A novel coumarin-based fluorescent probe for sensitive detection of copper(II) in wine

Construction of a reaction-based fluorescent sensor for tandem detection of Cu2+ and glutathione in wine

The purpose of this study was to develop a novel reaction-based fluorescent sensor for the detection of Cu2+ and glutathione in real wine samples. The sensor, tris-(2-pyridyl)-methylamine rhodol derivative, was synthesized and validated for the tandem and selective detection of both Cu2+ and glutathione. The sensor exhibited a strong linear correlation between fluorescence intensity and Cu2+ concentration ranging from 100 to 900 nM, while the in situ generated Cu2+ ensemble selectively detected glutathione with a robust linear response from 3 to 30 μM. The detection limits for Cu2+ and glutathione were as low as 28 nM and 0.60 μM, respectively. Additionally, the sensor enabled quantitative detection of Cu2+ and glutathione in real wine samples. This work provides the first reaction-based fluorescence sensor with an "on-off-on" fluorescence response for the tandem detection of Cu2+ and glutathione in wine, offering potential applications in food and beverage quality control.

Ionophore-based nanospheres enable selective and sensitive fluorescence detection of copper ions

A novel ionophore-based fluorescent nanosensor has been successfully fabricated for the sensitive and selective detection of Cu2+ ions. The nanosensor was constructed through self-assembly of amphiphilic block copolymers, incorporating elesclomol as a Cu2+ ionophore and long-chain dialkylcarbocyanines (DiD) as a fluorescent dye. This design exhibits an "ON/OFF" fluorescence response, where Cu2⁺ ions are selectively sequestered within the nanosensors, resulting in fluorescence quenching of DiD. This strategy enables rapid and highly selective Cu2⁺ sensing with remarkable fluorescence quenching efficiency (up to 93.5 %) and an exceptionally low detection limit of 28.6 nM. The linear detection range extends over two orders of magnitude (0.05-10 μM). Furthermore, the feasibility of this nanosensor for practical applications was confirmed through successful determination of Cu2+ in real water and beer samples, with excellent recovery rates. This nanosensor offers advantages of simplicity, rapidity, and cost-effectiveness, holding significant potential for sensitive and selective Cu2+ detection in various biological and environmental samples.

Fructose@histone synergistically improve the performance of DNA-templated Cu NPs: rapid analysis of LAM in tuberculosis urine samples using a handheld fluorometer and a smartphone RGB camera

This study presented a nanoparticle-enhanced aptamer-recognizing homogeneous detection system combined with a portable instrument (NASPI) to quantify lipoarabinomannan (LAM). This system leveraged the high binding affinity of aptamers, the high sensitivity of nanoparticle cascade amplification, and the stabilization effect of dual stabilizers (fructose and histone), and used probe-Cu2+ to achieve LAM detection at concentrations ranging from 10 ag mL-1 to 100 fg mL-1, with a limit of detection of 3 ag mL-1 using a fluorometer. It can also be detected using an independently developed handheld fluorometer or the red-green-blue (RGB) camera of a smartphone, with a minimum detection concentration of 10 ag mL-1. We validated the clinical utility of the biosensor by testing the LAM in the urine of patients. Forty urine samples were tested, with positive LAM results in the urine of 18/20 tuberculosis (TB) cases and negative results in the urine of 6/10 latent tuberculosis infection cases and 10/10 non-TB cases. The assay results revealed a 100% specificity and a 90% sensitivity, with an area under the curve of 0.9. We believe that the NASPI biosensor can be a promising clinical tool with great potential to convert LAM into clinical indicators for TB patients.

An AIE Controlled "Off-On" Cu2+-Sensitive Probe for Early Detection of Renal Fibrosis

Early detection of renal fibrosis (RF) is very important given that it is irreversible when it progresses to the terminal stage. A key marker of RF pathogenesis is activation of myomyofibroblasts, and its targeted imaging may be a promising approach for early detection of RF, but no study has directly imaged activation of renal myomyofibroblasts. Cu2+ plays a major role in the fibrotic activity of myofibroblasts. Herein, inspired by that Cu2+ can complex with bovine serum albumin (BSA), BSA-Ag2S quantum dots (QDs) with aggregation-induced emission (AIE) property are synthesized. Then BSA-Ag2S QDs are modified by chitosan (CS) with renal targeting and hyaluronic acid (HA) with myofibroblast targeting to obtain the AIE assay system (QDs@CS@HA). The system is simple to synthesize, and produces a rapid NIR fluorescence signal turn-on response and a low detection limit of 75 × 10-9 m to Cu2+. In addition, cellular and animal experiments have shown that QDs@CS@HA has good biosafety and cell-targeted imaging capability for RF. Based on the successful application of QDs@CS@HA and the mechanism of RF progression in early RF detection, it is expected that QDs@CS@HA may detect RF before the appearance of clinical symptoms.

