Glutathione-capped Copper Nanoclusters Research Articles

A reliable and selective ratiometric sensing probe for fluorometric determination of P2O74− based on AIE of GSH@CuNCs-assisted by Al-N@CQDs

In this study, a novel composite material was developed for the ratiometric detection of pyrophosphate anion (P2O74−). This composite consisted of Al and nitrogen co-doped carbon dots (Al-N@CQDs) and glutathione-capped copper nanoclusters (GSH@CuNCs). The Al-N@CQDs component, with its high reserved coordination capacity of Al3+, induced the non-luminescent behavior of GSH@CuNCs, resulting in an aggregation-induced emission (AIE) effect. The hybrid material (Al-N@CQDs/GSH@CuNCs) exhibited dual-emission signals at 620 nm and 450 nm after integrating the two independent materials utilizing the AIE effect and the fluorescence resonance energy transfer (FRET) approach. This approach represents the first utilization of this composite for ratiometric detection. Nevertheless, upon the addition of P2O74−, the AIE and FRET processes were hindered due to the higher coordination interaction of Al3+ towards P2O74− compared to the amino/carboxyl groups on Al-N@CQDs. This successful interference of the AIE and FRET processes allowed for the effective estimation of P2O74−. The response ratio (F450/F620) increased with increasing the concentration of P2O74− in the range of 0.035–160 µM, with an impressive detection limit of 0.012 µM. This innovative approach of utilizing hybrid CQDs/thiolate-capped nanoclusters as a ratiometric fluorescent sensor for analytical applications introduces new possibilities in the field. The as-fabricated system was successfully applied to detect P2O74− in different real samples such as water, serum, and urine samples with acceptable results.

Selective fluorescence turn-on detection of combination cisplatin-etoposide chemotherapy based on N-CDs/GSH-CuNCs nanoprobe.

Cisplatin (CIS) and etoposide (ETP) combination therapy is highly effective for treating various cancers. However, the potential for pharmacokinetic interactions between these drugs necessitates selective sensing methods to quantitate both CIS and ETP levels in patient's plasma. This work develops a dual fluorescence probe strategy using glutathione-capped copper nanoclusters (GSH-CuNCs) and nitrogen-doped carbon dots (N-CDs) for the simultaneous analysis of CIS and ETP. The fluorescence signal of GSH-CuNCs at 615 nm increased linearly with CIS concentration while the N-CD emission at 480 nm remained unaffected. Conversely, the N-CD fluorescence was selectively enhanced by ETP with no interference with the CuNC fluorescence. Extensive materials characterization including UV-vis, fluorescence spectroscopy, XRD, and TEM confirmed the synthesis of the nanoprobes. The sensor showed high sensitivity with limits of detection of 6.95 ng mL-1 for CIS and 7.63 ng mL-1 for ETP along with excellent selectivity against potential interferences in rabbit plasma. Method feasibility was demonstrated with application to real rabbit plasma samples. The method was further applied to estimate the pharmacokinetic parameters of CIS before and after ETP coadministration. The dual nanoprobe sensing strategy enables rapid and selective quantitation of CIS and ETP levels to facilitate therapeutic drug monitoring and optimization of combination chemotherapy regimens.

A smartphone-based ratiometric fluoroprobe based on blue-red dual-emission signals of thiochrome and copper nanoclusters for sensitive assay of metam-sodium in cucumbers

