Read all about it: Graphene oxide (GO) sensors can be formed on microporous membranes for the visual detection of peptides, protein, and DNA. Silver nanoparticles (AgNPs) modified with ligands, ...antibodies, and oligonucleotides adsorb onto the surface of GO nanosheets and quench the fluorescence. Upon addition of analytes, the AgNPs disassociate from the nanosheets, and thus the fluorescence is immediately restored.
•Automatic measurement of particle size distribution from micrographs.•The proposed algorithm is mainly based on local adaptive Canny edge detection and modified circular Hough transform.•The ...robustness and reliability of the algorithm were verified by several micrographs with different complexity.
To obtain size distribution of nanoparticles, scanning electron microscope (SEM) and transmission electron microscopy (TEM) have been widely adopted, but manual measurement of statistical size distributions from the SEM or TEM images is time-consuming and labor-intensive. Therefore, automatic detection methods are desirable. This paper proposes an automatic image processing algorithm which is mainly based on local adaptive Canny edge detection and modified circular Hough transform. The proposed algorithm can utilize the local thresholds to detect particles from the images with different degrees of complexity. Compared with the results produced by applying global thresholds, our algorithm performs much better. The robustness and reliability of this method have been verified by comparing its results with manual measurement, and an excellent agreement has been found. The proposed method can accurately recognize the particles with high efficiency.
A simple and effective ratiometric fluorescence nanosensor for the selective detection of Cu(2+) has been developed by covalently connecting the carboxyl-modified red fluorescent cadmium telluride ...(CdTe) quantum dots (QDs) to the amino-functionalized blue fluorescent carbon nanodots (CDs). The sensor exhibits the dual-emissions peaked at 437 and 654 nm, under a single excitation wavelength of 340 nm. The red fluorescence can be selectively quenched by Cu(2+), while the blue fluorescence is a internal reference, resulting in a distinguishable fluorescence color change from pink to blue under a UV lamp. The detection limit of this highly sensitive ratiometric probe is as low as 0.36 nM, which is lower than the U.S. Environmental Protection Agency (EPA) defined limit (20 μM). Moreover, a paper-based sensor has been prepared by printing the hybrid carbon dots-quantum dots probe on a microporous membrane, which provides a convenient and simple approach for the visual detection of Cu(2+). Therefore, the as-synthesized probe shows great potential application for the determination of Cu(2+) in real samples.
Intracellular lipid metabolism occurs in lipid droplets (LDs), which is critical to the survival of cells. Imaging LDs is an intuitive way to understand their physiology in live cells. However, this ...is limited by the availability of specific probes that can properly visualize LDs in vivo. Here, an LDs-specific red-emitting probe is proposed to address this need, which is not merely with an ultrahigh signal-to-noise (S/N) ratio and a large Stokes shift (up to 214 nm) but also with superior resistance to photobleaching. The probe has been successfully applied to real-time tracking of intracellular LDs behaviors, including fusion, migration, and lipophagy processes. We deem that the proposed probe here offers a new possibility for deeper understanding of LDs-associated behaviors, elucidation of their roles and mechanisms in cellular metabolism, and determination of the transition between adaptive lipid storage and lipotoxicity as well.
To detect trace trinitrotoluene (TNT) explosives deposited on various surfaces instantly and on-site still remains a challenge for homeland security needs against terrorism. This work demonstrates a ...new concept and its utility for visual detection of TNT particulates on various package materials. The concept takes advantages of the superior fluorescent properties of quantum dots (QDs) for visual signal output via ratiometric fluorescence, the feasibility of surface grafting of QDs for chemical recognition of TNT, and the ease of operation of the fingerprint lifting technique. Two differently sized CdTe QDs emitting red and green fluorescences, respectively, have been hybridized by embedding the red-emitting one in silica nanoparticles and covalently linking the green-emitting one to the silica surface, respectively, to form a dual-emissive fluorescent hybrid nanoparticle. The fluorescence of red QDs in the silica nanoparticles stays constant, whereas the green QDs functionalized with polyamine can selectively bind TNT by the formation of Meisenheimer complex, leading to the green fluorescence quenching due to resonance energy transfer. The variations of the two fluorescence intensity ratios display continuous color changes from yellow-green to red upon exposure to different amounts of TNT. By immobilization of the probes on a piece of filter paper, a fingerprint lifting technique has been innovated to visualize trace TNT particulates on various surfaces by the appearance of a different color against a yellow-green background under a UV lamp. This method shows high selectivity and sensitivity with a detection limit as low as 5 ng/mm2 on a manila envelope and the attribute of being seen with the naked eye.
