-ondes, ultrasons) et caractérisés par diffractométrie de rayons X, spectrométrie à plasma à couplage inductif, spectroscopies UV et de fluorescence moléculaire. En conclusion, deux entités, le 4-HO-OPA et des QD possédant des ligants de type mercaptosuccinique, ont été réalisées en vue de la mise en place d'un dispositif innovant d'analyse d'histamine. / The biogenic amines (BA) are physiologically active substances resulting from the enzymatic decarboxylation of free amino acids. In the body, they are involved in the transmission of informations and in regulating physiological functions but, at high levels, they can also have damaging health effects. Many BA are recorded in literature, such as histamine, cadaverine and putrescine. Currently, the control of histamine in fish flesh is only regulated in the case of some Scombridae species (CE N° 2073/2005). As a consequence, histamine chemical analysis techniques are widely documented. They can be semi-quantitative (thin layer chromatography) or quantitative (molecular fluorescence). At present, high-performance liquid chromatography remains the only approved method by public heath authorities. Next to the commonly used methods, the challenge of a fast inexpensive system that allows a more systematic control of food animates both the scientific community and the economic world. In this context, a study of the relevance of using Quantum Dots (QD) functionalized by an ortho-phtalaldehyde (OPA) derivative (OPA), used as molecular fluorescence derivation agent for BA, was undertaken. During this project, two key elements of the system were realized and characterized. The first corresponds to OPA functionalized derivates (4-MeO-OPA and 4-HO-OPA). They have been successfully achieved through three synthesis ways. The first two are optimizations of 4-HO-OPA referenced syntheses from furfuryl alcohol or 3,4-dimethylphenol. Finally, the last one uses 3-methoxybenzoic acid and is a 4-Me-OPA reference synthesis adaptation. In a second part, the 4-MeO-OPA properties as a bypass agent for histamine analysis were evaluated and compared with OPA ones. In this case, optimal complexation conditions were analyzed by ultra-violet (UV) and molecular fluorescence spectroscopies. The second components are QD, which are fluorescent nanostructures with molecular properties. We selected water soluble cadmium and selenium QD which were stabilized by mercaptosuccinic acid. They were synthesized by three activation modes (thermal, microwave, ultrasound) and characterized by X-ray diffractometry, inductively coupled plasma spectrometry, UV spectroscopy and molecular fluorescence. In conclusion, two entities, 4-HO-OPA and QD, both having a mercaptosuccinic-type shell, were created as the innovative set up for histamine analysis.

Nous utilisons un microscope à effet tunnel (STM) associé à un microscope optique inversé pour l’excitation et la détection des plasmons de surface propagatifs et/ou localisés. L’excitation de ces plasmons est assurée par passage d’un courant tunnel inélastique entre la pointe du STM et la surface d’un film métallique mince (épaisseur de 50 nm) d’or ou d’argent déposé sur une lamelle de verre. Les fuites radiatives des plasmons de surface propagatifs et la lumière émise par les plasmons localisés dans le substrat de verre sont collectées par un microscope optique via un objectif à immersion. Il est alors possible de déterminer à la distribution spatiale et angulaire des émissions issues de ces plasmons de surface excités par STM, ainsi qu’à leur distribution en longueurs d’onde. Dans cette thèse, nous nous sommes intéressés au fonctionnement et à l’émission de lumière sous la pointe d’un microscope à effet tunnel fonctionnant à l’air. Nous montrons que la présence d’eau adsorbée au sein de la jonction tunnel, associée à la boucle d’asservissement du STM induit un mode de fonctionnement oscillant et périodique du STM sans lequel il serait difficile d’exciter les plasmons de surface. Ensuite, nous avons montré qu’il est possible de contrôler la directivité des plasmons de surface propagatifs excités par STM en excitant localement un nanofil d’or déposé sur le film d’or. L’étude détaillée de cette directivité nous a permis de démontrer que, contrairement au cas du nanofil d’or déposé sur verre, un nanofil d’or déposé sur film d’or ne se comporte pas comme un résonateur Fabry Pérot. Nous avons proposé un modèle simple dans lequel le nanofil est assimilé à un réseau linéaire d’antennes. Ce modèle permet de rendre compte des structurations spectrales et spatiales des plasmons de surface sur le film d’or résultant de l’ajout du nanofil d’or. Puis, nous avons étudié le couplage entre des nanofibres