Academic literature on the topic 'Photoluminescent semiconductor nanocrystals'
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Journal articles on the topic "Photoluminescent semiconductor nanocrystals"
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Roland Menzel, E., Steve M. Savoy, Sydney J. Ulvick, Kwan H. Cheng, Russell H. Murdock, and Mark R. Sudduth. "Photoluminescent Semiconductor Nanocrystals for Fingerprint Detection." Journal of Forensic Sciences 45, no. 3 (2000): 14727J. http://dx.doi.org/10.1520/jfs14727j.
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Marin, Brandon C., Su-Wen Hsu, Li Chen, et al. "Plasmon-Enhanced Two-Photon Absorption in Photoluminescent Semiconductor Nanocrystals." ACS Photonics 3, no. 4 (2016): 526–31. http://dx.doi.org/10.1021/acsphotonics.6b00037.
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Martin-Trasanco, Rudy, Hilda Esparza-Ponce, Pedro Ortiz та ін. "In-Situ Preparation of CdTe Quantum Dots Capped with a β-Cyclodextrin-Epichlorohydrin Polymer: Polymer Influence on the Nanocrystal’s Optical Properties". Nanomaterials 8, № 11 (2018): 948. http://dx.doi.org/10.3390/nano8110948.
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β-Cyclodextrin (βCD), the less water soluble of the cyclodextrins, has been used as a capping agent in the preparation of semiconductor nanocrystals or quantum dots (QDs). Nevertheless, no reports have been found in the use of the highly water-soluble polymer of this, prepared by the crosslinking of the βCD units with epichlorohydrin in basic medium (βCDP). This polymer, besides to overcome the low solubility of the βCD, increases the inclusion constant of the guest; two parameters that deserve its use as capping agent, instead of the native cyclodextrin. In the present manuscript, we afforded the in-situ aqueous preparation of cadmium telluride (CdTe) QDs capped with βCDP. The polymer influence on the photoluminescent properties of the nanocrystals was analyzed. The βCDP controls the nanocrystals growth during the Oswald ripening stage. Consequently, the CdTe capped βCDP QDs showed lower Stokes-shift values, higher photoluminescent efficiency, and narrower size distribution than for nanocrystals obtained in the absence of polymer. Transmission electron microscopy (TEM) micrographs and energy dispersive X-ray spectroscopy (EDS) analysis revealed the composition and crystallinity of the CdTe QDs. This βCDP capped CdTe QDs is a potential scaffold for the supramolecular modification of QDs surface.
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Guzatov, Dmitry V., Sergey V. Gaponenko, and Hilmi V. Demir. "Colloidal Photoluminescent Refractive Index Nanosensor Using Plasmonic Effects." Zeitschrift für Physikalische Chemie 232, no. 9-11 (2018): 1431–41. http://dx.doi.org/10.1515/zpch-2018-1127.
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Abstract Fluorescence enhancement by metal nanostructures which is sensitive to refractive index n of an ambient medium is suggested as an operation principle of a novel refractive index sensor for liquids. Calculations are made for spherical and spheroidal Ag particles, and potential feasibility of sensitivity of the order of Δn=10−4 is demonstrated. Sensors of this type can be made fully colloidal with metal bodies deposited on a substrate or comprising a metal layer covering colloidal assembly of dielectric particles to serve as a test strip as well as placed on a fiber tip end to get local probing of refractive index in the tip-enhanced refractometry mode. Colloidal core-shell semiconductor nanocrystals may become the best candidates for this type of sensors whereas molecular probes may be affected by chemical properties of tested liquids.
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Nifontova, Galina, Victor Krivenkov, Mariya Zvaigzne, et al. "Nanoparticle-Doped Hybrid Polyelectrolyte Microcapsules with Controlled Photoluminescence for Potential Bioimaging Applications." Polymers 13, no. 23 (2021): 4076. http://dx.doi.org/10.3390/polym13234076.
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Fluorescent imaging is widely used in the diagnosis and tracking of the distribution, interaction, and transformation processes at molecular, cellular, and tissue levels. To be detectable, delivery systems should exhibit a strong and bright fluorescence. Quantum dots (QDs) are highly photostable fluorescent semiconductor nanocrystals with wide absorption spectra and narrow, size-tunable emission spectra, which make them suitable fluorescent nanolabels to be embedded into microparticles used as bioimaging and theranostic agents. The layer-by-layer deposition approach allows the entrapping of QDs, resulting in bright fluorescent microcapsules with tunable surface charge, size, rigidity, and functional properties. Here, we report on the engineering and validation of the structural and photoluminescent characteristics of nanoparticle-doped hybrid microcapsules assembled by the deposition of alternating oppositely charged polyelectrolytes, water-soluble PEGylated core/shell QDs with a cadmium selenide core and a zinc sulfide shell (CdSe/ZnS), and carboxylated magnetic nanoparticles (MNPs) onto calcium carbonate microtemplates. The results demonstrate the efficiency of the layer-by-layer approach to designing QD-, MNP-doped microcapsules with controlled photoluminescence properties, and pave the way for the further development of next-generation bioimaging agents based on hybrid materials for continuous fluorescence imaging.
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Shen, Hao, Huabao Shang, Yuhan Gao, Deren Yang, and Dongsheng Li. "Efficient Sensitized Photoluminescence from Erbium Chloride Silicate via Interparticle Energy Transfer." Materials 15, no. 3 (2022): 1093. http://dx.doi.org/10.3390/ma15031093.
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In this study, we prepare Erbium compound nanocrystals and Si nanocrystal (Si NC) co-embedded silica film by the sol-gel method. Dual phases of Si and Er chloride silicate (ECS) nanocrystals were coprecipitated within amorphous silica. Effective sensitized emission of Er chloride silicate nanocrystals was realized via interparticle energy transfer between silicon nanocrystal and Er chloride silicate nanocrystals. The influence of density and the distribution of sensitizers and Er compounds on interparticle energy transfer efficiency was discussed. The interparticle energy transfer between the semiconductor and erbium compound nanocrystals offers some important insights into the realization of efficient light emission for silicon-based integrated photonics.
