Characterization of catalytically active solid-liquid interfaces by scanning electrochemical microscopy (SECM) [Elektronische Ressource] = Charakterisierung von katalytisch aktiven Fest-flüssig-Grenzflächen unter Nutzung des elektrochemischen Rastermikroskops (SECM) / von Carolina Nunes Kirchner

Carolina Nunes Kirchner

Informations

• Publié par: carl_von_ossietzky_universitat_oldenburg
• Publié le: 01 janvier 2008
• Nombre de lectures: 40
• Langue: English
• Poids de l'ouvrage: 7 Mo

Extrait

Characterization of Catalytically Active Solid-Liquid
Interfaces by Scanning Electrochemical Microscopy
(SECM)
(Charakterisierung von katalytisch aktiven fest-flüssig-Grenzflächen unter
Nutzung des elektrochemischen Rastermikroskops (SECM))


Von der Fakultät für Mathematik und Naturwissenschaften
der Carl von Ossietzky Universität Oldenburg
zur Erlangung des Grades und Titels einer

Doktorin der Naturwissenschaften (Dr. rer. nat.)

angenommene Dissertation

von Frau Chem. Ing.
Carolina Nunes Kirchner

geboren am 01.04.1979
in São Paulo, Brasilien

Oldenburg, November 2008
This work was carried out from September 2003 to July 2008 at the Carl von Ossietzky
University of Oldenburg, Faculty of Mathematics and Science, Center of Interface Science
(CIS), Department of Pure and Applied Chemistry and Institute of Chemistry and Biology of
the Marine Environment under the guidance of Prof. Dr. Gunther Wittstock.
Part of this work has been published and is cited as [A#]. The list of own cited work is given
after the Bibliography.























Gutachter: Prof. Dr. Gunther Wittstock
Zweitgutachterin: Prof. Dr. Katharina Al-Shamery
Tag der Disputation: 14. November 2008
Acknowledgements
First and foremost, I would like to thank my advisor Prof. Dr. Gunther Wittstock.
Without his guidance, great ideas and support, this dissertation would not have been possible.
I am indebted to him not only for what he has taught me technically, but also for believing in
me, it motivated me to complete this thesis. I am especially grateful for his patience and
advice when progress was difficult.
I would like to thank all my former and current colleagues in our group, specially Malte
Burchardt, Dr. Yan Shen and Dr. Jatin Sinha for their active cooperation. I would like to thank
Markus Träuble for providing me the simulations and for his patience. I would also
acknowledge my former colleague Dr. Chuan Zhao for introducing me to the SECM. I am
very grateful to Sascha Pust for invaluable help through several discussions and of course, his
"computer help" and for correcting the manuscript. I would like to express my deepest thanks
to Prof. Dr. Sabine Szunerits from LEPMI for the exciting cooperation and enthusiasm for the
results. I would like to thank Dr. Karl Heinz Hallmeier from University of Leipzig for the
XPS measurement. My deepest thanks are also to Mr. Folkert Roelfs and Mr. Harry Happatz
from the University of Oldenburg who helped me with SECM construction. Especially, I
would like to acknowledge Carl von Ossietzky Universität Oldenburg for financial support.
I would like to thank Elke and Dora Schwetje who helped me a lot at the beginning of
my stay in Germany (without you I would not be here). I would thank my parents in law
Eckart Kirchner and Maria Apke for the immense help and for always being there. I cannot
forget to thank all my friends from Oldenburg that made my life more colorful throughout
these years, specially Anne, Jörn, Anna and Tolga. I would like to express my sincere
gratitude to Thais and Carlos for their constant support and friendship.
I would like to thank all of my family and friends in São Paulo, without their emotional
support it would be impossible to have the peace of mind to work away from home. I would
like to express my gratitude especially to my sisters Nathalia and Gabriela, to my
brother-in-law Caio, and my dear nephew Arthur. I would like to thank my parents, João and
Iara, who have provided love and support to me for my life and school career. They have been
my strongest supporting foundation and my biggest fans through everything. I am forever
indebted to them for all they have done for me and for making me who I am. Last but not
least, I would like to thank Thomas who makes me laugh everyday, for his continuous
support, patience, friendship, and love.













