Identification of quantum dot bioconjugates and cellular protein co-localization by hybrid gel blotting

New approaches are needed to address the interaction of nanoparticles and cellular proteins at the molecular level. We present a modification of PAGE co-immunoprecipitation, QD-based PA-AGE electrophoresis blotting, and apply this to identify quantum dot (QD) bioconjugate-cellular protein association. This method provides the capability to isolate and evaluate the action of QD bioconjugate-protein complexes in intact cells and to correlate these identified interactions with their location in cells.     

Polymerization of nanocrystal quantum dot-tubulin bioconjugates

Nanocrystal quantum dot (NQD)-tubulin bioconjugates were prepared using a two-step crosslinking procedure. NQD-decorated microtubules were successfully polymerized directly from the NQD-tubulin conjugates to form nonaggregated, full-length (several micrometers) biopolymers. However, polymerization kinetics were slowed in comparison with unmodified tubulin and tubulin modified with small-molecule dyes or biotin. Association with the relatively large nanocrystals, therefore, interferes to some extent with tubulin's ability to polymerize. These results suggest that before NQDs are used extensively as fluorescent labels in studies of biomolecular activity, the impact of NQD bioconjugation must be well understood     

Improved peptidyl linkers for self-assembly of semiconductor quantum dot bioconjugates

We demonstrate improved peptide linkers which allow both conjugation to biomolecules such as DNA and self-assembly with luminescent semiconductor quantum dots. A hexahistidine peptidyl sequence was generated by standard solid phase peptide synthesis and modified with the succinimidyl ester of iodoacetamide to yield a thiol-reactive iodoacetyl polyhistidine linker. The reactive peptide was conjugated to dye-labeled thiolated DNA which was utilized as a model target biomolecule. Agarose gel electrophoresis and fluorescence resonance energy transfer analysis confirmed that the linker allowed the DNA to self-assemble with quantum dots via metal-affinity driven coordination. In contrast to previous peptidyl linkers that were based on disulfide exchange and were thus labile to reduction, the reactive haloacetyl chemistry demonstrated here results in a more stable thioether bond linking the DNA to the peptide which can withstand strongly reducing environments such as the intracellular cytoplasm. As thiol groups occur naturally in proteins, can be engineered into cloned proteins, inserted into nascent peptides or added to DNA during synthesis, the chemistry demonstrated here can provide a simple method for self-assembling a variety of stable quantum dot bioconjugates.      

Stability of ‘quantum dot human epidermal growth factor’ bioconjugates prepared using quantum dots synthesised in aqueous solution

As advantaged nanoscale fluorescent bioprobes, quantum dot (QD) bioconjugates have been widely used in biomedical research. However, the stability of these bioconjugates stored over a period of time has been rarely reported. Here, we synthesised water-soluble QDs by conjugating the human epidermal growth factor (EGF) to these low-cost QDs using 1-ethyl-3(3-dimethylamino propyl)-carbodiimide (EDC) as a cross-linking reagent. These bioconjugates nanomaterials were then used to label cancer cells (MDA-MB-435S and SMMC-7721) and normal cells (HL-7702) whose surfaces expressed high-level (for the cancer cells) and low-level (for the normal cells) EGF receptors (EGFR). We found that although the fluorescence intensity of these bioconjugates decreased with prolonged storage time at 4°C for more than 4 months, their aqueous solution retained a transparent appearance, good particle dispersion and very bright fluorescence. Furthermore, the bioconjugates could still well recognise cancer cells. As a control, the normal cells were labelled with a small amount of the fresh and stored bioconjugates. The results presented in this work indicated that QD bioconjugates prepared with QDs synthesised in aqueous solution may be used as a low-cost biomedical test kit for biomedical imaging and diagnosis, where the QD bioconjugates could be stored for long periods of time.     

Analytical ultracentrifugation for characterizing nanocrystals and their bioconjugates

Analytical ultracentrifugation (AU) provides a general way to probe the polydispersity of nanoparticles and the formation of bioconjugates in solution. Unconjugated gold nanocrystals show sedimentation coefficient distributions that are in agreement with size distributions as measured by TEM. AU is sensitive to the size/shape changes elicited by conjugation, in this case to lactose repressor (LacI). AU data reveal saturating protein concentrations for conjugates that correspond to the measured stoichiometry of the complex under these conditions.     

Evolutionary experiments for self-assembling amphiphilic systems

Some amphiphilic molecules in particular environments may self-assemble and originate chemical entities, such as vesicles, which are relevant in technological applications. Experimentation in this field is difficult because of the high dimensionality of the search space and the high cost of each experiment. To tackle the problem of designing a relatively small number of experiments to achieve the relevant information on the problem, we propose an evolutionary design of experiments based on a genetic algorithm. We built a particular algorithm where design and laboratory experimentation interact leading the search toward the optimality region of the space. To get insight in the process we then modelled the experimental results with different classes of regression models; from modelling we could identify the special role played by some molecules and the relevance of their relative weight in the composition. With modelling we “virtually” explored the experimental space and predicted compositions likely to generate very high yields. Models then provide valuable information for the redesign of the experiments and can be considered as an essential addition to the evolutionary approach.     

