Complexes In Quantum Dots Research Articles

DNA‐Programmed Dynamic Assembly of Quantum Dots for Molecular Computation

AbstractDespite the widespread use of quantum dots (QDs) for biosensing and bioimaging, QD‐based bio‐interfaceable and reconfigurable molecular computing systems have not yet been realized. DNA‐programmed dynamic assembly of multi‐color QDs is presented for the construction of a new class of fluorescence resonance energy transfer (FRET)‐based QD computing systems. A complete set of seven elementary logic gates (OR, AND, NOR, NAND, INH, XOR, XNOR) are realized using a series of binary and ternary QD complexes operated by strand displacement reactions. The integration of different logic gates into a half‐adder circuit for molecular computation is also demonstrated. This strategy is quite versatile and straightforward for logical operations and would pave the way for QD‐biocomputing‐based intelligent molecular diagnostics.

DNA-programmed dynamic assembly of quantum dots for molecular computation.

Despite the widespread use of quantum dots (QDs) for biosensing and bioimaging, QD-based bio-interfaceable and reconfigurable molecular computing systems have not yet been realized. DNA-programmed dynamic assembly of multi-color QDs is presented for the construction of a new class of fluorescence resonance energy transfer (FRET)-based QD computing systems. A complete set of seven elementary logic gates (OR, AND, NOR, NAND, INH, XOR, XNOR) are realized using a series of binary and ternary QD complexes operated by strand displacement reactions. The integration of different logic gates into a half-adder circuit for molecular computation is also demonstrated. This strategy is quite versatile and straightforward for logical operations and would pave the way for QD-biocomputing-based intelligent molecular diagnostics.

Design of 4-electrode optical device for application of vector electric fields to self-assembled quantum dot complexes

Self-assembled InAs quantum dots (QDs) are of great interest as components of optoelectronic devices that can operate at the quantum limit. The charge configuration, interdot coupling, and symmetry of complexes containing multiple QDs can all be tuned with applied electric fields, but the magnitude and angle of the electric field required to control each of these parameters depend on the orientation of the QD complex. We present a 4-electrode device compatible with optical excitation and emission that allows application of electric fields with arbitrary magnitudes and angles relative to isolated QD complexes. We demonstrate the electric field tunability of this device with numerical simulations.

Resonance energy transfer in nano-bio hybrid structures can be modulated by UV laser irradiation

A method for targeted variation of the radiation properties of quantum dots (QDs) to control the efficiency of resonance energy transfer in nanocrystal assemblies and nano-bio hybrid materials has been developed. The method is based on strong ultraviolet (UV) laser irradiation of QDs and allows the extinction and luminescence spectra to be controlled and the luminescence quantum yield and decay kinetics to be varied. Water-soluble QDs have been synthesized and used for analyzing the effect of energy transfer from semiconductor nanocrystals on the photocycle of the photosensitive protein bacteriorhodopsin (bR) in bR–QD complexes. The UV irradiation mode has been selected in a way permitting the modulation of QD optical parameters without modification of their structure or physico-chemical properties. It is concluded that the QD interaction with bR accelerates its photocycle, but this acceleration is determined by electrostatic interactions, rather than Förster resonance energy transfer from QDs to bR. The method of UV laser irradiation of fluorescent semiconductor QDs has proven to be an efficient technique for variation of nanocrystal optical properties without affecting their structure, as well as for fine modulation of the energy transfer processes in the nanocrystal assemblies and nano-bio hybrid materials.

Surface complexation reaction for phase transfer of hydrophobic quantum dot from nonpolar to polar medium.

Chemical reaction between oleate-capped Zn(x)Cd(1-x)S quantum dots (Qdots) and 8-hydroxyquinoline (HQ) led to formation of a surface complex, which was accompanied by transfer of hydrophobic Qdots from nonpolar (hexane) to polar (water) medium with high efficiency. The stability of the complex on the surface was achieved via involvement of dangling sulfide bonds. Moreover, the transferred hydrophilic Qdots--herein called as quantum dot complex (QDC)--exhibited new and superior optical properties in comparison to bare inorganic complexes with retention of the dimension and core structure of the Qdots. Finally, the new and superior optical properties of water-soluble QDC make them potentially useful for biological--in addition to light emitting device (LED)--applications.

