Tunable excitation properties of ZnCdS:Mn/ZnS quantum dots for cancer imaging

Water‐soluble ZnS:Mn quantum dots (QDs) were synthesized using a hydrothermal method with 3‐mercaptopropionic acid as stabilizer. The optical properties of ZnS:Mn QDs were thoroughly investigated by tuning the doping concentration of Mn²⁺ and the Zn/S precursor ratio, to obtain an optimal parameter for QDs with excellent fluorescence characteristics. ZnS:Mn QDs excited at only one wavelength, however, which seriously limited their further application. Here, a trace Cd ion was doped into a ZnS host, resulting in QD excitation covering a wide adjustable waveband. Furthermore, when a ZnS shell was coated onto the surface of the ZnCdS:Mn QDs, photoluminescence intensity and stability were further enhanced. After coupling with an anti‐CK 19 antibody, the ZnCdS:Mn/ZnS core/shell QDs were able to function by labeling cancer cells, indicating that they could be considered as a suitable bio‐probe for cells and tissue imaging.     

A novel phosphorescence sensor for Co2+ ion based on Mn‐doped ZnS quantum dots

N‐acetyl‐l ‐cysteine‐capped Mn‐doped ZnS quantum dots (QDs) were prepared by hydrothermal methods. It could emit phosphorescence at 583 nm with the excitation wavelength at 315 nm. The phosphorescence intensity of QDs could be quenched dramatically by increasing the concentration of Co²⁺ ion. The novel phosphorescence sensor based on N‐acetyl‐l ‐cysteine‐capped QDs was developed for detecting Co²⁺ ion with a linear dynamic range of 1.25 × 10^–6–3.25 × 10^–5 m . The limit of detection and RSD were 6.0 × 10^–8 m and 2.3%, respectively. Interference experiments showed excellent selectivity over numerous cations such as alkali, alkaline earth and transitional metal ions. The possible quenching mechanism was also examined by phosphorescence decays. The proposed phosphorescence method was further applied to the trace determination of Co²⁺ ion in tap and pond water samples with recoveries of 97.75–103.32%. Copyright © 2013 John Wiley & Sons, Ltd.     

Characterization and cancer cell targeted imaging properties of human antivascular endothelial growth factor monoclonal antibody conjugated CdTe/ZnS quantum dots

High luminescence quantum yield water‐soluble CdTe/ZnS core/shell quantum dots (QDs) stabilized with thioglycolic acid were synthesized. QDs were chemically coupled to fully humanized antivascular endothelial growth factor₁₆₅ monoclonal antibodies to produce fluorescent probes. These probes can be used to assay the biological affinity of the antibody. The properties of QDs conjugated to an antibody were characterized by ultraviolet and visible spectrophotometry, fluorescent spectrophotometry, sodium dodecyl sulfate–polyacrylamide gel electrophoresis, transmission electron microscopy and fluorescence microscopy. Cell‐targeted imaging was performed in human breast cancer cell lines. The cytotoxicity of bare QDs and fluorescent probes was evaluated in the MCF‐7 cells with an MTT viability assay. The results proved that CdTe/ZnS QD–monoclonal antibody nanoprobes had been successfully prepared with excellent spectral properties in target detections. Surface modification by ZnS shell could mitigate the cytotoxicity of cadmium‐based QDs. The therapeutic effects of antivascular endothelial growth factor antibodies towards cultured human cancer cells were confirmed by MTT assay. Copyright © 2014 John Wiley & Sons, Ltd.     

