Browsing by Subject "Nanoparticles."

Now showing 1 - 20 of 27

Open Access
Analysis of the in-vitro nanoparticle-cell interactions via smoothing splines mixed effects model
(2013) Doğruöz, Elifnur
A mixed effects statistical model is developed to understand the nanoparticle(NP)- cell interactions and predict the cellular uptake rate of NPs. NP-cell interactions are crucial for targeted drug delivery systems, cell-level diagnosis, and cancer treatment. The NP cellular uptake depends on the size, charge, chemical structure, concentration of NPs, and incubation time. The vast number of combinations of those variable values disallows a comprehensive experimental study of NP-cell interactions. A mathematical model can, however, generalize the findings from some limited number of carefully designed experiments and can be used for the simulation of NP uptake rates for the alternative treatment design, planning, and comparisons. We propose a mathematical model based on the data obtained from in-vitro NPhealthy cell experiments conducted by the Nanomedicine and Advanced Technologies Research Center in Turkey. The proposed model predicts the cellular uptake rate of Silica, polymethyl methacrylate, and polylactic acid NPs given the incubation time, size, charge and concentration of NPs. This study implements the mixed model methodology in nanomedicine area for the first time and is the first mathematical model that predicts NP cellular uptake rate based on sound statistical principles. Our model provides a cost effective tool for researchers developing targeted drug delivery systems.
Open Access
Analysis of the in-vitro nanoparticle-cell interactions via support vector regression model
(2013) Akbulut, Nur Muhammed
In this research a Support Vector Regression model is developed to understand the nanoparticle (NP)-cell interactions and to predict the cellular uptake rate of the nanoparticles, which is the rate of NPs adhered to the cell surface or entered into the cell. Examination of nanoparticle-cell interaction is important for developing targeted drug delivery systems and cell-level detection and treatment of diseases. Cellular uptake rate of NPs depends on NP type, size, shape, surface charge, concentration and incubation time. Conducting numerous experiments on the combinations of those variables to understand NP-cell interaction is impractical. Hence, a mathematical model of the cellular uptake rate will therefore be useful. The data for this study are obtained from in-vitro NP-healthy cell experiments conducted by a Nano-Medicine Research Center in Turkey. The proposed support vector regression model predicts the cellular uptake rate of nanoparticles with respect to incubation time given the size, charge and concentration properties of NPs.
Open Access
Artificial neural networks modeling and simulation of the in-vitro nanoparticles - cell interactions
(2012) Cenk, Neslihan
In this research a prediction model for cellular uptake efficiency of nanoparticles (NPs), which is the rate of NPs adhered to the cell surface or entered into the cell, is investigated via Artificial Neural Network (ANN) method. Prediction of cellular uptake rate of NPs is an important study considering the technical limitations of volatile environment of organism and the time limitation of conducting numerous experiments for thousands of possible variations of different variables that have an impact on NP uptake rate. Moreover, this study constitutes a basis for the targeted drug delivery and cell-level detection, treatment and diagnoses of existing pathologies through simulating experimental procedure of NP-Cell interactions. Accordingly, this study will accelerate nano-medicine researches. The research focuses on constructing a proper ANN model based on multilayered feed-forward back-propagation algorithm for prediction of cellular uptake efficiency which depends on NP type, NP size, NP surface charge, concentration and time. NP types for in-vitro NP-healthy cell interaction analysis are polymethyl methacrylate (PMMA), silica and polylactic acid (PLA) all of whose shapes are spheres. The proposed ANN model has been developed on MATLAB Programming Language by optimizing number of hidden layers, node numbers and training functions. The data sets for training and testing of the network are provided through in-vitro NP-cell interaction experiments conducted by a Nano-Medicine Research Center in Turkey. The dispersion characteristics and cell interactions of the different nanoparticles in organisms are explored through constructing and implementing an optimal prediction model using ANNs. Simulating the possible interactions of targeted nanoparticles with cells via ANN model could lead to a more rapid, more convenient and less expensive approach in comparison to numerous experimental variations.
