Red-emitting BSA-stabilized copper nanoclusters acted as a sensitive probe for fluorescence sensing and visual imaging detection of rutin

A Ratio Fluorescence Method Based on Dual Emissive Copper Nanoclusters for the Detection of Vanillin

In this study, a novel double-emission fluorescence probe at 340 and 400 nm was synthesized by one-pot method using phenylalanine (Phe) and ascorbic acid (AA) as stabilizing and reducing agents. It was found that the fluorescence intensity of the probe at 400 nm could be controlled by controlling the temperature within a certain range, and the ratio of double-emission fluorescence probe could be further regulated. Under the optimal conditions, the fluorescence intensity at 340 nm decreased significantly, while it only showed a slight decrease at 400 nm, which constituted the ratio fluorescence probe. The synthesized fluorescence probe showed good linearity in the range of 0.2-32 μM, and its detection limit was 63.4 nM. Moreover, the method was successfully employed to determine VA in vanilla drink and perfumes, and corresponding results were consistent with those of HPLC.

Copper Nanoclusters as Novel Podium for Cancer Detection, Imaging, and Therapy Applications

Nanoclusters (NCs) are meticulously small, kinetically stable, crystalline materials which hold immense potential as multifaceted catalysts for a broad range of biomedical applications. Metal NCs are atomically precise and exist within the range of Fermi wavelength of electrons. They are highly advantageous as functional materials as their physicochemical properties can be customized to meet specific requirements. Copper NCs (CuNCs) are emerging as an efficient substitute to the other existing metal NCs. The synthesis of CuNCs is highly methodical, fast, cost effective and does not involve any complicated manipulation. On the contrary to gold and silver NCs, copper is a vital trace element for humans that can be excreted easily out the body. Further, the relatively inexpensiveness and easy availability of copper aids in potential nanotechnological applications in large quantity. As such, CuNCs have attracted great interest among the research community recently. The modern developments in the strategy, synthesis, surface modifications, and use of CuNCs in diagnosis of disease, imaging and treatment have been discussed in the present review. Approaches to regulate and augment the emission of CuNCs, challenges and drawbacks have also been considered. This review brings to light the multifarious applications of CuNCs and their potential as emerging theranostic agents. It is anticipated that the visions and directions for translating existing developments in CuNCs from the laboratory to the clinic can be further improved and enhanced.

Histidine-capped copper nanoclusters for in situ amplified fluorescence monitoring of doxycycline through inner filter effect

There is a significant need to accurately measure doxycycline concentrations in view of the adverse effects of an overdose on human health. A fluorescence (FL) detection method was adopted and copper nanoclusters (CuNCs) were synthesized using chemical reduction technology. Based on FL quenching with doxycycline, the prepared CuNCs were used to explore a fluorescent nanoprobe for doxycycline detection. In an optimal sensing environment, this FL nanosensor was sensitive and selective in doxycycline sensing and displayed a linear relationship in the range 0.5-200 μM with a detection limit of 0.092 μΜ. A characterization test demonstrated that CuNCs offered active functional groups for identifying doxycycline using electrostatic interaction and hydrogen bonds. Static quenching and the inner filter effect (IFE) resulted in weakness in the FL of His@CuNCs with doxycycline with great efficiency. This suggested nanosensor was revealed to be a functional model for simple and rapid detection of doxycycline in real samples with very pleasing accuracy.

Fast Determination of Rutin on a Biosensor Made Using a Layered Double Hydroxide Nanocomposite Modified Electrode

In this study, a nanocomposite of LDH/graphene/polyaniline/gold (LDH/rGO/PANI/Au) was synthesized and characterized. The results of characterization showed that the composite material preserved the layered structure of LDH. The composite was dropped onto the glassy carbon electrode and laccase was then immobilized. Electrochemical tests showed that the composite could accelerate the electron transfer between the enzyme and the electrode. The composite/laccase showed an obvious response to rutin and the optimal detection conditions were discussed. The oxidative peak current of the biosensor constructed using the modified electrode was negatively correlated with rutin in the range of 0.05-4 μg/mL. The detection limit was 0.0017 μg/mL at a signal-to-noise ratio of 3. This biosensor of rutin also possessed high sensitivity, excellent anti-interference ability, and stability. The contents of rutin in tablets, first determined using HPLC, were also detected using the sensor constructed in this research as an application, and the results were acceptable. This research here provides a facile way for the fast detection of rutin in real samples.

