Ultrasensitive detection of Cr(VI) (Cr2O72-/CrO42-) ions in water environment with a fluorescent sensor based on metal-organic frameworks combined with sulfur quantum dots

An "on-off-on" fluorescent sensor based on Sm:ZnO-NH2 QDs for hexavalent chromium detection

The problems of poor water solubility, poor stability, and poor selectivity encountered in the determination of hexavalent chromium (Cr(VI)) in water using ZnO QDs need to be addressed. In this study, we successfully prepared Sm-doped, -NH2-modified Sm:ZnO-NH2 QDs via the sol-gel method. Sm doping was used to enhance the fluorescence intensity of ZnO QDs, while 3-aminopropyltrietoxysilane (APTEs) capping improved their water solubility and fluorescence stability. The fluorescence of Sm:ZnO-NH2 quantum dots was quenched after the addition of Cr(VI) due to the internal filtration effect(IFE), and was restored after the addition of ascorbic acid due to the redox reaction between ascorbic acid (AA) and Cr(VI). Leveraging the fluorescence response patterns of the Sm:ZnO-NH2 QDs system when exposed to Cr(VI) and AA, we developed an ''on-off-on'' fluorescent sensor that can specifically detect Cr(VI) and AA without interference from Cu2+ ions. The "on-off-on" fluorescent sensor exhibited a linear response to Cr(VI) concentrations ranging from 0.05 to 1.5 μg/mL, with a limit of detection (LOD) of 6.15 ng/mL. It exhibited excellent selectivity and repeatability. Furthermore, the Sm:ZnO-NH2 QDs fluorescent sensor was effectively utilized for detecting Cr(VI) in tap water, offering a new method for heavy metal detection via an "on-off-on" fluorescence switching mechanism.

Intelligent sensing platform based on europium-doped carbon dots for dual-functional detection of ciprofloxacin/Ga3+ and its tracking in vivo

Ciprofloxacin (CIP) and gallium (Ga) are widely used in many fields and their excessive presences will pose serious threats to the environment and life health. Therefore, developing an intelligent detection method for rapidly tracking and determination of CIP and Ga3⁺ concentration in environments and organisms is of great significance. In this work, a europium-doped carbon dots (Eu-CDs) with unique structure and performances was prepared by a one-pot hydrothermal method. Eu-CDs can efficiently overcome the problem of aggregation-induced fluorescence quenching in complex environments to track CIP and Ga3⁺ with highly sensitivity. The "antenna effect" of non-radiative energy transfer is introduced to explain the pathway on fluorescence transition of Eu-CDs through DFT theoretical calculations and mechanism investigations, which provide a theoretical basis for the design and development of novel carbon dots with specific functions. Eu-CDs can successfully be applied to fluorescence imaging in organisms, moreover, it also exhibits excellent application potentials in the field of anti-tumor and antibacterial. In addition, a portable intelligent detection platform based on Eu-CDs-hydrogel device have been developed, which provides a new strategy for rapidly detection of CIP and Ga3⁺ in real samples.

Smart paper-based materials incorporating nitrogen and boron co-doped MXene quantum dots for rapid adsorption and sensitive detection of Cr2O72. J Colloid Interface Sci 2025;679:510-520. [PMID: 39378686 DOI: 10.1016/j.jcis.2024.10.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Dichromate ion (Cr2O72-) is a highly toxic chromium-containing compound that poses significant hazards to the digestive, respiratory systems, skin, and mucous membranes. Currently, the detection and adsorption of Cr2O72- face significant challenges, including the time-consuming and low sensitivity nature of traditional analytical methods. The limited efficiency and capacity of existing adsorbents hinder their practical application in real-time water quality monitoring and environmental remediation. Herein, using polyethyleneimine-functionalized (PEI) pulp fiber paper as the substrate, we developed smart paper-based materials (designated as NB-MQDs@PP) incorporated with nitrogen and boron co-doped MXene quantum dots (NB-MQDs) for rapid adsorption and sensitive detection of Cr2O72-. Compared to undoped MQDs, NB-MQDs exhibited longer excitation wavelength and enhanced oxidation stability. As anticipated, NB-MQDs achieved rapid (response time of 10 s) and sensitive (detection limit of 1.2 μM) recognition of Cr2O72- within a wide pH range with a quenching efficiency of 99.9%. Simultaneously, two on-site detection methods, immersion and cyclic filtration, were constructed based on NB-MQDs@PP. The detection limit of the immersion method was 17.0 nM, while the cyclic filtration method had a detection limit as low as 3.8 nM, surpassing the majority of those reported literatures. Remarkably, NB-MQDs@PP exhibited outstanding enrichment capacity towards Cr2O72-, with an adsorption capacity of up to 162.4 mg/g. This work provides a novel strategy for creating unique paper-based materials with excellent capture and monitoring dual-function, which can be customized according to the requirements of various application scenarios.

