Water-soluble Copper Nanoclusters Research Articles

A facile synthesis of water-soluble copper nanoclusters as label-free fluorescent probes for rapid, selective and sensitive determination of alizarin red

Copper nanoclusters (FA@CuNCs) emitting blue fluorescence were successfully developed via a one-pot technique. In this method, the copper chloride, folic acid and hydrazine hydrate were applied as a precursor, protective agent and reducing agent, respectively. The absorption, fluorescence excitation and emission spectra of FA@CuNCs were carried out by using ultraviolet–visible and fluorescence spectrometry, respectively. The morphology, particle size, functional groups, oxidation states of elements of FA@CuNCs were discussed via using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The stability of FA@CuNCs was studied under various conditions, such as storage time at 25 ℃, ultraviolet radiation time, sodium chloride solutione and pH. The FA@CuNCs displayed blue fluorescence under the excitation wavelength of 361 nm, and the fluorescence quantum yield was 7.45 %. As a result of the inner filter effect, the alizarin red could significantly weaken the blue fluorescence of FA@CuNCs. Thus, the as-prepared FA@CuNCs could be utilized as fluorescence nanosensors for the trace determination of alizarin red. This platform suggested an excellent linear range for alizarin red varying from 0.5 to 200 μM with a fitting coefficient of 0.9955. The detection limit was calculated to be 0.064 μM in the light of the 3b/k (b and k refer to the standard deviation and slope of fitted curve, respectively). Furthermore, the as-developed FA@CuNCs could be used to detect the alizarin red in real samples and for the sensing of temperature.

Thunnus albacares protein-mediated synthesis of water-soluble Copper nanoclusters as sensitive fluorescent probe for Ferric ion detection

In this work, single-step reduction method for the synthesis of highly stable water-soluble copper nanoclusters (CuNCs) at ambient conditions in which Thunnus albacares fish protein (FP) played the dual role of a capping and reducing agent is reported. The physicochemical properties of the prepared CuNCs were characterized by using UV-Visible Spectroscopy, FTIR, TEM and time resolved fluorescence spectroscopic studies. The FP-CuNCs showed high photo stability under different ionic strength, pH, with good quantum yield. It showed maximum emission at 446 nm upon its excitation at 330 nm. The excellent fluorescent properties of FP-CuNCs were further utilized to detect Fe3+ ions in aqueous condition within the concentration range of 0–50 µM and the sensing assay exhibited a limit of detection of 0.68 µM. The mechanism involved in the fluorescence detection is ascribed to the synergistic static and IFE induced fluorescence quenching of FP-CuNCs. The practical applicability of the detection probe was further established by carrying out Fe3+ ion detection in environmental sample analysis.

A highly sensitive and selective “turn off” fluorescent sensor based on water soluble copper nanoclusters for morin and temperature sensing

A novel fluorescence detection method was developed for the determination of morin and temperature based on water soluble copper nanoclusters (Cu NCs) for the first time, which was fabricated by using tannic acid (TA) as the protecting agent and ascorbic acid as the reducing agent. The TA protected Cu NCs (TA-Cu NCs) were characterized through a series of methods. The characterization results showed that the as-prepared TA-Cu NCs possessed good water solubility and high photostability. Interestingly, the fluorescence intensity of TA-Cu NCs was obviously quenched in the presence of morin. Then, a rapid and facile morin probe was established based on TA-Cu NCs, and the fluorescence quenching mechanism was ascribed to the inner filter effect. The as-prepared probe showed excellent sensitivity and selectivity towards morin with a wider linear range from 0.5 to 110 μM (R2 = 0.9949), and a lower detection limit could reach 0.062 μM. In addition, the TA-Cu NCs were employed for temperature sensing. The practicability of the TA-Cu NCs for morin detection in bovine serum samples was also verified with the recoveries range from 92.5% to 107.7%, illustrating this detection method with great potential application in the field of analysis.