Fluorescence enhancement of cadmium selenide quantum dots assembled on silver nanoparticles and its application to glucose detection.

In this work, a new assembled glucose sensor based on the Ag nanoparticle (AgNP)-enhanced fluorescence of CdSe quantum dots (QDs) was developed. The mercaptoglycerol-modified AgNPs and aminophenylboronic acid-functionalized CdSe QDs are assembled into AgNP-CdSe QD complexes through the formation of a boronate ester bond. As compared to that of bare CdSe QDs, up to a 9-fold fluorescence enhancement and a clear blue shift of the emission peak for AgNP-CdSe QD complexes were observed, which is attributed to the surface plasmon resonance of AgNPs. In addition, the as-formed complexes are gradually disassembled in the presence of glucose molecules because they can replace the AgNPs by competitive binding with boronic acid groups, resulting in the weakening of fluorescence enhancement. The decrease in fluorescence intensity presents a linear relationship with glucose concentration in the range from 2 to 52 mM with a detection limit of 1.86 mM. Such a metal-enhanced QDs fluorescence system may have promising applications in chemical and biological sensors.

Controlled influence of quantum dots on purple membranes at interfaces

The development of bio-sensitized nanofilms engineered from biomembrane components and inorganic nanoparticles is a promising field of colloid and interface science and technologies. Recent nano-bioengineering approaches employing quantum dots (QDs) permit the enhancement of the purple membrane (PM) “light-harvesting capacity” compared to native PMs. The influence of QDs on the PM properties, especially the bacteriorhodopsin (bR) photocycle, has been found that has both fundamental (mechanisms of photoreception) and applied implications (including the fabrication of hybrid bionanomaterials). Samples of PM–QD complexes capable of energy transfer and characterized by increased rates of M-intermediate formation and decay have been obtained. The modified bR photocycle kinetic parameters may be explained by changes in the PM interface upon QD adsorption. The increase and decrease in absorption at 410nm (or photopotential) for PM–QD complexes are, on average, several times more rapid than for PM suspensions or PM dry films. These results provide a strong impetus for the development of nanomaterials with advanced properties.

Enhanced photoluminescence and thermal stability of zinc quinolate following complexation on the surface of quantum dots

Reaction between colloidal ZnS nanocrystals (NCs) and 8-hydroxy quinoline (HQ) led to complexation on the surface of the NCs. The quantum dot complex (QDC), with ZnQ2 attached to the surface of the NC, has a longer emissive lifetime, higher fluorescence quantum yield and enhanced thermal stability, making it a better LED material than ZnQ2.

First-Principles Studies of the Ground- and Excited-State Properties of Quantum Dots Functionalized by Ru(II)–Polybipyridine

Ru(II)–polybipyridine complexes are efficient oxidizers and charge-transfer agents. Combined with semiconductor quantum dots (QDs) they show promising potential for solar energy conversion. Using density functional theory (DFT) and time-dependent DFT (TD-DFT), we study the ground- and excited-state properties of PbSe and ZnO QDs functionalized by Ru(II)–trisbipyridine derivatives. The calculated binding energies elucidate that the most stable QD–complex structures occur through binding of the complex in a bridging mode, when the carboxylate group of the complex is bound to the two metal ions on the QD surface. However, independent of the attachment and the type and size of the QD, the complex introduces unoccupied molecular orbitals near the edge of the conduction band of the QD, while occupied orbitals localized on Ru(II) are deep inside the QDs’ valence band. Such an energy alignment of the complex’s and QD’s orbitals makes the hole transfer from the photoexcited QD to the complex energetically unfavorable but supports a scenario of electron and energy transfer from the photoexcited complex to the QD. For small 1 nm PbSe and ZnO QDs, the lowest absorption peak originates from the complex and is well-separated from the next peak associated with the QD transitions, thus providing well-controlled excitation of either the QD or the complex. For PbSe QDs 2 nm in size and larger, however, the first absorption peak belongs to the QD transitions, while the next peak in the absorption spectra originates from both the QD’s and the complex’s transitions. The overlap between complex’s and QD’s optical transitions tends to hinder controllable excitation and regulated charge-transfer processes in experimental probes.

