1,721,002 research outputs found
Application of Raman Spectroscopy for the characterization of carbon materials
Get PDFThis dissertation discusses the applications of Raman spectroscopy for the characterization of carbon materials, through the investigation of heterogeneous hydrogenation, estimation of elemental and organic carbon from diesel emission particulate and automated classification. Carbon materials are present in several aspects of human life. Some illustrative examples come from technological use of graphite, diamond and glassy carbon and the impact of diesel emissions in human health. The general objective of the dissertation is to improve the characterization of carbon materials and show the potential and limitations of methods that combines Raman spectroscopy and chemometrics for carbon materials characterization.
The literature is vast about the utility of Raman spectroscopy for characterizing carbon materials. However, some methods are either not clearly described in terms of reproducibility and implementation, or very specific to a particular type of material. Also, some studies describe their material based in a single spectrum instead of a spatial and statistical characterization.
Chapter 2 demonstrates the usefulness of Raman maps for characterizing carbon films obtained chemically. The study investigated the heterogeneous hydrogenation in the samples and showed the effect of different parameters on the homogeneity of the material. Due to heterogeneous hydrogenation, some regions could be assigned to different types of carbon materials and could lead to different properties. This is highly relevant for potential use in industry as quality control tool. For the scientific community, this chapter showed the importance of the fluorescent background in the Raman spectrum for proper characterization of carbon materials.
Organic carbon and elemental carbon are general classifications for particulate matter present in diesel emissions. These two species present potential harm to the health of workers, monitoring their presence is thus paramount for a safe workplace environment. The literature offers different approaches for estimating elemental carbon and the comparison with different techniques. Most of them ignore the organic fraction and don’t compare with the North American standard technique (NIOSH method). The fluorescent background and the correlation with hydrogenation of carbon materials that were observed in chapter 2 inspired the use of the background as source of information for estimating organic carbon content. The results from Raman and partial least squares in chapter 3 suggest the background as an important source of information for estimating organic carbon and total carbon. The predictions of total carbon agreed with the values obtained from the standard technique in the range between 60 and 600 µg.
Although Raman spectroscopy is largely used for characterization of carbon materials, it is not rare to find misinterpretation of the spectra. Chapter 4 presents an automated prediction of carbon materials based on their Raman spectra and using principal component analysis followed by linear discriminant analysis. The Raman spectra used in for training the model were obtained from highly oriented pyrolytic graphite, glassy carbon, diamond-like carbon, hydrogenated graphite-like carbon and hydrogenated polymer-like carbon. The testing dataset was based on Raman spectra from the literature and from samples synthesized in the lab. The results showed accuracy of 97 % and some assignments found in the literature could be corrected by the model proposed in this chapter.
Chapter 5 offers a summary of the research projects presented in this dissertation and discuss the possible future projects for developing the use of Raman spectroscopy and machine learning for carbon materialsGraduat
SERS Study of N-heterocyclic Carbenes Absorbed on a Silver Electrode
No full textSERS (surface-enhanced Raman spectroscopy) has the potential to be used in a variety of commercial and basic applications, which often rely on molecules that are bound to a nanostructured metal surface. Thiols are usually used as the intermediate to modify the substrate surface for SERS. In recent years, N-heterocyclic carbene (NHC) has been introduced as an alternative approach for metal surface modification. Nanostructured gold surfaces suitable for SERS had been modified by NHC species. Those studies showed the promising of the NHC modification route for the fabrication of a robust platform for SERS.
The objective of this work is to explore the SERS characteristics of NHC species on silver surfaces. The interactions between two different NHC molecules and a nanostructured silver surface, instead of a gold surface, were studied for the first time. The experiments were realized in electrochemical conditions, using a three-electrodes system, to fully test the stability of the NHC-modified surfaces. The SERS spectra were compared to theoretical calculations and normal Raman in order to identify the vibrational characteristics of the NHC molecules. The effects of different NHC molecule substituents on the electrochemical stability of the surface were also discussed. The results showed that NHC molecules can be decomposed on the silver surface easily under electrochemical conditions. This contrast with the observations in gold, where the NHC monolayers showed a high level of stability.
This work also discusses potential side products which may be derived from the decomposition of the NHC molecules. Raman spectra of potential side products were collected and compared to the NHC SERS collected under electrochemical control at different potentials.
This study provides insights into the influence of the substituents at the NHC on their stability under the electrochemical condition, which should guide the development of future applications.Graduat
Electrochemical investigations on the reduction of short chain SAMs from a Au(111) electrode
Get PDFSelf-assembled monolayers (SAMs) derived from long chain alkanethiols are
known to exhibit generalized trends as a function of chain length where n denotes the
number of methylene units (CH2). For n 3, these trends are no longer manifest. It can
be shown that SAMs of short chain lengths are much more affected by the presence and
type of functional group. The reduction of electrochemically induced SAMs derived
from cysteine (cys), cystine ((cys)2), mercaptopropionic acid (MPA) and
mercaptoethylamine (MEA) from Au(111) highlight the effect of the two functional
groups evaluated (R-CO2
- and R-NH2). The reductive desorption of these species was
monitored by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) in
0.1 M KClO4 and 0.1 M NaOH. The work presented herein demonstrates that under
short time frames of immobilization, the presence of NH2 provides a stabilizing effect to
the SAM.
