Modified Quantum Dots Research Articles

Enhanced Performance of Planar Perovskite Solar Cell by Graphene Quantum Dot Modification

In organic–inorganic halide perovskite solar cells (PSCs), the perovskite layer is the main source of photogenerated electron–hole pairs. Therefore, the premier concern in PSCs is to improve the quality of the perovskite film (PF). In the present research, graphene quantum dots (GQDs) were prepared and incorporated in the perovskite precursor, and due to the merits of dangling bonds, quantum size, and excellent electronic conductivity of GQDs, PF of higher-quality with flat surface and pinhole-free hallmarks was garnered. It is delightful that the PFs with GQDs exhibit higher light absorption and faster charge extraction. Consequently, the power conversion efficiency (PCE) of PSCs incorporating GQDs achieves an improvement of 11% compared with the pristine ones. Our work confirms that incorporating GQDs is a viable approach to obtain high-quality PF with more efficient charge extraction for superior planar PSCs.

Functionalized Graphene Quantum Dot Modification of Yolk-Shell NiO Microspheres for Superior Lithium Storage.

Yolk-shell NiO microspheres are modified by two types of functionalized graphene quantum dots (denoted as NiO/GQDs) via a facile solvothermal treatment. The modification of GQDs on the surface of NiO greatly boosts the stability of the NiO/GQD electrode during long-term cycling. Specifically, the NiO with carboxyl-functionalized GQDs (NiO/GQDsCOOH) exhibits better performances than NiO with amino-functionalized GQDs (NiO/GQDsNH2 ). It delivers a capacity of ≈1081 mAh g-1 (NiO contribution: ≈1182 mAh g-1 ) after 250 cycles at 0.1 A g-1 . In comparison, NiO/GQDsNH2 electrode holds ≈834 mAh g-1 of capacity, while the bald NiO exhibits an obvious decline in capacity with ≈396 mAh g-1 retained after cycling. Except for the yolk-shell and mesoporous merits, the superior performances of the NiO/GQD electrode are mainly ascribed to the assistance of GQDs. The GQD modification can support as a buffer alleviating the volume change, improve the electronic conductivity, and act as a reservoir for electrolytes to facilitate the transportation of Li+ . Moreover, the enrichment of carboxyl/amino groups on GQDs can further donate more active sites for the diffusion of Li+ and facilitate the electrochemical redox kinetics of the electrode, thus together leading to the superior lithium storage performance.

Optimizing Surface Modifications for Quantum Dot Labelled DNA SAMs Using Electrochemistry Coupled Fluorescence Imaging

Electrochemical biosensors are being developed for detecting specific sequences of nucleic acids using DNA modified gold surfaces[1]. A single crystal gold bead electrode was used to study the arrangement on DNA on different gold surfaces[2]. The gold surface was prepared with a mercaptoundecanol (MUDOL) self-assembled monolayer (SAM). Using a specific desorption potential of -0.850 V/SCE, the MUDOL was reductively desorbed from the Au(111) facet. The defects in the SAM were passivated with a shorter alkylthiol, mercaptohexanol. Thiol modified DNA which is also labeled with a fluorophore was allowed to populate the 111 facet specifically. This was studied using fluorescence microscopy coupled with electrochemical control. A fluorescence image of the gold bead (Figure a) showed that only the 111 facets were modified. The density of the DNA modification was also evaluated using the reorientation of DNA based on the electrode charge density. At positive potentials the DNA was positioned close to the electrode and the fluorescence was quenched. At negative potentials the DNA was repelled and the fluorescence increased. This change in fluorescence is indicative of the density of DNA on the surface. The same approach will be used to assemble DNA modified Quantum Dots (QDs) onto the Au(111) facets. A complementary ssDNA was attached to a glutathione capped quantum dot vis a his-tag peptide. The QD labelled ssDNA was allowed to hybridize with the ssDNA on the gold electrode. Figure (b) is the cartoon depiction of such a layer. Recent research results will be described on the characterization of QD labelled DNA SAMs. The QDs due to their broad absorption and narrow emission spectrum also offer the advantage of building more complicated multiplexed systems in future. (1) Hsieh, K.; Ferguson, B. S.; Eisenstein, M.; Plaxco, K. W.; Soh, H. T. Integrated Electrochemical Microsystems for Genetic Detection of Pathogens at the Point of Care. Acc. Chem. Res. 2015, 48, 911–920. (2) Yu, Z. L.; Casanova-Moreno, J.; Guryanov, I.; Maran, F.; Bizzotto, D. Influence of Surface Structure on Single or Mixed Component Self-Assembled Monolayers via in Situ Spectroelectrochemical Fluorescence Imaging of the Complete Stereographic Triangle on a Single Crystal Au Bead Electrode. J. Am. Chem. Soc 2015, 137, 276–288. Figure 1

