Green preparation of carbon dots from Momordica charantia L. for rapid and effective sensing of p-aminoazobenzene in environmental samples

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.

SERS Detection of Trace Carcinogenic Aromatic Amines Based on Amorphous MoO3 Monolayers

Aromatic amines are important commercial chemicals, but their carcinogenicity poses a threat to humans and other organisms, making their rapid quantitative detection increasingly urgent. Here, amorphous MoO3 (a-MoO3) monolayers with localized surface plasmon resonance (LSPR) effect in the visible region are designed for the trace detection of carcinogenic aromatic amine molecules. The hot-electron fast decay component of a-MoO3 decreases from 301 fs to 150 fs after absorption with methyl orange (MO) molecules, indicating the plasmon-induced hot-electron transfer (PIHET) process from a-MoO3 to MO. Therefore, a-MoO3 monolayers present high SERS performance due to the synergistic effect of electromagnetic enhancement (EM) and PIHET, proposing the EM-PIHET synergistic mechanism in a-MoO3. In addition, a-MoO3 possesses higher electron delocalization and electronic state density than crystal MoO3 (c-MoO3), which is conducive to the PIHET. The limit of detection (LOD) for o-aminoazotoluene (o-AAT) is 10-9 M with good uniformity, acid resistance, and thermal stability. In this work, trace detection and identification of various carcinogenic aromatic amines based on a-MoO3 monolayers is realized, which is of great significance for reducing cancer infection rates.

Constructing an eco-friendly and ratiometric fluorescent sensor for highly efficient detection of mercury ion in environmental samples

Mercury ion (Hg2+) is a highly toxic and ubiquitous pollutant, whose effective detection has aroused widespread concern. A novel ratiometric fluorescent sensor has been designed to rapidly and efficiently detect Hg2+ based on blue/red carbon dots (CDs) with environmental friendliness. This sensor was well characterized via TEM, FTIR, XPS, UV-vis, and zeta potential analysis and displayed excellent fluorescence properties and stability. The fluorescence of blue CDs at 447 nm was significantly quenched with the addition of Hg2+ resulted from the static quenching, whereas that of red CDs at 650 nm remained invariable. A sensitive method for Hg2+ determination was constructed in the range of 0.05-7.0 nmol mL-1 with optimal conditions, and the detection limit was down to 0.028 nmol mL-1. Meanwhile, compared to other 17 metal ions, the ratiometric fluorescent sensor exhibited high selectivity for Hg2+. Furthermore, satisfied recoveries had also been obtained for measuring trace Hg2+ in practical environmental samples. This developed ratiometric fluorescent sensor provided a reliable, environmental-friendly, rapid, and efficient platform for the detection of Hg2+ in environmental applications.

Selective fluorescent probe for sensitive determination of bisphenol A based on molecularly imprinted polymers decorated carbon dots derived from citric acid and ethylenediamine

Bisphenol A (BPA) is an endocrine disrupting chemical and poses a grave threat to the human health. Herein, a fluorescent probe constructed with molecularly imprinted polymers decorated carbon dots (CDs@MIPs) was proposed for determination of BPA with high selectivity. The CDs@MIPs were constructed using BPA, 4-vinylpyridine and ethylene glycol dimethacrylate as template, functional monomer and cross linker, respectively. The obtained fluorescent probe not only owned a highly selective recognition function derived from MIPs but also displayed an excellent sensitivity for sensing BPA stemmed from CDs. The fluorescence intensity of CDs@MIPs was varied before and after the removal of BPA templates. The fluorescent decrease fraction of the fluorescent probe demonstrates a nice linearity in BPA concentration range of 10-2000 nM (r² = 0.9998) and the detection limit is as low as 1.5 nM. The fluorescent probe was triumphantly utilized to sense the level of BPA in real aqueous and plastic samples with good results. Moreover, the fluorescent probe offered a wonderful means for fast identification and sensitive detection of BPA from environmental aqueous samples.

A critical review on the environmental applications of carbon dots

The discovery of zero-dimensional carbonaceous nanostructures called carbon dots (CDs) and their unique properties associated with fluorescence, quantum confinement and size effects have intrigued researchers. There has been a substantial increase in the amount of research conducted on the lines of synthesis, characterization, modification, and enhancement of properties by doping or design of composite materials, and a diversification of their applications in sensing, catalysis, optoelectronics, photovoltaics, and imaging, among many others. CDs fulfill the need for inexpensive, simple, and continuous environmental monitoring, detection, and remediation of various contaminants such as metals, dyes, pesticides, antibiotics, and other chemicals. The principles of green chemistry have also prompted researchers to rethink novel modes of nanoparticle synthesis by incorporating naturally available carbon precursors or developing micro reactor-based techniques. Photocatalysis using CDs has introduced the possibility of utilizing light to accelerate redox chemical transformations. This comprehensive review aims to provide the reader with a broader perspective of carbon dots by encapsulating the concepts of synthesis, characterization, applications in contaminant detection and photocatalysis, demerits and research gaps, and potential areas of improvement.

