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Optical studies of semiconductor Quantum Dots

Yükselici, H. | Allahverdi, C. | Aşikoglu, A. | Ünlü, H. | Baysal, A. | Çulha, Mustafa | Athalin, H.

Article | 2013 | NanoScience and Technology77 , pp.101 - 117

Optical absorption (ABS), steady-state photoluminescence (PL), resonant Raman, and photoabsorption (PA) spectroscopies are employed to study quantumsize effects in II-VI semiconductor quantum dots (QDs) grown in glass samples. We observe a size-dependent shift in the energetic position of the first exciton peak and have examined the photoinduced evolution of the differential absorption spectra. The Raman shifts of the phonon modes are employed to monitor stoichiometric changes in the composition of the QDs during growth. Two sets of glass samples were prepared from color filters doped with CdSxSe1-xand ZnxCd1-xTe. We analyze the opt . . .ical properties of QDs through the ABS, PL, resonant Raman, and PA spectroscopies. The glass samples were prepared from commercially available semiconductor doped filters by a two-step thermal treatment. The average size of QDs is estimated from the energetic position of the first exciton peak in the ABS spectrum. A calculation based on a quantized-state effective mass model in the strong confinement regime predicts that the average radius of QDs in the glass samples ranges from 2.9 to 4.9 nm for CdTe and from 2.2 to 9.3 nm for CdS0:08Se0:92. We have also studied the nonlinear optical properties of QDs by reviewing the results of size-dependent photoinduced modulations in the first exciton band of CdTe QDs studied by PA spectroscopy. © Springer-Verlag Berlin Heidelberg 2013 Daha fazlası Daha az

Surface-enhanced Raman spectroscopy based 3D spheroid culture for drug discovery studies

Altunbek, M. | Çetin, D. | Suludere, Z. | Çulha, Mustafa

Article | 2019 | Talanta191 , pp.390 - 399

Three-dimensional (3D) spheroid cultures are more realistic tissue mimicking structures for drug discovery studies. However, analysis of 3D spheroid cultures is a challenge task because available techniques are destructive, which results with the loss of biochemical information confined in a spatial arrangement inside of spheroids. In this study, a surface-enhanced Raman scattering (SERS) based non-destructive approach is reported to study 3D cultures. Since the technique uses gold nanoparticles (AuNPs) as SERS substrates, the cells treated with AuNPs are used for the preparation of spheroids. Since SERS spectra originate from molec . . .ular species near AuNPs and their aggregates in endolysosomes, the obtained spectral information can provide significant level of information about biomolecular processes taking place in endolysosomes and dependently in cells. The performance of the approach is evaluated by monitoring the spectral changes upon external stimuli with Doxorubicin (Dox) and Paclitaxel (Pac). A layer-by-layer depth-scan SERS analysis of Dox and Pac treated spheroids reveals the spectral changes at around 555 cm-1 and 675 cm-1 originating from cholesterol and guanine, respectively, compared to control (un-treated) spheroids. Higher spectral variation is observed from the inner to the outer layers of spheroid surface. The results demonstrate that the approach can be used to monitor the intracellular responses, which are in correlation with endolysosomal pathway according to the depth-layers of intact and living 3D spheroids upon external stimuli. © 2018 Elsevier B.V Daha fazlası Daha az

Differentiation of healthy brain tissue and tumors using Surface-enhanced Raman scattering

Aydin, O. | Altaş, M. | Kahraman, M. | Bayrak, O.F. | Çulha, Mustafa

Article | 2009 | Applied Spectroscopy63 ( 10 ) , pp.1095 - 1100

Surface-enhanced Raman scattering (SERS) is a powerful technique for characterization of biological samples. SERS spectra from healthy brain tissue and tumors are obtained by sudden freezing of tissue in liquid nitrogen and crashing and mixing it with a concentrated silver colloidal suspension. The acquired spectra from tissues show significant spectral differences that can be used to identify whether it is from a healthy region or tumor. The most significant change on SERS spectra from the healthy/peripheral brain tissue to tumor is the increase of the ratio of the peaks at around 723 to 655 cm -1. In addition, the spectral changes . . . indicate that the protein content in tumors increases compared to the peripheral/healthy tissue as observed with tumor invasion. The preliminary results show that SERS spectra can be used for a quick diagnosis due to the simplicity of the sample preparation and the speed of the spectral acquisition. © 2009 Society for Applied Spectroscopy Daha fazlası Daha az