Construction of a novel flavonol fluorescent probe for copper (II) ion detection and its application in actual samples

Copper is an essential trace element in the human body, and its level is directly related to many diseases. While the source of copper in human body is mainly intake from food, then the detection of copper ions (Cu2+) in food becomes crucial. Here, we synthesized a novel probe (E)-3-hydroxy-2-styryl-4H-benzo[h]chromen-4-one (NSHF) and explored the binding ability of NSHF for Cu2+ using nuclear magnetic resonance hydrogen spectroscopy (1H NMR), high-resolution mass spectrometry (HRMS), Job's plot method and density functional theory (DFT). NSHF shows the advantages of fast response time, good selectivity and high sensitivity for Cu2+. The fluorescence intensity ratio (F/F0) of NSHF shows a good linear relationship with the concentration of Cu2+ and the detection limit is 0.061 μM. NSHF was successfully applied to the detection of Cu2+ in real samples. In addition, a simple and convenient Cu2+ detection platform was constructed by combining NSHF with a smartphone and a UV lamp, which can realize the rapid detection of Cu2+. This work provides an effective tool for the real-time detection of Cu2+.

Fabrication of chitosan-based fluorescent hydrogel membranes cross-linked with bisbenzaldehyde for efficient selective detection and adsorption of Fe2

Chitosan, as a natural biomass material, is green, recyclable, sustainable and well biocompatible. The molecular chain is rich in active groups such as amino and hydroxyl groups, and its preparation of fluorescent probes has the advantages of biocompatibility and efficient detection performance. In this study, a bis(benzaldehyde) (BHD) fluorescent functional molecule was designed. Then a series of fluorescent chitosan-based hydrogel films (CSBHD) were prepared using chitosan as raw material and BHD as cross-linking agent. As a fluorescent probe for metal ions, CSBHD was able to efficiently detect Fe2+ with a linear correlation of fluorescence intensity in the range of 0-160 μM, and the limit of detection (LOD) was 0.55 μM. Moreover, it has excellent adsorption performance for Fe2+ ions, with a maximum adsorption capacity of 223.5 g/mg at 500 mg/L Fe2+ concentration. Finally, we characterised the structure and microscopic morphology of CSBHD films and found that CSBHD as a hydrogel film has a high cross-linking density, good water resistance, excellent thermal stability, strong resistance to swelling, and excellent stability in cycling tests. Hence, it has great potential for application in adsorption and detection of Fe2+ ions. It also provides a good strategy for the application of chitosan based fluorescent probe materials in environmental monitoring and heavy metal ion adsorption.

Rational synthesis of 1,3,4-thiadiazole based ESIPT-fluorescent probe for detection of Cu2+ and H2S in herbs, wine and fruits

Here, 1,3,4-thiadiazole unit was employed as novel excited state intramolecular proton transfer (ESIPT) structure to prepare favorable fluorescent probe. High selectivity and rapid response to Cu2+ was obtained and the settling reaction was also used to recover ESIPT characteristics of probe to achieve sequential detection of H2S. Remarkable color change of solution from colorless to bright yellow and fluorescence emission from green to dark realized the visual detection of Cu2+ by naked eyes and transition of probe into portable fluorescent test strips. As expected, L-E could be utilized to quantitatively sense Cu2+ and H2S in different actual water and food samples including herbs, wine and fruits. The limits of detection for Cu2+ and H2S were as low as 34.5 nM and 38.6 nM. Also, probe L-E achieved real-time, portable, on-site quantitative detection of Cu2+ via a colorimeter and a smartphone platform with limit of detection to 90.3 nM.

A resorufin-based fluorescent probe for hydrazine detection and its application in environmental analysis and bioimaging

Hydrazine (N2H4) is an important industrial raw material that has been widely used in industrial production and agricultural interventions, but its widespread application also inevitably causes environmental pollution. In this study, based on resorufin, we constructed a novel "turn-on" fluorescent probe RFT for the selective detection of hydrazine under complex environmental conditions and in vivo. The probe RFT exhibited excellent stability and selectivity towards the detection of hydrazine with a low detection limit of 260 nM. In addition, RFT was successfully applied to the detection of hydrazine in environmental water samples and living cells. Most importantly, RFT could not only detect the exogenous hydrazine in zebrafish and mice, but also image and visualize the up-regulation of endogenous hydrazine induced by isoniazid in zebrafish.

Development and validation of an eco-compatible UV-Vis spectrophotometric method for the determination of Cu2+ in aqueous matrices

Cu2+ are ubiquitous ions in the ecosystem and are responsible of serious environmental pollution. Indeed, the development of sensitive methods for Cu2+ detection is an urgent demand. In this work, we proposed a new spectrophotometric method for Cu2+ determination in different water matrices (distilled water, drinking water, wastewater, and river water). The method employs a bio-based organic ligand namely tetrasodium iminodisuccinate (IDS) able to form a stable complex with the analyte with a maximum absorption at 710 nm. Within the linear range of 6.3-381 mg L-1, the limit of detection (LOD) was determined to be as 1.43 mg L-1. Moreover, the recovery data of the spiked analysis of drinking/river/wastewater water samples were also satisfactory and verified the feasibility of the method for the analysis of Cu2+ in natural conditions. Finally, the AGREE assessment tool was used for a quantitative evaluation of the proposed method and reference method, in agreement with the green analytical chemistry principles. The results showed the lower environmental impact of the proposed method and the suitability of this novel approach for Cu2+ in water matrices.

Construction of a water-soluble fluorescent probe for copper (II) ion detection in live cells and food products

The quality of wine can be affected by excess Cu²⁺ due to the occurrence of oxidation reactions or precipitation. Therefore, it is essential to use simple and effective testing methods to ensure the Cu²⁺ content in wine. In this work, we designed and synthesized a rhodamine polymer fluorescent probe (PEG-R). The water solubility of PEG-R was improved by the introduction of polyethylene glycol, which improved the performance and broadened its application in the food field. The PEG-R was characterized by high sensitivity, selectivity and fast response to Cu²⁺ and was able to complete the response process within 30 s, with approximately 29-fold fluorescence enhancement of the probe after exposure to Cu²⁺, the limit of detection (LOD) was 1.295 × 10^-6 M. The probe can be used for the determination of Cu²⁺ in living cells, zebrafish, white wine and food products, and it was made into practical gels and test strips.

