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Since inorganic phosphate ion (PO 4 3- is highly desired. Owing to the superior optical properties, graphene quantum dots (GQDs) have been developed as a promising emitting material in fluorescence analysis. Herein, we reported the first example of negatively charged molybdate-mediated nitrogen doped graphene quantum dots (Mo 4 3- is highly desired. Owing to the superior optical properties, graphene quantum dots (GQDs) have been developed as a promising emitting material in fluorescence analysis. Herein, we reported the first example of negatively charged molybdate-mediated nitrogen doped graphene quantum dots (Mo 7 O 24 6- -mediated N-GQDs) as a fluorescence "off-on" probe for PO 4 3- via "anion ion-mediated" strategy. The N-GQDs was firstly modified with Mo 7 O 24 6- through a complex bonding system containing ionic and hydrogen bonds. The formation of N-GQDs/Mo 7 O 24 6- complex leaded to photoluminescence (PL) quenching of N-GQDs. In the presence of PO 4 3- , strong affinity between PO 4 3- and Mo 7 O 24 6- produced ammonium phosphomolybdate, which destroyed the pre-formed N-GQDs/Mo 7 O 24 6- structure and detached Mo 7 O 24 6- from N-GQDs surface. Thus, the PL of N-GQDS was in turn switched on. Under optimal conditions, this probe exhibited a good linear relationship between PL response and PO 4 3- concentration in the range from 7.0 to 30.0 μM with a limit of detection of 50 nM. Also this probe with high selectivity and sensitivity has been successfully used to sense PO 4 3- in natural water, biological fluid, and living cells., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Development of the fluorescent pH detection method is promising due to the sensitivity, easy operation, and low-cost, etc. However, traditional organic fluorophores have still some disadvantages such as the tedious preparation and purification as well as low photostability and water solubility, which limits the rapid detection application. Semiconductor quantum dots (QDs) have recently risen to prominence as an alternative for organic fluorophores in fluorescence analysis by virtue of their convenient synthesis and superior optical properties. In this study, we report on sodium 4-mercaptophenolate functionalized CdSe/ZnS QDs (denoted as - OPhS-QDs), which can serve as a selective "on-off" fluorescence probe for aqueous media pH. - OPhS-QDs exhibit strong fluorescence in near neutral medium. As a Lewis organic base, - OPhS- moieties on QDs surface easily binds to proton under acidic conditions to yield 4-mercaptophenol capped QDs (i.e. HOPhS-QDs), which acts as an efficient hole trapper. As a result, the QDs photoluminescence (PL) is switched off. Under optimal conditions, the present probe exhibits a good linear relationship between fluorescence response and pH values in the pH range 3.0-5.2. 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., (Copyright © 2017 John Wiley & Sons, Ltd.)

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 Hg(2+). 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 Hg(2+), while the green-emitting smaller sized ones are covalently conjugated onto the silica nanoparticles surface and sensitive to Hg(2+). The addition of Hg(2+) 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 Hg(2+) concentration. Based on this feature, the dual-emission QDs nanocomposites can be used to develop a ratiometric fluorescence probe for the visual detection of Hg(2+). Under the optimized conditions, the ratiometric fluorescence QDs probe shows a linear relationship between fluorescence intensity ratio and Hg(2+) concentration in the range of 5-300 nM. The detection limit of this probe was found to be 3.1 nM. This ratiometric assay also exhibits a high selectivity and it has been successfully used in the determination of Hg(2+) content in fetal bovine serum and human urine., (© 2013 Elsevier B.V. All rights reserved.)

