Browsing by Author "Aras, Nadir"

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A comparative study of thin-film coated silicon wafer surfaces for laser-induced breakdown spectroscopic analysis of liquids
(Izmir Institute of Technology, 2021-07) Aras, Nadir; Yalçın, Şerife Hanım; Izmir Institute of Technology
Laser-Induced Breakdown Spectroscopy, LIBS, is a relatively new atomic emission spectroscopic technique that shows rapid growth due to its many special peculiarities, like its ability to provide spectral signatures of all chemical species at the same time, in all environments of solid, liquid, or gas. Liquid sample analysis by LIBS is more troublesome compared to analysis of solids. Therefore, liquid analysis by LIBS requires some pretreatment steps to be applied before direct analysis of the samples. In the literature, a variety of approaches has been successfully applied and there is still plenty of room to improve methodologies used in the liquid-LIBS analysis. The main purpose of this thesis study was to perform studies for the development of a LIBS-TARGET for sampling liquids on it, after drying, by repetitive laser pulses. With this purpose, silicon wafer-based substrates with differing surface compositions; uncoated (crystalline silicon, c-Si), oxide-coated silicon, SiO2, and nitride coated silicon, Si3N4, were tested for several experimental parameters. Within the content of this study, a fast and accurate methodology for direct analysis of aqueous samples by LIBS is proposed. This methodology has two important attributes: one is the use of the non-metal substrate, silicon wafer, for the first time for direct analysis of aqueous samples dried on, and two is the use of high energy laser pulses focused outside the minimum focal point of a plano-convex lens at which relatively large laser beam spot covers the entire droplet area for plasma formation. Si-wafer-based substrates were used for both qualitative and quantitative analysis of Cd, Cr, Cu, Mn, and Pb elements, and analytical figures of merit were determined. The analytical performance of each substrate was evaluated from the experiments performed with aqueous standards and real water samples. Silicon nitride-coated substrate has shown superior properties in terms of enhancing the LIBS signal and as low as 11 pg detection limits for Pb were obtained.
Identification and detection of phosphorylated proteins by laser induced breakdown spectroscopy
(Izmir Institute of Technology, 2011) Aras, Nadir; Yalçın, Şerife
Laser-Induced Breakdown Spectroscopy (LIBS) is an optical atomic emission spectroscopic technique that uses an energetic laser source to generate a luminous plasma. Spectrochemical analysis of the light emitted from the plasma reveals information about the elemental composition of the sample. Phosphorylation is an important regulatory mechanism that activates or deactivates many proteins and enzymes in a wide range of cellular process. Identification and detection of phosphoproteins have a crucial importance in phosphopeptide mapping. This study is based on the assessment of the capabilities and limitations of LIBS as a quick and simple method for in-gel identification and determination of phosphorylated proteins, specifically casein and ovalbumin before mass spectrometric analysis for the elucidation of phosporylation sites. For this purpose, an optical LIBS set-up was constructed from its commercially available parts and the system was optimized for LIBS analysis of polyacrylamide gels. Nd:YAG laser operating at 532 nm wavelength and at 10 Hz frequency was used to create plasma on dry gel surfaces. Emitted light from a luminous plasma was analyzed and detected by an Echelle type spectrograph containing Intensified CCD, detector. With this study, LIBS detection of phosphorous proteins after electrophoretic separation of phosphorylated proteins has been shown, for the first time. After SDS-PAGE gel separation process, phosphoproteins were recognized from prominent P(I) lines (at 253.5 nm and 255.3 nm) in a plasma formed by the focused laser pulses on the gel, just in the center or in the vicinity of the electrophoretic spot. Spectral emission intensity of P(I) lines from LIBS data has been optimized with respect to laser energy and detector timing parameters by using standard Na2HPO4. It has been shown that phosphorylated proteins (casein and ovalbumin in mixture) can be identified by LIBS after both coomassie brilliant blue and silver staining procedures. Technique shows a great promise in microlocal spotting of phosphorylated proteins in gel before MS analysis for the determination of the phosphorylation sites.