Open Access
Conjugated polymer nanoparticles for biomedical applications including bioimaging and drug delivery
(2013) Ünal, Özlem
Open Access
Covalently functionalized MSNs as potential photosensitizing agents for PDT
(2011) Türkşanlı Kaplan, Merve
Photodynamic therapy (PDT) is a novel approach for the treatment of some cancers and other non-malignant diseases. PDT aims to kill cancer tissue by the generation of singlet oxygen as a result of excitation of the photosensitizer (PS) by illuminating with a light source at a certain wavelength. Mesoporous silica nanoparticles are promising in PDT issue due to their chemical inertness, biocompatibility, lowtoxicity, hydrophility and ease of surface modification. We have synthesized and characterized novel boradiazaindacene (BODIPY)-based PS that is covalently attached to the pore of mesoporous silica nanoparticles (MSNs). We have observed that near infrared absorbing photosensitizer attached MSNs successfully generate cytotoxic singlet oxygen.
Open Access
EBL fabricated plasmonic nanostructures for sensing applications
(2013) Cinel, Neval A
Plasmonics is a major branch of photonics dealing with light-matter interactions in metallic nanostructures. Plasmonic devices provide extreme confinement of electromagnetic oscillations to very small volumes beyond diffraction limit at optical frequencies. Our aim in this thesis study is to demonstrate the utilization of plasmonics for several applications such as optical localized surface plasmon resonance (LSPR) biosensor design, enhancement of signal intensity in surface enhanced Raman spectroscopy (SERS) and absorption enhancement in photodetectors. Firstly, a sensor structure that detects the changes in the refractive index of the surrounding medium by optical transmission measurements was designed. Periodic silver nano-disk arrays on sapphire substrate written by Electron-Beam Lithography (EBL) were used for this aim. Optical characterization was done through transmission/reflection measurements and supported by finite difference time domain (FDTD) simulations. The sensor was first verified by a biotinavidin bioassay. Real time binding studies showed that the sensor response was saturated within the first 30 minutes of application. Concentration dependency of the sensor structure showed an adequate response at the 1 nM-100 nM range. The refractive index sensitivity of the sensor was determined as 354 nm/RIU. The idea was finally applied to the detection of heat killed E.Coli bacteria. Promising results that indicate the possibility of using the sensor for bacteria detection was obtained. Secondly, tandem truncated nano-cones composed of Au-SiO2-Au layers that exhibit highly tunable double resonance behavior were shown to increase SERS signal intensity, for the first time. Enhancement factor (EF) calculations indicated an enhancement factor of 3.86 x107 . The double resonance design showed a 10 fold better enhancement when compared to its single resonance counterpart. This enhancement is believed to be even more prominent for applications such as NIR-SERS and Surface Enhanced Hyper Raman Scattering (SEHRS). Another SERS substrate containing dual layer, periodic, “coupled” concentric rings, separated by a dielectric spacer provided Raman signal intensity 630 times larger than plain gold film and 8 times larger than an “etched” concentric ring structure. The design provided an enhancement factor of 1.67x107 . Finally, Al nanoparticles with plasmonic resonance at UV wavelengths fabricated in between the Schottky contacts of an MSM detector on semi-insulating GaN was shown to yield 1.5 fold enhancement in absorption and photocurrent collection. Plasmonic enhancement in UV was studied for the first time with this study. Another UV-MSM photodetector on GaN that includes subwavelength apertures surrounded by nano-structured metal gratings was compared to a conventional design without gratings. Results indicated an 8 fold enhancement in the photocurrent at the resonant wavelength.
