Over the last century, despite enormous advancements in biomedical research and the development of sophisticated analytical instruments many diseases continue to be a burden on humankind particularly on the aged. This is because of a lack of complete understanding of the pathogenesis and specific therapies. Due to the complexity involved, we need to explore all facets of diagnosis and therapies. Therefore, there is a requirement for different strategies to combat these diseases. A quick diagnosis is the primary step towards improving treatment and increasing the chance of survival. To realize this goal we entail to monitor multiple biomarkers which will also help us to understand the progression of disease. Mid-Infrared (MIR) and Raman spectroscopic techniques are well established analytical methods to understand the molecular structure and chemical composition of heterogeneous systems. These techniques are rapid, non-destructive and offer multiple component analysis (global/multiplex) in a single measurement without any labels. Importantly, biological materials like proteins, carbohydrates, lipids, nucleic acids etc. have unique structures and therefore we can obtain unique spectral fingerprints of these molecules in different physiological and pathological conditions. This will provide a potential route to obtain diagnostic markers for diseases. Also, to improve the ability to diagnose and treat human diseases much more efficiently, understanding the mechanisms involved in the progression of disease is necessary. It would be time consuming and often unethical to perform these studies directly on humans. Therefore, there is a need for model organisms to explore the complexity of various diseases. A model organism is an animal, plant or microbe that is being studied to understand a range of biological phenomena. They should meet certain criteria such as short life cycles, easy to breed and maintain in large numbers under laboratory conditions, and the data generated through use of the model should be applicable to other higher organisms like humans. The microbial system, mouse, rat, Drosophila (fruitfly), C Elegans (nematode worm) and zebrafish are being used extensively for this purpose. The most adaptable organisms to study diseases in humans are the mice as they share almost 99% of their genes with humans. Mice are similar to humans in most physiological and pathological features such as nervous, cardiovascular, immune, liver etc. In addition to mice, Drosophila melanogaster (fruitfly) has been used for years as an attractive model organism to understand the mechanisms of underlying human diseases. This is because 75% of human disease genes have counterparts in Drosophila and it meets the above mentioned criteria to be a model organism. It also plays an important role for studying genetics and development biology. The average life span of Drosophila is 60-80 days; therefore it is a suitable model to study age related diseases. In the present thesis, the ability to probe low-micrometer domains using Raman and Fourier Transform Infrared (FTIR) microspectroscopy was utilized to monitor the chemical changes during various biomedical conditions using model systems. Chapter 1 of the thesis discusses about the origin of Raman and FTIR microspectroscopy along with instrumentation and applications. Various data analysis methods (both univariate & multivariate) and the validation criterion are described in chapter 2. Depending on the objective of the study and based on the technique (Raman or FTIR) used, one (or more) of these methods can be applied for effective interpretation of the data. Further, the thesis includes four different investigations; a) the FTIR spectroscopic study of hepatotoxicity due to acetaminophen using mice as model, b) the Raman spectroscopic studies of muscle-related disorders using Drosophila as a model, c) Vibrational spectroscopic study of septic shock using mice as model, d) Surface Enhanced Raman Spectroscopy (SERS) study of serum components using Lab-on-a-chip (LOC). The first part comprises mainly the FTIR microspectroscopy study of hepatotoxicity in mice post oral dosing of acetaminophen (paracetamol), which is extensively used worldwide as an analgesic and antipyretic drug (chapter 3). The infrared spectra of acetaminophen treated livers in BALB/c mice show a decrease in glycogen and an