Energy Materials & Technology
Shawqi Al Dallal; Khalil Ebrahim Jasim
Abstract
Third generation solar cells, such as dye and quantum dot sensitized solar cells are attracting attention of many research groups. In this investigation we explore the role of dye extract on the enhancement of the photovoltaic properties of quantum dot sensitized solar cells (QDSSCs). Lead sulfide quantum ...
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Third generation solar cells, such as dye and quantum dot sensitized solar cells are attracting attention of many research groups. In this investigation we explore the role of dye extract on the enhancement of the photovoltaic properties of quantum dot sensitized solar cells (QDSSCs). Lead sulfide quantum dots of different sizes have been used to sensitize a nanostructured titanium oxide electrode. We compare the open circuit voltage, the short circuit current, and power conversion efficiency of QDSSCs with the same quantities as obtained for dye-enhanced system using pomegranate dye extract. An open circuit voltage of 166 mV, a short circuit current of 0.1 mA, and an efficiency of 0.32% were obtained for 2.4 nm radius lead sulfide quantum dot sensitized solar cells. Using pomegranate dye extract reveals a considerable enhancement of the above characteristics. The combined dye-quantum dot system produces an open circuit voltage of 300 mV, a short circuit current of 0.55 mA, and an efficiency of 3.4%. For 3.2 nm radius QDs, the efficiency is substantially higher, reaching about 7%. A model describing the structure and processes leading to the above enhancement of the assembled solar cell characteristics is presented. In this model we explain the interplay between the transfer of electrons between the dye, quantum dots, and subsequent injection in the wide band gap titanium dioxide semiconductor.
Pragati Malik; Rita Kakkar
Abstract
Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) play important roles in the storage of genetic information and protein biosynthesis. Nucleobases, which are nitrogenous bases, are the functional units of these nucleic acids. It is very important to detect changes in the sequence of DNA/RNA, as ...
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Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) play important roles in the storage of genetic information and protein biosynthesis. Nucleobases, which are nitrogenous bases, are the functional units of these nucleic acids. It is very important to detect changes in the sequence of DNA/RNA, as any mutations in them may cause harm to the organism. Our aim is to verify the use of (CdSe)3 Quantum Dots (QDs), owing to their distinctive optical and electronic properties, for sensing changes in DNA/RNA. Hence, in this work, we have focused on studying the interaction between (CdSe)3 QDs and the five nucleobases (adenine, guanine, cytosine, thymine and uracil) at various probable sites by means of density functional calculations. Several structural, electronic and optical properties, and charge transfer on interaction between the two, have been discussed. The present band gap and charge transfer calculations indicate that binding of (CdSe)3 to guanine is strongest and is weakest with uracil. The vibrational spectral analysis indicates that the intensities of the peaks due to (CdSe)3 enhance on interacting with the nucleobase, and a blue shift is observed in all the interactions. The presence of both the frontier orbitals (HOMO and LUMO) on the QD indicates that (CdSe)3 acts as a guardian of DNA and prevents it from damage. Hence, our studies direct that CdSe QDs can be successfully employed as sensors for these nucleobases.
Bhavani P. Nenavathu; Geetanjali
Abstract
An efficient theragnostic which offers diagnosis and therapy of cancer is developed using a polymer based nanocarrier embedded with fluorescent quantum dots by the ionotropic gelation method. The FTIR spectra provide direct evidence of formation of polymer based nanocarrier comprising chitosan-alginate ...
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An efficient theragnostic which offers diagnosis and therapy of cancer is developed using a polymer based nanocarrier embedded with fluorescent quantum dots by the ionotropic gelation method. The FTIR spectra provide direct evidence of formation of polymer based nanocarrier comprising chitosan-alginate micro beads (CS-ALG beads). Notably, the SEM images showed highly porous structure of polymeric beads without Ag NPs and CdS QDs. The morphology of CS-ALG beads loaded with Ag NPs and CdS QDs showed smooth surface, glossy, homogenous shape under scanning electron microscopy and it could be due to high loading of fluorescent and silver NPs. The EDX analysis of as synthesised nanoparticle embedded polymeric beads showed X-ray peaks of Cd, S corresponds to CdS NPs. And the X- Ray peaks of C, O corresponds to the polymer beads. Characterization of nanocarrier for the presence of polymers has been confirmed by studies carried out using thermogravimetric analysis (TGA) showed complete degradation of Chitosan at about 450 °C while calcium alginate exhibits three-step decomposition. Further, the swelling studies of dried CS-ALG beads were carried out at room temperature and about 97% of swelling is being observed at pH 5 in 45 min. and 44% swelling is observed at pH 2. Copyright © VBRI Press.
