Browsing by Subject "Silver nanoparticles"
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Item Open Access Disintegration and machine-learning-assisted identification of bacteria on antimicrobial and plasmonic Ag–CuxO nanostructures(American Chemical Society, 2023-03-08) Şahin, F.; Çamdal, A.; Şahin, G. D.; Ceylan, A.; Ruzi, M.; Önses, Mustafa SerdarBacteria cause many common infections and are the culprit of many outbreaks throughout history that have led to the loss of millions of lives. Contamination of inanimate surfaces in clinics, the food chain, and the environment poses a significant threat to humanity, with the increase in antimicrobial resistance exacerbating the issue. Two key strategies to address this issue are antibacterial coatings and effective detection of bacterial contamination. In this study, we present the formation of antimicrobial and plasmonic surfaces based on Ag–CuxO nanostructures using green synthesis methods and low-cost paper substrates. The fabricated nanostructured surfaces exhibit excellent bactericidal efficiency and high surface-enhanced Raman scattering (SERS) activity. The CuxO ensures outstanding and rapid antibacterial activity within 30 min, with a rate of >99.99% against typical Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria. The plasmonic Ag nanoparticles facilitate the electromagnetic enhancement of Raman scattering and enables rapid, label-free, and sensitive identification of bacteria at a concentration as low as 103 cfu/mL. The detection of different strains at this low concentration is attributed to the leaching of the intracellular components of the bacteria caused by the nanostructures. Additionally, SERS is coupled with machine learning algorithms for the automated identification of bacteria with an accuracy that exceeds 96%. The proposed strategy achieves effective prevention of bacterial contamination and accurate identification of the bacteria on the same material platform by using sustainable and low-cost materials.Item Open Access Effects of laser ablated silver nanoparticles on Lemna minor(Elsevier, 2014) Üçüncü, E.; Özkan, A. D.; Kurşungöz, C.; Ülger, Z. E.; Ölmez, T. T.; Tekinay, T.; Ortaç, B.; Tunca E.Item Open Access Machine learning-assisted pesticide detection on a flexible surface-enhanced raman scattering substrate prepared by silver nanoparticles(American Chemical Society, 2022-09-12) Onses, M. Serdar; Ruzi, M.; Ceylan, A.; Sakir, M; Camdal, A.; Celik, N.; Sahin, F.Access to clean water is a pressing challenge affecting millions of lives and the aquatic body of the Earth. Sensitive detection of pollutants such as pesticides is particularly important to address this challenge. This study reports eco-friendly preparation of the surface-enhanced Raman scattering (SERS) substrate for machine learning-assisted detection of pesticides in water. The proposed SERS platform was prepared on a copy paper by reducing a silver salt using the extract of a natural plant, Cedrus libani. The fabricated SERS platform was characterized in detail using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The high-density formation of silver nanoparticles with an average diameter of 41 nm on the surface of the paper enabled detection of analytes with a nanomolar level sensitivity. This SERS capability was used to collect Raman signals of four different pesticides in water: myclobutanil, phosmet, thiram, and abamectin. Raman spectra of the pesticides are highly complex, challenging accurate determination of the pesticide type. To overcome this challenge and distinguish pesticides, machine learning (ML) approach was used. The ML-mediated detection of harmful pesticides on a versatile, green, and inexpensive SERS platform appears to be promising for environmental applications.Item Open Access Multiphase flow displacement application of novel green nanoparticle synthesis in glycerol and reconfigurable nanoemulsions in reservoir-on-a-chip(Bilkent University, 2024-01) Jahangir, RobabNanofluids and oil in water (O/W) nano/micro emulsions have been extensively investigated for their potential in multiphase displacement applications such as enhanced oil recovery (EOR). However, the potential of metal nanofluids and water-in-oil nanoemulsions (W/O) has not been readily studied and the under-lying mechanisms are yet to be investigated. Moreover, most nanofluids pose toxicity risks to reservoirs, and a high