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Since controlling hydrogen ion concentration ( i.e. pH) is fairly important in various fields, developing a facile pH detection method is highly desired. Owing to the superior optical properties, semiconductor quantum dots (QDs) have been developed as a promising alternative for organic fluorophores in fluorescence analysis. In this study, a hydrophilic p -aminothiophenol (pATP) capped CdSe/ZnS QDs (denoted as pATP-QDs) as a selective “turn-on” fluorescence probe for pH in aqueous media is reported. The pATP-QDs probe easily obtained via ligand exchange are characterized by various analytic techniques including ultraviolet-visible, fourier transform infrared, fluorescence, time-resolved fluorescence spectroscopies, and transmission electron microscope etc . pATP-QDs exhibits weak fluorescence since pATP acts as an effective hole trapper. As an organic base, pATP easily binds to proton and the formation of pATP-H + complex alters the energetic position of HOMO for pATP, which enables pATP-QDs unfavorable for the effective hole transfer. Thus, the QDs photoluminescence (PL) was switched on. PL “off-on” mode, high PL quantum yield of QDs as well as extremely high stability of pATP-H + complex (log K s =7.47) enables pATP-QDs to exhibit an excellent pH detection performance. Under optimal conditions, the present probe exhibits a good linear relationship between fluorescence response and pH values in pH range 3.2–6.0. Furthermore, the present probe exhibits a high selectivity for proton over other common cations and has been successfully used for pH detection in real water samples. [ABSTRACT FROM AUTHOR]

Two novel cyanine-based 1-amino-1-deoxy-β-glucose conjugates (Glu-1N-Cy3 and Glu-1N-Cy5) were designed, synthesized and their fluorescence characteristics were studied. Both Glu-1N-Cy3 and Glu-1N-Cy5 accumulate in living HT29 human colon cancer cells, which overexpress glucose transporters (GLUTs). The cellular uptake of the bioprobes was inhibited by natural GLUT substrate d -glucose and 2-deoxy- d -glucose. The GLUT specificity of the probes was validated with quercetin, which is both a permeant substrate via GLUTs and a high-affinity inhibitor of GLUT-mediated glucose transport. Competitive fluorometric assay for GLUT substrate cell uptake revealed that Glu-1N-Cy3 and Glu-1N-Cy5 are 5 and 10 times more sensitive than 2-NBDG, a leading fluorescent glucose bioprobe. This study provides fundamental data supporting the potential of these two conjugates as new powerful tools for GLUT-mediated theranostics, in vitro and in vivo molecular bioimaging and drug R&D. [ABSTRACT FROM AUTHOR]

The liver is the largest detoxification organ in the human body, with an array of functions that help support metabolism, immunity, digestion, and vitamin storage, among other functions, and maintains the health and stability of the internal environment. Liver injury causes the concentration fluctuation of related biomarkers, small molecules, and enzymes, and in turn, the structure and function of the liver are changed by those alterations. With the principles of early detection, early diagnosis, and early treatment, it is crucial to design and synthesise a tool for detecting related biomarkers during liver damage and lesion, among which fluorescent probes have attracted attention in recent years. In the course of liver diseases, the asialoglycoprotein receptors (ASGPR) are overexpressed on the hepatoma cells, which can specifically recognize the galactose variant. Several galactose-based fluorescent probes have been developed to target hepatocytes via specific receptor-mediated endocytosis and release fluorophores after reacting with specific small molecules and enzyme biomarkers. The change in fluorescence intensity reflects the level of substances, such as reactive oxygen species, reactive nitrogen species, reactive sulfur species, enzymes or metal ions, etc. The application of fluorescent probes in vivo can aid in monitoring the dynamic changes of endogenous and exogenous biomarkers. This Highlight provides an update on the progress, limitations, and prospects of galactose-based fluorescent probes applications in the early diagnosis of liver diseases. [ABSTRACT FROM AUTHOR]