Influence of transition metal alloying and surface modification of the CdTe quantum dots on their optical properties, band structure and electrochemical activity

We report a study of CdTe quantum dots modification bythe alloying of with Zn2+ and Hg2+ ions and shell growth. Optical and cyclic voltammetry measurements were used to explain changes in the band structure of the particles via shell growth and during the alloying. Influence of stabilizer on the electrochemical behavior of the particles is also discussed. Obtained nanostructures demonstrate photoluminescence in the wider range of wavelengths than pure CdTe QDs.

SpyCatcher-SpyTag mediated in situ labelling of progeny baculovirus with quantum dots for tracking viral infection in living cells.

A non-invasive labelling strategy is proposed to label baculovirus via genetic insertion of a SpyTag into the viral glycoprotein, followed by specific conjugation with the SpyCatcher protein on modified quantum dots (QDs) through an isopeptide bond. The labelling method is convenient and efficient and shows little attenuation of viral infectivity. Therefore, it is a biologically compatible technique for tracking viral infection.

Boosted electrochemical properties from the surface engineering of ultrathin interlaced Ni(OH)2 nanosheets with Co(OH)2 quantum dot modification.

Nanoscale surface engineering of electroactive architectures is of paramount importance in high-performance supercapacitor applications based on surface-controlled charge storage mechanisms. Herein, we exploit Co(OH)2 quantum dots (CoQDs) as a surface modifier and report a simple and effective strategy for anchoring CoQDs on ultrathin interlaced Ni(OH)2 nanosheets. Impressively, the 2D/0D heterostructure of CoQD-interspersed Ni(OH)2 nanosheets (Ni(OH)2-CoQD) exhibits greatly enhanced capacitive behavior compared with pristine Ni(OH)2 nanosheets, exhibiting a higher capacitance (3244 F g-1vs. 2124 F g-1 at 5 mA cm-2), superior rate capability and better cycling stability. Density functional theory (DFT) calculations reveal the accumulation of additional electrons and reduced adsorption energy of OH- at the Ni(OH)2-CoQD interphase, which are the primary reasons for the enhanced electrochemical performance. An asymmetric full cell with Ni(OH)2-CoQD as the positive electrode has been fabricated, achieving a maximum energy density of 46 W h kg-1 at 141 W kg-1, and excellent cycling stability, where 84.1% of the initial capacitance is retained over 5000 cycles. This work brings a new opportunity to pseudoactive electrode material design by employing semiconductive quantum dots for surface modification.

One-pot synthesis of polythiol ligand for highly bright and stable hydrophilic quantum dots toward bioconjugate formation

A fast and efficient one-pot synthesis of thiol-terminated poly(vinylpirrolidone-co-maleic anhydride-co-ethylene glycol dimethacrylate) based heterobifunctional polymer (PTVP) has been developed. The polymer was used for the modification of quantum dots (QDs) to prepare water soluble and stable QDs with emission quantum yield as high as 80%. Using carbodiimide method, PTVP-capped red light-emitting QDs were conjugated to model monoclonal antibodies specific to glycoprotein B (gB) of Aujeszky’s disease virus (ADV) and successfully used in the lateral flow assay (LFA) for the detection of ADV gB in biological fluids. A comparative analysis of the sensitivity of the method was carried out using three types of QDs emitting in the red and far-red region.

Quantum Dots as Biological Optical Imaging Tools

Quantum dots are semiconducting nanocrystals having dimensions in the range of nanometers that have attracted for their clinical and diagnostic applications Their surface modification or functionalization has been in significant progress over last decades to make them precise nanoprobes for biological imaging This practice is carried out with bioconjugation of prepared quantum dots in to various biological chemical molecules with broad absorption spectra bright emission and photophysical robustness This surface modified quantum dots might be further improved tool for nbsp brain targeted or cell imaging for getting accurate localization of tumor or diseased tissues to achieve effective diagnostic biopsy and complete surgical resection for improved surgical management of brain or cell tumors as improved optical imaging and optical spectroscopy tools

Quaternary Ammonium Polyamidoamine Dendrimer Modified Quantum Dots as Fluorescent Probes for p-Fluorophenoxyacetic Acid Detection in Aqueous Solution.