Martin Moebius; Joerg Martin; Melinda Hartwig; Ricardo Decker; Lothar Kroll; Reinhard R. Baumann; Thomas Otto
Abstract
Fibre-reinforced plastics offer excellent mechanical properties at low weight. Hence, such materials are ideally suited to reduce energy consumption and CO2 emission, e.g. in aircraft and automotive engineering, shipbuilding or in the field of renewable energies. However, in contrast to e.g. metals, ...
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Fibre-reinforced plastics offer excellent mechanical properties at low weight. Hence, such materials are ideally suited to reduce energy consumption and CO2 emission, e.g. in aircraft and automotive engineering, shipbuilding or in the field of renewable energies. However, in contrast to e.g. metals, lightweight structures are sensitive to mechanical loads exceeding a certain approved range. In order to detect mechanical overloads at an early stage and to avoid consequential failures in lightweight structures, we recently proposed a novel concept of a thin-film sensor for visualization of mechanical loads by using photoluminescence quenching of quantum dots. Here, we present results according to the optimization of the ionization efficiency of the cadmium selenide quantum dots by using poly(N-vinylkarbazol)(PVK) as charge transport material with favorable energy levels. Measurements of the photoluminescence intensity and electrical power confirm an increase of efficiency with almost the same photoluminescence drop compared to N,N,N′,N′-Tetrakis(3-methylphenyl)-3,3′-dimethyl-benzidine (HMTPD), most likely by the higher valence band offset between quantum dots and PVK. Furthermore, an integration of a layer stack with connected ceramic piezoelectric transducer demonstrates the successful use of the sensor system for mechanical load detection in lightweight structures.
Ragini Singh;Sanjay Singh
Abstract
Nanomaterials (NMs) have found extensive commercial use in industries, healthcare and household applications however, their ecotoxicological effects remain elusive. Since, microbial communities play beneficial role in ecosystem like element cycling, bioremediation, nitrogen fixation, etc., effect of ...
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Nanomaterials (NMs) have found extensive commercial use in industries, healthcare and household applications however, their ecotoxicological effects remain elusive. Since, microbial communities play beneficial role in ecosystem like element cycling, bioremediation, nitrogen fixation, etc., effect of NMs over beneficial microbe’s physiology and viability remains to be studied in detail. Some beneficial microbe communities are severely affected by the release of NMs in the environment. Deinococcus radiodurans is known for its tolerance to oxidative stress caused due to irradiation. In this study, we have used metal, metal oxides, quantum dots (QDs) and carbon based NMs to assess their effect on the cell viability, uptake and ROS generation in D. radiodurans cells. The present study demonstrates in real-time by flow cytometry the internalization of different metal, metal oxide, QDs and carbon based NMs in D. radiodurans. Results show that all the tested NMs are significantly internalized in to the bacterial cells however, carbon based NMs exhibited highest internalization. Toxicity studies revealed that AgNPs exhibited maximum toxicity and reactive oxygen species (ROS) generation followed by QDs, CuO NPs and GO but, AuNPs and TiO2 NPs shows no toxic response in bacterial cells. The oxidative stress and uptake studies will provide insight about the mechanism of oxidative stress tolerance of D. radiodurans.
Karen M. Gambaryan
Abstract
For the thermophotovoltaic (TPV) and other mid-infrared applications, the narrow bandgap quantum dot (QD) diode structures and photoresistors (PR) based on InAsSbP alloys and InAs industrial substrates are fabricated and investigated. For the nucleation of InAsSbP composition strain-induced QDs in Stranski–Krastanow ...
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For the thermophotovoltaic (TPV) and other mid-infrared applications, the narrow bandgap quantum dot (QD) diode structures and photoresistors (PR) based on InAsSbP alloys and InAs industrial substrates are fabricated and investigated. For the nucleation of InAsSbP composition strain-induced QDs in Stranski–Krastanow growth mode, as well as at the growth of emitter epilayer lattice-matched with the InAs(100) substrate, the modified liquid phase epitaxy (MLPE) technique is employed. The HR-SEM and AFM microscopes are used for characterization. The grown QDs surface density equals to (3-8)×109 cm -2 , with height and width dimensions ranges from 4 nm to 15 nm and 10 nm to 35 nm, respectively. The current-voltage characteristics and photoresponse spectra of QD TPV and PR structures are also explored. The redshift of the absorption edge, as well as enlargement toward the short wavelength region is revealed for both QD-based devices. The quantitative calculations show increasing of QD-based TPV structures efficiency up to 16% compared with the same structures without QDs.
Sreenu Bhanoth; Aakriti Tyagi; Anita K. Verma; Pawan K. Khanna
Abstract
Enhanced understanding of diseases at the molecular level has made a paradigm shift towards identifying new biological indicators especially in nanomaterials. It is important to make Quantum Dots (QDs) more than just passive bio-probes/labels for biological imaging and cellular studies as they offers ...