increase in amounts of cholesteryl esters and DNA. Importantly, analysis of sera identified the lowering of glycogen and increase in DNA and chlolesteryl esters earlier than the increase in alanine aminotransferase, which is routinely used to diagnose liver damage. Similar changes are also observed in C57BL/6 and Nos2−/− mice. Revert experiments using an antidote (L-methionine) demonstrate that depletion in glycogen and increase in DNA are abrogated with pre-treatment, but not post-treatment, with L-methionine. In the second study Raman spectroscopy is applied to discriminate between various muscle defects in Drosophila, since it can provide a unique molecular fingerprint of tissues on the basis of their biochemical composition (chapter 4). Raman spectra were collected from Indirect Flight Muscles (IFM) of mutants upheld1 (up1), heldup2 (hdp2), Myosin heavy chain7 (Mhc7), Actin88FKM88 (Act88FKM88), upheld101 (up101) and Canton-S (CS) for both 2 and 12-days old flies. The difference spectra (mutant minus CS) of all mutants have shown an increase in nucleic acids (DNA/RNA) content along with an increase in β-sheet and/or random coil content at the expense of α-helix. Interestingly, 12th day sample of up1 & Act88FKM88 exhibit significantly higher levels of glycogen and carotenoids than CS. A Principal Components based Linear Discriminant Analysis (PC-LDA) classification model was developed, which classifies the mutants according to their pathophysiology and yielded overall accuracy (OA) of 97% and 93% for 2 and 12-days old flies respectively. up1 & Act88FKM88 (nemaline myopathy phenotypes) form a group which is clearly separated in a Linear Discriminant (LD) Plane from up101 & hdp2 (cardiomyopathy phenotypes). In the third part we investigated septic shock, a life threatening condition associated with multiple organ dysfunctions, in mice (chapter 5). Salmonella typhimurium were given to BALB/c and 129/SvJ mice via the intraperitoneal route to induce infection. Liver, spleen and sera samples were studied using FTIR microspectroscopy. The infrared spectra of liver, spleen and serum samples in BALB/c (Nramp1-deficient) mice show significant spectral changes as early as 1 hour post infection but spleen shows changes only after 6 hour. Interestingly, 129/SvJ (Nramp1-sufficient) mice were resistant to sepsis and show significant spectral changes only at 12 hour post infection. This study demonstrates that suppression of Nramp-1, a renowned gene known to control susceptibility to infections by intracellular bacteria can be an effective cure for sepsis. The final study presented in this thesis demonstrates the use and benefits of lab-on-a-chip (LOC) devices in surface enhanced Raman spectroscopy (SERS) which is used to enhance the weak Raman signals (chapter 6). Most of the diseases have related proteins or analytes present in serum although in early stages their concentration in blood are low. The idea is to detect at low concentration using SERS the serum components which are related to progression of disease. Here, we have compared the effect of different aggregating agents on silver colloids and the resulting enhancement in Raman signals for tryptophan and Bovine Serum Albumin (BSA). Reproducibility issues, the key concern of static phase SERS, can be overcome by performing SERS spectroscopic measurements in automated flow cells. Further, pyridine and tryptophan were used to demonstrate SERS in a segmented flow system. The spectra from different drops were compared and demonstrate the high reproducibility in comparision to static SERS. Lastly, chapter 7 summarizes the entire work of the present thesis with future prospects of Raman and FTIR microspectroscopy to study the progression mechanism of various diseases like neurodegenerative diseases which is easy to follow in drosophila due to their short life span. Also, technological developments in the field of nanotechnology and micro-fluidics will enable the detection of early biochemical changes in bodily fluids such as urine, cerebral spinal fluid, tears etc. Building on the results demonstrated in this thesis, hopefully label-free vibrational (Raman and FTIR) microspectroscopic studies using model organisms would help in understanding the underlying mechanisms of progression of various other diseases which in turn would facilitate the development of effective therapies.

