Esra Evrim Yalcinkaya

Amine-intercalated montmorillonite matrices for enzyme immobilization and biosensing applications

Clay based biosensors were developed using montmorillonite (Mont) modified with methyl (M) and dimethylamine (DM). X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential and thermal gravimetric measurements were used to characterize the modified clays. After immobilization of glucose oxidase (GOx) via clay on the glassy carbon electrode, its application as a glucose biosensor was investigated in detail. The best response characteristics were obtained by DM-Mont and optimization of enzyme amount, reproducibility of biosensor fabrication, repeatability of measurements and operational stability were all evaluated. The optimized biosensor showed a very good linearity between 0.05 mM and 1.0 mM, a 7 s response time and a limit of detection to glucose of 0.038 mM. Also, kinetic parameters and stabilities were determined. Apparent Km and Imax values were found as 0.73 mM and 2.955 μA, respectively. As well as batch configuration, the DM-Mont/GOx biosensor was successfully applied in the flow injection analysis mode. Finally, the performance of the DM-Mont/GOx biosensor to analyze glucose in a wine sample was compared with HPLC.

Folic acid-modified clay: targeted surface design for cell culture applications

Here we report the preparation, characterization and application of folic acid modified Montmorillonite clay (FA-Mont) as a cell culture material. Clays exhibit unique properties such as good mechanical and chemical stabilities, high surface area, low toxicity and easy combination with functional organic groups. FA was used as a modifier to facilitate adhesion of folate positive cells on the clay surface. FA-Mont was characterized using FT-IR, XRD, zeta potential measurements as well as thermogravimetric analyses. Finally, the usage potential of FA-Mont as a receptor mediated cell adhesion material was successfully proved by using folate receptor (FR) rich HeLa and FR poor A-549 cells. The cell adhesion studies were monitored and imaged by fluorescence and scanning electron microscopy techniques.

Ionic liquid intercalated clay sorbents for micro solid phase extraction of steroid hormones from water samples with analysis by liquid chromatography–tandem mass spectrometry

Clay material plays an important role in the transport and retention of many compounds in the soil, therefore, clay based sorbents are promising alternatives for selective sorption of organic pollutants. In the present work, different chain length ionic liquids (ILs) namely, 1-methyl-3-octyl-imidazolium bromide, 1-methyl-3-undecyl-imidazolium bromide and 1-methyl-3-octadecyl-imidazolium bromide were intercalated in the galleries of montmorillonite (MMT) clay. Then, this novel nanofiller surface was utilized in micro extraction of estrogenic hormones for the first time. A fast procedure where sonication-assisted emulsification microextraction combined with vortex assisted micro-solid phase extraction (μ-SPE) was developed for the LC-MS/MS analysis of estrone (E1), 17β-estradiol (E2), estriol (E3) and ethynylestradiol (EE2). The parameters related to the μ-SPE procedure namely; pH, sorbent amount, extraction solvent type and volume, sonication and vortex time, sample volume and salt effect on the extraction efficiency were screened by applying Plackett-Burmann design. The selected parameters were then optimized by using Box-Behnken design. The method was validated for the determination of estrogenic hormone residues in river water samples. Linear calibration plots were obtained for all hormones whose regression coefficients were larger than 0.98. RSD values were found less than 10% for three levels of concentration. LOD levels were calculated as; 0.012, 0.062, 0.018 and 0.693 ng L(-1) for E1, E2, E3 and EE2, respectively. Recovery values were calculated in the range of 86.9-97.7%. Considering large sample volumes required for attaining low limits of these hormones, present method provides an ease for analyst as 10 mL of the sample is adequate for achieving the same sensitivity.

A novel polythiophene – ionic liquid modified clay composite solid phase microextraction fiber: Preparation, characterization and application to pesticide analysis

This report comprises the novel usage of polythiophene - ionic liquid modified clay surfaces for solid phase microextraction (SPME) fiber production to improve the analysis of pesticides in fruit juice samples. Montmorillonite (Mmt) clay intercalated with ionic liquids (IL) was co-deposited with polythiophene (PTh) polymer coated electrochemically on an SPME fiber. The surface of the fibers were characterized by using scanning electron microscopy (SEM). Operational parameters effecting the extraction efficiency namely; the sample volume and pH, adsorption temperature and time, desorption temperature and time, stirring rate and salt amount were optimized. In order to reveal the major effects, these eight factors were selected and Plackett-Burman Design was constructed. The significant parameters detected; adsorption and temperature along with the stirring rate, were further investigated by Box-Behnken design. Under optimized conditions, calibration graphs were plotted and detection limits were calculated in the range of 0.002-0.667ng mL(-1). Relative standard deviations were no higher than 18%. Overall results have indicated that this novel PTh-IL-Mmt SPME surface developed by the aid of electrochemical deposition could offer a selective and sensitive head space analysis for the selected pesticide residues.

Amine intercalated clay surfaces for microbial cell immobilization and biosensing applications

Trimethylamine (TM) intercalated montmorillonite (Mont) clay was prepared and characterized using X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential and thermal gravimetric measurements. Gluconobacter oxydans cells were immobilized on the micro-structured matrix and used in microbial sensor applications. Sensor responses were based on the respiratory activity of the cells and the consumption of oxygen was monitored at −0.7 V (vs. Ag/AgCl and platinum electrodes) by using glucose as a substrate. Stabilization of the bacteria was performed on the Mont using glutaraldehyde. Optimization of the TM-Mont/G. oxydans sensor and examination of the electrochemical mechanism were carried out in a batch system. Measurements concerning analytical characteristics, operational stability, repeatability and substrate specificity depending on the carbon source in the culture were investigated in a flow injection analysis (FIA) system. Linear ranges were found between 0.15 and 5.0 mM for the batch mode and 0.1 and 5.0 mM for the FIA system, respectively. Finally, real samples were analyzed and were compared with the results of a spectrophotometric method as reference.