Eco-friendly sensing of hexavalent chromium ions via copper-doped carbon quantum dots: a fluorescent probe for water safety

The hydrothermal synthesis is presented of copper-doped carbon dots (Cu-CDs) from citric acid, urea, and copper chloride, resulting in blue-fluorescent particles with stable emission at 438 nm when excited at 340 nm. Through comprehensive spectroscopic and microscopic characterization (FTIR, XPS, UV, and HRTEM), the Cu-CDs demonstrated remarkable stability across varying pH levels, ionic strengths, temperatures, and UV exposure. Notably, Cu-CDs exhibit ultra-sensitive and selective detection of hexavalent chromium [Cr(VI)] ions in aqueous environments driven by fluorescence quenching. The system showed a robust linear response to Cr(VI) in the 0-80 µM range, with an impressive limit of detection (LOD) of 0.186 µM, significantly lower than the WHO's permissible limit of 0.96 µM. These findings position Cu-CDs as an effective tool for environmental monitoring and water safety applications.

Advances in the synthesis and properties of sulfur quantum dots for food safety detection and antibacterial applications

Food safety is closely related to human health and has become a worldwide, pressing concern. Food safety analysis is essential for ensuring food safety. Sulfur quantum dots (SQDs), a new type of zero-dimensional metal-free nanomaterials, have recently become the focus of scientific research due to their good luminescence properties, dispersibility, biocompatibility, and inherent antibacterial properties. This review focuses on recent advances in SQDs, with emphasis on their practical applications in the food field. First, commonly used methods for the synthesis of SQDs are presented, including traditional and emerging strategies. The properties of SQDs are then analyzed in detail, particularly their luminescence properties, catalytic activities, and reducing properties. Next, the use of SQDs in food safety detection and antibacterial fields are elaborated. Finally, this review discusses the challenges associated with the use of SQDs in food safety detection and antimicrobial applications.

Simple fluorochromic detection of chromium with ascorbic acid functionalized luminescent Bio-MOF-1

The bioaccumulation of various heavy metals in the environment and agriculture is posing serious hazards to human health. Hexavalent chromium is one of the most encountered heavy metal pollutants. The routine monitoring of Cr(VI) via simple methods assumes great analytical significance in sectors like environmental safety, food quality, etc. This study reports a novel biocompatible and luminescent metal-organic framework (ascorbic acid functionalized Bio-MOF-1) based "Turn-on" nanoprobe for rapid and sensitive optical detection of Cr(VI). Bio-MOF-1 has been synthesized, functionalized with ascorbic acid (AA), and then comprehensively characterized for its key material properties. The presence of Cr(VI) results in the photoluminescence recovery of Bio-MOF-1/AA. Using the above approach, Cr(VI) is detected over a wide concentration range of 0.02 to 20 ng mL-1, with the limit of detection being 0.01 ng mL-1. The nanoprobe is capable of detecting Cr(VI) in real water as well as in some spiked food samples. Hence, the ascorbic acid functionalized Bio-MOF-1 nanoprobe is established as a potential on-field detection tool for Cr(VI).

Fluorescent chemosensors facilitate the visualization of plant health and their living environment in sustainable agriculture

Globally, 91% of plant production encounters diverse environmental stresses that adversely affect their growth, leading to severe yield losses of 50-60%. In this case, monitoring the connection between the environment and plant health can balance population demands with environmental protection and resource distribution. Fluorescent chemosensors have shown great progress in monitoring the health and environment of plants due to their high sensitivity and biocompatibility. However, to date, no comprehensive analysis and systematic summary of fluorescent chemosensors used in monitoring the correlation between plant health and their environment have been reported. Thus, herein, we summarize the current fluorescent chemosensors ranging from their design strategies to applications in monitoring plant-environment interaction processes. First, we highlight the types of fluorescent chemosensors with design strategies to resolve the bottlenecks encountered in monitoring the health and living environment of plants. In addition, the applications of fluorescent small-molecule, nano and supramolecular chemosensors in the visualization of the health and living environment of plants are discussed. Finally, the major challenges and perspectives in this field are presented. This work will provide guidance for the design of efficient fluorescent chemosensors to monitor plant health, and then promote sustainable agricultural development.