organiques fluorescentes (structures excitoniques) et les plasmons de surface propagatifs d’un film métallique d’or ou d’argent sur lequel ces nanofibres sont déposées. Nous avons ainsi montré que (i) la fluorescence de la nanofibre peut exciter des plasmons de surface à la surface du film d’or, (ii) la nanofibre organique agit comme un guide d’onde plasmonique et (iii) qu’il est possible d’injecter des plasmons de surface propagatifs du film excités par STM dans ces modes guidés par la nanofibre. D’autre part, en étudiant la figure d’interférences dans le plan de Fourier, nous avons pu confirmer que l’émission du dipôle sous la pointe STM et les plasmons de surface propagatifs excités par STM sont cohérents, donc issus du même événement tunnel. Enfin, nous discutons les effets du couplage entre des nanocristaux semiconducteurs (quantum dots) individuels et un monofeuillet de graphène. Nous montrons que la présence du graphène réduit d’un facteur ~10 la durée de vie de l’état excité des quantum dots déposés sur graphène par rapport aux quantum dots déposés sur verre. Pour les quantum dots déposés sur graphène, il résulte de cette réduction de la durée de vie de l’état excité, une baisse de l’intensité de fluorescence et une réduction du phénomène de scintillement avec un temps de résidence dans un état brillant globalement plus long que pour les quantum dots déposés sur verre. Les différents résultats obtenus au cours de cette thèse permettent de mieux comprendre l’excitation de plasmons de surface avec un microscope à effet tunnel, le couplage entre nanostructures plasmoniques et le couplage entre une structure plasmonique et une nanostructure excitonique. Ils ouvrent des perspectives intéressantes pour le développement de nanodispositifs hybrides plus complexes liants plasmons et excitons et contrôlés électriquement / We use a scanning tunnelling microscope (STM) to excite propagating and/or localised surface plasmons on a thin metallic film (50 nm thick) made of gold or silver deposited on a glass substrate. The leakage radiation of these STM-excited propagating surface plasmons, and the light emitted by localized plasmons into the glass substrate are collected by an inverted optical microscope equipped with an oil immersion objective. Using this setup, it is possible to image both the spatial and angular distribution of the light emitted into the glass substrate on a cooled-CCD. Sending this light to a spectrometer, it is also possible to obtain the wavelength distribution of these STM-excited plasmons. In this manuscript, we discuss the different operation modes of an STM in air. We show that the thin water layers adsorbed on both the STM tip and sample, along with the STM feedback loop, may give rise to an oscillatory mode of operation. Moreover, this mode turns out to be the most efficient one for plasmon excitation with a STM in air. We then show that, when the STM tip is used to locally excite plasmons on a gold nanowire deposited on a gold film, propagating surface plasmons may be preferentially launched along the nanowire axis. Precise understanding of this directivity allows us to demonstrate that, when deposited on a gold film, gold nanowires do not behave as Fabry-Perot resonators, but may be described quite accurately with a one dimensional antenna array model. With this model, it is thereby possible to explain the complex spatial and spectral characteristics of the STM-excited plasmons on the gold film after the addition of the nanowire. Next, we focus on the coupling between fluorescent organic nanofibres (excitonic nanostructures) and propagating surface plasmons on a metallic film (either gold or silver). We show that when the nanofibres are deposited on the metallic film, (i) their fluorescence can excite propagating surface plasmon, (ii) the nanofibre can act as a plasmonic waveguide, and (iii) it is possible to inject surface plasmons propagating onto the metallic film into the guided plasmonic modes of the nanofibre. Moreover, by studying Fourier space images, we confirmed that the vertical dipole localised under the STM tip and the STM-excited propagating surface plasmons are coherent. We finally study the coupling between individual semiconducting nanocrystals (quantum dots) and a graphene monolayer deposited on a glass substrate. We show that, when deposited on graphene, the fluorescence lifetime of the quantum dots is about 10 times shorter than for the quantum dots deposited on bare glass. This leads to a weaker fluorescence signal and reduced blinking behaviour with longer time spent into a bright state. These results improve our understanding of the STM excitation of surface plasmons. They also provide information on the coupling between plasmonic nanostructures and between plasmonic and excitonic entities. in particular, these results are a promising step toward the conception and the realisation of complex electrically driven hybrid plasmonic/excitonic nanodevices

