Hakan Erdogan

Large area uniform deposition of silver nanoparticles through bio-inspired polydopamine coating on silicon nanowire arrays for practical SERS applications

Despite the significant progress, the controlled deposition of nanoparticles onto the support materials having 3-D nano-morphologies is still facing challenges due to the limited diffusion of metal ions into the nanostructures and uncontrolled aggregation of nanoparticles. In this study, a simple yet versatile alternative is demonstrated to control the silver nanoparticle (AgNP) density and morphology onto the 3-D silicon nanowire (SiNW) arrays based on bio-inspired polydopamine (PDOP) coating and electroless plating approaches for practical Surface-Enhanced Raman Spectroscopy (SERS) applications. In order to control silver deposition and its morphology and to optimize the SERS performance of AgNP decorated SiNW arrays, the effect of some key experimental parameters including SiNW length and morphology, silver reduction time and PDOP thickness are investigated in detail. The optimized samples demonstrate remarkable surface-enhancement ability in Raman signals with high reproducibility (lower than ∼10% spot-to-spot and sample-to-sample). Interestingly, it is found that PDOP coating not only serves as a reducing agent for the deposition of AgNPs on SiNW arrays in a controlled manner, but also contributes to the observed SERS enhancements in terms of improving photon scattering and promoting electron transfer processes due to its organic semiconductor nature.

One-Dimensional Surface-Imprinted Polymeric Nanotubes for Specific Biorecognition by Initiated Chemical Vapor Deposition (iCVD)

Molecular imprinting is a powerful, generic, and cost-effective technique; however, challenges still remain related to the fabrication and development of these systems involving nonhomogeneous binding sites, insufficient template removing, incompatibility with aqueous media, low rebinding capacity, and slow mass transfer. The vapor-phase deposition of polymers is a unique technique because of the conformal nature of coating and offers new possibilities in a number of applications including sensors, microfluidics, coating, and bioaffinity platforms. Herein, we demonstrated a simple but versatile concept to generate one-dimensional surface-imprinted polymeric nanotubes within anodic aluminum oxide (AAO) membranes based on initiated chemical vapor deposition (iCVD) technique for biorecognition of immunoglobulin G (IgG). It is reported that the fabricated surface-imprinted nanotubes showed high binding capacity and significant specific recognition ability toward target molecules compared with the nonimprinted forms. Given its simplicity and universality, the iCVD method can offer new possibilities in the field of molecular imprinting.

Morphological Versatility in the Self-Assembly of Val-Ala and Ala-Val Dipeptides

Since the discovery of dipeptide self-assembly, diphenylalanine (Phe-Phe)-based dipeptides have been widely investigated in a variety of fields. Although various supramolecular Phe-Phe-based structures including tubes, vesicles, fibrils, sheets, necklaces, flakes, ribbons, and wires have been demonstrated by manipulating the external physical or chemical conditions applied, studies of the morphological diversity of dipeptides other than Phe-Phe are still required to understand both how these small molecules respond to external conditions such as the type of solvent and how the peptide sequence affects self-assembly and the corresponding molecular structures. In this work, we investigated the self-assembly of valine-alanine (Val-Ala) and alanine-valine (Ala-Val) dipeptides by varying the solvent medium. It was observed that Val-Ala dipeptide molecules may generate unique self-assembly-based morphologies in response to the solvent medium used. Interestingly, when Ala-Val dipeptides were utilized as a peptide source instead of Val-Ala, we observed distinct differences in the final dipeptide structures. We believe that such manipulation may not only provide us with a better understanding of the fundamentals of the dipeptide self-assembly process but also may enable us to generate novel peptide-based materials for various applications.

Laser-triggered degelation control of gold nanoparticle embedded peptide organogels.

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.

Preconcentration of Aluminum on Nano ZrO2/B2O3 and Its Determination by Flame Atomic Absorption Spectrometry

ABSTRACT This study presents a chelating agent free solid phase extraction method for preconcentration of Al(III) using hybrid nano zirconium dioxide–boron oxide (ZrO2/B2O3) sorbent. This method is based on the sorption of Al(III) ions directly onto nano sorbent, followed by the elution with 10 mL of 4 mol L−1 HNO3 and determination by flame atomic absorption spectrometry (FAAS). Preconcentration parameters, including pH of the sample solution, volume and concentration of the eluent, sample volume, and flow rate of the sample solution, that affect the recovery of the Al(III) ions have been optimized. Under the optimized experimental conditions, analytical parameters such as limit of detection, limit of quantification, linear working range, precision, and accuracy were determined. The analytical limit of detection for Al(III) was found as 7.71 µg L−1. The reusability and adsorption capacity of the new hybrid sorbent for Al(III) ions were also investigated. Interfering effects of matrix constituent on the recovery of the Al(III) ions were studied. The accuracy of the method was checked by determining Al(III) ions in a certified reference water sample (SPS-WW1 Waste Water). The proposed procedure was applied for the determination of Al(III) ions in dam waters.