polydispersity index of conventionally syn-thesized nanofluids adversely impacts displacement efficiencies. Hence, in this study, we synthesized two injection fluids including, a novel green nanofluid comprising of ultra-small silver nanoparticles (NPs) in glycerol and reconfigurable nanoemulsions to investigate their impact on displacement efficiencies. We have carried out the synthesis of green nanofluid comprising silver NPs in a customized microfluidic (Mf) chip, with 18 omega-shaped micromixers, by using glycerol as a promising green solvent and reducing agent at various concentrations (10-80 %), and simultaneous comparison of the results from batch synthesis. Interestingly, the experimental findings depicted that by varying different parameters, the spherical silver nanoparticles with an average ultra-small particle diameter of < 2nm were obtained at all glycerol concentrations (10-80 %) and variables, as compared to batch synthesis (giving a yield of 10-fold larger particles). The synthesis was then confirmed by Dynamic Light scattering (DLS), UV-visible spectroscopy, and Tunnelling Electron Microscope (TEM). Subsequently, the dis-placement efficiencies were then investigated in a reservoir-on-a-chip platform (filled with fluorescence-doped oil) for real-time visualization, quantification and pore-scale investigation. The measurement data for green nanofluid revealed the wettability alteration and IFT reduction with the increase in viscosity and size of NPs. No significant effect of the IFT on sweep efficiencies was observed, however, the contact angle of the injection fluids shifted from an oil-wet state (101◦-113◦) towards an intermediate wettability state (90◦-97◦) over 2 minutes. A shift to-wards intermediate wettability in a short time indicated the influence of AgNPs in displacing oil ganglia by structural disjoining pressure. It was reported that a critical glycerol viscosity (30 %) was essential to increase the sweep efficiency by 5 % in microfluidics-synthesized nanofluid (1.7 nm) and by 8 % in benchtop synthesized nanofluid (3.3 nm). Finally, the NPs-surfactant assemblies between SiO2 and Poly[dimethylsiloxane-co-(3-aminopropyl)methylsiloxane] copolymer were in-vestigated for the synthesis of reconfigurable nanoemulsions. The buckling phenomena was confirmed between pH 5 and 6 and nanoemulsions were synthesized with 3 different Oil: NPs concentrations i.e., 80:20, 70:30 and 60:40 at pH 3, 5, 6, and 8 (pH 3 and 8 taken as control groups). The sweep efficiency gradually increased in the order of 60:40 < 70:30 < 80:20, with the highest sweep efficiency obtained in the case of 80:20 nanoemulsions at pH 5, pH 6 and pH 5 in case of 70:30 nanoemulsions respectively, due to the displacement of oil because of formation of wedge film and in-situ emulsification.Item Open Access Nanofibrous nanocomposites via electrospinning(Bilkent University, 2011) Deniz, Ali EkremIn recent years, numerous studies have been reported for fabrication of composite nanofibers from polymeric and inorganic materials by using electrospinning method. In the first part of this study, TiO2 and ZnO inorganic nanofibers were produced by electrospinning from their precursors by using polymeric carrier matrix and their photocatalytic activity of these metal oxide nanofibers were studied. Moreover, electrospun TiO2 nanofibers were crushed into short nanofibers (TiO2-SNF) and embedded in electrospun polymeric nanofiber matrixes such as poly(methyl methacrylate) (PMMA), polyacrylonitrile (PAN), polyethylene terephthalate (PET), polycarbonate (PC) and polyvinylidene fluoride (PVDF). Different weight loading of TiO2-SNF ranging from 2% to 8% (w/w, respect to polymer) incorporated into PVDF nanofibrous matrix was applied and the structural and morphological changes along with their photocatalytic activities were also examined. In the second part, metallic nanoparticles produced by laser ablation method were incorporated into nanofibrous polymeric matrix by using electrospinning technique. For example, gold (Au) and silver (Ag) nanoparticles (NPs) were produced from their metallic sources by laser ablation method directly in the polymer solutions. The NPs/polymer mixtures were electrospun and surface plasmon resonance effect of Au-NPs and Ag-NPs on optical properties of the nanofibers was studied. In addition, germanium nanocrystals produced by means of laser ablation were mixed with