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Demirel G.B.,Gazi University | Buyukserin F.,TOBB University of Economics and Technology | Morris M.A.,Trinity College Dublin | Morris M.A.,University College Cork | And 2 more authors.
ACS Applied Materials and Interfaces | Year: 2012

One-dimensional nanoporous polymeric nanofibers have been fabricated within an anodic aluminum oxide (AAO) membrane by a facile approach based on selective etching of poly(dimethylsiloxane) (PDMS) domains in polystyrene-block- poly(dimethylsiloxane) (PS-b-PDMS) block copolymers that had been formed within the AAO template. It was observed that prior to etching, the well-ordered PS-b-PDMS nanofibers are solid and do not have any porosity. The postetched PS nanofibers, on the other hand, had a highly porous structure having about 20-50 nm pore size. The nanoporous polymeric fibers were also employed as a drug carrier for the native, continuous, and pulsatile drug release using Rhodamine B (RB) as a model drug. These studies showed that enhanced drug release and tunable drug dosage can be achieved by using ultrasound irradiation. © 2011 American Chemical Society.

Yilmaz M.,Gazi University | Yilmaz M.,Hacettepe University | Senlik E.,Gazi University | Senlik E.,Hacettepe University | And 6 more authors.
Physical Chemistry Chemical Physics | Year: 2014

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. © 2014 the Owner Societies.

Demirel G.,Gazi University | Demirel G.,Biyomedtek Center for Bioengineering | Tamer U.,Gazi University
Nanotechnology | Year: 2012

We demonstrated the fabrication and application of well-ordered and vertically aligned dipeptide nanostructures based on a simple gas phase deposition. Deposited nanostructures exhibited the superhydrophobic property with a very low sliding angle. Highly reproducible SERS data have also been obtained after combining deposited films with a thin layer of gold. In addition to these, directional peptide films were, for the first time, successfully fabricated based on the oblique angle deposition technique. We believe that such bio-inspired materials would have a great impact in several technological applications involving catalysis, tissue engineering and biosensors. © 2012 IOP Publishing Ltd.

Elen B.,Hacettepe University | Elen B.,Gazi University | Ekiz D.,Gazi University | Pikin E.,Hacettepe University | And 3 more authors.
Journal of Molecular Catalysis A: Chemical | Year: 2011

Herein, a simple but versatile method to develop supported-metal catalysts based on a polydopamine (PDOP) coating and electroless plating of silver nanoparticles (AgNPs) onto nanomaterials (e.g., anodic aluminum oxide (AAO) membranes and polystyrene (PS) nanotubes) for catalytic reduction is demonstrated. The PDOP coating was inspired by the composition of adhesive proteins in mussels. A comparative study on the catalytic activities of the individual AgNPs, AgNPs/PDOP/AAOs with different pore sizes (20-200 nm) and AgNPs/PDOP/PS nanotubes in the reduction of o-nitroaniline (o-NA) to 1,2-benzenediamine (BDA) was carried out. The results indicated that both AgNPs/PDOP/AAO (200 nm) and AgNPs/PDOP/PS exhibited significantly higher catalytic activities than individual AgNPs. We also observed that the PDOP coating alone had the ability to reduce o-NA to BDA. Given their simplicity, efficiency, and flexibility, we believe that these types of green catalysts might find a wide range of applications in organic synthesis and catalysis. © 2011 Elsevier B.V.

Erdogan H.,Gazi University | Sakalak H.,Selcuk University | Yavuz M.S.,Selcuk University | Demirel G.,Gazi University | Demirel G.,Biyomedtek Center for Bioengineering
Langmuir | Year: 2013

