Metal nanostructures exhibit a wide variety of interesting physical and chemical properties, which can be tailored by altering their size, morphology, composition, and environment. Gold and silver nanostructures have received considerable attention for many decades because of their widespread use in applications such as catalysis, photonics, electronics, optoelectronics, information storage, chemical and biological sensing, surface plasmon resonance and surface-enhanced Raman scattering (SERS) detection. This thesis is composed of three main parts about the synthesis, characterization and SERS applications of shape-controlled and surface modified noble metal nanoparticles. The first part is related to a simple synthesis of shape controlled solid gold, hollow gold, silver, gold-silver core-shell, hollow gold-silver double-shell nanoparticles by applying aqueous solution chemistry. Nanoparticles obtained were used for SERS detection of dye molecules like brilliant cresyl blue (BCB) and crystal violet (CV) in aqueous system. v The second part involves the synthesis of surface modified silver nanoparticles for the detection of dopamine (DA) molecules. Determination of a dopamine molecule attached to a iron-nitrilotriaceticacid modified silver (Ag-Fe(NTA)) nanoparticles by using surface-enhanced resonance Raman scattering (SERRS) was achieved. The Ag-Fe (NTA) substrate provided reproducibility and excellent sensitivity. Experimental results showed that DA was detected quickly and accurately without any pretreatment in nM levels with excellent discrimination against ascorbic acid (AA) (which was among the lowest value reported in direct SERS detection of DA). In the third part, a lanthanide series ion (Eu3+) containing silver nanoparticle was prepared for constructing a molecular recognition SERS substrate for the first time. The procedure reported herein, provides a simple way of achieving reproducible and sensitive SERS spectroscopy for organophosphates (OPP) detection. The sensing of the target species was confirmed by the appearance of an intense SERS signal of the methyl phosphonic acid (MPA), a model compound for nonvolatile organophosphate nerve agents, which bound to the surface of the Ag-Eu3+ nanostructure. The simplicity and low cost of the overall process makes this procedure a potential candidate for analytical control processes of nerve agents.

Raman spectroscopy offers much better spectral selectivity but its usage has been limited by its poor sensitivity. The discovery of surface-enhanced Raman scattering (SERS) effect, which results in increased sensitivities of up to 108-fold for some compounds, has eliminated this drawback. A new SERS active substrate was developed in this study. Silver nanoparticle-doped polyvinyl alcohol (PVA) coated SERS substrate prepared through chemical and electrochemical reduction of silver particles dispersed in the polymer matrix. Performances of the substrates were evaluated with some biologically important compounds. The specific detection of DNA has gained significance in recent years since increasingly DNA sequences of different organisms are being assigned. Such sequence knowledge can be employed for identification of the genes of microorganisms or diseases. In this study, specific proteasome gene sequences were detected both label free spectrophotometric detection and SERS detection. In label free spectrophotometic detection, proteasome gene probe and complementary target gene sequence were attached to the gold nanoparticles separately. Then, the target and probe oligonucleotide-modified gold solutions were mixed for hybridization and the shift in the surface plasmon absorption band of gold nanoparticles were followed. SERS detection of specific nucleic acid sequences are mainly based on hybridization of DNA targets to complementary probe sequences, which are labelled with SERS active dyes. In this study, to show correlation between circulating proteasome levels and disease state we suggest a Raman spectroscopic technique that uses SERGen probes. This novel approach deals with specific detection of elevated or decreased levels of proteasome genes&rsquo / transcription in patients as an alternative to available enzyme activity measurement methods. First, SERGen probes were prepared using SERS active labels and specific proteasome gene sequences. Then DNA targets to complementary SERGen probe sequences were hybridized and SERS active label peak was followed.