Nitrogen and sulphur doped carbon dot: An excellent biocompatible candidate for in-vitro cancer cell imaging and beyond

Carbon dots (CDs) are an exquisite class of carbon allotrope that is already well nourished for their good biocompatibility, water-solubility, excellent photostability, and magnificent photoluminescence property. Doping strategy with heteroatoms is an efficacious way to modify the physicochemical and optical properties, making the carbon dots an exceedingly potential candidate. This work reports the fabrication and cancer cell imaging application of photoluminescent heteroatom-doped carbon dots by use of cysteine and urea as carbon, nitrogen, and sulphur sources through a straightforward and highly productive hydrothermal procedure. The fabricated luminescent carbon dots are spherical in shape, with an average diameter of 3.5 nm. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) characterization revealed key facts about the surface functional groups and chemical compositions of carbon dots. The excitation-dependent photoluminescence (PL) peak appeared at around 445 nm against the excited wavelength of 350 nm. Moreover, under the provided experimental conditions, all the carbon dots are non-toxic and safe. The cytotoxicity and the safety profiles of the carbon dots were found to be in the bearable range under normal in-vitro experimental circumstances. Cellular uptake was observed by the green fluorescence of carbon dots inside cells. Likewise, the carbon dots did not alter the cell viability of the normal glial cell line. Again, when treated with the carbon dots, there was no notable increase of apoptotic cells in the G2/M phase of cell cycle analysis that confirmed the imaging-trackable ability of the carbon dots.

Green Carbon Dots: Synthesis, Characterization, Properties and Biomedical Applications

Carbon dots (CDs) are a new category of crystalline, quasi-spherical fluorescence, "zero-dimensional" carbon nanomaterials with a spatial size between 1 nm to 10 nm and have gained widespread attention in recent years. Green CDs are carbon dots synthesised from renewable biomass such as agro-waste, plants or medicinal plants and other organic biomaterials. Plant-mediated synthesis of CDs is a green chemistry approach that connects nanotechnology with the green synthesis of CDs. Notably, CDs made with green technology are economical and far superior to those manufactured with physicochemical methods due to their exclusive benefits, such as being affordable, having high stability, having a simple protocol, and being safer and eco-benign. Green CDs can be synthesized by using ultrasonic strategy, chemical oxidation, carbonization, solvothermal and hydrothermal processes, and microwave irradiation using various plant-based organic resources. CDs made by green technology have diverse applications in biomedical fields such as bioimaging, biosensing and nanomedicine, which are ascribed to their unique properties, including excellent luminescence effect, strong stability and good biocompatibility. This review mainly focuses on green CDs synthesis, characterization techniques, beneficial properties of plant resource-based green CDs and their biomedical applications. This review article also looks at the research gaps and future research directions for the continuous deepening of the exploration of green CDs.

Fast and efficient "on-off-on" fluorescent sensor from N-doped carbon dots for detection of mercury and iodine ions in environmental water

A kind of nitrogen doped carbon dots (N-CDs) was facilely fabricated from polyethyleneimine and anhydrous citric acid, and which was adopted to develop a neoteric "on-off" and "off-on" fluorescent sensor for rapidly and efficiently sensing Hg²⁺ and I^-. The fluorescence of N-CDs was notably quenched (off) in the existence of Hg²⁺ derived from strong interaction and the electron transfer between N-CDs and Hg²⁺, while the quenched fluorescence of the N-CDs and Hg²⁺ system was strikingly regained by addition of I^- (on) resulted from the separation of N-CDs and Hg²⁺ due to the higher binding preference between Hg²⁺ and I^-. Under optimal conditions, the linear detection ranges were 0.01-20 μM for Hg²⁺ and 0.025-7 μM for I^-, respectively. Meanwhile, the detection limits could be down to 3.3 nM for Hg²⁺ and 8.5 nM for I^-, respectively. Satisfied recoveries had also been gained for measuring Hg²⁺ and I^- in practical water samples. The constructed "on-off-on" fluorescent sensor provided a simple, rapid, robust and reliable platform for detecting Hg²⁺ and I^- in environmental applications.

A stable and highly luminescent 3D Eu(III)-organic framework for the detection of colchicine in aqueous environment

The metal-organic framework materials have an important application as sensors. In this work, a microporous three-dimensional (3D) Eu(III)-organic framework (Eu-MOF), [Eu₂(3,5-bct)(phen)₂(ox)₂(H₂O)]·H₂O, was constructed from 3,5-bis(3'-carboxyphenyl)-1,2,4-triazole (3,5-H₂bct), oxalate (ox) and 1,10-phenanthroline (phen) as a luminescent sensor. The free volume was found to be 15.7% per unit volume ignoring the free water molecules. The Eu-MOF showed bright red light due to the emission at 622 nm (⁵D₀ → ⁷F₂ transition) of the Eu(III) with high quantum yield (QY, 52.51%). The Eu-MOF exerted high luminescence stability in common organic solvents as well as aqueous solutions within a wide pH range from 4 to 11. Based on the luminescent Eu-MOF, the sensing behavior for colchicine in the aqueous environment was studied. Highly selective and sensitive detection (LOD = 2.43 × 10^-5 mol L^-1) of colchicine was observed by the Eu-MOF even in the presence of potential interfering components. The sensing mechanism for colchicine was investigated by experimental and theoretical results. It is worth noting that a film (Film@Eu-MOF) prepared by loading Eu-MOF showed intense characteristic red light emission under UV light. The luminescence color changed immediately from red to colorless when the Film@Eu-MOF came in contact with colchicine. Highly sensitive and rapid detection of colchicine in wastewater was achieved using this Film@Eu-MOF, which could be identified by the naked eye. The experimental results suggest that the synthesized Eu-MOF has potential application as a luminescent sensing material for pollutants in the environmental system.