Advances in solution-processed quantum dots based hybrid structures for infrared photodetector

Infrared photodetector based on solution-processed colloidal quantum dots (QDs), which possess the special properties of wide-size-tunable bandgap, high quantum confinement potential and low-cost fabrication, have been employed successfully as a viable technological proposal for optical communication, biological imaging, night vision, surveillance, and remote sensing. However, QDs-based photodetector always fails to demonstrate excellent infrared photodetection performance because of low value of carrier mobility. Fortunately, QDs solutions can be easily deposited on various substrates, including 2D materials, film materials or other QDs, and these QDs-based hybrid structures can be engineered to achieve high mobility and light absorbance simultaneously through synergistic effect between QDs and other materials. Herein, we focus on how QDs-based hybrid structure developments have effectively facilitated the performance of infrared photodetectors enhancements, including three main types of QDs-based hybrid structure, optimization of infrared photodetector performance and integrated circuit engineering. Finally, we systematically summarize the current challenges and future development of infrared photodetector based on QDs and its hybrid structure.     

A hybrid system of GaAs whisker nanocrystals and PbS quantum dots on silicon substrate

It is shown that a hybrid nanocomposite structure can be created by integration of semiconducting materials with different dimensionalities: an array of quasi-1D GaAs whisker nanocrystals formed by molecular-beam epitaxy on a Si (111) substrate and 0D PbS colloidal quantum dots. The morphological and spectral properties of the resulting system are analyzed.     

Gain without inversion in hybrid quantum dot-metallic nanoparticle systems

We study the generation of tunable gain without inversion in semiconductor quantum dots using plasmonic effects. For this we investigate the impact of localized surface plasmons on coherent nonlinear exciton effects in a quantum dot when it is located in the vicinity of a metallic nanoparticle. It is shown that when such a system is exposed to a laser field and the distance between the quantum dot and the metallic nanoparticle is reduced the initial impact of plasmons is enhancement of the ac-Stark shift in the quantum dot. When this distance is reduced beyond a critical value, the results show abrupt formation of a significant of amount of gain without inversion in the quantum dot. We show that such a 'molecular' gain is associated with the plasmonic metaresonance (PMR) formed via combined effects of laser-induced coherence in the quantum dot and plasmons.     

Highly photoluminescent and photostable CdSe quantum dot-nylon hybrid composites for efficient light conversion applications

Highly photoluminescent hexadecylamine (HDA) capped core CdSe quantum dots (QDs) with fluorescent quantum yields (QYs) up to 60% were synthesized using a hot injection method and directly incorporated into nylon polymer. For the incorporation of crude CdSe QDs into nylon a simple reproducible and upscalable one pot approach was developed without the need of further purification steps. The photoluminescence (PL) properties of the core QDs and the resulting QD-polymer hybrid composites were investigated and compared. Red emitting hybrid materials exhibit a QY of 60% with a high potential for applications in direct light and energy conversion. The hybrid materials could be successfully utilized as LED conversion layers. By avoiding exposure to oxygen the hybrid films can be kept for a month without detecting a significant decrease in luminescence. Various three dimensional structures are easily available opening doors for further applications such as novel materials for fluorescence standard development in laser scanning microscopy (LSM).     

A quantum Rosetta stone for interferometry

Heisenberg-limited measurement protocols can be used to gain an increase in measurement precision over classical protocols. Such measurements can be implemented using, for example, optical Mach—Zehnder interferometers and Ramsey spectroscopes. We address the formal equivalence between the Mach—Zehnder interferometer, the Ramsey spectroscope and a generic quantum logic circuit. Based on this equivalence we introduce the 'quantum Rosetta stone', and we describe a projective-measurement scheme for generating the desired correlations between the interferometric input states in order to achieve Heisenberg-limited sensitivity. The Rosetta stone then tells us that the same method should work in atom spectroscopy.     

A hybrid model for prismatic solids

A finite prism approach for the approximate analysis of three-dimensional solids is proposed. The approach is based on a semi-algebraic assumed stress hybrid model, according to Pian's scheme. Prismatic solids with various end conditions can be analysed with a traditional matrix-displacement procedure, thus enlarging the possibilities offered by analogous compatible models.     

自组装制备铁质文物保护用纳米缓蚀颗粒

长效缓蚀材料对于铁质文物的长期保护有着至关重要的作用.通过层层自组装的方法,在带负电荷的SiO2胶粒表面交替组装上了带正电荷的聚乙烯亚胺(PEI)层,带负电荷的聚苯乙烯磺酸钠(PSS)层,以及带正电荷的缓蚀活性成分苯并三氮唑(BTA)层.利用透射电子显微镜、zeta电位仪、X射线光电子能谱仪(XPS)等对纳米缓蚀颗粒进行了表征.结果表明,随着组装过程的进行,胶体粒子尺寸依次增大,颗粒表面zeta电位出现负正交替变化,表面元素化学环境也随之改变,氮原子的结合能随静电作用的增强向高位移动.缓蚀剂的负载量可通过多层组装方式提高,BTA单层负载量可达到35.4mg/g SiO2.     

