Gökçen Birlik Demirel

Polymeric nanocarriers for expected nanomedicine: current challenges and future prospects

Polymeric nanocarriers have an increasingly growing potential for clinical applications. The current and future expectation from a polymeric nanocarrier is to exhibit both diagnostic and therapeutic functions. Living organisms are very complex systems and have many challenges for a carrier system such as biocompatibility, biodistribution, side-effects, biological barriers. Therefore, a designed polymeric nanocarrier should possess multifunctional properties to overcome these obstacles towards its target site. However, currently there are few polymeric systems that can be used for both therapy and imaging in clinic studies. In the literature, there are many studies for developing new generation polymeric nanocarriers to obtain future smart and multifunctional nanomedicine. In this review, we discuss the new generation and promising polymeric nanocarriers, which exhibit active targeting, triggered release of contents, and imaging capability for in vivo studies.

Soft biomimetic tapered nanostructures for large-area antireflective surfaces and SERS sensing†

We report a facile fabrication method for the fabrication of functional large area nanostructured polymer films using a drop casting technique. Reusable and tapered silicon molds were utilized in the production of functional polymers providing rapid fabrication of the paraboloid nanostructures at the desired structural heights without the requirement of any complex production conditions, such as high temperature or pressure. The fabricated polymer films demonstrate promising qualities in terms of antireflective, hydrophobic and surface enhanced Raman spectroscopy (SERS) features. We achieved up to 92% transmission from the single-side nanostructured polymer films by implementing optimized nanostructure parameters which were determined using a finite difference time domain (FDTD) method prior to production. Large-area nanostructured films were observed to enhance the Raman signal with an enhancement factor of 4.9 × 106 compared to bare film, making them potentially suitable as free-standing SERS substrates. The utilized fabrication method with its demonstrated performances and reliable material properties, paves the way for further possibilities in biological, optical, and electronic applications.

Molecular design of photoswitchable surfaces with controllable wettability

In this work, we developed a photocontrollable substrate which was prepared using an azobenzene-containing self-assembled monolayer (SAM) on the silicon surface via the chemisorption of 3-glycidoxypropyltrimethoxysilane (GPTS) and 4-(4′-aminophenylazo) benzoic acid (APABA). The prepared surfaces were chemically characterized by X-ray photoelectron spectroscopy (XPS). The reversible photoswitching performance of APABA molecules were investigated by UV spectroscopy in dimethylsulfoxide (DMSO) solution. To understand and control this reversible photoswitchable mechanism and wettability properties, contact angle measurements were performed by using a variety of liquids after UV and visible light irradiation. These contact angle results are used to approximate the components of the APABA-modified surface energy under UV and visible light using the Lifshitz–van der Waals/acid–base approach. The total surface energy (γs) after visible light irradiation (for trans formation) was calculated to be 37.28 mJ m−2, whereas the value after UV light exposure (for cis formation) was also calculated to be 36.95 mJ m−2. All the results demonstrate the great potential to control molecular events within and on the surfaces of molecular constructs using light.

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.

Nanoporous Polymeric Nanofibers Based on Selectively Etched PS-b-PDMS Block Copolymers

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.

Photocontrollable DNA hybridization on reversibly photoresponsive surfaces

Herein we have developed a new DNA sensor which displays the possibility of photocontrollable DNA hybridization by changing the orientation of azobenzene layers on the silicon wafer surface. Basically, the trans-form layers present a coordinating surface, the “on” state that can be switched “off” in the cis-form. Water contact angles of the prepared substrates have been measured after UV and visible light irradiation to understand the switchable properties of each form of the surface. The photocontrollable DNA chip was prepared using Cy3 labeled amino terminated single stranded probe-DNA (Cy3–ssDNA–NH2) molecules which were immobilized onto a COOH-terminated photoswitchable surface. The optimum hybridization conditions were performed with Cy5 labeled complementary-DNA (Cy5–ssDNA) using fluorescence microscopy. Furthermore, the photocontrolling of DNA hybridization onto prepared surfaces was verified by confocal microscopy before and after light irradiation. The percentage hybridization ratios from confocal microscopy for on and off positions of the DNA sensor were calculated to be 61% and 5%, respectively. These results show that the prepared surfaces can be reversibly photoswitched between two states efficiently. As a result we believe that the results demonstrate the great potential to control DNA hybridization within and on the surfaces of molecular constructs using light.

