Atomically precise copper nanoclusters as ultrasmall molecular aggregates:Appealing compositions,structures,properties,and applications

Metal nanoclusters(NCs)are ultrasmall molecular aggregates consisting of dozens to hundreds of metal atoms consolidated by organic ligands,which represent an emerging area of nanoscience.Amide a myriad of metal NCs,copper NCs(CuNCs)comprise a low-cost,high-value subclass that has attracted great attention.The variable copper cores and diversity of protecting ligands have rendered CuNCs interesting molecular aggregates featuring structural and compositional versatility,hence showing distinctive properties and potential applications.In the present review,we have summarized the progress on atomically precise CuNCs that exhibit a range of appealing properties and applications in different fields.This review is expected to provide not only an overview of the current development on atomically precise CuNCs,but also possible directions for the future design of novel CuNCs for fundamental studies and practical applications.

Fluorescent Copper Nanoclusters for Highly Sensitive Monitoring of Hypoxanthine in Fish

Hypoxanthine(Hx)is an important freshness indicator reflecting the initial freshness of aquatic products.In this work,a novel fluorescence method was established based on cysteine functionalized copper nanoclusters(Cys-CuNCs)for monitoring Hx in fish.The as-synthesized Cys-CuNCs exhibit favorable fluorescent property.Importantly,the fluorescence can be quenched significantly when the solution contained a small amount of hydrogen peroxide(H_(2)O_(2)),which was due to both the oxidation of H_(2)O_(2) towards Cys-CuNCs and the resulting Cu(II).Owing to that Hx can generate H_(2)O_(2) under dissolved oxygen and xanthine oxidase(XOD),a fluorescent method for Hx was established.Under the optimal conditions,the Hx concentration in the range of 8–400μmol/L has a good linear relationship with the fluorescence quenching e fficiency,and the detection limit is 0.7μmol/L.Finally,the as-established sensor was applied to determine Hx content in carp.By comparing to the total volatile basic nitrogen(TVB-N)results,the proposed method was feasible in the evaluation of carp freshness.

Histidine‑Stabilized Copper Nanoclusters as a Fluorescent Probe for Selective and Sensitive Determination of Vitamin B_(12)

Herein,we report the highly sensitive and selective determination of vitamin B_(12)(VB_(12))using histidine-stabilized copper nanoclusters(His-CuNCs)as a fluorescent probe by the spectrofluorometry method.The as-synthesized His-CuNCs were characterized by UV–Vis absorption,steady-state emission,and high-resolution transmission electron microscopy measurements.His-CuNCs exhibited an emission maximum around 443 nm,when excited at 350 nm.The emission intensity of His-CuNCs was significantly quenched by the addition of VB_(12),hinting that the synthesized probe can be employed for sensing of VB_(12).Based on the decrease in emission intensity,the concentration of VB_(12) was determined and the emission intensity of His-CuNCs can be quenched by VB_(12) via fluorescence resonance energy-transfer mechanism.His-CuNCs showed high selectivity toward the determination of VB_(12) in the presence of other potentially interfering vitamins,cations,and anions.In addition,the proposed sensing platform displayed a sensitive response to VB_(12) in the linear range of 4.00–28.00×10^(−6) mol dm^(−3) with a limit of detection of 3.30×10^(−9) mol dm^(−3).The proposed sensing system is simple,low cost,selective,and sensitive for the determination of VB_(12) in biological samples.

Facile and diverse logic circuits based on dumbbell DNA-templated fluorescent copper nanoclusters and S1 nuclease detection

DNA-based logic gates promote the development of molecular computing and show enormous potential in the fields of nanotechnology and biotechnology. Dumbbell oligonucleotides(DNA) with poly-thymine(poly-T) loops and a nicked random double strand have been demonstrated to be an efficient template for the formation of fluorescent copper nanoclusters(Cu NCs) in our previous work. Herein, a new platform technology is presented with which to construct molecular logic gates by employing Cu NCs probe as a basic output generator, coupling of functional nucleases as the inputs. Two dumbbell DNAs are used with the difference in stem length(8 bp and 16 bp, respectively). The degradation of DNA templates can be tuned by various nucleic acid enzymes, single-stranded nuclease(S1), double-stranded specific nuclease(DSN), E. coli DNA ligase, exonucleases Ⅰ and Ⅲ. Briefly, S1 can digest both DNA templates, while the cleavage ability of DSN will be resistant by the short stem of SS-DNA(short-stem DNA). Exonuclease Ⅰ and Ⅲ can degrade these two nicked DNA templates, which are inhibited due to the ligation of E. coli DNA ligase. With this novel strategy, a set of logic gates is successfully constructed at the molecular level,including “YES”, “PASS 0”, “OR”, “INHIBIT”, which take the advantages of no label, easy operation, fast speed, high efficiency and low cost. Furthermore, S1 nuclease, as the biomarker of numerous carcinogens,is selectively detected in the range of 0.05–50 U/m L with the detection limit of 0.005 U/m L(1×10^(−6)U)based on this platform.

