Powder carbonization to synthesize novel carbon dots derived from uric acid for the detection of Ag(I) and glutathione

Surface Amide-Mediated Synthesis of Bright Blue Fluorescent Carbon Dots for High-Sensitivity Detection of Hg2+ Ions

Mercury ions (Hg2+) seriously harm the central nervous system of humans, leading to brain damage and even heart failure and death. Therefore, effective detection of Hg2+ in water quality has become an urgent research field. It is very important to develop economically efficient fluorescent sensors to achieve rapid and sensitive detection of Hg2+. Therefore, the high fluorescence quantum yield fluorescent carbon dots (CDs) with amide group were prepared. The process of preparing CDs was regulated by multiple key factors (carbon source, proportion, time), and the CDs with the best fluorescence performance were selected. It was comprehensively characterized, including fluorescence performance, surface structure, phase, and morphological characteristics. The amide group endows CDs with the ability to act as both donors and acceptors for hydrogen bonding, forming complexes with metal ions, thus making them suitable for the detection of Hg2+. It is worth noting that CDs can quickly detect Hg2+ within 1 min, and there is a good linear relationship within the ranges of 0.001-200 μM and 200-500 μM. The detection limit of UC-CDs is 8.2 nM. This study provides a fluorescent sensor with fast reaction, excellent sensitivity, and selectivity for the efficient detection of Hg2+ in water.

A multifunctional fluorescent sensor for Ag+ and Hg2+ detection in seawater

In order to detect Ag+ and Hg2+ in seawater, we explored a multifunctional fluorescence sensor. A multifunctional Ag+ and Hg2+ sensor was designed by using gold nanoparticles (AuNPs) as quenching agent, PicoGreen dye as fluorescent probe of base pairing double-stranded deoxyribonucleic acid (DNA), and combining the characteristics of Ag+ making C base mismatch and Hg2+ making T base mismatch. Meanwhile, the DNA logic gate was constructed by establishing logic circuit, truth table, and logic formula. The relevant performances of the sensor were investigated. The results revealed that the sensor can detect Ag+ in the range of 100 to 700 nM with R2 = 0.98129, and its detection limit is 16.88 nM (3σ/slope). The detection range of Hg2+is 100-900 nM with R2 = 0.99725, and the detection limit is 5.59 nM (3σ/slope). An AND-AND-NOR-AND molecular logic gate has been successfully designed. With the characteristics of high sensitivity, multifunction, and low cost, the recommended detection method has the potential to be applied to the detection of Ag+ and Hg2+ in seawater.

Nitrogen and bromine co-doped carbon dots with red fluorescence for sensing of Ag+ and visual monitoring of glutathione in cells

Carbon dots (CDs) with red fluorescence emission have excellent advantages in cell imaging. Herein, novel nitrogen and bromine doped CDs (N,Br-CDs) were prepared with 4-bromo-1,2-phenylenediamine as precursor. The N, Br-CDs present the optimal emission wavelength at 582 nm (λ_ex = 510 nm) at pH 7.0 and 648 nm (λ_ex = 580 nm) at pH 3.0 ∼ 5.0, respectively. The fluorescence intensity of N,Br-CDs at 648 nm versus Ag⁺ concentration shows a good relationship from 0 to 60 μM with the limit of detection (LOD) of 0.14 μM. Furthermore, the fluorescence of N,Br-CDs/Ag⁺ is efficiently restored via the combination of glutathione (GSH) and Ag⁺ and linearly changes with GSH concentration from 0 ∼ 6.0 μM with LOD of 49 nM. This method has been successfully employed to monitor intracellular Ag⁺ and GSH with fluorescence imaging. The results suggest that the N,Br-CDs has application potential in the sensing of Ag⁺ and visual monitoring of GSH in cells.