Cys and (cys)2 SAMs that maintain both functional groups are generally found to
provide the lowest surface coverage under the short term conditions of assembly. The
thiol derived monolayers (cys) are consistently higher packed than the disulfide SAMs
iv
from (cys)2 in both media evaluated. In 0.1 M NaOH however, cys coverage is consistent
with coverages obtained from very long incubation times. In the presence of the strong
base the disulfide species, (cys)2, desorbs at potentials that are always more positive than
those of the thiol species (cys), further supporting poor monolayer formation.
Additionally, these monolayers also exhibit the presence of two separate processes in 0.1
M KClO4, whereas only desorption is noted in 0.1 M NaOH. It is likely that a deprotonation
of the amine group occurs prior to the desorption of the SAM. The SAM
desorption occurs near -0.65 V vs. SCE, and the de-protonation at about -0.50 V vs. SCE.
Since the monolayers formed from cys are better formed than those from (cys)2, this deprotonation
is much more pronounced in the cys SAMs.
The presence of only the CO2
- group (MPA) on the SAM, yields surface coverage
that is intermediate compared to the bi-functionalized SAMs formed from cys and (cys)2
and the NH2 containing SAMs of MEA. In the potential region up to and prior to
desorption, only one process is noted in both media.
SAMs derived from MEA provide the highest surface coverage of the four
species, approximating theoretical values. The presence of two surface species is
observed in both media, as a result of trans and gauche binding. Of the four species
evaluated, MEA appears to be most suitable for rapid SAM formation. The disulfide
species, (cys)2, is found to be unsuitable for short-term preparation of SAMs
Fabrication, modification and self-assembly of metallic nano-particles for localized surface plasmon resonance and surface enhanced vibrational spectroscopy applications
Get PDFMetallic nanoparticles (MNPs), especially those made of gold, silver, and copper, are of great importance in many scientific disciplines. The free electrons inside the MNPs can respond collectively to applied electromagnetic fields. This is called the excitation of localized surface plasmon resonance (LSPR).
One of tile most important aspects of surface plasmons (SPs) excitation is that it allows the localization of 'the electromagnetic field al certain regions of tile nanostructured surface (or, in other words, the local field is "enhanced"). Based on this. surface enhanced Ramlln scattering ( ERS) and localized surface plasmon resonance (LSPR) sensing can be realized.
The work in this thesis can be divided in two parts: These include the exploration of self-assembled MNPs as new substrates for surface enhanced vibrational spectroscopy: and the sensing applications of these assembled MNPs.
In the first part. the assembly ofMNPs on gold electrodes and glass slides were explored.
Firstly. "layer-by-layer"' self-assembly of Au NPs on gold electrode was used to construct n highly sensitive and reproducible SERS substrate that can work in an electrochemical environment. The SERS perfonlmnce. in terms of enhancement and reproducibility, with the the numbers Au NPs "Iayers", was examined. Meanwhile, the potential window. during which a reproducible in sit" SERS experiment can be performed, was investigated. The possibility of such kind of substrate to be used in surface enhanced polarization modulation infrared absorption spectroscopy (PM-IRRAS) was also discussed.
The "layer-by-layer" self-assembly idea was extended to Ag NPs supported on glass. The resulted substrate revealed that after multiple time self-assembly, the SERS enhancement performance of lhe substrate can be 3 to 4 orders of magnitude higher than just one Ag NPs deposition, depending on the wavelength used. Using this substrate, a near-single-molecule sensitivity has been achieved.
In the second pan, sensing applications of the assembled MNPs were examined. The multiple "layers" Au NPs on gold electrode was used to characterize a sample biofuel cell anode, which consists three molecular "layers": the linker 4-hydroxyphenol (HTP), the co-enzyme analog Cibacron blue (CB), and the formaldehyde dehydrogenase (FaIDH). (In situ) SERS spectra or the sample biofuel cell at different construction stages were recorded and compared.
The work about self-assembly ofAg NPs on glass was extended to fiber optics. The tip of a fiber optic was modified with multiple "layers" ofAg PSt and the analytical performance for remote sensing of this device was examined by the using of dyes with different structures and charges. It was found that this device was among one of the most sensitive SERS remote sensors when compared to the literature.
