Copper nanoclusters coated with bovine serum albumin as a regenerable fluorescent probe for copper(II) ion

Recyclable fluorescence sensing based on copper clusters for simultaneous determination of copper ions and ammonia

A one-step strategy for synthesizing fluorescent copper clusters stabilized by L-cysteine has been successfully established in aqueous solutions. The direct determination of copper ions was realized by the fluorescence enhancement phenomenon caused by the preparation and aggregation process. At the same time, ammonia treatment can lead to rapid fluorescence quenching, resulting from the influence on the aggregation behavior of Cu clusters, while the fluorescence can be recovered by the continuous addition of copper ions. Therefore, a recyclable fluorescence sensing system is constructed for the simultaneous determination of copper ions and ammonia. This method is simple, anti-interference and has been successfully applied to the determination of environmental samples.

Fluorescent folic acid-capped copper nanoclusters for the determination of rifampicin based on inner filter effect

Development of excellent sensors to determine trace concentrations of rifampicin is of intense importance for medicine analysis and human health. Herein, a facile and green fluorescent probe was established for the determination of rifampicin by using folic acid protected copper nanoclusters (FA-Cu NCs). Many characterization methods were applied for the analysis of the as-prepared FA-Cu NCs including UV-visible absorption spectra, fluorescence spectra, Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), fluorescence lifetime and X-ray photoelectron spectroscopy (XPS). The TEM image suggested that the as-prepared FA-Cu NCs were highly dispersed. The as-synthesized FA-Cu NCs emerged blue fluorescence under UV light and demonstrated maximum emission wavelength at 446 nm under the maximum excitation wavelength of 358 nm. After the addition of rifampicin, the FL intensities of FA-Cu NCs were uncommonly quenched. The related experimental data intimated that the quenching mechanisms were assumed to the inner filter effect (IFE) and static quenching. The as-proposed probe platform displayed an obvious linear relationship with rifampicin concentrations varying from 0.5 to 100 µM, and the corresponding detection limit (LOD) was 0.073 µM (S/N = 3). Finally, the as-established detection platform was successfully employed to analyze trace concentrations of rifampicin in real samples.

Synthesis of Copper Nanocluster and Its Application in Pollutant Analysis

Copper nanoclusters (Cu NCs) with their inherent optical and chemical advantages have gained increasing attention as a kind of novel material that possesses great potential, primarily in the use of contaminants sensing and bio-imaging. With a focus on environmental safety, this article comprehensively reviews the recent advances of Cu NCs in the application of various contaminants, including pesticide residues, heavy metal ions, sulfide ions and nitroaromatics. The common preparation methods and sensing mechanisms are summarized. The typical high-quality sensing probes based on Cu NCs towards various target contaminants are presented; additionally, the challenges and future perspectives in the development and application of Cu NCs in monitoring and analyzing environmental pollutants are discussed.

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.

Dual-emission copper nanoclusters-based ratiometric fluorescent probe for intracellular detection of hydroxyl and superoxide anion species

A fluorescent nanoprobe based on copper nanoclusters (CuNCs) has been developed for ratiometric detection of hydroxyl radicals (^•OH) and superoxide anion radicals (O₂^•-). Two differently luminescent CuNCs, namely cyan-emissive poly(methacrylic acid)-protected copper nanoclusters (PCuNCs) and orange-emissive bovine serum albumin-protected CuNCs (BCuNCs), were conjugated to obtain a hybrid, dual-emission nanoprobe (PCuNCs-BCuNCs) with the corresponding peaks at 445 nm and 652 nm at an excitation wavelength of 360 nm. In particular, the fluorescence peak at 445 nm gradually enhanced with the incremental addition of ^•OH and O₂^•-. However, the fluorescence emission at 652 nm was greatly quenched in the presence of ^•OH, while in case of O₂^•-, the fluorescence intensity remained constant. The differential response of the PCuNCs-BCuNCs towards ^•OH and O₂^•- formed the basis of ratiometric detection. Under optimal conditions, the PCuNCs-BCuNCs exhibited good sensitivity and linearity towards ^•OH and O₂^•- with limits of detection of 0.15 μM and 1.8 μM, respectively. Moreover, the nanoprobe exhibited high selectivity for ^•OH and O₂^•- over other potential ROS interferences. Besides, PCuNCs-BCuNCs were eventually applied for qualitative and quantitative ratiometric assessment of intracellular ^•OH and O₂^•- in L-132 cells. Therefore, this strategy unveils a new potential for copper nanocluster-based sensing of ROS.