A novel 3D coordination polymer constructed by dual-ligand for highly sensitive detection of purine metabolite uric acid

Uric acid (UA), as the final product of purine metabolism, exists in urine and serum, which plays an important role in human metabolism, immunity and other functions. The sensitive, efficient, and rapid detection of UA has far-reaching significance in clinical diagnosis and disease prevention. Herein, a novel coordination polymer constructed by dual-ligand was successfully prepared, which exhibited excellent thermal and water stability. The polymer was interlaced by coordination bonds and hydrogen bonds to form an infinitely extended three-dimensional framework, which showed a rare and novel topological structure. The complex selectively recognized UA through significant fluorescence quenching response in the presence of various interferences. The excellent detection sensitivity (the limited detection of 1.2 μM), outstanding anti-interference ability and remarkable recyclability marked the complex to be a promising sensor material towards UA. In addition, the detection mechanism of UA by the complex was investigated in detail by combining density functional theory (DFT) and a variety of other analytical methods.

Controlling the ligands of CdZnTe quantum dots to design a super simple ratiometric fluorescence nanosensor for silver ion detection

A super simple ratiometric fluorescence nanosensor has been fabricated by controlling the ligands of CdZnTe quantum dots (QDs), allowing the sensitive and visual detection of silver ions (Ag⁺). The green-emitting L-cysteine-protected CdZnTe QDs (Lcys-CdZnTe QDs) had a specific response to Ag⁺ and were used as the reporting probe, while the red-emitting N-acetyl-L-cysteine-protected CdZnTe QDs (NAC-CdZnTe QDs) showed no obvious response to all tested metal ions and were selected as the reference probe. Simply mixing them without any encapsulated synthesis ultimately produced a time-saving, low-cost detection method, allowing the sensitive and visual detection of Ag⁺ in samples. The proposed nanosensor exhibited a linear range of 0.5-4.0 μM along with a detection limit of 0.17 μM, and has been successfully applied in real tap water and lake water samples. This nanosensor also showed obvious color changes in the detection process and has potential in visual semi-quantitative detection. Our approach may provide a general and feasible strategy for designing ratiometric fluorescence nanosensors, which will attract a wide range of interest in sensing-related fields.

Phenanthroline Derivative Fluorescent Probe for Rapid and Sensitive Detection of Silver(I)

In the present work, a phenanthroline derivative (2-(2-methoxyphenyl)-4-phenyl-1,10-phenanthroline, MPP), as a fluorescent probe, was synthesized to realize a rapid, simple and sensitive detection of silver(I). The detection conditions of Ag⁺ were optimized. This fluorescent probe has the advantages of a fast reaction time, a wide pH applicable range, and a low detection limit, exhibiting a good linear response between the fluorescence intensity and the concentration in the range of 0.05 - 1.5 μmol/L for Ag⁺. The detection limit is as low as 3.38 × 10^-8 mol/L (S/N = 3). This probe had been used to detect Ag⁺ in real samples, and the recovery efficiency of spiked Ag⁺ had been also tested. The recovery efficiency is satisfactory, ranging from 92.0 to 105.4%. Therefore, this fluorescent probe should provide a new choice for the quantitative detection of silver ions in environmental water samples.

N-Doped Carbon Dots as a Fluorescent Nanosensor for Determination of Colchicine Based on Inner Filter Effect

In this study, a novel and simple fluorescent carbon quantum dots (CQDs) based nano-sensor for colchicine determination has been prepared. The nitrogen doped CQDs probe was prepared using uric acid as a carbon/nitrogen source via a one-step pyrolysis. The sensor is based on inner filter effect (IFE) where colchicine acts as a powerful absorber that affects the excitation of the fluorescer (CQDs). This overlap results in a quantitative attenuation of the fluorescence of CQDs with increasing colchicine concentration in the range of 2-25 μM. The developed sensor has the advantages of simplicity, less time-consuming, convenience and satisfactory selectivity for colchicine determination in pharmaceutical dosage forms.