A novel coumarin derivative-grafted dialdehyde cellulose-based fluorescent sensor for selective and sensitive detection of Fe3

A new fluorescent probe DAC-NCH with specific response to Fe³⁺ was synthesized via condensation reaction between dialdehyde cellulose and coumarin derivative. This probe exhibited a significant "turn-off" fluorescence response to Fe³⁺, accompanied by the fluorescence color change from bright pink to colorless. DAC-NCH was highly selective for Fe³⁺ and could achieve detection within a short time (<3 min). The detection limit of DAC-NCH for Fe³⁺ was determined to be as low as 91.7 nM. The complexation mechanism of DAC-NCH with Fe³⁺ was confirmed by Job's plot, FTIR analysis, ¹H NMR titration, and density functional theory (DFT) calculations. In addition, DAC-NCH could be used for the determination of Fe³⁺ in actual water samples, and DAC-NCH-embedded fluorescent membrane was able to serve as a reliable platform for the detection of Fe³⁺.

Democratization of Copper Analysis in Grape Must Following a Polymer-Based Lab-on-a-Chip Approach

Quality control in the food industry is of the upmost importance from the food safety, organoleptic and commercial viewpoints. Accordingly, the development of in situ, rapid, and costless analytical tools is a valuable task in which we are working. Regarding this point, the copper content of grape must has to be determined by wineries along the wine production process. For this purpose, grape must samples are sent to laboratories where the copper content is measured usually by flame atomic absorption spectrometry or by inductively coupled plasma mass spectrometry. We herein propose a straightforward, rapid, and inexpensive methodology based both on a film-shaped colorimetric polymer sensor and a smartphone method that at the same time can be used by unskilled personnel. The sensory polymer films change their color upon dipping them on the grape must, and the color evolution is analyzed using the digital color parameters of a picture taken to the film with a smartphone. Furthermore, the analytical procedure is automatically carried out by a smartphone app. The limit of detection of copper of the polymer sensor is 0.08 ppm. Following this approach, 18 production samples coming from the French Groupe ICV company were studied. The copper content of the samples was analyzed by the usual procedure carried out by the company (flame atomic absorption spectrometry) and by the method proposed in this work, ranging this content from 0.41 to 6.08 ppm. The statistical study showed that the results of both methods are fully consistent, showing the validity of the proposed method for the determination of copper in grape must within the frame of wine production wineries and industries.

Copper in grape and wine industry: Source, presence, impacts on production and human health, and removal methods

Heavy metals are of particular concern in grape and wine processing, especially copper. The sources of copper are diverse, including vineyard soil, copper-containing pesticides on the fruit surface, copper wine-making equipment, and exogenous addition in winemaking. Copper has potential risks to human nerves, metabolism, and others. It can inhibit yeast growth, delay fermentation, and also mediate oxidation reactions, which has a huge impact on the nutritional quality and sensory quality of fresh wine and aged wine. It is therefore crucial to detect, quantify, and remove copper from grapes and wine. However, the copper situations in the wine industries of various countries are complicated and diverse, and the existing forms of copper are quite different, which makes the research challenging. This review summarizes and analyzes the existence and influence of copper in the wine industry by analyzing the sources of, the current situation regarding, and the detection and removal methods for copper in wine. With the study, a better understanding of copper's impact on wine production will be gained, facilitating further control of copper in wine and helping the wine industry grow.

Development in Fluorescent OFF-ON Probes Based on Cu2+ Promoted Hydrolysis Reaction of the Picolinate Moiety

Anions and cations have a key role in our normal life. Cu²⁺ ion is a crucial trace element accountable for the part of several cellular enzymes and proteins, including cytochrome c oxidase, dopamine monooxygenase, Cu/Zn superoxide dismutase, and ceruloplasmin. WHO has found the extreme acceptable level of Cu²⁺ ions in drinking water is up to 2.0 ppm. Excess use of Cu²⁺ ions is associated with various human genetic disorders. Thus, the visualization of Cu²⁺ ions to avoid its toxic effects in chemical and biological systems is significant. In this review we have summarized sensors based on catalytic hydrolysis of picolinate to detect Cu²⁺ ions. The sensors based on hydrolysis of picolinate are very selective as compared to the other sensors for Cu²⁺ ions detection. We have focused on describing the structure, spectral properties, detection limits, and bioimaging model of the sensors.