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Enhanced understanding of diseases at the molecular level has made a paradigm shift towards identifying new biological indicators especially in nanomaterials. It is important to make Quantum Dots (QDs) more than just passive bio-probes/labels for biological imaging and cellular studies as they offers “smart” multifunctional nano-platforms. For any biomedical, optoelectronic device application, evaluation of cytotoxicity coupled with cellular uptake and internalization of QDs are imperative. This paper describes the cytotoxic studies of hydrophilic and hydrophobic QDs, capped with polyvinyl pyrrolidone (PVP) and oleic acid in human breast adenocarcinoma MCF-7, Human Embryonic Kidney (HEK-293) and Ehrlich Ascites Carcinoma (EAC) cancer cells that indicated a concentration and time dependent response in a 48 hr assay. The enhanced fluorescence emitted from the cytoplasm confirmed that the QDs were efficiently internalized by the cells. 35% cytotoxicity was observed by core-shell ZnSe/CdSe QDs in HEK-293 cells, while the hydrophobic CdSe exhibited less cytotoxicity in both MCF-7 and EAC cell lines in 48 hrs. Increased LDH leakage and decreased MTT reduction was observed in a time dependent manner. The decrease rate of LDH was found in PVP-CdSe relative to the value obtained from untreated/control cells post 24 hr. The oleic acid coating renders the core-shell CdSe QDs to be more hydrophobic thus making them less toxic due to possibly weak interaction with the cells, and low ionization of cadmium. Based on our experimental observation the sequence of cytotoxicity of tested QDs was hydrophilic greater than hydrophobic in all three cell lines.
Jai Kumar B; Sumanth Kumar D; Mahesh H. M
Abstract
The CdS quantum dots (QDs) were synthesized using double injection aqueous method and systematic studies were carried to determine optimum cation to anion (Cd:S) ratio to obtain mono sized CdS QDs. An efficient and convenient method is designed by utilizing the optical properties (absorbance and transmission ...
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The CdS quantum dots (QDs) were synthesized using double injection aqueous method and systematic studies were carried to determine optimum cation to anion (Cd:S) ratio to obtain mono sized CdS QDs. An efficient and convenient method is designed by utilizing the optical properties (absorbance and transmission spectra) as qualitative tool. CdS QDs was synthesized by varying cadmium and sulfur concentration from 0.01M to 0.1M and 0.01M to 0.05M respectively keeping MPA and other precursors constant. Through Concentration Optimization by Optical Spectra (COOS) method, it was found that for 0.02M sulfur and 0.04M MPA, 0.03 to 0.05M cadmium was the most favorable concentration and similarly for 0.04M cadmium and MPA the optimum concentration of sulfur was 0.02M. CdS QDs optical band gap varied from 3.09 eV to 3.69 eV with quantum dots size decreasing from 3.22 nm to 2.45 nm, respectively for Cadmium concentration from 0.02M to 0.07M. For Sulfur concentration variation, band gap varied from 3.55 eV to 3.03 eV, with size of QDs increasing from 2.58 nm to 3.33 nm, respectively for concentration 0.01M to 0.05M. All this results shows that synthesized quantum dots were well under quantum confinement effect. Further, the proposed COOS method can be extended to all QDs synthesis to obtain the optimum cation to anion ratio to synthesis QDs with narrow size distribution.
Bablu Mukherjee; Asim Guchhait; Yinthai Chan; Ergun Simsek
Abstract
We have studied the optical absorptance of lead sulfide (PbS) quantum dot (QD) coated thin crystalline layered material (TCLM) experimentally and numerically. Starting with the synthesis, fabrication and characterizations, a sample of PbS QDs deposited on trilayer molybdenum disulphide (MoS2) thin film ...
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We have studied the optical absorptance of lead sulfide (PbS) quantum dot (QD) coated thin crystalline layered material (TCLM) experimentally and numerically. Starting with the synthesis, fabrication and characterizations, a sample of PbS QDs deposited on trilayer molybdenum disulphide (MoS2) thin film has been probed locally using a reflection spectrometer set-up. Since transmittance is needed to calculate the absorbtance of the QD film/TCLM sample, we run a set of simulations using a 3D finite-difference time-domain full-wave electromagnetic solver. Based on the agreement between experimental and numerical results for the reflectance spectra, which verifies the accuracy of our QD and TCLM modelling, we have calculated the absorptance. Unlike metal nanoparticle decorated TCLMs in which metal nanoparticles act like induced dipoles and enhance the absorptance, here we have not observed the similar effect; rather we have found that the absorptance of QD film/TCLM sample is almost equal to the summation of QDs’ and TCLM’s individual absorptance in the wavelength range of 450-800 nm.