Facile detection of dopamine (DA) in biological samples for diagnostics remains a challenge. This paper reported an effective fluorescent sensor based on adenosine capped CdSe/ZnS quantum dots (A-QDs) for highly sensitive detection of DA in human urine samples. In this assay, adenosine serves as a capping ligand or stabilizer for QDs to render high-quality QDs dispersed in water, and as a receptor for DA to attach DA onto the surface of A-QDs. DA molecules can bind to A-QDs via non-covalent bonding, leading to the fluorescence quenching of A-QDs due to electron transfer. The A-QDs based fluorescence probe showed a limit of detection (LOD) of ca. 29.3 nM for DA detection. This facile method exhibited high selectivity and anti-interference in the presence of amino acid, ascorbic acid (AA), uric acid (UA) and glucide with 100-fold higher concentration in PBS solution. Furthermore, it was also successfully used in the detection of DA in the human urine samples with quantitative recoveries (94.80-103.40%).

Since zinc ions play an important role in various physiological activities, developing a facile detection method for Zn(2+) 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 Zn(2+) 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 Zn(2+), the formation of Zn(2+)-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 Zn(2+) concentration could be obtained in the range from 0.9 to 16 μM. The limit of detection for Zn(2+) was found to be 0.7 μM. Furthermore, the present probe exhibited a high selectivity for Zn(2+) over other common metal ions and was successfully used in the detection of Zn(2+) in simulated biological fluids.

Health or environmental issue caused by abnormal level of metal ions like Zn(2+) or Cd(2+) is a worldwide concern. Developing an inexpensive and facile detection method for Zn(2+) and Cd(2+) 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 Zn(2+) and Cd(2+) 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 (S(2-)). The presence of Zn(2+) (or Cd(2+)) can "turn-on" the weak fluorescence of QDs quenched by S(2-) due to the formation of ZnS (or CdS) passivation shell. Under optimal conditions, a good linear relationship between the fluorescence response and concentration of Zn(2+) (or Cd(2+)) could be obtained in the range from 1.6 to 35 μM (1.3-25 μM for Cd(2+)). The limit of detection (LOD) for Zn(2+) and Cd(2+) were found to be 1.2 and 0.5 μM, respectively. Furthermore, the present probe exhibited a high selectivity for Zn(2+) and Cd(2+) over other metal ions and was successfully used in the detection of Zn(2+) or Cd(2+) in real water samples., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Quantum dots (QDs) usually act as energy donors in Förster resonant energy transfer (FRET) in various application fields. We report, for the first time, a FRET process from a conventional naphthalimide chromophore 1 to CdSe/ZnS core/shell QDs (acting as energy acceptors) in (1)-QDs hybrid system in solution. This FRET process is supported by various spectroscopies, such as steady-state and time-resolved photoluminescence (PL) as well as PL excitation spectra. The highest energy transfer efficiency is estimated to be about 0.37. Interestingly, the role of QDs in FRET can be specifically reversed (from energy acceptors to energy donors) with the use of QDs with larger band-gaps.

Herein, we report the synthesis of novel narrow band gap phosphorus sulfide quantum dots (PSQDs)‐modified bismuth oxybromide (Bi24O31Br10) heterojunction (noted as BOB/PS) for the highly efficient photo‐degradation of hazardous organic pollutants including rhodamine B (RhB), methyl orange (MO), and malachite green (MG). Such a high photocatalytic activity of BOB/PSQDs heterojunction derives from the improved visible‐light response capacity, high surface area/pore volume, and suitable band structure for efficient electron transfer to generate reactive oxygen species (ROS). ROS trapping experiments demonstrate that hydroxy (⋅OH) and superoxide radicals (⋅O2−) play important roles in the photo‐degradation. A possible S‐scheme mechanism for the enhanced photocatalytic activity of BOB/PS is proposed. [ABSTRACT FROM AUTHOR]