A microdots array-based fluoremetric assay with superwettability profile for simultaneous and separate analysis of iron and copper in red wine

A microdots array-based fluoremetric method with superwettability profile has been developed for the simultaneous and separate detection of Fe³⁺ and Cu²⁺ ions in red wine samples. A wettable micropores array was initially designed with high density by using polyacrylic acid (PAA) and hexadecyltrimethoxysilane (HDS), followed by the NaOH etching route. Zinc metal organic frameworks (Zn-MOFs) were fabricated as the fluorescent probes to be immobilized into the micropores array to obtain the fluoremetric microdots array platform. It was found that the fluorescence of Zn-MOFs probes could decrease significantly in the presence of Fe³⁺ and/or Cu²⁺ ions towards their simultaneous analysis. Yet, the specific responses to Fe³⁺ ions could be expected if using histidine to chelate Cu²⁺ ions. Moreover, the developed Zn-MOFs-based microdots array with superwettability profile can enable the accumulation of targeting ions from the complicated samples without any tedious pre-processing. Also, the cross-contamination of different samples droplets can be largely avoided so as to facilitate the analysis of multiple samples. Subsequently, the feasibility of simultaneous and separate detection of Fe³⁺ and Cu²⁺ ions in red wine samples was demonstrated. Such a design of microdots array-based detection platform may promise the wide applications in analyzing Fe³⁺ and/or Cu²⁺ ions in the fields of food safety, environmental monitoring, and medical diseases diagnostics.

Sensitive and Selective Detection of Enterococcus faecalis Using a New Turn-on Fluorogenic β-glucosidase Substrate Combined with a Modified Selective Broth

A new, simple-to-synthesize and sensitive turn-on fluorogenic substrate (CFMU-Glu) for β-glucosidase activity was developed. This probe was based on a 7-hydroxycoumarin derivative (CFMU) that could emit green fluorescence and had the low pK_a value of 5.61 ± 0.01. CFMU-Glu could be used for sensitive monitoring of the almond βGLU and Enterococcus faecalis (E. faecalis) at the optimal pHs of 6.50 and 7.00, respectively. Moreover, a new sensitive and selective fluorogenic broth (PBF-B) for E. faecalis, utilizing CFMU-Glu and polymyxin B, was also developed. Polymyxin B was discovered to can significantly improve the detection selectivity and signal intensity. The proposed 4-four method using PBF-B and a microcentrifuge tube could provide fluorogenic detection limits of 5.01 × 10⁴ and 1.0 × 10⁵  CFU mL^-1 by fluorescence microplate reader and naked eye, respectively; it could also provide a turn-on chromogenic detection limit of 1.0 × 10⁶  CFU mL^-1 by naked eye. The proposed method could detect 8 CFU mL^-1 of E. faecalis in drinking water, Liangcha (herbal tea) and milk samples within 10 h, without pre-enrichment.

Study on effective synthesis of 7-hydroxy-4-substituted coumarins

Many coumarin derivatives have good biological activity and application value in fluorescent probes. Therefore, synthetic routes to coumarin derivatives have also attracted the attention of many research groups. In this work, based on the Pechmann coumarin synthesis method, the influence of various Lewis acids on the reaction was discussed, and the optimal synthesis conditions of 7-hydroxy-4-substituted coumarins were explored. Based on the experimental results, a possible mechanism was proposed, which provides a reference for future industrialized production of coumarins.

Development of a Rapid and Sensitive Fluorescence Sensing Method for the Detection of Acetaldehyde in Alcoholic Beverages

Acetaldehyde is regarded as an important flavor compound in alcoholic beverages. With the advantages of rapidity, low cost and high sensitivity, fluorescent probe could be used as a new tool for the detection of acetaldehyde. Here, an effective fluorescence sensing method based on fluorescent probe N1 (FPN1) was established in this study. The function of FPN1 relies on the nucleophile substitution reaction and photoinduced electron transfer (PET), resulting in a fluorescence increase. Remarkably, the pretreatment background removal method (BRM) was successfully applied for removal of the interference of pyruvate and acetal. The linearity range (LR), limit of detection (LOD) and recovery of the fluorescence sensing method with BRM were 0.0053–200 mg/L, 0.0016 mg/L and 94.02–108.12%, respectively, which showed a broader detection range and better performance on sensitivity compared with the traditional quantitation using gas chromatography (GC). Furthermore, successful application of the method in real samples indicated the advantages of low-cost and rapidity for small-scale detection while assuring the accuracy, which provides a new strategy for the detection of acetaldehyde concentration in alcoholic beverages.

Schiff Base Aggregation-Induced Emission Luminogens for Sensing Applications: A Review

Fluorescence sensing can not only identify a target substrate qualitatively but also achieve the purpose of quantitative detection through the change of the fluorescence signal. It has the advantages of immense sensitivity, rapid response, and excellent selectivity. The proposed aggregation-induced emission (AIE) concept solves the problem of the fluorescence of traditional fluorescent molecules becoming weak or quenched in high concentration or aggregated state conditions. Schiff base fluorescent probes have the advantages of simple synthesis, low toxicity, and easy design. They are often used for the detection of various substances. In this review we cover late developments in Schiff base compounds with AIE characteristics working as fluorescence sensors.

Novel Fluorescence Probe toward Cu2+ Based on Fluorescein Derivatives and Its Bioimaging in Cells

Copper is an important trace element that plays a crucial role in various physiological and biochemical processes in the body. The level of copper content is significantly related to many diseases, so it is very important to establish effective and sensitive methods for copper detection in vitro and vivo. Copper-selective probes have attracted considerable interest in environmental testing and life-process research, but fewer investigations have focused on the luminescence mechanism and bioimaging for Cu²⁺ detection. In the current study, a novel fluorescein-based A5 fluorescence probe is synthesized and characterized, and the bioimaging performance of the probe is also tested. We observed that the A5 displayed extraordinary selectivity and sensitivity properties to Cu²⁺ in contrast to other cations in solution. The reaction between A5 and Cu²⁺ could accelerate the ring-opening process, resulting in a new band at 525 nm during a larger pH range. A good linearity between the fluorescence intensity and concentrations of Cu²⁺, ranging from 0.1 to 1.5 equivalent, was observed, and the limit detection of A5 to Cu²⁺ was 0.11 μM. In addition, the Job’s plot and mass spectrum showed that A5 complexed Cu²⁺ in a 1:1 manner. The apparent color change in the A5–Cu²⁺ complex under ultraviolet light at low molar concentrations revealed that A5 is a suitable probe for the detection of Cu²⁺. The biological test results show that the A5 probe has good biocompatibility and can be used for the cell imaging of Cu²⁺.