It is of great importance to develop the highly efficient fluorescence strategy for rapid/sensitive detection of metam-sodium (MES) in evaluating its residual safety, especially in fresh vegetables. Herein, we prepared an organic fluorophore (thiochrome, TC) and glutathione-capped copper nanoclusters (GSH-CuNCs), and their combination (TC/GSH-CuNCs) was sucessfully employed as a ratiometric fluoroprobe by means of the blue-red dual emission. The fluorescence intensities (FIs) of TC decreased upon the addition of GSH-CuNCs via the fluorescence resonance energy transfer (FRET) process. When fortified at the constant levels of GSH-CuNCs and TC, MES substantially reduced the FIs of GSH-CuNCs, while this was not the case in the FIs of TC except for the prominent red-shift of ∼30 nm. Compared to the previous fluoroprobes, the TC/GSH-CuNCs based fluoroprobe supplied wider linear range of 0.2–500 μM, lower detection limit (60 nM), and satisfactory fortification recoveries (80–107%) for MES in the cucumber samples. Based on the fluorescence quenching phenomenon, a smartphone application was used to output RGB values of the captured images for the colored solution. The smartphone-based ratiometric sensor could be utilized for the visual fluorescent quantitation of MES by virtue of the R/B values in cucumbers, which gave linear range (1–200 μM) and LOD (0.3 μM). By means of blue-red dual-emission fluorescence, the smartphone-based fluoroprobe provides a cost-effective, portable and reliable avenue for the on-site, rapid and sensitive assay of MES's residues in complex vegetable samples.

A volatile basic nitrogens-responsive tag based on aggregation-induced emission luminogen for real-time monitoring and in situ visualization of salmon freshness

Given the ever-growing food safety issues, the establishment of efficient approaches for monitoring food freshness attracts increasing attention. Volatile basic nitrogens (VBNs), including biogenic amines and ammonia, serve as an important biomarker for monitoring food freshness. In this study, a novel VBNs-responsive tag using glutathione capped copper nanoclusters (GSH-CuNCs) aggregates was developed as a fluorescent probe for in situ and real-time visual monitoring of salmon freshness, and the prepared GSH-CuNCs aggregates were characterized and their sensitivity for detecting VBNs using biogenic amines and ammonium hydroxide as the model targets was evaluated. Based on their remarkable response in liquid status, the GSH-CuNCs aggregates-based tag as a gas indicator was then fabricated, which exhibited visible colour changes under UV light as a function of ammonia vapour concentrations. More importantly, through exploring the sensing mechanism of GSH-CuNCs aggregates in VBNs detection, the existence of ligand exchange between the GSH-CuNCs and VBNs was observed and verified for the first time, confirming the effect of hydrogen bonding reported in the literature. Moreover, the GSH-CuNCs aggregates-based tag was applied for quantitative analysis of salmon freshness during different storage periods, which was validated by the standard method for detection of total VBNs in salmon. In addition, a colour card was developed and its feasibility for application in monitoring salmon freshness was validated, which could be used for consumers to obtain the freshness level directly with the naked eye, demonstrating the feasibility of the fabricated tag for real-time and visual monitoring of salmon freshness, thus showing great potentials for its practical applications in the food industry.

A novel ratiometric nanoprobe based on copper nanoclusters and graphitic carbon nitride nanosheets using Ce(III) as crosslinking agent and aggregation-induced effect initiator for sensitive detection of hydrogen peroxide and glucose

Herein, glutathione-capped copper nanoclusters (CuNCs) and graphitic carbon nitride nanosheets (g-C3N4 NSs) were synthesized by a facile one-pot chemical reduction and directly thermal pyrolysis following ultrasonic exfoliation approaches, respectively. The introduction of Ce(III) (Ce3+) played dual functions in constructing a fluorescence-enhanced ratiometric nanoprobe (g-C3N4 NSs-Ce3+-CuNCs), i.e., triggering aggregation-induced emission of CuNCs and conjugating g-C3N4 NSs with CuNCs by virtue of electrostatic and coordination interactions. The as-fabricated nanohybrid displayed 460 and 625 nm dual-emitting peaks, attributing to the emission of g-C3N4 NSs and CuNCs, respectively. Upon addition of H2O2, the 625 nm emission was dramatically quenched, whereas the 460 nm emission remained nearly unchanged, thereby causing obvious color changes from purple to blue under a 365-nm UV lamp. A ratiometric fluorescent assay, based on g-C3N4 NSs-Ce3+-CuNCs, was devised for sensitive and visual detection of H2O2, which spanned the linear range of 2–100 μM with a detection limit of 0.6 μM. In the presence of glucose oxidase, the ratiometric nanoprobe could be simultaneously employed to detect glucose across the linear range of 1.6–320 μM with a detection limit of 0.48 μM. In milk and human serum samples, the fortified recoveries for H2O2 and glucose by the nanoprobe were in the range of 95.5–103.6% with RSDs <3.8%. The real detection levels for glucose are consistent with those by a standard glucometer. As such, the ratiometric nanoprobe offers a promising methodology for several practical applications, such as point-of-care diagnosis and workplace health evaluations.

