Carbon dots based fluorescent sensor for sensitive determination of hydroquinone

Carbon dots-based dual-emission ratiometric fluorescent sensors for fluorescence and visual detection of hypochlorite and Cu2

Carbon dots (CDs) with blue emission were synthesized by solvothermal method using hydroquinone and 5-aminoisphthalic acid as precursors. The strong oxidation of ClO- caused the fluorescence quenching of CDs at 405 nm, and synchronously generated a new emission peak at 500 nm. Furthermore, upon the addition of Cu2+ to CDs-ClO- system, the green fluorescence at 500 nm was quenched, while the blue emission at 405 nm remained unchanged, due to the complexation between Cu2+ and the amino group on the CDs surface. Meanwhile, the fluorescence color of system changed from blue to bright green and then to dark blue by sequentially increasing the concentrations of ClO- and Cu2+. The fluorescence signal of F500/F405 exhibited a linear relationship with the concentration of ClO- and Cu2+ in a certain range, respectively. Thus, a ratiometric fluorescence sensor based on the obtained CDs were developed to sequentially detect ClO- and Cu2+ with detection limits of 0.40 μM and 0.31 μM, respectively. Additionally, the CDs were mixed with polyvinyl alcohol hydrogel to form test strips, which were successfully used for visual detection of ClO- and Cu2+. Satisfactory results were also obtained in the analysis of ClO- and Cu2+ in actual water samples.

Facile Layer Diffusion Technique for Synthesis of Terbium-Based Metal Organic Framework for Fluorometric Sensing of Hydroquinone

A photoluminescent terbium (III)-based Metal Organic Framework (MOF) was synthesized at room temperature by layer diffusion method utilizing mixed carboxylate linkers (4,4'-oxybis(benzoic acid) and benzene-1,3,5 tricarboxylic acid). Synthesized MOF has crystalline nature and rod-shaped morphology and is thermally stable up to 455 °C. The fluorescence emission spectra and theoretical results revealed that carboxylate linkers functioned as sensitizers for Tb(III) photoluminescence which resulted in four distinct emission peaks at 495, 547, 584, and 621 nm corresponding to the transitions 5D4 → 7F6, 5D4 → 7F5, 5D4 → 7F4, and 5D4 → 7F3. Using synthesized MOF as fluorescent probe, hydroquinone was detected in aqueous medium with a detection limit of 0.048 μM, remarkable recovery (95.6-101.1%), and relative standard deviation less than 2.25%. The quenching phenomenon may be ascribed to electron transfer from synthesized probe to oxidized hydroquinone via carboxylic groups on the surface of MOF, which is further supported by photo-induced electron transfer mechanism. This study introduces a cheaper, faster, and more accurate method for hydroquinone detection.

Rhodamine B functionalized luminescent metal-organic frameworks for ratiometric fluorescence sensing of hydroquinone

The development of sensitive and selective detection methods for hydroquinone (HQ), a phenolic organic compound with high toxicity and low degradability, is of extraordinary importance. In this work, a fluorescent sensor based on functionalized luminescent metal-organic frameworks (LMOFs) was designed and applied for the ratiometric fluorescence sensing of HQ. The sensor was prepared by the functionalization of IRMOF-3 with rhodamine B (RhB), possessing dual-emission fluorescence properties. After the addition of HQ, the blue fluorescence of the IRMOF-3 framework was gradually weakened, while the red fluorescence of RhB remained unchanged, resulting in the continuous fluorescence change of RhB@IRMOF-3 with HQ concentrations. The sensing mechanism demonstrates that HQ changes the fluorescence of the sensor via electron transfer between benzoquinone and RhB@IRMOF-3. The RhB@IRMOF-3 sensor has the advantages of a wide linear range, quick response speed, and strong specificity for HQ detection. This work is the first attempt focusing on functionalized LMOFs for HQ fluorescence detection, which has superb potential for the application to real environmental water samples.