Development of an "on-off-on" fluoroprobe utilizing an anthrylimidazole-based fluorescent ionic liquid for sensitive Cr(VI) and ascorbic acid detection

Developing a rapid detection method of Cr(VI) and ascorbic acid (AA) is vital in the food and environmental fields. Herein, an anthrylimidazole-based fluorescent ionic liquid (AI-FIL) with the advantageous fluorescent properties was successfully prepared and used to construct a promising "on-off-on" fluoroprobe for rapid/sensitive Cr(VI) and AA detection. Cr(VI) could effectively quench the fluorescence of AI-FIL owing to the inner-filter effect and photoinduced electron-transfer process. However, the decreased fluorescence could be rapidly recovered by AA owing to the redox reaction between AA and Cr(VI). For Cr(VI) detection, a satisfactorily linear response (0.03-300 μM) was achieved with the corresponding detection limit of 9 nM. For AA detection, a good linearity from 1 to 1000 μM was obtained with the resultant detection limit of 0.3 μM. Moreover, the AI-FIL based fluoroprobe was successfully utilized for Cr(VI) and AA detection in food and water samples with satisfactory accuracy and precision.

Lanthanide MOFs based portable fluorescence sensing platform: Quantitative and visual detection of ciprofloxacin and Al3

In the current context of water environmental monitoring and pollution control, there's a crucial need for rapid and simple methods to detect multi-pollutant. We herein report an easy one-step hydrothermal synthesis method to produce Eu-based metal-organic frameworks (Eu MOFs), which was used as a fluorescent probe to detect the aquatic environmental pollutants of ciprofloxacin (CIP) and aluminum ions (Al3+). This fluorescent sensor enabled the cascade detection of CIP and Al3+ through fluorescence enhancement and ratio fluorescence response, respectively. The introduction of CIP significantly turned on the characteristic fluorescence of Eu MOFs at 595 nm and 616 nm through the "antenna effect". Based on this, the sensor enables quantitative detection of CIP within a linear range of 0-120 μM with a LOD as low as 50.421 nM. In the presence of Al3+, the fluorescence emission of Eu MOFs-CIP was sharply turned off due to strong Al3+ coordination with CIP, while the blue fluorescence emission of CIP was remarkably enhanced. And thus allowing ratio fluorescence quantitative detection of Al3+ (LOD = 2.681 μM). The introduction of CIP and Al3+ in cascade resulted in distinct fluorescence color changes from colorless to red and eventually to blue, exhibiting pronounced fluorescence characteristics. This observable phenomenon enables the visual detection of CIP and Al3+ in both aqueous phase and paper test strips. By combining the analysis of fluorescence chromaticity with the use of a smartphone, the fluorescence color of test papers allows for simple quantitative determination, which provides a convenient and accessible approach for quantifying CIP and Al3+ in water environments.

Coordination polymer gel mediated spectrophotometric, ICP-AES and spectrofluorimetric methods for trace As(III) determination in water and food samples

Herein, a coordination polymer gel is proposed for the determination of As(III) in real samples through multispectroscopic techniques viz. spectrophotometry, spectrofluorimetry, and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Taguchi L32 (46 21) design and adaptive neuro fuzzy inference system (ANFIS) optimized the controllable factors affecting the extraction yielding an experimental S/N ratio of 39.94 dB. The fluorescence quenching (KSV = 2.63 × 106 L mol-1) was static with photoelectron transfer being the main mechanism confirmed by the density functional theory calculations. The limits of detection (LODs), limits of quantification (LOQs) and linear ranges were 0.038 μg L-1, 0.13 μg L-1 and 1.67-116.67 μg L-1, 0.40 μg L-1, 1.21 μg L-1 and 1.67-33.33 μg L-1, 1.07 μg L-1, 3.24 μg L-1 and 3.32-35.37 μg L-1 for the developed enrichment coupled ICP-AES, spectrophotometry and fluorescence sensing methods. Among these methods, the enrichment - ICP-AES method has the lowest LOD, LOQ and the widest linear range followed by the enrichment - spectrophotometry and fluorescene sensing methods. Spectrofluorimetry offers high sensitivity, selectivity, and possible real time monitoring, spectrophotometry provides a cost-effective and versatile option, while ICP-AES manifests multi-element analysis with high sensitivity and low interference. The developed methods were validated and employed for the successful determination of trace As(III) in real samples. The employment of these methods enhances the overall analytical capability for a wide range of sample types and concentrations.