Open Access
Fabrication of an on-chip nanowire device with controllable nanogap for manipulation, capturing, and electrical characterization of nanoparticles
(2008) Uran, Can
One of the major challenges in nanofabrication commonly arises from the necessity to integrate nanostructures (e.g., nanoparticles) on the same chip with microcomponents (e.g., microelectrodes) that are orders-of-magnitude larger in size. For example, in order to make electrical contacts to colloidally synthesized nanoparticles (typically 1-100 nm in size) by integrating them with microelectrodes (typically in the few micrometers range on the critical side), a large size mismatch that easily ranges from 1:10 to 1:10,000 is required to be handled delicately for successful nano-to-micro integration. This necessitates the ability to manipulate and integrate nanoparticles with a sufficient level of precision on the microchip. In this thesis, to provide a convenient solution to this challenging problem, we proposed and demonstrated for the first time an onchip nanowire device that features a controllable nanogap in its architecture for capturing and electrical characterization of nanoparticles in the gap, all fully integrated on the same microchip. Our innovative approach relies on the use of dielectrophoretic electric-field assisted self-assembly of our segmented nanowires to construct a nanoscale device platform. For this purpose, we synthesized gold-silver-gold segmented nanowires and dielectrophoretically aligned them across our microfabricated array of electrodes. Subsequently, we selectively removed the middle silver segment to open a gap in the nanometer size between the self-aligned gold end segments. Using dielectrophoretic assembly once more, we captured nanoparticles in these nanogaps for further electrical characterization. One of the key benefits in our approach was that the aligned nanowires automatically provided electrical contacts to the captured nanoparticles to allow for electrical probing at the nanoscale. Our innovative approach enabled convenient full integration from nanoparticles to nanowires to microelectrodes to macroprobes on a single chip, spanning a size range of more than six orders of magnitude.
Open Access
Generalized linear models for in-vitro nanoparticle-cell interactions
(2013) Çuhacı, Z. Gülce
Nanomedicine techniques are quite promising in terms of treatment and detection of cancerous cells. Targeted drug delivery plays an important role in this field of cancer nanotechnology. A lot of studies have been conducted so far concerning nanoparticle (NP)-cell interaction. Most of them fail to propose a mathematical model for a quantitative prediction of cellular uptake rate with measurable accuracy. In this thesis, we investigate cell-NP interactions and propose statistical models to predict cellular uptake rate. Size, surface charge, chemical structure (type), concentration of NPs and incubation time are known to affect the cellular uptake rate. Generalized linear models are employed to explain the change in uptake rate with the consideration of those effects and their interactions. The data set was obtained from in-vitro NP-healthy cell experiments conducted by the Nanomedicine & Advanced Technologies Research Center in Turkey. Statistical models predicting cellular uptake rate are proposed for sphere-shaped Silica, polymethyl methacrylate (PMMA), and polylactic acid (PLA) NPs.
Open Access
Immunoregulatory activities of nanoparticle-forming oligodeoxynucleotides
(2009) Karatepe, Kutay
Innate immune system is activated by a wide range of microbial by products leading to an immediate immune activation primarily designed to neutralize and control the invading insult. The cells of the innate immune system also instruct the development of antigen-specific adaptive immunity. While TLR9 is triggered by bacterial DNA, extended and over-exuberant immune response poses a threat since it may exacerbate cell and tissue destruction leading to organ failure. Telomeric TTAGGG conserved motifs are previously reported to antagonize TLR mediated events. The down-regulatory effect of these motifs may help to restore the desired homeostatic balance of the immune system. While CpG ODN patterned after bacterial DNA can be harnessed in different clinical settings to provide an advantage to host to resist infectious diseases, control tumor growth or alleviate allergic symptoms, the immunosuppressive telomeric motifs could be effectively applied in controlling systemic anti-inflammatory or autoimmune related disorders. Several challenges exist in the utilization of synthetic ODNs in the clinic. The first challenge is that conventional classes of synthetic ODNs exhibit different properties. K-type ODNs are more effective in proliferation and activation of B cells and DC. D-type ODNs are in nanoparticle forms, lead to anti-viral type I IFN production and mature monocytes into DCs. Of note, the efficacy of these synthetic ODNs is reduced under physiological conditions due to premature clearance and low levels of internalization. Moreover, D-ODNs as one of the most potent IFNα inducing TLR9 ligands possess a large-scale production problem due to 3’polyGruns, which hamper their entry into the clinic. We have designed a novel class of ODN, designated as ODN420, devoid of polyGs that can undergo nanoparticle formation necessary for its IFNα induction. Ex vivo stimulation of mouse splenocytes and in vivo administration of ODN420 have revealed that this ODN exhibits higher immunostimulatory potential and is more stable than most commonly used ODNs due to its nanoparticle-forming ability. Another interesting finding is that ODN420 with the natural phosphodiester (PO) backbone is at least as potent as its more stable counterpart with the modified phosphorothioate backbone. Furthermore, it combines superior properties of conventional classes of K and D-ODNs. These results have been reproduced in human peripheral blood mononuclear cells by various assays. Next, we have analyzed whether this ODN could be utilized as a vaccine adjuvant and an anti-cancer agent with two independent experiments. Our immunization results demonstrate that ODN420 induces a higher level of Th1-mediated response than conventional ODNs and is a promising candidate as a vaccine adjuvant. This response is hampered when ODN420 is used in combination with ODN-A151. In the tumor xenograft model, ODN420 has promoted partial remission of the tumors or delayed the tumor growth. This knowledge will pave the way for more effective immunotherapeutic approaches.
