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The dynamics of DNA and RNA structures in live cells are important for understanding cell behaviors, such as transcription activity, protein expression, cell apoptosis, and hereditary disease, but are challenging to monitor in live organisms in real time. The difficulty is largely due to the lack of photostable imaging probes that can distinguish between DNA and RNA, and more importantly, are capable of crossing multiple membrane barriers ranging from the cell/organelle to the tissue/organ level. We report the discovery of a cationic carbon quantum dot (cQD) probe that emits spectrally distinguishable fluorescence upon binding with double‐stranded DNA and single‐stranded RNA in live cells, thereby enabling real‐time monitoring of DNA and RNA localization and motion. A surprising finding is that the probe can penetrate through various types of biological barriers in vitro and in vivo. Combined with standard and super‐resolution microscopy, photostable cQDs allow time‐lapse imaging of chromatin and nucleoli during cell division and Caenorhabditis elegans (C. elegans) growth. [ABSTRACT FROM AUTHOR]

Primary alkylamines are generally used as ligands for the synthesis of colloidal II–VI group quantum dots (QDs). However, knowledge of the effects of these ligands on the nanocrystalline structure in the literature is scarce and often contradictory. Herein, the structural evolution of CdSe QDs synthesized with primary alkylamines of different chain lengths and concentrations and at various reaction temperatures has been investigated. Absorption spectroscopy, XRD, HRTEM and Fourier transform imaging were applied to characterize the structure of the CdSe QDs. The results demonstrate that CdSe QDs preferentially form the wurtzite structure with shorter-chain and higher-concentration primary alkylamines at higher reaction temperatures. In contrast, the zinc blende structure is formed in the presence of longer-chain and lower-concentration primary alkylamines at lower reaction temperatures. By precisely controlling the experimental conditions, CdSe QDs with a pure zinc blende phase have been successfully achieved. [ABSTRACT FROM AUTHOR]

Cesium lead halide quantum dots (QDs) have tunable photoluminescence that is capable of covering the entire visible spectrum and have high quantum yields, which make them a new fluorescent materials for various applications. Here, the synthesis of CsPbX3 (X = Cl, Br, I, or mixed Cl/Br and Br/I) QDs by direct ion reactions in ether solvents is reported, and for the first time the synergetic effects of solvent polarity and reaction temperature on the nucleation and growth of QDs are demonstrated. The use of solvent with a low polarity enables controlled growth of QDs, which facilitates the synthesis of high-quality CsPbX3 QDs with broadly tunable luminescence, narrow emission width, and high quantum yield. A QD white LED (WLED) is demonstrated by coating the highly fluorescent green-emissive CsPbBr3 QDs together with red phosphors on a blue InGaN chip, which presents excellent warm white light emission with a high rendering index of 93.2 and color temperature of 5447 K, suggesting the potential applications of highly fluorescent cesium lead halide perovskite QDs as an alternative color converter in the fabrication of WLEDs. [ABSTRACT FROM AUTHOR]

A facile green approach has been developed to control the growth regime in the aqueous synthesis of CdxZn1-xTe semiconductor quantum dots (QDs) based on the electrochemistry method. The Low growth temperature and slow injection of Te precursor are used to prolong the diffusion controlled stage and thus suppress Ostwald ripening during the nanocrystal growth. The experimental results showed that a low concentration of Te precursor will definitely influence the growth procedure. The UV-visible absorption spectra, as well as transmission electron microscopy (TEM) shows the QDs a good monodispersity at any interval of the reaction procedure. The high-resolution transmission electron microscopy (HRTEM) images and powder X-ray diffraction (XRD) pattern suggested that the as-prepared QDs have high crystallinity and cubic structure. The size and composition-dependent fluorescent emission wavelength of the resultant CdxZn1-xTe alloyed QDs can be tuned from 460 to 610 nm, and their photoluminescent quantum yield can reach up to 70%. Especially in the wavelength range of 510-578 nm, the overall PL QYs of the as-prepared CdxZn1-xTe QDs were above 50%. The current work suggests that electrochemical method is an attractive approach to the synthesis of high-quality II-VI ternary alloyed semiconductor QDs at large-scale with a prominent cost advantage. [ABSTRACT FROM AUTHOR]