Fabrication of highly luminescent and thermally stable composites of sulfur nanodots through surface modification and assembly

Sulfur nanodots (S-dots) have emerged as a promising luminescent material to excel over traditional heavy metal-based quantum dots. However, their relatively low emission efficiency and poor thermal stability in the solid state have limited their wide applications in photoelectric devices. In this work, highly luminescent, with a photoluminescence quantum yield higher than 50%, and thermally stable composites of S-dots were produced through modulating their surface states and aggregation behaviors by introducing pyromellitic dianhydride (PMDA) and benzoyleneurea (BEU), respectively. PMDA eliminated the relatively short-lived surface states and defects on the surface of S-dots and BEU regulated the aggregation states and facilitated the energy transfer from BEU to S-dots. The as-obtained composites also showed significantly improved thermal stability compared to S-dots, aided by the hydrophobic chemical groups and dense matrix of PMDA and BEU, which extended their applications in fabricating light-emitting diodes. Our presented results provide a new approach to produce highly luminescent S-dots, which widen their applications in the fields of bioimaging, sensing, photoelectric devices, and environmental science.

Multifunctional In-MOF and Its S-Scheme Heterojunction toward Pollutant Decontamination via Fluorescence Detection, Physical Adsorption, and Photocatalytic REDOX

A novel doubly interpenetrated indium-organic framework of 1 has been assembled by In3+ ions and highly conjugated biquinoline carboxylate-based bitopic connectors (H2L). The isolated 1 exhibits an anionic framework possessing channel-type apertures repleted with exposed quinoline N atoms and carboxyl O atoms. Owing to the unique architecture, 1 displays a durable photoluminescence effect and fluorescence quenching sensing toward CrO42-, Cr2O72-, and Cu2+ ions with reliable selectivity and anti-interference properties, fairly high detection sensitivity, and rather low detection limits. Ligand-to-ligand charge transition (LLCT) was identified as the essential cause of luminescence by modeling the ground state and excited states of 1 using DFT and TD-DFT. In addition, the negatively charged framework has the ability to rapidly capture single cationic MB, BR14, or BY24 and their mixture, including the talent to trap MB from the (MB + MO) system with high selectivity. Moreover, intrinsic light absorption capacity and band structure feature endow 1 with effective photocatalytic decomposition ability toward reactive dyes RR2 and RB13 under ultraviolet light. Notably, after further polishing the band structure state of 1 by constructing the S-scheme heterojunction of In2S3/1, highly efficient photocatalytic detoxification of Cr(VI) and degradation of reactive dyes have been fully achieved under visible light. This finding may open a new avenue for designing novel multifunctional MOF-based platforms to address some intractable environmental issues, i.e., detection of heavy metal ions, physical capture of pony-sized dyes, and photochemical decontamination of ultrastubborn reactive dyes and highly toxic Cr(VI) ions from water.

A dual-emitting Rhodamine B-encapsulated Zn-based MOF for the selective sensing of Chromium(VI)

A Rhodamine B-Zn-MOF composite (RhB-Zn-MOF) with dual emission intensity was synthesized through one pot synthesis by in-situ encapsulation of Rhodamine-B dye on a new Zn-MOF metal-organic framework [(Zn(OAc)2(4-BrIPh) (1,10-phenonthroline)(H2O)].H2O, (4-BrIPh = 4-Bromoisophthalic acid). The synthesized encapsulated material was characterized by elemental analysis, FTIR, UV-Visible spectroscopy, TGA, single crystal and powder X-ray diffraction and photoluminescence spectroscopy. The results showed that the synthesized composite, RhB-Zn-MOF could be used as an efficient probe for the selective sensing of Cr(VI) in the presence of Cr(III) as well as other metal ions.

