Probing Cancer Cells through Intracellular Aggregation-Induced Emission Kinetic Rate of Copper Nanoclusters

Fluorescent metal nanoclusters: From luminescence mechanism to applications in enzyme activity assays

Metal nanoclusters (MNCs) have outstanding fluorescence property and biocompatibility, which show widespread applications in biological analysis. Particularly, evaluation of enzyme activity with the fluorescent MNCs has been developed rapidly within the past several years. In this review, we first introduced the fluorescent mechanism of mono- and bi-metallic nanoclusters, respectively, whose interesting luminescence properties are mainly resulted from electron transfer between the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels. Meanwhile, the charge migration within the structure occurs through ligand-metal charge transfer (LMCT) or ligand-metal-metal charge transfer (LMMCT). On such foundation, diverse enzyme activities were rigorously evaluated, including three transferases and nine hydrolases, in turn harvesting rapid research progresses within past 5 years. Finally, we summarized the design strategies for evaluating enzyme activity with the MNCs, presented the major issues and challenges remained in the relevant research, coupled by showing some improvement measures. This review will attract researchers dedicated to the studies of the MNCs and provide some constructive insights for their further applications in enzyme analysis.

Prolonged near-infrared fluorescence imaging of microRNAs and proteases in vivo by aggregation-enhanced emission from DNA-AuNC nanomachines

Developing a comprehensive strategy for imaging various biomarkers (i.e., microRNAs and proteases) in vivo is an exceptionally formidable task. Herein, we have designed a deoxyribonucleic acid-gold nanocluster (DNA-AuNC) nanomachine for detecting tumor-related TK1 mRNA and cathepsin B in living cells and in vivo. The DNA-AuNC nanomachine is constructed using AuNCs and DNA modules that incorporate a three component DNA hybrid (TD) and a single-stranded fuel DNA (FD). Upon being internalized into tumor cells, the TK1 mRNA initiates the DNA-AuNC nanomachine through DNA strand displacement cascades, leading to the amplified self-assembly and the aggregation-enhanced emission of AuNCs for in situ imaging. Furthermore, with the aid of a protease nanomediator consisting of a mediator DNA/peptide complex and AuNCs (DpAuNCs), the DNA-AuNC nanomachine can be triggered by the protease-activated disassembly of the DNA/peptide complex on the nanomediator, resulting in the aggregation of AuNCs for in vivo protease amplified detection. It is worth noting that our study demonstrates the impressive tumor permeability and accumulation capabilities of the DNA-AuNC nanomachines via in situ amplified self-assembly, thereby facilitating prolonged imaging of TK1 mRNA and cathepsin B both in vitro and in vivo. This strategy presents a versatile and biomarker-specific paradigm for disease diagnosis.

Copper in Cancer: from transition metal to potential target

In recent years, with the continuous in-depth exploration of the molecular mechanisms of tumorigenesis, numerous potential new targets for cancer treatment have been identified, some of which have been further developed in clinical practice and have produced positive outcomes. Notably, researchers' initial motivation for studying copper metabolism in cancer stems from the fact that copper is a necessary trace element for organisms and is closely connected to body growth and metabolism. Moreover, over the past few decades, considerable progress has been made in understanding the molecular processes and correlations between copper and cancer. Certain achievements have been made in the development and use of relevant clinical medications. The concept of "cuproptosis," a novel concept that differs from previous forms of cell death, was first proposed by a group of scientists last year, offering fresh perspectives on the targeting capabilities of copper in the treatment of cancer. In this review, we introduced the fundamental physiological functions of copper, the key components of copper metabolism, and a summary of the current research contributions on the connection between copper and cancer. In addition, the development of new copper-based nanomaterials and their associated mechanisms of action are discussed. Finally, we described how the susceptibility of cancer cells to this metallic nutrition could be leveraged to further improve the existing cancer treatment paradigm in the new setting.