Pesticides abuse has drawn considerable attention in agriculture, environment and food safety in recent years. How to selective and on-site detection of pesticide residues with rapid operation and low cost is still a hot topic. In this work, we report a novel method for the detection of pesticide thiram using phosphorescent Mn-doped ZnS quantum dots (ZnS:Mn 2+ QDs) combined by an affinity reaction between thiram and Ag + ions. On the one hand, the phosphorescence of as-prepared ZnS:Mn 2+ QDs at 590 nm can be effectively quenched by Ag + ions due to the direct cation-exchange reaction at the surface of QDs. On the other hand, the presence of thiram can inhibit phosphorescence quenching through the formation of stable Ag-thiram complex. This inhibition resulted in a linear recovery in emission intensity with increasing the amount of thiram, which enables thiram residues to be identified under the UV light illumination. In buffer condition, thiram could be detected within the concentration range of 50 nM–2.5 μM with a detection limit of 25 nM. Moreover, the proposed method has been successfully applied to thiram residues identification at fresh fruit peels. The investigation provides a profile for instant and visual detection of surface residues using doped quantum dots. [ABSTRACT FROM AUTHOR]

Fluorescent colorimetric test strips normally have a narrow dynamic detection–range due to the limited responsive range from single responsive materials, which cannot meet the wide detection requirement in practical applications. Herein, we developed an approach to detect uranyl ions (UO 2 2+) with a broad detection range using the synthesized ZnS:Mn quantum dots (QDs) modified Zn 2 GeO 4 nanoellipsoids (Zn 2 GeO 4 @ZnS:Mn NEs), containing two responsive materials with the opposite signal responses at different UO 2 2+ concentrations. Specifically, a red to chocolate color change was observed at low analyte concentrations (0.01–100 μM) resulting from the photoinduced electron transfer effect from ZnS:Mn QDs to UO 2 2+. A sequentially olive drab to green color change has been observed when further increasing the UO 2 2+ concentration (100–1000 μM) as a result of the antenna effect between Zn 2 GeO 4 nanoellipsoids and UO 2 2+. In addition, a low-cost and portable fluorescent test strip has been further fabricated through embedding Zn 2 GeO 4 @ZnS:Mn NEs on a microporous structure membrane, demonstrating a facile yet effective colorimetric response to UO 2 2+ in lab water, lake water, and seawater with a wide dynamic range. Therefore, it is potentially attractive for real-time and on-site detection of UO 2 2+ in sudden-onset situations. [Display omitted] • A simple hydrothermal approach to synthesize Zn 2 GeO 4 @ZnS:Mn nanoellipsoids. • Expanding UO 2 2+ detection range up to 5 orders by combining PET and antenna effect. • A distinct color change form red to green at various UO 2 2+ concentrations. • Fluorescent test strip to quantitative detect UO 2 2+ by RGB analysis. [ABSTRACT FROM AUTHOR]

Abstract: A low-cost, green, and reproducibly non-injection one-pot synthesis of high-quality CdS quantum dots (QDs) is reported. The synthesis was performed in the open air by mixing precursors cadmium stearate and S powder into a new solvent N-oleoylmorpholine. An overlapped nucleation-growth stage followed by a dominated growth stage was observed. The resulting QDs exhibited well-resolved absorption fine substructure and a dominant band-edge emission with a narrow size distribution (the full width at half maximum (fwhm) was only 22–24nm). The maximum photoluminescence (PL) quantum yield (QY) was as high as 46.5%. Highly monodispersed CdS QDs with tunable sizes and similar PL fwhm and QYs could also be obtained from the CdS QDs in a large-scale synthesis. The high-resolution transmission electron microscopy (HRTEM) images and powder X-ray diffraction (XRD) pattern suggested that the as-prepared QDs with high crystallinity had a cubic structure. A significant PL improvement and a continuous QY increase for the CdS QDs were observed during a long storage time in air and in a glovebox under room temperature. A slow surface reconstruction was proposed to be the cause for the PL enhancement of CdS QDs. [Copyright &y& Elsevier]

Abstract: High-quality CdSe quantum dots with less common zinc blende structure were prepared in non-coordinating solvent 1-octadecene, with environment-friendly N,N-dimethyl-oleoyl amide as an alternative chemical to replace trioctylphoshine for Se powder, oleic acid as primary capping ligands, and benzophenone as secondary ligands. The temporal evolution of the optical properties of the nanocrystals with different growth temperature was monitored. Significant redshifts occurred with the increase of the growth temperature. The sharpness of the first absorption peaks and the narrow emission band with full width at the half-maximum of about 30nm indicates that the size distribution of the resulting quantum dots is narrow. [Copyright &y& Elsevier]

Abstract: A much cheaper and greener route to monodisperse CdSe quantum dots (QDs) with zinc-blende structure has been developed. The N,N-dimethyl-oleoyl amide was chosen as the solvent, eliminating the needs of air-sensitive and toxic trioctylphosphine (TOP) or tributylphosphine (TBP), and cadmium oxide and elemental selenium as sources. The as-prepared CdSe QDs show an apparent blue-shift in the ultraviolet and visible (UV–vis) absorption peaks. The emission peak of the QDs can be tuned by changing synthesis time only. [Copyright &y& Elsevier]