Finally, a LSPR biosensor based on self-assembly of Ag NPs on PET, a common type of plastic, has been developed. The advantage of this sensor is that the surface of the Ag Ps was able to be tailored into differenl functional groups, and therefore met different requirements. Sample analysis for biological relevant species was performed.Graduat
Paper Spray Mass Spectrometry for the Quantitation of Drugs of Abuse in Biofluids and Street Drug Samples
No full textPaper spray mass spectrometry (PS-MS) has been developed as a tool for the analysis of drugs of abuse (DoA) in street drug samples, urine, and oral fluid. PS-MS is presented as a viable alternative to the traditional gas chromatography and liquid chromatography-mass spectrometry methods. PS-MS achieves sensitive and quantitative results in as little as 1-2 minutes with little to no sample preparation. Initial research presented in this thesis illustrates how PS-MS was developed for the analysis of fentanyl and related analogs of powdered drug slurries acting as a proxy for street drug samples, as a proof of concept for real world drug checking. Analysis of DoA in these pseudo-drug samples demonstrated the potential for both quantitative and qualitative analysis of fentanyl analogs. PS-MS was then demonstrated and evaluated for its effectiveness for real world drug checking applications during a world first demonstration of PS-MS for on-site drug checking in the Downtown Eastside of Vancouver, British Columbia, a recognized epicenter of the opioid overdose crisis. During the pilot test, 113 samples were submitted for analysis and successfully quantified using PS-MS, which targeted and quantified 49 different drug targets. Of these 113 drug samples, 44% of all samples were found to contain fentanyl, with a median concentration of 3.6% (w/w). The benzodiazepine etizolam was detected in 10 samples, none of the people who submitted these 10 samples expected a benzodiazepine to be present in their sample. It was later found that other drug checking technologies in use were underreporting the presence of etizolam or other benzodiazepines present in drug samples. These results, coupled with the quantitative capabilities and low levels of detection observed during the pilot test of PS-MS for drug checking demonstrated the efficacy of PS-MS and inspired further development of the application. PS-MS was then implemented by the Vancouver Island Drug Checking Project for the routine quantitative measurement of thousands of drug samples. During the span of this routine measurement, two unidentified compounds began appearing in carfentanil-containing drug samples. High resolution accurate mass (HRAM) mass spectrometry was used to determine the chemical composition of these two unknowns as C23H29N3O2 (m/z 380.2333) and C23H29N2O3 (m/z 381.2137). Further tandem mass spectrometry experiments were used for structural elucidation and the unknowns were putatively identified as desmethylcarfentanil amide and desmethylcarfentanil acid. LC-MS data on different drug samples containing the same compounds further supported the identification of these carfentanil structural analogs. µ-Opioid receptor binding modeling determined that the binding poses, and binding energies of these structural analogs were nearly identical to that of carfentanil, suggesting potentially similar activities/toxicities. PS-MS was further applied to the analysis of cannabinoids in urine and oral fluid samples. Due to the inherently low ionization efficiencies and sensitivity to cannabinoids observed with PS-MS, a reactive paper spray ionization method utilizing a diazonium salt as a on-paper derivatization reagent was developed. The derivatization scheme dramatically lowered the limits of detection for tetrahydrocannabinol (THC) in oral fluid and THC metabolite in urine, to levels able to meet forensic and clinical cutoff values (low parts per billion). The quantitative results were compared to a LC-MS results from a commercial clinical laboratory, demonstrating good agreement between the two methods. The results presented herein demonstrate the applicability and dramatic benefits of PS-MS for drug checking applications, as well as for cannabinoids in oral fluid and urine. High resolution mass spectrometry is demonstrated for the structural elucidation and identification of unknown drug compounds in an ever-changing street drug supply.Graduat
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Self-directed Transport on Nanostructured Plasmonic Sensors
No full textAnalytical sensors using varying detection strategies have been widely and successfully employed for advances in areas such as drug discovery, disease diagnosis and study of biological systems. Many of these sensors utilize plasmonic metallic nanostructures which can concentrate electromagnetic fields in nanoscale regions leading to many fold enhancement in optical signal obtained from the molecules. They employ techniques including fluorescence, surface plasmon resonance (SPR)-based refractive index sensing, surface-enhanced Raman spectroscopy (SERS) and other forms of vibrational spectroscopy for molecular characterization. However, the performance of these devices relies on effective transport of the target molecules to these nanoscale detection sites. Guided transport is extremely important for fast detection in cases where the concentration of molecules is really low and for accurate measurements of protein–protein binding kinetics. In this chapter, we discuss nanostructured biosensing substrates which can spontaneously direct the flow of molecules in solution towards the sensing hotspots. These devices demonstrate improved detection sensitivity, while minimizing the limitations and complexity imposed upon the system. Additionally, they can trap biological particles such as organelles and liposomes on the sensor surface, facilitating on-chip analysis of single particles. This chapter discusses a few methods which have been utilized for concentration of molecules on plasmonic sensing surfaces, without the application of external power sources
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