Facile synthesis of bright yellow fluorescent nitrogen-doped carbon quantum dots and their applications to an off–on probe for highly sensitive detection of methimazole

Carbon Dots: A Review with Focus on Sustainability

Carbon dots (CDs) are an emerging class of nanomaterials with attractive optical properties, which promise to enable a variety of applications. An important and timely question is whether CDs can become a functional and sustainable alternative to incumbent optical nanomaterials, notably inorganic quantum dots. Herein, the current CD literature is comprehensively reviewed as regards to their synthesis and function, with a focus on sustainability aspects. The study quantifies why it is attractive that CDs can be synthesized with biomass as the sole starting material and be free from toxic and precious metals and critical raw materials. It further describes and analyzes employed pretreatment, chemical-conversion, purification, and processing procedures, and highlights current issues with the usage of solvents, the energy and material efficiency, and the safety and waste management. It is specially shown that many reported synthesis and processing methods are concerningly wasteful with the utilization of non-sustainable solvents and energy. It is finally recommended that future studies should explicitly consider and discuss the environmental influence of the selected starting material, solvents, and generated byproducts, and that quantitative information on the required amounts of solvents, consumables, and energy should be provided to enable an evaluation of the presented methods in an upscaled sustainability context.

Fast and eco-friendly synthesis of carbon dots from pinecone for highly effective detection of 2,4,6-trinitrophenol in environmental samples

2,4,6-Trinitrophenol (TNP) has high explosive risks and biological toxicity, and there has been considerable concern over the determination of TNP. In the present work, fluorescent carbon dots (CDs) stemmed from a green carbon source of pinecone by the facile hydrothermal approach. A novel environment- friendly fluorescent probe was developed to efficiently detect TNP by using the obtained CDs with remarkable fluorescence stability. The fluorescent CDs exhibited obvious excitation dependence with the highest peaks for excitation and emission occurring at 321 and 411 nm, respectively. The fluorescence intensity is significantly reduced by TNP owing to the inner filter effect with the CDs. The probe exhibited good linearity with TNP concentrations in the range of 0.025-20 μg mL-1, and the limit of detection was as low as 8.5 ng mL-1. Additionally, the probe proved successful in sensing TNP quantitatively in actual environmental samples with satisfied recoveries of 95.6-99.6%. The developed fluorescent probe offered an environment-friendly, efficient, rapid, and reliable platform for detecting trace TNP in the environmental field.HighlightsNovel carbon dots were synthesised from green precursors of pineal powder.The highly effective quenching process was put down to the inner filter effect.The as-constructed fluorescent probe was successfully utilised for sensing 2,4,6-trinitrophenol in environmental samples.The proposed method was simple, rapid, efficient, economical, and eco-friendly.

A Novel Enhanced-Fluorescent Probe Based on DHLA-Stabilized Red-Emitting Copper Nanoclusters for Methimazole Detection Via Aggregation-Induced Emission Effect

Herein, an aqueous phase synthesis approach was presented for the fabrication of copper nanoclusters (Cu NCs) with aggregation-induced emission (AIE) property, utilizing lipoic acid and NaBH4 as ligands and reducing agent, respectively. The as-synthesized Cu NCs exhibit an average size of 3.0 ± 0.2 nm and demonstrate strong solid-state fluorescence upon excitation with UV light. However, when dissolved in water, no observable fluorescent emission is detected in the aqueous solution of Cu NCs. Remarkably, the addition of Methimazole induced a significant red fluorescence from the aqueous solution of Cu NCs. This unexpected phenomenon can be ascribed to the aggregation of negatively charged Cu NCs caused by electrostatic interaction with positively charged imidazole groups in Methimazole, resulting in enhanced fluorescence through AIE mechanism. Therefore, there exists an excellent linear correlation between the fluorescent intensities of Cu NCs aqueous solution and the concentration of Methimazole within a range of 0.1-1.5 mM with a low limit of detection of 82.2 µM. Importantly, the designed enhanced-fluorescent nanoprobe based on Cu NCs exhibits satisfactory performance in assaying commercially available Methimazole tablets, demonstrating its exceptional sensitivity, reliability, and accuracy.