Ligand-induced Assembly of Copper Nanoclusters with Enhanced Electrochemical Excitation and Radiative Transition for Electrochemiluminescence

Copper nanoclusters (CuNCs) are emerging electrochemiluminescence (ECL) emitters with unique molecule-like electronic structures, high abundance, and low cost. However, the synthesis of CuNCs with high ECL efficiency and stability in a scalable manner remains challenging. Here, we report a facile gram-scale approach for preparing self-assembled CuNCs (CuNCsAssy ) induced by ligands with exceptionally boosted anodic ECL and stability. Compared to the disordered aggregates that are inactive in ECL, the CuNCsAssy shows a record anodic ECL efficiency for CuNCs (10 %, wavelength-corrected, relative to Ru(bpy)3 Cl2 /tripropylamine). Mechanism studies revealed the unusual dual functions of ligands in simultaneously facilitating electrochemical excitation and radiative transition. Moreover, the assembly addressed the limitation of poor stability of conventional CuNCs. As a proof of concept, an ECL biosensor for alkaline phosphatase detection was successfully constructed with an ultralow limit of detection of 8.1×10-6  U/L.

Determination of 2, 6-dipicolinic acid as an Anthrax biomarker based on the enhancement of copper nanocluster fluorescence by reversible aggregation-induced emission

The weak fluorescence efficiency of copper nanoclusters (Cu NCs) limits their wide applications in biosensing and bioimaging areas, while the aggregation-induced emission (AIE) effect is anticipated to increase their luminescence intensity. Herein, the weak red emission of Cu NCs is increased considerably by the addition of lanthanide Tb³⁺, ascribed to the AIE effect. Monitoring of spores contamination can be carried out by determining the level of 2, 6-dipicolinic acid (DPA), which is a marker of spores. Due to the stronger synergy between DPA and Tb³⁺ for its clamped configuration of adjacent pyridine nitrogen group with the carboxylic acid group, the addition of DPA leads Tb³⁺ to be taken away from Cu NCs through a stronger coordination effect, causing Cu NCs to return to the dispersed state and weakened fluorescence. Based on this, an "off-on-off" fluorescent probe for DPA sensing was built, in which Tb³⁺ was used as a bridge to achieve AIE enhanced fluorescence effect on Cu NCs as well as a specific recognizer of DPA. The detection range for DPA was 0.1-60 μM and the detection limit was 0.06 μM, which was much lower than the infectious dose of anthrax spores. Since DPA is a unique biomarker for bacterial spores, the method was applied to the detection of actual bacterial spores and satisfactory results were obtained with a detection limit of 4.9*10³ CFU mL^-1.

Perspectives of different colour-emissive nanomaterials in fluorescent ink, LEDs, cell imaging, and sensing of various analytes

In the past 2 decades, multicolour light-emissive nanomaterials have gained significant interest in chemical and biological sciences because of their unique optical properties. These materials have drawn much attention due to their unique characteristics towards various application fields. The development of novel nanomaterials has become the pinpoint for different application areas. In this review, the recent progress in the area of multicolour-emissive nanomaterials is summarized. The different emissions (white, orange, green, red, blue, and multicolour) of nanostructure materials (metal nanoclusters, quantum dots, carbon dots, and rare earth-based nanomaterials) are briefly discussed. The potential applications of different colour-emissive nanomaterials in the development of fluorescent inks, light-emitting diodes, cell imaging, and sensing devices are briefly summarized. Finally, the future perspectives of multicolour-emissive nanomaterials are discussed.

Assembly-Induced Emission Enhancement in Glutathione-Capped Bimetallic Gold and Copper Nanoclusters by Al3+ Ions and Further Application in Myricetin Determination

A significant emission enhancement (>100-fold) of glutathione-capped bimetallic gold and copper nanoclusters (AuCuNC@GSH) was achieved by assembling with Al3+ ions and by assembly-induced emission enhancement (AIEE). Further chelation of myricetin to Al3+ resulted in emission quenching of AuCuNC-Al3+, which was applied to specifically detect myricetin. Two linear responses were shown in the range of 0−1.5 μM and 1.5−50 μM, separately, leading to a low limit of detection at 8.7 nM. The method was successfully and accurately applied to myricetin determination in grape juice, which showed good application for real samples. Finally, the in-depth mechanism revealed that both the chelation of myricetin and Al3+ and the inner filter effect (IFE) between myricetin-Al3+ and AuCuNC-Al3+ greatly contributed to the quenching response of myricetin. Therefore, the present study provides an easy way to improve the fluorescence property of metal nanoclusters. Additionally, it supplies a cost-effective and easily performed approach to detect myricetin with high selectivity and sensitivity.