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Pashchenko, G. A. "PHOTOLUMINESCENCE OF NANOCRYSTALLINE CdTe, INTRODUCED INTO POROUS SILICON." Optoelektronìka ta napìvprovìdnikova tehnìka 56 (December 7, 2021): 123–28. http://dx.doi.org/10.15407/iopt.2021.56.123.
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A method of colloidal synthesis of monodisperse nanocrystals (NC) with high stability, narrow bands of photoluminescence (PL) and high quantum yield has been developed. The process of colloidal synthesis took place at room temperature and for the passivation of NC used a variety of surfactants. The surface of NC CdTe was modified by introducing them into a matrix, organic or crystalline. In our case, the matrix was porous Silicon (PS), that is a composite structure was formed on the basis of the matrix and NC semiconductor. Nanocomposite structures of PS – NC CdTe were obtained by introducing colloidal solutions of NC CdTe into the solid matrix of PS and subsequent processing at a certain temperature regime. The photoluminescent properties of a composite system in which the matrix is microcrystalline PS and the second component is NC CdTe deposited from a colloidal solution of NC CdTe have been studied. The peculiarity of this system is that both components have PL of different intensities.The large difference in PL intensities and different positions of the radiation bands allowed, comparing the PL spectra of the colloidal solution of NC CdTe, PS and NC CdTe – PS at different stages of introduction of CdTe nanoparticles into the porous Silicon surface, to identify the interaction and mutual influence of the two constituent materials. The main disadvantages of the method are its relative novelty, which leads to the need for empirical selection of some parameters of the synthesis. The planned change of properties of PS and colloidal solutions of NC CdTe by variation of technological methods of synthesis and processing methods will allow to control the physical properties of this composite system and use it to develop new principles of design and creation of new generation sensor devices.
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Mohammadrezaee, Mohammad, Naser Hatefi-Kargan, and Ahmadreza Daraei. "Enhancing crystal quality and optical properties of GaN nanocrystals by tuning pH of the synthesis solution." Zeitschrift für Naturforschung A 75, no. 6 (2020): 551–56. http://dx.doi.org/10.1515/zna-2019-0378.
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AbstractGallium nitride nanocrystals as a wide bandgap semiconductor material for optoelectronic applications can be synthesized using chemical methods. In this research using co-precipitation and nitridation processes gallium nitride nanocrystals have been synthesized, and by tuning pH of the synthesis solution at the co-precipitation step, crystal quality and optical property of the resultant gallium nitride nanocrystals have been enhanced. Gallium nitride nanocrystal samples were synthesized using solutions with pH values of 2.1, 4.8, 7.8, and 9.0, and then nitridation at 950 °C under the flow of ammonia gas. The synthesized nanocrystal samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and photoluminescence techniques. The XRD data show that the nanocrystals have hexagonal wurtzite crystal structure, and using Scherer’s equation the sizes of the synthesized nanocrystals are 23.6, 26.6, 19.7, and 10.4 nm for the samples synthesized using the solutions with pH values of 2.1, 4.8, 7.8, and 9.0 respectively. The sizes of the nanocrystals obtained from SEM images are larger than the values obtained using Scherer’s equation, due to the aggregation of nanocrystals. EDX spectra show that pH of the synthesis solution affects the elemental stoichiometry of the gallium nitride nanocrystals. We obtained better stoichiometry for the nanocrystal sample synthesized using solution with the pH of 4.8. Photoluminescence spectra show that for this sample the emission intensity is higher than the others.
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Ding, Yong Ling, Hua Dong Sun, Kang Ning Sun, and Fu Tian Liu. "Water-Based Route to Synthesis of High-Quality UV-Blue Photoluminescing ZnSe/ZnS Core/Shell Quantum Dots and their Physicochemical Characterization." Key Engineering Materials 680 (February 2016): 553–57. http://dx.doi.org/10.4028/www.scientific.net/kem.680.553.
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Epitaxially overgrowing a semiconductor material with higher bandgap around the QDs has proven to be a crucial approach for improving the PL efficiency and stability of nanocrystals. In this paper, a ZnS shell was deposited around ZnSe nanocrystal cores via a noninjection approach in aqueous media. The deposition procedure conducted at 100°C in a reaction flask in the presence of the shell precursor compounds, together with the crude ZnSe nanocrystal cores and the thiol ligand glutathione. The influences of various experimental variables, including the reaction time, amount of thiourea, as well as pH value, on the growth rate and luminescent properties of the obtained core/shell nanocrystals have been systematically investigated. In comparison with the original ZnSe nanocrystals, the PL efficiency of the obtained ZnSe/ZnS core/shell nanostructures can be improved significantly with a QY up to 62.8%.
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Sercel, Peter C., Andrew Shabaev, and Alexander L. Efros. "Symmetry Breaking Induced Activation of Nanocrystal Optical Transitions." MRS Advances 3, no. 14 (2018): 711–16. http://dx.doi.org/10.1557/adv.2018.19.
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ABSTRACTWe have analysed the effect of symmetry breaking on the optical properties of semiconductor nanocrystals due to doping by charged impurities. Using doped CdSe nanocrystals as an example, we show the effects of a Coulomb center on the exciton fine-structure and optical selection rules using symmetry theory and then quantify the effect of symmetry breaking on the exciton fine structure, modelling the charged center using a multipole expansion. The model shows that the presence of a Coulomb center breaks the nanocrystal symmetry and affects its optical properties through mixing and shifting of the hole spin and parity sublevels. This symmetry breaking, particularly for positively charged centers, shortens the radiative lifetime of CdSe nanocrystals even at room temperature, in qualitative agreement with the increase in PL efficiency observed in CdSe nanocrystals doped with positive Ag charge centers [A. Sahu et.al., Nano Lett. 12, 2587, (2012)]. The effect of the charged center on the photoluminescence and the absorption spectra is shown, with and without the presence of compensating charges on the nanocrystal surface. While spectra of individual nanocrystals are expected to shift and broaden with the introduction of a charged center, configuration averaging and inhomogeneous broadening are shown to wash out these effects. The presence of compensating charges at the NC surface also serves to stabilize the band edge transition energies relative to NCs with no charge centers.
