Anodic electrochemiluminescence of CdTe quantum dots and its energy transfer for detection of catechol derivatives

This work reported for the first time the anodic electrochemiluminescence (ECL) of CdTe quantum dots (QDs) in aqueous system and its analytical application based on the ECL energy transfer to analytes. The CdTe QDs were modified with mercaptopropionic acid to obtain water-soluble QDs and stable and intensive anodic ECL emission with a peak value at +1.17 V (vs Ag/AgCl) in pH 9.3 PBS at an indium tin oxide (ITO) electrode. The ECL emission was demonstrated to involve the participation of superoxide ion produced at the ITO surface, which could inject an electron into the 1Se quantum-confined orbital of CdTe to form QDs anions. The collision between these anions and the oxidation products of QDs led to the formation of the excited state of QDs and ECL emission. The ECL energy transfer from the excited CdTe QDs to quencher produced a novel methodology for detection of catechol derivatives. Using dopamine and L-adrenalin as model analytes, this ECL method showed wide linear ranges from 50 nM to 5 microM and 80 nM to 30 microM for these species. Both ascorbic acid and uric acid, which are common interferences, did not interfere with the detection of catechol derivatives in practical biological samples.     

Hydrothermal synthesis for high-quality CdTe quantum dots capped by cysteamine

We present a facile hydrothermal approach to synthesize high-quality cysteamine (CA)-capped CdTe quantum dots (QDs). Oil bath heating and vigorous stirring were used to obtain better heat transfer and more homogenous solutions during the synthesis process. By this approach, the quantum yield (QY) of the resultant QDs can reach as high as 19.7%, which is the best reported data for CA-stabilized CdTe QDs. The synthesis process is under a high concentration of the precursor (> 10 mM), suggesting the potential of this route to be used in mass production of CA-capped CdTe QDs. Moreover, the pH-dependent optical properties of CA-capped CdTe QDs were also investigated.     

Tuning spin properties of excitons in single CdTe quantum dots by annealing

Using polarization-resolved photoluminescence imaging in external magnetic fields we measure statistically significant distributions of exchange splitting, diamagnetic shift and effective g-factor of excitons in tens of single CdTe quantum dots. Comparison between the as-grown and annealed structures shows strong suppression of ensemble inhomogeneities, with the average exchange splitting reduced by half and significant narrowing of the g-factor distribution. Remarkably, the average value of the excitonic g-factor remains unchanged. This unique ability to yield highly uniform quantum dot ensembles without hampering the exciton Zeeman splitting makes annealing a highly attractive means for tuning the spin properties of quantum dot excitons.     

Surface modification of CdSe quantum dots for biosensing applications: Role of ligands

For an optimum performance of colloidal nanocrystal devices for a variety of applications such as photonic devices, solar cells and biological labelling, the determining factors are the nanocrystal surface and size. In this work, these two factors have been tuned via wet chemistry to tailor the material properties: The absorption and emission spectra have been tailored by choice of the nanocrystal size; nanocrystal shape by surface modification and photoluminescence (PL) efficiency determined by surface traps, has been tuned via appropriate selection of the nanocrystal capping ligands. Here, we have shown that through ligand-exchange process, the surface of the CdSe quantum dots (QDs) can be modified by replacing the longer-chain ligands of conventional trioctyl phosphine oxide (TOPO) or oleic acid (OA) with shorter-chain ligand of butyl amine. This imparts colloidal stability and water solubility to CdSe QDs for its potential applications in biosensors and biological imaging. It is conjectured that crystallite sizes, oxidation potential of CdSe QDs and stereochemical compatibility of ligands (TOPO, oleic acid and butyl amine) greatly influences the photophysics and photochemistry of CdSe QDs.     

Conjugation behaviours of CdTe quantum dots and antibody by a novel immunochromatographic method

Three water-soluble CdTe quantum dots (QDs) (green-emitting, yellow-emitting and red-emitting) were synthesised for different refluxing time with 3-mercaptopropionic acid (MPA) as stabiliser. Then the red-emitting CdTe QDs and mouse immunoglobulin G (IgG) were taken as the representative to study the conjugation behaviour of QDs and antibody by a novel immunochromatographic method. After comparing with several methods, that is, direct conjugation, 1-ethyl-3(3-dimethylaminopropyl) carbodiimides hydrochloride (EDC)-mediated conjugation, N-hydroxysuccinimide (NHS)-mediated conjugation, EDC/NHS-mediated conjugation by immunochromatographic strips, EDC and NHS were selected together as coupling agents to conjugate QDs with antibody efficiently. Finally, the K562 leukaemia cells were incubated with the EDC/NHS-mediated conjugates to evaluate the performance in practical application, and the result from fluorescence images showed that it was successfully applied to label cells. The immunochromatographic strip was a superior method to study the conjugation of the fluorophore and antibody.     