Raman optical activity (ROA) is a powerful probe of the structure and behaviour of biomolecules in aqueous solution for a number of important problems in molecular biology. Although ROA is a very sensitive technique for studying biological samples, it is a very weak effect and the conditions of high concentration and long data collection time required limit its application for a wide range of biological samples. These limitations could possibly be overcome using the principle of surface enhanced Raman scattering (SERS). The combination of ROA with SERS in the form of surface enhanced ROA (SEROA) could be a solution for widening the application of ROA. In the last few years, the generation of reliable SEROA spectra of biomolecules has been problematic due to non-homogenous colloidal systems forming and low signal-to-noise ratios which complicated detection of the true SEROA signal from the analyte. L- and D-enantiomers give full or partially mirror image chiroptical spectra, this property of enantiomers can be employed to prove the chiroptical activity of the SEROA technique. In this thesis we employed a hydrophilic polycarbopol polymer as stabilising media which has led to the first report of mirror image SEROA bands for enantiomeric structures. This new technique of incorporating the hydrogel polymer as a means to stabilise the colloidal system has proven to be reliable in obtaining high quality SEROA spectra of D- and L-enantiomers of ribose and tryptophan. In an extension of the hydrogel-stabilised SEROA work, we also demonstrate that single nanoparticle plasmonic substrate such as silver silica nanotags can enhance the weak ROA effect. These dye tagged silica coated silver nanoparticles have enabled a chiral response to be transmitted from a chiral analyte to the plasmon resonance of an achiral metallic nanostructure. The measurement of mirror image SERROA bands for the two enantiomers of each of ribose and tryptophan was confirmed for this system. The generation of SEROA for both systems was achieved and confirmed SEROA as a new sensitive tool for analysis of biomolecular structure. In a related project, Raman and ROA spectra were measured for adenosine and seven of its derivative ribonucleotides. Both of these spectroscopic techniques are shown to be sensitive to the site and degree of phosphorylation, with a considerable number of marker bands being identified for these ribonucleotides. Moreover, the SERS studies of these ribonucleotides were also performed. The obtained SERS spectra were shown similar features that confirm these analytes interact with the surface in a similar manner, hence limiting the structural sensitivity of this method towards phosphate position. Short dipeptides such as diketopiperazine (DKP) have been investigated during the last decades as both natural and synthetic DKPs have a wide variety of biological activities. Raman and ROA spectra of linear and cyclic dialanine and diserine were measured to charecterize their solution structures. Density functional theory (DFT) calculations were carried out by a collaborator to assist in making vibrational band assignments. Considerable differences were observed between the ROA bands for the cyclic and linear forms of both dialanine and diserine that reflect large differences in the vibrational modes of the polypeptide backbone upon cyclicization. In this study, the ROA spectra of cyclic dialanine and diserine have been reported for the first time which demonstrated that ROA spectroscopy when utilised in combination with computational modelling clearly provides a potential tool for characterization of cyclic peptides.