Dissertations / Theses on the topic "Photoluminescent semiconductor nanocrystals"
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Ho, Minh Q. "Colloidal Synthesis and Optical Characterizations of Semiconductor Nanocrystals from Nontoxic Elements." VCU Scholars Compass, 2015. http://scholarscompass.vcu.edu/etd/3915.
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To date, the search efforts have shifted from the toxic II-VI, III-V and IV-VI semiconductors to more environmentally friendly materials. Among Group II-V semiconductors, Zn3P2 has shown to be a more benign option, similar to Group IV (Ge, Si) materials, for future applications in photovoltaics and optoelectronics. This work is dedicated to the development of wet-chemical synthetic routes of (1) Zn3P2 and (2) Group IV (Ge, Si, Si1-xGex) nanocrystals with precise control over composition, crystal structure, size and dispersity by adjusting different reaction parameters such as temperature, time and solvent composition. Different characterizations will also be employed to probe the size- and composition-dependent physical and optical properties of resulting products.
The first part of this work illustrates the synthesis of luminescent Zn3P2 nanocrystals, an earth-abundant and a direct-gap semiconductor possessing high absorption coefficient and long carrier diffusion length, which uphold promising potential in many optoelectronic applications. A hot injection method by using highly reactive P and Zn precursors (P[Si(CH3)3]3 and diethyl zinc) in hexadecylamine and octadecene was developed to prepare a series of alkyl-amine-passivated tetragonal Zn3P2 crystallites with varying size sizes. Substantial blue shifts in the absorption onsets (2.11−2.73 eV) in comparison to the bulk counterpart (1.4−1.5 eV) and a clear red shift with increasing particle size indicates the quantum confinement effects. This is also consistent with the photoluminescent studies with the size-tunable maxima in the visible region (469−545 nm) as a function of growth temperature and time. The phase purity and alkyl-amine passivation of the nanocrystals were determined by structural and surface analysis, confirming the presence of N–Zn and N–P bonds on the tetragonal Zn3P2 crystallites.
The second part of this works focuses on the development of a colloidal synthetic strategy of alkyl-amine capped Si1-xGex nanocrystals with control over size- and composition-dependent optical properties. Despite their high miscibility at all compositions, developing a wet-chemical synthesis of Si1-xGex alloys in the nanoscale remains a challenging task, owing to the difference of their crystallization temperatures and the high surface oxidation of Si. Thus an adapted colloidal method is utilized to fabricate single-element Ge and Si nanocrystals. Powder X-ray diffraction indicates successful production of cubic crystalline Ge and amorphous Si nanoparticles individually in oleylamine/octadecene (surfactant/solvent) mixture at 300°C. Absorption onset values of 1.28 eV and 3.11 eV are obtained for resulting Ge and Si colloids, respectively. By alloying these two materials in their nano-regime, tunable optical properties can be achieved throughout the visible to the near IR region by simply varying their elemental compositions. The success of this bandgap engineering process offers more options for new material design by taking advantage of unique properties from each component material.
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Urgessa, Zelalem Nigussa. "Growth and characterization of ZnO nanorods using chemical bath deposition." Thesis, Nelson Mandela Metropolitan University, 2012. http://hdl.handle.net/10948/d1021124.
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Semiconductor devices are commonplace in every household. One application of semiconductors in particular, namely solid state lighting technology, is destined for a bright future. To this end, ZnO nanostructures have gained substantial interest in the research community, in part because of its requisite large direct band gap. Furthermore, the stability of the exciton (binding energy 60 meV) in this material, can lead to lasing action based on exciton recombination and possibly exciton interaction, even above room temperature. Therefore, it is very important to realize controllable growth of ZnO nanostructures and investigate their properties. The main motivation for this thesis is not only to successfully realize the controllable growth of ZnO nanorods, but also to investigate the structure, optical and electrical properties in detail by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy (steady state and time resolved) and X-ray diffraction (XRD). Furthermore, strong rectification in the ZnO/p-Si heterojunction is demonstrated. Nanorods have been successfully synthesized on silicon by a two-step process, involving the pre-coating of the substrate by a seed layer, followed by the chemical bath deposition of the nanorods. ZnO seed layers with particle sizes of about 5 nm are achieved by the thermal decomposition of zinc acetate dihydrate dissolved in ethanol. The effects of the seed layer density on the distribution, alignment and uniformity of subsequently grown nanorods were studied. The aspect ratio, orientation and distribution of nanorods are shown to be well controlled through adjusting the density of the ZnO nanoparticles pre-coated onto the substrates. It is shown that the seed layer is a prerequisite for the growth of well aligned ZnO nanorods on lattice mismatched Si substrate. The influence of various nanorod growth parameters on the morphology, optical and electrical properties of the nanorods were also systematically studied. These include the oxygen to zinc molar ratio, the pH of the growth solution, the concentration of the reactants, the growth temperature and growth time, different hydroxide precursors and the addition of surface passivating agents to the growth solution. By controlling these xii parameters different architectures of nanostructures, like spherical particles, well aligned nanorods, nanoflowers and thin films of different thicknesses are demonstrated. A possible growth mechanism for ZnO nanostructures in solution is proposed. XRD indicated that all the as-grown nanostructures produced above 45 C crystallize in the wurtzite structure and post growth annealing does not significantly enhance the crystalline quality of the material. In material grown at lower temperature, traces of zinc hydroxide were observed. The optical quality of the nanostructures was investigated using both steady-state PL and time-resolved (TR) PL from 4 K to room temperature. In the case of as-grown samples, both UV and defect related emissions have been observed for all nanostructures. The effect of post-growth annealing on the optical quality of the nanostructures was carefully examined. The effect of annealing in different atmospheres was also investigated. Regardless of the annealing environment annealing at a temperature as low as 300 C enhances the UV emission and suppresses defect related deep level emission. However, annealing above 500 C is required to out-diffuse hydrogen, the presence of which is deduced from the I4 line in the low temperature PL spectra of ZnO. TRPL was utilized to investigate lifetime decay profiles of nanorods upon different post growth treatments. The bound exciton lifetime strongly depends on the post-growth annealing temperature: the PL decay time is much faster for as grown rods, confirming the domination of surface assisted recombination. In general, the PL analysis showed that the PL of nanorods have the same characteristics as that of bulk ZnO, except for the stronger contribution from surface related bound excitons in the former case. Surface adsorbed impurities causing depletion and band bending in the near surface region is implied from both time resolved and steady state PL. Finally, although strong rectification in the ZnO/p-Si heterojunction is illustrated, no electroluminescence has been achieved. This is explained in terms of the band offset between ZnO and Si and interfacial states. Different schemes are proposed to improve the performance of ZnO/Si heterojunction light emitting devices.