A copper nanoclusters probe for dual detection of microalbumin and creatinine

A fluorescent probe based on glutathione-capped copper nanoclusters (GSH-CuNCs) was developed for the detection of dual targets, human serum albumin (HSA) and creatinine, in human urine. The GSH-CuNCs were synthesized by a one-pot green method using ascorbic acid as a reducing agent. The detection of HSA was in a turn-on mode via electrostatic interaction in a basic condition while the detection of creatinine was in a turn-off mode via non-covalent bonding in an acidic condition. Under optimal conditions, the linear range and detection limit of HSA were 5.0 nM to 150 nM and 1.510 ± 0.041 nM, while those of creatinine were 30 μM to 1000 μM and 13.0 ± 1.0 μM. This easily fabricated nanocluster probe provided a fast response with high sensitivity, and good selectivity. Recoveries from urine samples were in the range of 81.44 ± 0.25 to 109.22 ± 0.57% for HSA and 80.57 ± 0.16 to 109.0 ± 0.10% for creatinine. The urinary analytical results from the fluorescent probe were in good agreement (P > 0.05) to those obtained from immunoturbidimetric and enzymatic methods, signifying the excellent performance of this sensing system.

Confining copper nanoclusters on exfoliation-free 2D boehmite nanosheets: Fabrication of ultra-sensitive sensing platform for α-glucosidase activity monitoring and natural anti-diabetes drug screening

α-Glucosidase (α-Glu) and its inhibitors play critical roles in diabetes therapy. Herein, a simple and ultra-sensitive fluorescence sensing approach was fabricated for α-Glu activity monitoring and natural inhibitor screening by electrostatically confining negatively charged glutathione-capped copper nanoclusters (GSH-CuNCs) on exfoliation-free and positively charged 2D boehmite (Boe) nanosheets. Boe significantly improved the fluorescence emission/stability of GSH-CuNCs and simultaneously led to an obvious blue-shift of the excitation peak of CuNCs from 365 nm to 330 nm. As a result, the fluorescence emission of Boe@GSH-CuNCs was efficiently quenched by 4-nitrophenyl-α-D-glucopyranoside (PNPG) with a maximum absorbance peak (λmax) at 310 nm via inner filter effect, and sequentially recovered by α-Glu through the hydrolysis of PNPG to p-nitrophenol (λmax = 410 nm). Accordingly, an ultra-sensitive fluorescence assay for the determination of α-Glu activity was proposed by using Boe@GSH-CuNCs as fluorescence probes. The detection limit of 0.43 U/L was achieved, which was lower than most of other α-Glu activity assays. Furthermore, this method was capable of screening α-Glu inhibitors originated from actinomycetes, peanut, sophora flower, celery, and orange as potential anti-diabetes drugs. Taken together, this work provided a promising strategy for clinical treatment of diabetes and discovery of anti-diabetes drugs.

Fluorescent and visual assay of H2O2 and glucose based on a highly sensitive copper nanoclusters-Ce(III) fluoroprobe.