A novel copper ion sensing fluorescent probe for fast detection of pyrophosphate and alkaline phosphatase

A Cu²⁺ sensing fluorescent probe is synthesized via a Mannich reaction and is applied in the fluorescence detection of pyrophosphate and alkaline phosphatase.

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.

Highly selective visual sensing of copper based on fluorescence enhanced glutathione-Au nanoclusters

A blue emission glutathione stabilized Au nanoclusters prepared by an Au/Histidine complex with ligand-exchanges method was used for sensing of copper ions. We found that the glutathione stabilized Au NCs which has fluorescence emission hundred times higher than the Au/Histidine complex and has a highly selective fluorescence quenching response to copper ion. Other common metal ions, such as mercury, lead, iron and zinc, which could obviously quench or enhance the fluorescence of Au/Histidine complex, do not interfere the sensing of copper using glutathione stabilized Au nanocluster. The possible quenching mechanism and the dynamic quenching process for copper detection were also discussed. The results indicated that copper in the range from 0.5 to 300.0μM could be linearly detected and the detection could be finished quickly in 5min. A visual detection method for copper ion that may be used to fast warn copper pollution in waters by naked eyes observation was also be developed using the glutathione stabilized Au NCs probe.

A Simple and Cost Effective Turn off Fluorescence Sensor for Biliverdin and Bilirubin Based on L-Cysteine Modulated Copper Nanoclusters

The present article reports the efficiency of L-cysteine modulated copper nanoclusters (L-cys-CuNCs) as a fluorescent probe for the selective determination of naturally occurring bile pigments biliverdin (BVD) and bilirubin (BLR). These pigments were found to quench the fluorescence of L-cys-CuNCs through static processes. Under optimized conditions, the proposed strategy permitted the quantification of BVD and BLR in the range 4.00 × 10^-5 to 5.00 × 10^-7M and 1.00×10^-5 to 1.00×10^-6 M respectively with limits of detection 2.33 × 10^-7M and 2.29 × 10^-7 M. The practical utility of the developed sensor have been investigated in spiked blood and urine samples.

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.

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:

Fast synthesis of porous copper nanoclusters for fluorescence detection of iron ions in water samples

Copper nanoclusters (Cu NCs) have attracted great research interest in recent years owing to its unique physical, electrical and optical properties. Macromolecules have been widely used as templates to synthesize fluorescent Cu NCs. In this study, a simple method for synthesis of albumin chicken egg capped porous copper nanoclusters (p-Cu NCs) was developed for the first time. The obtained p-Cu NCs exhibited intense emission and excitation peaks at 280 nm and 340 nm, respectively. Besides, the p-Cu NCs fluorescence probe could be quenched by Fe³⁺ ions in aqueous solutions. Therefore, the p-Cu NCs can be excellently candidated as fluorescent probe for the detection of Fe³⁺ ions. Under optimized conditions, this fluorescent probe exhibited a wide linear response concentration range (0.2 to 100 μM) to Fe³⁺ with a detection limit of 0.0234 μM. In addition, the fluorescent probe has been successfully used for the detection of Fe³⁺ in natural water samples with satisfactory result.