One-pot synthesis of copper nanocluster/Tb-MOF composites for the ratiometric fluorescence detection of Cu2

The increasing degradation of ecosystems due to heavy metal residues has led to environment and food contamination, prompting the development of convenient platforms for monitoring heavy metals. Here, a new dual-emission fluorescent sensor CuNCs@Tb@UiO-66-(COOH)₂ for the detection of copper ions (Cu²⁺ ) has been synthesized by one-pot encapsulation of Tb (III) and glutathione-stabilized copper nanoclusters (CuNCs) into metal-organic frameworks (MOFs) UiO-66-(COOH)₂ . In this ratiometric sensor, the fluorescence intensity of Tb³⁺ decreased significantly upon the addition of Cu²⁺ , while that of CuNCs showed good stability, together with an apparent color change. Therefore, ratiometric fluorescence detection of Cu²⁺ can be accomplished by measuring the ratio of the fluorescence intensity at the 450 nm (F₄₅₀ ) wavelength of CuNCs to the 548 nm (F₅₄₈ ) emission of Tb³⁺ in the fluorescence spectra of the CuNCs@Tb@UiO-66-(COOH)₂ suspension. Moreover, the obtained fluorescent probe shows good results in the detection of actual samples. This work can provide the basis of method for the exploration of ratiometric fluorescence and visual sensors of trace pollutants analysis in complicated samples.

A Highly Sensitive and Selective Fluorescein-Based Cu2+ Probe and Its Bioimaging in Cell

Copper is a vital trace metal in human body, which plays the significant roles in amounts of physiological and pathological processes. The application of copper-selective probe has attracted great interests from environmental tests to life process research, yet a few of sensitive Cu²⁺ tests based on on-site analysis have been reported. In this paper, a novel fluorescein-based fluorescent probe N4 was designed, synthesized, and characterized, which exhibited high selectivity and sensitivity to Cu²⁺ comparing with other metal ions in ethanol–water (1/1, v/v) solution. The probe N4 bonded with Cu²⁺ to facilitate the ring-opening, and an obvious new band at 525 nm in the fluorescence spectroscopy appeared, which could be used for naked-eye detection of Cu²⁺ within a broad pH range of 6–9. Meanwhile, a good linearity between the fluorescence intensity and the concentrations of Cu²⁺ ranged 0.1–1.5 eq. was observed, and the limit of detection of N4 to Cu²⁺ was calculated to be as low as 1.20 μm. In addition, the interaction mode between N4 and Cu²⁺ was found to be 1:1 by the Job's plot and mass experiment. Biological experiments showed that the probe N4 exhibited low biological toxicity and could be applied for Cu²⁺ imaging in living cells. The significant color shift associated with the production of the N4-Cu²⁺ complex at low micromolar concentrations under UV light endows N4 with a promising probe for field testing of trace Cu²⁺ ions.

Colorimetric determination of cysteine and copper based on the peroxidase-like activity of Prussian blue nanocubes

Prussian blue nanocubes were synthesized via a hydrothermal method. Significantly, the redox couple Ni3+/Ni2+ provided rich oxidation and reduction reactions, which enhance catalytic activity. Furthermore, PBNCs mimic peroxidase activity which could oxidise colourless tetramethyl benzidine (TMB) to a blue colour (TMB+) in the presence of H2O2. Thus, it can be used as a colorimetric sensing platform for detecting cysteine and Cu2+. The addition of cysteine to a TMB + PBNCs sensing system decreases the intensity of the blue colour in the solution with a decrease in the absorption peak at 652 nm in the UV visible spectrum. Subsequently, the addition of Cu2+ into the TMB + PBNCs + Cys sensing system increases the intensity of the blue colour due to complex formation of Cu and cysteine. Therefore, the change in intensity of the blue colour of TMB is directly proportional to the concentration of Cys and Cu2+. As a result, this sensing system is highly sensitive and selective with an effective low detection limit of 0.002 mM for cysteine and 0.0181 mM for Cu2+. Furthermore, this method was applied to the detection of cysteine and copper in spiked real samples and gave satisfactory results.

Rapid determination of trace Cu2+ by an in-syringe membrane SPE and membrane solid-phase spectral technique

A new in-syringe membrane SPE and solid-phase visible spectral method was proposed for the rapid extraction and visible spectral determination of trace Cu²⁺. The chelation and membrane SPE can be accomplished in a syringe. The yellow Cu(DDTC)₂ complex was separated using a polyethersulfone membrane from the sample solution. Then, the complex can be detected directly on the polyethersulfone membrane utilizing solid-phase visible absorbance spectra without elution. The proposed method simplified the experimental procedure and improved the sensitivity to the μg L^-1 level. Furthermore, this method is environmentally friendly since it avoids the use of organic solvents. After the investigation of the influence of different variables on the membrane SPE procedure, water and blood plasma were analyzed to validate the proposed method. A LOD of 0.04 μg L^-1 and recoveries of 96.0-103.7% confirmed that the present work can be applied for the determination of trace Cu²⁺ in water and blood plasma samples.