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Serincan, Ugur. "Formation Of Semiconductor Nanocrystals In Sio2 By Ion Implantation." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/3/12605016/index.pdf.
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In this study, we used ion implantation technique to synthesize semiconductor
(Ge, Si) nanocrystals in SiO2 matrix. Ge and Si nanocrystals have been
successfully formed by Ge and Si implantation and post annealing. Implanted
samples were examined by characterization techniques such as TEM, XPS, EDS,
SAD, SIMS, PL, Raman and FTIR spectroscopy and the presence of Ge and Si
nanocrystals in the SiO2 matrix has been evidenced by these measurements. It
was shown that implantation dose, implantation energy, annealing temperature,
annealing time and annealing ambient are important parameters for the formation
and evolution of semiconductor nanocrystals embedded in SiO2 matrix. The
size and size distribution of Ge and Si nanocrystals were estimated successfully
by fitting Raman and PL spectra obtained from Ge and Si implanted samples, respectively. It was demonstrated that Si implanted and post annealed samples
exhibit two broad PL peaks at &<br>#8764<br>625 and 850 nm, even at room temperature.
Origin of these peaks was investigated by temperature, excitation power and excitation
wavelength dependence of PL spectrum and etch-measure experiments
and it was shown that the peak observed at &<br>#8764<br>625 nm is related with defects
(clusters or chain of Si located near the surface) while the other is related to the
Si nanocrystals. As an expected effect of quantum size phenomenon, the peak
observed at &<br>#8764<br>850 nm was found to depend on the nanocrystal size. Finally,
the formation and evolution of Ge and Si nanocrystals were monitored by FTIR
spectroscopy and it was shown that the deformation in SiO2 matrix caused by
ion implantation tends to recover itself much quicker in the case of the Ge implantation.
This is a result of effective segregation of Ge atoms at relatively low
temperatures.
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Ma, Xuedan [Verfasser], and Alf [Akademischer Betreuer] Mews. "Manipulation of Photoluminescence from Semiconductor Nanocrystals by Bandgap Engineering and Surface Plasmons / Xuedan Ma. Betreuer: Alf Mews." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2011. http://d-nb.info/1020418745/34.
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Leubner, Susanne. "On the ligand shell complexity of strongly emitting, water-soluble semiconductor nanocrystals." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-163298.
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Colloidal semiconductor nanocrystals (NCs) have attracted a great deal of interest as bright and stable chromophores for a variety of applications. Their superior physicochemical properties depend on characteristics of the inorganic core, as well as on the chemical nature and structure of the stabilizing organic ligand shell. To evaluate the promising material, a thorough knowledge of structure-property relationships is still demanded. The present work addresses this challenge to three water-soluble NC systems, namely thiol-capped CdTe, thiol-capped CdHgTe, and DNA-functionalized CdTe NCs with special emphasis on the investigation of structure, modification, and influence of the ligand shell.
Remarkably, CdTe NCs show bright emission in the visible spectral region and can be synthesized in high quality directly in water. It was shown that the aqueous synthesis also facilitates the preparation of strongly near-infrared (NIR) emitting CdHgTe NCs. The current work presents a detailed study on parameters, by which the emission can be tuned, such as the growth time, the initial Cd : Hg ratio, and the choice of ligand. These insights contribute to the knowledge, which is essential for the design of highly emissive and long-term stable NIR emitting NCs. Further variations of the NC/ligand system include the modification of the ligand shell of CdTe NCs with oligonucleotides based on the strong attachment of DNA molecules to the NC. The successful functionalization of NCs with single-stranded DNA molecules is very promising for the precise and programmable assembly of NCs using DNA origami structures as templates.
For both, functionality and optical properties, the surface chemistry of the NCs plays a substantial role and was subject to an extensive investigation. As there is no generally applicable technique to determine the amount of stabilizers and the structure of the ligand shell, the presented study is based on a combination of various methods particularly tailored to the analysis of water-soluble CdTe NCs capped by short-chain thiols. CdTe NCs served as a model system for the described analysis of the ligand shell, since they are thoroughly studied regarding synthesis and features of the core. Aiming for the quantification of thiols, a straightforward colorimetric assay, the Ellman\'s test, is for the first time introduced for the analysis of NCs. Accompanied by elemental analysis an approximate number of thiols per NC becomes accessible.
