Fluorescence Of CuNCs Research Articles

Cobalt oxyhydroxide nanosheet-modulated ratiometric fluorescence platform for the selective detection of malachite green in fish.

A ratiometric fluorescence platform was developed based on the cobalt oxyhydroxide (CoOOH) nanosheet-modulated fluorescence response of blue emissive copper nanoclusters (Cu NCs) and yellow emissive o-phenylenediamine (OPD). CoOOH nanosheets showed dual function of strong absorption and oxidation ability, which can effectively quench the blue fluorescence of Cu NCs, with an excitation and emission peak maximum at 390 and 450nm, respectively, and transfer the OPD into yellow fluorescence products, with an excitation and emission peak maximum at 390 and 560nm, respectively. Upon introducing butyrylcholinesterase (BChE) and its substrates, CoOOH nanosheets were decomposed into Co2+, and malachite green (MG) showed strong inhibition ability to this process. This resulted in the obvious difference on the ratio of blue and yellow fluorescence recorded on the system in the presence and absence of MG, which was utilized for the quantitative detection of MG, with a limit of detection of 0.140μM and a coefficient of variation of 3.5%. Thefluorescence ratiometric assay showed excellent detection performances in practical sample analysis.

High-Performance Formaldehyde Sensing Using Paper-Based Fluorescent Copper Nanoclusters

Highly sensitive detection of formaldehyde (FA) is of great importance to protect human health against its adverse effect. Herein, we constructed copper nanoclusters (Cu NCs) with strong luminescence capable of rapid, sensitive, and visual detection of FA, which was self-assembled using D-penicillamine (DPA) as the protecting ligand. Common physical measurements were carried out to analyze the as-fabricated samples (DPA-Cu NCs). Experimental results revealed its strong red fluorescence (FL), large Stokes shift, and a long fluorescence lifetime. Furthermore, DPA-Cu NCs presented self-assembled aggregation-induced emission (SAIE) property and achieved a fluorescence quantum yield (FLQY) as high as 76.26% in the solid state. Notably, FA could quench the fluorescence of Cu NCs effectively. The possible quenching mechanism was attributed to static quenching. Moreover, a paper-based visual sensor was built by immobilizing the DPA-Cu NCs probe on the filter paper, which can achieve on-site detection of FA.

Highly Selective Detection of Paraoxon in Food Based on the Platform of Cu Nanocluster/MnO2 Nanosheets.

Selective and sensitive identification of paraoxon residue in agricultural products is greatly significant for food safety but remains a challenging task. Herein, a detection platform was developed by integrating Cu nanoclusters (Cu NCs) with MnO2 nanosheets, where the fluorescence of Cu NCs was effectively quenched. Upon introducing butyrylcholinesterase and butyrylcholine into the system, their hydrolysate, thiocholine, leads to the decomposition of the platform through a reaction between the MnO2 nanosheets and thiol groups on thiocholine. The electron-rich groups on thiocholine can further promote the fluorescence intensity of Cu NCs through host–guest interactions. Adding paraoxon results in the failure of fluorescence recovery and further promotion, which could be utilized for the quantitative detection of paraoxon, and a limit of detection as low as 0.22 ng/mL can be achieved. The detection platform shows strong tolerance to common interference species, which endows its applications for the detection of paraoxon in vegetables and fruit. These presented results not only open a new door for the functionalization of metal nanoclusters but also offer an inspiring strategy for analytic techniques in nanomedicine and environmental science.

A novel ratiometric aptasensor based on dual-emission fluorescent signals and the conformation of G-quadruplex for OTA detection