Engineering colloidally stable, highly fluorescent and nontoxic Cu nanoclusters via reaction parameter optimization

Metal nanoclusters (NCs) composed of the least number of atoms (a few to tens) have become very attractive for their emerging properties owing to their ultrasmall size. Preparing copper nanoclusters (Cu NCs) in an aqueous medium with high emission properties, strong colloidal stability, and low toxicity has been a long-standing challenge. Although Cu NCs are earth-abundant and inexpensive, they have been comparatively less explored due to their various limitations, such as ease of surface oxidation, poor colloidal stability, and high toxicity. To overcome these constraints, we established a facile synthetic route by optimizing the reaction parameters, especially altering the effective concentration of the reducing agent, to influence their optical characteristics. The improvement of the photoluminescence intensity and superior colloidal stability was modeled from a theoretical standpoint. Moreover, the as-synthesized Cu NCs showed a significant reduction of toxicity in both in vitro and in vivo models. The possibility of using such Cu NCs as a diagnostic probe toward C. elegans was explored. Also, the extension of our approach toward improving the photoluminescence intensity of the Cu NCs on other ligand systems was demonstrated.

The Multifarious Applications of Copper Nanoclusters in Biosensing and Bioimaging and Their Translational Role in Early Disease Detection

Nanoclusters possess an ultrasmall size, amongst other favorable attributes, such as a high fluorescence and long-term colloidal stability, and consequently, they carry several advantages when applied in biological systems for use in diagnosis and therapy. Particularly, the early diagnosis of diseases may be facilitated by the right combination of bioimaging modalities and suitable probes. Amongst several metallic nanoclusters, copper nanoclusters (Cu NCs) present advantages over gold or silver NCs, owing to their several advantages, such as high yield, raw abundance, low cost, and presence as an important trace element in biological systems. Additionally, their usage in diagnostics and therapeutic modalities is emerging. As a result, the fluorescent properties of Cu NCs are exploited for use in optical imaging technology, which is the most commonly used research tool in the field of biomedicine. Optical imaging technology presents a myriad of advantages over other bioimaging technologies, which are discussed in this review, and has a promising future, particularly in early cancer diagnosis and imaging-guided treatment. Furthermore, we have consolidated, to the best of our knowledge, the recent trends and applications of copper nanoclusters (Cu NCs), a class of metal nanoclusters that have been gaining much traction as ideal bioimaging probes, in this review. The potential modes in which the Cu NCs are used for bioimaging purposes (e.g., as a fluorescence, magnetic resonance imaging (MRI), two-photon imaging probe) are firstly delineated, followed by their applications as biosensors and bioimaging probes, with a focus on disease detection.

A simple strategy to enhance the luminescence of metal nanoclusters and its application for turn-on detection of 2-thiouracil and hyaluronidase

Metal nanoclusters (NCs) as promising nanomaterials for sensing applications have attracted significant attention because of their unique photoluminescence properties. However, the quantum yields of metal NCs are still relatively low when compared to conventional quantum dots and organic dyes, posing a major obstacle to their assay application. It is challenging but important to pursue a way to improve the luminescence of metal NCs. In this work, we developed a novel strategy to enhance the luminescence of silver nanoclusters (Ag NCs) based on the binding with 6-aza-2-thiothymine (ATT) via Au³⁺ bridging. We studied the possible mechanism of this binding-induced luminescence enhancement and attributed it to the ligands rigidifying. Since 2-thiouracil (2-TU), a common anticancer, antithyroid, and antiviral agent, featured a similar molecular structure of ATT, this luminescence enhancement strategy can be designed to sensitive and selective turn-on detect 2-TU. As far as we know, this is the first report for the fluorescent turn-on detect 2-TU. Benefiting from the good performance of this method and the advantages of fluorescence assay, intracellular imaging of 2-TU, which has yet to be achieved based on currently developed analytical methods for 2-TU, was carried out via our approach. Moreover, to further expand the sensing application of the developed luminescence enhancement method, we constructed a universal detection platform. Taking hyaluronidase as a target, the feasibility of the detection platform was confirmed. The discoveries in this study offer a simple route to improve the optical properties of NCs and design their sensing applications.