The wide use of pesticide p-fluorophenoxyacetic acid has caused the serious environmental contaminant. A novel fluorescent probe for sensitive detection of p-fluorophenoxyacetic acid in aqueous solutions based on 3.0G quaternary ammonium polyamidoamine (PAMAM) dendrimer modified quantum dots (QDs) (PAMAM@QDs) was reported. Through the solvent-evaporation method, quaternary ammonium PAMAM was employed to modify the QDs. Poloxamer 188 was used to improve the solubility and stability. The resultant PAMAM@QDs dispersed well in water. Fluorescence (FL) spectroscopic study showed that the FL intensity of the PAMAM@QDs was enhanced in the presence of p-fluorophenoxyacetic acid. Under optimal conditions, the enhanced FL intensity as a function of concentration matched very well in the range of 1 ~ 200µg/mL of p-fluorophenoxyacetic acid, while the lower limits of detection were found to be 0.16µg/mL. These results show that PAMAM@QDs is a promising luminescent probe for the detection of pesticides.

The delivery of doxorubicin of multifunctional β-cyclodextrin-modified CdSe/ZnS quantum dots for bioactivity and nano-probing.

The modified quantum dots (QDs) have been used in intracellular probing and drug delivery because of their special chemical and physical properties. In this paper, two β-cyclodextrin (β-CD)-modified CdSe/ZnS QDs with strong optical emission properties were synthesized as drug carriers to induce apoptosis. The positively charged l-Arginine (l-Arg) and neutral l-Tryptophan (l-Trp) were selected as ligands to compare the effect of charge on bioactivity of QDs nanoparticles. The in vitro assays revealed that these modified QDs showed good Dox carrier ability and significantly high inhibition rate to cancer cells. Especially, the more positively charged β-CD-l-Arg-polyamine-coated CdSe/ZnS QDs could effectively deliver the doxorubicin (Dox) into cells and exhibit excellent cell selectivity in cancer versus normal cells. The Dox-loaded QDs could enter intracellular, which showed that the Dox can efficiently go through the membranes at the existence of β-CD. Several lines of evidence suggest that the Dox-loaded QDs can efficiently induce apoptosis likely related to the production of ROS. We expect that the modified QDs can enhance the amount of hydrophobic antitumor drugs in cells and can also be used as fluorescent imaging agents.

Current Application of Quantum Dots (QD) in Cancer Therapy: A Review.

Semiconductor quantum dots proved themselves as efficient fluorescent probes in cancer detection and treatment. Their size, high stability, non-photobleaching and water solubility made them a unique fluorophore in place of conventional organic dyes. Newly emerged theranostic drug delivery system using quantum dots helped us in better understanding of the drug delivery mechanism inside the cells. Surface modified Quantum dots and their applications became wide in bioimaging, immunohistochemistry, tracking intracellular drug and intracellular molecules target. We have highlighted various applications of quantum dots in cancer treatment, drug delivery, flow cytometry, and theranostics.

Selective biosensing of Staphylococcus aureus using chitosan quantum dots

Selective biosensing of Staphylococcus aureus (S. aureus) using chitosan modified quantum dots (CTS@CdS QDs) in the presence of hydrogen peroxide is reported. The method is based on the intrinsic positive catalase activity of S. aureus. CTS@CdS quantum dots provide high dispersion in aqueous media with high fluorescence emission. Staphylococcus aureus causes a selective quenching of the fluorescence emission of CTS@CdS QDs in the presence of H2O2 compared to other pathogens such as Escherichia coli and Pseudomonas aeruginosa. The intrinsic enzymatic character of S. aureus (catalase positive) offers selective and fast biosensing. The present method is highly selective for positive catalase species and requires no expensive reagents such as antibodies, aptamers or microbeads. It could be extended for other species that are positive catalase.

Interleukin-13 conjugated quantum dots for identification of glioma initiating cells and their extracellular vesicles.

Functionalized quantum dots are flexible semiconductor nanomaterials which have an immense application in biomedical research. In particular, when they are functionalized with biomolecules like proteins or antibodies, they have the specialized ability to detect the expression of receptors and antigens in cells and tissues. In this study we designed a cytokine (interleukin-13) functionalized quantum dot to detect a cancer associated receptor expressed in cancer stem cells and the extracellular vesicles (exosomes) secreted by the cancer cells themselves. The binding pattern of these cytokine modified quantum dots to the cancer stem cells and exosomes alters the physical properties of the complex in the fixed and suspended form. This altered binding pattern can be monitored by a variety of techniques, including transmission electron microscopy, atomic force microscopy and flow cytometry, and subsequent characterization of this quantum dot binding profile provides useful data that can be utilized as a fingerprint to detect cancer disease progression. This type of functionalized quantum dot fingerprint is especially useful for invasive cancers including brain and other metastatic cancers and may allow for earlier detection of disease progression or recurrence, thus saving the lives of patients suffering from this devastating disease.

