Yazar "Ayhan, Muhammed Emre" seçeneğine göre listele
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Öğe A facile immobilization of polyphenol oxidase enzyme on graphene oxide and reduced graphene oxide thin films: An insight into in-vitro activity measurements and characterization(Elsevier Science Bv, 2019) Gur, Bahri; Ayhan, Muhammed Emre; Turkhan, Ayse; Gur, Fatma; Kaya, Elif DuyguGraphene oxide (GO) and reduced graphene oxide (rGO) Langmuir-Blodgett (LB) films with specific surface properties and functional groups were prepared as negative ideal substrates. Immobilization of the polyphenol oxidase (PPO) enzyme on these films was easily accomplished by electrostatic interaction without the need for any chemical bonding or surface modification. The PPO binding regions to GO and rGO surfaces were shown by an electrostatic surface potential map for pH: 5.0 value. The catalytic performances of the enzyme immobilized on GO and rGO substrates were found to be higher in GO-PPO LB films compared to RGO-PPO LB films in-vitro media. The reason why in-vitro enzyme activity is higher in GO-PPO LB films than in rGO-PPO LB films was also proved by SEM studies. The immobilization onto both the GO and rGO thin films as the GO-PPO and rGO-PPO complexes were further demonstrated by FT-IR measurement. This study revealed that the immobilized PPO enzyme on biodegradable GO is superior to the inorganic materials in terms of its use in biological systems. In addition, the fact that regular film structures with a single molecule thickness were prepared by LB film technique, contributed to the stability and recycling of immobilization of PPO enzyme on GO and rGO. In this respect, the in-vitro storage stability of immobilization on both film structures was determined to be one month at + 4 degrees C.Öğe The Mo catalyzed graphitization of amorphous carbon: an in situ TEM study(Royal Soc Chemistry, 2019) Sharma, Subash; Jaisi, Balaram Paudel; Araby, Mona Ibrahim; Elnobi, Sahar; Ayhan, Muhammed Emre; Kalita, Golap; Tanemura, MasakiFor the fabrication of graphene-based nano-scale interconnects, precise control over their position and proper nanoscale soldering are essential. In this work, we report the Joule heat-induced conversion of amorphous carbon to graphene in an in situ TEM setup, using Mo as a catalyst. The catalytic role of Mo during graphene formation has been less explored compared to other metals like Cu or Ni. Compared to metals like Cu, Mo is less subject to electromigration and brittleness, making it suitable for high-temperature electronics. We found that during the electromigration of Mo, amorphous carbon nanofibers (CNFs) can be converted to highly crystalline few-layered graphene. It was also found that during the graphene formation process, agglomerated Mo particles can be effectively channeled to the end of graphene by voltage-driven electromigration. An agglomerated Mo particle between the probe and graphene acted as a soldering agent, providing the prospect of the further exploration of Mo as a nanoscale soldering material. This work explores the double role of Mo: as a catalyst for graphene synthesis and as a soldering material.Öğe One-step synthesis of spontaneously graphitized nanocarbon using cobalt-nanoparticles(Springer International Publishing Ag, 2020) Elnobi, Sahar; Sharma, Subash; Ohsugi, Tetsuya; Paudel, Balaram; Kalita, Golap; Yusop, Mohd Zamri Mohd; Ayhan, Muhammed EmreAmorphous carbon (a-C) films containing metallic Cobalt nanoparticles (Co NPs) were deposited onto microgrids and SiO2/Si substrates by a magnetron sputter-deposition technique at room temperature (RT) using aC target with an attachment of a small Co platelet. Transmission electron microscopy (TEM) with a fast Fourier-transform (FFT) revealed the short-range ordering of the lattice corresponding to graphite (002) between Co NPs in the amorphous C matrix. The 2D peak and graphite (002) peak were clearly observed in Raman spectra and x-ray diffraction (XRD), respectively, for the Co-C films. X-ray photoelectron spectroscopy analyses were used to determine the metallic state of Co NPs and sp(2) graphitization in the film. Thus, the Co NPs exhibited higher catalytic activity in spontaneous graphitization at low-temperature than Ni-NPs prepared under the same conditions. So, the metallic NPs were concluded to be promising as the catalyst for the ultra-low temperature graphitization in the solid-phase reaction.Öğe Room-temperature graphitization in a solid-phase reaction(Royal Soc Chemistry, 2020) Elnobi, Sahar; Sharma, Subash; Araby, Mona Ibrahim; Paudel, Balaram; Kalita, Golap; Yusop, Mohd Zamri Mohd; Ayhan, Muhammed EmreGraphitized carbon including graphene has recently become one of the most investigated advanced materials for future device applications, but a prerequisite for broadening its range of applications is to lower its growth temperature. Here we report a great decrease in graphitization temperature using the well-known catalyst Ni. Amorphous carbon films with Ni nanoparticles (NPs) were deposited, using a simple one-step magnetron sputtering method, onto microgrids and a SiO2/Si substrate for transmission electron microscopy (TEM) and Raman spectroscopy analyses, respectively. The amorphous carbon surroundings and locations between the Ni NPs started to become graphitized during the film deposition even at room temperature (RT) and 50 degrees C. The graphitization was confirmed by both high-resolution TEM (HR-TEM) and Raman 2D peak analyses. The increase in the relative amount of Ni in the amorphous carbon film led to the partial oxidation of the larger Ni NPs, resulting in less graphitization even at an elevated deposition temperature. Based on the detailed HR-TEM analyses, a decreased oxidation of NPs and enhanced solubility of carbon into Ni NPs were believed to be key for achieving low-temperature graphitization.