Simultaneous and ultra-sensitive detection of Cu2+ and Mg2+ in wine and beer based on dual DNA tweezers and entropy-driven three-dimensional DNA nanomachine

Simultaneous and ultra-sensitive detection strategy of Cu²⁺ and Mg²⁺ in wine and beer was developed based on dual DNA tweezers and entropy-driven three-dimensional DNA nanomachine. The dual DNAzyme can simultaneously respond to two kinds of metal ions and cause two kinds of "turn-on" fluorescent signals. The working principle of this strategy was indirectly proven. In addition, some key experimental parameters were also optimized. Under the optimum conditions, the limit of detection was 10 pM for Cu²⁺ and 2 nM for Mg²⁺ respectively which was significantly improved by entropy driven amplification. This strategy also showed good selectivity and specificity. It was successfully used to detect of Cu²⁺ and Mg²⁺ in wine and beer with 5.26% to 9.12% of relative standard deviation and 90.4% to 110.5% of recoveries.

The recent advance of organic fluorescent probe rapid detection for common substances in beverages

The beverage industry is confronted with tremendous challenges in terms of quality assurance. The allowed contents of common ingredients such as copper ions, hydrogen sulfide, cysteine and caffeine are stipulated by various governing bodies, and the beverage industry must ensure that it meets these requirements. Due to its unique advantages of high sensitivity, low cost and relatively low toxicity over high-performance liquid chromatography, atomic absorption spectrometry and nanomaterials, the use of organic fluorescent probes for the rapid detection of beverage contents has become a hot research topic. This review summarizes the detection of common substances in wine, tea, mineral water, milk and other beverages. Furthermore, the preparation of test paper and simple colour comparison are discussed to display the rapid qualitative capability of designed probes. To improve the current state of beverage safety, future trends and strategies for fast organic fluorescent probe detection in the beverage industry are also discussed.

Construction of a dual-response fluorescent probe for copper (II) ions and hydrogen sulfide (H2S) detection in cells and its application in exploring the increased copper-dependent cytotoxicity in present of H2S

Multiple types of metal ions and active small molecules (reactive nitrogen species, reactive oxygen species, reactive sulfur species, etc.) exist in living organisms. They have connections to each other and can interact and/or interfere with each other. To investigate the relationship of metal ions and active small molecules in living cells, it is necessary and critical to develop molecular tools that can track two kinds of associated certain metal ions and reactive molecules with multiple fluorescence signals. However, this is a challenging task that requires an ingenious molecular design to achieve this goal. Here, we present a fluorescent probe (D-CN) that can offer fluorescence imaging of H₂S and copper (II) ions with different response signals. Recognition of H₂S and Cu (II) by the new probe can result in green and red emissions, respectively, providing different signal responses to the two substances in living cells and zebrafish. In addition, we used this probe to visually prove that the cytotoxicity of copper ions in living cells increases in the presence of hydrogen sulfide and could lead to cell apoptosis.

Self-powered liquid chemical sensors based on solid-liquid contact electrification

Triboelectric nanogenerators (TENGs) have attracted many research endeavors as self-powered sensors for force, velocity, and gas detection based on solid-solid or solid-air interactions. Recently, triboelectrification at liquid-solid interfaces also showed intriguing capability in converting physical contacts into electricity. Here, we report a self-powered triboelectric sensor for liquid chemical sensing based on liquid-solid electrification. As a liquid droplet passed across the tribo-negative sensor surface, the induced surface charge balanced with the electrical double layer charge in the liquid droplet. The competition between the double layer charge and surface charge generated characteristic positive and negative voltage spikes, which may serve as a "binary feature" to identify the chemical compound. The sensor showed distinct sensitivity to three amino acids including glycine, lysine and phenylalanine as a function of their concentration. The versatile sensing ability was further demonstrated on several other inorganic and organic chemical compounds dissolved in DI water. This work demonstrated a promising sensing application based on the triboelectrification principle for biofluid sensor development.

A novel AIE fluorescent probe based on myrtenal for Cu2+ detection in a near-perfect aqueous medium and bioimaging in vegetables and zebrafish

An AIE-active fluorescent probe MHTS with good sensitivity and selectivity for the detection of Cu2+ was synthesized from myrtenal.

A dual-emission ratiometric fluorescent nanoprobe based on silicon nanoparticles and carbon dots for efficient detection of Cu(ii)

A novel dual-emission ratiometric fluorescent nanoprobe of Si NP–CD nanocomposites for highly sensitive and selective detection of Cu²⁺.

A turn-on red-emitting fluorescent probe for determination of copper(II) ions in food samples and living zebrafish

Herein, we developed a turn-on red-emitting fluorescent probe for the sensitive and selective detection of copper ions (Cu²⁺) in food samples and living zebrafish. The probe employs a hemicyanine scaffold as the fluorophore and a 2-pyridinecarbonyl group as the recognition receptor and quenching moiety. The 2-pyridinecarbonyl moiety can be specifically cleaved by Cu²⁺ and results in an approximately 18-fold fluorescence enhancement of the probe, thereby providing a fluorescence turn-on assay for Cu²⁺. Additionally, the probe exhibited excellent selectivity, high sensitivity, a broad linear relationship (0.020 to 8.0 μM), and a low limit of detection (4.0 nM, S/N = 3) for Cu²⁺. Concomitantly, the probe exhibited satisfactory analytical performance when used with actual food samples. Moreover, the probe could be used for in situ determination of Cu²⁺ in both living plant tissues and in living zebrafish.