Synthesis of copper nanoclusters from Bacopa monnieri leaves for fluorescence sensing of dichlorvos

In this work, a facile one-step green synthesis was developed for the fabrication of blue fluorescent copper nanocluster (Brahmi-CuNCs) from the extract of Bacopa monnieri (common name is Brahmi) via a microwave method. The as-prepared Brahmi-CuNCs emitted blue fluorescence at 452 nm when excited at 352 nm and showed a quantum yield of 31.32%. Brahmi-derived blue fluorescent CuNCs acted as a probe for fluorescence sensing of dichlorvos. Upon the addition of dichlorvos, the blue emission for Brahmi-CuNCs was gradually turned off, favouring establishment of a calibration graph in the range 0.5-100 μM with a detection limit of 0.23 μM. The as-synthesized Brahmi-CuNCs exhibited marked sensitivity and selectivity towards dichlorvos, favourable for assaying dichlorvos in various samples (cabbage, apple juice, and rice).

A sensitive multicolor fluorescence sensing strategy for chlorotetracycline based on bovine serum albumin-stabilized copper nanocluster

Fluorescent probes with on-site visual detection function have received extensive attention in the detection of chlortetracycline (CTC), which was widely used in aquaculture and animal husbandry. Copper nanoclusters (Cu NCs) with excellent optical properties were prepared using bovine serum albumin (BSA) as a template, and a multicolor fluorescence strategy based on BSA-stabilized Cu NCs (BSA-Cu NCs) for detecting CTC was proposed. BSA-Cu NCs had a red emission at 640 nm. After the addition of CTC, the red emission of BSA-Cu NCs gradually decreased for internal filtering effect, while the green emission of CTC was significantly enhanced under the sensitization of BSA. This simple sensing process can be achieved in real time by directly mixing the target sample with BSA-Cu NCs, and the detection limit (LOD) of the system for CTC was 12.01 nM. Based on this sensing strategy, a fluorescence film sensing detection platform was constructed to achieve ultra-fast detection of CTC within 30 s. This work provided a fluorescent film sensor with the advantages of portability, ultra-fast and low cost, which provided a feasible alternative for on-site ultra-fast screening of CTC.

Ratiometric upconversion luminescence nanoprobes from construction to sensing, imaging, and phototherapeutics

In terms of the combined advantages of upconversion luminescence (UCL) properties and dual-signal ratiometric outputs toward specific targets, the ratiometric UCL nanoprobes exhibit significant applications. This review summarizes and discusses the recent advances in ratiometric UCL nanoprobes, mainly including the construction of nanoprobe systems for sensing, imaging, and phototherapeutics. First, the construction strategies are introduced, involving different types of nanoprobe systems, construction methods, and ratiometric dual-signal modes. Then, the sensing applications are summarized, involving types of targets, sensing mechanisms, sensing targets, and naked-eye visual detection of UCL colors. Afterward, the phototherapeutic applications are discussed, including bio-toxicity, bio-distribution, biosensing, and bioimaging at the level of living cells and small animals, and biomedicine therapy. Particularly, each section is commented on by discussing the state-of-the-art relevant studies on ratiometric UCL nanoprobe systems. Moreover, the current status, challenges, and perspectives in the forthcoming studies are discussed. This review facilitates the exploration of functionally luminescent nanoprobes for excellent sensing, imaging, biomedicine, and multiple applications in significant fields.

Preparation of Nitrogen and Sulfur Co-Doped Fluorescent Carbon Dots from Cellulose Nanocrystals as a Sensor for the Detection of Rutin

The poor water solubility, large particle size, and low accessibility of cellulose, the most abundant bioresource, have restricted its generalization to carbon dots (CDs). Herein, nitrogen and sulfur co-doped fluorescent carbon dots (N, S-CDs) were hydrothermally synthesized using cellulose nanocrystals (CNC) as a carbon precursor, exhibiting a small particle size and excellent aqueous dispersion. Thiourea was selected as a nitrogen and sulfur dopant to introduce abundant fluorescent functional groups into N, S-CDs. The resulting N, S-CDs exhibited nanoscale size (6.2 nm), abundant functional groups, bright blue fluorescence, high quantum yield (QY = 27.4%), and high overall yield (16.2%). The excellent optical properties of N, S-CDs endowed it to potentially display a highly sensitive fluorescence "turn off" response to rutin. The fluorescence response for rutin allowed a wide linear range of 0-40 mg·L^-1, with a limit of detection (LOD) of 0.02 μM, which revealed the potential of N, S-CDs as a rapid and simple sensing platform for rutin detection. In addition, the sustainable and large-scale production of the N, S-CDs in this study paves the way for the successful high-value utilization of cellulose.