Quantification of 2-chlorohydroquinone based on interaction between N-doped carbon quantum dots probe and photolysis products in fluorescence system

As a member of chlorophenolic compounds, 2-chlorohydroquinone (H₂QCl) has been widely used as intermediates in various chemical industries and leaded to serious threat on the environment. It is urgent to develop simple and robust analytical method for sensitive and selective determination of H₂QCl. Carbon quantum dots (CQDs), a promising photoluminescence nanomaterial, have gained sufficient concern as optical sensors owing to their outstanding photochemical properties. In this work, nitrogen doped carbon quantum dots (N-CQDs) were successfully synthesized by a simple secondary hydrothermal method and applied as a fluorescent probe for the quantitation of H₂QCl. A new fluorescence region centered at excitation wavelength of 310 nm and emission wavelength of 390 nm appeared after nitrogen doping. It was found that the N-CQDs exhibited a high selectivity towards H₂QCl with sensitive fluorescence response and the fluorescence quenching of N-CQDs was linear with the concentration of H₂QCl in the range of 30-90 μM (Y = 0.0049X + 0.1255, R² = 0.996). This is the first time that the dual role of excitation light was observed in the fluorescence detection system. The ultraviolet light acted as not only the excitation energy source for N-CQDs photoluminescence, but also the light source for photolysis of H₂QCl. In the detection process, H₂QCl was degraded to p-benzoquinone by light, and then the CQDs combined with p-benzoquinone through Michael addition reaction under the action of doped nitrogen. The electron transfer from N-CQDs to the linked p-benzoquinone caused the quenching of fluorescence originated from the edge state of N-CQDs. Furthermore, this established method can be applied for the quantitative determination of H₂QCl in environmental water samples with satisfactory recoveries between 94.31 and 105.51%.

Sensitive detection of picric acid in an aqueous solution using fluorescent nonconjugated polymer dots as fluorescent probes

Nonconjugated polymer dots (NPDs) were successfully used as fluorescent probes to selectively and sensitively detect picric acid (PA). The NPDs were prepared from polyethylenimine and 1,4-phthalaldehyde under mild conditions and had excitation and emission maxima of 351 and 474 nm, respectively. Fluorescence of the NPDs was efficiently quenched by PA through the inner filter effect because of the overlapping PA absorption band and NPD excitation spectrum. The NPDs allowed PA to be determined with a high degree of sensitivity. The linear range was 0-140μM and the detection limit was 0.5μM. The work involved developing a novel method for synthesizing NPDs and a promising platform for determining PA in environmental media.

Facile synthesis of doped CxNy QDs as photoluminescent matrix for direct detection of hydroquinone

In this work, we are reporting facile hydrothermal synthesis of a highly photoluminescent doped carbon nitride quantum dots (C_xN_yQDs) and implied it for direct detection of hydroquinone (H₂Q) by photoluminescence quenching phenomenon. Oxygen and sulphur moieties are regarded as dopant species in C_xN_yQDs and sourced from cheap solid precursors viz. cysteine and maleic acid. Morphological studies of C_xN_yQDs have done by SEM and TEM techniques, while structural analysis has carried out using FTIR, XPS, EDS and UV-Visible spectroscopy. The strong tendency of dispersivity of this QD in water has revealed by its zeta potential value of -32.4 mV. Optical properties of the as-prepared QDs have optimized at different excitation wavelengths. The photoluminescence stability of the dispersion is tested in various pH solutions and under continuous UV irradiation (365 nm). After that, sensing property is observed in quenching of photoluminescence feature of as-prepared QDs by direct addition of various concentrations of H₂Q. We obtained lower detection limit (LOD) of 50 nM (S/N = 3) in linear range from 12 to 57.5 μM. The reduction in photoluminescence of QDs may be attributed to electron transfer from QDs to oxidized H₂Q via -S^- and -COO^- groups present at its surface. Further, as-prepared QDs matrix exhibited high selectivity for hydroquinone over a range of potential interfering agents. Thus, the present work shows cost-effective facile synthesis of highly stable O- and S-doped carbon nitride (C_xN_y) quantum dots as promising photoluminescent sensor for pollutant hydroquinone without help of any enzyme or polymer assisted system.

