Browsing by Author "Acar, H."
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Item Open Access Amyloid-like peptide nanofiber templated titania nanostructures as dye sensitized solar cell anodic materials(Royal Society of Chemistry, 2013) Acar, H.; Garifullin, R.; Aygun, L. E.; Okyay, Ali Kemal; Güler, Mustafa O.One-dimensional titania nanostructures can serve as a support for light absorbing molecules and result in an improvement in the short circuit current (Jsc) and open circuit voltage (Voc) as a nanostructured and high-surface-area material in dye-sensitized solar cells. Here, self-assembled amyloid-like peptide nanofibers were exploited as an organic template for the growth of one-dimensional titania nanostructures. Nanostructured titania layers were utilized as anodic materials in dye sensitized solar cells (DSSCs). The photovoltaic performance of the DSSC devices was assessed and an enhancement in the overall cell performance compared to unstructured titania was observed.Item Open Access Grating coupler integrated photodiodes for plasmon resonance based sensing(Royal Society of Chemistry, 2011) Turker, B.; Guner, H.; Ayas S.; Ekiz, O. O.; Acar, H.; Güler, Mustafa O.; Dâna, A.In this work, we demonstrate an integrated sensor combining a grating-coupled plasmon resonance surface with a planar photodiode. Plasmon enhanced transmission is employed as a sensitive refractive index (RI) sensing mechanism. Enhanced transmission of light is monitored via the integrated photodiode by tuning the angle of incidence of a collimated beam near the sharp plasmon resonance condition. Slight changes of the effective refractive index (RI) shift the resonance angle, resulting in a change in the photocurrent. Owing to the planar sensing mechanism, the design permits a high areal density of sensing spots. In the design, absence of holes that facilitate resonant transmission of light, allows an easy-to-implement fabrication procedure and relative insensitivity to fabrication errors. Theoretical and experimental results agree well. An equivalent long-term RI noise of 6.3 × 10 -6 is obtained by using an 8 mW He-Ne laser, compared to a shot-noise limited theoretical sensitivity of 5.61 × 10-9. The device features full benefits of grating-coupled plasmon resonance, such as enhancement of sensitivity for non-zero azimuthal angle of incidence. Further sensitivity enhancement using balanced detection and optimal plasmon coupling conditions are discussed. © 2011 The Royal Society of Chemistry.Item Open Access Self-assembled one-dimensional soft nanostructures(Royal Society of Chemistry, 2010) Toksoz, S.; Acar, H.; Güler, Mustafa O.The self-assembly process is a bottom-up approach and is the spontaneous aggregation of many different subunits into well-defined functional structures with varying properties. Self-assembly is an attractive method to develop one-dimensional nanostructures and is controlled by many factors including temperature, pH and electrolyte addition. Novel self-assembled one-dimensional nanostructures are finding applications in regenerative medicine and electronics as well as in fabrication of nanoscale electronic, mechanic, magnetic, optical, and combinatorial devices. Their utility comes from their high ratio of surface area to volume, and their quantum-confinement effects. This paper reviews one-dimensional self-assembled organic nanostructures classified according to the noncovalent forces acting on their formation.Item Open Access Self-assembled peptide nanofiber templated one-dimensional gold nanostructures exhibiting resistive switching(American Chemical Society, 2012) Acar, H.; Genc, R.; Urel, M.; Erkal, T. S.; Dana, A.; Güler, Mustafa O.An amyloid-like peptide molecule self-assembling into one-dimensional nanofiber structure in ethanol was designed and synthesized with functional groups that can bind to gold ions. The peptide nanofibers were used as templates for nucleation and growth of one-dimensional gold nanostructures in the presence of ascorbic acid as reducing agent. We performed multistep seed-mediated synthesis of gold nanoparticles by changing peptide/gold precursor and peptide/reducing agent ratios. Gold nanostructures with a wide range of morphologies such as smooth nanowires, noodle-like one-dimensional nanostructures, and uniform aggregates of spherical nanoparticles were synthesized by use of an environmentally friendly synthesis method. Nanoscale electrical properties of gold-peptide nanofibers were investigated using atomic force microscopy. Bias dependent current (IV) measurements on thin films of gold-peptide nanofiber hybrid revealed tunneling dominated transport and resistive switching. Gold-peptide nanofiber composite nanostructures can provide insight into electrical conduction in biomolecular/inorganic composites, highlighting their potential applications in electronics and optics. © 2012 American Chemical Society.Item Open Access Template-directed synthesis of silica nanotubes for explosive detection(American Chemical Society, 2011) Yildirim, A.; Acar, H.; Erkal, T. S.; Bayındır, Mehmet; Güler, Mustafa O.Fluorescent porous organic-inorganic thin films are of interest of explosive detection because of their vapor phase fluorescence quenching property. In this work, we synthesized fluorescent silica nanotubes using a biomineralization process through self-assembled peptidic nanostructures. We designed and synthesized an amyloid-like peptide self-assembling into nanofibers to be used as a template for silica nanotube formation. The amine groups on the peptide nanofibrous system were used for nucleation of silica nanostructures. Silica nanotubes were used to prepare highly porous surfaces, and they were doped with a fluorescent dye by physical adsorption for explosive sensing. These porous surfaces exhibited fast, sensitive, and highly selective fluorescence quenching against nitro-explosive vapors. The materials developed in this work have vast potential in sensing applications due to enhanced surface area. © 2011 American Chemical Society.Item Open Access Using nanogap in label-free impedance based electrical biosensors to overcome electrical double layer effect(Springer Verlag, 2017) Okyay, Ali Kemal; Hanoglu, O.; Yuksel, M.; Acar, H.; Sülek, S.; Tekcan, B.; Agan, S.; Bıyıklı, Necmi; Güler, Mustafa O.Point-of-care biosensor applications require low-cost and low-power solutions. They offer being easily accessible at home site. They are usable without any complex sample handling or any kind of special expertise. Impedance spectroscopy has been utilized for point-of-care biosensor applications; however, electrical double layer formed due to ions in the solution of interest has been a challenge, due to shielding of the electric field used for sensing the target molecules. Here in this study, we demonstrate a nanogap based biosensor structure with a relatively low frequency (1–100 kHz) measurement technique, which not only eliminates the undesired shielding effect of electrical double layer but also helps in minimizing the measurement volume and enabling low concentration (µ molar level) detection of target molecules (streptavidin). Repeatability and sensitivity tests proved stable and reliable operation of the sensors. These biosensors might offer attributes such as low-cost label-free detection, fast measurement and monolithic chip integrability.