Fabrication of transparent and luminescent CdTe/TiO2 hybrid film with enhanced photovoltaic property

A novel strategy for fabricating surface modified quantum dots (QDs)/titania hybrid films with increased synergistic property is reported. Through electrostatic interaction, anionic CdTe QDs are enwrapped with a cationic surfactant bearing hydroxyl groups at hydrophobic terminal, forming a surfactant-encapsulated QD complex particle with hydroxyl active sites on its periphery. The complex is covalently doped into titania matrix by means of a sol—gel approach of tetraethyl orthotitanate. In comparison to the well designed materials with inorganic core and shell nanostructure, the present study utilizes the inorganic core but organic shell, which can further alloy to titiania supports evenly. The original luminescent property of QDs and the flexibility of titania sol—gel materials are well retained in the resulting hybrid films. The monodispersion of QDs in the matrices brings about high transparent titania films, leading to an enhanced photovoltaic effect and a visible region response for light excitation.

Study of Interaction between Metallothionein and CdTe Quantum Dots

Quantum dots (QDs) belong to a new class of fluorescent agent for biochemical, medicinal or other purposes. However, QDs based on cadmium or other metals can be risky for an organism. As one of the mechanism how to detoxify cadmium-based QDs expression of metallothioneins (MT) can be considered. Due to high affinity of metallothionein to cadmium(II) ions, we attempted to develop an approach for studying of possible interaction with QDs. We prepared QDs with CdTe core and studied the interaction with MT, which we isolated from livers of Cd-administered rabbits. To study the interaction, we used the mixture of both components MT (3.6 μM): CdTe QDs (0, 0.34, 0.68, 1.02, 1.36, 1.7, 2.04 and 2.47 μM). The mixtures were studied by spectrophotometry within the range from 200 to 750 nm with detected maxima at 260 and 505 nm. Same mixtures were also analysed by differential pulse voltammetry Brdicka reaction, which supported data from spectrophotometry. Subsequently, we used fast protein liquid chromatography for purification of protein–quantum dot conjugates. We obtained the different chromatograms for (1) Apo MT, (2) CdTe QDs and (3) MT–QD complex. We also collected the fractions and subsequently analysed them on the content of Cd and MT, which confirmed the formation of CdTe QDs–MT complex.

Superlocalization Spectral Imaging Microscopy of a Multicolor Quantum Dot Complex

The key factor of realizing super-resolution optical microscopy at the single-molecule level is to separately position two adjacent molecules. An opportunity to independently localize target molecules is provided by the intermittency (blinking) in fluorescence of a quantum dot (QD) under the condition that the blinking of each emitter can be recorded and identified. Herein we develop a spectral imaging based color nanoscopy which is capable of determining which QD is blinking in the multicolor QD complex through tracking the first-order spectrum, and thus, the distance at tens of nanometers between two QDs is measured. Three complementary oligonucleotides with lengths of 15, 30, and 45 bp are constructed as calibration rulers. QD585 and QD655 are each linked at one end. The measured average distances are in good agreement with the calculated lengths with a precision of 6 nm, and the intracellular dual-color QDs within a diffraction-limited spot are distinguished.