Controlling the Chemistry of Nanoclusters: From Atomic Precision to Controlled Assembly

Metal nanoclusters have gained prominence in nanomaterials sciences, owing to their atomic precision, structural regularity, and unique chemical composition. Additionally, the ligands stabilizing the clusters provide great opportunities for linking the clusters in higher order dimensions, eventually leading to the formation of a repertoire of nanoarchitectures. This makes the chemistry of atomic clusters worth exploring. In this mini review, we aim to focus on the chemistry of nanoclusters. Firstly, we summarize the important strategies developed so far for the synthesis of atomic clusters. For each synthetic strategy, we highlight the chemistry governing the formation of nanoclusters. Next, we discuss the key techniques in the purification and separation of nanoclusters, as the chemical purity of clusters is deemed important for their further chemical processing. Thereafter which we provide an account of the chemical reactions of nanoclusters. Then, we summarize the chemical routes to the spatial organization of atomic clusters, highlighting the importance of assembly formation from an application point of view. Finally, we raise some fundamentally important questions with regard to the chemistry of atomic clusters, which, if addressed, may broaden the scope of research pertaining to atomic clusters.

Aggregation-Induced Emission-Based Platforms for the Treatment of Bacteria, Fungi, and Viruses

The prevention and control of pathogenic bacteria, fungi, and viruses is a herculean task for all the countries since they greatly threaten global public health. Rapid detection and effective elimination of these pathogens is crucial for the treatment of related diseases. It is urgently demanded to develop new diagnostic and therapeutic strategies to combat bacteria, fungi, and viruses-induced infections. The emergence of aggregation-induced emission (AIE) luminogens (AIEgens) is a revolutionary breakthrough for the treatment of many diseases, including pathogenic infections. In this review, the main focus is on the applications of AIEgens for theranostic treatment of pathogenic bacteria, fungi, and viruses. Due to the AIE characteristic, AIEgens are promising fluorescent probes for the detection of bacteria, fungi, and viruses with excellent sensitivity and photostability. Moreover, AIEgen-based theranostic platforms can be fabricated by introducing bactericidal moieties or designing AIE photosensitizers and AIE photothermal agents. The current strategies and ongoing developments of AIEgens for the treatment of pathogenic bacteria, fungi, and viruses will be discussed in detail.

Metal-Based Aggregation-Induced Emission Theranostic Systems

Efficient theranostic systems can realize better outcomes in disease treatment because of precise diagnosis and the concomitant effective therapy. Aggregation-induced emission luminogens (AIEgens) are a unique type of organic emitters with intriguing photophysical properties in the aggregate state. Among the AIEgens studied for biomedical applications, so far, metal-based AIE systems have shown great potential in theranostics due to the enhanced multimodal bioimaging ability and therapeutic effect. This research field has been growing rapidly, and many rationally designed systems with promising activities to cancer and other diseases have been reported recently. In this review, we summarized the recent progress of metal-based AIE materials in bioimaging and biological theranostics, and deciphered the pertinent design strategies. We hope that this review can offer new insights into the development of this growing field.

AIE materials for cancer cell detection, bioimaging and theranostics

AIE materials exhibit weakly emissive or non-emissive properties in dilute solutions while emit powerful fluorescence in the aggregated/solid state. Recently, AIE based materials have gained immense attention due to their multifunctional role in cancer cell detection, bioimaging and cancer theranostics. In this present book chapter, we will highlight recent advancements of AIE materials for different cancer theranostics applications.

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.

Copper nanocluster composites for analytical (bio)-sensing and imaging: a review

As an ideal substitute for traditional organic fluorescent dyes or up-conversion nanomaterials, copper nanoclusters (CuNCs) have developed rapidly and have been involved in exciting achievements in versatile applications. The emergence of novel CuNCs composites improves the poor stability and fluorescence intensity of CuNCs. With this in mind, great efforts have been made to develop a wide variety of CuNCs composites, and impressive progress has been made in the past few years. In this review, we systematically summarize absorption, fluorescence, electrochemiluminescence, and catalytic properties and focus on the multiple factors that affect the fluorescence properties of CuNCs. The fluorescence properties of CuNCs are discussed from the point of view of core size, surface ligands, self-assembly, metal defects, pH, solvent, ions, metal doping, and confinement effect. Especially, we illustrate the research progress and representative applications of CuNCs composites in bio-related fields, which have received considerable interests in the past years. Additionally, the sensing mechanism of CuNCs composites is highlighted. Finally, we summarize current challenges and look forward to the future development of CuNCs composites. Schematic diagram of the categories, possible sensing mechanisms, and bio-related applications of copper nanoclusters composites.