Electrokinetic Properties of Acid-Activated Montmorillonite Dispersions

In this study, the influence of pH, electrolyte concentration, and type of ionic species on the electrokinetic properties (zeta potential and electrokinetic charge density) of the acid-activated montmorillonite mineral have been investigated using the microelectrophoresis method. The electrokinetic properties of acid-activated montmorillonite dispersions have been determined in aqueous solutions of mono-, di-, and trivalent salts and divalent heavy metal salts. Zeta potential experiments have been performed to determine the point of zero charge (pzc) and potential determining ions (pdi). The zeta potential values of the acid-activated montmorillonite particles were negative and did not vary significantly within the pH range studied. Acid-activated montmorillonite dispersions do not have point of zero charge (pzc). The valence of the electrolytes has a great influence on the electrokinetic behavior of the suspension. A gradual decrease in the zeta potential (from −25 mV to −5 mV) occurs with the monovalent electrolytes when concentration increased. Divalent and heavy metal electrolytes have less negative z-potentials due to the higher valence of ions. A sign reversal of z-potential has been observed at AlCl3, FeCl3, and CrCl3 electrolytes (potential determining ions) and zeta potential values have had a positive sign at high electrolyte concentrations. The electrokinetic charge density of acid-activated montmorillonite has shown similar trends for variation in mono- and divalent electrolyte solutions. Up to concentrations of ca. 10−3 M, it has remained practically constant at approximately 0.5 × 10−3 C m−2 For higher concentrations of monovalent electrolytes more negative values (−16 × 10−3 C m−2) were observed. It has less negative values in divalent electrolyte concentrations according to monovalent electrolytes (−5 × 10−3 C m−2). For low concentrations of trivalent electrolytes, the electrokinetic charge density of montmorillonite particles is constant, but at certain concentrations it rapidly increased and changed its sign to positive.

Calixarene modified montmorillonite: a novel design for biosensing applications†

Here we report the synthesis, characterization and application of calixarene (Calix) modified montmorillonite (Mt) as a platform for bio-applications such as biomolecule immobilization and biosensing technologies. This modification enhanced the biomolecule immobilization capability of Mt. Initially, amino-functionalised calixarenes (Calix-NH2) were synthesized and used as a modifier. X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential and thermal gravimetric analysis were performed to verify the modification of the clay minerals. For the biosensor construction, Calix-NH2 modified Mt (Calix-NH2/Mt), bovine serum albumin (BSA), glutaraldehyde (GA) and pyranose oxidase were immobilized on the surface of a glassy carbon electrode which was then referred to as a Calix-NH2/Mt/PyOx biosensor. After optimization of the enzyme amount and pH, analytical characteristics were investigated in detail.

Modification of polydivinylbenzene microspheres by a hydrobromination/click-chemistry protocol and their protein-adsorption properties.

Hydrophobic- and/or hydrophilic-polymer-grafted PDVB microspheres are synthesized by the combination of hydrobromination and click-chemistry processes. The modified-PDVB microspheres and the intermediates at various stages of synthesis are characterized using GPC, ¹H NMR and FTIR spectroscopy and TGA analysis. Use of the microspheres as a support matrix for reversible protein immobilization via adsorption is investigated. The system parameters such as the adsorption conditions (i.e., enzyme concentration, medium pH) and desorption are studied and evaluated with regards to the biocatalytic activity and adsorption capacity.

In situ synthesis of poly(N-vinylimidazole)/montmorillonite nanocomposites using intercalated monomer and thermal properties

A series of poly(N-vinylimidazole)/montmorillonite nanocomposites were prepared by in situ polymerization. This method is the first example of in situ polymerization of VI monomers within the montmorillonite layers for the preparation of nanocomposites at different clay loading degrees. N-vinyl imidazole was first intercalated into the interlayer regions of clay minerals by ion exchange reaction. Then, this organomodified clay was dispersed in the fluid VI monomers at different loading degrees to conduct the in situ polymerization. Polymerization through the interlayer of the clay led to the exfoliated poly(N-vinylimidazole)/montmorillonite nanocomposite formation. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses indicated that the resultant nanocomposites exhibited exfoliated morphologies with homogeneous clay platelet distribution. The PVI/5MMT nanocomposite was selected for the calculation of the decomposition activation energy via the Kissinger method, due to its highest thermal stability. The results showed that activation energy values at both stages for the poly(N-vinylimidazole)/montmorillonite nanocomposite are higher than those of neat poly(N-vinylimidazole), indicating that addition of the clay mineral improves the thermal stability of poly(N-vinylimidazole).

Ionic liquid intercalated clay nanofillers for chromatographic applications

In this study, the preparation and characterization of ionic liquid (IL) intercalated montmorillonite (MMT) and their application as a micro-solid phase extraction material for the determination of Chlorpyrifos (CP) pesticide in water samples were reported. The ionic liquids bearing different chain lengths [1-methyl-3-octylimidazolium bromide (C8mimBr), 1-methyl-3-undecyl-imidazolium bromide (C12mimBr) and 1-methyl-3-octadecyl-imidazolium bromide (C18mimBr)] were intercalated in the galleries of MMT. The IL-intercalated MMTs were characterized by means of XRD and TG methods. The (C12mimBr)-intercalated MMT had the highest sorption efficiency for the CP, which was 32 times higher than the original MMT. We also optimized the parameters for extracting CP from the (C12mimBr)-intercalated MMT.