Aggregation-induced emission of copper nanoclusters

Copper nanoclusters(Cu NCs)have recently emerged as promising luminophores,featuring ultra-small size,reasonable photostability,large Stokes shift,and long emission lifetimes.Aggregation-induced emission(AIE)has been often used to further improve both the emission intensity and stability of these clusters,with plenty of potential applications in the fields of chemical sensing and bioimaging.This review starts with a summary of the current understanding of emission mechanisms of Cu NCs and proceeds with the analysis of contributions from the Cu metal core and the organic ligands.We summarize the recent research progress on the design of ligands,and the ways on how to induce aggregation of the Cu NCs through electrostatic charge neutralization,host-guest interactions,and the use of templates.We also discuss the current understanding of emission mechanisms of Cu NCs experiencing AIE,such as the often-cited restriction of intramolecular motion and contributions from Cu(I)molecular complexes.We finish this review by providing concluding remarks and offering our own perspective on the active field of AIE of Cu NCs,with a hope to further promote the research on the fundamental aspects of this useful phenomenon.

A novel sensitive non-enzymatic glucose sensor

Cu nanoclusters were electrochemically deposited on the film of a Nafion-solubilized multi-wall carbon nanotubes (CNTs) modified glassy carbon electrode (CNTs-GCE), which fabricated a Cu-CNTs composite sensor (Cu-CNTs-GCE) to detect glucose with non-enzyme. The linear range is 7.0 × 10?7 to 3.5 × 10?3 mol/L with a high sensitivity of 17.76 μA/(mmol L), with a low detection limit 2.1 × 10?7 mol/L, fast response time (within 5 s), good reproducibility and stability.

Ovalbumin-stabilized gold nanoclusters with ascorbic acid as reducing agent for detection of serum copper

Ovalbumin-stabilized gold nanoclusters （OVA@AuNCs） were prepared with ascorbic acid as a reducing agent. This strategy could realize the synthesis of water-soluble OVA@AuNCs within 20 min. The asprepared fluorescent probe showed a red fluorescence emission at 630 nm. Moreover, the properties of the OVA@AuNCs were characterized by transmission electron microscope, dynamic light scattering, ultraviolet-visible spectroscopy, fluorescent spectroscopy. Based on the surface electron density decrease-induced fluorescence quenching mechanism, the OVA@AuNCs provided high sensitivity and selectivity for sensing copper ions. A good linear relationship was obtained between the fluorescence intensity of OVA@AuNCs and the concentration of copper ions in the range of 5.0-100.0pumol/L （R2z0.999） with a detection limit of 640 nmol/L. Furthermore, the rat serum copper contents were determined by using the OVA@AuNCs based assay, indicating great potential of fluorescent probes for application in biological and clinical analysis.

How ligand coordination and superatomic-states accommodate the structure and property of a metal cluster:Cu_(4)(dppy)_(4)Cl_(2)vs.Cu_(21)(dppy)_(10)with altered photoluminescence

We have synthesized two copper nanoclusters(NCs)with a protection of the same ligand diphenylphosphino-2-pyridine(C_(17)H_(14)NP,dppy for short),formulated as Cu_(4)(dppy)_(4)Cl_(2)and Cu21(dppy)10,respectively.The former one bears a distorted tetrahedron Cu4 core with its six edges fully protected by chlorine and dppy ligands,while the latter presents a symmetric Cu_(21)core on which ten dppy molecules function as monolayer protection via well-organized monodentate or bidentate coordination.Interestingly,the Cu_(4)(dppy)_(4)Cl_(2)cluster exhibits a strong yellow emission at∼577 nm,while Cu_(21)(dppy)_(10)displays dual emissions in purple(∼368 nm)and green(∼516 nm)regions respectively.In combination with TD-DFT calculations,we demonstrate the origin of altered emissions and unique stability of the two copper nanoclusters pertaining to the ligand coordination and metallic superatomic states.

11-Mercaptoundecanoic acid functionalized gold nanoclusters as fluorescent probes for the sensitive detection of Cu^(2＋) and Fe^(3＋) ions

Metal ions are physiologically essential,but excessive metal ions may cause severe risk to plants and animals.Here,we prepared gold nanoclusters（Au NCs） protected by 11-mercaptoundecanoic acid（11-MUA）,which have excellent fluorescence properties for the detection of metal ions.The results showed that the copper ions（Cu^（2＋）） and iron ions（Fe^（3＋）） in the solution have obvious quenching effect on the fluorescence intensity of Au NCs.The detection range of Fe^（3＋） was 0.8-4.5 mmol/L（R^2= 0.992） and 4.5-11.0 mmol/L（R^2= 0.997）.And Cu^（2＋） has a lower linear range（0.1-1.0 mmol/L,R2= 0.993）.When EDTA was added into the reaction system,it was observed that the quenching effect of Cu^（2＋） and Fe^（3＋）on Au NCs showed different phenomenon.Then,the effect of metal ions on the fluorescence of Au NCs was investigated.The selective detection of Cu（2＋） was achieved by EDTA masking of Fe^（3＋）.In addition,we realized the metal ions detection application of Au NCs in the serum