CuInS2 quantum dots as a near-infrared fluorescent probe for detecting thrombin in human serum

This paper describes a novel, simple method for the highly sensitive and selective detection of thrombin using fibrinogen (Fib) and CuInS(2) quantum dots (QDs) as biosensing probes. Water-soluble near-infrared CuInS(2) QDs capped by mercaptopropionic acid (MPA) were directly synthesized by a hydrothermal method. Addition of fibrinogen to the CuInS(2) QDs solution led to the formation of a Fib-CuInS(2) QDs complex through electrostatic interactions and hydrogen bonding, and resulting in the enhancement of photoluminescence (PL) intensity and a red shift of the PL peak. Once thrombin was introduced into the Fib-CuInS(2) QDs system, it catalyzed the polymerization of the free and conjugated fibrinogen species to form insoluble fibrillar fibrin-CuInS(2) QDs agglutinates. After centrifugation, the PL intensity of the supernatants decreased upon increasing the concentration of thrombin. This Fib-CuInS(2) QDs probe provided a highly specific selectivity and a linear detection of thrombin in the range of 6.7 × 10(-11) to 3.9 × 10(-7) mol L(-1) with a detection limit (LOD) of about 8.7 × 10(-12) mol L(-1), and realized the thrombin detection in human serum samples directly. Compared with those obtained by using other nanomaterials and aptamer-based detection methods, this approach provided a lower LOD for thrombin detection. The proposed approach provides a simple and fast-responding procedure, which might hold a promising potential for application in the diagnosis of diseases associated with coagulation abnormalities and cancers.

Microwave-assisted synthesis of CdSe quantum dots: can the electromagnetic field influence the formation and quality of the resulting nanocrystals?

Microwave-assisted syntheses of colloidal nanocrystals (NCs), in particular CdSe quantum dots (QDs), have gained considerable attention due to unique opportunities provided by microwave dielectric heating. The extensive use of microwave heating and the frequently suggested specific microwave effects, however, pose questions about the role of the electromagnetic field in both the formation and quality of the produced QDs. In this work a one-pot protocol for the tunable synthesis of monodisperse colloidal CdSe NCs using microwave dielectric heating under carefully controlled conditions is introduced. CdSe QDs are fabricated using selenium dioxide as a selenium precursor, 1-octadecene as a solvent and reducing agent, cadmium alkyl carboxylates or alkyl phosphonates as cadmium sources, 1,2-hexadecanediol to stabilize the cadmium complex and oleic acid to stabilize the resulting CdSe QDs. Utilizing the possibilities of microwave heating technology in combination with accurate online temperature control the influence of different reaction parameters such as reaction temperature, ramp and hold times, and the timing and duration of oleic acid addition have been carefully investigated. Optimum results were obtained by performing the reaction at 240 °C applying a 5 min ramp time, 2 min hold time before oleic acid addition, 90 s for oleic acid addition, and a 5 min hold time after oleic acid addition (8.5 min overall holding at 240 °C). By using different cadmium complexes in the microwave protocol CdSe QDs with a narrow size distribution can be obtained in different sizes ranging from 0.5-4 nm by simply changing the cadmium source. The QDs were characterized by TEM, HRTEM, UV-Vis, and photoluminescence methods and the size distribution was monitored by SAXS. Control experiments involving conventional conductive heating under otherwise identical conditions ensuring the same heating and cooling profiles, stirring rates, and reactor geometries demonstrate that the electromagnetic field has no influence on the generated CdSe QDs. The resulting CdSe NCs prepared using either conductive or microwave dielectric heating exhibited the same primary crystallite size, shape, quantum yield and size distribution regardless of the heating mode.

PAMAM-functionalized water soluble quantum dots for cancer cell targeting

Herein, the phase-transfer reaction of quantum dots (QDs) with amine-terminated polyamidoamine (PAMAM) dendrimers with controllable ligand molar ratios was achieved. The unique properties of PAMAM allowed us to build up structurally and electrostatically stabilized water soluble QD complexes. Synthesized conjugates were characterized in terms of fluorescence and UV-Vis profiles, hydrodynamic size, number of surface dendrimer groups, and stability. Cytotoxic effects of conjugates for MCF-7, A-549 and HEP-G2 cancer cells were assessed based on cell viability using MTT assay. Cytotoxicity results were expressed as no observable adverse effect concentration (NOAEC), 50% inhibitory concentration (IC50) and total lethal concentration (TLC) values (μM). Furthermore, HER2 receptor-mediated targeting efficiency of antibody labelled P/QDs conjugates was evaluated by successful staining of MCF-7 cells with bioconjugates. Uniquely, effective cell internalization was achieved with well-characterized antibody coupled P/QDs in contrast to antibody free P/QDs conjugates. Fluorescence microscopy images demonstrated that the designed PAMAM-derivatized QDs nanoparticles show great potential in the areas of cellular imaging and targeted therapy.