Ochratoxin A (OTA) is known as an important mycotoxin that is widely distributed in food products. The increasing requirement for sensitive and convenient OTA detection has promoted the development of aptasensors based on nanomaterials and elegant design strategy for aptamer probes. Ratiometric fluorescence aptasensors greatly reduce the probability of generating false-positive signals, compared to one-signal detection methods. In this work, an efficient ratiometric aptasensor was constructed, based on the dual-emission fluorescence of N-methyl mesoporphyrin IX (NMM) and copper nanoclusters (CuNCs). The key binding region of aptamer was obtained by theoretical results of molecular docking, and experiments of optimizing the length of complementary DNA (cDNA) verified the conjecture. With the addition of OTA, CuNCs-cDNA dissociated from the aptamer sequence, and the fluorescence of CuNCs (λem=510 nm) decreased. Meanwhile, the aptamer contained G-quadruplex structure and enhanced the fluorescence of NMM (λem=610 nm). In this way, fluorescence intensity at the emission wavelength of 610 nm and 510 nm were monitored and I610/I510 was set as the signal output of this aptasensor. Stability tests indicated that the established aptasensor can reduce the interference of pH and storage time. The limit of detection (LOD) was as low as 0.045 ng/mL, with a wide linear range of 0.05–100 ng/mL. Moreover, specificity tests provided excellent selectivity towards other common mycotoxins, and the applicability was confirmed by performing real sample analysis, indicating that the NMM/CuNCs ratiometric biosensor for OTA detection has practical application prospects in food samples.

Copper nanoclusters with/without salicylaldehyde-modulation for multifunctional detection of mercury, cobalt, nitrite and cyanide ions in aqueous solution and bioimaging

The sensitive determination of multiple heavy metal ions and toxic anions is important in biological and environmental fields. Here we report a facile strategy to construct a multifunctional chemosensor for the detection of Hg2+, Co2+, and CN− in aqueous solution based on the fluorescent copper nanoclusters (Cu NCs). It was interesting to find that salicylaldehyde (SA) could effectively modulate the fluorescence property and sensing behavior of Cu NCs. In the absence of SA, Cu NCs showed ‘on-off’ fluorescence responses at the addition of Hg2+ and under different quenching mechanisms. Upon the presence of SA, Cu NCs exhibited a strong intramolecular charge transfer emission at 500 nm, accompanied by the decrease of the initial fluorescence of Cu NCs at 430 nm. This fluorescence on-state of Cu NC–SA at 500 nm was found to be exclusively turned off by Co2+ and enhanced by CN−. Spectroscopy results combined with thermodynamic analysis provided sufficient information to deduce the sensing mechanisms. Finally, the Cu NCs showed high biocompatibility and were able to be used for fluorescence bioimaging in living cells. This study provided a novel and simple strategy to construct the multifunctional chemosensors for bioanalytical applications.

A dual-channel colorimetric and fluorescent sensor for the rapid and ultrasensitive detection of kanamycin based on gold nanoparticles-copper nanoclusters.

In this work, a dual-channel assay was constructed for the colorimetric and fluorescent detection of kanamycin (KAN) based on gold nanoparticles (Au NPs) and copper nanoclusters (Cu NCs). Initially, the fluorescence of Cu NCs was quenched by 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT)-functionalized Au NPs due to the inner filter effect (IFE). The existence of KAN acted as a molecular bridge to interact with AHMT via hydrogen bonds and induced the aggregation of AHMT-Au NPs, leading to a change in the color of the gold colloidal solution from reddish-violet to blue within 2 min. Moreover, the aggregated AHMT-Au NPs can weaken its IFE toward Cu NCs and result in fluorescence restoration. With the sensor employed here, the concentration of KAN can be quantitatively analyzed through double channels, and a low LOD (limit of detection) of 1.9 nM and 1.2 nM was realized by the colorimetric and fluorescent method, respectively. Benefitting from the short response time, high sensitivity, and good reliability, the established assay offered great opportunities for the on-site monitoring of antibiotics in environmental samples.