Modeling 3D melt electrospinning writing by response surface methodology

Dayan, C.B. | Afghah, F. | Okan, B.S. | Yıldız, M. | Menceloglu, Y. | Çulha, Mustafa | Koc, B.

Article | 2018 | Materials and Design148 , pp.87 - 95

Three-dimensional (3D) melt electrospinning writing (MEW) is a promising technique for 3D printing of porous scaffolds with well-defined geometrical features. The diameter of electrospun fibers strongly affect the achievable resolution and consequently several other physical, mechanical, and structural properties of the fabricated scaffold. However, there are a few process parameters which significantly affect the size of electrospun fibers. In this study, response surface methodology (RSM) was used to investigate the critical and optimized process parameters and their interaction effects on the desired fiber diameter. Four process . . .parameters, including collector speed, tip-to-collector distance, applied pressure, and voltage were studied considering their practical ranges. The results showed that all the parameters except the applied voltage had a significant effect on the printed fiber diameters. A generalized model for the interaction effects of the parameters was introduced which can be used as a framework for selecting the process parameters to achieve the desired fiber diameter. The developed model was validated by choosing random process parameters and printing three-dimensional scaffolds. The results confirm that the predicted fiber diameters match closely with the actual fiber diameters measured directly from the printed scaffold. © 2018 Elsevier Lt Daha fazlası Daha az

Simultaneous Intracellular Detection of Plasmonic and Non-Plasmonic Nanoparticles Using Dark-Field Hyperspectral Microscopy

Akhatova, F. | Danilushkina, A. | Kuku, G. | Saricam, M. | Çulha, Mustafa | Fakhrullin, R.

Article | 2018 | Bulletin of the Chemical Society of Japan91 ( 11 ) , pp.1640 - 1645

Herein we report the detection and differentiation of plasmonic and non-plasmonic nanoparticles simultaneously administered to A549 lung epithelium cells using dark-field microscopy and hyperspectral imaging. Reflectance spectra-based hyperspectral mapping and image analysis allows for the effective quasi-quantitative identification of nanomaterials in cultured human cells. © 2018 The Chemical Society of Japan.

Label-free detection of proteins from self-assembled protein-silver nanoparticle structures using surface-enhanced raman scattering

Kahraman, M. | Sur, I. | Çulha, Mustafa

Article | 2010 | Analytical Chemistry82 ( 18 ) , pp.7596 - 7602

Proteins are one of the most versatile groups of molecules with vital functional roles in living systems. Their enormous diversity and structural flexibility make the detection of these molecules a challenging task. A simple and sensitive label-free protein detection method based on assembly of proteins and colloidal silver nanoparticles (AgNPs) on surfaces and surface-enhanced Raman scattering (SERS) is reported. The SERS spectra from the assembled AgNP/protein films show excellent reproducibility and high quality regardless of the proteins' charge status and size. A detection limit down to 0.5 µg/mL for three acidic proteins; BSA, . . . catalase and pepsin, and three basic proteins; cytochrome c, avidin and lysozyme, is easily achieved. The minimum improvement in detection limit is more than 1 order of magnitude compared to the previously reported detection limits using the technique and the approach has the potential for label-free protein detection and identification. © 2010 American Chemical Society Daha fazlası Daha az

