Rong Sheng Li

Highly fluorescent carbon dots as selective and visual probes for sensing copper ions in living cells via an electron transfer process

As an integral part of many important enzymes, Cu2+ is involved in a number of vital biological processes, which is linked to the oxidative damage and environmental contamination when Cu2+ is excessive. In this work, Cu2+ can be captured by the amino groups of carbon dots (CDs) to form complexes, resulting in a strong fluorescence quenching of CDs via a nonradiative electron transfer process, which offered a rapid, visual, and selective methodology for Cu2+ detection. The probe exhibited a wide response concentration range (0.01-2μM) to Cu2+ with a detection limit of 6.7nM. Significantly, the CDs presented excellent biocompatibility and high photostability, which were applicable for the visualization of Cu2+ dynamic invasion into living cells and Tilapia mossambica. Furthermore, the toxicity of Cu2+ ions to living cells could be inhibited with CDs by the formation of complexes.

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.

Plasmonic platforms for colorimetric sensing of cysteine

Abstract Cysteine plays a crucial role in physiological processes, as well as in the food, pharmaceutical, and even personal care industries, which is of great significance to control its concentration. Plasmonic nanomaterials have attracted increasing interest in colorimetric sensing, due to their outstanding optical, chemical, and catalytic properties. Their colors, derived from the absorption of the localized surface plasmon resonance (LSPR), strongly depend on the shape, size, constituent, and aggregates states, which could be tuned by cysteine. This review highlights the recent advances in cysteine detection with plasmonic nanoparticles as colorimetric platforms, wherein the colors of nanomaterials change upon the introduction of cysteine, which could be easily followed by the naked eye without requiring any instrumentation. The selective and sensitive detection mechanisms are discussed. The presence of cysteine could adjust the shape, size, constituent, and interparticle distance of nanomaterials, leading to the color transformation. In addition, the introduction of cysteine could adjust the catalytic capability of nanomaterials, resulting in the color variance. Based on those mechanisms, the colorimetric detection of cysteine could be achieved in a facile way. Finally, challenges and future perspectives are outlined.

Heparin sodium-selective ‘on–off’ and lysine-selective ‘off–on’ fluorescence switching of cadmium telluride quantum dots and their analytical applications

Sensing biomolecules such as heparin sodium and lysine are of great significance. In this work, a “turn-off–on” fluorescence switching of cadmium telluride quantum dots (CdTe QDs) was designed for both heparin sodium and lysine. Even though both heparin sodium and thioglycolic acid (TGA)-capped CdTe QDs are negatively charged, they are capable of forming a self-assembly and even aggregates through hydrogen bonding, depending on the concentration of heparin sodium, which leads to the sensitive fluorescence quenching of CdTe QDs. Thus, a fluorescence ‘turn-on’ analytical method for heparin sodium sensing could be established with a detection range of 0.200–5.000 μg mL−1 and the detection limit was 0.033 μg mL−1, which is applicable to determining heparin sodium in injection samples. Whats more, a sensitive and selective “turn-off–on” nanosensor was developed for lysine analysis with the detection range of 2–200 μmol L−1 and the detection limit as low as 0.146 μmol L−1. This approach offers a new, simple, fast and selective method for determining heparin sodium and lysine.

Visual Identification of Light-Driven Breakage of the Silver-Dithiocarbamate Bond by Single Plasmonic Nanoprobes

Insight into the nature of metal-sulfur bond, a meaningful one in life science, interface chemistry and organometallic chemistry, is interesting but challenging. By utilizing the localized surface plasmon resonance properties of silver nanoparticles, herein we visually identified the photosensitivity of silver-dithiocarbamate (Ag-DTC) bond by using dark field microscopic imaging (iDFM) technique at single nanoparticle level. It was found that the breakage of Ag-DTC bond could be accelerated effectively by light irradiation, followed by a pH-dependent horizontal or vertical degradation of the DTC molecules, in which an indispensable preoxidation process of the silver was at first disclosed. These findings suggest a visualization strategy at single plasmonic nanoparticle level which can be excellently applied to explore new stimulus-triggered reactions, and might also open a new way to understand traditional organic reaction mechanisms.

Stable gold nanoparticles as a novel peroxidase mimic for colorimetric detection of cysteine

In this work, a novel method for colorimetric detection of cysteine was proposed based on the inhibition of peroxidase-like behavior of AuNPs. Kiwi juice prepared gold nanoparticles presented strong catalytic activity, which could catalyze H2O2–TMB to generate a blue product, resulting in strong absorption at 650 nm. In HAc–NaAc (pH 4.0) buffer, cysteine induced the aggregation of gold nanoparticles through covalent Au–S bonds and electrostatic as well as hydrogen bonding, leading to the reduction of the catalytic activity of gold nanoparticles with a weakened blue color product and a lower absorbance. Under optimal conditions, the concentrations of cysteine were proportional to the degree of reduced absorbance. This approach offers a new, simple, sensitive and selective assay for cysteine.

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.

Color Encoded Assays for the Simultaneous Quantification of Dual Cancer Biomarkers

For the first time, the scattering light of noble nanoparticles was applied for the simultaneous detection of dual cancer biomarkers. Two nanoprobes with dual scattering light colors were used for the simultaneous imaging of alpha-fetoprotein (AFP) and carcinoembryonic antigen (CEA) based on the sandwich-type immunoassay. Since AFP can combine anti-AFP-modified gold nanoparticles, which have green scattering light under the dark-field microscopic imaging (iDFM) technique, while CEA can conjugate anti-CEA-immobilized silver nanoparticles, which have blue scattering light, the simultaneous determination of AFP and CEA can be achieved by separately counting the number of green and blue light spots in iDFM. The mutual interference between the detection processes of AFP and CEA in the dual detection was investigated, and a negligible interference was found when the concentration of the antigen was in the range of 0.5-10 ng/mL, indicating the practicability of the simultaneous sensitive detection of dual targets. Furthermore, AFP and CEA in serum samples were also quantified directly without additional sample pretreatment, demonstrating the potential applications of the developed method in clinical diagnosis.

The aggregation induced emission quenching of graphene quantum dots for visualizing the dynamic invasions of cobalt(II) into living cells

A highly sensitive and selective approach for cobalt(ii) detection based on the aggregation induced emission quenching strategy, which is opposite to aggregation induced emission enhancement, was developed using graphene quantum dots (GQDs). The detection could be achieved in the range of 10 nM-5 μM and the limit of detection was 2 nM. Importantly, the as-prepared GQDs showed a specific response to cobalt(ii) with excellent stability in A549 cells owing to their good biocompatibility and long-time anti-photobleaching. Thus, these environmentally and bio-friendly carbon nanomaterials were employed to visualize and monitor significant physiological changes of living cells induced by cobalt(ii). This shows great potential for in vitro analysis of cobalt(ii).