Fanyong Yan

The quenching of the fluorescence of carbon dots: A review on mechanisms and applications

AbstractCarbon dots (CDs) possess unique optical properties such as tunable photoluminescence (PL) and excitation dependent multicolor emission. The quenching and recovery of the fluorescence of CDs can be utilized for detecting analytes. The PL mechanisms of CDs have been discussed in previous articles, but the quenching mechanisms of CDs have not been summarized so far. Quenching mechanisms include static quenching, dynamic quenching, Förster resonance energy transfer (FRET), photoinduced electron transfer (PET), surface energy transfer (SET), Dexter energy transfer (DET) and inner filter effect (IFE). Following an introduction, the review (with 88 refs.) first summarizes the various kinds of quenching mechanisms of CDs (including static quenching, dynamic quenching, FRET, PET and IFE), the principles of these quenching mechanisms, and the methods of distinguishing these quenching mechanisms. This is followed by an overview on applications of the various quenching mechanisms in detection and imaging. Graphical abstractSchematic representation of the quenching mechanisms of carbon dots (CDs) which include static quenching, dynamic quenching, Förster resonance energy transfer (FRET), photoinduced electron transfer(PET), surface energy transfer (SET), Dexter energy transfer (DET) and inner filter effect (IFE). All these effects can be used to detect and image analytes.

Carbon dots serve as an effective probe for the quantitative determination and for intracellular imaging of mercury(II)

AbstractWe describe a new method for synthesis of water-soluble photoluminescent carbon dots (CDs) by one-pot hydrothermal treatment of adipic acid and triammonium citrate. The CDs have excitation/emission maxima of 340/440 nm, a quantum yield of 0.13, and are shown to be a viable fluorescent probe for the determination of Hg(II). It shows a linear relationship in the 4 to 18 μM mercury ion concentration range. The detection limit is as low as 2.47 μM. The CDs were applied to intracellular sensing and imaging of Hg(II) where they showed low toxicity. Graphical AbstractCarbon dots synthesized by hydrothermal method can be used as “turn-off” fluorescent probe Hg2+ determination. Besides, the carbon dots were applied to intracellular sensing and imaging of Hg2+.

Highly luminescent organosilane-functionalized carbon dots as a nanosensor for sensitive and selective detection of quercetin in aqueous solution.

The organosilane-functionalized carbon dots (SiCDs) were synthesized using citric acid with N-(b-aminoethyl)-g-aminopropyl methyldimethoxy silane (AEAPMS). The as-synthesized SiCDs were characterized by IR, TEM, XPS, NMR and fluorescence. The SiCDs showed a strong emission at 455 nm with excitation at 365 nm. The SiCDs exhibited analytical potential as sensing probes for quercetin (QCT) determination. pH effect, temperature effect, interferences, and analytical performance of the method were investigated. It suggested that SiCDs exhibited high sensitivity and selectivity toward QCT: the linear ranges of SiCDs were estimated to be 0-40 μM while the limit of detection (LOD) was calculated to be 79 nM.

Rhodamine-based ratiometric fluorescent probes based on excitation energy transfer mechanisms: construction and applications in ratiometric sensing

Ratiometric fluorescent probes allow the simultaneous measurement of two fluorescence signals at different wavelengths followed by calculation of their intensity ratio, which can provide more precise measurement results than intensity-based fluorescent probes. Excitation energy transfer is widely used in the design of ratiometric fluorescent probes. Rhodamine is a convenient platform for the construction of “OFF–ON” ratiometric chemosensors. Rhodamine-based ratiometric fluorescent probes based on the excitation energy transfer mechanism can be constructed by conjugated or non-conjugated connections with other chromophores. In this review, we summarized the recent advances regarding rhodamine-based ratiometric fluorescent probes based on excitation energy transfer. We reviewed these probes according to the classification of “through-space” and “through-bond” probes; we focused on the contributions of different donor fluorophores and the types of connections between the energy donors and acceptors.

A rhodamine derivative as selective fluorescent and colorimetric chemosensor for mercury (II) in buffer solution, test strips and living cells.

In this paper, we reported a new rhodamine derivative bearing 2,4-dichloroquinazoline as a selective fluorescent chemosensor for Hg(2+). The ring-opening process of spirolactam enabled the large fluorescent enhancement and colorimetric change by Hg(2+) induced configuration transformation of the rhodamine. Moreover, the fluorescence changes of the chemosensor were dramatically specific for Hg(2+) in the presence of other metal ions, which could meet the selective requirements for practical application. Under optimized experimental conditions, the linear response range covered the concentration range of Hg(2+) from 0 to 1.0×10(-6)M, and the limit of detection was calculated to be 2.7×10(-8)M. In addition, the probe was also successfully applied to the determination of Hg(2+) in water samples, test strips and living cells.