Paper-based device for the selective determination of doxycycline antibiotic based on the turn-on fluorescence of bovine serum albumin-coated copper nanoclusters

An enhanced ratiometric fluorescence sensor was built for on-site visual detection of doxycycline (DOX) through the interaction with bovine serum albumin on the surface of red emissive copper nanoclusters. Upon the addition of weakly fluorescent DOX, the red fluorescence from copper nanoclusters gradually decreased through the inner-filter effect (IFE), while a green fluorescence appears and significantly increases, forming an interesting fluorescent isosbestic point, which was assigned to DOX due to sensitization effect of bovine serum albumin. On the basis of this ratiometric fluorescence, the system possessed good limit of detection (LOD) of 45 nM and excellent selectivity for DOX over other tetracyclines. Based on these findings, a paper-based sensor has been fabricated for distinct visual detection of trace DOX and combined with smartphone color recognizer for quantitative detection of DOX (LOD = 83 nM). This method shows broad application prospects in environmental monitoring and food safety.

Synthesis of Copper Nanoclusters and Their Application for Environmental Pollutant Probes: A Review

Copper nanoclusters (CuNCs) as a new type of probe for environmental contaminants are gaining increasing attention because of its low cost, superior water dispersibility, wide availability and excellent optical properties. Compared with the other probes such as quantum dots and organic dyes, CuNCs show much more potential in practical application for their excellent photostability, large Stokes shift, low toxicity and other preponderance, especially in the fields of biosensing and environmental monitoring. Recently, the template-assisted synthesis of metal nanoclusters (MNCs) has been widely studied. A variety of templates such as proteins, small thiol molecules, polymers, and DNA with different spatial configuration have been used for the preparation of MNCs so far. This review primarily described recent advances in CuNCs in terms of the synthesis of CuNCs from different templates, the methods to improve the fluorescence (FL) properties of CuNCs, as well as the basic detection mechanisms based on the FL properties or catalytic properties. Finally, to promote the practical application of CuNCs probes, the challenges and prospects of CuNCs multifunctional probes are also discussed.

Visualization of copper nanoclusters for SARS-CoV-2 Delta variant detection based on rational primers design

Here, based on the design of rational primers and copper nanoclusters (CuNCs), we present a method for the accurate detection of the SARS-CoV-2 Delta variant, which is capable of distinguishing the Delta variant with its single nucleotide polymorphism from the 'wild type' coronavirus (NC_045512.2), and realizing visualization signal out. Specifically, we show that dual priming oligonucleotide (DPO) primers and AT primers can be used to distinguish between wild types and mutations of this virus by polymerase chain reaction (PCR) analysis and that visualization can be achieved via the red fluorescence of CuNCs in ultraviolet radiation. Among the results, it was found that the R-1-down (DPO)-6I and F-1-30 AT, with the single nucleotide deletion site designed at the 3' end of the downstream primer, showed the best specificity towards the Delta variant. Moreover, the use of AT primers increased the AT contents of the PCR products, thus meeting the template requirements generated by the CuNCs. It was also found that the AT primers could assist with improving detection specificity. Finally, we demonstrate that the visualization of the CuNCs-based detection assay exhibited a linear relationship in 0.5 pg μL^-1-50 ng μL^-1, with a limit of quantitation (LOQ) of 0.5 pg μL^-1.

One facile fluorescence strategy for sensitive determination of baicalein using trypsin-templated copper nanoclusters

Herein, we established a fluorescent detection platform for baicalein (Bai) based on copper nanoclusters, which were prepared by using copper sulfate as the precursor, trypsin (Tryp) as the template and hydrazine hydrate as the reducing agent. The entire preparation and testing process were rapid, facile and green. Many characterization methods, such as UV-vis absorption spectroscopy, fluorescence spectroscopy, fourier transform infrared spectroscopy (FT-IR), fluorescence lifetime, transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS), were applied for the analysis of trypsin-templated copper nanoclusters (Cu NCs@Tryp). The Cu NCs@Tryp released green fluorescence at maximum emission wavelength of 457 nm under maximum excitation wavelength of 377 nm. More importantly, the fluorescence of Cu NCs@Tryp was efficiently quenched by Bai. According to this phenomenon, a facile, rapid and selective turn-off fluorescence probe for Bai sensing was developed. Under the optimized testing conditions, the ln(F₀/F) value and concentration of Bai displayed excellent linear relationship changing from 0.5 to 60 μM (R² = 0.9969), and the detection limit was 0.078 μM. Furthermore, the Cu NCs@Tryp has been successfully employed to measure the amount of Bai in bovine serum samples with satisfactory recoveries.