Highly sensitive and selective fluorescence sensing of nitrofurantoin based on water-soluble copper nanoclusters

In this contribution, dopamine-protected copper nanoclusters as a novel fluorescent nanosensor was employed to detect nitrofurantoin (NFT) for the first time, which were prepared by using dopamine as the stabilizing agent and sodium borohydride (NaBH4) and hydrazine hydrate (N2H4·H2O) as the reducing agents. A series of methods were used to analyze the structure and optical properties of as-prepared Cu NCs, such as UV-Vis absorption spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It possessed high dispersion, excellent water solubility, good photostability and strong green fluorescence under UV lamp (365 nm). Significantly, the FL intensities of Cu NCs were quenched with addition of NFT. The analytical method possessed good linear relationship between the relative fluorescence intensity (F0/F) and the NFT concentrations (range from 5 to 120 μM), and the limit of detection (LOD) could reach 0.73 μM. The fluorescence detection mechanisms were attributed to the static quenching and inner filter effect (IFE). In addition, this proposed fluorescence sensor has been successfully used for the detection of NFT in bovine serum samples.

Ligand-modulated aqueous synthesis of color-tunable copper nanoclusters for the photoluminescent assay of Hg(II).

Water-soluble Cu nanoclusters (NCs) with tunable emission were synthesized through an eco-friendly one-pot aqueous method. Blue-, green-, and red-emitting NCs with the emission peaks at 420nm, 505nm, and 630nm were obtained by employing ethanediamine, cysteine, and glutathione as surface ligands, respectively. The ligand effects on the optical properties of Cu NCs were studied by the single variable method. It has been revealed by systematic characterizations that the dependence of emission color on the structures of ligands was mainly attributed to their different size-tuning effects. Glutathione has the strongest chelating ability and it can significantly reduce the monomer reactivity and thus decrease the supersaturation degree of the reaction, which is favorable for modulating Cu precursor to grow into larger NCs. In contrast, ethanediamine ligand resulted in smaller nanoclusters due to its weaker binding capability. Because of the strong emission and terrific fluorescent stability, Cu NCs capped with ethanediamine, possessing an emission peak at 420nm when excited at awavelength of 350nm, were directly used for probing Hg(II) with satisfying selectivity, presenting a linear range of 0.1-5.0mM and a detection limit of 33μM. The sensor showed good performance in real sample analysiswith recoveries ranging from 99% to 103%, and comparable accuracy with atomic fluorescence spectroscopy, manifesting the reliability of the current strategy for sensing Hg(II). Graphical abstract Water-soluble copper nanoclusters with blue, green, and red emissions were synthesized by employing ethanediamine, cysteine, and glutathione as surface ligands respectively, and the blue-emitting nanoclusters with strong emission and terrific stability were directly used for selectively sensing Hg2+.

Aluminum-Enhanced Fluorescence of Cu8 Nanoclusters: An Effective Method for Sensitive Detection of Fluoride in Aqueous and Bioimaging.

Here, we report glutathione-protected water-soluble copper nanoclusters (Cu8 NCs) with excellent properties of high stability, large Stokes shift, and low toxicity. The molecular formula and structure of the Cu8 NCs were confirmed through good agreement between spectroscopic results and theoretical calculations. The origin of optical properties and chemical stability of the Cu8 NCs was determined through natural bond orbital analysis combined with time-dependent density functional theory calculations. It was found that the fluorescence emission and quantum yields of Cu8 NCs could be effectively enhanced by aluminum(III) ions (Al3+) through the aggregation-induced enhanced emission mechanism. On the basis of the strong reaction of Al3+ with F-, the enhanced fluorescence of the obtained Cu8 NC-Al3+ ensemble could be selectively turned off by fluoride ions (F-), achieving highly sensitive detection of F- in aqueous with a detection limit of 0.16 μM. Also, the fluorescence of Cu8 NC-Al3+ ensemble quenched by F- could be enhanced again upon binding additional Al3+. In addition, the proposed Cu8 NC-Al3+ ensemble with enhanced fluorescence was used for bioimaging in vitro and in vivo. These results indicated that Cu8 NCs are promising materials for sequential sensing and bioimaging in the future.

Lysozyme coated copper nanoclusters for green fluorescence and their utility in cell imaging

Green fluorescent, pH dependent and water soluble copper nanoclusters (3–5 nm) were synthesized by stabilizing with lysozyme and these were demonstrated for imaging in both healthy and cancer cell lines as an alternate to green fluorescent protein.