Surface-Enhanced Raman Scattering for Label-Free Living Single Cell Analysis

Kuku, G. | Altunbek, M. | Çulha, Mustafa

Article | 2017 | Analytical Chemistry89 ( 21 ) , pp.11160 - 11166

Single cell analysis is an active research area with the hope that cellular process can be deciphered from a single living cell other than a cell population. Surface enhanced Raman scattering (SERS) has been increasingly investigated for single cell analysis with its ability to provide information about real-time dynamics of molecular processes taking place in living cells, especially upon external stimulation, in a contactless, noninvasive, and nondestructive way. In this perspective, the fundamental concepts of single cell-SERS analysis including origin of spectral bands and experimental parameters for spectral reproducibility are . . . summarized along with the recent developments. © 2017 American Chemical Society Daha fazlası Daha az

A cross-species and model comparison of the acute toxicity of nanoparticles used in the pigment and ink industries

Brown, D.M. | Johnston, H.J. | Gaiser, B. | Pinna, N. | Caputo, G. | Çulha, Mustafa | Fernandes, T.F.

Article | 2018 | NanoImpact11 , pp.20 - 32

A major user of nanoparticles (NPs) is the pigment and ink industry, where NPs are incorporated into numerous products (e.g. paints, food, plastics, printers, personal care products, and construction materials). Assessment of NP toxicity requires potential impacts on human health and the environment to be evaluated. In this study, we examined the toxicity of a range of NPs, of varied physico-chemical properties, used in the pigment and ink industries including silver (Ag), iron oxide (Fe2O3), titanium dioxide (TiO2), aluminium oxide (Al2O3), zinc oxide (ZnO), cobalt aluminium oxide (CoAl2O4) and cadmium selenide/zinc sulphide (CdSe/ . . .ZnS) quantum dots (QDs). Acute toxicity exerted by this NP panel to mammalian cells in vitro (macrophages, hepatocytes and alveolar epithelial cells) and aquatic environmental organisms (Raphidocelis subcapitata Daphnia magna, Lumbriculus variegatus) was investigated. For mammalian cells, cytotoxicity was assessed 24 h post exposure, at concentrations ranging from 1 to 125 µg/ml using the LDH and WST-1 assays. The aquatic toxicity of the NP panel was assessed according to OECD protocols (201, 202, 315), up to 96 h post exposure. Rats were exposed to selected NPs via intratracheal instillation (62 µg) and the pulmonary inflammatory response quantified 24 h post exposure. This cross-species comparison revealed that Ag, QDs and ZnO NPs were consistently more toxic than the other NPs tested. By looking across mammalian and aquatic ecotoxicological models we obtained a better understanding of the sensitivity of each model, and thus which models should be prioritised for selection in the future when assessing the mammalian and ecotoxicity of NPs, and in particular when screening the toxicity of a panel of NPs. We recommend that macrophage and daphnia models are prioritised when assessing the mammalian toxicity and ecotoxicity of NPs, respectively, due to their increased sensitivity, compared to the other models tested. Of interest is that the in vitro and invertebrate models used were able to predict the toxic potency of the NPs in rodents, and thus our approach has the potential to enhance the implementation of the 3Rs principles in nanotoxicology and reduce reliance on rodent testing when assessing NP safety. By identifying hazardous NPs the data obtained from this study can feed into the selection of (low toxicity) NPs to use in products and will also contribute to the safe design of future generations of NPs used by the pigment and ink industries. © 201 Daha fazlası Daha az

Influence of protein size on surface-enhanced Raman scattering (SERS) spectra in binary protein mixtures

Avci, E. | Çulha, Mustafa

Article | 2014 | Applied spectroscopy68 ( 8 ) , pp.890 - 899

The size-dependent interactions of eight blood proteins with silver nanoparticles (AgNPs) in their binary mixtures were investigated using surface-enhanced Raman scattering (SERS). Principal component analysis (PCA) was performed on the SERS spectra of each binary mixture, and the differentiation ability of the mixtures was tested. It was found that the effect of relative concentration change on the SERS spectra of the binary mixtures of small proteins could be detected using PCA. However, this change was not observed with the binary mixtures of large proteins. This study demonstrated that the relative interactions of the smaller pr . . .oteins with an average size of 50 nm AgNPs smaller than the large proteins could be monitored, and this information can be used for the detection of proteins in protein mixtures Daha fazlası Daha az