Novel composite nanomaterials based on magnetic molecularly imprinted polymers for selective extraction and determination of rutin in fruit juice

In this work, with the attempt to further improve the selectivity, magnetism and loading proportion of existing adsorbents, a novel composite (MGO/MHNTs@MIPs) was synthesized by electrostatically combining molecularly imprinted polymer based on the surface of magnetic halloysite nanotubes (MHNTs@MIPs) with magnetic graphene oxide (MGO). Then some characterizations were done to prove its successful synthesis. Besides, the bonding experiment showed that it possessed a loading capacity of up to 132 mg·g^-1, and the adsorption behavior of MGO/MHNTs@MIPs was elucidated by Langmuir isotherm model and Pseudo-second order model. By comparing its adsorption capacity to analogues, we concluded that the MGO/MHNTs@MIPs with the MHNTs@MIPs as basic elements exhibited higher selectivity (imprinting factor = 2.25) than that of MGO/MHNTs@NIPs based on MHNTs@NIPs for template rutin. Furthermore, a series of solid phase extraction conditions were optimized, and then the materials were used for the extraction and detection of rutin in fruit juice under the optimal conditions.

Highly sensitive electrochemical determination of rutin based on the synergistic effect of 3D porous carbon and cobalt tungstate nanosheets

Rutin, a flavonoid found in fruits and vegetables, is a potential anticancer compound with strong anticancer activity. Therefore, electrochemical sensor was developed for the detection of rutin. In this study, CoWO₄ nanosheets were synthesized via a hydrothermal method, and porous carbon (PC) was prepared via high-temperature pyrolysis. Successful preparation of the materials was confirmed, and characterization was performed by transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. A mixture of PC and CoWO₄ nanosheets was used as an electrode modifier to fabricate the electrochemical sensor for the electrochemical determination of rutin. The 3D CoWO₄ nanosheets exhibited high electrocatalytic activity and good stability. PC has a high surface-to-volume ratio and superior conductivity. Moreover, the hydrophobicity of PC allows large amounts of rutin to be adsorbed, thereby increasing the concentration of rutin at the electrode surface. Owing to the synergistic effect of the 3D CoWO₄ nanosheets and PC, the developed electrochemical sensor was employed to quantitively determine rutin with high stability and sensitivity. The sensor showed a good linear range (5–5000 ng/mL) with a detection limit of 0.45 ng/mL. The developed sensor was successfully applied to the determination of rutin in crushed tablets and human serum samples.

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Highly sensitive electrochemical sensor based on 3D porous carbon and CoWO₄ nanosheets.

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Electrochemical signal of rutin is mainly based on its concentration at the electrode surface.

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The introduction of porous carbon improved the electrochemical performance of 3D CoWO₄.

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The sensor was successfully applied to determine rutin in human serum samples.

Sensitive detection of S. Aureus using aptamer- and vancomycin -copper nanoclusters as dual recognition strategy

The proposed aptamer- and antibiotic-based dual detection sensor, combines copper nanoclusters (CuNCs) as an effective approach for the recognition and quantification of Staphylococcus aureus (S. aureus) as a pathogenic bacteria. A facile method for CuNCs based on vancomycin as the template using a fluorescence platform was proposed for the recognition of the S. aureus whole cells via antibiotic and aptamer. Using dual receptor functionalized CuNCs linked to vancomycin and a specific aptamer and during aggregation induce emission process enhanced fluorescence signal linearly with S. aureus concentrations between 10²-10⁸ CFU/mL, and the detection limit was 80 CFU/mL after 45 min as the optimum incubation time. Non-target bacteria generated negative results, proving the high specificity of the presented sensor. This strategy showed recoveries ranging 86%-98% in milk as real sample and can be used for the development of universal detection platforms for efficient and specific S. aureus detection with great potential applications for monitoring pathogenic bacteria.