Nanoscience dominates almost all areas of science and technology in the 21st century. Nanoparticles are of fundamental interest since they possess unique size dependent properties (optical, electrical, mechanical, chemical, magnetic etc.), which are quite different from the bulk and the atomic state. The research work presented in the thesis is on the preparation, characterization and studies on Ir, Os and graphene oxide-based systems. Interconnected Ir and Os nanochains are prepared under environmentally friendly conditions in aqueous media and subsequently used as substrates for surface enhanced Raman scaterring studies and also as electrocatalysts for oxygen reduction and formaldehyde oxidation. Ir and IrOx nanostructures are prepared using borohydride at different temperatures. The nature of interaction of heme proteins with IrOx is studied using spectroscopic techniques. Electrochemical studies on reduced graphene oxide include sensing of biomolecules with high sensitivity and oxygen reduction reaction (ORR) in aqueous alkaline medium. rGO is also used as support for anchoring Ir nanoparticles and the catalyst is used for the oxidation of benzyl amines to corresponding imines. The thesis is divided in to seven chapters and details are given below. Chapter 1 gives an introduction about the synthetic strategies and properties of metal nanostructures. This is followed by literature survey on Ir, Os and graphene oxide-based systems relevant to the present study. Aim and scope of the present investigation is given at the end. Chapter 2 discusses the experimental procedures and characterization techniques used in the present study. Chapter 3 involves the preparation, characterization and studies on interconnected Ir nanochains. Assemblies of small sized nanoparticles forming network-like structures have attracted enormous interest and different metal nanoassemblies have been reported using different procedures. Ir3+ reduction is kinetically not a very favourable process and hence there are not many attempts to synthesize Ir-based nanostructures. Assemblies of interconnected Ir nanoparticles have been synthesized in the present studies using borohydride as reducing agent and ascorbic acid as capping agent, at high temperatures. Polyfunctional capping molecules such as ascorbic acid and vitamin P play important role for the formation of network- like Ir nanostructures. Optical properties of the networks are probed using UV-Vis spectroscopy and evolution of coupled plasmon of Ir nanochains at 418 nm (figure 1) is observed. The nanochains are used as substrates for SERS studies while the catalytic activity is followed for the reduction of nitroaromatics. Electrocatalytic activity of Ir nanochains is exemplified using oxygen reduction and formaldehyde oxidation. Ir nanochains show better electrocatalytic activities than nanoparticles as shown in figure 2. Figure 1. Time dependent UV-Vis absorption spectra of Ir nanoparticles recorded at various time intervals of (a) 5; (b) 15; (c) 30 and (d) 60 minutes of reduction of Ir3+ using borohydride and the corresponding TEM images. Figure 2. Polarization curves for oxygen reduction on (i) Ir nanochains and (ii) Ir nanoparticles in (A) 0.5 M H2SO4 and (B) 0.1 M KOH at a scan rate of 0.005 V/s. Rotation speed used is 1000 rpm. Chapter 4 discusses the preparation of Ir and IrOx using borohydride. The reaction temperature determines the product. Various physicochemical, microscopic and spectroscopic techniques have been used to understand the evolution of nanostructures. Borohydride reduces Ir3+ at high temperatures to form high surface area foams, while at 25oC, it results in an alkaline environment that helps in the hydrolysis of the Ir precursor to form IrOx nanoparticles. Porous IrOx is formed when Ir foams are annealed at high temperatures. Water oxidation has been demonstrated using IrOx nanoparticles and foams. Biocompatibility of IrOx is used to study the nature of interaction of heme proteins and the formation of bioconjugates using spectroscopic techniques. IrOx forms bioconjugates with substantial changes observed in secondary and tertiary structures of proteins. Chapter 5 explores the synthesis of interconnected ultrafine Os nanoclusters and the nanostructured materials are used as SERS substrates. Os nanochains are prepared under environmentally friendly conditions using polyfunctional molecules like ascorbic acid and vitamin P as both reducing agent and capping agent in aqueous media. Small sized (1-1.5 nm) Os nanoparticles spontaneously self-assemble to form clusters of few tens of nm that in turn self-organize to form branched nanochains of several microns in size. The as-formed nanochains show surface plasmon absorption in the visible region 540 nm which make them active substrates for surface enhanced Raman