A novel analytical technique was developed where gaseous hydrogen selenide formed by sodium tetrahydroborate reduction is transported to and trapped on a resistively heated gold-coated W-coil atom trap for in situ preconcentration. The atom trap is held at 165 &ordm / C during the collection stage and is heated up to 675 &ordm / C for revolatilization / analyte species formed are transported to an externally heated quartz T-tube where the atomization takes place and the transient signal is obtained. For gold, a high volume gas liquid separator (HVGLS) was designed to improve the detection limit of Au down to the ng mL-1 levels. In this apparatus, analyte and reductant solutions are collected in a limited volume and volatile analyte species are formed. After separation of the volatile analyte species from liquid phase, the entire analyte vapor is sent to an atomizer. A W-coil trap was used to further decrease the detection limit. The enhancement factor for the characteristic concentration was found to be 10.7 when compared to HG-AAS performance without W-coil trap by using peak height values. Furthermore, the generation of analytically useful volatile form of Au has been studied. The flow injection generation was performed in a dedicated generator consisting of a special mixing apparatus and gas-liquid separator design. The on-line atomization in the quartz tube multiatomizer for atomic absorption (AAS) detection has been employed as the convenient atomization/detection mean. 198Au, 199Au radioactive indicator of high specific activity together with AAS measurements was used to track quantitatively the transfer of analyte in the course of generation and transport to the atomizer. In-situ trapping in GF for AAS was explored as an alternative to the on-line atomization. Transmission electron microscopy measurements proved the presence of Au nanoparticles of diameter of approximately 10 nm and smaller transported from the generator by the flow of carrier Ar. For silver, three types of GLS which are U-shaped, cylindrical and high volume gas liquid separators (HVGLS) were used to compare the sensitivities of these GLSs during Ag determination. The DL (3s) values were found as 29 ng mL-1, 0.4 ng mL-1 and 0.05 ng mL-1 for U-shaped GLS, cylindrical GLS with W-coil trap and HVGLS with W-coil trap, respectively. For indium, two types of GLS which are cylindrical and HVGLS with W-coil trap were used. The LOD and characteristic concentration were found as 148 and 317 ng mL-1 with cylindrical shape GLS. HVGLS with W-coil trap was used to improve sensitivity. In this case, LOD and characteristic concentration were found to be 0.46 and 0.98 ng mL-1, respectively. Moreover, to increase the reactivity between indium and reductant solutions, Ru(acac)3 catalyst was used. In this case, LOD and characteristic concentration were found to be 0.13 and 0.23 ng mL-1, respectively. In the case of using this catalyst, sensitivity was enhanced around 1378 fold with respect to cylindrical GLS.

Detection of chemicals is a vital part of chemistry. For this reason, many detection systems are developed by scientists and every detection system has its own advantages. Raman spectroscopy is one of these detection systems having many advantages. However, this technique suffers from low signal intensity disadvantage. By developing a well prepared substrate, this problem can be easily solved / moreover, even single molecule detection can be possible. In this study, a novel surface enhanced Raman scattering (SERS) substrate was prepared in two steps: In the first step, ethylenedioxythiophene (EDOT) monomer was polymerized electrochemically onto indium tin oxide (ITO) coated glass. In the next step, silver ions were reduced electrochemically onto surface prepared in the previous step.In the substrate preparation part, the reduction potential of silver ion, the concentration of silver ions in solution, the polymer film thickness and reduced silver amount on substrates were optimized to get the best SERS performances from substrates. The prepared substrates were characterized by cyclic voltammetry (CV), ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) attached to SEM. In the SERS performance investigation part, homogeneity and the shelf life of the prepared silver-PEDOT substrates were tested. Homogeneity is very important in terms for the applications of Raman technique in quantitative analysis since most of the reported substrates are lack homogeneity consideration, our study will be an important contribution to the literature. The stability of the substrate was investigated for a period of one month. The very small change in the signal at the end of one month indicated that the substrate can be used even longer time with high efficiency. In all the studies, brilliant cresyl blue (BCB) is used as a model compound. Some important Raman active chemicals, namely, rhodamine 6G (R6G) and 4-mercapto benzoic acid (4-MBA) were detected by using the prepared substrates.