Herein, we report a novel narrow band gap sulfur quantum dots (SQDs)‐modified BiOCl heterojunction (BOC/SQDs) for the photo‐degradation of hazardous organic pollutants via rhodamine B (RhB)‐sensitization. Such a high photocatalytic activity of RhB‐sensitized BOC/SQDs heterojunction derives not only from the improved visible‐light response capacity, high surface area/pore volume, suitable band structure for efficient electron transfer, but also from the surge of the number of electrons via RhB‐sensitization for reactive oxygen species (ROS) generation. Superoxide radicals (⋅O2−), holes (h+), and hydrogen peroxide (H2O2) play the important roles in the photo‐degradation. A possible mechanism for RhB‐sensitization enhanced degradation performance for treating organic pollutants by BOC/SQDs is proposed. The combination of dye‐sensitization with BOC/SQDs heterojunction can explore a greener, energy saving, and efficient photo‐induced nanoplatform for treating organic pollutants in aqueous media. [ABSTRACT FROM AUTHOR]

Abstract: Development of the fluorescent pH detection method is promising due to the sensitivity, easy operation, and low‐cost, etc. However, traditional organic fluorophores have still some disadvantages such as the tedious preparation and purification as well as low photostability and water solubility, which limits the rapid detection application. Semiconductor quantum dots (QDs) have recently risen to prominence as an alternative for organic fluorophores in fluorescence analysis by virtue of their convenient synthesis and superior optical properties. In this study, we report on sodium 4‐mercaptophenolate functionalized CdSe/ZnS QDs (denoted as −OPhS‐QDs), which can serve as a selective “on–off” fluorescence probe for aqueous media pH. −OPhS‐QDs exhibit strong fluorescence in near neutral medium. As a Lewis organic base, −OPhS‐ moieties on QDs surface easily binds to proton under acidic conditions to yield 4‐mercaptophenol capped QDs (i.e. HOPhS‐QDs), which acts as an efficient hole trapper. As a result, the QDs photoluminescence (PL) is switched off. Under optimal conditions, the present probe exhibits a good linear relationship between fluorescence response and pH values in the pH range 3.0–5.2. 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]

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]

Pentaerythritol tetrakis 3-mercaptopropionate (PTMP) grafted poly(acryl acid) (PAA) ionic hydrophilic oligomer PAA-PTMP (PP) and dihydrolipoic acid (DHLA) grafted methoxypoly(ethylene glycol) (mPEG) nonionic hydrophilic oligomer mPEG-DHLA (PD) have been designed, synthesized and used as co-capping ligands in water-solubilization of hydrophobic quantum dots (QDs) via ligand exchange. The obtained oligomers with multi-thiol groups could bind strongly to the surface atoms of QDs. Meanwhile, the carboxyl groups (from PP) and mPEG segment (from PD) can render QDs water-soluble, and the free carboxylic groups can possibly be used for the further bioconjugation. The resulting water-soluble QDs have been characterized by ultraviolet-visible (UV-Vis), fluorescence, Fourier transform infrared (FTIR) spectroscopy as well as transmission electron microscopy (TEM) and dynamic light scattering (DLS) techniques. The water-soluble QDs have relatively small hydrodynamic size (1012 nm), and importantly, retain high fluorescence quantum yields (up to 45%) compared with that of the originally hydrophobic QDs (49%). In addition, they have tunable surface charges and show excellent colloidal stability over a relatively broad pH range (), in high salt concentration, and even after thermal treatment at 100C. These results indicate that the water-soluble QDs coated by PP and PD oligomers have potential applications in cellular imaging and biosensor. Ionic and nonionic hydrophilic ligands have been successfully synthesized and were used as capping ligands for the access to water-soluble quantum dots. The resulting QDs possess relatively small hydrodynamic size, high fluorescence quantum yield, and exhibit excellent colloidal stability over a relatively broad pH range, in high salt concentration, and even after thermal treatment at high temperature. Furthermore, the free carboxylic groups at terminal of ligands (PP) may be suitable for further bioconjugation. [ABSTRACT FROM AUTHOR]

