Diazonium-based anchoring of PEDOT on Pt/Ir electrodes via diazonium chemistry

Conducting polymers, specifically poly (3,4-ethylenedioxythiophene) (PEDOT), have recently been coated onto Pt/Ir electrodes intended for neural applications, such as deep brain stimulation (DBS). This modification reduces impedance, increases biocompatibility, and increases electrochemically active surface area. However, direct electropolymerization of PEDOT onto a metallic surface results in physically adsorbed films that suffer from poor adhesion, precluding their use in applications requiring in vivo functionality (i.e. DBS treatment). In this work, we propose a new attachment strategy, whereby PEDOT is covalently attached to an electrode surface through an intermediate phenylthiophene layer, deposited by electrochemical reduction of a diazonium salt. Our electrodes retain their electrochemical performance after more than 1000 redox cycles, whereas physically adsorbed films begin to delaminate after only 40 cycles. Additionally, covalently attached PEDOT maintained strong adhesion even after 10 minutes of ultrasonication (vs. 10 s for physically adsorbed films), confirming its suitability for long-term implantation in the brain. The simple two-step covalent attachment strategy proposed here is particularly useful for neural applications and could also be adapted to introduce other functionalities on the conducting surface

Investigation of live cell processes using scanning electrochemical microscopy

This thesis presents an electrochemical approach for the non-invasive study of biological systems, and demonstrates the usefulness of scanning electrochemical microscopy (SECM) for quantification of chemical flux in live cells. We first explore the presence of D-serine within the brain. This neurotransmitter plays an important role in proper brain development, and has also been linked to several pathological diseases such as schizophrenia and Alzheimer's disease. Consequently, quantification of local changes in D-serine concentration is essential to further understanding of its role in these processes. A biosensor was thus developed for the detection of D-serine with high sensitivity. Using this microscale biosensor, the release of endogenous D-serine was measured in vivo inside the brain of Xenopus laevis tadpoles, revealing an overall concentration of 2.5 µM. However, the primary site and mechanism of release of D-serine remained unclear, requiring a more localized measurement. After optimizing for improved response time and selectivity, the biosensor was used in a SECM configuration to measure localized release of D-serine from a model system. This SECM methodology provided quantitative imaging of D-serine with high spatial resolution, and could be useful to investigate chemical flux in other biological samples. We then shifted our focus to quantitative imaging of another complex live cell process, specifically multidrug resistance. This defensive mechanism allows cancer cells to pump out chemotherapeutic drugs before they can kill the cell, severely impeding treatment success. Most investigations of transmembrane efflux pumps, including multidrug resistance-associated protein 1 (MRP1), focus on expression to determine their effect in specific cancer types. Researchers have been unable to establish a clear correlation between expression and patient survival. However, the relationship between transporter expression and functional activity is often overlooked. Using SECM with complementary redox mediators and novel cell patterning substrates, we measured MRP1 functional activity in single cancer cells. By challenging parental cell lines with doxorubicin, a drug used in many chemotherapy regimens, we produced six cell populations with increasing MRP1 expression, and measured their concurrent functional activity. This comparative study revealed that in fact MRP1 expression and functional activity do not correlate, and suggest that the measurement of functional activity should be prioritized to identify the effect of MRP1 on chemotherapy treatment success.Cette thèse présente une approche électrochimique pour l'étude non-invasive des systèmes biologiques, et démontre l'utilité de la microscopie électrochimique à balayage (SECM) pour la quantification du flux chimique dans les cellules vivantes.Nous commençons en explorant la présence de la D-serine dans le cerveau. Ce neurotransmetteur joue un rôle important dans le développement du cerveau et est aussi lié à plusieurs maladies pathologiques telles que la schizophrénie et la maladie d'Alzheimer. La quantification des changements locaux de la D-serine est essentielle pour mieux comprendre son rôle dans ces processus. Ainsi, un biosenseur a été développé pour détecter la D-serine avec une haute sensibilité. Le relâchement de la D-serine a été mesuré in vivo dans le cerveau d'un têtard, démontrant une concentration générale de 2.5 µM. Cependant, le point d'origine et le mécanisme de relâchement ne sont pas bien définis, nécessitant une mesure beaucoup plus localisée. Après une optimisation pour améliorer le temps de réponse et la sélectivité, le biosenseur a été utilisé avec une configuration SECM pour mesurer le relâchement de la D-serine d'un système modèle. Cette méthodologie SECM a fourni une quantification de la D-serine avec une haute résolution spatiale, et peut être utile pour investiguer le flux chimique dans d'autres échantillons biologiques. Nous avons ensuite concentré nos efforts sur la quantification de la résistance multidrogue, un processus cellulaire qui permet aux cellules cancéreuses d'expulser les drogues chimiothérapeutiques avant qu'elles puissent les tuer, ce qui diminue sévèrement le succès du traitement. La plupart des investigations sur les protéines transmembranaires, incluant la protéine associée à la résistance multidrogue (MRP1), se concentre sur l'expression pour déterminer leurs effets dans des cancers spécifiques. Les chercheurs ont été incapables d'établir une corrélation claire entre l'expression et le succès des traitements chimiothérapeutiques. Cependant, la relation entre l'expression et l'activité fonctionnelle est souvent négligée. En utilisant la SECM et des nouveaux substrats pour adhérences sélectives des cellules, l'activité fonctionnelle de la MRP1 a été mesurée dans des cellules cancéreuses individuelles. En traitant des lignées cellulaires parentales avec de la doxorubicine, une drogue utilisée dans plusieurs traitements chimiothérapeutiques, nous avons produit six populations cellulaires avec une expression croissante et déterminé leur activité fonctionnelle concurrente. Cette étude comparative a démontré que l'expression et l'activité fonctionnelle n'ont pas de corrélation directe, et suggère que la détermination de l'activité fonctionnelle devrait être priorisée pour identifier l'effet de la MRP1 sur le succès des traitements chimiothérapeutiques

