Dilek Odaci Demirkol

Nanostructured Amphiphilic Star-Hyperbranched Block Copolymers for Drug Delivery

A robust drug delivery system based on nanosized amphiphilic star-hyperbranched block copolymer, namely, poly(methyl methacrylate-block-poly(hydroxylethyl methacrylate) (PMMA-b-PHEMA) is described. PMMA-b-PHEMA was prepared by sequential visible light induced self-condensing vinyl polymerization (SCVP) and conventional vinyl polymerization. All of the synthesis and characterization details of the conjugates are reported. To accomplish tumor cell targeting property, initially cell-targeting (arginylglycylaspactic acid; RGD) and penetrating peptides (Cys-TAT) were binding to each other via the well-known EDC/NHS chemistry. Then, the resulting peptide was further incorporated to the surface of the amphiphilic hyperbranched copolymer via a coupling reaction between the thiol (-SH) group of the peptide and the hydroxyl group of copolymer by using N-(p-maleinimidophenyl) isocyanate as a heterolinker. The drug release property and targeting effect of the anticancer drug (doxorobucin; DOX) loaded nanostructures to two different cell lines were evaluated in vitro. U87 and MCF-7 were chosen as integrin αvβ3 receptor positive and negative cells for the comparison of the targeting efficiency, respectively. The data showed that drug-loaded copolymers exhibited enhanced cell inhibition toward U87 cells in compared to MCF-7 cells because targeting increased the cytotoxicity of drug-loaded copolymers against integrin αvβ3 receptor expressing tumor cells.

Polypeptide Functional Surface for the Aptamer Immobilization: Electrochemical Cocaine Biosensing

Electroanalytical technologies as a beneficial subject of modern analytical chemistry can play an important role for abused drug analysis which is crucial for both legal and social respects. This article reports a novel aptamer-based biosensing procedure for cocaine analysis by combining the advantages of aptamers as selective recognition elements with the well-known advantages of biosensor systems such as the possibility of miniaturization and automation, easy fabrication and modification, low cost, and sensitivity. In order to construct the aptasensor platform, first, polythiophene bearing polyalanine homopeptide side chains (PT-Pala) was electrochemically coated onto the surface of an electrode and then cocaine aptamer was attached to the polymer via covalent conjugation chemistry. The stepwise modification of the surface was confirmed by electrochemical characterization. The designed biosensing system was applied for the detection of cocaine and its metabolite, benzoylecgonine (BE), which exhibited a linear correlation in the range from 2.5 up to 10 nM and 0.5 up to 50 μM for cocaine and BE, respectively. In order to expand its practical application, the proposed method was successfully tested for the analysis of synthetic biological fluids.

Chitosan-ferrocene film as a platform for flow injection analysis applications of glucose oxidase and Gluconobacter oxydans biosensors

Chitosan-ferrocene (CHIT-Fc) hybrid was synthesized through covalent modification and its electrochemical properties in immobilized form were studied by using cyclic voltammetry. The hybrid film exhibited reversible electrochemistry with a formal potential of +0.35 V (vs. Ag/AgCl) at pH 5.5. The Fc in CHIT matrix retained its electrocatalytic activity and did not diffuse from the matrix. This redox-active hybrid was further employed as a support for immobilization of glucose oxidase (GOx) and whole cells of Gluconobacter oxydans using glutaraldehyde on a glassy carbon electrode (GCE). The experimental conditions were optimized and the analytical characteristics of enzyme and microbial biosensors were evaluated for glucose in flow injection analysis (FIA) system. Under optimized conditions, both enzyme and microbial biosensors exhibited wide linear ranges for glucose from 2.0 to 16.0 mM and from 1.5 to 25.0 mM, respectively. Moreover, the biosensors have the advantages of relatively fast response times, good reproducibility and stability in FI mode. It was demonstrated that CHIT-Fc provides a biocompatible microenvironment for both bioctalysts and an electron transfer pathway. Additionally, integration of the enzyme and microbial biosensors into the FIA system has several advantages including capability of automation and high throughput at low cost. This promising redox hybrid can be utilized as an immobilization matrix for biomolecules in biosensor systems.

