Ugur Tamer

Magnetic gold nanoparticles in SERS-based sandwich immunoassay for antigen detection by well oriented antibodies.

The aim of the study was to develop an indirect, robust and simple in application method for the detection of bovine leukemia virus antigen gp51. Surface-enhanced Raman scattering (SERS) was applied as detection method. Magnetic gold nanoparticles (MNP-Au) modified by antibodies in oriented or random manner were used for the binding of gp51. The high performance liquid chromatography analysis indicated that the best antibody immobilization and antigen capturing efficiency was achieved using fragmented antibodies obtained after reduction of intact antibodies with dithiothreitol. In order to increase efficiency and sensitivity of immunoassay Raman labels consisting of gold nanorods coated by 5-thio-nitrobenzoic acid layer with covalently bounded antibodies have been constructed. The LOD and LOQ of the proposed immunoassay for antigen gp51 detection were found to be 0.95μgmL(-1) and 3.14μgmL(-1), respectively. This immunoassay was successfully applied for the detection of gp51 in milk samples in a rapid, reliable and selective manner. We believe that the proposed SERS-based immunoassay format can be applied for the detection of other proteins.

A novel glucose biosensor platform based on Ag@AuNPs modified graphene oxide nanocomposite and SERS application

This study represents a novel template demonstration of a glucose biosensor based on mercaptophenyl boronic acid (MBA) terminated Ag@AuNPs/graphene oxide (Ag@AuNPs-GO) nanomaterials. The nanocomposites were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) method. The TEM image shows that Ag@AuNPs in the nanocomposite is in the range of diameters of 10-20 nm. The nanocomposite was used for the determination of glucose through the complexation between boronic acid and diol groups of glucose. Thus, a novel glucose biosensor was further fabricated by immobilizing glucose oxidase (GOD) into MBA terminated Ag@AuNPs-GO nanocomposite film (MBA-Ag@AuNPs-GO). The linearity range of glucose was obtained as 2-6mM with detection limit of 0.33 mM. The developed biosensor was also applied successfully for the determination of glucose in blood samples. The concentration value of glucose in blood samples was calculated to be 1.97±0.002 mM from measurements repeated for six times.

Rapid analysis of sugars in honey by processing Raman spectrum using chemometric methods and artificial neural networks

The aim of this study was to quantify glucose, fructose, sucrose and maltose contents of honey samples using Raman spectroscopy as a rapid method. By performing a single measurement, quantifications of sugar contents have been said to be unaffordable according to the molecular similarities between sugar molecules in honey matrix. This bottleneck was overcome by coupling Raman spectroscopy with chemometric methods (principal component analysis (PCA) and partial least squares (PLS)) and an artificial neural network (ANN). Model solutions of four sugars were processed with PCA and significant separation was observed. This operation, done with the spectral features by using PLS and ANN methods, led to the discriminant analysis of sugar contents. Models/trained networks were created using a calibration data set and evaluated using a validation data set. The correlation coefficient values between actual and predicted values of glucose, fructose, sucrose and maltose were determined as 0.964, 0.965, 0.968 and 0.949 for PLS and 0.965, 0.965, 0.978 and 0.956 for ANN, respectively. The requirement of rapid analysis of sugar contents of commercial honeys has been met by the data processed within this article.

Electrochemical control of solid phase micro-extraction: conducting polymer coated film material applicable for preconcentration/analysis of neutral species

Exploitation of the physical, chemical and electrically conductive properties of poly(3-dodecylthiophene) (P3DDT) for the preconcentration and release in solid phase microextraction (SPME) of organometallic arsenobetaine (AsB) from aqueous media was investigated. Hydrophobic interactions between this neutral arsenic species and an undoped polythiophene (no applied potential) with n-substituted alkyl groups (n=12) in the three position were used for the diffusion-controlled preconcentration. After absorption into the polymer matrix, the chemical properties of this conductive polymer were changed by applying an external potential. This potential provides a sufficient driving force for desorption of the analyte from the extraction phase into an aqueous solution for subsequent analysis. The applied positive potential oxidizes the polymer to its charged hydrophilic state, which releases the neutral analyte. The concentration and speciation of the analyte from the sample matrix was analyzed by HPLC coupled to an ICP-MS. The diffusion-controlled uptake was fast (equilibrium attained within minutes) and did not require pretreatment of the analyte. The electrochemically-controlled release of the analyte is also very rapid (within minutes). This conducting polymer film system, therefore, can offer analytical applications for the convenient preconcentration and subsequent analysis of neutral environmental species.