Sulfur quantum dots as a novel platform to design a sensitive chemiluminescence probe and its application for Pb2+ detection

The monitoring of Pb as a hazardous heavy metal element for the environment and human health is of high importance. In this study, a simple and sensitive chemiluminescence (CL) probe based on sulfur quantum dots (SQDs) was designed for the determination of Pb²⁺ . To the best of our knowledge, this is the first report about the analytical application of the CL method based on SQDs. For this purpose, SQDs were synthesized by a simple hydrothermal method and characterized by TEM, FT-IR, XPS and X-ray diffraction. Then, the direct chemiluminescence (CL) of SQDs elicited by common oxidants was investigated. The highest CL intensity was observed for the SQDs-KMnO₄ reaction, and its CL mechanism was studied. We indicated that the CL intensity of introduced system can be diminished as a result of interaction between Pb²⁺ and SQDs, and exploited this fact for designing a CL-based probe for the determination of Pb²⁺ . The CL intensity of SQDs-KMnO₄ reaction was linearly quenched by Pb²⁺ at the range of 50 to 2000 nM with a limit of detection as 16 nM (S/N=3). The probe was employed for the determination of Pb²⁺ in different water samples and the recovery results (95.2 to 102.8%) indicated the good analytical performance of the developed method.

Synthesis of Metal–Organic Frameworks Quantum Dots Composites as Sensors for Endocrine-Disrupting Chemicals

Hazardous chemical compounds such as endocrine-disrupting chemicals (EDCs) are widespread and part of the materials we use daily. Among these compounds, bisphenol A (BPA) is the most common endocrine-disrupting chemical and is prevalent due to the chemical raw materials used to manufacture thermoplastic polymers, rigid foams, and industrial coatings. General exposure to endocrine-disrupting chemicals constitutes a serious health hazard, especially to reproductive systems, and can lead to transgenerational diseases in adults due to exposure to these chemicals over several years. Thus, it is necessary to develop sensors for early detection of endocrine-disrupting chemicals. In recent years, the use of metal–organic frameworks (MOFs) as sensors for EDCs has been explored due to their distinctive characteristics, such as wide surface area, outstanding chemical fastness, structural tuneability, gas storage, molecular separation, proton conductivity, and catalyst activity, among others which can be modified to sense hazardous environmental pollutants such as EDCs. In order to improve the versatility of MOFs as sensors, semiconductor quantum dots have been introduced into the MOF pores to form metal–organic frameworks/quantum dots composites. These composites possess a large optical absorption coefficient, low toxicity, direct bandgap, formidable sensing capacity, high resistance to change under light and tunable visual qualities by varying the size and compositions, which make them useful for applications as sensors for probing of dangerous and risky environmental contaminants such as EDCs and more. In this review, we explore various synthetic strategies of (MOFs), quantum dots (QDs), and metal–organic framework quantum dots composites (MOFs@QDs) as efficient compounds for the sensing of ecological pollutants, contaminants, and toxicants such as EDCs. We also summarize various compounds or materials used in the detection of BPA as well as the sensing ability and capability of MOFs, QDs, and MOFs@QDs composites that can be used as sensors for EDCs and BPA.

Synthesis of Fluorescent Sulfur Quantum Dots for Bioimaging and Biosensing

The rapid industrialization has had a serious impact on the environment, leading to an increase in disease and healthcare problems. The development of simple and effective biosensors to achieve specific analyte detection and bioimaging can provide useful information for disease prevention and treatment. Sulfur quantum dots (SQDs), a new class of metal-free fluorescent nanomaterial, are being studied and applied in diagnostic fields such as bioimaging and biosensing due to their advantages of simple synthetic process, unique composition, ultrasmall size, adjustable fluorescence, and low toxicity. This minireview highlights the main synthetic methods to synthesize fluorescent SQDs and their recent progress in cell and tissue imaging, as well as detection of biomolecules, metal ions, and temperature. Finally, the future development and some critical challenges of SQDs as a fluorescent probe in the field of bioimaging and biosensing are also discussed.

Research Update of Emergent Sulfur Quantum Dots in Synthesis and Sensing/Bioimaging Applications

Due to their unique optical property, low toxicity, high hydrophilicity, and low cost, sulfur quantum dots (SQDs), an emerging luminescent nanomaterial, have shown great potential in various application fields, such as sensing, bioimaging, light emitting diode, catalysis, and anti-bacteria. This minireview updates the synthetic methods and sensing/bioimaging applications of SQDs in the last few years, followed by discussion of the potential challenges and prospects in their synthesis and sensing/bioimaging applications, with the purpose to provide some useful information for researchers in this field.