Aqueous synthesis of CdTe/CdS/ZnS quantum dots and their optical and chemical properties

In this paper, we described a strategy for synthesis of thiol‐coated CdTe/CdS/ZnS (core–shell–shell) quantum dots (QDs) via aqueous synthesis approach. The synthesis conditions were systematically optimized, which included the size of CdTe core, the refluxing time and the number of monolayers and the ligands, and then the chemical and optical properties of the as‐prepared products were investigated. We found that the mercaptopropionic acid (MPA)‐coated CdTe/CdS/ZnS QDs presented highly photoluminescent quantum yields (PL QYs), good photostability and chemical stability, good salt tolerance and pH tolerance and favorable biocompatibility. The characterization of high‐resolution transmission electron microscopy (HRTEM), X‐ray powder diffraction (XRD) and fluorescence correlation spectroscopy (FCS) showed that the CdTe/CdS/ZnS QDs had good monodispersity and crystal structure. The fluorescence life time spectra demonstrated that CdTe/CdS/ZnS QDs had a longer lifetime in contrast to fluorescent dyes and CdTe QDs. Furthermore, the MPA‐stabilized CdTe/CdS/ZnS QDs were applied for the imaging of cells. Compared with current synthesis methods, our synthesis approach was reproducible and simple, and the reaction conditions were mild. More importantly, our method was cost‐effective, and was very suitable for large‐scale synthesis of CdTe/CdS/ZnS QDs for future applications. Copyright © 2010 John Wiley & Sons, Ltd.     

Aqueous synthesis of highly luminescent surface Mn2+‐doped CdTe quantum dots as a potential multimodal agent

Mn²⁺‐doped CdTe quantum dots (QDs) were synthesized directly via a facile surface doping strategy in aqueous solution. The best optical property emerged when the added amount of Mn²⁺ was 5% compared to Cd²⁺ in the CdTe nanoparticles and the reaction temperature was 60 °C. The fluorescence and magnetic properties of the QDs were studied. The as‐prepared Mn²⁺‐doped CdTe QDs have high quantum yield (48.13%) and a narrow distribution with an average diameter of 3.7 nm. The utility of biological imaging was also studied. Depending on the high quantum yield, cells in culture were illuminated and made more distinct from each other compared to results obtained with normal QDs. They also have a prominent longitudinal relaxivity value (r₁ = 4.2 mM^?1s^?1), which could indicate that the Mn²⁺‐doped CdTe QDs can be used as a potential multimodal agent for fluorescence and magnetic resonance imaging. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermoluminescence of mercaptoethanol‐capped ZnS:Mn nanoparticles

The thermoluminescence (TL) of nanoparticles has become a matter of keen interest in recent times but is rarely reported. This article reports the synthesis of ZnS:Mn nanocrystals using a chemical route, with mercaptoethanol (ME) as the capping agent. The particle sizes for the nanocrystals were measured by X‐ray diffraction (XRD) and also by studying transmission electron microscopy (TEM) patterns. The particle sizes of the synthesized samples were found to be between 1 and 3 nm. For samples with different concentrations of the capping agent, it was found that the TL intensity of the ZnS:Mn nanoparticles increased as the particle size decreased. A shift in the peak position of the TL glow curve was also seen with decreasing particle size. The TL intensity was found to be maximal for samples with 1.2% of Mn. A change in the peak position was not found for samples with different concentrations of Mn. The half‐width glow peak curve method was used to determine the trap‐depth. The frequency factor of the synthesized samples was also calculated. The stability of the charge carriers in the traps increases with decreasing nanoparticle size. The higher stability may be attributed to the higher surface/volume ratio and also to the increase in the trap‐depth with decreasing particle size. Copyright © 2014 John Wiley & Sons, Ltd.     