Quantitative structure–activity relationship between antioxidant capacity of phenolic compounds and the plasmonic properties of silver nanoparticles

Bhutto, A.A. | Kalay, S. | Sherazi, S.T.H. | Çulha, Mustafa

Article | 2018 | Talanta189 , pp.174 - 181

Plasmonic response of silver nanoparticles (AgNPs) reduced with phenolic compounds were evaluated and correlated with the antioxidant capacities of corresponding phenolic compounds and their relative chemical structures. The reference methods including DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)) radical scavenging assays were used for the measurement of antioxidant capacity of phenolic compounds which was positively correlated with redox characteristics of these compounds against the formation of AgNPs. It is found that the higher plasmonic response of AgNPs corresponds to th . . .e highest antioxidant capacity of phenolic acids, which in turn depends on chemical structures and degree of hydroxylation. The higher degree of hydroxylation in chemical structures of phenolic compounds demonstrated the higher radical scavenging capacity and higher tendency to reduce Ag+ to AgNPs. The influence of reaction time and temperature on reducing efficiency of the tested phenolic compounds is found to be different. Some phenolic compounds such as quercetin, rutin and gallic acid reacted fast (< 1.0 min) while others were found slow reacting. This study establishes the relationship between the antioxidant capacity of phenolic acids and corresponding optical response by means of plamonics, which can be used as an innovative antioxidant detection assay for samples rich in phenolic compounds. © 201 Daha fazlası Daha az

On sample preparation for surface-enhanced Raman scattering (SERS) of bacteria and the source of spectral features of the spectra

Kahraman, M. | Keseroglu, K. | Çulha, Mustafa

Article | 2011 | Applied Spectroscopy65 ( 5 ) , pp.500 - 506

The characterization, detection, and identification of bacteria using surface-enhanced Raman scattering (SERS) spectroscopy is drawing considerable attention due to its ability to provide rich intrinsic molecular information about molecules and molecular structures in close proximity to noble metal surfaces. However, sample preparation methods and experimental conditions must be carefully evaluated in order to obtain healthy, interpretable, and comparable results. In this study, several bacterial species including E. coli, B. megaterium, S. aureus, and S. cohnii were systematically evaluated to demonstrate the source of the spectral . . . features of bacterial SERS spectra. It was found that the features observed in bacterial SERS spectra originate mostly from the bacteria surface with some contributions from metabolic activity or molecular species detached from the bacteria surface during sample preparation. © 2011 Society for Applied Spectroscopy Daha fazlası Daha az

Understanding and Discrimination of Biofilms of Clinically Relevant Microorganisms Using Surface-Enhanced Raman Scattering

Keleştemur, S. | Çulha, Mustafa

Article | 2017 | Applied Spectroscopy71 ( 6 ) , pp.1180 - 1188

Biofilm formation is a defense mechanism for microorganisms to survive under both natural and stress conditions. Clinically relevant microorganisms threaten patient health through biofilm formation on medical devices and implants. It is very important to identify biofilm formation in order to suppress their pathogenic activities in early stages. With the aim for better understanding biofilm formation and possibility of detection, in this study, biofilm formation of clinically important microorganisms, Pseudomonas aeruginosa, Staphylococcus epidermidis, and Candida albicans are monitored with surface-enhanced Raman scattering (SERS). . . . The SERS spectra were collected by mapping a dried droplet area where a volume of colloidal silver nanoparticle (AgNP) suspension is placed on microorganism culture plate. The spectral changes on the SERS spectra with increasing incubation time of the model microorganisms from 4 to 120 h are monitored. The unique spectra originating from the biofilms of three pathogenic microorganisms and the spectral changes as a result of time-dependent concentration fluctuations of biomolecular species in their biofilms including carbohydrates, lipids, proteins, and genetic materials allow not only identification but also discrimination of biofilms using principal component analysis. © 2016, © The Author(s) 2016 Daha fazlası Daha az

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