PVDF polymer solution and consequently electrospun into composite polymeric nanofiber matrix.Item Open Access One-step green synthesis of antibacterial silver nanoparticles embedded in electrospun cyclodextrin nanofibers(Elsevier, 2019) Çelebioğlu, Aslı; Topuz, Fuat; Yıldız, Zehra İrem; Uyar, TamerAntibacterial electrospun nanofibers based on cyclodextrin (CD) and silver nanoparticles (Ag-NPs) were produced by solution electrospinning from aqueous and DMF solutions using different Ag contents. CD molecules acted as the reducing agent and catalyzed the formation of Ag-NPs. The nanofibers with smaller diameters were observed for the fibers generated from DMF solutions than those produced from aqueous solutions. TEM and STEM analyses revealed the Ag-NPs (∼2–5 nm depending on solvent-type and Ag loading) in nanofibers, while FTIR and surface enhanced Raman scattering (SERS) analyses showed the apparent frequency shift of OH stretching band and the enhancement of Raman bands of CD molecules with the incorporation of the Ag-NPs. The polycrystalline structure of the Ag-NPs was shown by XRD and SAED analyses over {111}, {200}, {220} and {311} planes. The nanofibers showed significant inhibition against the growth of Escherichia coli and Staphylococcus aureus owing to the antibacterial activity of the Ag-NPs.Item Open Access One-step synthesis of size-tunable Ag nanoparticles incorporated in electrospun PVA/cyclodextrin nanofibers(Pergamon Press, 2014) Celebioglu A.; Aytac Z.; Umu, O. C. O.; Dana, A.; Tekinay, T.; Uyar, TamerOne-step synthesis of size-tunable silver nanoparticles (Ag-NP) incorporated into electrospun nanofibers was achieved. Initially, in situ reduction of silver salt (AgNO3) to Ag-NP was carried out in aqueous solution of polyvinyl alcohol (PVA). Here, PVA was used as reducing agent and stabilizing polymer as well as electrospinning polymeric matrix for the fabrication of PVA/Ag-NP nanofibers. Afterwards, hydroxypropyl-beta-cyclodextrin (HPβCD) was used as an additional reducing and stabilizing agent in order to control size and uniform dispersion of Ag-NP. The size of Ag-NP was ∼8 nm and some Ag-NP aggregates were observed for PVA/Ag-NP nanofibers, conversely, the size of Ag-NP decreased from ∼8 nm down to ∼2 nm within the fiber matrix without aggregation were attained for PVA/HPβCD nanofibers. The PVA/Ag-NP and PVA/HPβCD/Ag-NP nanofibers exhibited surface enhanced Raman scattering (SERS) effect. Moreover, antibacterial properties of PVA/Ag-NP and PVA/HPβCD/Ag-NP nanofibrous mats were tested against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria.Item Open Access Polylactic acid (PLA)/Silver-NP/VitaminE bionanocomposite electrospun nanofibers with antibacterial and antioxidant activity(Springer, 2014-10) Munteanu, B. S.; Aytac, Z.; Pricope, G. M.; Uyar, Tamer; Vasile, C.The antibacterial property of silver nanoparticles (Ag-NPs) and the antioxidant activity of Vitamin E have been combined by incorporation of these two active components within polylactic acid (PLA) nanofibers via electrospinning (PLA/Ag-NP/VitaminE nanofibers). The morphological and structural characterizations of PLA/Ag-NP/VitaminE nanofibers were performed by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy and X-ray diffraction. The average fiber diameter was 140 ± 60 nm, and the size of the Ag-NP was 2.7 ± 1.5 nm. PLA/Ag-NP/VitaminE nanofibers inhibited growth of Escherichia coli, Listeria monocytogenes and Salmonella typhymurium up to 100 %. The amount of released Ag ions from the nanofibers immersed in aqueous solution was determined by Inductively Coupled Plasma Mass Spectrometry, and it has been observed that the release of Ag ions was kept approximately constant after 10 days of immersion. The antioxidant activity of PLA/Ag-NP/VitaminE nanofibers was evaluated according to DPPH (2,2-diphenyl-1-picrylhydrazyl) method and determined as 94 %. The results of the tests on fresh apple and apple juice indicated that the PLA/Ag/VitaminE nanofiber membrane actively reduced the polyphenol oxidase activity. The multifunctional electrospun PLA nanofibers incorporating Ag-NP and Vitamin E may be quite applicable in food packaging due to the extremely large surface area of nanofibers along with antibacterial and antioxidant activities. These materials could find application in food industry as a potential preservative packaging for fruits and juices.Item Open Access Silver