Open Access
Laser synthesized gold nanoparticles for high sensitive strain gauges
(2013) Burzhuev, Salamat
Recently, the conduction properties of nanoparticle films have received great deal of attention due to their unique properties attributed to quantum tunneling effect. Quantum tunneling effect, highly dependent on quantum barrier height and width, is very attractive for sensor applications. Resistive strain gauges based on gold nanoparticle (Au-NP) films show high strain sensitivity. These strain gauges are applicable for miniature applications because of its size. In addition, this nanoparticle films could be also used for various applications such as pressure and vapor sensors. Clean surfaces of laser generated Au-NPs provide high tunneling decay constant. Therefore, these films are promising for high sensitive sensor applications. In our study, the Au-NPs were directly synthesized in deionized water by nanosecond laser ablation method. The clean surface, size and aggregate clusters of Au-NPs offer advantages for high sensitivity strain sensor. We prepared Au-NPs films on flexible PDMS substrate by using hands-on drop-cast method. To obtain high gauge factor, we also investigated the nanoparticle concentration on the thin films. Laser-generated AuNPs films demonstrated gauge factor of ∼300 for higher than 0.22% strain and ∼80 for the strain lower than 0.22%, which is favorably comparable to reported sensitivities for strain sensors based on Au-NPs. Mechanical characterizations for the prolonged working durations suggest long term stability of these strain sensors. We discuss several models describing conductance of Au-NP films in low and high strain regimes. To the best of our knowledge, the conduction of laser generated Au-NP films has not been studied up to date, and it is the first study that shows high strain sensitivity of these films. Au-NP films may be promising for sensor applications.
Open Access
Multifunctional conjugated polymer nanoparticles as an anticancer drug carrier and a fluorescent probe for cell imaging
(2012) Gezici, Özlem
The main motivation of this study is to develop multifunctional nanoparticles which can perform simultaneously the drug delivery and cell imaging tasks. To this end, firstly nanoparticles (Nps) with an average diameter of about 25 nm and based on a green emitting, hydrophobic conjugated polymer, poly[(9,9-bis{propenyl}fluorenyl-2,7- diyl))-co-(1,4-benzo-{2,1,3}-thiodiazole)] (PPFBT) and Nps with an average diameter of about 150 nm and based on a red emitting, hydrophobic conjugated polymer, poly[(9,9-bis{3-azido-propyl}fluorenyl-2,7-divinylene)-co-(1,4-benzo- {2,1,3}-thiodiazole)] (PAPFVBT) were prepared, characterized and their convenience as a fluorescent probe for cell imaging was evaluated via in vitro cell assays. Then, drug loaded nanocapsules in which PPFBT or PAPFVBT acts both as a fluorescent reporter and the main matrix of the nanocapsules accommodating an anticancer drug, camptothecin (CPT), were synthesized through a facile, single step reprecipitation method. CPT is a hydrophobic, water-insoluble drug but the encapsulation improved its water-solubility. The CPT loading efficiency in the nanoparticles has been determined to be 100% when a drug to polymer ratio of 1:25 (w/w) was used. Cell viability of Human hepatocellular carcinoma cell line (Huh7) was investigated in the absence and presence of CPT using Sulforhodamine B (SRB) assay. SRB assay results supported further by the fluorescence microscope cell images clearly confirmed that blank and CPT-loaded PPFBT Nps have been taken up by the cells very efficiently and these nanoparticles were accumulated in the cytoplasm. Time and dose dependent