Exploration of Sulfur-Containing Nanoparticles: Synthesis, Microstructure Analysis, and Sensing Potential

In this work, three different sulfur sources such as sulfur powder, sodium sulfide, and sodium thiosulfate are selected to prepare sulfur-derived quantum dots (S-QDs), Na₂S-derived nanoparticles (NS-NPs), and Na₂S₂O₃^--derived QDs (NSO-QDs) in the presence of NaOH or assisted by hydrogen peroxide etching. The low sulfur percentage in the above three samples and the synthesis experiments in the presence of nitrogen/oxygen all support that poly(ethylene glycol) (PEG) plays an important role during the assembly process and the definition of sulfur dots is not accurate. For photophysical features, remarkable green quantum dots (S-QDs) possess an excitation-independent emission peak at 500 nm. But NS-NPs and NSO-QDs demonstrate observable shift tendency, and the evolution of emission profiles varies from 480 to 586 nm. NSO-QDs can be used as a fluorescent probe for highly selective and quantitative detection of Ni²⁺ in an aqueous solution in the presence of potential interfering ions with a low detection limit (0.18 μM) and a wide linear range (8-380 μM). Their reusability performance has also been demonstrated by employing dimethylglyoxime as the restoration reagent.

Micropreconcentrators: Recent Progress in Designs and Applications

The detection of chemicals is a fundamental issue of modern civilisation, however existing methods do not always achieve the desired sensitivity. Preconcentrators, which are devices that allow increasing the concentration of the intended analyte via e.g., adsorption/desorption, are one of the solutions for increasing the sensitivity of chemical detection. The increased detection sensitivity granted by preconcentration can be used to miniaturise detection instruments, granting them portability. The primary goal of this review is to report on and briefly explain the most relevant recent developments related to the design and applications of preconcentrators. The key design elements of preconcentrators and the emerging area of liquid-phase preconcentrators are briefly discussed, with the most significant applications of these devices being highlighted.

A water-stable Zn4O-based MOF decorated with carbazolyl chromophores for multi-responsive fluorescence sensing of Fe3+, Cr2O72− and nitro-compounds

A MOF with strong deep blue light emission and high quantum efficiency has high selectivity and sensitivity for detecting 2,6-dichloro-4-nitroaniline.

Mitochondria-targeted acridine-based dual-channel fluorescence chemosensor for detection of Sn4+ and Cr2O72- ions in water and its application in discriminative detection of cancer cells

The goal of the present work was to fabricate a new low-cost, easy-to-prepare, dual-channel fluorescence chemosensor comprised of acridine-diphenylacetyl moieties (NDA) to enable remarkable Sn⁴⁺ detection in water and biological medium. The resulting NDA-Sn⁴⁺ complex was utilized for the distinguished identification of Cr₂O₇^2- ions from other anions and biomolecules. These investigations involve the absorption, fluorescence, and electrochemical methods for the detection of Sn⁴⁺ and Cr₂O₇^2- ions in pure water. The mechanism for NDA-mediated Sn⁴⁺ detection was experimentally determined by FT-IR, NMR titrations, mass (ESI) analyses, and DFT calculations. The obtained results indicate that the NDA chemosensor possessed excellent performance characteristics including good water solubility and compatibility, quick response time (less than 10 s), high sensitivity (Sn⁴⁺ = 0.268 μM and Cr₂O₇^2- = 0.160 μM), and selectivity against coexisting metals, anions, amino acids, and peptides. The chemosensor NDA induced negligible toxicity in live cells and was successfully utilized as a biomarker for the tracking of Sn⁴⁺ in human normal and cancer cells. More importantly, NDA demonstrates distinguished recognition of Sn⁴⁺ in human cancer cells rather than in normal live cells. Additionally, NDA was shown to act as a mitochondria-targeted probe in FaDu cells.

Low-cost devices with fluorescence spots brightness and size dual-mode readout for the rapid detection of Cr(VI) based on smartphones

Sensitive, convenient and rapid detection devices for toxic Cr(VI) suitable for filed use are required. Smartphone can be used as the detector, but the quality of images taken with a smartphone may depend on the ambient light and the operator. In this work, two types of low-cost and portable smartphone-based devices used for fluorescence spots brightness and size dual-mode detection of Cr(VI) were constructed with the aid of the 3D printing, which avoids the effect of ambient light and maintains a fixed position of the phone camera relative to the samples. Based on the brightness reflected by the blue channel of RGB values of the images of carbon nanodots, a linear relationship between quenching efficiency and concentration of Cr(VI) in a range of 0.2-150 μM with a limit of detection of 0.058 μM was attained, which is comparable to or better than that from fluorescence spectrometers. With the size variation of fluorescence spots, a linear range of 10-350 μM was acquired and it is more intuitive for direct naked-eye estimation of the concentration of Cr(VI). The applicability of the proposed devices for the detection of Cr(VI) was verified with water and soil samples with recoveries ranging in 95.0-108.2%.