Bright-yellow-emissive nitrogen-doped carbon nanodots as a fluorescent nanoprobe for the straightforward detection of glutathione in food samples

In this work, a novel yellow-emissive nanoprobe was for the first time developed for the fast detection of glutathione (GSH) based on nitrogen-doped carbon nanodots (N-CNDs) prepared via hydrothermal heating of o-Phenylenediamine. The N-CNDs and GSH could form non-fluorescent complex via static interaction, resulting in the fluorescence quenching of N-CNDs. Under optimal conditions, the N-CNDs served as a fluorescent nanoprobe for GSH sensing in a straightforward way with high selectivity and sensitivity. Two good linear responses were found for GSH detection in concentration ranges of 0.1-1.0 μM and 1.0-220.0 μM, respectively. The corresponding detection limits are as low as 0.059 μM and 5.54 μM, respectively. Meanwhile, the proposed sensing system was successfully applied for GSH determination in vegetable and fruit samples with high accuracy. This work highlights the detection of GSH in a simple, fast, cost-effective, selective and ultrasensitive way, which paves a new way for other food quality monitoring.

Small molecules derived carbon dots: synthesis and applications in sensing, catalysis, imaging, and biomedicine

Carbon dots (CDs) are the new fellow of carbon family having a size less than 10 nm and attracted much attention of researchers since the last decade because of their unique characteristics, such as inexpensive and facile synthesis methods, easy surface modification, excellent photoluminescence, outstanding water solubility, and low toxicity. Due to these unique characteristics, CDs have been extensively applied in different kind of scientific disciplines. For example in the photocatalytic reactions, drug-gene delivery system, in vitro and in vivo bioimaging, chemical and biological sensing as well as photodynamic and photothermal therapies. Mainly two types of methods are available in the literature to synthesize CDs: the top-down approach, which refers to breaking down a more massive carbon structure into nanoscale particles; the bottom-up approach, which refers to the synthesis of CDs from smaller carbon units (small organic molecules). Many review articles are available in the literature regarding the synthesis and applications of CDs. However, there is no such review article describing the synthesis and complete application of CDs derived from small organic molecules together. In this review, we have summarized the progress of research on CDs regarding its synthesis from small organic molecules (bottom-up approach) via hydrothermal/solvothermal treatment, microwave irradiation, ultrasonic treatment, and thermal decomposition techniques as well as applications in the field of bioimaging, drug/gene delivery system, fluorescence-based sensing, photocatalytic reactions, photo-dynamic therapy (PDT) and photo-thermal (PTT) therapy based on the available literature. Finally, the challenges and future direction of CDs are discussed.

An efficient turn-on fluorescence biosensor for the detection of glutathione based on FRET between N,S dual-doped carbon dots and gold nanoparticles

Fluorescence resonance energy transfer (FRET) is a kind of energy transfer mechanism depending on the distance between donor and acceptor, which exhibited potential application in biosensors. In this study, an efficient fluorescence "turn-on" strategy for the detection of glutathione (GSH) has been established based on FRET between nitrogen and sulfur dual-doped carbon dots (N,S-CDs) and gold nanoparticles (Au NPs). A novel N,S-CDs was synthesized by a one-pot hydrothermal treatment of 3-aminothiophenol, which possessed excellent fluorescence property with the maximum emission wavelength of 530 nm. Then, the as-prepared N,S-CDs served as energy donor to transfer energy to Au NPs via FRET process, resulting in fluorescence quenching of N,S-CDs. However, the fluorescence of N,S-CDs was recovered efficiently by adding GSH into the mixture solution of N,S-CDs and Au NPs. Therefore, the FRET assembly of N,S-CDs and Au NPs was used as a fluorescence probe for the "turn-on" sensing GSH with the linear range from 3.8 to 415.1 μM and the limit detection of 0.21 μM. This nanosensor platform was employed to monitor GSH in serum samples with satisfying results. Graphical abstract.