scattering (SERS) studies. High SERS activity is observed for fluorescent analyte, rhodamine 6G and non-fluorescent analyte, mercaptopyridine, with different laser excitation sources. Efficient energy transfer from fluorescent R6G dye to Os nanochains is observed based on steady state and time resolved fluorescence measurements.Figure 3. (I) Time dependent UV-Vis absorption spectra of Os nanochains recorded at different time intervals of (a) 5; (b) 7; (c) 15; (d) 30 and (e) 60 minutes. Inset shows the TEM images of Os nanochains after 60 minutes of reduction. (II) SERS spectra of 4-MPy adsorbed on Os nanochains from (a) 1 mM; (b) 10 µM and (c) 1 µM solutions using 514 nm laser excitation. Chapter 6 discusses the studies based on reduced graphene oxide. Reduced graphene oxide (rGO) is explored as electrodes for simultaneous determination of dopamine (DA), ascorbic acid (AA) and uric acid (UA) at low concentrations useful in medical diagnostics (figure 4A). It is also used as metal-free electrocatalyst for ORR (figure 4B). The use of rGO as a support for anchoring Ir nanoparticles is probed and subsequently the Ir/rGO is used as catalyst for direct aerobic oxidation of benzyl amine derivatives to corresponding imines. Chapter 7 describes the summary of the work and scope for further studies. Appendix 1 discusses the preparation of different Ir nanostructures using simple galvanic displacement reaction on copper foil while appendix 2 describes the preparation of different sized Ir nanoparticles and their electrocatalytic activity towards oxygen reduction reaction

Ce travail présente une méthode originale de détection et de quantification, sans étape de marquage, de la proportion de bases libres contenues dans des acides nucléiques. La spectrométrie de diffusion Raman exaltée de surface (DRES ou SERS en anglais) nous a permis d’obtenir la signature spectrale spécifique des nucléotides caractéristiques des ARN (adénosine, cytosine, guanosine et uridine), en utilisant des colloïdes d’argent comme substrat-DRES et des ajouts de MgCl2 comme agent d’agrégation. Les conditions de détection ont été optimisées pour établir un protocole de quantification de la proportion des nucléobases non-appariées par spectrométrie DRES. Les limites de détection obtenues sont de l’ordre de quelques dizaines de picomoles. L’amélioration de la reproductibilité des mesures par spectrométrie DRES passe par le contrôle précis des temps de réaction (adsorption et agrégation), qui peut être contrôlé grâce à l’utilisation de plateformes microfluidiques adaptées. Nous avons mis en œuvre deux types de plateformes microfluidiques, l’une basée sur des écoulements monophasiques et l’autre sur la génération de gouttes. Les espèces à analyser sont contenus dans les gouttes, permettant la détection in situ par spectrométrie DRES des divers nucléotides. / This work deals with the development of an original label-free method for free bases proportions detection and quantification of nucleic acids. The surface enhanced Raman spectroscopy (SERS) allowed obtaining the specific spectral signature of characteristic nucleotides of RNA (adenosine, cytosine, guanosine and uridine), using silver colloids as SERS substrate and MgCl2 addition as aggregating agent. Then, the condition detection have optimizing to establish a label-free quantification protocol of free nucleobases proportion by SERS spectroscopy. The detection limits obtained are order of few picomoles. The reproducibility improvement of SERS detection requires the precise control of time reaction (adsorption and aggregation), which could be control thanks to microfluidic chips use. We have implemented two different microfluidic chips, one based on single-phase flows and one other based on droplets generation. The analyzed species are containing in droplets, allowing in situ detection by spectroscopy SERS of various nucleotides.