Moreover, theoretical calculations were performed to estimate the amount of ligand that would cover the NC in a monolayer of covalently bound molecules. In contrast to these results, the experimental values point to a larger amount of thiols immobilized on the NC. Attempts to remove the ligand indicate the presence of Cd in the ligand shell and thermogravimetric studies show that the ligands are not loosely assembled in the ligand shell. The outstanding conclusion of these findings involves the presence of Cd-thiol complexes in the ligand shell. Further results unambiguously show that the amount of Cd-thiol complexes present in the NC solution strongly influences the concentration-dependent emission yield of the NCs. Additional studies dedicated to the considerable influence of the ligand shell highlight a strong effect of pH, NC concentration, type and purity of the solvent, and the number of precipitation steps on the emission of water-soluble semiconductor NCs. These substantial investigations emphasize the need to carefully control the conditions applied for handling, optical measurements, and application of NCs.
In order to gain a deeper insight into the complex structure of the native ligand shell, techniques deliberately chosen for the in situ analysis were applied for thioglycolic acid-capped CdTe NCs. Information from dynamic light scattering (DLS) regarding the stability and the shell thickness are consistent with previous results showing a large ligand network on the NC surface and a decreasing stability of the NCs upon dilution. Importantly, nuclear magnetic resonance (NMR) spectroscopy allows for the distinction of bound and free ligands directly in solution and proves the presence of these species for the NCs studied. In particular, the results indicate that the ligands are not strongly bound to the NC core and that both, free and bound ligand species, consist of modified thiol molecules, such as Cd-thiol complexes. These findings support previous assumptions and allow to establish a distinct picture of the ligand shell of water-soluble semiconductor NCs. Further insights were obtained from small-angle X-ray scattering (SAXS), which facilitates the identification and the determination of the composition of NC core as well as ligand shell. Element-specific SAXS yields the final proof of the presence of Cd in the ligand shell. The model developed for the optimal fitting of the experimental scattering curves additionally confirms the findings from the other methods.
In conclusion, the present work contributes to the challenging goal of a comprehensive knowledge of interactions between the NC core and the ligands. The fundamental development of a structural model of water-soluble CdTe NCs including information on stoichiometries is accomplished by the combination of the techniques presented and emphasizes the challenge to assign a clear border between the ligand shell and the Cd-thiol complexes in solution. Altogether, CdTe NCs capped by thioglycolic acid are best described by a crystalline core surrounded by a water-swollen Cd-thiolate shell that considerably affects the optical properties of the system. Notably, the results of the versatile study provide the opportunity to control the overall properties and to evaluate water-soluble semiconductor NCs for particular applications in photonics and optoelectronics.
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Pedetti, Silvia. "Synthesis and optical properties of II-VI colloidal two-dimensional nanocrystals : homo- and hetero-structures." Electronic Thesis or Diss., Paris 6, 2015. http://www.theses.fr/2015PA066755.
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Ces travaux de thèse ont porté sur une nouvelle classe de semi-conducteurs colloïdaux sous forme de nanoplaquettes composées de chalcogénures de cadmium. Ces nanocristaux, comparables à des puits quantiques, présentent un confinement excitonique dans une seule direction, l’épaisseur, qui est contrôlée au niveau atomique. Les nanoplaquettes sont caractérisées par une excellente résolution spectrale et de bons rendements quantiques. Par conséquence, elles représentent de potentiels candidats pour développer des dispositifs optoélectroniques comme des diodes électroluminescentes ou bien des photo-détecteurs. Toutefois, dans ce but, il est nécessaire d’élargir la gamme de longueurs d’ondes d’absorption et d’émission et d’augmenter leur rendement quantique. Pour cela, nous avons étudié la synthèse colloïdale de nanoplaquettes à base d’homo- et d’hétèro-nanoplaquetts des groupes II-VI. Les nanocristaux fabriqués ont été caractérisé par spectroscopie UV-visible et de fluorescence, par diffraction à rayons X et par microscopie électronique. Dans un premier temps, nous avons optimisé la préparation de nanoplaquettes de CdTe en utilisant des procédés de synthèse colloïdale par injection de précurseurs à hautes températures. Ensuite, des structures plus complexes ont été investiguées. Par exemple, nous avons synthétisé nanoplaquettes cœur/couronne de CdSe/CdTe qui possèdent une structure électronique de type-II. Nous avons également étudié la croissance de couches d’un deuxième semi-conducteur dans la direction de l’épaisseur de plaquettes cœur pour la fabrication de structures type cœur/coque. Grâce au contrôle de la composition chimique du cœur et de la coque, l’alignement de bande a été modulé pour obtenir structures électroniques de type-I, quasi type-II et type-II<br>This thesis project is based on the development of a novel class of colloidal two-dimensional nanocrystals, i.e. nanoplatelets (NPLs), composed of cadmium chalcogenides. These nanocrystals, in analogy to quantum wells, are characterized by an exciton confinement along one direction, i.e. the thickness, which can be controlled at atomic level. Nanoplatelets possess unique optical features as an excellent spectral resolution and good quantum yields. As consequence these nanocrystals are potential candidates for the fabrication of optoelectronic devices such as electroluminescent diodes or photo-detectors. However, for this aim it is necessary to enlarge the range of the absorption and emission wavelengths and to increase their quantum yield. For this reason, we investigated the colloidal synthesis of II-VI homo- and hetero-nanoplatelets which have been characterized by UV-Vis and photoluminescence spectroscopy, by X-ray diffraction and by electronic microscopy. First, we optimized the synthesis of CdTe NPLs using colloidal synthesis based on precursors injection at high temperatures. Then, we focused on more complexes hetero-structures. For example, through lateral extension reactions we obtained CdSe/CdTe core/crown NPLs which possess a type-II electronic structure. Successively, we studied the synthesis of core/shell NPLs by the growth of a second semiconductor layer along the thickness of NPLs cores. Depending on the core and shell chemical composition we could engineer the band gap of the nanoplatelets between type-I, quasi type-II and type-II electronic structures
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Ramanathan, Swati. "Polarization Studies of Coupled Quantum Dots." Ohio University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1194984001.