Silver is a precious metal having antibacterial property and widely used in industry mostly for water purification and medicinal products. Therefore, the determination of trace levels of silver is important for industrial applications. Flame atomic absorption spectrometry (FAAS) is a popular technique for the determination of relatively low concentration levels. This mature technique owes its widespread application to its simplicity and low cost. However, for some occasions, FAAS technique suffers from its low sensitivity because of low nebulization efficiency and relatively short residence time of analyte atoms in the measurement zone. In order to overcome this sensitivity problem, atom traps have been developed in recent years. Slotted quartz tube (SQT) is an accessory designed to use as an atom trap in conventional flame atomic absorption burner head. This thesis study involves the development of a sensitive, simple and economical technique with the help of the SQT for the determination silver. Firstly, the technique known as SQT-FAAS was used to increase the residence time of analyte atoms in the measurement zone. In this case, limit of detection (LOD) and characteristic concentration (C0) values were found to be 19 ng/mL and 35 ng/mL, respectively. Enhancement in sensitivity with respect to FAAS was found to be 2.31 fold using SQT-FAAS. Regarding the angle between the two slots of the SQT, 180&deg / configuration was used. Secondly, in order to improve sensitivity further, the SQT was used as an atom trap (AT) where the analyte is accumulated in its inner wall prior to re-atomization. The signal is formed after reatomization of analyte atoms on the trap surface by introduction of organic solvent. For this purpose, uncoated SQT was used as a trap medium. However, there was a memory effect. Therefore, the SQT inner surface was coated with different coating elements and theoptimum conditions were found by using W-coated SQT-AT-FAAS technique. In the presence of a lean air-acetylene flame, analyte atoms were trapped in the inner surface of the SQT for 5.0 min and then revolatilized with the introduction of 25 &mu / L isobutyl methyl ketone (IBMK) / afterwards, a transient signal was obtained. These optimized parameters were used for uncoated SQT, W-coated SQT and Zr-coated SQT atom trap techniques. Sample suction rate was 6.25 mL/min in all techniques. Sensitivity was increased 54 fold using uncoated SQT-AT-FAAS technique with respect to simple FAAS technique. When W-coated SQT-AT-FAAS technique was applied, 135 fold sensitivity enhancement was obtained with respect to FAAS technique. The best sensitivity enhancement, 270 fold, was obtained using Zr-coated SQT-AT-FAAS technique. In addition, the Ag signals were more reproducible (%RSD, 1.21) when Zr was used as a coating element. After the sensitive technique was developed, interference effects of some transition and noble metals and hydride forming elements on Ag signals were investigated. Finally, surface studies were done to determine the chemical state of Ag during trapping period by using X-ray Photoelectron Spectroscopy (XPS). It was observed that the Ag analyte is retained on the SQT surface in its oxide form.

Hydride generation technique is frequently used for the detection of elements as As, Se, Sb, Sn, Bi, Ge, Te and Pb that form volatile hydrides in solution using a reductant. In this study, a novel quartz trap for on-line preconcentration of volatile analyte species was designed. Pb, Sb and Cd were selected as analyte elements and chemical vapour generation technique was employed for generation of their volatile species in flow systems. The trapping medium was formed by external heating of either the inlet arm of the quartz tube atomizer or a separate cylindirical quartz tube. Generated analyte species were trapped on quartz surface heated to the collection temperature and the collected species were revolatilized when the trap was heated further to releasing temperature and hydrogen gas was introduced in the trapping medium. The conventional quartz T-tube and multiple microflame quartz tube were employed as atomizers. The influence of relevant experimental parameters on the generation, collection and revolatilization efficiencies was investigated. Optimum conditions, performance characteristics of the trap and analytical figures of merit are presented. Experimental design was used for optimizations in some cases. Standard reference materials were analyzed to assess the accuracy of the proposed method. For a collection period of 1.0 minute for Pb, 2.0 minutes for Sb and 3.0 minutes for Cd, 3&amp / #963 / limit of detections, in pg ml-1, were 19, 3.9 and 1.8, respectively. In cases of Sb and Cd, the limits of detections obtained are the same as the best attained with in-situ trapping in graphite furnaces.

Vapor generation in atomic spectrometry is a well established technique for the determination of elements that can be volatilized by chemical reactions. In-situ trapping in graphite furnaces is nowadays one of the most popular methods to increase the sensitivity. In this study, resistively heated W-coil was used as an online trap for preconcentration and revolatilization of volatile species of Bi, Cd and Pb. The collected analyte species were revolatilized rapidly and sent to a quartz Ttube atomizer for AAS measurement. Although the nature of revolatilized species of Bi and Pb are not clear, they are probably molecular since they can be transported at least 45 cm without any significant decrease in the peak height values. However, cadmium is revolatilized from the trap surface as atoms. The experimental parameters were optimized for the highest vapor generation, trapping and revolatilization efficiencies. The concentration limits of detection calculated by the 3 of blank solution were found to be 0.0027, 0.0040 and 0.015 ng/mL for Bi (18 mL), Cd (4.2 mL) and Pb (2 mL), respectively / enhancement factors in the sensitivity were 130, 31 and 20, respectively. These values are comparable with those obtained by in-situ trapping in graphite furnaces or even ICP-MS found in the literature or better. Sensitivity can be improved further for Bi and Cd using larger sample volumes, but purification of blank is required for Pb. Certified standard reference materials were analyzed for the assessment of accuracy of developed method.