PAMAM-functionalized water soluble quantum dots for cancer cell targeting

Herein, the phase-transfer reaction of quantum dots (QDs) with amine-terminated polyamidoamine (PAMAM) dendrimers with controllable ligand molar ratios was achieved. The unique properties of PAMAM allowed us to build up structurally and electrostatically stabilized water soluble QD complexes. Synthesized conjugates were characterized in terms of fluorescence and UV-Vis profiles, hydrodynamic size, number of surface dendrimer groups, and stability. Cytotoxic effects of conjugates for MCF-7, A-549 and HEP-G2 cancer cells were assessed based on cell viability using MTT assay. Cytotoxicity results were expressed as no observable adverse effect concentration (NOAEC), 50% inhibitory concentration (IC50) and total lethal concentration (TLC) values (μM). Furthermore, HER2 receptor-mediated targeting efficiency of antibody labelled P/QDs conjugates was evaluated by successful staining of MCF-7 cells with bioconjugates. Uniquely, effective cell internalization was achieved with well-characterized antibody coupled P/QDs in contrast to antibody free P/QDs conjugates. Fluorescence microscopy images demonstrated that the designed PAMAM-derivatized QDs nanoparticles show great potential in the areas of cellular imaging and targeted therapy.

A new set up for multi-analyte sensing: At-line bio-process monitoring

A multi-analyte sensing device is described, for simultaneous at-line monitoring of glucose, ethanol, pO₂-value and cell density. It consists of a dual biosensor, a modified microscope and a fiber optical pO₂-sensor that are integrated into a flow analysis (FA) system. The biosensor is based on a conventional thin layer flow-through cell equipped with a gold (Au) dual electrode (serial configuration). The biosensors with no cross-talking were produced by modifying the electrochemical transducers. Each Au surface was initially modified by self-assembled monolayer (SAM) of cysteamine. Alcohol oxidase (AOx) and pyranose oxidase (PyOx) were immobilized each onto a gold surface by means of PAMAM (polyamidoamine) dendrimer via glutaraldehyde cross-linking. The responses for glucose and ethanol were linear up to 0.5 mM. The operational stability of the biosensors was very promising, after 11 h continuous operation, only 6.0% of the initial activity was lost. The potential of the described biosensor was demonstrated by parallel determination of ethanol and glucose in yeast fermentation process. Simultaneously the cell density of the culture was monitored with an in situ microscope (ISM), which was integrated into the FA system. Both the used in situ microscope and the image processing algorithm used for the analysis of the acquired image data are described. Furthermore the pO₂-value was monitored using a fiber optical sensor, which was embedded in a flow cell. The multi-sensor device allows the at-line monitoring of several process values without the need for further sampling or time consuming offline measurements.

Peptide-modified conducting polymer as a biofunctional surface: monitoring of cell adhesion and proliferation

Here, we report the electropolymerization of 3-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)aniline monomer on indium tin oxide (ITO) glass and its use as a coating material for cell culture applications. Functional amino groups on the conducting polymer provide post-modification of the surface with the arginylglycylaspartic acid (RGD) peptide via EDC chemistry. Scanning electron microscopy, atomic force microscopy, and contact angle and surface conductivity measurements were carried out for the surface characterization. The peptide-conjugated surface was tested for adhesion and proliferation of several cell lines such as monkey kidney epithelial (Vero), human neuroblastoma (SH-SY5Y), and human immortalized skin keratinocyte (HaCaT). These cells were cultured on RGD-modified, polymer-coated ITO glass as well as conventional polystyrene surfaces for comparison. The data indicate that the RGD-modified surfaces exhibited better cell adhesion and proliferation among all surfaces compared. Cell imaging studies up to 72 h in length were performed on these surfaces using different microscopy techniques. Therefore, the novel biofunctional substrate is a promising candidate for further studies such as monitoring the effects of drugs and chemicals on cellular viability and morphology as well as cell-culture-on-a-chip applications.