PH-responsive copper-cluster-based dual-emission ratiometric fluorescent probe for imaging of bacterial metabolism

The profiling of bacterial metabolism is of great significance in practical applications. Therefore, the development of ultrasensitive and highly selective probe for bacterial metabolism detection and imaging is extremely desirable. Herein, a novel dual-emission pH-response bacterial metabolism detection and imaging probe is successfully developed. This probe consists of large-sized and easily separated SiO2 microspheres, copper nanoclusters (Cu NCs) with red emission, and carbon dots (CDs) with blue emission through in-situ self-assembly. In this system, the fluorescence of Cu NCs is sensitive to pH change due to their obvious aggregation-induced emission enhancement (AIEE) property, while the blue fluorescence of CDs remained almost stable. Therefore, red fluorescence and blue fluorescence are compounded with different fluorescence intensity at different pH values, and their fluorescence ratio is also different. By observation of composite fluorescence color, the visual colorimetric pH detection can be realized with the change of pH value of 0.2 units. Utilizing this system, we are able to detect bacterial metabolism with high signal-to-noise ratio, and it can also be used for bacterial metabolic imaging. Therefore, the pH-responsive Cu NCs-based dual-emission ratiometric fluorescent probe we constructed can provide new ideas for bacterial detection, antimicrobial sterilization, and biological imaging.

Molecular inversion probe-rolling circle amplification with single-strand poly-T luminescent copper nanoclusters for fluorescent detection of single-nucleotide variant of SMN gene in diagnosis of spinal muscular atrophy

In this study, a simple fluorescent detection of survival motor neuron gene (SMN) in diagnosis of spinal muscular atrophy (SMA) based on nucleic acid amplification test and the poly-T luminescent copper nanoclusters (CuNCs) was established. SMA is a severely genetic diseases to cause infant death in clinical, and detection of SMN gene is a powerful tool for pre- and postnatal diagnosis of this disease. This study utilized the molecular inversion probe for recognition of nucleotide variant between SMN1 (c.840 C) and SMN2 (c.840 C > T) genes, and rolling circle amplification with a universal primer for production of poly-T single-strand DNA. Finally, the fluorescent CuNCs were formed on the poly-T single-strand DNA template with addition of CuSO4 and sodium ascorbate. The fluorescence of CuNCs was only detected in the samples with the presence of SMN1 gene controlling the disease of SMA. After optimization of experimental conditions, this highly efficient method was performed under 50 °C for DNA ligation temperature by using 2U Ampligase, 3 h for rolling circle amplification, and the formation of the CuNCs by mixing 500 μM Cu2+ and 4 mM sodium ascorbate. Additionally, this highly efficient method was successfully applied for 65 clinical DNA samples, including 4 SMA patients, 4 carriers and 57 wild individuals. This label-free detection strategy has the own potential to not only be a general method for detection of SMN1 gene in diagnosis of SMA disease, but also served as a tool for detection of other single nucleotide polymorphisms or nucleotide variants in genetic analysis through designing the different sensing probes.

One‐step Green Synthetic Approach for the Preparation of Orange Light Emitting Copper Nanoclusters for Sensitive Detection of Mercury(II) Ions

AbstractIn this paper, we synthesized water‐soluble fluorescent Cu nanoclusters (Cu NCs) through simple reduction reaction with 2‐mercaptobenzimidazole as a protective agent, polyvinyl pyrrolidone (PVP) as a stabilizer and ascorbic acid as a reducing agent for the first time. The optical properties and structures of as‐prepared Cu NCs were characterized by fluorescence spectroscopy, UV‐vis, FT‐IR, TEM and XPS. The characterization results showed that the Cu NCs had better fluorescence intensity, high dispersion and large Stokes shift. The Cu NCs had excellent stability against photo‐illumination and ionic strength and displayed an excitation‐independent fluorescence characteristic. The as‐prepared Cu NCs was selectively and sensitively quenched by Hg2+. Furthermore, the fluorescence of Cu NCs was linearly quenched in the range of 2–40 μM (concentration of Hg2+) with a detection limit of 23.0 nM. More importantly, this prepared Cu NCs could be successfully utilized as a probe for detection of Hg2+ in real water samples.