Copper nanoclusters: designed synthesis, structural diversity, and multiplatform applications

Atomically precise metal nanoclusters (MNCs) have gained tremendous research interest in recent years due to their extraordinary properties. The molecular-like properties that originate from the quantized electronic states provide novel opportunities for the construction of unique nanomaterials possessing rich molecular-like absorption, luminescence, and magnetic properties. The field of monolayer-protected metal nanoclusters, especially copper, with well-defined molecular structures and compositions, is relatively new, about two to three decades old. Nevertheless, the massive progress in the field illustrates the importance of such nanoobjects as promising materials for various applications. In this respect, nanocluster-based catalysts have become very popular, showing high efficiencies and activities for the catalytic conversion of chemical compounds. Biomedical applications of clusters are an active research field aimed at finding better fluorescent contrast agents, therapeutic pharmaceuticals for the treatment and prevention of diseases, the early diagnosis of cancers and other potent diseases, especially at early stages. A huge library of structures and the compositions of copper nanoclusters (CuNCs) with atomic precisions have already been discovered during last few decades; however, there are many concerns to be addressed and questions to be answered. Hopefully, in future, with the combined efforts of material scientists, inorganic chemists, and computational scientists, a thorough understanding of the unique molecular-like properties of metal nanoclusters will be achieved. This, on the other hand, will allow the interdisciplinary researchers to design novel catalysts, biosensors, or therapeutic agents using highly structured, atomically precise, and stable CuNCs. Thus, we hope this review will guide the reader through the field of CuNCs, while discussing the main achievements and improvements, along with challenges and drawbacks that one needs to face and overcome.

Application of micro/nanomaterials in adsorption and sensing of active ingredients in traditional Chinese medicine

Traditional Chinese medicine (TCM) has been widely applied for the prevention and cure of various diseases for centuries. Ingredient with pharmacological activity is the key to the application of TCM. Hence, it is of significance to separate and detect active ingredients in TCM effectively. Micro/nanomaterial is the promising candidate for adsorption and sensing due to its unique physical and chemical properties. For years, many efforts have been made to develop functional micro/nanomaterials to realize the effective adsorption or sensing of bioactive compounds in TCM. In this review, we discussed recent progresses in the application of various functional micro/nanomaterials for adsorption or detection (electrochemical detection, fluorescent detection, and colorimetric detection) of active ingredients. Based on the kind of matrix materials, micro/nano-adsorbents or sensors can be classified into following categories: metal-based micro/nanomaterials, porous materials, carbon-based materials, graphene/graphite-liked micro/nanomaterials and hybrid micro/nanomaterials.

A colorimetric method for screening α-glucosidase inhibitors from flavonoids using 3,3',5,5'-tetramethylbenzidine as a chromogenic probe

A facile and novel colorimetric method for screening of α-glucosidase inhibitors (AGIs) from flavonoids using 3,3',5,5'-tetramethylbenzidine (TMB) as a chromogenic probe is proposed. This method is based on the colorimetric detection of ascorbic acid (AA) through the TMB oxidation reaction catalyzed by horseradish peroxidase (HRP) in the presence of hydrogen peroxide (H₂O₂). In the TMB/H₂O₂/HRP system, HRP catalyzes the oxidation of H₂O₂ to ‧OH radical which oxidizes TMB to blue-colored oxidized TMB (oxTMB). In the presence of AA, the production of ‧OH radical is suppressed and causes the decrease of oxTMB, resulting in the fading of the blue color and the decrease of absorbance at 652 nm. Based on this, the existence of AA can be facilely identified. In the 2-O-α-d-glucopyranosyl-l-ascorbic acid (AA-2 G)/α-glucosidase (α-Glu) system, the produced AA inhibits the oxidation of TMB to blue-colored oxTMB. In the presence of AGIs, the production of AA is inhibited, which inhibits the reduction of oxTMB, resulting in a blue color recovery and an increase of the absorbance at 652 nm. Based on this, the colorimetric method is developed for screening of AGIs from 7 flavonoids.