Synthesis of blockwise alkylated tetrasaccharide–organic quantum dot complexes and their utilization for live cell labeling with low cytotoxicity

Bioimaging is a key to understanding immune responses, cell differentiation, and development. Quantum dots (QDs) conjugated with monoclonal antibodies and other biomolecules are currently utilized for flow cytometry and immunohistochemistry, but monoclonal antibody–QD complexes are of limited use when cell surface markers are not available. In this study, we synthesized novel amphiphilic blockwise alkylated tetrasaccharides and developed a simple method for labeling a wide variety of live cells with organic QDs encapsulated with these carbohydrates. The novel amphiphilic blockwise alkylated tetrasaccharides were as follows: methyl β-d-glucopyranosyl-(1 → 4)-β-d-glucopyranosyl-(1 → 4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1 → 4)-2,3,6-tri-O-methyl-d-glucopyranoside (1), methyl β-d-galactopyranosyl-(1 → 4)-β-d-glucopyranosyl-(1 → 4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1 → 4)-2,3,6-tri-O-methyl-d-glucopyranoside (2), ethyl β-d-glucopyranosyl-(1 → 4)-β-d-glucopyranosyl-(1 → 4)-2,3,6-tri-O-ethyl-β-d-glucopyranosyl-(1 → 4)-2,3,6-tri-O-ethyl-d-glucopyranoside, (3), and ethyl β-d-galactopyranosyl-(1 → 4)-β-d-glucopyranosyl-(1 → 4)-2,3,6-tri-O-ethyl-β-d-glucopyranosyl-(1 → 4)-2,3,6-tri-O-ethyl-d-glucopyranoside (4). The newly synthesized blockwise alkylated tetrasaccharides spontaneously assembled into micelle-like particles, in which the hydrophobic moiety of the blockwise alkylated tetrasaccharides played an important role. They were less toxic to human cells than octyl β-d-glucopyranoside, a commonly used amphiphilic glucoside. Flow cytometry and confocal laser scanning microscopy revealed that the blockwise alkylated tetrasaccharide–organic QD complexes were stably attached to live cells. The affinity of compounds 1 and 2 to the live cell surface was slightly higher than that of compounds 3 and 4. Because the preparation of these carbohydrate–QD complexes is simple and does not require sophisticated equipment, and because the complexes can be autonomously attached to a wide spectrum of cell lines, they can be used as cell labeling reagents in biomedical studies.

A quantum dot-based optical immunosensor for human serum albumin detection

In this study, a CdSe/ZnS quantum dot (QD)-based immunosensor using a simple optical system for human serum albumin (HSA) detection is developed. Monoclonal anti-HSA (AHSA) immobilized on 3-aminopropyltriethoxysilane (APTES)-modified glass was used to capture HSA specifically. Bovine serum albumin (BSA) was used to block non-specific sites. The solution, containing AHSA–QD complex prepared by mixing biotinylated polyclonal anti-HSA and streptavidin coated QD, was used to conjugate with the HSA molecules captured on AHSA/BSA/APTES-modified glass for the modification of HSA with QD. A simple optical system, comprising a diode laser (405nm), an optical lens, a 515-nm-long pass filter, and an Si-photodiode, was used to detect fluorescence and convert it to photocurrent. The current intensity was determined by the amount of QD specifically conjugated with HSA, and was therefore HSA-concentration-dependent and could be used to quantify HSA concentration. The detection limit of the pure QD solution was ∼3.5×10−12M, and the detection limit for the CdSe/ZnS QD-based immunosensor developed in this study was approximately 3.2×10−5mg/ml. This small optical biosensing system shows considerable potential for future applications of on-chip liver-function detection.