Die Charakterisierung der Protein-Nanopartikel-Wechselwirkungen in komplexen biomolekularen Systemen wie einer lebenden Zelle ist für die Pharma-, Medizin- und Umweltforschung von entscheidender Bedeutung. In solchen biomolekularen Systemen adsorbieren Proteine leicht auf der Oberfläche von Nanopartikeln, die die Proteinkorona bilden. Diese Arbeit konzentriert sich auf die Charakterisierung der Proteinkorona in lebenden Zellen, wobei verschiedene analytische Ansätze kombiniert werden. Experimente mit oberflächenverstärkter Raman-Streuung (SERS) an reinen Proteinlösungen zeigten die Konzentrationsabhängigkeit der Protein-Gold-Nanopartikel-Wechselwirkungen, die zu unterschiedlichen SERS-Spektren führten und ermöglichten die Bestimmung von Proteinsegmenten, die an Citrat-stabilisierte Gold-Nanopartikel binden. In SERS-Experimenten mit lebenden Zellen wurde die Anwesenheit von Proteinfragmenten in der innersten Schicht der Proteinkorona, die als harte Proteinkorona bezeichnet wird, festgestellt. Eine analytische Methode, die Natriumdodecylsulfat-Polyacrylamid-Gelelektrophorese und Hochleistungs-Flüssigchromatographie-gekoppelte Elektrospray-Ionisations-Massenspektrometrie kombiniert, wurde entwickelt, um die Bestandteile der Hartproteinkorona zu identifizieren. Die Proteomics-, SERS- und Cryo-Soft-X-Ray-Nanotomographiedaten, wobei letztere Informationen über die dreidimensionale Ultrastruktur der Zelle liefern, zeigen den Aufnahmemechanismus, die Verarbeitung, die Akkumulationsstelle, die molekulare Umgebung und die induzierten zellulären Reaktionen internalisierter Goldnanopartikel. Diese Arbeit validiert die Verwendung von SERS bei der Analyse der Proteinkorona in der Lösung von Modellproteinen und in lebenden Zellen und präsentiert eine geeignete Methode zur Analyse der unveränderten harten Proteinkorona, die in lebenden Zellen gebildet wird. / The characterization of the protein-nanoparticle interactions in complex biomolecular systems such as a living cell is vital for pharmaceutical, medical, and environmental research fields. In such biomolecular systems, proteins readily adsorb on the surface of nanoparticles forming the protein corona. This thesis focuses on the characterization of the protein corona in living cells combining different analytical approaches. Surface-enhanced Raman scattering (SERS) experiments on pure protein solutions revealed the concentration dependence of the protein-gold nanoparticle interactions resulting in different SERS spectra, and allowed for the determination of protein segments binding to citrate-stabilized gold nanoparticles. In live cell SERS experiments, the presence of protein fragments in the innermost layer of the protein corona, called the hard protein corona, was revealed. An analytical method combining sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-performance liquid chromatography-coupled electrospray ionization mass spectrometry was developed to identify the constituents of the hard protein corona. The proteomics, SERS, and cryo soft X-ray nanotomography data, the latter providing information of the three dimensional ultrastructure of the cell, reveal the uptake mechanism, processing, accumulation site, molecular environment, and the induced cellular responses of internalized gold nanoparticles. This work validates the use of SERS in the analysis of the protein corona in the solution of model proteins and in living cells, and presents a suitable method for the analysis of the unaltered hard protein corona formed in living cells.

No description available.

Die Elektrochemie und die Spektroelektrochemie von selbst-organisiererten Monoschichten (selfassembled monolayers, SAMs) gebildet aus 2-Mercaptopyridin (2MP) und 4-Mercaptopyridin (4MP) wurden an polykristallinen Goldelektroden in wässrigen Elektrolytlösungen untersucht. Folgende Untersuchungsmethoden wurden angewandt: zyklische Voltammetrie, elektrochemische Impedanzmessungen (EIM) und oberflächenverstärkte Raman Streuung (surface-enhanced Raman scattering, SERS). Die elektrochemischen Untersuchungen von 2MP und 4MP in wässriger saurer Lösung (0.5 M H2SO4) zeigten, dass 2MP stärker adsorbiert wird als 4MP aufgrund der Bildung eines S-Au-N Chelates, wobei die S-Au-Interaktionen bei 4MP stärker sind. Die Bildung eines Chelates im Falle von 2MP verringert die Wahrscheinlichkeit der Bildung eines Dimers. In sauren Lösungen wird das N-Atom von 2MP protoniert, was zu einer schwächeren Bindung von 2MP-Molekülen zur Substratoberfläche führt. Die Ergebnisse der SERS-Untersuchungen stimmen mit den Resultaten