Herein, we synthesized and characterized glutathione-capped copper nanoclusters (CuNCs) using a convenient one-pot chemical reduction approach based on glutathione as capping and reducing agents. The Ce(III) induced aggregation-induced emission of CuNCs to form a CuNCs-Ce3+ fluoroprobe due to electrostatic and coordination interactions between Ce3+ and CuNCs. In contrast to CuNCs, the fluorescent intensities (FLs) of CuNCs-Ce3+ were enhanced by ~ 40-fold concomitant with 20-nm blue-shift of the maximum emission, and a 3.45-fold lengthening of the average fluorescent lifetime. The FLs of CuNCs-Ce3+ were selectively quenched at 650 nm by hydrogen peroxide (H2O2) via the redox reaction. Based on this phenomenon, the sensitive assay of H2O2 was realized, and the linear range spanned over the range of 14-140 μM. Notably, the visualization of the fluorescence quenched effect of H2O2 could be easily attained. Additionally, glucose could be specifically oxidized by glucose oxidase to produce H2O2, and thus the detection of glucose was achieved according to changes in the concentrations of H2O2. Under optimized conditions, the fluorescent assay of glucose based on the CuNCs-Ce3+ system offered the linear range of 8-48 μM with detection limit of 2.4 μM. Meanwhile, high selectivity of the as-constructed fluorescent assay allows the sensitive detection of H2O2 and glucose in real-world care products and human serum samples, showing a great application potential in their conventional monitoring.

Blue-emitting glutathione-capped copper nanoclusters as fluorescent probes for the highly specific biosensing of furazolidone

Herein, a facile, straightforward and green method was developed to prepare copper nanoclusters by using glutathione (GSH) as the protecting agent and ascorbic acid as the reducing agent. The glutathione-templated copper nanoclusters (GSH-Cu NCs) were characterized through fluorescence spectroscopy, UV–vis absorption spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and fluorescence lifetime analysis. The as-synthesized Cu NCs showed blue fluorescence with a peak centered at 426 nm. The Cu NCs had excellent water solubility, stability and dispersibility. Based on the inner filter effect and static quenching mechanism, Cu NCs were employed to detect furazolidone in bovine serum samples. Under optimal detection conditions, a good linear relationship was observed between F0/F and the furazolidone concentration from 0.05 to 60 μM. The detection limit (LOD) was 0.012 μM. Furthermore, the fluorescence probe was successfully used in the quantification of furazolidone in bovine serum samples. In addition, this analytical method provides a rapid, easy and ultrasensitive fluorescence platform for the detection of furazolidone.

Electrostatically confined in-situ preparation of stable glutathione-capped copper nanoclusters for fluorescence detection of lysozyme

The fundamental challenges in application of copper nanoclusters (CuNCs) to fluorescence sensing are their poor stability, weak fluorescence intensity, and time-consuming preparation. In this work, an efficient and green method was developed by using a positively charged natural polysaccharide, chitosan (CS), as confining agent to electrostatically trap the negatively charged glutathione (GSH) as reducing-cum-protecting ligand for the in-situ synthesis of CuNCs. The synthesis can be completed within 1 min and CS-GSH-CuNCs emits intense orange fluorescence with an emission peak at 574 nm, which is much higher than that of GSH-CuNCs prepared in the absence of CS. Meanwhile, owning to both confinement and antioxidant effects of CS, CS-GSH-CuNCs shows excellent stability against time, temperature, salt, UV irradiation, and pH. Furthermore, the emission intensity of CS-GSH-CuNCs can be quenched by lysozyme (Lys) through the enzymatic hydrolysis of CS by Lys. Based on that, a fluorescence method was developed for the Lys determination with a linear range of 5–110 nM and a detection limit of 1.6 nM. Moreover, this approach shows high selectivity to Lys over various common substances in the biological environment, and thus can be used to determine Lys in human serum.

Computational design and clinical demonstration of a copper nanocluster based universal immunosensor for sensitive diagnostics.