Deposition of CdS,CdS/ZnSe and CdS/ZnSe/ZnS shells around CdSeTe alloyed core quantum dots: effects on optical properties

In this work, we synthesized water‐soluble L ‐cysteine‐capped alloyed CdSeTe core quantum dots (QDs) and investigated the structural and optical properties of deposition of each of CdS, CdS/ZnSe and CdS/ZnSe/ZnS shell layers. Photophysical results showed that the overcoating of a CdS shell around the alloyed CdSeTe core [quantum yield (QY) = 8.4%] resulted in effective confinement of the radiative exciton with an improved QY value of 93.5%. Subsequent deposition of a ZnSe shell around the CdSeTe/CdS surface decreased the QY value to 24.7%, but an increase in the QY value of up to 49.5% was observed when a ZnS shell was overcoated around the CdSeTe/CdS/ZnSe surface. QDs with shell layers showed improved stability relative to the core. Data obtained from time‐resolved fluorescence measurements provided useful insight into variations in the photophysical properties of the QDs upon the formation of each shell layer. Our study suggests that the formation of CdSeTe/CdS core/shell QDs meets the requirements of quality QDs in terms of high photoluminescence QY and stability, hence further deposition of additional shells are not necessary in improving the optical properties of the core/shell QDs. Copyright © 2015 John Wiley & Sons, Ltd.     

The interaction of CuInS2/ZnS/TGA quantum dots with tyrosine kinase inhibitor and its application

The interactions between thioglycolic acid‐capped‐CuInS₂/ZnS quantum dots (CuInS₂/ZnS/TGA QDs) and tyrosine kinase inhibitor (TKI) were investigated using fluorescence, ultraviolet–visible spectrometry and Fourier transform infrared spectrometry. The results indicated that the fluorescence intensity of CuInS₂/ZnS/TGA could be quenched by imatinib, dasatinib, nilotinib, gefitinib and erlotinib, which hinted that CuInS₂/ZnS/TGA QDs could be used in the detection of TKI in active pharmaceutical ingredients (API). Calibration curves showed good linear correlation and low detection limits. The average recovery was between 98 and 102%. Moreover, the nature of the fluorescence quenching mechanism of CuInS₂/ZnS/TGA QDs by TKI was discussed. A ground state complex was formed by hydrogen bonding between the carboxyl group of CuInS₂/ZnS/TGA QDs and the amino group of TKI. This led to an increase in non‐radiative transition and fluorescence quenching of CuInS₂/ZnS/TGA QDs. Copyright © 2014 John Wiley & Sons, Ltd.     

Nucleation temperature‐controlled synthesis and in vitro toxicity evaluation of l‐cysteine‐capped Mn:ZnS quantum dots for intracellular imaging

Quantum dots (QDs), one of the fastest developing and most exciting fluorescent materials, have attracted increasing interest in bioimaging and biomedical applications. The long‐term stability and emission in the visible region of QDs have proved their applicability as a significant fluorophore in cell labelling. In this study, an attempt has been made to explore the efficacy of l ‐cysteine as a capping agent for Mn‐doped ZnS QD for intracellular imaging. A room temperature nucleation strategy was adopted to prepare non‐toxic, water‐dispersible and biocompatible Mn:ZnS QDs. Aqueous and room temperature QDs with l ‐cysteine as a capping agent were found to be non‐toxic even at a concentration of 1500 µg/mL and have wide applications in intracellular imaging. Copyright © 2015 John Wiley & Sons, Ltd.     

Tuneable luminescence properties of EDTA‐assisted ZnS:Mn nanocrystals from a yellow‐orange to a red emission band

Luminescence technology has been improved with the help of semiconductor nanoparticles that possess novel optical and electrical properties compared with their bulk counterpart. The aim of this study was to design semiconductor nanocrystals in their pure (ZnS) or doped form (ZnS:Mn) with different concentrations of Mn²⁺ ions by a wet chemical route stabilized by ethylenediamine tetra‐acetic acid (EDTA) and to evaluate their luminescence properties. The nanocrystals were characterized by physicochemical techniques such as X‐ray diffraction (XRD), High‐resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SEAD), EDS, and ultraviolet (UV)–visible light and photoluminescence (PL) studies. These results showed the presence of cubic phase and spherically shaped nanocrystals. A blue shift with respect to their bulk counterpart was observed. PL emission spectra were observed with a fixed blue peak and the yellow‐orange bands were red shifted towards the red region under the same excitation wavelength. The orange‐red bands were attributed to the radiation transition of electrons in 3d5 unfilled shells of Mn²⁺ ions [⁴T₁(⁴G)‐⁶A₁(⁶S)]; the ZnS matrix varied with Mn²⁺ concentration. Shift and increase in the intensity of the PL and absorption bands were observed with increase in Mn content. The study showed that Mn²⁺‐doped ZnS nanocrystal emission bands can be tuned from the yellow‐orange to the red regions under a controlled synthesis process and could be used as promising luminescent emitters in the biology field upon functionalization with suitable materials. Further studies on construction with various other materials will be useful for practical applications.     