nitrate/oligo(ethylene oxide) surfactant/mesoporous silica nanocomposite films and monoliths(Academic Press, 2001) Samarskaya, O.; Dag, Ö.A lyotropic, liquid crystalline (LC) phase of a silver nitrate/oligo(ethylene oxide), water, and acid mixture was used for one-pot synthesis of mesoporous silica materials in which Ag+ ions are uniformly distributed. We established that the AgNO3-to-surfactant mole ratio is very important in a 50 wt% surfactant/water system to preserve the hexagonal LC phase before and after the addition of the silica source. Below a 0.6 AgNO3-to-surfactant mole ratio, the mixture is liquid crystalline and serves as a template for silica polymerization. However, between 0.6 and 0.8 AgNO3-to-surfactant mole ratios, one must control the composition of the mixture during the polymerization processes. Above a 0.8 mole ratio, Ag+ ions undergo phase separation from the reaction mixture by complexing with the surfactant molecules. The resulting silica materials obtained from AgNO3/surfactant ratio above 0.8 have anisotropy but without a hexagonal mesophase. Here, we establish a AgNO3 concentration range in which the LC phase is preserved to template the synthesis of mesoporous silica, and we discuss the structural behavior of the mixtures at AgNO3/surfactant mole ratios of 0.00-2.00, using POM, PXRD, FTIR, and UV-Vis absorption spectroscopy. © 2001 Academic Press.Item Open Access Simultaneous photoinduced electron transfer and photoinduced CuAAC processes for antibacterial thermosets(Elsevier, 2017) Oz, E.; Uyar, T.; Esen, H.; Tasdelen, M. A.A combination of simultaneous photoinduced electron transfer and photoinduced CuAAC processes enables the in-situ preparation of antibacterial thermosets containing silver nanoparticles (AgNPs) in one-pot. Upon photolysis of photoinitator, the generated radicals not only reduce Cu(II) into Cu(I) activator to catalyst the CuAAC click reaction, but also simultaneously generate AgNPs from AgNO3 through electron transfer reaction. Due to their reduction potentials difference, the polymer matrix is formed before the formation of AgNPs, assisting to eliminate the agglomeration of them. The thermoset structures are confirmed by FT-IR and solubility tests, whereas the presence of AgNPs is proven by transmission electron microscopy with energy dispersive X-ray system analyzer. The samples containing 5 and 10% AgNPs exhibited strong inhibition zones, where all kinds of bacteria (gram-positive (Staphylococcus Aureus) and gram-negative (Escherichia Coli)) were killed in the surrounding of the film samples.Item Open Access Surface enhanced Raman spectroscopy of unilamellar liposomes loaded with silver nanoparticles(American Scientific Publishers, 2017) Toren, P.; Tekinay, T.; Ayas S.; Dana, A.; Tunc, I.Imaging organic molecules using surface-enhanced Raman spectroscopy (SERS) has drawn attention due to its non-invasive nature and label-free approach. The SERS approach can be used in tracking organic molecules and monitoring unique Raman spectra of the organic molecules bound to metal nanoparticles (NPs). We prepared unilamellar liposomes composed of 1,2-dipalmitoylsn-glycero-3-phosphocholine (DPPC) molecules with a diameter of around 100 nm. Electrostatic binding of silver (Ag) NPs on the surface of the unilamellar liposomes was achieved by the reduction of silver nitrate (AgNO3) which produces SERS active silver colloidal particles on the unilamellar liposome surfaces. Highly enhanced electromagnetic fields localized around neighbouring Ag NPs provide hot-spot construction around the liposomes, due to the spatial distribution of SERS enhancement in the unilamellar liposomes. It was observed that the signals fluctuate on a second time scale, presumably due to conformational change of DPPC chain and local Brownian motion of liposomal spheres.Item Open Access Terahertz time-domain study of silver nanoparticles synthesized by laser ablation in organic liquid(IEEE Microwave Theory and Techniques Society, 2016-07) Koral, C.; Ortaç, B.; Altan, H.We report the investigation of laser-synthesized Ag nanoparticles (Ag-NPs) in an organic liquid environment by using terahertz time-domain spectroscopy (THz-TDS) technique. Colloidal Ag-NPs with an average diameter of 10 nm in two-propanol solution through nanosecond pulsed laser ablation were synthesized. THz-TDS measurements were performed on different volumetric concentration