SRB assay results indicate that the blank PPFBT Nps are not toxic to the Huh7 cells up to 25 µM. However, even a very low dose of CPT was found to be sufficient to induce the apoptosis of the cells when it was delivered through nanoparticles. Thus, at the end of 48 h, the half maximal inhibitory concentration (IC50) of free CPT and CPT-loaded PPFBT Nps were calculated to be 0.9 µM and 0.1 µM respectively, corresponding to that CPT-loaded PPFBT Nps are 9 times more effective than free CPT. However, at the end of 72 h, the IC50 of free CPT and CPT-loaded PPFBT Nps decreased to 0.1 µM and 0.008 µM, respectively. In this case, CPT-loaded PPFBT Nps are 12.5 times more effective than free CPT in inducing the apoptosis of Huh7 cells. Although the free drug (CPT) reaches IC50 of 0.1 µM after 72 h, it is possible to achieve this value with CPT-loaded Nps at the end of 48 h. On the other hand, dose dependent SRB assay results indicate that the blank PAPFVBT Nps are not toxic to the Huh7 cells up to 16 µM. At the end of 72 h, IC50 of free CPT and CPTloaded PAPFVBT Nps were calculated to be 0.03 µM and 0.1 µM respectively, corresponding to that CPT-loaded PAPFVBT Nps are 3.3 times less effective than free CPT. Having bigger size (~150 nm) of PAPFVBT Nps is the main reason of not being effective as PPFBT Nps (~25 nm).
Open Access
Nanofibrous nanocomposites via electrospinning
(2011) Deniz, Ali Ekrem
In 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.
Open Access
Nanostructured materials for biological imaging and chemical sensing
(2014-11) Yıldırım, Adem
In the recent years, the design and synthesis of fluorescent nanoparticles for biological and chemical sensing applications have received considerable attention due to the excellent photostability and emission intensity of fluorescent nanoparticles and the intrinsic sensitivity of fluorescence based methods. Although considerable progress has been made in their synthesis, there is still need for low-cost and high throughput methods for their widespread utilization in biological and chemical sensing applications. In addition, studies regarding their biocompatibility are necessary to identify the toxicological potential of these nanomaterials. In this context, this thesis seeks new methods for multifunctional fluorescent nanoparticle synthesis and investigates their interactions with living organisms. In addition, it reports the applications of the fluorescent nanomaterials in biological imaging, therapy and chemical sensing applications. First, we report a self-assembly method to prepare PEGylated or peptide functionalized mesoporous silica nanoparticles (MSNs) for cell labeling and drug delivery applications. The good cyto- and blood- compatibility of the functionalized nanoparticles were demonstrated. Next, we demonstrated a surfactant assisted method to synthesize ultrabright silica nanoparticles and studied their in vitro v cytocompatibility with several cell lines. We demonstrated the applications of ultrabright particles in cell labeling, chemo and photodynamic therapy and trace explosive sensing. Then, we discuss a template-free method (porosity difference based selective dissolution strategy) to prepare self-luminescent mesoporous hollow silica nanoparticles with tailored shapes. In addition, we studied the surface effects on blood compatibility of nanoparticles in detail using the MSNs possessing different surface functional groups (ionic, polar, neutral, and hydrophobic). Finally, we investigated the optical properties of polydopamine nanoparticles and showed that fluorescence of asprepared polydopamine nanoparticles can be used for sensitive and selective detection of the dopamine neurotransmitter.