Since zinc ions play an important role in various physiological activities, developing a facile detection method for Zn2+ is highly desirable. Owing to their superior optical properties, semiconductor quantum dots (QDs) have been developed as a promising alternative for organic fluorophores in fluorescence analysis. In this study, water soluble di-2-picolylamine-dithiolcarbamate (DPA-DTC)/proline-dithiolcarbamate (P-DTC) co-capped CdSe/ZnS QDs as a sensitive and selective “turn-on” fluorescence probe for Zn2+ was reported. The probe was easily obtained via ligand exchange. The initial bright fluorescence of QDs was effectively quenched by DPA-DTC that acted as an effective hole trapper. Upon complexation with Zn2+, the formation of Zn2+–DPA-DTC complex altered the energetic position of the HOMO for DPA-DTC, which rendered it unfavorable for the hole transfer. Thus the QDs PL was switched on. Under optimal conditions, a good linear relationship between the fluorescence response and Zn2+ concentration could be obtained in the range from 0.9 to 16 μM. The limit of detection for Zn2+ was found to be 0.7 μM. Furthermore, the present probe exhibited a high selectivity for Zn2+ over other common metal ions and was successfully used in the detection of Zn2+ in simulated biological fluids. [ABSTRACT FROM AUTHOR]

Abstract: Health or environmental issue caused by abnormal level of metal ions like Zn2+ or Cd2+ is a worldwide concern. Developing an inexpensive and facile detection method for Zn2+ and Cd2+ is in urgent demand. Due to their super optical properties, fluorescent quantum dots (QDs) have been developed as a promising alternative for organic dyes in fluorescence analysis. In this study, a CdTe QDs-based sensitive and selective probe for Zn2+ and Cd2+ in aqueous media was reported. The proposed probe worked in fluorescence “turn-on” mode. The initial bright fluorescence of CdTe QDs was effectively quenched by sulfur anions (S2−). The presence of Zn2+ (or Cd2+) can “turn-on” the weak fluorescence of QDs quenched by S2− due to the formation of ZnS (or CdS) passivation shell. Under optimal conditions, a good linear relationship between the fluorescence response and concentration of Zn2+ (or Cd2+) could be obtained in the range from 1.6 to 35μM (1.3–25μM for Cd2+). The limit of detection (LOD) for Zn2+ and Cd2+ were found to be 1.2 and 0.5μM, respectively. Furthermore, the present probe exhibited a high selectivity for Zn2+ and Cd2+ over other metal ions and was successfully used in the detection of Zn2+ or Cd2+ in real water samples. [ABSTRACT FROM AUTHOR]

Since hydrogen peroxide plays an important role in various fields, a facile, simple, highly selective, and stable analytic method for H2O2 is desirable. Semiconductor quantum dots (QDs) have acted as a potential alternative for organic fluorophores in fluorescence analytical fields due to their superior optical properties. Herein, we report hydrophilic p -hydroxy thiophenol (p -HTP) coated CdSe/ZnS QDs (denoted as p -HTP-QDs) acting as a selective fluorescence 'turn-on' probe for H2O2 in aqueous media. The obtained p -HTP-QD probe exhibits weak fluorescence, which stems from hole transfer from the QDs to p -HTP. The presence of H2O2 induces an oxidative structural transformation of p -HTP in p -HTP-QDs from a phenol structure to an α-hydroxy ketone derivative, which extremely reduces the driving force for hole transfer. Thus, the QDs photoluminescence (PL) was re-switched on. Under optimized conditions, an excellent linear relationship between fluorescence response and H2O2 concentration could be produced with a linear range from 0.309 to 4.900 mM. The limit of detection of this probe was found to be 0.135 mM. Moreover, the present probe exhibited a high selectivity of H2O2 over other reactive oxygen species/reactive nitrogen species (ROS/RNS) and was successfully used in the detection of H2O2 in real water samples. A quantum dots-based fluorescent probe obtained via ligand exchange by the use of commercially available p -hydroxy thiophenol as capping ligand was developed to detect H2O2 in aqueous media. The probe working in photoluminescence 'off-on' mode exhibited good H2O2 detection performance in real water samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • GPCRs enable the body to perceive changes in the internal or external environment. • GPCRs are pharmacologically important targets for drug discovery. • Fluorescent probes can monitor the behavior of receptors in disease conditions. Scientists Robert J. Lefkowitz and Brian K. Kobilka won the Nobel Prize in 2012 for reporting a groundbreaking discovery that revealed a crucial member of the receptor family, the G-protein-coupled receptors (GPCRs). GPCRs are the collective names for over 1,000 seven-transmembrane receptors that are responsible for multiple types of cell signaling responses. When activated by various stimuli (e.g., photons and small molecules), GPCRs interact with intracellular proteins to mediate downstream signals. The role of GPCRs in physiological and pathological processes renders them candidate targets in the development of many drugs. Recent research on GPCR structural biology has considerably improved our knowledge of GPCR signaling. However, the precise binding mechanism of diverse ligands to GPCRs to generate unique signal transduction and the involvement of GPCRs in disease pathogenesis remain controversial. The designing of tools for studying the pharmacology of GPCRs is critical to identifying safer and more effective therapies. Various molecular probes for investigating receptor structure and function have proven essential in GPCR research. This review summarizes the physiological functions of some GPCRs and discusses the molecular design strategies, applications, and development status of small molecule organic fluorescence probes of various GPCRs in humans. [ABSTRACT FROM AUTHOR]