of Ag-NPs suspensions placed in 2-mm path length quartz cuvette. Due to the dispersive and highly absorptive nature of the nano liquids, an approach based on extracting the optical properties through the changes in amplitude and phase solely around the main peak of THz waveform is developed. This approach allowed for an accurate estimation of the complex refractive index of the Metallic-NPs suspension for the different prepared volumetric concentrations. In addition, using Maxwell-Garnett theory, the NP concentration is also extracted. This method shows that the time-domain nature of the THz pulse measurement technique is extremely useful in instances where slight variations in highly dispersive samples need to be investigated.Item Open Access Toxicity of internalized laser generated pure silver nanoparticles to the isolated rat hippocampus cells(SAGE, 2017-02) Kursungoz, C.; Taş, S. T.; Sargon, M. F.; Sara, Y.; Ortaç, B.Silver nanoparticles (AgNPs) are the most commonly used nanoparticles (NPs) in medicine, industry and cosmetics. They are generally considered as biocompatible. However, contradictory reports on their biosafety render them difficult to accept as 'safe'. In this study, we evaluated the neurotoxicity of direct AgNP treatment in rat hippocampal slices. We produced pure uncoated AgNPs by a pulsed laser ablation method. NP characterization was performed by Ultraviolet (UV) visible spectrophotometer, scanning electron microscope, transmission electron microscope (TEM) and energy-dispersive X-ray spectroscopy. Rat hippocampal slices were treated with AgNPs for an hour. AgNP exposure of hippocampal tissue resulted in a significant decrease in cell survival in a dose-dependent manner. Our TEM results showed that AgNPs were distributed in the extracellular matrix and were taken into the cytoplasm of the neurons. Moreover, we found that only larger AgNPs were taken into the neurons via phagocytosis. This study showed that the pure AgNPs produced by laser ablation are toxic to the neural tissue. We also found that neurons internalized only the large NPs by phagocytosis which seems to be the major mechanism in AgNP neurotoxicity.Item Open Access Ultraviolet-printing-assisted surface-confined growth of silver nanoparticles on flexible polymer films for Cu2+ and H2S sensing(American Chemical Society, 2021-08-27) Ashfaq, B.; Azeem, I.; Sohail, M.; Yüce, F. G.; Çitoǧlu, S.; Nayab, S.; Abdullah, M.; Duran, Hatice; Yameen, B.Metal nanoparticles (NPs) confined on the surface of flexible polymers films are highly sought after for a diverse range of applications. Herein, we report a facile substrate-independent strategy for surface-confined growth of silver NPs (AgNPs) on the surfaces of chemically diverse flexible polymer film substrates represented by polypropylene (PP), polyvinyl chloride (PVC), and polyethylene terephthalate (PET). The surfaces of polymer films were subjected to ultraviolet-printing and conjugated to the hyperbranched polyethyleneimine (PEI). The PEI-functionalized surfaces were subjected to surface-confined growth of AgNPs via three approaches. Besides PEI, the ability of quaternary amine and carboxylic acid functional groups to assist surface-confined growth of AgNPs is also evaluated. All the films with surface-confined AgNPs exhibited absorbance due to the surface plasmon resonance (SPR) characteristic of AgNPs. The AgNPs confined on the surface of PP films were functionalized with 4-mercaptobenzoic acid, and the λmax for SPR absorbance of the resulting platform was found to exhibit a markedly higher bathochromic shift when exposed to Cu2+ ions. This Cu2+ ions sensor could sense Cu2+ ions with a limit of detection of 2.6 ppm. Besides Cu2+ sensing via a bathochromic shift in λmax for SPR absorbance, the SPR absorbance of AgNPs confined on the surface of PP films was found to diminish upon exposure to the aqueous solution of sodium hydrosulfide (NaSH), which acts as a hydrogen sulfide (H2S) donor. The intensity of the SPR absorbance was found to decrease >40% upon exposure to 5 μM aqueous NaSH solution, whereas the SPR signal almost completely disappeared with visual decoloration when the films were exposed to 50 μM aqueous NaSH solution. This highlights the H2S sensing ability of the AgNPs confined on the surface of PP films. In brief, this study is a step toward the future development of flexible chemical sensor platforms and beyond.