Multifunctional quantum-dot-based siRNA delivery for HPV18 E6 gene silence and intracellular imaging

The functional quantum dots (QDs) were specifically designed to overcome barriers in siRNA delivery such as siRNA protection, cellular penetration, endosomal release, carrier unpacking, intracellular transport and gene silencing. In this paper, two l-arginine-functional-modified CdSe/ZnSe QDs were synthesized as siRNA carriers to silence HPV18 E6 gene in HeLa cells. Using such constructs, these QDs showed significantly low cellular cytotoxicity and good siRNA protection. Flow cytometric and confocal microscopic analyses confirmed that the QDs delivered siRNA into HeLa cells efficiently. Importantly, superior gene silencing efficiency was achieved as evaluated by Reverse Transcription-PCR (RT-PCR) and Western blotting and HeLa cells growth was inhibited in xCELLigence installation analysis and MTT assay when treated with QD-siRNA complexes. Interestingly, the QDs coated with β-CD- l-Arg showed optimized property compared with those coated with l-Arg. Furthermore, these QDs complexes could also be used as nanocrystal probing agents, allowing real-time tracking and localization of QDs during delivery and transfection. The properties and capabilities of these QDs showed that amino acid-modified QDs could be used as useful siRNA carriers to effectively silence a target gene as well as fluorescence probes to analyze intracellular imaging in vivo.

BIOCONJUGATED QUANTUM DOTS BASED RAPID DETECTION OF PATHOGENIC BACTERIA FROM WATER SAMPLES

A sensitive and rapid method for the detection of pathogenic bacteria (Salmonella typhi) in water sample was developed using core-shell CdSe / ZnS quantum dots (QDs) as fluorescence label. Surface-functionalized core-shell quantum dots were synthesized by successive ion layer adsorption and reaction (SILAR) technique and were made hydrophilic by ligand exchange method. Developed hydrophobic and hydrophilic QDs were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and spectrofluorimetry. Carboxy- terminated QDs were conjugated with bacteria-specific antibodies (S. typhi-specific IgG) for the preparation of photostable fluorescent label and were characterized by various techniques like spectrofluorimetry and enzyme-linked immunosorbent assay (ELISA) for their photoluminescence and successful bioconjugation. Antibody (Ab)-conjugated QDs were incubated with bacteria-contaminated water for S. typhi detection. Microscopic images and spectral profile of bacteria–Ab conjugated QDs complex were recorded by confocal laser scanning microscopy (CLSM). A sensitivity of 103 organisms/mL of targeted bacteria (S. typhi) could be attained in a period of about 2 h.

Rapid Detection of Listeria monocytogenes in Different Food Samples Using Magnetic Nanobeads and a Quantum Dots Based Fluorescent Immunosensor Method

A fluorescent immunosensor method based on magnetic nanobeads and quantum dots (QDs) was evaluated for rapid detection of Listeria monocytogenes in wash solutions of chicken carcasses, ground beef, fresh-cut broccoli, and fresh-cut lettuce. First, streptavidin-conjugated magnetic nanobeads (145 nm in diameter) and streptavidin-conjugated QDs (605 nm emission wavelength) were separately coated with biotin conjugated anti-L. monocytogenes antibody. Second, to bind the target bacteria (L. monocytogenes), the magnetic nanobeads coated with the antibody were mixed with a wash solution of chicken carcasses, ground beef, broccoli, or lettuce. Third, in order to label the captured target bacteria, the magnetic nanobead and L. monocytogenes conjugates were mixed with the QDs coated with the antibody. During these steps, non-target components in the food sample and unattached QDs were removed by washing while a magnetic field (0.4 T) was applied. Finally, a portable spectrometer was used to measure the fluorescence intensity of the complexes of magnetic nanobeads, Listeria cells, and QDs. The results indicated that this method could detect L. monocytogenes at concentrations as low as 2 to 3 cfu per 0.1 mL in all tested food samples with less than 1.5 h of total detection time from sample preparation to final results. This immunosensor method has great potential to be applied to the rapid detection of different bacterial pathogens in various foods.