Controlling uni-directional wetting via surface chemistry and morphology

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.

Plasmon-Enhanced Photocatalysis on Anisotropic Gold Nanorod Arrays

The field of photocatalysis is an active area owing to the possible contributions to solve some challenging problems such as sustainable energy production, environmental pollution control, and even global warming. Unfortunately, traditional photocatalysts, especially semiconductors, suffer from inherent deficiencies, which include high activation barriers, the low mobility of charge carriers, and poor long‐term stabilities. Herein, we demonstrate a plasmonic photocatalyst based on unidirectional gold nanorod arrays fabricated by using the oblique‐angle deposition (OAD) technique. The fabricated gold nanorod arrays exhibit a remarkable plasmonic anisotropy, which depends on the direction of the incoming light. By employing these arrays as a plasmonic catalyst, a clear improvement and control in the catalytic reduction of o‐nitroaniline to 1,2‐benzenediamine, depending on the directionalities and anisotropic plasmonic properties of the gold nanorods, was obtained. These results suggest that such unique characteristics of directional gold nanorod arrays could greatly impact several technological areas, not only in plasmon‐enhanced photocatalysis but in biosensing and optofluidic applications.

The fabrication of plasmonic nanoparticle-containing multilayer films via a bio-inspired polydopamine coating

Herein, we introduce a simple approach for the fabrication of plasmonic nanoparticle-containing multilayer films using a bio-inspired polydopamine coating. This fabrication methodology represents a promising new development in the future application of plasmonic films in sensing and catalysis applications.

Fabrication of Plasmonic Nanorod-Embedded Dipeptide Microspheres via the Freeze-Quenching Method for Near-Infrared Laser-Triggered Drug-Delivery Applications.

Control of drug release by an external stimulus may provide remote controllability, low toxicity, and reduced side effects. In this context, varying physical external stimuli, including magnetic and electric fields, ultrasound, light, and pharmacological stimuli, have been employed to control the release rate of drug molecules in a diseased region. However, the design and development of alternative on-demand drug-delivery systems that permit control of the dosage of drug released via an external stimulus are still required. Here, we developed near-infrared laser-activatable microspheres based on Fmoc-diphenylalanine (Phe-Phe) dipeptides and plasmonic gold nanorods (AuNRs) via a simple freeze-quenching approach. These plasmonic nanoparticle-embedded microspheres were then employed as a smart drug-delivery platform for native, continuous, and pulsatile doxorubicin (DOX) release. Remarkable sustained, burst, and on-demand DOX release from the fabricated microspheres were achieved by manipulating the laser exposure time. Our results demonstrate that AuNR-embedded dipeptide microspheres have great potential for controlled drug-delivery systems.

Preconcentration and Determination of Manganese and Nickel from Various Water Samples by Nano Zirconium Oxide/Boron Oxide

ABSTRACT This work assesses the potential of the adsorptive material nano zirconium oxide/boron oxide (ZrO2/B2O3) for removal of trace Mn(II) and Ni(II) from environmental samples. This method is based on the sorption of Mn(II) and Ni(II) ions directly onto nanosorbent, followed by the elution and determination by flame atomic absorption spectrometry (FAAS). Experimental parameters, including pH of sample solution, volume and concentration of eluent, sample volume, and flow rate of sample solution, that affect the recovery of the Mn(II) and Ni(II) ions from model solutions have been optimized. Under the optimum conditions, adsorption isotherms and adsorption capacities have been examined. The recoveries of Mn(II) and Ni(II) were 96% ± 2% and 95% ± 3% at 95% confidence level, respectively. The analytical detection limits for Mn(II) and Ni(II) were 1.9 and 4.9 µ g L−1, respectively. Adsorption capacities of the nano ZrO2/B2O3 were found as 92.8 mg g−1 for Mn and 168.4 mg g−1 for Ni. The accuracy of the method was checked by analyzing certified reference material (SPS-WW1 wastewater) and spiked real samples. The method was applied for the determination of analytes in water samples.