Aos meus pais Iara e João,
e ao meu marido Thomas
Abstract
The development and optimization of biosensor components with respect to sensitivity,
biospecificity, response time, reliability and costs has been the object of research for many years.
Scanning electrochemical microscopy (SECM) has been used in this context to analyze the functional
properties of sensor components, mainly in a qualitative or comparative way. This thesis deals with
the quantitative characterization of such materials and active layers using SECM. The results were are
compared to theoretical models and corroborated with other electrochemical techniques.
The SECM feedback mode has been used to analyze new electrode materials and insulating
cover materials. Titanium nitride thin film electrodes have been analyzed regarding their suitability as
electrode material that offers access to nanostructured transducers. It was shown that enhanced surface
area, cover layers from contaminations or surface oxidation have a large influence on the charging
currents and the electron transfer rate. Silicon dioxide (SiOx) layers were investigated as insulating
coatings. The insulation properties of gas-phase-deposited SiOx varied with film thickness. The
electrochemical characterization of SiOx layers showed only electrochemical activity for 6.5 nm
thickness due to presence of pinholes, while thicker layers showed a very good insulating
characteristic.
Many electrochemical biosensors, but also biofuel cells show a very complicated interplay of
intrinsic chemical kinetics of the materials and various mass-transport limitation. These relations were
investigated using model systems agglomerates of paramagnetic microbeads that were coated with the
enzyme β-galactosidase. By variation of the ratio between modified and unmodified beads, the size of
the bead agglomerates and the solution composition, the internal and external diffusion of reagents and
products was varied independently and product fluxes were measured by the generation-collection
mode of SECM. The fluxes could be compared to the results of digital simulations. The analysis of the
external diffusion demonstrated that there was enough substrate to diffuse within the agglomerate. The
apparent Michaelis-Menten constant extracted from the SECM measurements has been compared with
a digital simulation and showed that the model used to analyze the SECM is a good approximation for
quantification of spot systems. Relating this flux to the number of enzyme-modified beads in the
agglomerate gave quantitative results on the shielding of mass transport by bare beads in agreement
with numerical models.
SECM in the generator-collector configuration has been used to determine the surface
concentration of accessible oligonucleotides (ODN) bound to microelectrochemically deposited
polypyrrole. The ODN strands were hybridized with an enzyme-labeled ODN strand. The
measurements were calibrated using bead-immobilized enzymes. Feedback effects as possible
interference were investigated and showed to become insignificant at distances larger than 3
microelectrode radii. A SECM image of the ODN pattern has been recorded, providing the amount of
ODN that were available for hybridization in such systems.
Zusammenfassung
Die Entwicklung von Biosensorkomponenten in Bezug auf Sensitivität, Biospezifität,
Antwortverhalten, Zuverlässigkeit und Kosten ist seit vielen Jahren Gegenstand der Forschung. Die
elektrochemische Rastermikroskopie (SECM) wurde in diesem Zusammenhang genutzt, um die
funktionellen Eigenschaften von Sensorkomponenten hauptsächlich in qualitativer oder vergleichender
Hinsicht zu untersuchen. Diese Arbeit beschäftigt sich mit der quantitativen Charakterisierung solcher
Materialien und aktiver Schichten mit der SECM. Die Resultate werden mit theoretischen Modellen
verglichen und durch Ergebnisse anderer elektrochemischer Messverfahren gestützt.
Der SECM-Feedback-Modus wurde eingesetzt, um neue Elektrodenmaterialien und isolierende
Deckschichten zu untersuchen. Titannitrid-Dünnschichtenelektroden wurden auf ihre mögliche
Eignung als Elektrodenmaterial untersucht, das einen Zugang zu nanostrukturierten Transducern
ermöglicht. Es wurde nachgewiesen, dass eine vergrößerte Oberfläche und Deckschichten aus
Kontaminationen oder Oberflächenoxidation einen großen Einfluss auf die Ladeströme und die
Elektronentransfergeschwindigkeit haben. Siliziumdioxid (SiO )-Schichten wurden als isolierende x
Beschichtungen untersucht. Die isolierenden Eigenschaften von gasphasenabgeschiedenem SiO x
variierte mit der Schichtdicke. Die elektrochemische Charakterisierung der SiO -Schichten zeigte x
elektrochemische Aktivitäten nur für Schichten von 6.5 nm Dicke, die auf die Gegenwart von kleinen
Kanälen (pinholes) zurückzuführen ist. Dickere Schichten zeigte gute isolierende Eigenschaften unter
elektrochemischen Bedingungen.
Viele elektrochemische Biosensoren, aber auch Biobrennstoffzellen zeigen ein sehr