Open Access
Novel nanocomposite coatings of nanoparticles
(2011) Toru, Refik Sina
Incorporating nanoparticles into nanocomposite thin-films enables coatings with multi-functionality depending on the particle type and size, and the film morphology. These multiple functions may include, for example, combinations of photocatalysis, hydrophobicity, scratch resistance, and antibacterial property. Here we proposed and demonstrated a new encapsulation nanocomposite with controllable refractive index and potentially additional functional properties for coating photonic devices, for instance, light-emitting diodes (LEDs). To design and implement this nanocomposite coating with tunable refractive index, we employed TiO2 nanoparticles of various diameters because of their relatively high refractive index. We embedded these nanoparticles in our encapsulation sol-gel material during synthesis. In addition, we incorporated several polymerforming chemicals during synthesis to control additional functions such as hydrophobicity and scratch resistance. We used characterization tools of atomic force microscopy, refractometry, contact angle measurement, and scanning electron microscopy to study material properties.
Open Access
The phase behavior and synthesis of mesostructured coupled semiconductor thin films : MESO-CdS-TiO2
(2009) Okur, Halil İbrahim
Mesostructured [Cd(H2O)4](NO3)2 - titania - P123 ((PEO)20(PPO)70(PEO)20, PEO = -OCH2CH2-, PPO = -OCH(CH3)CH2-) materials have been investigated by changing the [Cd(H2O)4](NO3)2 and titania content of the structures. This has been achieved by making thick samples by casting and thin film samples by spin coating of a butanol solution of [Cd(H2O)4](NO3)2, P123, nitric acid and Ti(OC4H9)4. The film samples are named as meso-xCd(II)-yTiO2, where x is the Cd(II)/P123 and y is TiO2/P123 mole ratios. Increasing the titania amount in the media has transformed the samples from LC-like to soft and then to rigid mesostructured materials. Changing the amount of [Cd(H2O)4](NO3)2 salt in the media only influenced the mesostructure, such that no change on the mechanical properties is observed. However, the synthesis of rigid mesostructured titania materials required controlled humidity. The rigid film samples were prepared first by spin coating and then by aging under a 50% humidity oven. The mesostructure remains stable upon H2S reaction, in the soft and rigid materials region. However, only rigid samples stand to removal of nitrates from the media that is important to keep the CdS nanoparticles stable in or on the pore walls of mesostructured film samples. The phase behavior of the meso-Cd(II)-TiO2, the structural properties of the meso-xCdS-yTiO2 samples, coordination and elimination of the NO3 - ions and the particle size of the CdS nanocrystallites were investigated using diffraction (XRD), spectroscopy (FT-IR, Raman and UV-Vis absorption, EDS) and microscopy (POM, SEM, and TEM) techniques.
Open Access
Photocatalytic nanocomposites for increased optical activity
(2008) Tek, Sümeyra
To combat environmental pollution, photocatalytic decomposition provides degradation of organic and inorganic contaminants near the surface of the photocatalyst nanoparticles by converting optical energy of the absorbed light into chemical energy for the redox reactions. However, photocatalytic activities of such semiconductor metal-oxide nanoparticles are limited with their bandgap energy that allows for optical absorption typically in the ultraviolet spectral range. Yet another limitation is that the photocatalytic activity of these semiconductor nanoparticles is substantially reduced when they are immobilized in solid thin films, resulting from their effectively decreased active surface area. But such immobilized nanoparticles are much more desired in industrial applications, e.g., for mass environmental decontamination and outdoors/indoors self-cleaning on large surfaces. To address these issues, in this thesis, we investigated and demonstrated the spectral behavior and time evolution of optical activity curves of immobilized TiO2 and ZnO nanoparticles. We studied the nanoparticle size effect for the optical activity and demonstrated significant increase in the resulting photocatalysis with decreasing the size of such immobilized nanoparticles for the first time. We obtained optimal excitation conditions for TiO2 and ZnO nanocomposite films separately. We achieved maximum optical recovery levels of 93% for TiO2 nanoparticles and 55% for ZnO nanoparticles at the excitation wavelengths of 310 nm and 290 nm, respectively, after optical irradiation with an excitation density of 7.3 J/cm2 , where we observed no optical recovery for their respective negative control groups (with no nanoparticles). In these comparative spectral studies, we showed strong correlation between the differential optical recovery and the photocatalytic activity. For further substantial enhancement in the near ultraviolet and visible spectral ranges, we also proposed and demonstrated the use of a unique combination of TiO2-ZnO nanoparticles integrated together into the same resin. In this novel approach, we observed higher levels of photocatalytic activity under optical irradiation at and above 380 nm compared to the cases of only TiO2 or only ZnO nanocomposite films with the same total metal-oxide nanoparticle density. At 400 nm in the visible, we accomplished an optical recovery level of ~30% with the combination of TiO2-ZnO nanoparticles together while this level was only ~14% for the TiO2 nanoparticles alone and ~3% for the ZnO nanoparticles alone under identical conditions. Even at 440 nm, we obtained ~20% optical recovery using the TiO2-ZnO photocatalytic synergy, despite the optical activity of the single type of nanoparticles alone close to the zero base-line of their control group. These proof-of-concept experimental demonstrations indicate that such TiO2-ZnO combined nanocomposite films hold great promise for efficient environmental decontamination in daylight.