Fluorescent sensing platform for low-cost detection of Cu2+ by coumarin derivative: DFT calculation and practical application in herbal and black tea samples

A fluorogenic probe based on a coumarin-derivative for Cu2+ sensing in CH3CN/H2O media (v/v, 95/5, 5.0 μM) was developed and applied in real samples. 3-(4-chlorophenyl)-6,7-dihydroxy-coumarin (MCPC) probe was obtained by synthetic methodologies and identified by spectral techniques. The probe MCPC showed remarkable changes with a "turn-off" fluorogenic sensing approach for the monitoring of Cu2+ at 456 nm under an excitation wavelength of 366 nm. The response time of the probe MCPC was founded as only 1 min. The detection limit of the probe MCPC was recorded to be 1.47 nM. The binding constant and possible stoichiometric ratio (1:1) values were determined by Benesi-Hildebrand and Job's plot systems, respectively. The mechanism of the probe MCPC with Cu2+ was further confirmed by ESI-MS and FT-IR analyses, as well as supported by theoretical calculations. Furthermore, the probe MCPC was successfully employed for the practical applications to sense Cu2+ in different herbal and black tea samples. The proposed sensing method was also verified by ICP-OES method.

A fluorescence imaging protocol for correlating intracellular free cationic copper to the total uptaken copper by live cells

A variety of fluorescence probes have been developed for fluorescence imaging of metals in biological cells. However, accurate quantification of metals with fluorescent approaches is challenging due to the difficulty in establishing a standard calibration curve in living cells. Herein, a fluorescence imaging protocol is developed for imaging intracellular Cu²⁺ and its correlation with the cellular uptake of copper. The total amount of intracellular Cu is detected by inductively coupled plasma mass spectrometry (ICP-MS) in parallel. Fluorescence imaging of Cu²⁺ is accomplished with Rhodamine B derivative modified carbon dots (CDs-Rbh) based on fluorescence resonance energy transfer (FRET) from CDs to rhodamine. Intracellular Cu²⁺ is correlated with fluorescence ratio at λ_em 500-600 nm (rhodamine) to λ_em 425-475 nm (CDs) with excitation at λ_ex 405 nm. It is found that Cu²⁺ is linearly correlated with the total intracellular uptaken copper content, with a linear correlation between the relative fluorescence ratio in fluorescence imaging and intracellular Cu derived from ICP-MS, including both Cu(I) and Cu(II) species. The linear calibration equation is lg(F₂/F₁) = 0.00148 m[Cu]-0.3622. This approach facilitates further investigation and elucidation of copper transition in live cells and the evaluation of their cytotoxicity.

Simultaneous determination of five metal ions by on-line complexion combined with micelle to solvent stacking in capillary electrophoresis

A direct on-line complexion combined with micelle to solvent stacking method was proposed for simultaneous determination of metal ions by capillary electrophoresis coupled diode array detector. During the experiment, a plug of complexing agent was first injected to the inlet of capillary, followed by introducing the micelle-bound metal ions. Then the metal ions produced a micelle-to-solvent stacking effect and interacted with the complexing agent under a positive voltage. Continued application of voltage, the analytes were effectively focused and separated in the capillary zone electrophoresis. Repeatability was ranged from 1.89% to 1.94% for the migration time. The detection limits were 2.66-27.9 ng mL^-1 for Ni²⁺, Co²⁺, Cu²⁺, Hg²⁺ and Cd²⁺. Furthermore, the developed method showed a great potential for the determination of metal ions in the crayfish, beebread and Dendrobium officinale samples.

Fluorescence "Turn On-Off" Sensing of Copper (II) Ions Utilizing Coumarin-Based Chemosensor: Experimental Study, Theoretical Calculation, Mineral and Drinking Water Analysis

Herein, we report the preparation of a fluorescent sensor based on coumarin derivative for copper (II) ion sensing in CH₃CN/HEPES media. 6,7-dihydroxy-3-(4-(trifluoro)methylphenyl)coumarin (HMAC) sensor was fabricated and analyzed by spectroscopic techniques. The sensor demonstrates "turn on-off" fluorescence quenching in the presence of copper (II) ions at 458 nm. A clear complex between the chemosensor HMAC and copper (II) ions was characterized by ESI-MS as well as the Job's method. Also, the limit of detection (LOD, 3σ/k) value was determined as 24.5 nM in CH₃CN/HEPES (95/5, v/v) buffer media (pH = 7.0). This value is lower than the admissible level of copper (II) ions in drinking water (maximum 31.5 μM) reported by EU Water Framework Directive (WFD) and World Health Organization (WHO) guidelines. The theoretical calculations (density functional theory, DFT) have been performed for the geometric optimized structures. As a final stage, real sample analyses have successfully been performed by using HMAC, as well as ICP-OES method. The relative standard deviation for copper (II) in mineral and drinking water samples has been determined to be below 0.15% and recovery values are in the range of 95.48-109.20%.