Nitrogen, silicon co-doped carbon dots as the fluorescence nanoprobe for trace p-nitrophenol detection based on inner filter effect

P-nitrophenol (PNP) has been widely applied to industry processing for many purposes, but the persistence and toxicity of residuum may pose risks to human health. To analyze PNP in industrial and agricultural wastewater, a versatile fluorescent probe sensing platform was proposed. In this work, we devised a fluorescence approach that utilized nitrogen, silicon co-doped carbon dots (N,Si-CDs) to monitor PNP originating from the inner filter effect (IFE). The N,Si-CDs were generated in a one-step hydrothermal synthesis, and which possessed outstanding fluorescence signal and water-dispersity. Emission at 441 nm was monitored with excitation at 360 nm using a common spectrofluorometer. The method achieved an exceptionally low limit of detection (LOD) of 0.011 μM. Furthermore, this method not only eliminates the interference from metal ions and acid ions, but also provides a potential application prospect for N,Si-CDs in the field of water monitoring. Analysis of tap and lake water led to 93.30-106.30% recoveries and <1% relative standard deviation at 2.5-25 μM PNP concentrations.

Nanocomposite of Ag nanoparticles and catalytic fluorescent carbon dots for synergistic bactericidal activity through enhanced reactive oxygen species generation

Microwave mediated synthesis of catalytic fluorescent carbon dots (Cdots) has been reported using biodegradable starch as precursor. The as-synthesized Cdots were then characterized using various techniques such as fluorescence spectroscopy, fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) analysis. Interestingly, Cdots showed high catalytic activity in the photo-reduction of Ag⁺ to silver nanoparticles (Ag NPs). During the photo-reduction process, no additional surface passivating agents was needed to stabilize the Ag NPs. Further, TEM results indicated the formation of Cdot-Ag NP nanocomposite i.e. Ag NPs surrounded with Cdots, and the emission intensity of Cdots was significantly decreased whereas the lifetime of Cdots remained almost unaltered in the presence of Ag NPs following static quenching. Finally, combination therapy of Cdots and Ag NPs using Cdot-Ag NP nanocomposite was performed which indicated synergistic bactericidal activity against antibiotic resistant recombinant E. coli bacteria. The treatment elevated the reactive oxygen species (ROS) level as compared to its individual components. Additionally, the flow cytometer study demonstrated that combination therapy causing bacterial cell wall perforation that was possibly leading to synergistic bactericidal activity against both Gram positive and Gram negative bacteria. The presence of Cdots on the surface of the Ag NPs due to their ground state complexation, possibly facilitated electrons towards Ag NPs which enhanced the ROS production in comparison to only Ag NPs.

A double carbon dot system composed of N, Cl-doped carbon dots and N, Cu-doped carbon dots as peroxidase mimics and as fluorescent probes for the determination of hydroquinone by fluorescence

A fluorescence method is described for the determination of hydroquinone based on the double carbon dot system as peroxide mimic enzymes and fluorescent probes. Deep eutectic solvent (DES)-based fluorescent carbon dots (N/Cl-CDs) and copper-doped carbon dots (N/Cu-CDs) were prepared by the hydrothermal method. Both carbon dots were characterized with transmission electron microscopy (TEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), ultraviolet-visible (UV-Vis) spectroscopy, X-ray photoelectron spectrometry (XPS), Fourier transform infrared (FT-IR) spectroscopy, and fluorescence spectroscopy. N/Cl-CDs displayed intrinsic peroxidase-like activity and were able to catalyze the oxidation of hydroquinone (H₂Q) to p-benzoquinone (BQ) along with an intermediate. The intermediate (BQ) did quench the N/Cu-CD photoluminescence (PL) at 450 nm using an excitation wavelength of 347 nm. Based on the results, a fluorescent platform is proposed for the determination of hydroquinone with a promising determination limit of 0.04 μM (linear range, 1.0-75 μM). The recoveries of spiked water samples were in the range 89.5-105.1%, with relative standard deviations (RSDs) of 1.5-2.9%. This method was applied to determination of H₂Q in environmental water samples. Graphical abstract A fluorescence method was established for the determination of hydroquinone based on the double carbon dot system as peroxide-mimic enzymes and fluorescent probes. Chlorine-doped carbon dots (N/Cl-CDs) derived from deep eutectic solvent (DES) displayed intrinsic peroxidase-like activity, and were able to catalyze the oxidation of hydroquinone (H2Q) to p-benzoquinone (BQ) along with an intermediate. The intermediate (BQ) did quench the N/Cu-CD photoluminescence (PL). This method was applied to H2Q in environmental water samples.