All-quantum-dot emission tuning and multicolored optical films using layer-by-layer assembly method

In this report, all-quantum-dot multilayer photoluminescent films (PLFs) based on two types of modified quantum dots (MA-C8-QDs and PEI-QDs) were fabricated through the layer-by-layer (LBL) self-assembly method, providing a new kind of luminescent material with emission color covering blue to red spectral region. Aqueous QDs with high stability and photoluminescence properties were obtained by an efficient phase transfer, followed by fabrication of (PEI-QDs/MA-C8-QDs)n PLFs with alternate adsorbing the layer of the MA-C8-QDs endowed with negative (COO−) charges and PEI-QDs endowed with positive (NH3+) charges using electrostatic interactions between each layer. The resulting single color films preserved good color purity and strong luminescence of original QDs, PL intensities increased linearly with the number of bilayers n, which indicated that growth of the film is regular and uniform. In addition, the uniform and smooth PLFs as prepared have high visible light transmittance. Furthermore, by emission tuning, multicolor and white light-emitting PLFs with the color coordinates at (0.3292, 0.3418) have been easily obtained by assembly of two types of modified red, green, blue QDs. Therefore, these PLFs (especially white-light PLFs) show promise for the development of novel multiplexed biological sensors, full-color displays, intelligent response, photonic, and optoelectronic devices.

Surface ligands engineering of semiconductor quantum dots for chemosensory and biological applications

Featuring size-tunable electrical and optical properties, semiconductor quantum dots (QDs) are appealing intensive interests in developing ingenious luminescent materials for chemosensory and biological applications. The surface modification of QDs with functional ligands not only fine-tunes the physiochemical properties and fluorescence emission behaviors, but also induces the designated interplay between analytes and probes for special determination. In this review, the fundamental principles guiding the rational design of high-efficiency luminescent sensors with surface engineering are overviewed. The state-of-the-art applications of QDs-based probes are highlighted for the sensing of molecular substrates and ionic species as well as various biological applications, with the inherent recognition mechanisms elaborated for representative cases. The challenge and future research direction in this emerging and promising research field are also discussed.

Encapsulation of highly confined CdSe quantum dots for defect free luminescence and improved stability

This is the first report on the generation of trap states and their effective elimination in highly confined CdSe quantum dots in order to obtain enhanced and stable optical properties prepared by aqueous route. Surface plays an important role in optical properties of quantum dots (QDs) and surface modification of quantum dots can improve optical properties. In present work luminescent CdSe QDs were prepared using 2-Mercaptoethanol (2-ME) as stabilizing agent and encapsulated by polymer. Different concentrations of 2-ME were used to tune the emission spectra with respect to their reduced size. Addition of 2-ME to CdSe QDs enhances the trap emission and quenching band edge emission due to (i) increased surface to volume ratio and; (ii) presence of high concentration of sulfide ions as confirmed from EDX analysis as sulfide ions possesses the hole scavenging characteristics. Polymer encapsulation of QDs was carried out to make them stable and to improve their optical properties. Even though there are previous reports addressing the improved optical properties by polymer encapsulation and silica encapsulation but experimentally it has not been reported yet experimentally. In this work we have synthesized and characterized water soluble polymer encapsulated QDs and proved the facts experimentally. Photoluminescence spectroscopy clearly reveals the role of polymer encapsulation in boosting the optical properties of CdSe QDs. FTIR spectra validate the presence of biocompatible functional groups on CdSe4/PEG (Polymer encapsulated QDs).

All-solution-processed high-brightness hybrid white quantum-dot light-emitting devices utilizing polymer modified quantum dots

White quantum dot light-emitting devices (WQLEDs) are promising candidates for high-brightness, high-efficiency, and color-saturated displays. However, it is still challenging to integrate various quantum dot (QD) emitters into one device and overcome their low blue luminous efficiencies. In this paper, we report the design and fabrication of all-solution-processed WQLEDs using a trichromatic hybrid with red, green, and blue (RGB)-emitting colloidal QDs and a blue-emitting homopolymer (poly[9,9-dioctylfluorenyl-2,7-diyl]-end capped with N,N-Bis(4-methylphenyl)-aniline, ADS329BE) in the device emission region. The white emission results from the integration of the RGB emission from the QDs and the blue emission generated by ADS329BE. The obtained results indicate that the hybrid WQLEDs exhibit pure white emission with an optimized concentration and charge balance in the emission layer (EML) and the occurrence of fluorescent resonance energy transfer between ADS329BE and the RGB QDs. The proposed devices show excellent performance with a maximum luminance of 15,950 cd/m2, a current efficiency at maximum luminance of 1.43 cd/A, and a low turn-on voltage of ≤2.0 V, with Commission Internationale de l'Enclairage coordinates of (0.33, 0.34). These results indicate that the proposed method is an alternative and effective approach to achieve high performance in WQLEDs as well as other optoelectronic devices.