Öğe Silver nanoparticle decorated graphene-based SERS electrode towards procalcitonin detection(Elsevier, 2023) Selimoglu, Faysal; Ayhan, Muhammed EmreMonitoring procalcitonin levels (PCT) is critical for early diagnosis of sepsis, chronic disease, COVID-19 and other time-dependent pathologic cases. In this work, silver nanoparticles (AgNps) doped graphene-based Surface-enhanced Raman scattering (SERS) electrode was demonstrated for the first time to rapid detection of PCT biomarkers. An excellent combination of AgNps and single-layer graphene (SLG) was achieved, resulting in effective SERS enhancement. Due to the smooth and large surface area of SLG, many antibody molecules bind to the surface of SERS electrode and interact with PCT protein. The SERS enhancement factors (EFs) for R6G and PCT protein molecules were calculated to be 1012 and 1.6 x 109, respectively. The limits of detection (LODs) for R6G and PCT protein molecules were reported to be 10-13 M and 4 ngmL-1, respectively. These high EFs and lower LODs indicate that the fabricated AgNp/Gr@ ITO SERS electrodes have perfect SERS performance. SERS studies showed that there is a perfect interaction between PCT protein and AgNps and SLG, which leads to the enhancement of electromagnetic mechanism (EM) and chemical mechanism (CM) in the fabricated SERS ma-terials. The developed eco-friendly SERS platform can provide reliable and sensitive test results, faster analysis compared to conventional biosensors, mobile applications and cost-effective clinical management.Öğe Silver nanoparticle doped graphene-based impedimetric biosensor towards sensitive detection of procalcitonin(Elsevier, 2023) Selimoğlu, Faysal; Gür, Bahri; Ayhan, Muhammed Emre; Gür, Fatma; Kalita, Golap; Tanemura, Masaki; Alma, Mehmet HakkıIn the early detection of sepsis, procalcitonin (PCT) appears to be a highly sensitive biomarker for severe inflammation and infection. A significant interaction between the electrode material to be used in the design of the biosensor and the material to be attached to the surface is of great importance. Here, we demonstrated a silver nanoparticle (AgNp) doped graphene-based sensitive PCT biosensor with low-cost, environmentally friendly materials. Cyclic voltammetry curves showing the reusability of the electrodes obtained were obtained and showed antibody-protein adhesion on the AgNp/SLG@ITO surface. The anodic and cathodic peak currents values after 20 cycles show that these values are suitable even after 20 measurements. Electrochemical impedance spectroscopy (EIS) studies confirmed the effects of PCT on binding events due to increasing con-centration at a constant PCT-antibody concentration. The limit of detection (LOD) value of the fabricated PCT/ Ab/AgNp/SLG@ITO impedimetric biosensor was determined as 0.55 ngmL-1. The low LOD value can be attributed to the uniform and large surface area of single-layer graphene (SLG) and noble AgNp. The LOD value based on the EIS studies has revealed that the PCT/Ab/AgNp/SLG@ITO impedimetric biosensor can be employed in real samples.Öğe Surface enhancement Raman spectroscopy of CVD graphene and graphene oxide(Taylor & Francis Inc, 2024) Ayhan, Muhammed Emre; Emeller, NagihanSERS has been of interest as an influential analytical characterization method for scientific studies to detect chemical and biological molecules. The selection of suitable SERS substrates is a major challenge for specific detection of molecules. Here, two different types of graphene-based SERS substrates were prepared and their SERS activities were compared. Our chemical vapor-deposited graphene (CVDG) SERS substrates showed an excellent limit of detection of 10-13 M. 10-13 M is the lowest concentration achieved so far in the as grown graphene-based SERS substrates without the use of noble metal or other materials for R6G molecules. When a flexible and transparent SERS substrate with a large surface area is desired, substrates made of CVDG SERS substrates are more suitable, while modified graphene oxide (MGO) may be preferred in powder, colloid and thin film SERS applications. MGO showed better signal enhancement compared to CVDG and SiO2 reference substrates in high concentration R6G solution. The differences between the SERS activities of the substrates were discussed in detail in terms of the differences in the chemical, electrical, optical, and surface properties of CVDG and MGO. Understanding the enhancement activities of non-resonant graphene-based SERS materials is critical for the next generation of Raman spectrometer instruments.Öğe Ultraviolet radiation-induced photovoltaic action in ?-CuI/?-Ga2O3 heterojunction(Elsevier, 2020) Ayhan, Muhammed Emre; Shinde, Mandar; Todankar, Bhagyashri; Desai, Pradeep; Ranade, Ajinkya K.; Tanemura, Masaki; Kalita, GolapWe report on the fabrication of gamma-phase copper iodide (gamma-Cul) and beta-gallium oxide (beta-Ga2O3) heterostructure device and obtaining the ultraviolet (UV) radiation responsive photovoltaic action. The crystalline gamma-Cul with predominant (1 1 1) plane orientation was deposited on the beta-Ga2O3 by thermal evaporation process under vacuum condition. The electrical analysis revealed that the gamma-Cul/gamma-Ga2O3 heterojunction possess an excellent rectifying diode characteristic with high rectification ratio and turn-on voltage. The fabricated heterojunction device showed a photovoltaic action under solar-blind UV irradiation (254 nm) with outstanding photovoltage of 0.706 V and photocurrent of 2.49 mA/W. The device also showed a photovoltaic action under illumination of 365 nm and 300-400 nm wavelength of UV light, corresponding to absorption due to the gamma-Cul layer. The UV irradiation-induced photovoltaic action in the gamma-Cul/beta-Ga2O3 with outstanding photovoltage and excellent diode characteristics can be significant for self-powered UV photodetector applications. (C) 2019 Elsevier B.V. All rights reserved.