Flow Analysis in a Radial Flow Fixed Bed Reactor

When designing radial flow fixed bed reactors, one of the most prevalent design tasks is ensuring proper distribution through the catalyst bed. Utilizing Comsol Multiphysics, a 2-D axis symmetric model was tested to evaluate the level of maldistribution of flow through the catalyst bed. Specifically, the effects of flow direction, catalyst size, overall and variable screen resistance, and the total amount of flow through the reactor. Maldistribution findings were based on a velocity profile through the catalyst bed

Localized detection of d-serine by using an enzymatic amperometric biosensor and scanning electrochemical microscopy

d-Serine acts as an endogenous co-agonist for N-methyl-d-aspartate receptors at synapses, making it essential for proper brain development and function. This amino acid has also been linked to several neurodegenerative diseases such as Alzheimer's disease and dementia. Nevertheless, the primary site and mechanism of d-serine release remains unclear. We recently demonstrated the use of an enzymatic amperometric biosensor for the in vivo quantification of endogenous d-serine release in Xenopus laevis tadpoles. Herein, we investigate the effect of the permselective poly(meta-phenylenediamine) electropolymerization conditions on the biosensor's response time and selectivity. Scanning electrochemical microscopy (SECM) is then used with the optimized biosensor to measure localized release of d-serine from a model system. This SECM methodology, which provides high spatial and temporal resolution, could be useful to investigate the primary site and mechanism of d-serine release in other biological samples

<i>(Invited)</i> Detection of D-serine using an enzymatic amperometric biosensor and its localized detection using scanning electrochemical microscopy

D-Serine acts as an endogenous co-agonist for N-methyl-D-aspartate receptors at synapses, making it essential for proper brain development and function. This amino acid has also been linked to several neurodegenerative diseases such as Alzheimer's disease and dementia. Nevertheless, the primary site and mechanism of D-serine release remains unclear. We recently demonstrated the use of an enzymatic amperometric biosensor for the in vivo quantification of endogenous D-serine release in Xenopus laevis tadpoles. We also investigate the effect of the permselective polymer layer thickness on the biosensor's response time and selectivity. Finally, scanning electrochemical microscopy (SECM) is then used with the optimized biosensor to measure localized release of D-serine from a model system. This SECM methodology, which provides high spatial and temporal resolution, could be useful to investigate the primary site and mechanism of D-serine release in other biological samples

Master of Arms

This project studied the Higgins Armory Museum’s copy of the martial arts treatise The Art of Combat, written by Joachim Meyer in 1570. The team researched the author’s life and times, and studied the longsword, rapier, halberd, and other weapons from the treatise to understand their history and their use in Meyer’s time. The outcome was an instructional video and documentary to accompany the artifact and to enrich the Armory’s historic combat classes