Evaluation of red CdTe and near infrared CdHgTe quantum dots by fluorescent imaging

Non-invasive fluorescent imaging of preclinical animal models in vivo is a rapidly developing field with new emerging technologies and techniques. Quantum dot (QD) fluorescent probes with longer emission wavelengths in red and near infrared (NIR) emission ranges are more amenable to deep-tissue imaging, because both scattering and autofluorescence are reduced as wavelengths are increased. We have designed and synthesized red CdTe and NIR CdHgTe QDs for fluorescent imaging. We demonstrated fluorescent imaging by using CdTe and CdHgTe QDs as fluorescent probes both in vitro and in vivo. Both CdTe and CdHgTe QDs provided sensitive detection over background autofluorescence in tissue biopsies and live mice, making them attractive probes for in vivo imaging extending into deep tissues or whole animals. The studies suggest a basis of using QD-antibody conjugates to detect membrane antigens.     

Heterostructures with CdTe/ZnTe quantum dots for single photon emitters grown by molecular beam epitaxy

We report on the molecular beam epitaxy (MBE) of heterostructures with CdTe/ZnTe quantum dots (QDs) with relatively low surface density, which could be used as single-photon emitters. The QDs were formed on the surface of a 3.1- to 4.5-monolayer-thick two-dimensional strained CdTe layer by depositing amorphous Te layer and its fast thermal desorption. Subsequent thermal annealing of the surface with QDs in the absence of external Te flux led to strong broadening and short-wavelength shift of the QD photoluminescence (PL) peak. Measurement of the micro-PL spectra of individual CdTe/ZnTe quantum dots in fabricated mesastructures with a diameter of 200—1000 nm allowed estimation of the QD surface density as ~10¹⁰ cm^–2.     

CdSe-ZnS quantum dots for selective and sensitive detection and quantification of hypochlorite

Four types of water-soluble quantum dots (QDs) grafted with different organic coating layers were fabricated, and their sensitivities for hypochlorite/hypochlorous acid (HClO) were examined. It was found that QDs with HClO reactive (methylamino and sulphide groups) coating layers exhibited a protective effect on HClO quenching of QD fluorescence, whereas QDs with hydrocarbon and carboxylate coating layers showed least protection to QD fluorescence quenching by HClO and, thus, has the highest sensitivity for the detection of HClO. The QDs with carboxylate coating layers (QDs-poly-CO(2)(-)) was successfully applied to the quantification of HClO in tap water. The excellent selectivity of the QDs-poly-CO(2)(-) toward hypochlorite against other reactive oxygen species allowed us to monitor myeloperoxidase activity. Finally, the QDs-poly-CO(2)(-) was also used for the detection of hypochlorite in HL60 cells by fluorescent imaging. Hence, QD-poly-CO(2)(-) exhibits great promise as a selective and sensitive HClO probe in chemical and biological systems.     

Exploring feasibility of multicolored CdTe quantum dots for in vitro and in vivo fluorescent imaging

We report the use of novel multicolored CdTe quantum dots (QDs) as fluorophores for biological fluorescence imaging. The CdTe QDs were prepared to exhibit emission wavelengths in the green, yellow, and red range by using trifluoroacetic acid (TFA), L-cysteine and thioglycolic acid (TGA) as surface stabilizers, respectively. The particles have good water solubility and photostability. Fluorescence imaging potential was evaluated in vitro and in vivo using a multispectral Maestro CRI Fluorescence Imaging system. The results show that different colored CdTe QDs allow sensitive detection simultaneously or separately both in vitro and in vivo against background fluorescence. The studies indicate that CdTe QDs can provide alternative fluorescent probes for biological imaging.     

Nanoscale, catalytically enhanced local oxidation of silicon-containing layers by 'burrowing' Ge quantum dots

A new phenomenon of highly localized, nanoscale oxidation of silicon-containing layers has been observed. The localized oxidation enhancement observed in both Si and Si(3)N(4) layers appears to be catalyzed by the migration of Ge quantum dots (QDs). The sizes, morphology, and distribution of the Ge QDs are influenced by the oxidation of the Si-bearing layers. A two-step mechanism of dissolution of Si within the Ge QDs prior to oxidation is proposed.     