Sunita Gulia;Rita Kakkar
Abstract
Quantum dots (QDs), highly luminescent semiconductor nanocrystals, have found extensive applications in different fields, ranging from optoelectronic to bio-imaging. Numerous applications are emerging daily. Among these, ZnO QDs have higher biological significance because of their relative non-toxicity. ...
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Quantum dots (QDs), highly luminescent semiconductor nanocrystals, have found extensive applications in different fields, ranging from optoelectronic to bio-imaging. Numerous applications are emerging daily. Among these, ZnO QDs have higher biological significance because of their relative non-toxicity. The primary aim of this review is to overview the literature based on the biological applications of ZnO QDs, including gene therapy, drug delivery, optical imaging, allergen and antigen detection, cancer cell sensing, antibacterial agents and DNA detection. The luminescent properties of ZnO nanoparticles have attracted considerable attention for numerous applications like ultraviolet light emitting devices, flat panel displays, as low voltage phosphors and biosensing devices. The review throws light on the developments in fabrication techniques of nanometer-sized, water-dispersible, bio-compatible and stable ZnO QDs in aqueous medium for biological applications, including employing organic ligands, coating nanoparticles with inorganic shells, doping with a suitable element and capping nanoparticles surfaces with polymers. The low toxicity of ZnO and its high natural abundance make it a good alternative to cadmium based II-VI semiconductors, which cause toxicity via photoinduced reactive oxygen species (ROS) generation.
Pragati Malik; Sunita Gulia; Rita Kakkar
Abstract
The most widely researched and investigated disease, both medically and scientifically, in the current era is the formidable disease cancer. The chances of successful treatment and hence the curability increases if it is diagnosed at an early stage. This can be done only by increasing awareness amongst ...
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The most widely researched and investigated disease, both medically and scientifically, in the current era is the formidable disease cancer. The chances of successful treatment and hence the curability increases if it is diagnosed at an early stage. This can be done only by increasing awareness amongst people about its early diagnosis and screening tests. Cancer screening exams refers to the medical tests to identify people who have disease, often before symptoms of the illness occur. These tests help detecting cancer at its earliest stage when the chances for curing the disease are greatest. Advancements in nanotechnology have made the early screening of cancer possible. In this review, we have discussed the developments in nanotechnology that have encouraged the more recent innovative solutions for early diagnosis and treatment of cancer. Quantum dots, nanometer-sized semiconductors, are the new class of novel biosensors, now being exclusively employed as alternative fluorescent probes due to their unique properties, such as intense and stable fluorescence for a longer time, resistance to photobleaching, large molar extinction coefficients, and highly sensitive detection, due to their ability to absorb and emit light very efficiently. Their size approximates that of individual biomolecules, which offers unique possibilities for the ultrasensitive detection of cancer in persons’ serum, tissues, and other body fluids, when tagged with specific antibodies against specific tumor markers. In this review, we have account briefly the applications of semiconductor QDs employed for the early screening and diagnosis of cancer biomarkers between the years 2009-2012. We believe that this review will enable workers in the field to devise new applications of these materials for the early detection of cancer, and ultimate reduction in incidence of the disease.
P. Kumar; D. Kukkar; A Deep; S.C. Sharma; L.M. Bharadwaj
Abstract
Semiconductor inorganic nanocrystals or quantum dots (QDs) are nowadays extensively used for imaging and analysis of bio-molecules owing to their superior optical properties over conventional organic fluorophores. They have excellent potential for synthesizing molecular probes against various biological ...
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Semiconductor inorganic nanocrystals or quantum dots (QDs) are nowadays extensively used for imaging and analysis of bio-molecules owing to their superior optical properties over conventional organic fluorophores. They have excellent potential for synthesizing molecular probes against various biological markers such as free antigens, cell surface markers/antigens, bacteria, viruses and tissues. Traditional synthesis protocols of the QDs generally lead to the formation of hydrophobic nanocrystals. For biological applications, post-synthesis modifications need to be introduced to render required hydrophilicity. However, such additional steps make the tiny QDs structures bulky, which is unwanted in subsequent in-vivo executions. The present work reports a simple method for the direct synthesis of hydrophilic carboxyl (–COOH) functionalized CdS QDs using mercaptopropionic acid as a sulfur source and stabilizer. This aqueous synthesis route avoids the requirement of extra surface modification steps. The size and surface morphology of the synthesized CdS QDs were studied by electron microscopy. The average diameter of the QDs has been found to be in the range of 2-3.5nm. Spectral studies confirmed the grafting of –COOH terminal on the synthesized nanocrystals. Band gap energy and the theoretical size of the particles were calculated and found in good agreement with the experimental analysis. Due to the size quantization effect, the estimated band gap energy (2.6eV) of the QDs was on a higher side than that reported (2.4eV) for the bulk material. The synthesized nanocrystals can be further conjugated with bio-molecules for high-throughput drug screening, clinical immunological assays and protein-protein interaction studies.
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