N, B-doped carbon dots as a sensitive fluorescence probe for Hg(2+) ions and 2,4,6-trinitrophenol detection for bioimaging.

Nitrogen and boron co-doped carbon dots (BCNDs1-3) were prepared from three kinds of borate via a facile hydrothermal method. The as-prepared BCNDs did not shift with the change of excitation wavelength and possess good water dispersibility, strong fluorescence emission with high fluorescent quantum yield of 29.01%, 51.42%, 68.28%, respectively. Subsequently, these BCNDs were exploited as excellent Hg(2+) ion and 2,4,6-trinitrophenol (TNP) probe. The efficient selective detection of Hg(2+) can be attributed to non-radiative electron/hole recombination annihilation through an effective electron transfer process and the detection of TNP can be attributed to the fluorescence resonance energy transfer process (FRET). The results show that the BCNDs2 is the most sensitive fluorescence probe for Hg(2+) ions and TNP detection as low as Hg(2+) 7.3nM and TNP 0.35μM compared with BCNDs1 and BCNDs3. The as-prepared BCNDs possess the advantages of good selectivity, fast response and a broad linear detection. They were applied to sensing and imaging of human umbilical vein endothelial cells, showing low cytotoxicity and good biocompatibility.

Formation of N, S-codoped fluorescent carbon dots from biomass and their application for the selective detection of mercury and iron ion

Biomass is regarded as an excellent candidate for the preparation of heteroatom-doped carbon nanomaterials. We have developed a simple and facile one-pot synthesis of nitrogen and sulfur codoped fluorescent carbon dots from pigeon feathers, egg and manure via the pyrolysis carbonization method. The as-prepared four PCDs have high fluorescence quantum yield about 24.87% (PCDs-f), 17.48% (PCDs-w), 16.34% (PCDs-y), 33.50% (PCDs-m), respectively, which is higher than the other carbon dots preparing from biomass. We found that the preparation of PCDs-m with pigeon manure has no favourable selectively with heavy metal ions. However, other PCDs exhibit highly sensitive and selective detection behavior of Hg2+/Fe3+ ions with a low detection limit of 10.3 and 60.9nM. They were applied to imaging of human umbilical vein endothelial cells, showing low cytotoxicity and good biocompatibility.

P-doped carbon dots act as a nanosensor for trace 2,4,6-trinitrophenol detection and a fluorescent reagent for biological imaging

A simple and rapid method for sensitive and selective detection of 2,4,6-trinitrophenol (TNP) was developed with the use of water-soluble carbon dots (CDs) as a nanosensor. The CDs with a fluorescence quantum yield of 21.8% are easily prepared by hydrothermal treatment of a sucrose phosphate solution. In this sensing system, the fluorescence of CDs would be significantly quenched by TNP, while other nitroaromatic derivatives and common reagents exhibited little influence on the detection of TNP. The efficient selective detection of TNP can be attributed to the fluorescence resonance energy transfer process (FRET). This phenomenon can be used for the selective sensing of TNP with a limit of detection of 16.9 nM and a linear range of 0.2–17.0 μM. The recovery result for TNP in real samples by this assay method was satisfying, demonstrating its potential application as a fluorescence sensor. Furthermore, the resulting CDs solution could replace traditional colorings and was successfully applied for Escherichia coli labeling and intracellular imaging.

A rhodamine based fluorescent probe for Hg2+ and its application to cellular imaging.

A new rhodamine-based fluorescent probe (Rh-F) for detection of Hg(2+) ions was synthesized, which could bind Hg(2+) in aqueous ethanol (7:3, v/v) at pH 7.0 with detectable change in color and fluorescence. The response is based on a ring opening reaction and formation of a 1:1 complex, while ring-opening process of spirolactam enables large fluorescent enhancement and colorimetric change upon the addition of Hg(2+). The response is reversible and linear in the range between 200nM and 1000nM, with a detection limit of 4.2nM. Selectivity and competition experiments with various other metal ion revealed that Rh-F possesses highly selective fluorescent response to Hg(2+). Furthermore, the probe was successfully applied to fluorescent imaging of Hg(2+) in L-929 cells confirm that Rh-F can be used as a fluorescent probe for monitoring Hg(2+) in living cells.

Cobalt(II) ions detection using carbon dots as an sensitive and selective fluorescent probe

A simple method was designed for detecting cobalt ions (Co2+) based on the analyte-induced fluorescence quenching of carbon dots (CDs). CDs with a quantum yield of 38.7% were synthesized by hydrothermal treatment of Carbopol 934 and diethylenetriamine. Through the metal–ligand interaction, the prepared CDs can allow highly sensitive and selective detection of Co2+. The color change (from transparent to brown) of the solution can be clearly seen with the naked eye. This effective sensing platform shows high sensitivity and selectivity towards Co2+. Moreover, the CDs are also successfully utilized for monitoring the Co2+ content of natural water.