Sensitization enhancement of europium in ZnSe/ZnS core/shell quantum dots induced by efficient energy transfer

Eu‐doped ZnSe:/ZnS quantum dots (formed as ZnSe:Eu/ZnS QDs) were successfully synthesized by a two‐step wet chemical method: nucleation doping and epitaxial shell growing. The sensitization characteristics of Eu‐doped ZnSe and ZnSe/ZnS core/shell QD are studied in detail using photoluminescence (PL), PL excitation spectra (PLE) and time‐resolved PL spectroscopy. The emission intensity of Eu ions is enhanced and that of ZnSe QDs is decreased, implying that energy was transferred from the excited ZnSe host materials (the donor) to the doped Eu ions (the acceptor). PLE reveals that the ZnSe QDs act as an antenna for the sensitization of Eu ions through an energy transfer process. The dynamics of ZnSe:Eu/ZnS core/shell quantum dots with different shell thicknesses and doping concentrations are studied via PL spectra and fluorescence lifetime spectra. The maximum phosphorescence efficiency is obtained when the doping concentration of Eu is approximately 6% and the sample showed strong white light under ultraviolet lamp illumination. By surface modification with ZnS shell layer, the intensity of Eu‐related PL emission is increased approximately three times compared with that of pure ZnSe:Eu QDs. The emission intensity and wavelength of ZnSe:Eu/ZnS core/shell quantum dots can be modulated by different shell thickness and doping concentration. The results provide a valuable insight into the doping control for practical applications in laser, light‐emitting diodes and in the field of biotechnology. Copyright © 2014 John Wiley & Sons, Ltd.     

Tracking bio‐molecules in live cells using quantum dots

Single particle tracking (SPT) techniques were developed to explore bio‐molecules dynamics in live cells at single molecule sensitivity and nanometer spatial resolution. Recent developments in quantum dots (Qdots) surface coating and bio‐conjugation schemes have made them most suitable probes for live cell applications. Here we review recent advancements in using quantum dots as SPT probes for live cell experiments. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bioinspired multicolour carbon dots: comprehensive cytotoxicity,phytotoxicity, and bioimaging in animal cells and plants

During the past decades, carbon dots (CDs) as a kind of nanoparticles with interesting fluorescence properties have retained their place as one of the best bioimaging agents, although their effects on plants have been rarely studied. In this study, we synthesized two kinds of concentration-dependent multicolour CDs using two solvent approaches, phosphate-buffered saline (PBS) and ethanol 20%. We confirmed the nature of the CDs through Fourier transform infrared spectroscopy, atomic force microscopy, dynamic light scattering, zeta potential, X-ray powder diffraction, and high-resolution transmission electron microscopy. Afterwards, the cytotoxicity, phytotoxicity, and bioimaging of animal cells and plants using both synthesized CDs were examined. Eventually, PBS-based CDs were recommended during this study as an efficient bioimaging agent for animal cells and plants because of the appealing features of this CD, such as a small size range of less than 10 nm, surface charge with an average of −24 mV, a high quantum yield of 35.82%, the higher fluorescence intensity of ~400 a.u. for blue fluorescence light and 250 a.u. for green fluorescence light. Other features showing the superiority of PBS-based CDs include high photostability, low phytotoxicity (p ≤ 0.05 and p ≤ 0.01) and above all, there was no significant cytotoxicity at the concentration range of 500–7.81 μg/ml.     

