Ayça Atılır Özcan

Development of a disposable and low-cost electrochemical sensor for dopamine detection based on poly(pyrrole-3-carboxylic acid)-modified electrochemically over-oxidized pencil graphite electrode

In this study, preparation of a single-use electrochemical sensor for the selective and sensitive determination of dopamine (DOP) was investigated by electrochemical polymerization of pyrrole-3-carboxylic acid on electrochemically over-oxidized pencil graphite electrode (p(P3CA)/EOPGE). Cyclic voltammetry measurements of Fe(CN)64-/3- indicated that the electrochemically over-oxidized PGE (EOPGE) showed superior electron transfer characteristics according to bare PGE. The ionized carboxyl groups found in the structure of poly(pyrrole-3-carboxylic acid) (p(P3CA)) showed high affinity towards positively charged DOP. The combination of the advantages of EOPGE and p(P3CA) in p(P3CA)/EOPGE led to a synergistic effect on the electrochemical oxidation of DOP. The effects of experimental variables on the voltammetric performance of the p(P3CA)/EOPGE were examined by preparing the electrodes at different conditions. The p(P3CA)/EOPGE showed high selectivity towards DOP by discriminating its oxidation potential from the common interfering substances such as ascorbic and uric acids. The p(P3CA)/EOPGE showed linear responses in the electrochemical oxidation of DOP between the concentration values of 0.025µM and 7.5µM. Detection limit was determined as 0.0025µM according to signal to noise ratio (S/N: 3). Analytical application of p(P3CA)/EOPGE was successfully tested in the determination of DOP in blood serum and pharmaceutical samples.

Investigation of photosensitively bioconjugated targeted quantum dots for the labeling of Cu/Zn superoxide dismutase in fixed cells and tissue sections

This study presents the development of targeted and antibody cross-linked QDs and explores whether these bioconjugates could specifically and effectively label Cu/Zn superoxide dismutase (SOD1) on fixed cells and tissues. QD-antibody conjugation was achieved by using our previously invented AmiNoacid (monomer) Decorated and Light Underpining Conjugation Approach (ANADOLUCA) method. In this method, we have used a photosensitive aminoacid monomer having ruthenium complex which is a synthetic and inexpensive material for the preparation of bioconjugates. Its specificity was demonstrated by extracting the active enzyme from rat liver lysate by using the bioconjugate. It provided accurate antibody orientation, high specificity and mechanic stability. The protocol steps for QD-antibody conjugation and specimen preparation were described in detail. The nanobioconjugates were prepared under mild conditions (for example in day light), independent of pH and temperature, without affecting conformation and function of protein. This protocol is simple, inexpensive and can be successfully adapted to detect other targets on different cell types and tissues.

Molecular Imprinted Solid-Phase Extraction System for the Selective Separation of Oleuropein from Olive Leaf

Oleuropein has many antimicrobial, antiviral, and anticancer features found in olive leaf. Therefore, its isolation from olive leaf is very important in such kinds of applications. In this study, a solid-phase extraction system based on the molecularly imprinted polymer (MIP) was proposed for the selective separation of oleuropein from olive leaf. First, oleuropein imprinted polymer has been prepared by the suspension polymerization using methacrylolamidoantiprine–iron (III) metal-chelate monomers. After that, the oleuropein adsorption capacity and selectivity of the prepared imprinted polymer has been determined. The maximum adsorption capacity of oleuropein has found to be 140 mg g−1. Finally, MIP has been used as a sorbent in the solid-phase extraction for the separation of oleuropein from crude extract of olive leaves. The oleuropein analyses have been realized by high performance liquid chromatography. The obtained results indicated that the prepared molecularly imprinted sorbent could be used for at least 10 times for purification of oleuropein from olive leaf. The application of the proposed system in the real sample showed that 24.2 mg pure oleuropein could be obtained from 1.0 g of crude olive leaf extract. As a result, the low cost, simple, and selective adsorbent has been developed for oleuropein adsorption. Supplemental materials are available for this article. Go to the publishers online edition of Separation Science & Technology to view the supplemental file.

Preparation of a novel hydrophobic affinity cryogel for adsorption of lipase and its utilization as a chromatographic adsorbent for fast protein liquid chromatography

In this study, we have prepared a hydrophobic cryogel for the chromatographic separation of lipase from its aqueous solutions including single protein and protein mixture and also Yarrowia lipolytica cell extract. N‐methacryloyl‐(l)‐phenylalanine methyl ester was used as a monomer to provide the hydrophobic character to the prepared cryogels. The highest adsorption capacity was observed at pH 5.0 at 0.5 mL min−1 flow rate. The chromatographic separation of lipase was achieved from a binary mixture of lipase:bovine serum albumin (BSA) and lipase:lysozyme, and was also achieved from triple‐mixture of lipase:lysozyme:BSA by using fast protein liquid chromatography. Finally, lipase purification was performed from Yarrowia lipolytica cell extract used as a natural source. These studies have shown that the hydrophobic cryogel has good chromatographic performance for the separation and purification of lipase not only from aqueous solution, but also from cell extract as a natural source of lipase.