Open Access
Plasmonic nanoparticles by laser dewetting of thin metallic films
(2013) Sarıtaş, Seval
In this work, formation of metal nanoparticles via laser induced dewetting and their plasmonic properties have been investigated. The effects of metal film, substrate type, laser power density and dwell time on dewetting phenomenon were analyzed. Silver and gold thin films were fabricated with thermal evaporation on various substrates. Next, they were characterized by the ellipsometry, UV-VIS spectroscopy and atomic force microscopy (AFM) as the characteristic of the thin film affects dewetting. Samples were then processed by a cw argon laser. Varying the dwell time and power density, Ag and Au nanoparticles with different morphology were obtained. At the final stages of dewetting, nanoparticles attained spherical shapes. Particle size distribution and length scale analysis were performed using the images obtained from scanning electron microscope (SEM). Using these results, relations between the average particle size and film thickness, as well as the relation between length scale and film thickness were obtained to verify the occurrence of dewetting. Substrate and film type were observed to affect the particle morphology and particle size. Moreover, plasmonic resonance effect of Ag and Au nanoparticles were observed via the optical absorbance measurements. Multilayered metallic nanoparticles and embedded nanoparticles were fabricated and were found to display plasmonic properties.
Open Access
Plasmonics from metal nanoparticles for solar cell applications
(2013) Günendi, Mehmet Can
In today’s economy, need for development in energy is essential. Solar energy is safe, and at the same time is one of the cleanest, cheapest choices of energy alternative to fossil fuels. In this perspective, using the sun light effectively is in fundamental importance. One of the problems, because of the indirect band gap of the material Si, is small energy conversion ratios of various solar cell structures and limited absorption of red light. Because of the material properties, Si cells cannot absorb red light, which contributes great amount of the sun light. One of the recent developed techniques to use red light is using metal nanoparticles (MNP) embedded in a semiconductor medium as sub-wavelength antennas or MNP scatterers, hence increasing the effective path length of light in the cell. Absorption and scattering are mostly in plasmon resonances. Shifting the plasmon resonance peaks is possible by changing various parameters of the system like the size of the MNPs. In this work, Finite-Difference Time-Domain (FDTD) method is used to analyze various systems worked. Mainly the MEEP package, developed at MIT, is used to simulate systems and other codes, related to analytical work, have also used to compare results. The plasmon resonances of various sizes of Ag MNPs embedded in different mediums at different positions are analyzed. Critical parameters like particle size, shape, dielectric medium, film thickness are discussed for improved solar cell applications.