Sensitive and selective determination of tetracycline in milk based on sulfur quantum dot probes

A novel fluorescent probe based on sulfur quantum dots (SQDs) was fabricated for sensitive and selective detection of tetracycline (TC) in milk samples. The blue emitting SQDs were synthesized via a top-down method with assistance of H2O2. The synthesized SQDs showed excellent monodispersity, water solubility and fluorescence stability, with a quantum yield (QY) of 6.30%. Furthermore, the blue fluorescence of the obtained SQDs could be effectively quenched in the presence of TC through the static quenching effect (SQE) and inner filter effect (IFE) between TC and SQDs. Under the optimum conditions, a rapid detection of TC could be accomplished within 1 min and a wide linear range could be obtained from 0.1 to 50.0 μM with a limit of detection (LOD) of 28.0 nM at a signal-to-noise ratio of 3. Finally, the SQD-based fluorescent probe was successfully applied for TC determination in milk samples with satisfactory recovery and good relative standard deviation (RSD). These results indicate that the SQD-based fluorescent probe shows great potential in practical analysis of TC in real samples with high rapidity, selectivity, and sensitivity.

Mixed matrix membranes containing fluorescent coordination polymers for detecting Cr2O72- with high sensitivity, stability and recyclability

Three coordination polymers (CPs) were synthesized by using CdII, fluorescent 9,10-di(4-pyridyl)anthracene (dpa), and cyclohexane-1,4-dicarboxylic acid (H2cda), and they are [Cd2(dpa)2(cda)Cl2]n (1), [Cd(dpa)2(cda)]n (2) and [Cd(dpa)(cda)(H2O)]n (3). Both 1 and 2 are fluorescent and contain nonporous layers. 3 is an isomer of 2 and contains a porous diamondoid network. Fluorescent mixed matrix membranes were prepared by dispersing the particles of 1 or 2 within the matrix of polymethyl methacrylate, and showed high sensitivity and selectivity for detecting Cr2O72- in water. Both stability and recyclability of the MMMs were remarkably higher than those of the CP powders.

Accelerated FeIII/FeII redox cycle of Fenton reaction system using Pd/NH2-MIL-101(Cr) and hydrogen

In this paper, a novel improvement in the catalytic Fenton reaction system named MHACF-NH₂-MIL-101(Cr) was constructed based on H₂ and Pd/NH₂-MIL-101(Cr). The improved system would result in an accelerated reduction in Fe^III, and provide a continuous and fast degradation efficiency of the 10 mg L^-1 4-chlorophenol which was the model contaminant by using only trace level Fe^II. The activity of Pd/NH₂-MIL-101(Cr) decreased from 100% to about 35% gradually during the six consecutive reaction cycles of 18 h. That could be attributed to the irreversible structural damage of NH₂-MIL-101(Cr).

Hydrothermal synthesis of two-dimensional cadmium(II) micro-porous coordination material based on Bi-functional building block and its application in highly sensitive detection of Fe3+ and Cr2O72

Metal-organic framework (MOFs), also known as porous coordination polymers (PCPs), is a new kind of crystalline porous materials, which has received extensive attention in the past few decades. As a new type of sensing material, MOFs stand out from many other traditional fluorescence sensors because of its crystal characteristics, structural diversity, stable porosity and adjustable functional characteristics. In this work, the bi-functional building block containing aromatic carboxylic acid and triazole moieties, namely 3-(1H-1,3,4-triazol-1-yl) benzoic acid, was selected as the linker to synthesize {[Cd(µ₅-L)⋅I}_n (1, HL = 3-(1H-1,3,4-triazol-1-yl)benzoic acid) by hydrothermal method with transition Cd^II metal centers. Firstly, the preliminary characterization of 1 was carried out by means of PXRD, FT-IR, and then the UV and fluorescence tests were conducted to study the fluorescence properties of 1. The crystal structure analysis indicates that Cd^II is the center and the ligand is bridged to form a two-dimensional porous structure. In addition, 1 has good selectivity for Fe³⁺ and Cr₂O₇^2-, meanwhile, it has high detection sensitivity (K_sv quenching efficiency for Fe³⁺: 1.2 × 10⁴ M^-1 and Cr₂O₇^2- 1.85 × 10⁴ M^-1) and low detection limit (Fe³⁺: 19.21 μM and Cr₂O₇^2-: 12.46 μM). The results of photoluminescence test show that 1 can detect cations and anions with high sensitivity, resist the interference of other ions, and have good reusability. As far as we know, 1 is the first example of ultra-stable two-dimensional (2D) Cadmium (II) microporous coordination material as a fluorescence sensor for Fe³⁺ and Cr₂O₇^2-.