A nopinone based multi-functional probe for colorimetric detection of Cu2+ and ratiometric detection of Ag. Photochem Photobiol Sci 2020;19:49-55. [PMID: 31793618 DOI: 10.1039/c9pp00297a]

A dual-signal probe PPN based on the natural β-pinene derivative nopinone was synthesized for the colorimetric detection of Cu2+ and ratiometric detection of Ag+. Upon the addition of Ag+, a significant fluorescence change from blue to green was observed with a low detection limit (0.86 μM). However, upon the addition of Cu2+, a significant color change from colorless to yellow was observed with a low detection limit (0.56 μM). The novel probe PPN was applied as a probe for the colorimetric detection of Cu2+ and ratiometric detection of Ag+ with a high selectivity, good sensitivity and fast response time. The detection mechanisms of probe PPN for Cu2+/Ag+ were confirmed by 1H NMR and HRMS-ESI. Besides, probe PPN could sense Cu2+/Ag+ on test strips. Additionally, probe PPN could be applied to quantitatively detect the concentration of Ag+ in water samples and image Ag+ in living cells.

Revealing the Hydrolysis Mechanism of a Hg2+-Reactive Fluorescein Probe: Novel Insights on Thionocarbonated Dyes

As one of the most toxic metal pollutants, mercury is the subject of extensive research to improve current detection strategies, notably to develop sensitive, selective, fast, and affordable Hg²⁺-responsive fluorescent probes. Comprehending the sensing mechanism of these molecules is a crucial step in their design and optimization of their performance. Herein, a new fluorescein-based thionocarbonate-appended Hg²⁺-sensitive probe was synthesized to study the hydrolysis reactions involved in the sensing process. Autohydrolysis was revealed as a significant component of the signal generation mechanism, occurring concurrently with Hg²⁺-catalyzed hydrolysis. This knowledge was used to investigate the effects of key experimental conditions (pH, temperature, chloride ions) on sensing efficiency. Overall, the chemical and physical properties of this new thionocarbonated dye and the insights into its sensing mechanism will be instrumental in designing reliable and effective portable sensing strategies for mercury and other heavy metals.

Embedding carbon dots and gold nanoclusters in metal-organic frameworks for ratiometric fluorescence detection of Cu2

Herein, a dual-emission metal-organic framework based ratiometric fluorescence nanoprobe was reported for detecting copper(II) ions. In particular, carbon dots (CDs) and gold nanoclusters (AuNCs) were embedded into ZIF-8 (one of the classical metal-organic frameworks) to form CDs/AuNCs@ZIF-8 nanocomposites, which exhibited dual-emission peaks at UV excitation. In the presence of Cu²⁺, the fluorescence attributed to AuNCs can be rapidly quenched, while the fluorescence of CDs serves as reference with undetectable changes. Therefore, the CDs/AuNCs@ZIF-8 nanocomposites were utilized as a ratiometric fluorescence nanoprobe for sensitive and selective detection of Cu²⁺. A good linear relationship between the ratiometric fluorescence signal of CDs/AuNCs@ZIF-8 and Cu²⁺ concentration was obtained in the range of 10^-3-10³ μM, and the detection limit was as low as 0.3324 nM. The current ratiometric fluorescence nanoprobe showed promising prospects in cost-effective and rapid determination of Cu²⁺ ions with good sensitivity and selectivity. Furthermore, this nanoprobe has been successfully applied for the quantitative detection of Cu²⁺ in serum samples, indicating its value of practical application. Graphical abstract Carbon dots (CDs) and gold nanoclusters (AuNCs) were embedded into metal-organic frameworks (ZIF-8) to form CDs/AuNCs@ZIF-8 nanocomposites, which exhibited dual-emission peaks at 365 nm excitation. In the presence of Cu²⁺, the fluorescence emission peak at 574 nm can rapidly respond by quenching, while the fluorescence at 462 nm serves as reference with undetectable changes.

Insight into triphenylamine and coumarin serving as copper (II) sensors with "OFF" strategy and for bio-imaging in living cells

Chemosensing is one of the widest and powerful techniques for response to anions and cations in living systems serving as bio-probes. Meanwhile, copper(II) (Cu(II)) widely exists in the environment and the human body as a common trace element, which plays an necessary role in most physiological processes. Thus, it is extremely urgent to explore means for effective, rapid and convenient detection of Cu(II) in living cells. Herein, we introduce a novel strategy for designing triphenylamine (TS) and coumarin-based (CS) functional sensors for Cu(II) detection with fluorescence "OFF" switching mechanism by blocking intramolecular charge transfer (ICT). Based on this design strategy, we have demonstrated two kinds of fluorophores sensors with aunique new fluorescent dye and excellent photophysical properties, which have shown rapid recognition of Cu(II) via a stoichiometric ratio of 2:1 and the proposed binding mode was confirmed by the single-crystal structure of CS-Cu(II) complex. In addition, we have carried out density functional theory (DFT) calculation with the B3LYP exchange functional employing RB3LYP/6-31G basis sets to get insight into the mechanism of Cu(II)-sensors alongside their optical properties. Furthermore, the sensors were capable of bio-imaging Cu(II) in living cancer cells (HepG2, A549 and Hela) with low cytotoxicity and good biocompatibility shown. Taken together, We expect that this novel strategy would provide new insight into the development of Cu(II) detection techniques and could be used more for biomedical applications.