As toxic gaseous pollution, carbon monoxide (CO) plays an essential role in many pathological and physiological processes, well-known as the third gasotransmitter. Owning to the reducibility of CO, the Pd0-mediated Tsuji-Trost reaction has drawn much attention in CO detection in vitro and in vivo, using allyl ester and allyl ether caged fluorophores as probes and PdCl2 as co-probes. Because of its higher decaging reactivity than allyl ether in the Pd0-mediated Tsuji-Trost reaction, the allyl ester group is more popular in CO probe design. However, during the application of allyl ester caged probes, it was found that bovine serum albumin (BSA) in the fetal bovine serum (FBS), an irreplaceable nutrient in cell culture media, could hydrolyze the allyl ester bond, and thus give erroneous imaging results. In this work, dicyanomethylenedihydrofuran (TCF) and dicyanoisophorone (DCI) were selected as electron acceptors for constructing near-infrared-emission fluorophores with electron donor phenolic OH. An allyl ester and allyl ether group were installed onto TCF-OH and DCI-OH, constructing four potential CO fluorescent probes, TCF-ester, TCF-ether, DCI-ester, and DCI-ether. Our data revealed that ester bonds of TCF-ester and DCI-ester could completely hydrolyze in 20 min, but ether bonds in TCF-ether and DCI-ether tolerate the hydrolysis of BSA and no released fluorescence was observed even up to 2 h. Moreover, passing through the screen, it was concluded that TCF-ether is superior to DCI-ether due to its higher reactivity in a Pd0-mediated Tsuji-Trost reaction. Also, the large stokes shift of TCF-OH, absorption and emission at 408 nm and 618 nm respectively, make TCF-ether desirable for fluorescent imaging because of differentiating signals from the excitation light source. Lastly, TCF-ether has been successfully applied to the detection of CO in H9C2 cells. [ABSTRACT FROM AUTHOR]

A CO probe with PEGylation is synthesized, achieving the detection of CO in pure water solution with high intensity color change and fluorescence enhancement. Importantly, this probe with high affinity to paper strips and low toxicity to living cells is successfully used for sensing CO in air and in living cells. [ABSTRACT FROM AUTHOR]

Abstract: Fluorescence analysis by means of a single fluorescence signal output usually leads to the signal fluctuation caused by various external factors. Ratiometric fluorescence probes that can significantly eliminate the external effects by self-calibration of two different emission bands are preferable for the detection of real samples. In this work, we designed a dual-emission quantum dots (QDs) nanocomposite as a ratiometric probe for the visual detection of Hg2+. The dual-emission QDs nanocomposite consists of two differently sized CdTe/CdS QDs. The red-emitting larger sized CdTe/CdS QDs embeded in silica nanoparticles are insensitive to Hg2+, while the green-emitting smaller sized ones are covalently conjugated onto the silica nanoparticles surface and sensitive to Hg2+. The addition of Hg2+ can only quench green fluorescence in the dual-emission QDs nanocomposites, which triggers the change of fluorescence intensity ratio of two different emission wavelengths and hence induces the evolution of fluorescence color of the probe solution with variation of Hg2+ concentration. Based on this feature, the dual-emission QDs nanocomposites can be used to develop a ratiometric fluorescence probe for the visual detection of Hg2+. Under the optimized conditions, the ratiometric fluorescence QDs probe shows a linear relationship between fluorescence intensity ratio and Hg2+ concentration in the range of 5–300nM. The detection limit of this probe was found to be 3.1nM. This ratiometric assay also exhibits a high selectivity and it has been successfully used in the determination of Hg2+ content in fetal bovine serum and human urine. [Copyright &y& Elsevier]