Nanoparticle based sensors are good alternatives for non-enzymatic sensing applications due to their high stability, superior photoluminescence, biocompatibility and ease of fabrication, with the only disadvantage being the cost of the synthesis process (owing to the expensive precursors and infrastructure). For the first time, we report the design of an immunosensor employing streptavidin conjugated copper nanocluster, developed at a much lower cost compared to other nanomaterials like noble metal nanoparticles and quantum dots. Using in silico tools, we have tried to establish the dynamics of conjugation of nanocluster to the streptavidin protein, based on EDC-NHS coupling. The computational simulations have successfully explained the crucial role played by the components of the immunosensor leading to an efficient design capable of high sensitivity. In order to demonstrate the functioning of the Copper Nanocluster ImmunoSensor (CuNIS), HIV-1 p24 biomarker test was chosen as the model assay. The immunosensor was able to achieve an analytical limit of detection of 23.8 pg mL−1 for HIV-1 p24 with a linear dynamic range of 27–1000 pg mL−1. When tested with clinical plasma samples, CuNIS based p24 assay showed 100% specificity towards HIV-1 p24. With the capability of multiplexed detection and a cost of fabrication 100 times lower than that of the conventional metal nanoclusters, CuNIS has the potential to be an essential low-cost diagnostic tool in resource-limited settings.

Aluminum(III) triggered aggregation-induced emission of glutathione-capped copper nanoclusters as a fluorescent probe for creatinine.

Glutathione-capped copper nanoclusters (CuNCs) are presented that display aggregation-induced emission (AIE). This feature was exploited for selective and sensitive quantification of creatinine (CRN) which is an important diagnostic parameter. In the presence of Al3+ ions, suchCuNCs rapidly aggregate, and thisinduces enhanced a redemission. The AIE nature of CuNCs was proven via TEM and fluorimetry. On addition of CRN, the coordination between CRN and Al3+ ions led to the quenching of fluorescence due to weakening the AIE. The best fluorescence intensity was measured at excitation/emission peaks of 360/585nm. Quenched fluorescence intensity showed a linear dependence on the concentrations of CRN in the range of 2.5-34 μgL-1 with a detection limit of 0.63 μgL-1. The sensing mechanism of probe for CRN detection is discussed. The probe was applied to thedetermination of CRN in spikedhuman serum samples and gave satisfactory results. Graphical abstract Aluminum(III) ions triggerthe aggregation-induced emission (AIE) in glutathione-capped copper nanoclusters (CuNCs). Introduction of creatinine leads to deaggregation of CuNC aggregates, and this is accompanied by the quenching of the luminescence. This phenomenon was exploited inan assay for creatinine.

Photoluminescence light-up detection of zinc ion and imaging in living cells based on the aggregation induced emission enhancement of glutathione-capped copper nanoclusters

In this work, we prepared glutathione (GSH)-capped copper nanoclusters (Cu NCs) with red emission by simply adjusting the pH of GSH/Cu2+ mixture at room temperature. A photoluminescence light-up method for detecting Zn2+ was then developed based on the aggregation induced emission enhancement of GSH-capped Cu NCs. Zn2+ could trigger the aggregation of Cu NCs, inducing the enhancement of luminescence and the increase of absolute quantum yield from 1.3% to 6.2%. GSH-capped Cu NCs and the formed aggregates were characterized, and the possible mechanism was also discussed. The prepared GSH-capped Cu NCs exhibited a fast response towards Zn2+ and a wider detection range from 4.68 to 2240μM. The detection limit (1.17μM) is much lower than that of the World Health Organization permitted in drinking water. Furthermore, taking advantages of the low cytotoxicity, large Stokes shift, red emission and light-up detection mode, we explored the use of the prepared GSH-capped Cu NCs in the imaging of Zn2+ in living cells. The developed luminescence light-up nanoprobe may hold the potentials for Zn2+-related drinking water safety and biological applications.