Comparison of sensing strategies in SPR biosensor for rapid and sensitive enumeration of bacteria.

Rapid and sensitive detections of microorganisms are very important for biodefence, food safety, medical diagnosis and pharmaceutics. The present study aims to find out the most proper bioactive surface preparation method to develop rapid, sensitive and selective bacteria biosensor, based on surface plasmon resonance (SPR) spectroscopy. Escherichia coli (E. coli) was used as a model bacterium and four sensing strategies in SPR were tested. Three of these strategies are antibody immobilization methods that are non-specific adsorption, specific adsorption via the avidin-biotin interaction, and immobilization of antibodies via self-assembled monolayer formation. The fourth strategy is a novel method for bacteria enumeration based on the combination of the SPR spectroscopy and immunomagnetic separation with using gold-coated magnetic nanoparticles. According to results, the most efficient SPR method is the one based on gold-coated magnetic nanoparticles. This method allows to specifically separate E. coli from the environment and to quantify rapidly without any labeling procedure. The developed method has a linear range between 30 and 3.0 × 10(4)cfu/ml, and a detection limit of 3 cfu/ml. The selectivity of the method was examined with Enterobacter aerogenes and Enterobacter dissolvens, which did not produce any significant response. The usefulness of the method to detect E. coli in real water samples was also investigated, and the results were compared with the results from plate-counting method. There was no significant difference between the methods (p>0.05).

Attomole sensitivity of staphylococcal enterotoxin B detection using an aptamer-modified surface-enhanced Raman scattering probe.

In this report, we present a new homogeneous detection method for staphylococcal enterotoxin B (SEB) utilizing core-shell-structured iron-gold magnetic nanoparticles and a gold nanorod surface-enhanced Raman scattering (SERS) probe in solution. Peptide ligand (aptamer) functionalized magnetic gold nanorod particles were used as scavengers for target SEB. After the SEB molecules were separated from the matrix, the sandwich assay procedure was tested by gold nanorod particles that act as SERS probes. The binding constant between SEB and peptide-nanoparticle complex was determined as 8.0 × 10(7) M(-1). The correlation between the SEB concentration and SERS signal was found to be linear within the range of 2.5 fM to 3.2 nM. The limit of detection for the homogeneous assay was determined as 224 aM (ca. 2697 SEB molecules/20 μL sample volume). Also, gold-coated surfaces were used as capture substrates and performances of the two methods were compared. Furthermore, the developed method was evaluated for investigating the SEB specificity on bovine serum albumin (BSA) and avidin and detecting SEB in artificially contaminated milk, blood, and urine.

Electrochemically controlled solid-phase microextraction (EC-SPME) based on overoxidized sulfonated polypyrrole

A method for the extraction and selective determination of cations is proposed using electro-synthesized overoxidized sulfonated polypyrrole film. The polymer film is used for the selective extraction of trace levels of nickel and cadmium ions by solid-phase microextraction (SPME). The cation uptake and release properties of the overoxidized sulfonated polypyrrole film electrode were examined under both open circuit and controlled potential conditions for prospective applications in electrochemically controlled solid-phase microextraction. Increased extraction efficiency and selectivity toward cations were achieved in high saline content of water. Simple preparation of film coatings on a platinum wire was possible using a constant potential method. Applied positive and negative potentials facilitated the extraction and desorption of cations, respectively. Nickel and cadmium ions were desorbed into sample aliquot and determined by electrothermal atomic absorption spectrometry (ETAAS). The cation uptake and release mechanism is affected both by the cation exchange at the negative sulfonate and carboxylate moiety on the film and the altered solution pH occurring at the counter electrode caused by the applied potential. The method was validated using a standard reference material and tested for the determination of cadmium ion in commercial table salt samples.