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

In this article, red-emitting copper nanoclusters (Cu NCs) were prepared in the matrix of bovine serum albumin (BSA) through using N2H4·H2O as a reducing agent and BSA as a stabilizer. In the aqueous suspension of BSA-Cu NCs, the addition of rutin enabled the combination of rutin with BSA around Cu NCs via hydrogen bond and electrostatic interactions between functional groups of BSA and rutin. The approaching of rutin to Cu NCs induced that the fluorescence (FL) of Cu NCs was quenched by rutin due to the electron transfer from Cu NCs to rutin. Under the optimal conditions, the FL of Cu NCs was linearly decreased with the increase of rutin concentration from 0.1 to100 μM, together with a low detection limit of ca. 0.02μM. The FL quenching responses of Cu NCs were highly selective and sensitive towards rutin, over potential interferents in real human serum samples. Based on BSA-Cu NCs, this as-proposed FL probe exhibited a superior capability of rutin detection in real human serum samples. Significantly, this probe of rutin could realize the FL sensing of rutin and the naked-eye visual FL imaging detection of rutin in aqueous solution and on filter paper.

Aptamer based fluorescence biosensor for protein kinase activity detection and inhibitor screening

Herein, we firstly used double-strand-templated DNA Cu nanoclusters (Cu NCs) as a simple, lable-free and sensitive fluorescence (FL) probe to detect protein kinase (PKA) activity. This method was based on the strong interaction between adenosine triphosphate (ATP) aptamer and ATP. When ATP was added, fluorescent Cu NCs could not be formed due to the lack of effective substrate and the fluorescence of Cu NCs decreased. However, when PKA was added, the fluorescence of Cu NCs recovered because that ATP had been translated into ADP by PKA and ADP can not combine with ATP aptamer. We can effective monitored the activity of protein kinase according to the variation of fluorescence signal in the range of 0.1–1000mU/μL. The detection limit (LOD) is 0.041mU/μL. We also used this method to detect protein kinase inhibitor H-89. In addition, this method was also used to explore the activity of drug-induced PKA in Hela cells, which makes the sensor had a great application value in biochemistry and targeted kinase drug discovery research.

A fluorescent glucose bioassay based on the hydrogen peroxide-induced decomposition of a quencher system composed of MnO2 nanosheets and copper nanoclusters

The authors describe a fluorometric glucose assay that is based on the use of MnO2 nanosheets and copper nanoclusters (CuNCs) acting as nanoprobes. The CuNCs were synthesized by using bovine serum albumin as a template by chemical reduction of copper(II) sulfate. On addition of MnO2 nanosheets to a colloidal solution of CuNCs, the fluorescence of CuNCs (measured at excitation/emission wavelengths of 335/410 nm) is quenched. However, in the presence of enzymatically generated H2O2, the MnO2 nanosheets are reduced to form Mn(II) ions. As a result, fluorescence intensity recovers. The glucose assay is based on the enzymatic conversion of glucose by glucose oxidase to generate H2O2 and glucuronic acid. The calibration plot is linear in the 1 μM to 200 μM glucose concentration range, and the detection limit is 100 nM. The method was successfully applied to the determination of glucose in spiked human serum samples.

One-pot green synthesis of highly fluorescent glutathione-stabilized copper nanoclusters for Fe3+ sensing

Herein, we reported a simple one-pot green method for preparation of fluorescent copper nanoclusters (Cu NCs) with a high quantum yield up to 8.6%, using glutathione as the stabilizing agent. The as-prepared Cu NCs had good water solubility, excellent stability and ultrafine size through the characterization of UV–vis absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. Experimental results showed that the fluorescence of Cu NCs was linearly quenched by the Fe3+ concentrations in the range of 1–100μM, with the detection limit of 0.3μM. The as-formed Cu NCs were explored for the assay of Fe3+ in real water samples.

Copper nanoclusters as an on-off-on fluorescent probe for ascorbic acid

We report that copper nanoclusters (CuNCs) represent a viable fluorescent probe for ascorbic acid. The CuNCs were stabilized by tannic acid and characterized by high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, UV–vis, time-correlated single photon counting and fluorescence spectroscopy. It is found that the fluorescence of CuNCs (at excitation/emission peaks of 355/430 nm) is quenched by ferric ion due to electron-transfer between CuNCs and Fe(III) ions. If ascorbic acid is added, Fe(III) is reduced to Fe(II) and quenching is suppressed. The process is completed within 5 min. Under optimal conditions, a linear relation exists between fluorescence recovery and the concentration of ascorbic acid in the 0.5 μM to 10 μM concentration range. The detection limit is 0.11 μM. The method was applied to the determination of ascorbic acid in (spiked) fruit and vegetables and gave recoveries ranging from 89 to 110 %.