[Display omitted] Multichannel detection platforms for S 2 O 8 2− by fluorescent carbon quantum dots (CQDs) have been developed. The detection of S 2 O 8 2− was realized by one-pot derived CQDs via fluorescence on–off, colorimetric, ratiometric fluorescent, and ratiometric colorimetric modes. The pure water phase application environment and ratiometric colorimetric/fluorescent detection modes facilitate our detection platforms to have broader application prospects. • One-pot reaction derived carbon quantum dots for S 2 O 8 2− detection. • Carbon quantum dots based four channel detection platform for S 2 O 8 2− was developed. • The multichannel platform exhibiting high selectivity to S 2 O 8 2−. • Rapid response and naked eye recognition suitable for real-time/on-site detection. Here we report the multichannel detection of S 2 O 8 2− by fluorescent carbon quantum dots (CQDs) in aqueous media. The one-pot reaction derived yellow emitting CQDs (Y-CQDs) and red emitting ones (R-CQDs) were used to establish the multichannel detection platform (i.e. fluorescence on–off, colorimetric, and ratio fluorescent/colorimetric) for S 2 O 8 2− based on their different responses to S 2 O 8 2−. [ABSTRACT FROM AUTHOR]

Abstract: A new bifunctional ligand (IA-PEG-DTC), poly(ethylene glycol) (PEG) appended dithiocarbamate derived from iminodiacetic acid, has been designed and synthesized. The obtained IA-PEG-DTC ligand with the dithiocarbamate group strongly bonding to the surface atom of quantum dots (QDs), the PEG segment rendering QDs water-soluble, and the free carboxylic group available for further bioconjugation was used successfully to transfer initial oil-soluble QDs into water-soluble ones. The resulting IA-PEG-DTC capped water-soluble QDs have relatively small hydrodynamic size, and importantly, retain high fluorescence quantum yield of the original hydrophobic QDs. In addition, the obtained water-soluble QDs exhibit excellent colloidal stability under conditions of wide pH range (2–13), long-term UV-irradiation, the boiling state, and high salt concentrations. These results indicate that the water-soluble QDs coated by the bifunctional IA-PEG-DTC ligand have potential for applications in cellular imaging and biosensor. [Copyright &y& Elsevier]

An I 2 -mediated N-GQDs was developed to fluorescent probes for S 2 O 3 2− and oxidative compounds such as H 2 O 2 via iodimetry reaction oriented strategy. This nanoprobe with the excellent selectivity and sensitivity (93 pM) has been successfully applied in biological fluids and living cells for S 2 O 3 2−. [Display omitted] • a I 2 -mediated N-GQDs nanocomposite as a fluorescence probe for S 2 O 3 2− and oxidative compounds. • S 2 O 3 2− detection by I 2 -mediated N-GQDs via "iodimetry reaction oriented" strategy. • I 2 -mediated N-GQDs exhibiting the high selectivity and the super low LOD of 93 pM towards S 2 O 3 2−. • successful detection of S 2 O 3 2− in real water samples, biological fluids, and living cells. Owing to the huge threat to human health and environment from thiosulfate anion (S 2 O 3 2−) widely used in various fields, the development of an effective detection method for S 2 O 3 2− is urgently desired. Herein, we developed an iodine (I 2) mediated nitrogen-doped graphene quantum dots (I 2 -mediated N-GQDs) as a fluorescence "off-on" probe for S 2 O 3 2− by iodimetry reaction oriented strategy. Firstly, I 2 interacted with N-GQDs to form non-fluorescent N-GQDs/I 2 complex due to the inner filter effect (IFE). In the presence of S 2 O 3 2−, the iodimetry reaction between I 2 and S 2 O 3 2− disintegrated N-GQDs/I 2 complex and re-switched on the quenched photoluminscence of N-GQDs. The I 2 -mediated N-GQDs nanoprobe with a limit of detection down to 93 pM has been successfully used to sense S 2 O 3 2- in biological fluids and living cells. Moreover, the I 2 -mediated N-GQDs/S 2 O 3 2− nanoplatform could further detect oxidative compounds such as hydrogen dioxide, dichromate, permanganate, iron ion (III), copper ion (II), and cerium ion (IV). [ABSTRACT FROM AUTHOR]