A novel organic–inorganic hybrid conducting copolymer for mediated biosensor applications

A novel ferrocenyldithiophosphonate (TPFc) functionalized monomer and its conductive copolymer were synthesized, characterized and its potential use for biosensor applications was investigated. The structure of copolymer (P(TPFc-co-TPA)) which has free amino and ferrocene (Fc) groups was characterized by various techniques such as NMR and cyclic voltammetry. Afterwards, covalent immobilization of glucose oxidase (GOx) was carried out with glutaraldehyde using the amino groups on both the conducting copolymer and GOx. Fc on the backbone played a role as redox mediator during the electrochemical measurements. Therefore, the proposed copolymer P(TPFc-co-TPA) served as a functional platform for stable biomolecule immobilization and for obtaining the oxygen free mediated electrochemical responses. The current signals were recorded using glucose as substrate, at +0.45 V vs. Ag/AgCl in Na-acetate buffer (pH 4.5; 50 mM). Additionally, Kappm (20.23 mM), Imax (3.03 μA) and sensitivity (0.10 μA mM−1 cm−2) values were determined. Finally, the biosensor was successfully applied to glucose analysis in various beverages and the results were compared with data obtained from the spectrophotometric glucose detection kit as a reference method.

Gold nanoparticle modified conducting polymer of 4-(2,5-di(thiophen-2-yl)-1H-pyrrole-1-l) benzenamine for potential use as a biosensing material

Gold nanoparticle (AuNP) modified conducting polymer of 4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzenamine (SNS-NH2) was used as the biosensing platform for glucose analysis. Electrochemical measurements were carried out by following the consumed oxygen due to the enzymatic reaction of glucose oxidase (GOx) at -0.7V vs Ag/AgCl. Optimisation of pH, enzyme loading, stability experiments were carried out. Effect of NP was investigated by monitoring the signal responses at different AuNP sizes and amounts. A linear relation of y=1.597x+0.264 (R(2)=0.993) was found for glucose concentrations between 0.002 and 5.0mM. The analytical characteristics of the system were also evaluated for glucose determination in flow injection analysis (FIA) mode. Finally, the system was checked for glucose detection on real samples.

Ferrocene-Functionalized 4-(2,5-Di(thiophen-2-yl)-1H-pyrrol-1- yl)aniline: A Novel Design in Conducting Polymer-Based Electrochemical Biosensors

Herein, we report a novel ferrocenyldithiophosphonate functional conducting polymer and its use as an immobilization matrix in amperometric biosensor applications. Initially, 4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)amidoferrocenyldithiophosphonate was synthesized and copolymerized with 4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzenamine at graphite electrodes. The amino groups on the polymer were utilized for covalent attachment of the enzyme glucose oxidase. Besides, ferrocene on the backbone was used as a redox mediator during the electrochemical measurements. Prior to the analytical characterization, optimization studies were carried out. The changes in current signals at +0.45 V were proportional to glucose concentration from 0.5 to 5.0 mM. Finally, the resulting biosensor was applied for glucose analysis in real samples and the data were compared with the spectrophotometric Trinder method.

Electrochemical deposition of polypeptides: bio-based covering materials for surface design

A simple and efficient approach for the electrochemical deposition of polypeptides as bio-based covering materials for surface design is described. The method involves N-carboxyanhydride (NCA) ring-opening polymerization from its precursor to form a thiophene-functionalized polypeptide macromonomer (T-Pala), followed by electropolymerization. The obtained conducting polymer, namely polythiophene-g-polyalanine (PT-Pala), was characterized and utilized as a matrix for biomolecule attachment. The biosensing applicability of PT-Pala was also investigated by using glucose oxidase (GOx) as a model enzyme to detect glucose. The designed biosensor showed a very good linearity for 0.01–1.0 mM glucose. Finally, the antimicrobial activities of newly synthesized T-Pala and PT-Pala were also evaluated by using the disc diffusion method.