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Flores, Yesica. "Hybrid semiconducting nanoplatelets : synthesis and molecule-driven assembly." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS464.
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Ce doctorat avait pour objet l’exploration des propriétés chimiques de nanoplaquettes de séléniure de cadmium en les fonctionnalisant par des complexes paramagnétiques de coordination. En effet, l’association des propriétés magnétiques des complexes avec les propriétés optiques très originales de ces objets pourrait conduire à la découverte de nouvelles propriétés magnéto-optiques. Cette thèse, en cohérence avec des résultats récents de la littérature, a confirmé que la forme plaquettaire de ces nano-objets induisait leur empilement lorsqu’ils sont recouverts de ligands appropriés et dispersés dans des solvants adaptés. Cette thèse présente trois chapitres portant sur (i) la description des nanoplaquettes de CdSe du point de vue de leur structure et de leurs propriétés, (ii) une étude de l’assemblage des plaquettes lorsque celles-ci sont fonctionnalisées par des molécules de type azobenzène isomérisable et (iii) l’étude de l’assemblage des nanoplaquettes par l’intermédiaire de phtalocyanines de cobalt(II) conduisant à des matériaux composites. Nous avons montré que la fonctionnalisation des nanoplaquettes par des molécules d’azobenzène permettait leur assemblage hors équilibre c’est à dire sous apport continu d’énergie. Par ailleurs, deux voies d’assemblage des nanoplaquettes avec la phtalocyanine de cobalt ont été explorées. Ces deux voies permettent d’obtenir des composites de structures différentes et dans un cas il a été observé une émission de lumière polarisée circulairement sous champ magnétique. Ce résultat montre l’existence d’une rupture de symétrie dans le composite liée à la présence du complexe de cobalt et donc l’apparition de propriétés magnéto-optiques<br>This Ph.D. aimed at a better understanding of the chemical properties of cadmium selenide nanoplatelets by functionalization by paramagnetic coordination complexes. Indeed, the original optical properties of the platelets associated to the paramagnetism of transition metal complexes could lead to new magneto-optic properties. In agreement with recent literature results, this Ph.D. confirms that the planar morphology of these nano-objets induces their stacking when covered by appropriate ligands and dispersed in appropriate solvents. This thesis presents three chapters about (i) the description of the structure and the properties of CdSe nanoplatelets, (ii) a study of azobenzenedecorated nanoplatelets and (iii) the self-assembly of CdSe nanoplatelets mediated by cobalt(II) phtalocyanines to produce composite materials. This work shows that functionalizing CdSe nanoplatelets with azobenzene moieties allows their out-of-equilibrium assembly. Furthermore, two ways of assembling nanoplatelets with cobalt(II) phtalocyanines have been developed leading to composites bearing different structures. For one of these structures a circularly polarized light is emitted under magnetic field revealing a symmetry braking in the composite thanks to the cobalt complex and thus magneto-optic effects
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Shiman, Dmitriy I., Vladimir Sayevich, Christian Meerbach, et al. "Robust Polymer Matrix Based on Isobutylene (Co)polymers for Efficient Encapsulation of Colloidal Semiconductor Nanocrystals." American Chemical Association, 2019. https://tud.qucosa.de/id/qucosa%3A74322.
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We introduce new oxygen- and moisture-proof polymer matrixes based on polyisobutylene (PIB) and its block copolymer with styrene [poly(styrene-block-isobutylene-blockstyrene), PSt-b-PIB-b-PSt] for the encapsulation of colloidal semiconductor nanocrystals. In order to prepare transparent and processable composites, we developed a special procedure of nanocrystal surface engineering including ligand exchange of parental organic ligands to inorganic species followed by the attachment of specially designed short-chain PIB functionalized with an amino group. The latter provides excellent compatibility of the particles with the polymer matrixes. As colloidal nanocrystals, we chose CdSe nanoplatelets (NPLs) because they possess a large surface and thus are very sensitive to the environment, in particular in terms of their limited photostability. The encapsulation strategy is quite general and can be applied to a wide variety of semiconductor nanocrystals, as demonstrated on the example of PbS quantum dots. All obtained composites exhibited excellent photostability, being tested in a focus of a powerful white-light source, as well as exceptional chemical stability in a strongly acidic media. We compared these properties of the new composites with those of widely used polyacrylate-based materials, demonstrating the superiority of the former. The developed composites are of particular interest for application in optoelectronic devices, such as color-conversion light-emitting diodes, laser diodes, luminescent solar concentrators, etc.
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Monahan, Bradley Michael. "Synthesis and Characterization of Phase-pure Copper Zinc Tin Sulfide (Cu2ZnSnS4) Nanoparticles." University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1404732007.
Full textBook chapters on the topic "Photoluminescent semiconductor nanocrystals"
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Gangopadhyay, P. "Optical, Photoluminescence, and Vibrational Spectroscopy of Metal Nanoparticles." In Semiconductor Nanocrystals and Metal Nanoparticles. CRC Press, 2016. http://dx.doi.org/10.1201/9781315374628-5.
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Huy, P. T., and P. H. Duong. "Intense Photoluminescence and Photoluminescence Enhancement of Silicon Nanocrystals by Ultraviolet Irradiation." In Semiconductor Photonics: Nano-Structured Materials and Devices. Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-471-5.74.
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Xu, Zhihua, and Mircea Cotlet. "Probing Photoluminescence Dynamics in Colloidal Semiconductor Nanocrystal/Fullerene Heterodimers with Single Molecule Spectroscopy." In UV-VIS and Photoluminescence Spectroscopy for Nanomaterials Characterization. Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-27594-4_15.
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Filonovich, Sergey A., Yurii P. Rakovich, Mikhail I. Vasilevskiy, et al. "Probing the Exciton Density of States in Semiconductor Nanocrystals Using Integrated Photoluminescence Spectroscopy." In Nanostructured Materials. Springer Vienna, 2002. http://dx.doi.org/10.1007/978-3-7091-6740-3_15.