A dual (colorimetric and fluorometric) detection scheme for glutathione and silver (I) based on the oxidase mimicking activity of MnO2 nanosheets

A fluorimetric and colorimetric method is described for the determination of glutathione (GSH) and silver (I). It is based on the use of MnO₂ nanosheets that were prepared by solution mixing and exfoliation. They display oxidase-mimicking activity and can catalyze the oxidation of o-phenylenediamine (OPD) to form yellow 2,3-diaminophenazine (DAP) with an absorption maximum at 410 nm. DAP also has a yellow fluorescence (with a peak at 560 nm). The MnO₂ nanosheets can be rapidly reduced to Mn²⁺ by GSH. This reduces the efficiency of the oxidase mimic MnO₂ and causes a decrease in fluorescence and absorbance intensity. However, on addition of Ag⁺, a complex is formed with GSH. It prevents the destruction of MnO₂ nanosheets so that the enzyme mimicking activity is retained. A dual-method for the determination of GSH and Ag(I) was developed. It has excellent sensitivity for GSH with lower detection limits of 62 nM (fluorimetric) and 0.94 μM (colorimetric). The respective data for Ag(I) are 70 nM and 1.15 μM. The assay was successfully applied to the determination of GSH and Ag(I) in spiked serum samples. Graphical abstract Schematic presentation of a method for colorimetric and fluorometric determination of glutathione (GSH) and silver(I). MnO₂ nanosheets are reduced to Mn(II) by GSH. This reduces the enzyme-mimicking activity of MnO₂ nanosheets and causes a decrease in fluorescence and absorbance. On addition of Ag(I), the enzyme-like activity is increasingly retained. A decrease in fluorescence and absorbance is not observed any longer.

Facile synthesis of fluorescent carbon dots from Prunus cerasifera fruits for fluorescent ink, Fe3+ ion detection and cell imaging

Carbon dots (CDs) synthesized from natural products have drawn numerous attentions due to some unique properties. Here, Prunus cerasifera fruits were used as carbon source to synthesize high luminescent CDs by hydrothermal method. The obtained CDs were characterized by TEM, FTIR and XPS methods, founding the CDs were near-spherical and contained abundant nitrogen element. The CDs aqueous solution exhibited bright blue fluorescence under ultraviolet illumination, with the maximum emission at 450 nm. They could be potentially used as invisible fluorescent ink by written on the paper and irradiated by UV light, due to their fluorescent properties. Moreover, the CDs were found being selectively quenched by Fe³⁺ ion. The quench of CDs was linearly related to the concentration of Fe³⁺ ion in the range of 0-0.5 mM, meaning they could be developed as fluorescent probe of Fe³⁺ ion. At last, the CDs were used for cell imaging, founding they were low toxicity to HepG2 cells and exhibited blue and green fluorescence under a fluorescence microscope. In summary, the CDs prepared from Prunus cerasifera fruits exhibited excellent fluorescence properties, and could be potentially applied in the field of fluorescent ink, Fe³⁺ ion detection and cell imaging.

Dual role of BSA for synthesis of MnO2 nanoparticles and their mediated fluorescent turn-on probe for glutathione determination and cancer cell recognition

A MnO₂ nanoparticle (MnO₂ NP)-mediated fluorescent turn-on probe for sensitively and selectively detecting glutathione (GSH) and recognizing cancer cells was established in this work. MnO₂ NPs were synthesized simply and quickly through an in situ redox reaction by mixing bovine serum albumin (BSA) and KMnO₄, in which BSA served the dual roles of template and reductant. It was found that the MnO₂ NPs served as an effective energy acceptor and quenched the fluorescence intensity of carbon dots (CDs), owing to the fluorescence resonance energy transfer (FRET) process. Further, the addition of GSH triggered the decomposition of MnO₂, breaking the FRET between MnO₂ NPs and CDs and thus restoring the fluorescence intensity of CDs. Based on this mechanism, quantitative determination of GSH was performed. Under optimal conditions, a satisfactory linear range of 0.05-90 μM and limit of detection of 39 nM were obtained, and GSH content in human serum samples was detected. Moreover, taking advantage of the higher levels of GSH in cancer cells than in normal cells, the MnO₂ NP-CD probe was applied to distinguish SMMC-7721 cancer cells from L02 normal cells. The FRET was interrupted by GSH in cancer cells, and strong fluorescence was observed. This work provides a facile approach for synthesizing MnO₂ NPs, and this rapid, low-cost method with no need for reductants makes synthesis green and convenient. The MnO₂ NP-mediated fluorescent turn-on response to GSH could improve the MnO₂ nanomaterial-based biochemical analysis applications.