Further understanding of the interactions between nanoparticles (NPs) and biological molecules offers new possibilities in the applications of nanomedicine and nanodiagnostics. The properties of NPs, including size, shape, and surface functionality, play a decisive role in these interactions. Herein, we evaluated the influences of gold NPs (AuNPs) with different sizes (5-60 nm) and shapes (i.e., spherical, rod, and cage) on the self-assembly of diphenylalanine (Phe-Phe) dipeptides. We found that the size of AuNPs smaller than 10 nm did not affect the self-assembly process of Phe-Phe, while bigger AuNPs (>10 nm) caused the formation of starlike peptide morphologies connected to one center. In the case of shape differences, nanorod and nanocage morphologies acted differently than spherical ones and caused the formation of densely packed, networklike dipeptide morphologies. In addition to these experiments, by combining photothermal properties of AuNPs with a Phe-Phe-based organogel having a thermo-responsive property, we demonstrated that the degelation process of AuNPs embedded organogels may be controlled by laser illumination. Complete degelation was achieved in about 10 min. We believe that such control may open the door to new opportunities for a number of applications, such as controlled release of drugs and tissue engineering. © 2013 American Chemical Society.

Sahin F.,Gazi University | Turan E.,Gazi University | Tumturk H.,Gazi University | Demirel G.,Gazi University | Demirel G.,Biyomedtek Center for Bioengineering
Analyst | Year: 2012

Core-shell magnetic nanoparticles (MNPs) offer tremendous opportunities in a large range of applications in biomedicine due to their superior magnetic properties, biocompatibility and suitability for modification. In most cases, these characteristic features are determined by their shell chemistry and morphology. Herein, we demonstrate a comparative study of silica and polydopamine (PDOP) coating onto MNP surfaces based on synthesis, characterization and usage in a bio-separation platform. It was found that monodispersed MNPs may be easily obtained on silica coating of varying shell thickness, whereas a continuous PDOP layer observed around the MNPs prevents the formation of the dispersed form. On the other hand, PDOP coated MNPs exhibited better superparamagnetic behavior and biological modification ability compared to the silica coated form. © 2012 The Royal Society of Chemistry.

Demirel G.,Gazi University | Demirel G.,Biyomedtek Center for Bioengineering | Buyukserin F.,TOBB University of Economics and Technology
Langmuir | Year: 2011

There is an increasing interest for the utilization of biomolecules for fabricating novel nanostructures due to their ability for specific molecular recognition, biocompatibility, and ease of availability. Among these molecules, diphenylalanine (Phe-Phe) dipeptide is considered as one of the simplest molecules that can generate a family of self-assembly based nanostructures. The properties of the substrate surface, on which the self-assembly process of these peptides occurs, play a critical role. Herein, we demonstrated the influence of surface texture and functionality on the self-assembly of Phe-Phe dipeptides using smooth silicon surfaces, anodized aluminum oxide (AAO) membranes, and poly(chloro-p-xylylene) (PPX) films having columnar and helical morphologies. We found that helical PPX films, AAO, and silicon surfaces induce similar self-assembly processes and the surface hydrophobicity has a direct influence for the final dipeptide structure whether being in an aggregated tubular form or creating a thin film that covers the substrate surface. Moreover, the dye staining data indicates that the surface charge properties and hence the mechanism of the self-assembly process are different for tubular structures as opposed to the peptidic film. We believe that our results may contribute to the control of surface-induced self-assembly of peptide molecules and this control can potentially allow the fabrication of novel peptide based materials with desired morphologies and unique functionalities for different technological applications. © 2011 American Chemical Society.

Kubus L.,Gazi University | Kubus L.,Hacettepe University | Erdogan H.,Gazi University | Piskin E.,Hacettepe University | And 3 more authors.
Soft Matter | Year: 2012

Inspiration from natural designs offers opportunities to develop novel functional materials having unique properties. An active area of research in this field is the construction of anisotropic nanostructured surfaces, which exhibit direction dependent wetting behavior. Here, we demonstrated the effects of surface chemistry and morphology on the directional wetting phenomenon. The nanofilms having directionality were fabricated at varying tilt angles (β) via oblique angle deposition (OAD) technique. The chemical modifications of engineered nanofilms were then carried out by using thiol molecules having different end groups (i.e., -CF3, -CH3, and -phenyl). We found that surface morphology and chemistry are extremely important parameters in the control of directional wetting. By this way, it was possible to manipulate the movement of a water droplet on the nanostructured surfaces. Such a control would have a great impact for several technological applications involving catalysis, tissue engineering, and biosensors. This journal is © 2012 The Royal Society of Chemistry.

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