Meng Li Liu

A large-scale synthesis of photoluminescent carbon quantum dots: a self-exothermic reaction driving the formation of the nanocrystalline core at room temperature

Carbon quantum dots (CQDs), a rising star family in photoluminescent (PL) nanomaterials, have been identified to have a core–shell structure with the nanocrystalline core of sp2-hybridized carbon clusters and the functional group formed shell of sp3-hybridized carbons, in which the core formation usually needs high-temperature carbonization. Herein, we develop a route to prepare CQDs on a large scale by using hydroquinone and ethylenediamine (EDA) as the precursors and the EDA-catalyzed decomposition of hydrogen peroxide at room temperature. The released heat from this highly exothermic reaction system can rapidly prompt the formation of the nanocrystalline core. The as-prepared CQDs in situ show green PL properties around 525 nm under excitation at 320 to 420 nm with the absolute quantum yield of 24.6%, and can find applications in visual analysis and other fields.

Highly selective and sensitive detection of 2,4,6-trinitrophenol by using newly developed blue–green photoluminescent carbon nanodots

Though many methods of detecting 2,4,6-trinitrophenol (TNP) mainly have been developed recent years, quantification of TNP in environmental matrixes still faces up to great challenges because all the nitroaromatic explosives reveal highly similar chemical structure. In the present work, we have developed a selective and sensitive method for detection of TNP by amorphous photoluminescent carbon nanodots (CNDs), which are prepared through a simple hydrothermal route using spermine and m-phenylenediamine (MPD) as precursors. The as-prepared CNDs are found to show blue-green photoluminescence, excitation-wavelength independence, and excellent chemical and optical stability. Owing to the strong characteristic absorption of TNP at 356nm (ε=1.048×104cm-1M-1), which has a good spectral overlap with the excitation band of CNDs, the fluorescence intensity of CNDs at 490nm is linearly quenched with the adding concentration of TNP in the range of 0.1-100μM. The developing assay based on inner filter effect (IFE) mechanism for the detection of TNP is selective and convenient, showing that the as-prepared CNDs have applicable prospect in the concept of simplicity and specificity in analytical chemistry.

Cu(I)-Doped carbon quantum dots with zigzag edge structures for highly efficient catalysis of azide–alkyne cycloadditions

Photoluminescent (PL) carbon quantum dots (CQDs), in which Cu(I) was doped stably owing to their specific zigzag edge structure, were used for catalyzing the Huisgen 1,3-dipolar cycloaddition between azides and alkynes, the prototypical reaction of “click chemistry”. The results showed the great potential of the as-prepared CQDs in catalysis chemistry applications.

Large-scale simultaneous synthesis of highly photoluminescent green amorphous carbon nanodots and yellow crystalline graphene quantum dots at room temperature

Photoluminescent (PL) carbon dots (CDs) as a new type of carbon nanomaterial have attracted increasing attention owing to their fascinating properties. Herein, we develop a facile, energy-efficient, large-scale route to prepare highly PL CDs with a quantum yield of up to 35.3% at room temperature. These PL CDs can be further separated out into green-emissive amorphous carbon nanodots (CNDs) and yellow-emissive crystalline graphene quantum dots (GQDs) through a silica gel column. Both the as-prepared CNDs and GQDs, even when having the same particle-size distribution and chemical groups, have different degrees of surface oxidation. As characterized by X-ray photoelectron spectroscopy (XPS), the yellow-emissive crystalline GQDs have a much higher surface oxidation degree than that of the green-emissive amorphous CNDs. A further finding is that the characteristic emission peaks of the CDs show an obvious red shift from 518 nm to 543 nm with the increase in the surface oxidation degree, which can be attributed to the decrease in their band gap between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO). That is, the difference in band gap is closely related to the oxidation degree of the CDs, rather than the particle size or chemical groups. Moreover, the amorphous CNDs are very easily photobleached under 140 W xenon lamp irradiation as compared to the crystalline GQDs, indicating that the photostability is dependent on the crystalline structure of the CDs, which is beneficial for the top-down design and development of suitable CDs for different application purposes.

Highly selective detection of phosphate ion based on a single-layered graphene quantum dots-Al 3+ strategy

Determination of phosphate ion (PO43-) is important in biomedical and environmental arrays because its controlling concentrations are associated with different pathologies or the quality of water. Herein, we report a new type of photoluminescence (PL) probe for highly selective detection of PO43- based on a single-layered graphene quantum dots chelating with aluminium ions (s-GQDs-Al3+) system. The PL of s-GQDs can be enhanced by Al3+ through the aggregation-induced emission enhancement (AIEE) effect. With the addition of PO43-, the PL of the s-GQDs-Al3+ system is faded away because PO43- has stronger coordination with Al3+ which results in the elimination of AIEE effect and the decrease in the PL intensity of the s-GQDs-Al3+ system. Therefore, the s-GQDs-Al3+ system can behave as an on-off type PL probe for PO43- detection. It is found that the PL intensity ratio (I/I0) of s-GQDs in the presence of Al3+ at 463nm is proportional to the concentration of PO43- in the range of 0.25-7.5μM with the limit of detection as low as 0.1μM. This selective assay has a great application prospect in the complex matrixes owing to its simplicity and specificity for PO43- detection.

Boron and nitrogen co-doped single-layered graphene quantum dots: a high-affinity platform for visualizing the dynamic invasion of HIV DNA into living cells through fluorescence resonance energy transfer

High-affinity binding of carbon nanomaterials with nucleobases, which is still a challenge, is the basis for DNA directed assembly and sensing. In this work, boron and nitrogen co-doped single-layered graphene quantum dots (BN-SGQDs) are designed as a high-affinity platform for nucleic acid detection and imaging in living cells, which has been confirmed by density functional theory (DFT) simulation and experiments. Owing to their excellent absorption and photoluminescence ability, the high quantum yield (QY 36.5%) yellow fluorescent BN-SGQDs could act as an energy donor in the fluorescence resonance energy transfer (FRET) process for nucleic acid detection. Furthermore, this BN-SGQD based sensing platform has been successfully adopted to visualize the dynamic invasion of human immunodeficiency virus (HIV) DNA into HeLa cells. The high-affinity platform has shown potential for biosensing in complicated biological samples.

Anthrax biomarker: An ultrasensitive fluorescent ratiometry of dipicolinic acid by using terbium(III)-modified carbon dots

The highly sensitive detection of dipicolinic acid (DPA), a biomarker of the biological threat-agent anthrax, is strongly associated with the sensing of Bacillus anthracis (B. anthracis) in environmental and food samples. In this study, we developed a novel, ultrasensitive method for the detection of DPA by using a ratiometric fluorescent terbium ions modified carbon dots (CDs-Tb). The CDs-Tb showed two fluorescent emission bands at 459 nm and 495 nm when excited at the single wavelength of 260 nm. DPA could specifically bind with terbium ions on the surface of CDs through strong chelate-conjugation to produce antenna effect, resulting in significantly enhancement of the 495 nm emission peak without affecting the 459 nm emission peak. The fluorescence intensity ratio (I495/I459) of CDs-Tb was proportional to the concentration of DPA in the range of 0.5 nM to 2.5 μM with the limit of detection as low as 100 pM. This selective and ultrasensitive assay had a great application prospect in the complex matrixes owing to its simplicity and specificity for DPA. Meanwhile, the CDs-Tb-based paper sensor was successfully developed for sensitive and visual detection of DPA.