Effects of surface modification of quantum dots on viability and migration of triple-negative breast cancer cells

Triple-negative breast cancer (BC) shows strong metastasis and has a bad prognosis. There are few effective approaches until date to detect BC cells at an early stage. Quantum dots (QDs) are one of the most promising nanomaterials for the detection of BC cells. QDs are usually modified with some functional molecules, such as PEG and BSA, to decrease or possibly eliminate their toxicity. Although a large number of studies have investigated the cytotoxicity of QDs, the effects of surface modification of QDs on biological behaviors of triple-negative BC cells remain unclear. In this work, QDs were prepared using the hydrothermal method and chemically modified with PEG and BSA. The optical performance of QDs was recorded with a digital camera. Their absorption and fluorescence (FL) properties were analyzed by UV–Vis spectrometer and FL spectrophotometer, respectively. The effects of QDs and surface modification on viability and migration were principally investigated. The possible mechanism was primarily analyzed. The results show that QDs exhibit excellent optical performance under ultraviolet irradiation. Surface modification slightly reduces the photon count reaching the QDs surface. Moreover, surface modification results in a blue-shift of FL peak of QDs, which is ascribed to the change in surface chemical environment because of PEG and BSA modifications. In addition, QDs, PEG coated QDs (PEG@CdTe) and BSA coated QDs (BSA@CdTe) can reduce viability and inhibit migration of BC cells. The inhibition effects are time- and concentration-dependent. In addition, PEG and BSA modified QDs exhibit lower inhibition effects on BC cells, as compared with unmodified QDs. In this process, Reactive oxygen species (ROS) does not appear to play an important role, and other pathways should be considered. This work provides experimental support and useful clinical guidance for QDs-applications in BC detection.

Rapid detection of bacteria based on homogenous immunoassay using chitosan modified quantum dots

In this study, a fast and sensitive sandwich assay has been developed with the combination of immunomagnetic separation (IMS) and fluorescence techniques to enumerate Escherichia coli (E.coli). Iron oxide core gold shell (Fe3O4@Au) magnetic nanoparticles were prepared and modified with biotinylated antibodies specific to E.coli. Fluorescence labels have been constructed by preparing chitosan coated CdTe quantum dots (CdTe QDs) with a diameter of 3±1nm. The amounts of magnetic nanoparticles and CdTe QDs are optimized to get the best sensitivity. The calibration graph fluorescence intensity versus E.coli concentration was linear in the range of 102–108cfumL−1 with a coefficient of determination (R2) of 0.9905. The limit of detection (LOD) and limit of quantification (LOQ) values are calculated as 30 and 100cfumL−1, respectively. Selectivity of the method is examined by applying the same procedure to bacteria, namely Enterobacter aerogenes (E. aerogenes), Enterobacter dissolvens (E. dissolvens), Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa), and no interference has been observed. The applicability of the developed method has also been examined in spiked urine samples. As a result, it was found that, this novel method is sensitive to target E.coli and a rapid method with a total analysis time less than 120min.

Dissecting the Factors Affecting the Fluorescence Stability of Quantum Dots in Live Cells.

Labeling and imaging of live cells with quantum dots (QDs) has attracted great attention in the biomedical field over the past two decades. Maintenance of the fluorescence of QDs in a biological environment is crucial for performing long-term cell tracking to investigate the proliferation and functional evolution of cells. The cell-penetrating peptide transactivator of transcription (TAT) is a well-studied peptide to efficiently enhance the transmembrane delivery. Here, we used TAT peptide-conjugated QDs (TAT-QDs) as a model system to examine the fluorescence stability of QDs in live cells. By confocal microscopy, we found that TAT-QDs were internalized into cells by endocytosis, and transported into the cytoplasm via the mitochondria, Golgi apparatus, and lysosomes. More importantly, the fluorescence of TAT-QDs in live cells was decreased mainly by cell proliferation, and the low pH value in the lysosomes could also lower the fluorescence intensity of intracellular QDs. Quantitative analysis of the amount of QDs in the extracellular region and whole cells indicated that the exocytosis was not the primary cause of fluorescence decay of intracellular QDs. This work facilitates a better understanding of the fluorescence stability of QDs for cell imaging and long-term tracking in live cells. Also, it provides insights into the utility of TAT for transmembrane transportation, and the preparation and modification of QDs for cell imaging and tracking.