aus der zyklischen Voltammetrie überein. Man erhält eine Au-S-Streckschwingungsbande für 2MP zwischen 225 bis 250 cm-1 bei Abscheidung aus wässriger oder saurer Lösung und für 4MP bei ca. 263 cm-1 in beiden Lösungen. Die SERS-Experimente ergaben eine senkrechte Orientierung zur Goldoberfläche sowohl für 2MP als auch für 4MP. Die Thion-Thiol-Tautomerie von 2- Mercaptopyridinen wurde ebenfalls in Betracht gezogen. Die Unter- und Überpotentialabscheidung von Kupfer auf einer polykristallinen Goldelektrode in wässriger 0.1 M Schwefelsäure in An- und Abwesenheit von SAMs von 2- und 4- Mercaptopyridin wurde mit zyklischer Voltammetrie untersucht. Es zeigte sich, daß bei Vorhandensein der SAMs die Elektrodeposition von Kupfer verhindert wird, was auf starke Wechselwirkungskräfte zwischen dem Adsorbat (MP) und der Goldoberfläche zurückzuführen ist. 2MP zeigt eine grössere Inhibierung, was höchstwahrscheinlich auf die Bildung der Chelatstruktur zurückzuführen ist. Es wurden ebenso Untersuchungen zum Einfluss von 2MP und 4MP auf die abgeschiedene Kupfermonolage auf der Goldelektrode durchgeführt. Es zeigte sich, daß die Kupfermonolage teilweise durch 2MP oder 4MP ersetzt wird. Die Elektronenaustauschgeschwindigkeit für das Fe2+/Fe3+-Redoxsystem in An- und Abwesenheit von 2MP- oder 4MP-Monolagen wurde mit zyklischer Voltammetrie und elektrochemischen Impedanzmessungen (EIM) untersucht. Es stellte sich heraus, dass der Elektronenaustausch höchstwahrscheinlich über Defektstellen in der Monolage (Pinholes) erfolgt. In einer wässrigen Lösung verringert 4MP den Elektronenaustausch stärker als 2MP. Da die Packungsdichte bei 4MP größer ist als bei 2MP ist wahrscheinlich auch die Zahl der Pinholes geringer in der 4MP-Monolage. In saurer Lösung liegen die N-Atome protoniert vor. Man kann davon ausgehen, dass in saurer Lösung zwei Prozesse gleichzeitig ablaufen, die für den Elektronenaustausch entscheidend sind. Erstens kommt es zu einer Abstoßung zwischen der positiv geladenen Monolage und den positiv geladenen Redoxionen. Und zweitens erfolgt eine Abstoßung zwischen den positiv geladenen Molekülen der SAMs, was zu einer geringeren Packungsdichte führt. Der Ladungsaustausch wird dominiert durch den zweiten Effekt. Mit Hilfe von EIM wurden die Elektronenaustauschgeschwindigkeit und der Bedeckungsgrad bestimmt. Die korrosionshemmende Wirkung von 2MP und 4MP auf Stahl in 3.5 % wässriger NaCl-Lösung wurde mit Hilfe der EIM untersucht. 2MP zeigte eine grössere Hemmung als 4MP. / The electrochemistry and spectroelectrochemistry of the self-assembled monolayers (SAMs) prepared of 2-mercaptopyridine (2MP) and 4-mercaptopyridine (4MP) dissolved either in water or 0.1 M H2SO4 have been investigated at polycrystalline gold electrodes in aqueous electrolyte solutions using cyclic voltammetry, electrochemical impedance measurements (EIM) and surface enhanced Raman spectroscopy (SERS). Electrochemical studies of 2MP and 4MP monolayers in aqueous acidic solution (0.5 M H2SO4) suggest that 2MP is adsorbed more strongly than 4MP due to the formation of S-Au-N chelate. However, the S-Au bond was found to be stronger in 4MP as compared with 2MP. The formation of the chelate in case of 2MP diminishes the probability of dimer formation. In the acidic solvent, the N-atom of 2MP molecule will be protonated leading to a weaker interaction of 2MP molecules with the substrate surface. The SERS results are in good agreement with the cyclic voltammetry results. The Au-S stretching band was obtained in the region from 215 to 245 cm-1 for 2MP deposited from water and acidic solvent and around 263 cm-1 for 4MP in both solvents. The SERS measurements showed also a perpendicular orientation of both 2MP and 4MP on the gold surface. In explaining the SERS results, the thione-thiol tautomerisations of the mercaptopyridines were also taken into consideration. The under- and overpotential deposition of copper on a polycrystalline gold electrode in aqueous 0.1 M sulfuric acid in the presence and in the absence of SAMs of 2- and 4-mercaptopyridine has been studied using cyclic voltammetry. In general, the presence of these SAMs has been found to inhibit the electrodeposition process of copper, suggesting very strong interactions between these adsorbates and the Au surface. 