Facile and green synthesis of chlorophyll-derived multi-color fluorescent carbonized polymer dots and their use for sensitive detection of hemin

Due to the very important role in physiological process, a simple and sensitive hemin detection method is necessarily required. Biomass-based carbonized polymer dots (CPDs) have been widely studied especially as fluorescence probe owing to the advantages of low toxicity and the variety of fluorescence color, yet there are still challenges in developing their multi-color emission property from the same raw materials. In this work, red, white and blue emissive CPDs derived from chlorophyll have been synthesized via hydrothermal method. Then white-emitted CPDs (white-CPDs) with the Commission International d'Eclairage (CIE) coordinates at (0.34, 0.32) were used to develop a fluorescence quenched sensing system for hemin determination. There is a good linear relationship between (F0-F)/F0 and concentration of hemin in the range of 0.1-0.95 μM with a detection limit of 0.043 μM, and the quenching mechanism was considered to be caused by inner filter effect (IFE). Moreover, it has been successfully used for hemin detection in serum and also for visual determination, which indicating great potential in applications of disease diagnoses and trace identification.

Carbon quantum dot with co-doped nitrogen and phosphorus for tazettine ratiometric fluorescent sensing

An overdose of tazettine (TZ) has toxic side effects, which makes it extremely important to rapidly and subtly determine the TZ. In this study, double-emitting, nitrogen-phosphorus co-doped carbon quantum dots (N,P-CQDs) were prepared using cis-butenedioic acid, phosphoric acid, and p-phenylenediamine. An effective inner filter effect (IFE) can occur between TZ and N,P-CQDs, resulting in their fluorescence quench. Therefore, a ratio fluorescent probe was constructed for detecting the TZ was constructed. After optimizing the experimental conditions, the quenching efficiency showed a strong linear connection with the TZ concentration in the range of 0.01-30 µmol/L, with the detection limit of 0.002 µmol/L. This method could be satisfactorily applied to detect TZ in mouse plasma samples.

Recent Applications of Quantum Dots in Pharmaceutical Analysis

Nanotechnology has emerged as one of the most potential areas for pharmaceutical analysis. The need for nanomaterials in pharmaceutical analysis is comprehended in terms of economic challenges, health and safety concerns. Quantum dots (QDs)or colloidal semiconductor nanocrystals are new groups of fluorescent nanoparticles that bind nanotechnology to drug analysis. Because of their special physicochemical characteristics and small size, QDs are thought to be promising candidates for the electrical and luminescent probes development. They were originally developed as luminescent biological labels, but are now discovering new analytical chemistry applications, where their photo-luminescent properties are used in pharmaceutical, clinical analysis, food quality control and environmental monitoring. In this review, we discuss QDs regarding properties and advantages, advances in methods of synthesis and their recent applications in drug analysis in the recent last years.

A Turn-On Fluorescence Sensor Based on Nitrogen-Doped Carbon Dots and Cu2+ for Sensitively and Selectively Sensing Glyphosate

Glyphosate has excellent herbicidal activity, and its extensive use may induce residue in the environment and enter into humans living through the food chain, causing negative impact. Here, water-soluble 1.55 nm size nitrogen-doped carbon quantum dots (NCDs) with strong blue fluorescence were synthesized using sodium citrate and adenine. The maximum excitation and emission wavelengths of NCDs were 380 nm and 440 nm, respectively. The above synthesized NCDs were first used for the construction of a fluorescence sensor for glyphosate detection. It was found that Cu²⁺ could quench the fluorescence of NCDs effectively through the photoinduced electron transfer (PET) process, which was confirmed using fluorescence lifetime measurements. Additionally, the fluorescence was restored with the addition of glyphosate. Hence, a sensitive turn-on fluorescence sensor based on NCDs/Cu²⁺ for glyphosate analysis was developed. The LODs of glyphosate for water and rice samples were recorded as 0.021 μg/mL and 0.049 μg/mL, respectively. The sensor was applied successfully for ultrasensitive and selective detection of glyphosate in environmental water and rice samples with satisfied recoveries from 82.1% to 113.0% using a simple sample pretreatment technique. The proposed strategy can provide a significant potential for monitoring glyphosate residue in water and agricultural product samples.

Cane Molasses Derived N-Doped Graphene Quantum Dots: Dynamic Quenching Synergistically Photoinduced Electron Transfer for the Instant Detection of Nitrofuran Antibiotics

The development of a highly selective, simple, and rapid detection method for nitrofuran antibiotics (NFs) is of great significance for food safety, environmental protection, and human health. To meet these needs, in this work, cyan-color highly fluorescent N-doped graphene quantum dots (N-GQDs) were synthesized using cane molasses as the carbon source and ethylenediamine as the nitrogen source. The synthesized N-GQDs have an average particle size of 6 nm, a high fluorescence intensity with 9 times that of undoped GQDs, and a high quantum yield (24.4%) which is more than 6 times that of GQDs (3.9%). A fluorescence sensor based on N-GQDs for the detection of NFs was established. The sensor shows advantages of fast detection, high selectivity, and sensitivity. The limit of detection for furazolidone (FRZ) was 0.29 μM, the limit of quantification (LOQ) was 0.97 μM, and the detection range was 5-130 μM. The fluorescence quenching mechanism of the sensor was explored by fluorescence spectroscopy, UV-vis absorption spectroscopy, Stern-Volmer quenching constant, Zeta potential, UV-vis diffuse reflectance spectroscopy, and cyclic voltammetry. A fluorescence quenching mechanism of dynamic quenching synergized with photoinduced electron transfer was revealed. The developed sensor was also successfully applied for detecting FRZ in various real samples, and the results were satisfactory.