Functional gadolinium-based nanoscale systems for cancer theranostics

Cancer theranostics is a new strategy for combating cancer that integrates cancer imaging and treatment through theranostic agents to provide an efficient and safe way to improve cancer prognosis. Design and synthesis of these cancer theranostic agents are crucial since these agents are required to be biocompatible, tumor-specific, imaging distinguishable and therapeutically efficacious. In this regard, several types of gadolinium (Gd)-based nanomaterials have been introduced to combine different therapeutic agents with Gd to enhance the efficacy of therapeutic agents. At the same time, the entire treatment procedure could be monitored via imaging tools due to incorporation of Gd ions, Gd chelates and Gd/other imaging probes in the theranostic agents. This review aims to overview recent advances in the Gd-based nanomaterials for cancer theranostics and perspectives for Gd nanomaterial-based cancer theranostics are provided.

Capping 1,3-propanedithiol to boost the antibacterial activity of protein-templated copper nanoclusters

We have prepared copper nanoclusters (Cu NCs) in the presence of bovine serum albumin (BSA) and 1,3-propanedithiol (PDT). The PDT/BSA-Cu NCs possess great activities against different types of bacteria, including non-multidrug-resistant bacteria (Escherichia coli, Salmonella Enteritidis, Pseudomonas aeruginosa, and Staphylococcus aureus) and multidrug-resistant bacteria (methicillin-resistant S. aureus). Their minimal inhibitory concentration (MIC) values are at least 242-fold and 10-fold lower than that of the free PDT and BSA-Cu NCs, respectively. The PDT/BSA-Cu NCs are strongly bound to the bacterial membrane, in which they induce the generation of ascorbyl (Asc) and perhydroxyl (HOO) radicals that result in disruption of their membrane integrity. At a concentration of 100-fold higher than their MIC for Escherichia coli, the PDT/BSA-Cu NCs exhibit negligible cytotoxicity towards the tested mammalian cells and show insignificant hemolysis. We have further demonstrated that low-cost PDT/BSA-Cu NCs-coated carbon fiber fabrics (CFFs) are effective against antibacterial growth, showing their great potential for antifouling applications.

Biocompatible thiolate protected copper nanoclusters for an efficient imaging of lung cancer cells

We report, the one-pot synthesis of water-soluble and biocompatible 3-mercaptopropylsulfonate (MPS) protected novel copper nanoclusters (CuNCs). Interestingly, the TEM image of MPS protected CuNCs exhibits an ultrasmall nanoclusters of particle size <2-nm, similar to its Au and Ag analogue. The hydrophilic and biocompability property of thiolate protected CuNCs. i.e., MPS stabilized CuNCs and its luminescent nature gave rise to maximum quantum yield of 1.5%. Further, as achieved CuNCs was investigated for haemocompatibility, cell viability and fluorescent microscopic analysis with A549 lung cancer cell line. Haemolytic study was examined using human RBCs in the concentration range of 4 to 22 μg/mL for which 7.5% of haemolysis was obtained for an optimum concentration of 22 μg/mL of CuNCs. The cell viability analysis was carried out by MTT assay using A549 lung cancer cells for the minimum (10 μg/mL) and maximum (45 μg/mL) concentration of CuNCs which reports 93.1% and 38.2% cell viability respectively. The inverted light microscopic images from the control and CuNCs treated (20 μg/mL) cells exhibited an excellent biocompatibility with a normal morphology. Upon increasing the concentration of CuNCs upto 45 μg/mL, the cell viability trends to decrease and the cell morphology also denature gradually. Further, the bio-imaging application of CuNCs was analyzed with A549 lung cancer cells. The efficient imaging with CuNCs treated (20 μg/mL) A549 cells resulted in a green colour emission using FITC filter (460- 490 nm). Thereby the obtained results confirm the applicability of CuNCs for the biomedical and cancer diagnosis applications.

Colorimetric Differentiation of Flavonoids Based on Effective Reactivation of Acetylcholinesterase Induced by Different Affnities between Flavonoids and Metal Ions

Flavonoids are closely related to human health, and the distinguishiment of flavonoids is an important but difficult issue. We herein unveil a novel colorimetric sensor array for the rapid identification of 7 flavonoids (e.g., gallocatechin (GC), morin hydrate (MH), puerarin (Pu), epigallocatechin gallate (EGCG), catechin (C), rac Naringenin (rN), and Flavone (Fla)) for the first time. The colorimetric performances of gold nanoparticles (AuNPs) are characteristically correlated with thiocholine, which is issued from the enzymatic hydrolysis of acetylcholine (AcCh). Therefore, as a proof-of-concept design, three sensors (Cu²⁺/acetylcholinesterase (AcChE)/AcCh/AuNPs, Zn²⁺/AcChE/AcCh/AuNPs, and Mn²⁺/AcChE/AcCh/AuNPs) were constructed to form our sensor array. The distinct affinities between flavonoids and metal ions would cause varying degrees of effective reactivation of AcChE, leading to unique colorimetric response patterns upon being challenged with the seven flavonoids for their pattern recognition, enabling an excellent identification of the seven flavonoids at a concentration of 20 nM and different concentrations of individual flavonoids, as well as mixtures of them.