Cu nanoclusters-based ratiometric fluorescence probe for ratiometric and visualization detection of copper ions

Copper is a highly toxic environmental pollutant with bioaccumulative properties. Therefore, sensitive detection of Cu2+ is very important to prevent over-ingestion, and visual detection is preferred for practical applications. In this work, we developed a simple and environmental friendly approach to synthesize hyperbranched polyethyleneimine-protected copper nanoclusters (hPEI-Cu NCs) with great stability against extreme pH, high ionic strength, thiols etching and light illumination, which were then conjugated to the surface of silica coated CdSe quantum dots (QDs) to design a ratiometric fluorescence probe. In the presence of different amounts of Cu2+ ions, the fluorescence of Cu NCs can be drastically quenched, while the emission from QDs stayed constant to serve as a reference signal and the color of the probe changed from yellow-green to red, resulting in ratiometric and visualization detection of Cu2+ ion with high accuracy. The detection limit for Cu2+ was estimated to be 8.9 nM, much lower than the allowable level of Cu2+ in drinking water (∼20 μM) set by U.S. Environmental Protection Agency. Additionally, this probe can be also applied for the determination of Cu2+ ion in complex real water samples.

Förster resonance-energy-transfer detection of 2,4,6-trinitrophenol using copper nanoclusters.

Nitroaromatic compounds, for example trinitrotoluene and 2,4,6-trinitrophenol (TNP), are well-known primary constituents of many unexploded landmines worldwide. These compounds are recognized as environmental contaminants and as toxic to living organisms. Therefore, Förster resonance energy transfer (FRET) for TNP detection was developed on the basis of spectral overlap between the fluorescence spectrum of copper nanoclusters (CuNCs) and absorption spectrum of TNP (the calculated Förster distance R 0 of the donor CuNCs and the acceptor TNP is 2.8 nm). Water-soluble fluorescent CuNCs capped with bovine serum albumin have fluorescence emission from 350 nm to 500 nm with maximum fluorescence emission at 400 nm, which overlaps with the absorption spectra of TNP from 350 nm to 450 nm. Inspired by FRET structures, an unprecedented energy-donor-and-acceptor pair of fluorescent CuNCs and TNP is developed in this work. Fluorescence of CuNCs is quenched in the presence of TNP as a result of FRET from fluorescent CuNCs to TNP. Therefore a fluorescence quenching method for the determination of TNP is developed. It achieves TNP detection from 0.8 μmol L(-1) to 100 μmol L(-1), with response within 1 min and with good selectivity compared with that for other nitroaromatic compounds, including 2,4-dinitrotoluene, p-nitrotoluene, and nitrobenzene, and phenol. Graphical Abstract Förster resonance-energy-transfer detection of 2,4,6-trinitrophenol using copper nanoclusters was first developed. It achieves TNP detection from 0.8 mmol L(-1) to 100 mmol L(-1) within 1 min with good selectivity compared with other nitroaromatic compounds.

Copper nanocluster-based fluorescent sensors for sensitive and selective detection of kojic acid in food stuff

We utilized bovine serum albumin-capped copper nanoclusters (CuNCs) to develop a new fluorometric method for the identification and determination of kojic acid (KA) with good sensitivity and selectivity. The fluorescence of CuNCs was quenched effectively by KA, but not by the possible coexisting substances. Based on multiple spectroscopic studies, we propose that selective binding of KA to copper ions of CuNCs promotes the formation of copper kojate on the surface of CuNCs, which statically quenches CuNCs fluorescence. The as-proposed biosensor allows selective determination of KA in the range from 0.2μM to 50μM, with a detection limit of 0.07μM at a signal-to-noise ratio of 3. The CuNC-based fluorescent sensor provides a simple, rapid, cost-effective, and label-free platform for KA detection. Furthermore, we demonstrated this fluorescent sensor can be used for KA detection in food samples.