Submitted by Irene Nascimento (irene.kessia@ufpe.br) on 2016-06-28T16:52:16Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Denilson Digital.pdf: 4230195 bytes, checksum: 254e94141d3bf5cb07e451a017faacd5 (MD5) / Made available in DSpace on 2016-06-28T16:52:16Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Denilson Digital.pdf: 4230195 bytes, checksum: 254e94141d3bf5cb07e451a017faacd5 (MD5) Previous issue date: 2015-04-10 / FACEPE / A necessidade de metodologias sintéticas verdes vem aumentando significativamente nos últimos anos. O uso de materiais tóxicos e de metodologias caras vem sendo evitadas, sendo necessário o desenvolvimento de novas metodologias de síntese para Quantum Dots (QDs). Portanto, com o objetivo de baratear e diminuir a toxicidade dos QDs formados, devido à presença de agentes redutores presentes nas metodologias de síntese tradicionais, nesse trabalho foi desenvolvida uma metodologia de síntese eletroquímica para síntese de QDs de CdTe e CdSe estabilizados pelo ácido tioglicólico (TGA). A metodologia de síntese eletroquímica desenvolvida consiste na redução eletroquímica de alguns calcogênios (telúrio e selênio) em solução aquosa de NaOH 0,2 mol L-1 (pH = 13) e atmosfera inerte, para posterior reação com o precursor metálico,CdCl2/TGA. Os QDs obtidos a partir dessa metodologia apresentaram boa estabilidade e alta luminescência, com tamanhos médios de 3,9 nm para o CdTe e de 2,6 nm para o CdSe. Também foi avaliada a fluorescência dos QDs na presença do íon Hg2+, sendo observado que estas nanopartículas podem ser considerados promissores sensores químicos para determinação analítica de íons metálicos. / The demand for green synthetic methodologies has increased significantly in recent years. The use of toxic materials and expensive methodologies has been avoided, requiring the development of new methods of synthesis for Quantum Dots (QDs). Therefore, in order to cheapen and reduce the toxicity of QDs sintetizados, due to the need of reducing agents in the traditional synthetic methods, in this work we developed an electrochemical method for the synthesis of CdSe and CdTe QDs, stabilized by thioglycolic acid (TGA ). The electrochemical methodology developed involves the electrochemical reduction of some chalcogenes (tellurium and selenium) in aqueous solution (pH = 13) and inert atmosphere, for subsequent reaction with the metal precursor, CdCl2/TGA. The QDs obtained from this methodology showed good stability and high luminescence, with average sizes 3.9 nm for CdTe and 2.6 nm for CdSe. The fluorescence of the QDs in the presence of Hg2+ ion was also evaluated. It was observed that the electrochemically synthesized nanoparticles can be considered promising chemical sensors for analytical determination of metal ions.

This dissertation addresses the delicate problem of aging in complex systems characterized by non-Poissonian statistics. With reference to a generic two-states system interacting with a bath it is shown that to properly describe the evolution of such a system within the formalism of the continuous time random walk (CTRW), it has to be taken into account that, if the system is prepared at time t=0 and the observation of the system starts at a later time ta>0, the distribution of the first sojourn times in each of the two states depends on ta, the age of the system. It is shown that this aging property in the fractional derivative formalism forces to introduce a fractional index depending on time. It is shown also that, when a stationary condition exists, the Onsager regression principle is fulfilled only if the system is aged and consequently if an infinitely aged distribution for the first sojourn times is adopted in the CTRW formalism used to describe the system itself. This dissertation, as final result, shows how to extend to the non-Poisson case the Kubo Anderson (KA) lineshape theory, so as to turn it into a theoretical tool adequate to describe the time evolution of the absorption and emission spectra of CdSe quantum dots. The fluorescence emission of these single nanocrystals exhibits interesting intermittent behavior, namely, a sequence of "light on" and "light off" states, departing from Poisson statistics. Taking aging into account an exact analytical treatment is derived to calculate the spectrum. In the regime fitting experimental data this final result implies that the spectrum of the "blinking" quantum dots must age forever.