The instant and on-site detection of trace aqueous mercuric ion still remains a challenge for environmental monitoring and protection. This work demonstrates a new analytical method and its utility ...for visual detection of aqueous Hg2+ on the basis of a novel water-soluble CdSe-ZnS quantum dots (QDs) functionalized with a bidentate ligand of 2-hydroxyethyldithiocarbamate (HDTC). The fluorescence of the aqueous HDTC modified QDs (HDTC-QDs) could be selectively and efficiently quenched by Hg2+ through a surface chelating reaction between HDTC and Hg2+, and the detection limit was measured to be 1 ppb. Most interestingly, the orange fluorescence of the HDTC-QDs gradually changes to red upon the increasing amount of Hg2+ added besides the decreasing of the fluorescence intensity. By taking advantage of this optical phenomenon, a paper-based sensor for aqueous Hg2+ detection has been developed by immobilizing the HDTC-QDs on cellulose acetate paper which has low background fluorescence in the wavelength range. The paper-based sensor showed high sensitivity and selectivity for Hg2+ visual detection. When Hg2+ was dropped onto the paper-sensor, an obviously distinguishable fluorescence color evolution (from orange to red) could be clearly observed depending on the concentration of Hg2+. The limit of detection of the visual method for aqueous Hg2+ detection was as low as 0.2 ppm. The very simple and effective strategy reported here should facilitate the development of portable and reliable fluorescence chemosensors for mercuric pollution control.
Classical pH test papers are widely used to measure the acid–base degree of media in a qualitative or semiquantitative manner. However, the extension of portable and inexpensive methods to a wide ...range of analytes so as to eliminate the tediousness of instrumental assays remains unsuccessful. Here, we report a novel kind of dual-colored carbon dot (CD) ratiometric fluorescent test paper for the semiquantitative assay of copper ions (Cu2+) by a dose-sensitive color evolution. The preparation of the test paper is based on the following two interesting findings: on the one hand, residual p-phenylenediamine at the surface of as-synthesized red CDs (r-CDs) efficiently binds Cu2+ ions to produce a strong visible absorption that overlaps the emission of blue CDs (b-CDs); on the other hand, the Cu2+ ions render the adsorption of small b-CDs onto the surface of larger r-CDs through their dual-coordinating interactions with the surface ligands of both r-CDs and b-CDs. These two mechanisms lead to a specific spectral energy transfer to quench the fluorescence of b-CDs with a sensitive detection limit of 8.82 nM Cu2+, whereas the red fluorescence of r-CDs is unaffected as a stable internal standard. Ratiometric fluorescent test papers have been prepared using a mixture of r-CDs and b-CDs (1:7) as ink by jetprinting on a piece of paper. With the addition of Cu2+ ions, the blue test paper produces a consecutive wide-colored evolution from blue to orange-red, with a dose-discerning ability as low as 25 nM.
Satellite laser ranging (SLR) stations in the International Laser Ranging Service (ILRS) global tracking network come in different shapes and sizes and were built by different institutions at ...different times using different technologies. In addition, those stations that have upgraded their systems and equipment are often operating a complementary mix of old and new. Such variety reduces the risk of systematic errors across all ILRS stations, and an operational advantage at one station can inform the direction and choices at another station. This paper describes the evolution of the ILRS network and the emergence of a new generation of SLR station, operating at kHz repetition rates, firing ultra-short laser pulses that are timestamped by epoch timers accurate to a few picoseconds. It discusses current trends, such as increased automation, higher repetition rate SLR and the challenges of eliminating systematic biases, and highlights possibilities in new technology. In addition to meeting the growing demand for laser tracking support from an increasing number of SLR targets, including a variety of Global Navigation Satellite Systems satellites, ILRS stations are striving to: meet the millimetre range accuracy science goals of the Global Geodetic Observing System; make laser range measurements to space debris objects in the absence of high optical cross-sectional retro-reflectors; further advances in deep space laser ranging and laser communications; and demonstrate accurate laser time transfer between continents.
The white backlight in displays is generated by optimizing the proportions of individual emitters with different wavelengths by variations in materials composition, phase, and structure. Color pixels ...usually result from the separation of white light or the excitation with multiwavelength or multipulse sources. However, it is a challenge to develop a material that comprises a single structure and emits over the full visible spectrum, but where the emission wavelengths can be controlled by a simple excitation source. Herein, we report an upconversion nanostructure that incorporates several lanthanide ions in the same core@shell@shell structure. The combination of multiple narrow spectral bands results in the emission of white light. The emission colors can be tuned by changing the excitation power density, which manipulates the photon transfer pathways. Applications such as flat‐panel displays and imaging have been demonstrated.
Seeing the light: An upconversion nanostructure comprises several lanthanide ions integrated in a single system. The balance of numerous narrow emission bands covering the full visible spectrum results in white‐light emission. The emission colors can be determined by changing the excitation power density (see picture), which manipulates the photon transfer pathways to bring potential applications such as multicolor displays or imaging.
Visualizing and dynamic tracking lipid droplets (LDs) are of great importance to biological research. Herein, two-photon absorption fluorescent small bioprobes based on lipophilic coumarin were ...developed, which exhibited high selectivity toward LDs in HeLa cells. Because of good biocompatibility and excellent photostability, the probes were applied to realize specific super-resolution visualization of the intracellular LDs in HeLa cells, offering us the quantitative results of the amount and diameters of LDs as well. Furthermore, the bioprobes were capable of monitoring the movements of the LDs in real time. We believe that bioprobes would provide new avenues to designing bioimaging and biological diagnosis.
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