The synthesis of newly modified CdTe quantum dots and their application for improvement of latent fingerprint detection

Motivated by the urgent demand for the detection of latent fingerprints using fluorescence-based nanotechnology, this work was devoted to developing a simple synthetic approach to obtain positively charged CdTe QDs with enhanced fluorescence and affinity for the improvement of latent fingerprint detection. Through this synthetic method, the positively charged CdTe-COONH(3)NH(3)(+) QDs were successfully achieved by using hydrazine hydrate as both the surface stabilizer and pH adjuster during the preparation process. In comparison to the negatively charged CdTe-COO(-) QDs prepared by using sodium hydroxide as the pH adjuster, the CdTe-COONH(3)NH(3)(+) QDs showed enhanced fluorescence. The effectiveness of CdTe-COO(-) and CdTe-COONH(3)NH(3)(+) QDs for detection of latent fingerprints present on a large variety of smooth objects was systematically and comparatively studied. The results indicate that the detection of latent fingerprints by using CdTe-COONH(3)NH(3)(+) QDs as fluorescent labeling marks was greatly enhanced, and more characteristic finger ridge details were detected and identified due to their enhanced affinity with latent fingerprints, in comparison to the detection by using CdTe-COO(-) QDs as fluorescent labeling marks. The CdTe-COONH(3)NH(3)(+) QDs show superior detection capability than the CdTe-COO(-) QDs, which greatly improves the applicability of CdTe QDs for practical application in latent fingerprint detection.     

Photoelectronic behaviors of self-assembled ZnSe/ZnS/L-Cys quantum dots synthesized at low temperature

The photogenerated carriers’ transport and microstructure of self-assembled core–shell ZnSe/ZnS/L-Cys quantum dots (QDs), which was synthesized at room temperature, are studied via the surface photovoltaic and transient photovoltaic techniques, X-ray diffraction, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy and ultraviolet–visible absorption spectra. The results suggest that the ZnSe nanocrystals prepared at room temperature prefer to nucleate at (111) and (220) faces, and grow a shell–ZnS at (220) face rather than at (311) face. The quantum well depth in some interface space charge region (SCR) of the QDs prepared at room temperature is smaller than that prepared at 90 °C. The evolution of the band bending from a depletion layer to an accumulation layer may occur in the graded-band-gap and at the side of the interface SCR, as compared the QDs with p-type photovoltaic characteristic synthesized at room temperature to that at 90 °C. This electron structural shift may be ascribed to the reduced quantum well depth and then an obvious resonance quantum tunneling of the QDs synthesized at room temperature.     

Type-II CdSe/CdTe/ZnTe (core-shell-shell) quantum dots with cascade band edges: the separation of electron (at CdSe) and hole (at ZnTe) by the CdTe layer

The rational design and synthesis of CdSe/CdTe/ZnTe (core-shell-shell) type-II quantum dots are reported. Their photophysical properties are investigated via the interband CdSe-->ZnTe emission and its associated relaxation dynamics. In comparison to the strong CdSe (core only) emission (lambda(max) approximately 550 nm, Phi(f) approximately 0.28), a moderate CdSe-->CdTe emission (lambda(max) approximately 1026 nm, Phi(f) approximately 1.2 x 10(-3)) and rather weak CdSe-->ZnTe interband emission (lambda(max) approximately 1415 nm, Phi(f) approximately 1.1 x 10(-5)) are resolved for the CdSe/CdTe/ZnTe structure (3.4/1.8/1.3 nm). Capping CdSe/CdTe with ZnTe results in a distant electron-hole separation between CdSe (electron) and ZnTe (hole) via an intermediate CdTe layer. In the case of the CdSe/CdTe/ZnTe structure, a lifetime as long as 150 ns is observed for the CdSe-->ZnTe (1415 nm) emission. This result further indicates an enormously long radiative lifetime of approximately 10 ms. Upon excitation of the CdSe/CdTe/ZnTe structure, the long-lived charge separation may further serve as an excellent hole carrier for catalyzing the redox oxidation reaction.     

Polyamine-functionalized carbon quantum dots as fluorescent probes for selective and sensitive detection of copper ions

A novel sensing system has been designed for Cu(2+) ion detection based on the quenched fluorescence (FL) signal of branched poly(ethylenimine) (BPEI)-functionalized carbon quantum dots (CQDs). Cu(2+) ions can be captured by the amino groups of the BPEI-CQDs to form an absorbent complex at the surface of CQDs, resulting in a strong quenching of the CQDs' FL via an inner filter effect. Herein, we have demonstrated that this facile methodology can offer a rapid, reliable, and selective detection of Cu(2+) with a detection limit as low as 6 nM and a dynamic range from 10 to 1100 nM. Furthermore, the detection results for Cu(2+) ions in a river water sample obtained by this sensing system agreed well with that by inductively couple plasma mass spectrometry, suggesting the potential application of this sensing system.     

