Mürvet Volkan

SURFACE-ENHANCED RAMAN SCATTERING (SERS) METHOD AND INSTRUMENTATION FOR GENOMICS AND BIOMEDICAL ANALYSIS

The development of a surface-enhanced Raman scattering (SERS) method and instrument for use in biomedical and genomics analysis is described. The technology uses DNA gene probes based on SERS labels for gene detection and DNA mapping. The detection method uses nanostructured metallic substrates as SERS-active platforms. The surface-enhanced Raman gene (SERGen) probes can be used to detect DNA targets via hybridization to DNA sequences complementary to these probes. The probes do not require the use of radioactive labels and have great potential to provide both sensitivity and selectivity. Advanced instrumental systems designed for point-source spectral measurements and for multi-spectral imaging (MSI) are described. The MSI concept allows recoding the entire SERS spectrum for every pixel on the two-dimensional hybridization platform in the field of view with the use of a rapid-scanning solid-state device, such as the acousto-optic tunable filter (AOTF). The usefulness of the SERGen approach and its applications in biomedical diagnostics, high-throughput analysis and DNA mapping and sequencing are discussed. Copyright

Pre-concentration of some trace metals from sea water on a mercapto-modified silica gel

Silica modified by the addition of mercapto chelating groups has been developed for the pre-concentration of trace metals from natural waters. This material removes cadmium, copper, lead and zinc from aqueous solution and can be employed for the pre-concentration of these metals by both column and batch techniques. Under column and batch conditions recoveries larger than 95% were common. For batch extractions of cadmium, zinc, copper and lead from sea water, recoveries of 91 ± 5, 98 ± 4, 97 ± 4 and 96 ± 5%, respectively, were obtained.

Copper(0) nanoparticles supported on silica-coated cobalt ferrite magnetic particles: cost effective catalyst in the hydrolysis of ammonia-borane with an exceptional reusability performance.

Herein we report the development of a new and cost-effective nanocomposite catalyst for the hydrolysis of ammonia-borane (NH(3)BH(3)), which is considered to be one of the most promising solid hydrogen carriers because of its high gravimetric hydrogen storage capacity (19.6% wt) and low molecular weight. The new catalyst system consisting of copper nanoparticles supported on magnetic SiO(2)/CoFe(2)O(4) particles was reproducibly prepared by wet-impregnation of Cu(II) ions on SiO(2)/CoFe(2)O(4) followed by in situ reduction of the Cu(II) ions on the surface of magnetic support during the hydrolysis of NH(3)BH(3) and characterized by ICP-MS, XRD, XPS, TEM, HR-TEM and N(2) adsorption-desorption technique. Copper nanoparticles supported on silica coated cobalt(II) ferrite SiO(2)/CoFe(2)O(4) (CuNPs@SCF) act as highly active catalyst in the hydrolysis of ammonia-borane, providing an initial turnover frequency of TOF = 2400 h(-1) at room temperature, which is not only higher than all the non-noble metal catalysts but also higher than the majority of the noble metal based homogeneous and heterogeneous catalysts employed in the same reaction. More importantly, they were easily recovered by using a permanent magnet in the reactor wall and reused for up to 10 recycles without losing their inherent catalytic activity significantly, which demonstrates the exceptional reusability of the CuNPs@SCF catalyst.

Selective pre-concentration of selenite from aqueous samples using mercapto-silica

Silica gel modified with 3-mercaptopropyl-trimethoxysilane was used for the selective separation and pre-concentration of selenite (Se(IV)) from aqueous solutions containing Se(IV) and selenate (Se(VI)). Over a wide range of acidity, from 2 mol l(-1) HCl to pH 9.00, Se(IV) was taken up by the mercaptopropyl-silica with nearly 100% efficiency; Se(VI) however was unretained. Se(IV) content was determined by hydride generation atomic absorption spectrometry (HGAAS), following batch release of the selenium from the pre-concentration medium by acidic periodate. The overall pre-concentration efficiency, including both take-up and elution, in the range of 89-106%. The method was applied to spiked seawater samples containing as low as 800 ng l(-1) Se in selenite form. This solid-phase extraction system offers several major advantages over conventional solvent extraction procedures. It firstly exhibits high selectivity for Se(IV) over Se(VI). Using the solid-phase media, pre-concentration of Se(IV) in dilute water samples can be carried out in the field, stabilizing the selenite-selenium in a convenient form for transport and storage. In addition, selenium stored on silica is derived solely from Se(IV) overcoming problems of selenium redox speciation changes and loss during storage.

Surface-Enhanced Raman of Dopamine and Neurotransmitters Using Sol-Gel Substrates and Polymer-Coated Fiber-Optic Probes

Surface-enhanced Raman spectroscopy (SERS) is used to detect catecholamines—viz., dopamine, norepinephrine, epinine, and isoproterenol—using a new substrate prepared with sol-gel technology. Catecholamines are complexed at the surface by iron(III) ions, which were introduced during the reduction of the silver ions embedded inside the sol-gel matrix. With the use of a He-Ne laser at a power of only 12 mW, it is possible to measure dopamine in the micromolar concentration range. A single-fiber SERS probe system was also introduced that has great potential for sampling in microenvironment applications such as in vivo measurements of dopamine. In this microprobe design both excitation and SERS signals are transmitted through the same fiber simultaneously. The tips of tapered fibers were coated with a polyvinyl alcohol polymer doped with metallic silver particles. The potential of the SERS method and microprobes for medical diagnostics is discussed.