Surface plasmon-assisted optical bistability in the quantum dot-metal nanoparticle hybrid system

We theoretically investigated optical bistability (OB) of a coupled excition–plasmon hybrid system in a unidirectional ring cavity. It is found that the threshold and the region of OB can be tuned by adjusting the center–center distance between the quantum dot and metal nanoparticle (MNP), the Rabi frequency of the control field and the radius of the MNP. Due to the significantly enhanced optical nonlinearity by the surface plasmon effect, the threshold of OB can be decreased greatly when the probe field is parallel to the major axis of the hybrid system. The enhanced OB may have promising applications in optical switching and optical storage.     

Electrically driven quantum dot/wire/well hybrid light-emitting diodes

Electrically driven quantum dot, wire, and well hybrid light-emitting diodes are demonstrated by using nanometer-sized pyramid structures of GaN. InGaN quantum dots, wires, and wells are formed at the tops, edges, and sidewalls of pyramids, respectively. The hybrid light-emitting diodes containing low-dimensional quantum structures are good candidates for broad-band highly efficient visible lighting sources.     

Dynamic behaviors of lipid-like self-assembling peptide A6D and A6K nanotubes

Nanoscience and nanotechnology require development of nanomaterials that are amiable for molecular design from bottom up. Molecular designer self-assembling peptides are one of such nanomaterials that will become increasingly important for the endeavor. Peptides have not only been used in all aspects of biomedical and pharmaceutical research and medical products, but also have had enormous impact in nascent field of designed biological materials. We here report the dynamic structures of lipid-like designer peptide A6D (AAAAAAD) and A6K (AAAAAAK) that undergo self-assembly into nanotubes in water and salt solution. We not only analyzed their self-assemblies using dynamic light scattering to determine the critical aggregation concentration (CAC), but also use atomic force microscope to observe their nanostructures. We also propose a simple scheme by which these lipid-like peptides self-assemble into dynamic nanostructures. Since the knowledge of CAC is important for uses of these peptides for a variety of applications, these findings may have significant implications in the study of molecular self-assembly and for a wide range of utilities of designer self-assembling peptide materials.     

A novel method to enhance quantum yield of silica-coated quantum dots for biodetection

In this paper, based on selecting the appropriate type of quantum dots (QDs), a novel method is developed to enhance the quantum yield (QY) of silica-coated QD nanoparticles (SQDNPs). The effect of varying types of QDs on the QY after silica encapsulation is systematically studied. The results show that QDs with appropriate structure and composition of shells can much better retain the initial QY after silanization. The seven-layered shell/core QDs with QY of 47.8% nearly completely retain the original QY and is the best type among six types of QDs for silica modification. In the aspect of shell composition, the CdS plays an important role for QY retention since the lattice mismatch between CdSe and CdS is lower than that of CdSe and ZnS. After the appropriate type of QDs is chosen for silica coating, the highly fluorescent SQDNPs are chemically modified with amine, thiol and carboxyl groups, and then labeled by antibodies for particle-based immunofluorescence assay. The results indicate that the SQDNPs-antibody bioconjugates are alternative fluorescent probes useful for biodetection.     

A hybrid algorithm for reducing matrix bandwidth

A hybrid algorithm for reducing the bandwidth of symmetric matrices is described in terms of a finite element grid. The new algorithm produces significantly lower bandwidths than either the commonly-used Gibbs–Poole-Stockmeyer (GPS) or Cuthill–McKee (CM) algorithms, with run times comparable to the original CM algorithm. The new hybrid algorithm uses the GPS algorithm as a preprocessor to provide a good initial node numbering for the author's node-shuffling algorithm, which accounts for variable degrees-of-freedom per node (DOF/node). The hybrid algorithm was tested on the 30 benchmark problems that were compiled by Everstine, and on 10 supplemental problems with variable DOF/node. Bandwidths and CPU times are presented for all problems.     

A hybrid method for calibrating acoustic arrays

A method to calibrate the elements of large arrays devoted to underwater applications is presented. The goal is to measure the sensitivity and directivity of the elements over their full bandwidth. The main constraint comes from the bounded geometry of the experimental setups that limits the duration of the time windows available for analyzing the received signals. Using a short wideband pulse is detrimental to obtaining high signal-to-noise ratios. A classical method for handling this problem is time-delay spectrometry (TDS), which is based on the transmission of a linear frequency- modulated signal combined with a sliding frequency filter. An alternative, hybrid method based on the transmission of a sequence of time-frequency-limited signals is proposed. This hybrid method is shown to provide the same spectral density as TDS in the frequency scanning, but the filtering process is quite different. The transmitted signals are designed to take advantage of the coherent sums of the received signals to track the time of flight of the direct paths between the source and the elements. In addition, a fitting process based on the calibration geometry of data acquisition enables the boundaries of the interference-free time windows to be precisely delineated. An example of the application is described.