One-pot synthesis of highly luminescent CdTe quantum dots by microwave irradiation reduction and their Hg2+-sensitive properties

A facile one-pot microwave irradiation reduction route has been developed for the synthesis of highly luminescent CdTe quantum dots using Na₂TeO₃ as the Te source in an aqueous environment. The synthesis parameters of this simple and rapid approach, including the reaction temperature and time, the pH of the reaction solution and the molar ratio of the 3-mercaptopropionic acid (MPA) stabilizer to Cd²⁺, have considerable influence on the particle size and photoluminescence quantum yield of the CdTe quantum dots. The photoluminescence quantum yield of CdTe quantum dots prepared using relatively short reaction times (10–40 min) reached 40%–60% (emission peaks at 550–640 nm). Furthermore, the resulting products could be used as fluorescent probes to detect Hg²⁺ ions in aqueous media. The response was linearly proportional to the concentration of Hg²⁺ ion in the range 8.0×10⁻⁹ mol/L to 2.0×10⁻⁶ mol/L with a detection limit of 2.7×10⁻⁹ mol/L. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Self-assembled growth of GaAs anti quantum dots in InAs matrix by migration enhanced molecular beam epitaxy

Self-assembled GaAs anti quantum dots (AQDs) were grown in an InAs matrix via migration enhanced molecular beam epitaxy. The transmission electron microscopy image showed that the 2D to 3D transition thickness is below 1.5 monolayers (MLs) of GaAs coverage. The average diameter and height of the GaAs AQDs for 1.5 ML GaAs coverage taken from the atomic force microscopy image were approximately 29.0 nm and 1.4 nm, respectively. The density was approximately 6.0 x 10(10) cm(-2). The size of the AQDs was enlarged in the InAs matrix compared with that on the surface. These results indicate that the GaAs AQDs in the InAs matrix under tensile strain can be effectively formed with the assistance of the migration enhanced epitaxy method.     

Unraveling the physical properties of Mn-doped CdS diluted magnetic semiconductor quantum dots for potential application in quantum spintronics

Journal of Materials Science: Materials in Electronics - The tunability of structural, optical, electronic, and magnetic properties in semiconductor quantum dots (QDs) makes them promising...     

Novel magnetic Fe3O4@CdSe composite quantum dot-based electrochemiluminescence detection of thrombin by a multiple DNA cycle amplification strategy

A novel small magnetic electrochemiluminescent Fe(3)O(4)@CdSe composite quantum dot (QD) was facilely prepared and successfully applied to sensitive electrochemiluminescence (ECL) detection of thrombin by a multiple DNA cycle amplification strategy for the first time. The as-prepared composite QDs feature intense ECL, excellent magnetism, strong fluorescence, and favorable biocompatibility, which offers promising advantages for ECL biosensing. ECL of the composite QDs was efficiently quenched by gold nanoparticles (NPs). Taking advantages of the unique and attractive ECL and magnetic characteristics of the composite QDs, a novel DNA-amplified detection method based on ECL quenching was thus developed for a sensitive assay of thrombin. More importantly, the DNA devices by cleavage reaction were cycled multiple rounds, which greatly amplified the ECL signal and much improve the detection sensitivity. This flexible biosensing system exhibits not only high sensitivity and specificity but also excellent performance in real human serum assay. The present work opens a promising approach to develop magnetic quantum dot-based amplified ECL bioassays, which has wider potential application with more favorable analytical performances than other ECL reagent-based systems. Moreover, the composite QDs are suitable for long-term fluorescent cellular imaging, which also highlights the promising directions for further development of QD-based in vitro and in vivo imaging materials.     

Optimization of process parameter for synthesis of silicon quantum dots using low pressure chemical vapour deposition

Si quantum dots-based structures are studied recently for performance enhancement in electronic devices. This paper presents an attempt to get high density quantum dots (QDs) by low pressure chemical vapour deposition (LPCVD) on SiO ₂ substrate. Surface treatment, annealing and rapid thermal processing (RTP) are performed to study their effect on size and density of QDs. The samples are also studied using Fourier transformation infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM) and photoluminescence study (PL). The influence of Si–OH bonds formed due to surface treatment on the density of QDs is discussed. Present study also discusses the influence of surface treatment and annealing on QD formation.