A covalent triazine framework as an oxidase mimetic in the luminol chemiluminescence system: application to the determination of the antioxidant rutin

It is found that a covalent triazine framework (CTF-1) (that was prepared from 1,4-dicyanobenzene) exhibits oxidase-like activity toward the oxidation of luminol with dissolved oxygen in alkaline condition to produce intense blue chemiluminescence (CL). The reaction follows Michaelis-Menten kinetics and shows strong specificity for luminol. Reactive oxygen species including ¹O₂, ^•OH and O₂^•- are testified to be involved in the reaction and responsible for the CL. The reaction was applied to the determination of the radical-scavenging activity of antioxidants, with rutin, kaempferol and ferulic acid serving as model scavengers. A sensitive CL method was developed for the determination of rutin based on its inhibitory effect on the reaction. The CL system gave a linear response to the concentration of rutin in the range of 0.03-0.25 μmol·L^-1 with a limit of detection of 0.015 μmol·L^-1. The practicability of the method was demonstrated by successful determination of rutin in tablets and in Flos Sophorae Immaturus. Graphical Abstract.

Recent progress in copper nanocluster-based fluorescent probing: a review

Copper nanoclusters (CuNCs) are an attractive alternative to other metal nanoclusters. The synthesis of CuNCs is highly efficient and fast, with low-cost and without any complicated manipulation. Because of their tunable fluorescence and low toxicity, CuNCs have been highly exploited for biochemical sensing. This review (with 172 refs.) summarizes the progress that has been made in the field in the past years. Following an introduction into the fundamentals of CuNCs, the review first focuses on synthetic methods and the fluorescence properties of CuNCs (with subsections on the use of proteins, peptides, DNA and other molecules as templates). This is followed by a section on the use of CuNCs in fluorometric assays, with subsections on the detection of small molecules, proteins, nucleic acids, various other biomolecules including drugs, and of pH values. A further large chapter summarizes the work related to environmental analyses, specifically on determination of metal ions, anions and pollutants. Graphical abstract Schematic representation of the synthesis and potential applications of copper nanocluster (CuNCs) in biochemical analysis, emphatically reflected in some vital areas such as small molecule analysis, biomacromolecule monitoring, cell imaging, ions detection, toxic pollutant, etc.

Copper nanoclusters: an efficient fluorescence sensing platform for quinoline yellow

Fluorescence quenching behavior of artificial food colorant quinoline yellow (QY), on interaction with l-cysteine stabilized copper nanoclusters (l-Cys-CuNCs) is investigated in this work. For this purpose, l-cysteine stabilized CuNCs were synthesized and characterized using various analytical techniques. Results demonstrated that the synthesized probe (size ~2 nm) had very promising optical features such as bright blue fluorescence, significant quantum yield and excellent photostability. l-Cys-CuNCs can function as a fluorescence sensor by selectively sensing QY among other yellow colorants, giving a detection limit as low as 0.11 μM. The developed sensor exhibited a linear concentration range from 5.50 to 0.20 μM. The developed fluorescence assay was successfully applied for testing commercial samples, thereby making this sensing strategy significant for quality control of food stuffs.

Ultrasmall hybrid protein–copper sulfide nanoparticles for targeted photoacoustic imaging of orthotopic hepatocellular carcinoma with a high signal-to-noise ratio

A schematic illustration of CuS@BSA-RGD nanoparticle synthesis and the application of photoacoustic imaging in an orthotopic HCC model.

Environment dependent photophysical and fluorescence turn-off sensing properties of Fe(iii) by substituted phenyl isochromenopyrrol-5-ones

The proposed isochromenopyrrolones can serve as highly selective and sensitive sensors for iron(iii) in pharmaceutical, industrial and biological applications.