2MP shows a higher degree of inhibition, which is due to a stronger interaction probably due to the formation of the chelate structure. Studies have also been made of the influence of mercaptopyridines SAMs on the copper monolayer electrodeposited on the gold surface. The copper adlayer was found to be partially displaced by 2MP and 4MP monolayers. The rate of electron transfer for the Fe3+/2+ redox system on the gold electrode has been probed in the absence and presence of 2MP and 4MP monolayers by cyclic voltammetry and electrochemical impedance measurements (EIM). The charge transfer process was suggested to occur through the defects (pinholes) in the monolayer. In case of aqueous solvent 4MP decreases the electron transfer reaction stronger than 2MP. Since the packing density for 4MP is higher than that of 2MP the number of pinholes might be lower in 4MP monolayer. In acidic solvent the N-atoms of the mercaptopyridines will be protonated. It is proposed that two effects, which exist at the same time, are responsible for the electron transfer process in acidic solution. First, there will be a repulsive interaction between the positively charged monolayer and the positively charged redox probe. Second, there is a repulsion among the positively charged monolayer molecules that results in a less compact monolayer. The charge transfer is dominated due to the latter effect. With the EIM the rate of electron transfer and the surface coverage were determined. 2MP and 4MP were examined as steel corrosion inhibitors in 3.5% aqueous NaCl solution using EIM. 2MP shows higher inhibition efficiency than 4MP.

Efficient substrates for surface-enhanced Raman spectroscopy (SERS) are under constant development, since time-consuming and costly fabrication routines are often an issue for high-throughput spectroscopy applications. In this research, we use a two-step fabrication method to produce self-organized parallel-oriented plasmonic gold nanostructures. The fabrication routine is ready for wafer-scale production involving only low-energy ion beam irradiation and metal deposition. The optical spectroscopy features of the resulting structures show a successful bidirectional plasmonic response. The localized surface plasmon resonances (LSPRs) of each direction are independent from each other and can be tuned by the fabrication parameters. This ability to tune the LSPR characteristics allows the development of optimized plasmonic nanostructures to match different laser excitations and optical transitions for any arbitrary analyte. Moreover, in this study, we probe the polarization and wavelength dependence of such bidirectional plasmonic nanostructures by a complementary spectroscopic ellipsometry and Raman spectroscopy analysis. We observe a significant signal amplification by the SERS substrates and determine enhancement factors of over a thousand times. We also perform finite element method-based calculations of the electromagnetic enhancement for the SERS signal provided by the plasmonic nanostructures. The calculations are based on realistic models constructed using the same particle sizes and shapes experimentally determined by scanning electron microscopy. The spatial distribution of electric field enhancement shows some dispersion in the LSPR, which is a direct consequence of the semi-random distribution of hotspots. The signal enhancement is highly efficient, making our SERS substrates attractive candidates for high-throughput chemical sensing applications in which directionality, chemical stability, and large-scale fabrication are essential requirements.

The adsorbate formed by adsorption of thiophenol on a polycrystalline gold electrode and brought into contact with aqueous solutions of 1 M HClO4 and 0.1 M KClO4 has been studied using cyclic voltammetry and surface-enhanced Raman spectroscopy. A strong adsorption is deduced from observations made using cyclic voltammetry. From the SER spectra, interactions of thiophenol with the gold surface via a gold–sulfur bond with the aromatic ring pointing away from the surface is concluded for both electrolyte solutions. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

No description available.