Effect of Pore-Forming Agent Type on Swelling Properties of Macroporous Poly(N-[3-(dimethylaminopropyl)]-methacrylamide-co-acrylamide) Hydrogels

Macroporous poly(N-[3-(dimethylaminopropyl)]methacrylamide-co-acrylamide) [P(DMAPMA-co-AAm)] hydrogels were prepared by free-radical crosslinking copolymerization of corresponding monomers in water using two different pore-forming agents such as hydroxypropyl celluose (HPC) and poly(ethylene glycol) (PEG). The effect of these pore-forming agents on the volume phase transition temperature (VPT-T), interior morphology and swelling/deswelling kinetics of the P(DMAPMA-co-AAm) hydrogels was investigated. Scanning electron micrographs revealed that the interior network structure of the hydrogel matrix became more porous due to the presence of HPC or PEG pore-forming agents. The more porous matrix provided numerous water channels for water diffusion in or out of the matrix and, therefore, an improved response rate to the external stimuli. Particularly, due to its unique macroporous structure, the PEG-modified hydrogel showed a tremendously faster response to the external temperature changes during deswelling process and the swelling process at 22°C.

Anemone-like nanostructures for non-lithographic, reproducible, large-area, and ultra-sensitive SERS substrates

The melt-infiltration technique enables the fabrication of complex nanostructures for a wide range of applications in optics, electronics, biomaterials, and catalysis. Here, anemone-like nanostructures are produced for the first time under the surface/interface principles of melt-infiltration as a non-lithographic method. Functionalized anodized aluminum oxide (AAO) membranes are used as templates to provide large-area production of nanostructures, and polycarbonate (PC) films are used as active phase materials. In order to understand formation dynamics of anemone-like structures finite element method (FEM) simulations are performed and it is found that wetting behaviour of the polymer is responsible for the formation of cavities at the caps of the structures. These nanostructures are examined in the surface-enhanced-Raman-spectroscopy (SERS) experiment and they exhibit great potential in this field. Reproducible SERS signals are detected with relative standard deviations (RSDs) of 7.2-12.6% for about 10,000 individual spots. SERS measurements are demonstrated at low concentrations of Rhodamine 6G (R6G), even at the picomolar level, with an enhancement factor of ∼10(11). This high enhancement factor is ascribed to the significant electric field enhancement at the cavities of nanostructures and nanogaps between them, which is supported by finite difference time-domain (FDTD) simulations. These novel nanostructured films can be further optimized to be used in chemical and plasmonic sensors and as a single molecule SERS detection platform.

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.

A Novel pH/Light‐Triggered Surface for DNA Adsorption and Release

A simple strategy for the immobilization of Cy3-labeled single strand DNA (Cy3-ssDNA) on a Si(001) surface and its release under control of both light and pH stimuli is presented. In order to prepare a dual pH/light-triggered surface, positively chargeable azobenzene molecules are self-assembled on the Si(001) surface. The surface wettability of this substrate can be changed under influence of both light and pH conditions. The substrates can be positively charged under mildly acidic conditions. The pH-sensitive behavior of the film allows binding of Cy3-ssDNA on the functionalized Si(001) surface through effective electrostatic interactions with the negatively charged polynucleotide backbone. Moreover, irradiation of the film with UVA light induces trans-cis isomerization of the azobenzene units on the surface. As a result, the binding affinity for DNA decreases due to the changing surface hydrophilicity. In order to understand and control the reversible photoswitchable mechanism of this surface, water contact angles are measured after UVA and visible light irradiation. The release of DNA from a dual pH/light-sensitive sample is performed using fluorescence microscopy. The results show that irradiation of the film with UVA light induces trans-cis isomerization of the photoresponsive azobenzene units; this leads to significant changes in the surface hydrophilicity and reduces the binding affinity for DNA.