Biomass-Derived Carbon Dots and Their Sensing Applications

Carbon dots (CDs) can be widely used in the field of sensing because of its good water solubility, low toxicity, high fluorescence stability and excellent biocompatibility. It has become a popular trend to prepare high-value, inexpensive, renewable and environmentally friendly CDs sensors from biomass resources. This article reviewed the research progress of biomass-derived CDs as chemical, physical and biological sensors in recent years and studied their preparation processes and sensing abilities. Furthermore, the prospects and challenges of biomass-CDs sensors were discussed. This article is expected to provide inspirations for the design, preparation and application of biomass-CDs sensors in the future.

Carbon quantum dots with blue/near infrared emissions for ratiometric fluorescent lornoxicam sensing and bio-imaging

An economical and eco-friendly hydrothermal method for the preparation of nitrogen-doped carbon quantum dots (N-CQDs) was studied with rambutan peel and lysine. The morphology, structure, and optical properties of N-CQDs were characterized by transmission electron microscopy, Fourier transform infrared spectrometry, X-ray powder diffractometer, X-ray photoelectron spectrometry, and UV spectrophotometry. The synthesized N-CQDs have excellent characteristics such as strong fluorescence, good dispersion, high stability, and excellent water solubility. The absolute fluorescence quantum yield is 1.02%, the average particle size is 1.63 nm, and the maximum excitation wavelength is 340 nm. The maximum emission wavelengths are 430 nm and 800 nm. As a quencher, lornoxicam (LNX) was used to quench the fluorescence of N-CQDs with the mechanism of inner filter effect. The fluorescence ratio of N-CQDs (F₄₃₀/F₈₀₀) shows a good linear relationship to the concentration of LNX. The linear range and the detection limit of LNX are 0.01‒100 and 0.003 μmol/L, respectively. An effective ratiometric fluorescence probe for the detection of LNX was constructed. The method has the advantages of low detection limit, high sensitivity, wide linear range, and can be applied to the determination of LNX in real samples. Moreover, according to the excitation-dependent fluorescence behavior, dual-wavelength emission, and biocompatibility of N-CQDs, it has been applied to cell imaging.

Fluorescence "off-on" probe for lead (II) detection based on Atractylodes III CQDs and bioimaging

In this work, a type of carbon quantum dots (CQDs) with bright blue emission were readily fabricated through one-step hydrothermal treatment from Atractylodes III. We explored the surface morphology and optical properties of CQDs by Transmission electron microscope (TEM), X-ray diffraction patterns (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and UV-vis spectrophotometer. The obtained CQDs possessed good photoluminescence properties, water solubility and biocompatibility. The fluorescence quantum yield of them was 3.72%. It was found that the fluorescence intensity of CQDs will be quenched by picric acid (PA). After adding lead (II), the fluorescence can be effectively recovered. Hence, an "off-on" fluorescence probe was designed to detect lead (II) in the range of 0-580 μM and the limit of detection (LOD) was 0.068 μM. In the meanwhile, the experiments showed that the CQDs can be successfully used in bioimaging and as a hidden fluorescent ink.

High quantum yield nitrogen and boron co-doped carbon dots for sensing Ag+, biological imaging and fluorescent inks

Herein, bright blue-green fluorescent nitrogen and boron co-doped carbon dots (N, B-CDs) with a quantum yield (QY) up to 33.04% were synthesized viahydrothermal treatment from ammonium citrate tribasic and 3-aminophenylboronic acid. The synthesized N, B-CDs showed outstanding water solubility. According to the principle of the static quenching effect (SQE), the synthesized N, B-CDs were utilized as an efficient sensor for sensing Ag⁺. The linear range and limit of detection (LOD) of the sensor for Ag⁺ are 0.99-26.04 μM and 9.03 nM (3σ/m). The proposed method was successfully adopted to detect Ag⁺ in environmental water, which is of great significance to environmental detection. Furthermore, due to the excellent fluorescence performance, the N, B-CDs were found to be an effective tool for biological imaging and as a fluorescent ink, which widens the horizons for the multifunctional applications of N, B-CDs.