A highly sensitive and selective detection of picric acid using fluorescent sulfur‐doped graphene quantum dots

The development of an analytical probe to monitor highly mutagenic picric acid (PA) carries enormous significance for the environment and for health. A novel, simple and rapid fluorescence analytical assay using sulfur‐doped graphene quantum dots (SGQDs) was designed for the highly sensitive and selective detection of PA. SGQDs were synthesized via simple pyrolysis of 3‐mercaptopropionic acid and citric acid and characterized using advanced analytical techniques. Fluorescence intensity (FI) of SGQDs was markedly quenched by addition of PA, attributed to the inner filter effect and dominating static quenching mechanism between the two, in addition to a significant colour change. The calibration curve of the proposed assay exhibited a favourable linearity between quenched FI and PA concentration over the 0.1–100 μΜ range with a lowest detection limit of 0.093 μΜ and a correlation coefficient of 0.9967. The analytical assay was investigated for detection of trace amounts of PA in pond and rain water samples and showed great potential for practical applications with both acceptable recovery (98.0–100.8%) and relative standard deviation (1.24–4.67%). Analytical performance of the assay in terms of its detection limit, linearity range, and recovery exhibited reasonable superiority over previously reported methods, thereby holding enormous promise as a simple, sensitive, and selective method for detection of PA.     

Synthesis and application of a targeting diagnosis system via quantum dots coated by amphiphilic polymer for the detection of liver cancer cells

Water‐soluble quantum dots (QDs) for liver cancer diagnosis were prepared using QDs with oleylamine ligand coated with poly(aspartate)–graft–poly(ethylene glycol)–dodecylamine (PASP–Na–g–PEG–DDA). Dynamic light scattering and transmission electron microscopy imaging showed that the novel QDs have an ellipsoidal morphology with a size of ~ 45 nm which could be used for biomedical application. Furthermore, the PASP–Na–g–PEG–DDA was then modified with anti‐(vascular endothelial growth factor) (VEGF antibody), and a 1‐(4,5‐dimethylthiazol‐2‐yl)‐3,5‐diphenylformazan (MTT) assay showed that the novel anti‐VEGF‐targeting QDs in vitro had low toxicity. Confocal laser scanning microscopy observations revealed an intracellular (HepG2) distribution of the novel anti‐VEGF‐targeting QDs and the targeting efficiency of anti‐VEGF. These novel QDs could be used as a probe for liver cancer cell imaging because of anti‐VEGF targeting. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis of highly luminescent and biocompatible CdTe/CdS/ZnS quantum dots using microwave irradiation: a comparative study of different ligands

We compared the effects of several ligands frequently used in aqueous synthesis, including L‐cysteine, L‐cysteine hydrochloride, N‐acetyl‐L‐cysteine (NAC), glutathione and 3‐mercaptopropionic acid, for microwave synthesis of CdTe quantum dots (QDs) in a sealed vessel with varied temperatures and times, and then developed a rapid microwave‐assisted protocol for preparing highly luminescent, photostable and biocompatible CdTe/CdS/ZnS core–multishell QDs. The effects of molecular structures of these ligands on QD synthesis under high temperatures were explored. Among these ligands, NAC was found to be the optimal ligand in terms of the optical properties of resultant QDs and reaction conditions. The emission wavelength of NAC‐capped CdTe QDs could reach 700 nm in 5 min by controlling the reaction temperature, and the resultant CdTe/CdS/ZnS core–multishell QDs could achieve the highest quantum yields up to 74% with robust photostability. In addition, the effects of temperature, growth time and shell–precursor ratio on shell growth were examined. Finally, cell culturing indicated the low cytotoxicity of CdTe/CdS/ZnS core–multishell QDs as compared to CdTe and CdTe/CdS QDs, suggesting their high potential for applications in biomedical imaging and diagnostics. Copyright © 2014 John Wiley & Sons, Ltd.     