Enhanced the photoelectrochemical performance of Bi2XO6 (X = W, Mo) for detecting hexavalent chromium by modification of CuS

In this work, Bi₂XO₆ (X = W, Mo) are synthesized at different temperatures. The results of tests find the optimal temperatures of Bi₂WO₆ and Bi₂MoO₆ are 180 and 160°C (BW-180, BM-160). Then, BW-180 and BM-160 are further compounded with different contents of CuS. The results of photoelectrochemical (PEC) tests show that CuS can improve the PEC performance of semiconductor materials, and it has better performance when CuS mass fraction is 5%. These maybe the photoelectron potentials generated by CuS/Bi₂XO₆ (X = Mo, W) heterojunction reduce the combination of photogenerated electrons and holes. When the PEC sensor based on 5%-CuS/BW-180 detects Cr(VI), it has a linear range of 1-80 μmol/L with detection limit of 0.95 μmol/L, while the PEC sensor based on 5%-CuS/BM-160 detects Cr(VI) has a linear range of 0.5-230 μmol/L and a detection limit of 0.12 μmol/L. Thus, 5%-CuS/Bi₂XO₆ has potential application in hexavalent chromium detection.

Hydrothermal synthesis of N-doped carbon quantum dots and their application in ion-detection and cell-imaging

Carbon quantum dots (CQDs), owing to their characteristic luminescent properties, have become a new favorite in the field of luminescence. They have been widely used in light emitting diode, ion detection, cell-imaging, ect. Herein a facile synthesis method of nitrogen-doped carbon quantum dots (N-CQDs) has been developedviaa one-step hydrothermal of glucose and m-phenylenediamine. The chemical composition, surface functional groups, and crystal structure of so prepared N-CQDs were systematically characterized. The characterizations indicate that nitrogen has been chemically doped in the CQDs and the N-CQDs crystallize in a graphene structure. Photoluminescence (PL) measurements show that the N-CQDs emit strong blue emission under the irradiation of ultraviolet. The emission is excitation-dependent, is resistant to photo bleaching and high ionic strength, and slightly decreases with the increase of temperature. The quantum yield of them is about 17.5%. The PL intensity of N-CQDs quenches linearly with the increase of the concentrations of Fe³⁺(0.5-1.0 mM) and CrO₄^2-(0.3-0.6 mM), which are a kind of excellent fluorescent probe for the detection of Fe³⁺ and CrO₄^2-. The quenching mechanism of Fe³⁺ and CrO₄^2-is verified to be a static quenching mechanism based on inner filter effect. The N-CQDs are also found to be a good cell-imaging reagent of Hela cells.

Emergence of sulfur quantum dots: Unfolding their synthesis, properties, and applications

Over the past few decades, the sphere of applied science has witnessed soaring demand in developing high performance, novel and sustainable materials due to ever-increasing population coupled with need for alternative-green-energy resources. Inevitably, sulfur research expands through the breadth of materials sciences including sustainable use of the by-products obtained from petroleum industry, preparation of biocompatible materials, and constructing energy harvesting devices, indispensable to our everyday lives. Congruous with popular heavy-metal free elemental quantum dots such as the carbon, silicon and phosphorus, emergence of sulfur quantum dots (SQDs) has drawn substantial attention due to their bright luminescence, infrequent to other sulfur allotropes. In this review article, we focus some of the pioneering advances on synthesis and characterizations of luminescent sulfur nanodots and their potential applications in bioimaging, fabrication of light emitting devices, sensing and catalysis. Finally, critical challenges along with future perspectives corresponding to this newly discovered research area have been discussed.