Enhancement of fluorescence brightness and stability of copper nanoclusters using Zn2 + for ratio-metric sensing of S2 −

It is acknowledged water soluble copper nanoclusters (Cu NCs) are extremely unstable in aqueous solutions, which limit their fluorescence applications to a great extent. In this work, it is found the fluorescence intensity and stability of water soluble Cu NCs could obviously be enhanced by the introduction of Zn2+. Then, the as modified Cu NCs will be stable enough to be applied as a ratio-metric sensor for S2−. This method may provide more broaden avenues for the application of fluorescent Cu NCs in the future.

Inducible Sequential Oxidation Process in Water-Soluble Copper Nanoclusters for Direct Colorimetric Assay of Hydrogen Peroxide in a Wide Dynamic and Sampling Range.

Direct and fast detection methods for H2O2 have great demand in materials science, biology, and medicine. Colorimetric assay of H2O2 has been regarded as one versatile approach that can avoid tedious operation and complicated setup. In this report, we provided a cost-effective and time-saving H2O2 colorimetric assay strategy based on a mercaptosuccinic acid (MSA)-stabilized Cu nanocluster (NC) probe without using any chromogenic reagent. Direct and fast colorimetric detection of H2O2 was realized based on the color change of MSA-capped Cu NCs in aqueous medium. It was found that the Cu NCs presented eligible resistance to natural oxidation either in concentrated solution or in the powder state. However, the dissolved oxygen in a highly diluted solution of the Cu NCs could trigger the aggregation of the Cu NCs and their further fusion into small Cu nanoparticles (NPs). When this diluted solution served as a probe solution for detecting H2O2, a sequential oxidation process occurred in the newly formed Cu NPs, including the cleavage of MSAs on the surface and conversion of Cu into Cu2O, leading to the probe with capacity for H2O2 assay in a wide dynamic and sampling range. The sensitive solution color change was attributed to the growth of the Cu NPs (fading of plasmonic absorption) upon the addition of low levels of H2O2 and the transition of the valence states of Cu (color reactions) upon the addition of high levels of H2O2. A concentration range of H2O2 from 1 μM to 1 M could be detected by a small dose of the probe. Moreover, the Cu NCs powder subsequent to storage for 10 months could maintain a similar sensitivity for H2O2 assay, which provides possibilities for a wide range of practical applications in water samples.

One-step rapid synthesis of single thymine-templated fluorescent copper nanoclusters for “turn on” detection of Mn2+

Single base T was confirmed to be a template to synthesize water-soluble copper nanoclusters for the first time, which was successfully used to detect Mn2+.

One-pot development of water soluble copper nanoclusters with red emission and aggregation induced fluorescence enhancement

The binding of Zn2+ and Al3+ to OH on the copper core of Cu NCs promotes the formation of Cu NC–OH–Zn–OH–Cu NCs and Cu NC–OH–Al–OH–Cu NCs aggregates, which enables aggregation induced fluorescence enhancement.

One-step aqueous synthesis of fluorescent copper nanoclusters by direct metal reduction

A one-step aqueous synthesis of highly fluorescent water-soluble copper nanoclusters (CuNCs) is here described, based on direct reduction of the metal precursor with NaBH4 in the presence of bidentate ligands (made of lipoic acid anchoring groups, appended with a poly(ethylene glycol) short chain). A complete optical and structural characterization was carried out: the optical emission was centred at 416 nm, with a luminescence quantum yield in water of 3.6% (the highest one reported so far in water for this kind of nanocluster). The structural characterization reveals a homogeneous size distribution (of 2.5 nm diameter) with spherical shape. The CuNCs obtained offer long-term stability (the luminescence emission remained unaltered after more than two months) under a broad range of chemical conditions (e.g. stored at pH 3–12 or even in a high ionic strength medium such as 1 M NaCl) and high photostability, keeping their fluorescence emission intact after more than 2 h of daylight and UV-light exposition. All those advantageous features warrant synthesized CuNCs being promising fluorescent nanoprobes for further developments including (bio)applications.