Investigation of applicability of Electro-Fenton method for the mineralization of naphthol blue black in water

In this study, mineralization and color removal performance of electro-Fenton method were examined in water containing naphthol blue black (NBB), a diazo dye. NBB was totally converted to intermediate species in a 15-min electrolysis at 60 mA, but complete de-colorization took 180 min. A very high oxidation rate constant ((3.35 ± 0.21) x 1010 M-1s-1) was obtained for NBB, showing its high reactivity towards hydroxyl radicals. A very high total organic carbon (TOC) removal value (45.23 mg L-1) was obtained in the first 60 min of the electro-Fenton treatment of an aqueous solution of NBB (0.25 mM) at 300 mA, indicating the mineralization efficiency of the electro-Fenton method. Mineralization current efficiency values obtained at 300 mA gradually decreased from 24.18% to 4.47% with the electrolysis time, indicating the presence of highly parasitic reactions. Gas chromatography-mass spectrometry analyses revealed that the cleavage of azo bonds of NBB led to formation of different aromatic and aliphatic oxidation intermediates. Ion chromatography analysis showed that ammonium, nitrate and sulfate were the mineralization end-products. The concentration of sulfate ion reached to its quantitative value at the 4th h of electrolysis. On the other hand, the total concentration of ammonium and nitrate ions reached to only 61% of the stoichiometric amount of initial nitrogen after a 7 h electrolysis. Finally, it can be said that the electro-Fenton method is a suitable and efficient method for the removal of NBB and its intermediates from water.

Preparation of a disposable and low-cost electrochemical sensor for propham detection based on over-oxidized poly(thiophene) modified pencil graphite electrode

In this study, an electrochemical sensor was developed for the determination of propham (PRO) in potato, human urine and river water samples based on the over-oxidized poly(thiophene) modified pencil graphite [PG/p(Thp)-Ox] electrode. Adsorptive stripping differential pulse voltammetry was used as a voltammetric method. The PG/p(Thp)-Ox electrode increased the oxidation peak current of PRO 30 times according to bare PG. Electrochemical polymerization and over-oxidation conditions were deeply optimized to increase the sensitivity of PG/p(Thp)-Ox. Characterization of PG/p(Thp)-Ox was performed via scanning electron microscopy and cyclic voltammetry analysis. Oxidation peak current value of PRO linearly increased with the concentration of PRO in the ranges of 0.005-1.0 μM and 2.0-15.0 μM. A very low limit of detection value (1.0 nM) was obtained. Intra-day and inter-day reproducibility of the PG/p(Thp)-Ox were determined as 2.96% (N: 10) and 4.77% (10 days), respectively. Satisfactory recovery values (98.07-104.4%) were observed with PG/p(Thp)-Ox electrode during the analysis of PRO in PRO-spiked potato, urine and river water samples. The results show that the PG/p(Thp)-Ox could be used safely in the determination of PRO.

PREPARATION OF A MODIFIED ELECTRODE FOR THE DETERMINATION OF LEVOFLOXACIN

In this study, modification of glassy carbon electrode with electrochemically reduced graphene oxide (ERGO) and acid treated multi-walled carbon nanotubes (A-MWCNT) was investigated for the voltammetric determination of LEV in body fluids and pharmaceutical products. Different combinations of GO, ERGO, MWCNT and A-MWCNT were searched and the best results obtained with GC/ERGO/A-MWCNT electrode. The prepared modified electrode showed electrocatalytic acitivity towards LEV oxidation by increasing oxidation peak currents 293 times. Characterizations of the modified electrode was performed with cyclic voltammetry, electrochemical impedance spectroscopy and raman measurements. The highest oxidation peak current was observed at pH value of 2.0. The oxidation peak currents of LEV increased linearly with the concentration of LEV in the range of 0.01 m M and 10 m M. The detection limit of the prepared sensor was determined as 0.0063 m M. After three weeks’ storage, the prepared electrode showed high stability by preserving 93% of its original activity towards 1.0 m M LEV. The prepared electrode successfully discriminates the voltammetric response of LEV from that of other fluoroquinolone antibiotics (enoxacin, norfloxacin, ciprofloxacin). Finally, the performance of the prepared electrode was tested in the determination of LEV in human blood serum, urine and pharmaceutical samples.