New Approach for the Surface Enhanced Resonance Raman Scattering (SERRS) Detection of Dopamine at Picomolar (pM) Levels in the Presence of Ascorbic Acid

The development of a novel surface-enhanced resonance Raman scattering (SERRS) platform that allows fast and sensitive detection of dopamine (DA) has been reported. The iron-nitrilotriacetic acid attached silver nanoparticle (Ag-Fe(NTA)) substrate provides remarkable sensitivity and reliable repeatability. The advantages of both the surface functionalization for specific analytes and the SERRS are integrated into a single functional unit. While the silver core gives the necessary enhancing properties, the Fe-NTA receptors can trap DA adjacent the silver core and the NTA-Fe-DA complex formed provides resonance enhancement with a 632.8 nm laser. DA could be detected in pM level without any pretreatment with a reliable discrimination against AA, by utilizing low laser power (10 mW) and short data acquisition time (10 s). The high sensitivity along with the improved selectivity of this sensing approach is a significant step toward molecular diagnosis of Parkinsons disease.

Cloud point preconcentration of germanium and determination by hydride generation atomic absorption spectrometry

Abstract Cloud point methodology has been successfully employed for the preconcentration of germanium at trace levels from aqueous samples prior to hydride generation flame atomic absorption spectrometry (HGAAS). Germanium was taken into complex with quercetin in aqueous non-ionic surfactant (Triton X-114) medium and concentrated in the surfactant rich phase by bringing the solution to the cloud point temperature (19°C). The preconcentration of only 50 ml of solution with 0.1% Triton X-114 and 2×10−5 M quercetin at pH 6.4 gives a preconcentration factor of 200. Under these conditions, the detection limit (3s) and the sensitivity of the cloud-point extraction-HGAAS system were 0.59 and 0.0620 μg l−1, respectively. The extraction efficiency was investigated at low germanium concentrations (10–30 μg l−1) and satisfactory recoveries (93–105%) were obtained.

A Novel Acetylcholinesterase Biosensor: Core–Shell Magnetic Nanoparticles Incorporating a Conjugated Polymer for the Detection of Organophosphorus Pesticides

To construct a sensing interface, in the present work, a conjugated polymer and core-shell magnetic nanoparticle containing biosensor was constructed for the pesticide analysis. The monomer 4,7-di(furan-2-yl)benzo[c][1,2,5]thiadiazole (FBThF) and core-shell magnetic nanoparticles were designed and synthesized for fabrication of the biosensing device. The magnetic nanoparticles were first treated with silica and then modified using carboxyl groups, which enabled binding of the biomolecules covalently. For the construction of the proposed sensor a two-step procedure was performed. First, the poly(FBThF) was electrochemically generated on the electrode surface. Then, carboxyl group modified magnetic nanoparticles (f-MNPs) and acetylcholinesterase (AChE), the model enzyme, were co-immobilized on the polymer-coated surface. Thereby, a robust and novel surface, conjugated polymer bearing magnetic nanoparticles with pendant carboxyl groups, was constructed, which was characterized using Fourier transform infrared spectrometer, cyclic voltammetry, scanning electron microscopy, and contact angle measurements. This novel architecture was then applied as an immobilization platform to detect pesticides. To the best of our knowledge, a sensor design that combines both conjugated polymer and magnetic nanoparticles was attempted for the first time, and this approach resulted in improved biosensor characteristics. Hence, this approach opens a new perspective in the field of enzyme immobilization and sensing applications. Paraoxon and trichlorfon were selected as the model toxicants. To obtain best biosensor performance, optimization studies were performed. Under optimized conditions, the biosensor in concern revealed a rapid response (5 s), a low detection limit (6.66 × 10(-3) mM), and high sensitivity (45.01 μA mM(-1) cm(-2)). The KM(app) value of poly(FBThF)/f-MNPs/AChE were determined as 0.73 mM. Furthermore, there was no considerable activity loss for 10 d for poly(FBThF)/f-MNPs/AChE biofilm.

A NEW SURFACE-ENHANCED RAMAN SCATTERING SUBSTRATE BASED ON SILVER NANOPARTICLES IN SOL-GEL

We report for the first time the development of a new surface-enhanced Raman scattering (SERS)-active silver chloride silica–glass substrate prepared by using in situ precipitation of silver chloride particles in sol–gel films as a precursor for nanoparticles of silver. The controlled precipitation of silver chloride was achieved by the reaction of silver nitrate with trichloroacetic acid, which leads to a slow release of chloride ions. Silver chloride particles were reduced to silver nanoparticles by FeSO4·7H2O. The sol–gel films prepared exhibit good optical properties and induce a strong SERS effect for several model compounds, including cresyl fast violet and brilliant cresyl blue. Optimization studies of substrate preparation and coating conditions were performed and are discussed in detail. The performance of this new substrate compares favorably with those of previously developed silver-coated alumina substrates. The SERS spectra of other compounds of environmental and biological interest, such as 1−aminonaphthalene, 2−aminopyrimidine, pyridine and p

Preconcentration of germanium on mercapto-modified silica gel☆

-aminobenzoic acid, were investigated to illustrate the usefulness of this novel type of SERS substrate for use in chemical and biological analysis. Copyright