Size-controlled atomically precise copper nanoclusters: Synthetic protocols, spectroscopic properties and applications

Noble metal nanoclusters (NCs) are a new class of nanomaterials which are considered being a missing link between isolated metal atoms and metal nanoparticles (NPs). The sizes of the NCs are comparable to the Fermi wavelength of the conduction electrons, and this renders them to be luminescent in nature. They exhibit size-dependent fluorescence properties spanning almost the entire breath of the visible spectrum. Among all the noble metal NCs being explored, copper NCs (CuNCs) are the most rarely investigated primarily because of their propensity of getting oxidised. In this chapter, we have given a comprehensive understanding as to why these NCs are luminescent in nature. We have also given a detailed overview regarding the various templates used for the synthesis of these CuNCs along with the respective protocols being followed. The various instrumental techniques used to characterize these CuNCs are discussed which provides an in-depth understanding as to how these CuNCs can be properly examined. Finally, we have highlighted some of the most recent applications of these CuNCs which make them unique to serve as the next-generation fluorophores.

Graphical Abstract:

Melamine-Induced Decomposition and Anti-FRET Effect from a Self-Assembled Complex of Rhodamine 6G and DNA-Stabilized Silver Nanoclusters Used for Dual-Emitting Ratiometric and Naked-Eye-Visible Fluorescence Detection

In this work, blue-emitting silver nanoclusters (AgNCs) were prepared in a matrix of single-stranded deoxyribonucleic acid (DNA) on the basis of ambient hydrothermal reactions. DNA acted as the stabilizer or coating agent, and NaBH₄ was used as the reducing agent. Through the interactions between rhodamine 6G (Rh6G) and the synthesized DNA-AgNCs, the self-assembled complex of DNA-AgNC-Rh6G was generated. Meanwhile, fluorescence emission of AgNCs was weakened as a result of fluorescence-resonance-energy transfer (FRET) from AgNCs (donor) to Rh6G (acceptor). In the DNA-AgNC-Rh6G complex aqueous suspension, the addition of melamine induced obvious emission recovery of AgNCs and fluorescence decrease of Rh6G, attributable to melamine-induced decomposition of the self-assembled complex and anti-FRET effects. There was a well-plotted linear relationship of ratiometric fluorescence intensities ( I_AgNCs/ I_Rh6G) versus melamine concentration in the range of 0.1-10 μM, with a low detection limit of 25 nM. Responses of I_AgNCs/ I_Rh6G to melamine were highly selective and sensitive over potential interferents. A novel dual-emitting ratiometric fluorescence sensor of melamine was facilely constructed on the basis of the DNA-AgNC-Rh6G complex. In particular, the sensor enabled visual fluorescence detection of melamine both in aqueous solution and on wetted filter paper. Superior detection results of the sensor were experimentally obtained and confirmed its high feasibility for melamine detection in practical samples.

Specific enzymatic synthesis of 2,3-diaminophenazine and copper nanoclusters used for dual-emission ratiometric and naked-eye visual fluorescence sensing of choline

This work reports a novel biosensor for dual-emission ratiometric and visual fluorescence detection of choline.

Ratiometric fluorescence, solution-phase and filter-paper visualization detection of ciprofloxacin based on dual-emitting carbon dot/silicon dot hybrids

This study demonstrates the ratiometric fluorescence, solution-phase and filter-paper visual detection of ciprofloxacin based on dual-emitting carbon dot/silicon dot hybrids.

A sensitive electrochemical sensor based on ZIF-8–acetylene black–chitosan nanocomposites for rutin detection

Herein, we fabricated a sensitive rutin electrochemical sensor via modifying glassy carbon electrode (GCE) with zeolitic imidazolate framework-8 (ZIF-8) and acetylene black (AB) in the presence of chitosan (CS). The electrochemical activity and experimental parameters of the ZIF-8-AB-CS/GCE sensor were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under the optimal conditions, the sensor presented a reasonable linear response in the range of 0.1–10 μM with a limit of detection (LOD) as low as 0.004 μM (S/N = 3). The sensor possessed good reproducibility and high stability, and was successfully applied to detect rutin tablet samples with satisfactory results, which was attributed to the synergistic effect between ZIF-8 and AB. Meanwhile, the sensor displayed a potential application for detection of other analytes in real samples. Furthermore, a probable interaction mechanism was proposed to account for the interaction between rutin and the nanocomposite electrode, which was not discussed in previous reports.

A sensitive ZIF-8-AB-CS/GCE for rutin detection is constructed and the interaction between them is discussed for the first time.