Open Access
Preparation and characterization of polymer composites containing gold nanoparticles
(2011) Yılmaz, Eda
In this study, light-assisted synthesis of gold nanoparticles in polymer films is demonstrated and characterization of gold nanoparticle-polymer composites using various techniques is shown. There are various methods introduced for the synthesis of gold nanoparticles in solution and their integration to the polymer films afterwards. However, synthesizing gold nanoparticles directly inside the polymer matrix is more advantageous for the production of polymer-nanoparticle composites. An advantage of synthesizing gold nanoparticles within polymer films is the opportunity of photo-patterning. Films having patterns made of regions with and without gold nanoparticles can be produced, using masks designed to cut off the radiation at desired places. Such patterned films were investigated with scanning electron microscope (SEM) and dark regions between irradiated regions and masked regions were observed. These dark regions are shown to be “ion depleted regions”, where gold ions diffuse through irradiated regions during the irradiation. These regions of about 10 m width, suggests a very large distance for gold ions to diffuse through a rigid matrix like Poly(methyl methacrylate)(PMMA), which is very interesting. Supporting evidence for the existence of these regions was obtained from fluorescence studies with Rhodamine 6G molecule and x-ray electron spectroscopy (XPS). The observations made through the formation of ion depleted regions can be used to estimate the diffusion constant of gold ions inside the PMMA matrix. Also the presence of ion depleted regions indicate the stability of photo-patterns created on the polymer film against smearing during light exposure after the production, by setting an upper limit to the critical feature size. During the characterization of gold nanoparticle-polymer composites, the electrical properties of PMMA with and without gold nanoparticles were investigated using charge resolved XPS, while applying external bias to the films with and without gold nanoparticles to probe the charging properties of the films. An enhancement of conductivity of PMMA films containing gold nanoparticles was observed using this technique. Additionally charge resolved XPS technique was also used to determine the charge storage characteristics of the polymer surfaces, which is important for the identification of charging mechanisms during contact and other electrification processes. It was shown that the PMMA surface is very susceptible to negative charging and even native negative charges on the PMMA surface can be observed prior to any treatment. Also when the surface is charged carbon and oxygen atoms of the carbonyl and methoxy groups of PMMA were observed to behave differently from the backbone of the polymer, which shows the chemical specificity of the charge accumulating spots on the surface.
Open Access
Self-nanoparticle forming immunostimulatory DNA : structure-function relationship studies
(2009) Mammadov, Rashad
Toll-like receptors (TLRs) are one the most critical and widely studied members of the family of pattern recognition receptors expressed on innate immune cells. They recognize microbial signatures, such as bacterial/viral DNA, LPS, from gram negative bacteria, peptidoglycan from gram positive bacteria, zymosan from yeast, lipopeptides or profilin protein from parasites, and even single or double stranded RNA of viruses. Among several members of TLR family, TLR9, that recognizes microbial unmethylated dinucleotide motifs on DNA initiate a robust Th1- biased inflammatory response. Synthetic oligodeoxynucleotides expressing unmethylated CpG motifs, mimic bacterial DNA effect and can be harnessed for the treatment of health problems ranging from infectious diseases to cancer, or to allergy/asthma as well as stand alone immunoprotective agents and also as a vaccine adjuvants that improve protection against pathogens. To date, various classes of CpG ODNs have been identified and were shown to induce differential immune activation in mice and man. Distinct structure-function relationship analyses revealed that these single-stranded linear ODNs alter the immune milieu as they are formulated to form complex multimeric DNA aggregates. Recently, Guanosine-rich D type CpG ODNs has been reported to form complex aggregates, that are differentially regulating immune cells to mount an anti-viral immunity. However, the clinical trials of this type are hampered mainly due to batch to batch variation during large-scale synthesis. To the best of our knowledge, there is no report on self-nanoparticle forming DNA except G-rich sequences. This thesis project was designed to generate stable, selfnanoparticle forming, G-run free, CpG expressing ODNs. In this thesis, we designed a new generation CpG ODN, then characterized their structural and immunological properties. Our results suggest that dendrimeric structure confers higher immunostimulatory potential unparallel to conventional ODNs. Following four hours of in vivo ODN administration into mice indicated that nanoparticle-forming CpG ODNs initiated substantially high spleen and peritoneal exudate cell activation as evidenced by IFNγ and IL-12 production from culture medium. In order to shed light on the uptake and binding mechanisms, blocking experiments revealed that at least one type of scavenger receptor is critical for nanoparticle ODN internalization. Collectively, these data suggested that the improved stability to nucleases along with significantly higher binding to immune cells (no additional ODN formulation is required) seem to be the critical factors contributing to the nanoparticle CpG ODN mediated immune activation. The in vitro and in vivo performances implicated that these next generation immune stimulatory DNA molecules are promising candidates for various clinical applications.