A method for determination of silver has been developed based on chemical vapour generation atomic absorption spectrometry (CVGAAS). Volatile species of silver in acidified medium were generated by the reduction of sodium tetrahydroborate / these species were sent to a flame-heated quartz tube atomizer (QTA) following isolation by using a gas-liquid separator. Flow injection (FI) was used for sample introduction. Optimization of parameters such as / concentrations of acid and NaBH4 concentration, flow rates of solutions and carrier gas were made. The influences of the well-known chemical modifier, Pd, and the effect of diethyldithiocarbomate (DDTC) were also examined. Interference study has been carried out for Ni(II), Co(II), Cu(II), Fe(III), Au(III), As(III), Pb(II), Se(IV) and Sn(II) . A detection limit of 7.5 ng mL-1 (n=11) was obtained with a 0.2 mL sample volume. With the FI-CVGAAS system 5.6 times sensitivity enhancement was achieved over flame atomic absorption spectrometry (FAAS).

The use of slotted quartz tube (SQT) as an atom trap in atomic absorption spectrometry (AAS) provides a more stable chemical environment for atomization / the technique is simple and easily applicable in any laboratory. This thesis study involves application of SQT together with some other approaches to thallium determination by AAS. The first stages involve the efforts to improve nebulization efficiency of conventional flame atomic absorption spectrometry (FAAS) with and without the use of SQT. This is achieved by mixing 100 &micro / L of propanol with 500 &micro / L of Tl standard solution using the optimum conditions. By this method, Propanol-SQT-FAAS, 4.49 times enhancement in sensitivity has been obtained with respect to conventional FAAS, method in which the characteristic concentration was calculated as 894 ng/mL. The second stage of investigation is about the use of SQT as an atom trap, AT, preconcentration device for thallium determination. The similar technique has been successfully applied to some other analytes such as Pb, Cd, Bi and Au / detection limits at the level of ng/mL were obtained in the previous studies. In the present work, the analyte atoms are trapped on the inner surface of SQT in the presence of a lean air-acetylene flame for few minutes. After this collection step, a volume of methyl isobutyl ketone, MIBK, amounting to 10-50 microliters is introduced via conventional nebulization / this causes a momentary alteration in the flame composition and thus results in the release of trapped analyte atoms from the quartz surface. This revolatilization step is followed by a rapid atomization and transient signal was obtained. In addition to this method, a novel approach has been investigated where the inner surface of SQT was modified by using a metal coating with low volatility. For this purpose, eight different coating materials which were tungsten, palladium, molybdenum, gold, tantalum, zirconium, titanium and osmium, have been applied to the inner surface of SQT and as osmium was found to be most appropriate one, the rest of the study was continued with Os-Coated-SQT. This modification provided a better surface than quartz alone so that analyte atoms are trapped more efficiently and also released easily. Although the working principle of the Coated-SQT-AT-FAAS method is same with SQT-AT-FAAS, the conditions for SQT-AT-FAAS and Os-Coated-SQT-AT-FAAS methods were optimized seperately. Limit of detections, 3s/m, has been found to be 38 ng/mL and 3.5 ng/mL for these cases, respectively. While the SQT-AT-FAAS method has provided 92 fold enhancement, the Os-Coated-SQT-AT-FAAS method has provided a 319 fold sensitivity improvement with respect to conventional FAAS method.

In this study, silver nanorods and nanospheroids were prepared both in aqueous solution and on the surface of glass slides through seed-mediated growth approach at room temperature and used as a surface enhanced Raman scattering (SERS) substrate. The synthesis of metallic nanorods was started with the production of silver nanospheres as seed utilizing sodium borohydride and trisodium citrate as reducing and capping agents, respectively. These seeds were then added to a growth solution containing additional silver salt, ascorbic acid and cetyltrimethylammonium bromide (CTAB.) Nanorod preparation conditions were first optimized in solution phase. The plasmon absorption of the formed nanocrystals was monitored by UV-Visible spectrometry. The largest red shift in the longitudinal plasmon resonance absorption of silver nanostructures was tried to be achieved in order to realize the highest electromagnetic enhancement in Raman measurements. The images of the formed nanorods were recorded using field emission scanning electron microscopy (FE-SEM). The optimized colloidal growth conditions were adopted for the growth of nanorods on the surface of the glass substrate. Sol-gel coated glass slides were used in order to increase the porosity on the surface for an effective seeding process. We reported the development of a novel SERS substrate prepared by growing silver nanorods directly on the surface of glass surface without using any linker molecule. The SERS performances of the nanorod growth surfaces were evaluated with crystal violet (CV), brilliant cresyl blue (BCB) and benzoic acid (BA). Some modifications such as the increase in the AgNO3 concentration in the growth solution and the addition of hydrocarbons to the growth solution were investigated for the enhancement of the SERS signal. The intense spectra obtained for the model compounds demonstrated the efficiency of the prepared substrate for the SERS enhancement and its potential as a SERS detection probe for chemical and biological analysis.