Full textConference papers on the topic "Photoluminescent semiconductor nanocrystals"
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Shcheglov, K. V., C. M. Yang, and H. A. Atwater. "Photoluminescence and Electroluminescence of Ge-Implanted Si/SiO2/Si Structures." In Microphysics of Surfaces: Nanoscale Processing. Optica Publishing Group, 1995. http://dx.doi.org/10.1364/msnp.1995.msab3.
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Although it was observation of efficient photoluminescence [PL] from porous silicon that prompted numerous investigations into the optoelectronic properties of group IV semiconductor nanocrystals, there is interest in other related materials which are more robust in various chemical and thermal ambients and which can be easily incorporated into standard silicon VLSI processing. A promising approach that meets the above requisites is synthesis of semiconductor nanocrystals in an SiO2 matrix accomplished by various techniques. In this letter we report on the fabrication of a Ge nanocrystal-based electroluminescent device using ion implantation and precipitation.
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Klimov, Victor I., and Vladimir A. Karavanskii. "Ultrafast Optical Nonlinearities in CuxS Nanocrystals." In Nonlinear Optics: Materials, Fundamentals and Applications. Optica Publishing Group, 1996. http://dx.doi.org/10.1364/nlo.1996.nthe.17.
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Three-dimensional (3D) carrier confinement in semiconductor nanocrystals (NC's) results in size-dependent photoluminescence and absorption spectra and significantly modifies the nonlinear optical properties and carrier dynamics with respect to those in bulk materials. So far, most experimental and theoretical studies have concentrated on NC's formed by direct-gap II-VI semiconductors such as CdS and CdSe. Recently, we reported the preparation, linear and picosecond nonlinear transmission of NC's of a new type: NC's formed by different copper sulfide phases [1]. Depending on the copper deficiency, the energy band gap in copper sulfide varies from 1.2 (x = 2) to 1.5 eV (x = 1.8) with an accompanying transformation of the semiconductor from indirect-gap to direct-gap one. These interesting properties as well as a small electron mass provide the broad phase/size controlled tuning range and give the opportunity to compare the effects of 3D confinement on nonlinear optical proterties in direct and indirect-gap semiconductors.
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Mei, Guang, Scott Carpenter, An Tu, L. E. Felton, and P. D. Persans. "Electron-hole effective mass in CdSxSe1-x semiconductor nanocrystals." In OSA Annual Meeting. Optica Publishing Group, 1991. http://dx.doi.org/10.1364/oam.1991.wl28.
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We report results of a study of the electron-hole effective mass in CdS x Se1-x nanocrystals embedded in a glass matrix. By varying annealing temperature and growth times, we obtained a series of samples with various crystallite sizes from 40 to 200 Å. Raman experiments and transmission electron microscopy were carried out to determine the composition and crystallite diameter of the semiconductor dots, respectively. The compositions of the semiconductor nanocrystals were found to be independent of particle size so the absorption peak position is solely due to the size. Electromodulation, absorption, and photoluminescence spectra were measured to identify the quantized energy levels. Two electromodulation peaks due to light and heavy hole bands are clearly resolved.
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KULAKOVICH, O. S., M. V. ARTEMYEV, A. YAROSHEVICH, and S. MASKEVICH. "ENHANCED PHOTOLUMINESCENCE OF SEMICONDUCTOR NANOCRYSTALS NEAR METAL COLLOIDS." In Physics, Chemistry and Application of Nanostructures - Reviews and Short Notes to Nanomeeting 2003. WORLD SCIENTIFIC, 2003. http://dx.doi.org/10.1142/9789812796738_0028.
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Klimov, Victor I., and Duncan W. McBranch. "Ultrafast Optical Nonlinearities and Carrier Dynamics in Direct- and Indirect-Gap Semiconductor Nanocrystals." In Chemistry and Physics of Small-Scale Structures. Optica Publishing Group, 1997. http://dx.doi.org/10.1364/cps.1997.ctua.3.
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Semiconductor nanocrystals (NCs) exhibit large and fast optical nonlinearities, and efficient photo- and electroluminescence that make them promising materials for applications in optoelectronics and ultrafast optical switching. The nonlinear optical and luminescent properties of NCs are significantly affected by carrier dynamics. Carrier trapping and a nonradiative Auger process are believed to play a major role in the early stages of carrier relaxation, resulting in ultrafast picosecond and subpicosecond dynamics measured in femtosecond pump-probe, photoluminescence (PL) up-conversion, and photoecho experiments.
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Vandyshev, E. N., G. A. Kachurin, and K. S. Zhuravlev. "Effect of external electric field on photoluminescence of silicon nanocrystals." In PHYSICS OF SEMICONDUCTORS: 28th International Conference on the Physics of Semiconductors - ICPS 2006. AIP, 2007. http://dx.doi.org/10.1063/1.2730262.
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Simoes Gamboa, A. L., and E. N. Bodunov. "Functions for Describing Nonexponential Photoluminescence Decay Kinetics in Semiconductor Nanocrystals." In 2022 International Conference Laser Optics (ICLO). IEEE, 2022. http://dx.doi.org/10.1109/iclo54117.2022.9839822.
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Chen, Kok Hao, and Jong Hyun Choi. "Nanoparticle-Aptamer: An Effective Growth Inhibitor for Human Cancer Cells." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-11966.
