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    Combining 3-D plasmonic gold nanorod arrays with colloidal nanoparticles as a versatile concept for reliable, sensitive, and selective molecular detection by SERS
    (ROYAL SOC CHEMISTRY, 2014) Yilmaz, Mehmet; Senlik, Erhan; Biskin, Erhan; Yavuz, Mustafa Selman; Tamer, Ugur; Demirel, Gokhan
    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 (a). It is found that gold nanorod arrays fabricated at alpha = 10 degrees 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.
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    Development of poly(3-aminophenylboronic acid) modified graphite rod electrode suitable for fluoride determination
    (ELSEVIER SCIENCE BV, 2014) Ciftci, Hakan; Oztekin, Yasemin; Tamer, Ugur; Ramanaviciene, Almira; Ramanavicius, Arunas
    Poly(3-aminophenylboronic acid), (PAPBA) film was formed on the graphite rod surface by potential cycling. The PAPBA-modified graphite rod (PAPBA/GR) electrode prepared in this way was used for potentiometric fluoride determination. The linear calibration range was from 5 x 10(-4) to 5 x 10(-2) M with the slope of the linear part of the calibration curve of 42.5 mV/log C. No interference effect of the most common ions such as sodium, potassium, chloride, nitrate, iodide, calcium, zinc, aluminum, sulfate and sorbitol was observed during electrochemical determination of fluoride. On the other hand, the PAPBA/GR electrode showed not only good sensitivity and selectivity, but also relatively rapid response to changes of analyte concentrations in the range of 20 s. The sensor was successfully applied for fluoride determination in real sample - toothpaste. (C) 2014 Elsevier B.V. All rights reserved.
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    Electrochemical biosensor based on glucose oxidase encapsulated within enzymatically synthesized poly(1,10-phenanthroline-5,6-dione)
    (ELSEVIER SCIENCE BV, 2014) Ciftci, Hakan; Oztekin, Yasemin; Tamer, Ugur; Ramanaviciene, Almira; Ramanavicius, Arunas
    This study is focused on the investigation of electrocatalytic effect of glucose oxidase (GOx) immobilized on the graphite rod (GR) electrode. The enzyme modified electrode was prepared by encapsulation of immobilized GOx within enzymatically formed poly(1,10-phenanthroline-5,6-dione) (pPD) film. The electrochemical responses of such enzymatic electrode (pPD/GOx/GR) vs. different glucose concentrations were examined chronoamperometrically in acetate-phosphate buffer solution (A-PBS), pH 6.0, under aerobic or anaerobic conditions. Amperometric signals of the pPD/GOx/GR electrode exhibited well-defined hyperbolic dependence upon glucose concentration. Amperometric signals at 100 mM of glucose were 41.17 and 32.27 mu A under aerobic and anaerobic conditions, respectively. Amperometric signals of the pPD/GOx/GR electrode decreased by 6% within seven days. The pPD/GOx/GR electrode showed excellent selectivity in the presence of dopamine and uric acid. Furthermore it had a good reproducibility and repeatability with standard deviation of 9.4% and 8.0%, respectively. (C) 2014 Elsevier B.V. All rights reserved.
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    Quantification of genistein and daidzein in two endemic Genista species and their antioxidant activity
    (SERBIAN CHEMICAL SOC, 2011) Orhan, Ilkay Erdogan; Tosun, Fatma; Tamer, Ugur; Duran, Ahmet; Alan, Burcu; Kok, Ali Fuat
    In the current research, the total and free genistein and daidzein contents were determined in two endemic Genista species (G. sandrasica and G. vuralii) by an HPLC method. The highest amount of total genistein and total daidzein was found in G. sandrasica, 0.582 and 0.113 %, respectively, whereas only the free daidzein content of G. sandrasica was higher than that of G. vuralii. The antioxidant activity of the crude methanol and hydrolyzed extracts of these species was evaluated by three in vitro methods; namely DPPH free radical scavenging, ferrous ion-chelating and ferric-reducing antioxidant power (FRAP) tests at 0.25, 0.50, and 1.0 mg ml(-1). The hydrolyzed extracts of both species displayed greater antioxidant activity than the crude methanol extracts in all tests. Total phenol and flavonoid contents in the extracts were determined via the Folin Ciocalteau and AlCl3 reagents, respectively. G. vuralii was richer in terms of total phenol and flavonoid contents compared to G. sandrasica.