Spatial energy transfer with observation of bimolecular singlet oxygen emission using quantum dots as donors and zinc‐phthalocyanine as acceptors

This study reports the influence of CdSe–ZnS core–shell quantum dots (QDs) for formation of singlet oxygen using zinc‐phthalocyanine (ZnPc) dyes in colloidal solutions. Using a microluminescence surface scan technique it was possible to measure accurately the photon diffusion length, or photon mean free path, inside the medium. Analyses were performed for a range of QD concentrations. Photon diffusion length was assigned to the bimolecular singlet oxygen emission at 707 nm. Related singlet oxygen emission was predicted by observing quenching of the photon diffusion length measured at the specific oxygen emission as a function of QD concentration, being a nontrivial phenomenon related to the QD donors. Diffusion length measured at 707 nm increased with QD concentration; in the absence of QDs, as in pure ZnPc samples, the emission peak at 707 nm was not observed.     

Cytotoxicity of CdSe-based quantum dots incorporated in glass nanoparticles evaluated using human keratinocyte HaCaT cells

CdSe quantum dots (QDs) are potential fluorescent reagents, but leakage of Cd and Se often induces cytotoxicity. Here we prepared CdSe-based QDs with glass to reduce their leakage and examined their cytotoxicity using keratinocyte cells. The cytotoxicity of the QDs with glass was obviously lower than that of the commercial QDs with polymer, suggesting their safety for biological applications.     

Interaction of digestive enzymes with tunable light emitting quantum dots: a thorough Spectroscopic investigation

In this article, we have examined the direct spectroscopic and microscopic evidence of efficient quantum dots‐ α‐chymotrypsin (ChT) interaction. The intrinsic fluorescence of digestive enzyme is reduced in the presence of quantum dots through ground‐state complex formation. Based on the fluorescence data, quenching rate constant, binding constant, and number of binding sites are calculated under optimized experimental conditions. Interestingly, fluorescence quenching method clearly illustrated the size dependent interaction of MPA‐CdTe quantum dots. Conformational change of ChT was traced using synchronous fluorescence measurements, circular dichroism and FTIR spectroscopic methods. Furthermore, the AFM results revealed that the individual enzyme molecule dimensions were changed after interacting with quantum dot. Consequently, this result could be helpful for constructing safe and effective utilisation of QDs in biological applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Fluorescence sensing of nitric oxide in aqueous solution by triethanolamine‐modified CdSe quantum dots

The water‐soluble luminescent CdSe quantum dots were prepared by ligand exchange with triethanolamine (TEA). Oxygen can reversibly enhance the fluorescence of the synthesized quantum dots (TEA‐CdSe‐QDs) in aqueous solution. Nitric oxide radical (NO) can react easily with dissolved oxygen in water and was found to have a significant quenching effect on the fluorescence of the TEA‐CdSe‐QDs. The fluorescence responses were concentration‐dependent and can be well described by the typical Stern–Volmer equation. A good linear relationship (R² = 0.9963) was observed over the range 5.92 × 10^?7 to 1.85 × 10^?5 mol/L nitric oxide. Above this concentration was a second linear region ranging from 2.12 × 10^?5 to 1.12 × 10^?4 mol/L NO with a gentler slope. The detection limit, calculated following the 3σ IUPAC criteria, was 3.02 × 10^?7 mol/L. The interference effect of some common interferents such as nitrite (NO₂^?), nitrate (NO₃^?), glucose and l ‐ascorbic acid on the detection of NO was negligible for the proposed system, demonstrating the potential utility of this probe for the detection of NO in biological systems. The possible mechanism was also discussed. Copyright © 2009 John Wiley & Sons, Ltd.