Coumarin-Modified Graphene Quantum Dots as a Sensing Platform for Multicomponent Detection and Its Applications in Fruits and Living Cells

In this work, coumarin derivatives (C) are used to enhance the fluorescence of graphene quantum dots (GQDs) by covalently linking the carboxyl groups on the edge of the GQD sheet. The as-synthesized coumarin-modified graphene quantum dots (C-GQDs) have a uniform particle size with an average diameter of 3.6 nm. Simultaneously, the C-GQDs have strong fluorescence emission, excellent photostability, and high fluorescence quantum yield. C-GQDs and CN- can form a C-GQDs+CN- system due to deprotonation and/or intermolecular interactions. The introduced hydroquinone (HQ) is oxidized to benzoquinone (BQ), and the interaction between BQ and the C-GQDs+CN- system could lead to fluorescence enhancement of C-GQDs. Meanwhile, the redox reaction between BQ and ascorbic acid (AA) can be used for quantitative detection of AA with CN- and HQ being used as substrates. Based on the above mechanism, C-GQDs are developed as a multicomponent detection and sensing platform, and the detection limits for CN-, HQ, and AA were 4.7, 2.2, and 2.2 nM, respectively. More importantly, satisfactory results were obtained when the platform was used to detect CN-, HQ, and AA in living cells and fresh fruits.

Electrodeposition-Assisted Rapid Preparation of Pt Nanocluster/3D Graphene Hybrid Nanozymes with Outstanding Multiple Oxidase-Like Activity for Distinguishing Colorimetric Determination of Dihydroxybenzene Isomers

Here, we demonstrate a facile bottom-up strategy to fabricate Pt nanoclusters (Pt NCs) grafted onto three-dimensional graphene foam (3D GF) assisted by cetyltrimethyl ammonium bromide (CTAB) using the electrodeposition method. The homogeneous grafting of Pt NC onto 3D GF is due to the formation of hemimicelles above some CTAB concentration. With the unique nanocluster structure and the high content of Pt⁰, the Pt NC/3D GF nanohybrid exhibits extremely high activity and shows higher reusability and stability. Apart from the intrinsic oxidase-like activity with 3,3',5,5'-tetramethylbenzidine (TMB) as the substrate, the Pt NC/3D GF nanohybrid can act simultaneously as an effective polyphenol oxidase (PPO) mimic, such as tyrosinase, catechol oxidase, and laccase. More importantly, utilizing intrinsic catechol oxidase-like activity and the oxidase-like activity with TMB as the substrate of the nanohybrid, distinguishing colorimetric determination of dihydroxybenzene isomers (catechol and hydroquinone) is performed. Distinguishing colorimetric analysis of dihydroxybenzene isomers was first developed using nanozymes. The present work provides a simple bottom-up approach for the reasonable fabrication of various nanostructured nanozymes with excellent performance using the electrodeposition method assisted with surfactants.

Biogreen Synthesis of Carbon Dots for Biotechnology and Nanomedicine Applications

Over the past decade, carbon dots have ignited a burst of interest in many different fields, including nanomedicine, solar energy, optoelectronics, energy storage, and sensing applications, owing to their excellent photoluminescence properties and the easiness to modify their optical properties through doping and functionalization. In this review, the synthesis, structural and optical properties, as well as photoluminescence mechanisms of carbon dots are first reviewed and summarized. Then, we describe a series of designs for carbon dot-based sensors and the different sensing mechanisms associated with them. Thereafter, we elaborate on recent research advances on carbon dot-based sensors for the selective and sensitive detection of a wide range of analytes, including heavy metals, cations, anions, biomolecules, biomarkers, nitroaromatic explosives, pollutants, vitamins, and drugs. Lastly, we provide a concluding perspective on the overall status, challenges, and future directions for the use of carbon dots in real-life sensing.