Cytidine-stabilized copper nanoclusters as a fluorescent probe for sensing of copper ions and hemin

We reported a sensitive and selective fluorescence “turn on–off” strategy for detection of Cu²⁺ and hemin, respectively. The fluorescence “turn on” sensor for Cu²⁺ detection had a wide linear range of 0.05–2.0 μM with a limit of detection (LOD) of 0.032 μM, and the fluorescence “turn off” sensor for hemin detection possessed a wide linear range of 0.05–4.0 μM with an LOD of 0.045 μM. The sensor for Cu²⁺ or hemin exhibited high selectivity over other possible substances. In addition, it was demonstrated by using various analytical characterization techniques that the fluorescence “turn on” sensor for Cu²⁺ was constructed on the basis of the formation of water-soluble fluorescent copper nanoclusters (CuNCs), and the fabrication of the fluorescence “turn off” sensor for hemin was predominately based on the inner filter effect of hemin on the fluorescence of the CuNCs. Finally, the proposed fluorescence “turn on–off” sensor system was successfully applied for detection of Cu²⁺ in lake water samples and hemin in duck blood samples.

A sensitive and selective fluorescence “turn on–off” strategy for simultaneous detection of Cu²⁺ and hemin was proposed on the basis of the formation of fluorescent CuNCs and the inner filter effect of hemin on the fluorescence of the CuNCs.

BSA capped bi-functional fluorescent Cu nanoclusters as pH sensor and selective detection of dopamine

Illustration of the preparation of bi-functional BSA-CuNCs, the pH sensing and the detection of dopamine (DA).

Synthesis, optical properties and applications of light-emitting copper nanoclusters

Metal nanoclusters (NCs) containing a few to a few hundreds of atoms bridge the gap between nanoparticles and molecular compounds. The last decade evidenced impressive developments of noble metal NCs such as Au and Ag. Copper is an earth abundant, inexpensive metal from the same group of the periodic table, which is increasingly coming into focus for NC research. This review specifically addresses wet chemical synthesis methods, optical properties and some emerging applications of Cu NCs. As surface protecting templates/ligands play an important role in the stability and properties of Cu NCs, we classified the synthetic methods by the nature of the capping agents. The optical properties of Cu NCs are discussed from the point of view of the effects of the metal core, surface ligands and environment (solvents and aggregation) on the emission of the clusters. Applications of luminescent Cu NCs in biological imaging and light emitting devices are considered.

Visual and fluorescence detection of pyrogallol based on a ratiometric fluorescence-enzyme system

Schematic illustration of the synthesis of a CQDs@SiO₂@CdTe QD nanohybrid as a ratiometric fluorescent probe for the detection of PG.

Fluorescent copper nanoparticles: recent advances in synthesis and applications for sensing metal ions

Fluorescent copper nanoparticles (F-CuNPs) have received great attention due to their attractive features, such as water solubility, wide availability, ease of functionalization and good biocompatibility, and considerable efforts have been devoted to the preparation and applications of F-CuNPs. This review article comprises three main parts. In the first part, we briefly present the fluorescence properties of F-CuNPs. Then we cover the fabrication strategies of various F-CuNPs functionalized by different ligands. In the third part, we focus on the applications of F-CuNPs for sensing metal ions, including Hg(2+), Pb(2+), Cu(2+), Fe(3+) and other metal ions. Lastly, we further discuss the opportunities and challenges of F-CuNPs in the synthetic strategies and applications for sensing metal ions.

Humic acid-assisted synthesis of stable copper nanoparticles as a peroxidase mimetic and their application in glucose detection

In this report, stable copper nanoparticles (Cu NPs) were prepared through a facile annealing process using humic acid as the reducing and stabilizing agents. The products were characterized by X-ray powder diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The prepared Cu NPs show remarkably intrinsic peroxidase-like activity, which can rapidly catalyze the oxidation of the peroxidase substrate, 3,3',5,5'-tetramethylbenzidine (TMB), in the presence of H₂O₂ to produce a blue-color reaction. The detection limit of H₂O₂ by Cu NPs can be as low as 1.32 × 10^-7 M. More importantly, the prepared Cu NPs show excellent stability, which can hardly be oxidized even after 6 months. Based on the aforementioned mechanism, a simple, rapid and selective colorimetric method for glucose detection was developed, and the detection limit of glucose was 6.86 × 10^-7 M. This study provides a novel method for the preparation of stable Cu NPs, which may have widespread applications in the detection of glucose in the human body and pear juice.