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Semiconductor nanocrystals have unique optical properties due to quantum confinement effects, and a variety of promising approaches have been devised to interface the nanomaterials with biomolecules for bioimaging and therapeutic applications. Such bio-interface can be facilitated via a DNA template for nanoparticles as oligonucleotides can mediate the aqueous-phase nucleation and capping of semiconductor nanocrystals.[1,2] Here, we report a novel scheme of synthesizing fluorescent nanocrystal quantum dots (NQDs) using DNA aptamers and the use of this biotic/abiotic nanoparticle system for growth inhibition of MCF-7 human breast cancer cells for the first time. Particularly, we used two DNA sequences for this purpose, which have been developed as anti-cancer agents: 5-GGT GGT GGT GGT TGT GGT GGT GGT GG-3 (also called, AGRO) and 5-(GT)15-3.[3–5] This study may ultimately form the basis of unique nanoparticle-based therapeutics with the additional ability to optically report molecular recognition. Figure 1a shows the photoluminescence (PL) spectra of GT- and AGRO-passivated PbS QD that fluoresce in the near IR, centered at approximately 980 nm. A typical synthesis procedure involves rapid addition of sodium sulfide in the mixture solution of DNA and Pb acetate at a molar ratio of 2:4:1. The resulting nanocrystals are washed to remove unreacted DNA and ions by adding mixture solution of NaCl and isopropanol, followed by centrifugation. The precipitated nanocrystals are collected and re-suspended in aqueous solution by mild sonication. Optical absorption measurements reveal that approximately 90 and 77% of GT and AGRO DNA is removed after the washing process. The particle size distribution in Figure 1b suggests that the GT sequence-capped PbS particles are primarily in 3–5 nm diameter range. These nanocrystals can be easily incorporated with mammalian cells and remain highly fluorescent in sub-cellular environments. Figure 1c serially presents an optical image of a MCF-7 cell and a PL image of the AGRO-capped QD incorporated with the cell. Figure 1. (a) Normalized fluorescence spectra of PbS QD synthesized with GT and AGRO sequences, which were previously developed as anti-cancer agents. The DNA-capped QD fluoresce in the near IR centered at ∼980 nm. (b) TEM image of GT-templated nanocrystals ranging 3–5 nm in diameter. (c) Optical image of an MCF-7 human breast cancer cell after a 12-hour exposure to aptamer-capped QD. (d) PL image of AGRO-QD incorporated with the cell, indicating that these nanocrystals remain highly fluorescent in sub-cellular environments. One immediate concern for interfacing inorganic nanocrystals with cells and tissue for labeling or therapeutics is their cytotoxicity. The nanoparticle cytotoxicity is primarily determined by material composition and surface chemistry, and QD are potentially toxic by generating reactive oxygen species or by leaching heavy metal ions when decomposed.[6] We examined the toxicity of aptamer-passivated nanocrystals with NIH-3T3 mouse fibroblast cells. The cells were exposed to PbS nanocrystals for 2 days before a standard MTT assay as shown in Figure 2, where there is no apparent cytotoxicity at these doses. In contrast, Pb acetate exerts statistically significant toxicity. This observation suggests a stable surface passivation by the DNA aptamers and the absence of appreciable Pb2+ leaching. Figure 2. Viability of 3T3 mouse fibroblast cells after a 2-day exposure to DNA aptamer-capped nanocrystals. There is no apparent dose-dependent toxicity, whereas a statistically significant reduction in cell viability is observed with Pb ions. Note that Pb acetate at 133 μM is equivalent to the Pb2+ amount that was used for PbS nanocrystal synthesis at maximum concentration. Error bars are standard deviations of independent experiments. *Statistically different from control (p&lt;0.005). Finally, we examined if these cyto-compatible nanoparticle-aptamers remained therapeutically active for cancer cell growth inhibition. The MTT assay results in Figure 3a show significantly decreased growth of breast cancer cells incorporated with AGRO, GT, and the corresponding templated nanocrystals, as anticipated. In contrast, 5-(GC)15-3 and the QDs synthesized with the same sequence, which were used as negative controls along with zero-dose control cells, did not alter cell viability significantly. Here, we define the growth inhibition efficacy as (100 − cell viability) per DNA of a sample, because the DNA concentration is significantly decreased during the particle washing. The nanoparticle-aptamers demonstrate 3–4 times greater therapeutic activities compared to the corresponding aptamer drugs (Figure 3b). We speculate that when a nanoparticle-aptamer is internalized by the cancer cells, it forms an intracellular complex with nucleolin and nuclear factor-κB (NF-κB) essential modulator, thereby inhibiting NF-κB activation that would cause transcription of proliferation and anti-apoptotic genes.[7] The nanoparticle-aptamers may more effectively block the pathways for creating anti-apoptotic genes or facilitate the cellular delivery of aptamers via nanoparticle uptake. Our additional investigation indicates that the same DNA capping chemistry can be utilized to produce aptamer-mediated Fe3O4 nanocrystals, which may be potentially useful in MRI and therapeutics, considering their magnetic properties and biocompatibility. In summary, the nanoparticle-based therapeutic schemes developed here should be valuable in developing a multifunctional drug delivery and imaging agent for biological systems. Figure 3. Anti-proliferation of MCF-7 human breast cancer cells with aptamer-passivated nanocrystals. (a) Viability of MCF-7 cells exposed to AGRO and GT sequences, and AGRO-/GT-capped QD for 7 days. The DNA concentration was 10 uM, while the particles were incubated with cells at 75 nM. (b) Growth inhibition efficacy is defined as (100 − cell viability) per DNA to correct the DNA concentration after particle washing.
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Hamanaka, Yasushi, Masakazu Tsuzuki, Kohei Ozawa, and Toshihiro Kuzuya. "Solution-phase synthesis and photoluminescence characterization of quaternary Cu[sub 2]ZnSnS[sub 4] nanocrystals." In THE PHYSICS OF SEMICONDUCTORS: Proceedings of the 31st International Conference on the Physics of Semiconductors (ICPS) 2012. AIP, 2013. http://dx.doi.org/10.1063/1.4848256.
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Kawanishi, Satoki, Masato Ohmori, Masatoshi Tanaka, and Hiroyuki Sakaki. "Observation of photoluminescence of semiconductor nanocrystal quantum dots in the core of photonic bandgap fiber." In 2006 IEEE LEOS Annual Meeting. IEEE, 2006. http://dx.doi.org/10.1109/leos.2006.279045.
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