Fluorescence method for quickly detecting ochratoxin A in flour and beer using nitrogen doped carbon dots and silver nanoparticles

In this paper, a FRET (Forster resonance energy transfer) based fluorescence method was developed for the quickly detection of ochratoxin A (OTA) in agricultural products (e.g., flour and beer). A highly fluorescent nitrogen doped carbon dots (CD) were served as energy donor, the DNA and MCH (6-mercapto-1-hexanol) modified Ag nanoparticles were served as energy acceptor in the FRET system. OTA can be detected in a concentration range between 10 and 5000 nM, the limit of detection is 8.7 nM. This method has three advantages: (1) an enhanced fluorescent intensity can be acquired by utilizing the nitrogen doped CD synthesized by one-step approach without sophisticated modification of nanoparticles; (2) OTA detection was accomplished quickly (less than 30 min) by using MCH as assistant molecule; (3) an extended OTA detection linear range was acquired, which may facilitate the OTA detection in real agricultural samples, and is helpful for solving food safety problems.

Conjugated polymer nanoparticles-based fluorescent biosensor for ultrasensitive detection of hydroquinone

This work describes a simple and sensitive fluorescent method for detection of hydroquinone utilizing conjugated polymer nanoparticles (CPNs). The CPNs serve both as a catalyst to accelerate the conversion of hydroquinone to benzoquinone and a fluorescent probe. In the presence of hydroquinone, the fluorescence of CPNs can be effectively quenched by benzoquinone. The detection limit of hydroquinone was down to 5 nM and excellent selectivity toward possible interferences was obtained. This method was successfully applied for hydroquinone detection in lake water and satisfactory results were achieved.

Carbon Nanomaterials in Biological Studies and Biomedicine

The "carbon nano-world" has made over the past few decades huge contributions in diverse scientific disciplines and technological advances. While dramatic advances have been widely publicized in using carbon nanomaterials such as fullerenes, carbon nanotubes, and graphene in materials sciences, nano-electronics, and photonics, their contributions to biology and biomedicine have been noteworthy as well. This Review focuses on the use of carbon nanotubes (CNTs), graphene, and carbon quantum dots [encompassing graphene quantum dots (GQDs) and carbon dots (C-dots)] in biologically oriented materials and applications. Examples of these remarkable nanomaterials in bio-sensing, cell- and tissue-imaging, regenerative medicine, and other applications are presented and discussed, emphasizing the significance of their unique properties and their future potential.

Formation of N, S-codoped fluorescent carbon dots from biomass and their application for the selective detection of mercury and iron ion

Biomass is regarded as an excellent candidate for the preparation of heteroatom-doped carbon nanomaterials. We have developed a simple and facile one-pot synthesis of nitrogen and sulfur codoped fluorescent carbon dots from pigeon feathers, egg and manure via the pyrolysis carbonization method. The as-prepared four PCDs have high fluorescence quantum yield about 24.87% (PCDs-f), 17.48% (PCDs-w), 16.34% (PCDs-y), 33.50% (PCDs-m), respectively, which is higher than the other carbon dots preparing from biomass. We found that the preparation of PCDs-m with pigeon manure has no favourable selectively with heavy metal ions. However, other PCDs exhibit highly sensitive and selective detection behavior of Hg²⁺/Fe³⁺ ions with a low detection limit of 10.3 and 60.9nM. They were applied to imaging of human umbilical vein endothelial cells, showing low cytotoxicity and good biocompatibility.

Determination of sunset yellow in soft drinks based on fluorescence quenching of carbon dots

Fluorescent carbon dots was prepared by heating N-(2-hydroxyethyl)ethylene diaminetriacetic acid in air. The carbon dots were not only highly soluble in water but also uniform in size, and possessed strong blue fluorescence and excitation wavelength-dependent emission properties with the maximum excitation and emission wavelength at 366nm and 423nm, respectively. Food colorant sunset yellow whose excitation and emission wavelength at 303nm and 430nm could selectively quench the fluorescence of carbon dots, efficient fluorescent resonance energy transfer between the carbon dots and sunset yellow is achieved. This was exploited to design a method for the determination of sunset yellow in the concentration range from 0.3 to 8.0μmolL(-1), with a limit of detection (3σ/k) of 79.6nmolL(-1). Furthermore the fluorimetric detection method was established and validated for sunset yellow in soft drinks samples with satisfactory results.

Fluorescence quenching and spectrophotometric methods for the determination of 6-mercaptopurine based on carbon dots

A carbon dot-based fluorescence probe was designed for detecting 6-mercaptopurine (6-MP) via fluorescence quenching.