published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

Quantum dots (QDs) CdS and CdSe were synthesized in three different media including reverse micelles, aqueous solution, and trioctylphosphine oxide/trioctylphosphine (TOPO/TOP). Transmission electron microscope (TEM), X-ray diffraction (XRD), UV-VIS, fluorescence spectroscopy and microscopy were used to characterize the QDs and their nanoassemblies. CdS QDs synthesized in reverse micelles showed broad emission spectra. CdSe-CdS QDs with core shell structure synthesized in aqueous solution showed more than 30% emission quantum yield. CdSe-CdS QDs of different emission colors were prepared. CdSe and CdSe-ZnS QDs were also synthesized in TOPO/TOP media. This synthesis route produced highly luminescent CdSe QDs with over 50% emission quantum yield. The application of QDs as ions probes and methods to encapsulate QDs in nanospheres including micelles, glyconanospheres and silica nanospheres and the use of these nanospheres in bioassays are described. CdS QDs capped with different ligands such as thioglycerol, cysteine and polyphosphate showed different responses to biological relevant ions. The emission intensity of polyphosphate capped CdS QDs was affected by all the tested ions and did not show a selective response. On the other hand, the emission of thioglycerol capped CdS QDs was selectively quenched by copper ions while the emission of cysteine capped CdS QDs was selectively enhanced by zinc ions. Stern-Volmer equation was applied to correlate the emission intensity of the CdS QDs and the copper ion concentration. A Lagmuir isotherm binding equation was used to describe the relation between the emission intensity of cysteine capped CdS QDs and zinc ion concentration. The possible mechanism to explain the effects of capping ligands on CdS QDs responses to ions is also discussed. CdSe QDs synthesized in TOPO/TOP media were encapsulated in nanospheres for bioassay applications. The glyconanospheres contained a large number of glucose residues on their surface and showed high binding activity towards the lectinic protein Concanavalin A (Con A). Silica nanospheres containing hundreds of CdSe QDs were functionalized with thiol groups to enable the conjugation of streptavidin to the nanospheres. The streptavidin modified silica nanospheres were used as luminescent indicators in a sandwich immunoassay for the detection of antiprotein A antibody. The advantages and disadvantages of the nanospheres based bioassay are discussed.

Thesis advisor: Torsten Fiebig / This dissertation examines the chemistry and photophysics of semiconductor quantum dots with the intent of studying their capabilities and limitations as they pertain to photovoltaic technologies. Specifically, experiments are presented detailing the first time-resolved measurements of electron transfer in electronically coupled quantum rods. Electron transfer from the conduction band of CdTe was measured to occur on the 400 fs timescale (<italic>k_ET</italic> = 2.5 x 10<super>12</super> s<super>-1</super>), more than 500x faster than previously believed. Additionally, the direct optical promotion of an electron from the valence band of CdTe was observed, occurring on the timescale of the pump pulse (~50 fs). Based on the determined injection rates, a carrier separation efficiency of > 90% has been calculated suggesting these materials are sufficient for use in solar energy capture applications where efficient carrier separation is critical. To this end, model photovoltaic cells were fabricated, and their power conversion efficiency and photon-to-current generation efficiency characterized. In devices based of CdSe and heteromaterial quantum rods we observed fill-factors on the order of 10-20% though with power conversion efficiencies of < 0.02%. It was discovered that using a high temperature annealing step, while critical to get electrochemically stable photoelectrodes, was detrimental to quantum confinement effects and likely removed any hQR specific capabilities. Additionally, a detailed study on the role of nucleotide triphosphate chemistry in stabilizing emissive CdS nanoparticles is presented. Specifically it was observed that in a neutral pH environment, GTP selectively stabilizes CdS quantum dots with diameters of ~4 nm while the other naturally occurring ribonucleotides do not yield emissive product. The selectivity is dependent on the presence of the nucleophilic N-7 electrons near a triphosphate pocket for Cd<super>2+</super> complexation as well as an exocyclic amine to stabilize the resulting product particles. However, in an elevated pH environment, the nucleobase specificity is relaxed and all NTPs yield photo-emissive quantum dots with PLQEs as high as 10%. / Thesis (PhD) — Boston College, 2009. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.