Determination of butter adulteration with margarine using Raman spectroscopy.

In this study, adulteration of butter with margarine was analysed using Raman spectroscopy combined with chemometric methods (principal component analysis (PCA), principal component regression (PCR), partial least squares (PLS)) and artificial neural networks (ANNs). Different butter and margarine samples were mixed at various concentrations ranging from 0% to 100% w/w. PCA analysis was applied for the classification of butters, margarines and mixtures. PCR, PLS and ANN were used for the detection of adulteration ratios of butter. Models were created using a calibration data set and developed models were evaluated using a validation data set. The coefficient of determination (R(2)) values between actual and predicted values obtained for PCR, PLS and ANN for the validation data set were 0.968, 0.987 and 0.978, respectively. In conclusion, a combination of Raman spectroscopy with chemometrics and ANN methods can be applied for testing butter adulteration.

Large area uniform deposition of silver nanoparticles through bio-inspired polydopamine coating on silicon nanowire arrays for practical SERS applications

Despite the significant progress, the controlled deposition of nanoparticles onto the support materials having 3-D nano-morphologies is still facing challenges due to the limited diffusion of metal ions into the nanostructures and uncontrolled aggregation of nanoparticles. In this study, a simple yet versatile alternative is demonstrated to control the silver nanoparticle (AgNP) density and morphology onto the 3-D silicon nanowire (SiNW) arrays based on bio-inspired polydopamine (PDOP) coating and electroless plating approaches for practical Surface-Enhanced Raman Spectroscopy (SERS) applications. In order to control silver deposition and its morphology and to optimize the SERS performance of AgNP decorated SiNW arrays, the effect of some key experimental parameters including SiNW length and morphology, silver reduction time and PDOP thickness are investigated in detail. The optimized samples demonstrate remarkable surface-enhancement ability in Raman signals with high reproducibility (lower than ∼10% spot-to-spot and sample-to-sample). Interestingly, it is found that PDOP coating not only serves as a reducing agent for the deposition of AgNPs on SiNW arrays in a controlled manner, but also contributes to the observed SERS enhancements in terms of improving photon scattering and promoting electron transfer processes due to its organic semiconductor nature.

Combining 3-D plasmonic gold nanorod arrays with colloidal nanoparticles as a versatile concept for reliable, sensitive, and selective molecular detection by SERS

The detection of molecules at an ultralow level by Surface-Enhanced Raman Spectroscopy (SERS) has recently attracted enormous interest for various applications especially in biological, medical, and environmental fields. Despite the significant progress, SERS systems are still facing challenges for practical applications related to their sensitivity, reliability, and selectivity. To overcome these limitations, in this study, we have proposed a simple yet facile concept by combining 3-D anisotropic gold nanorod arrays with colloidal gold nanoparticles having different shapes for highly reliable, selective, and sensitive detection of some hazardous chemical and biological warfare agents in trace amounts through SERS. The gold nanorod arrays were created on the BK7 glass slides or silicon wafer surfaces via the oblique angle deposition (OAD) technique without using any template material or lithography technique and their surface densities were adjusted by manipulating the deposition angle (α). It is found that gold nanorod arrays fabricated at α = 10° exhibited the highest SERS enhancement in the absence of colloidal gold nanoparticles. Synergetic enhancement was obviously observed in SERS signals when combining gold nanorod arrays with colloidal gold nanoparticles having different shapes (i.e., spherical, rod, and cage). Due to their ability to produce localized surface plasmons (LSPs) in transverse and longitudinal directions, utilization of colloidal gold nanorods as a synergetic agent led to an increase in the enhancement factor by about tenfold compared to plain gold nanorod arrays. Moreover, we have tested our approach to detect some chemical and biological toxins namely dipicolinic acid (DIP), methyl parathion (MP), and diethyl phosphoramidate (DP). For all toxins, Raman spectra with high signal-to-noise ratios and reproducibility were successfully obtained over a broad concentration range (5 ppm-10 ppb). Our results suggest that the slightly tangled and closely-packed anisotropic gold nanorod arrays reinforced by the gold nanoparticles may serve as an ideal SERS substrate to detect any analyte in trace amounts.