Driving Forces and Routes for Aggregation-Induced Emission-Based Highly Luminescent Metal Nanocluster Assembly

The development of ultrasmall, luminescent metal nanoclusters (MNCs) with aggregation-induced emission (AIE) characteristics is a relatively new research area that has gained significant attention in various multidisciplinary applications such as optoelectronics, sensing, imaging, and therapy. The numerous scientific breakthroughs in the AIE field provide many tools that, if incorporated into MNCs design strategies, could help realize various new and exciting MNC-based avenues that maximize the utilization of the AIE phenomenon. Indeed, leveraging the aggregation strategies from the AIE community with the judicious use of various covalent and noncovalent interactions has been demonstrated to be effective for constructing several MNC-based hybrid assemblies with enhanced AIE characteristics. In this Perspective, we summarize the key driving forces and routes of MNC assembly together with their impact on deciphering the working mechanism behind the AIE process. These strategies can inspire the design of highly luminescent MNC-based hierarchical functional materials across multiple length scales.

Nucleic acid-driven aggregation-induced emission of Au nanoclusters for visualizing telomerase activity in living cells and in vivo

Visual monitoring of telomerase activity in living cancer cells and in vivo is essential for clinical diagnosis and treatment. However, most detection methods were performed in vitro due to the difficulty of probes entering cells and the interferences from complex biological environments. Herein, we developed a novel probe based on Au nanoclusters (AuNCs) with a nucleic acid-driven aggregation-induced emission (AIE) property for the first time. The probe was applied for detection of telomerase with high sensitivity. Importantly, the probe could achieve telomerase imaging in living cells and in solid tumor tissue in vivo. The study provided a specific connection fashion of metal nanoclusters for AIE generation. It holds great potential for the development of AIE-active metal nanoclusters as a diagnostic tool for disease detection in vitro as well as in vivo.

Achieving full-color emission of Cu nanocluster self-assembly nanosheets by the virtue of halogen effects

Fluorescent Cu nanoclusters (NCs) have shown potential in lighting and display, because Cu is cheap and easily available. Despite recent successes in improving the emission intensity of Cu NCs on the basis of aggregation-induced emission enhancement and self-assembly-induced emission enhancement, the difficulty in tuning the emission color sheds the doubt for achieving high-performance white light-emitting diodes (WLEDs). In this work, halogen effects are utilized to tune the emission color of Cu nanocluster self-assembly nanosheets (NSASs). By altering the adsorbed halogens from Cl, Br to I, the emission peak of Cu NSASs is tunable from 495 to 674 nm. In this context, halogen atoms are capable of improving the charge transfer and molecular spin coupling of Cu NCs, and thereby narrow the S0T1 gap and facilitate the intersystem crossing of excitons from a singlet to triplet state. As a result, emission spectra redshift and the population of the exiton recombination via the triplet state pathway is increased, which leads to the improvement of the photoluminescence quantum yield (PLQY). By simply introducing and/or mixing different types of cuprous halides, Cu nanocluster co-assembly nanosheets (NCASs) with full-color emission are obtained. The as-prepared Cu NSASs and NCASs are further employed to fabricate monochrome and white LEDs.

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.

Engineering amino-mediated copper nanoclusters with dual emission and assembly-to-monodispersion switching by pH-triggered surface modulation

We synthesized l-cysteine (Cys)-mediated copper nanoclusters (CuNCs) with assembly-to-monodispersion switching by pH-triggered surface modulation, where aggregated red emissive (R)-CuNCs@Cys at pH = 3 turns to monodispersed blue emissive (B)-CuNCs@Cys at pH = 10.

Ultra-sensitive and selective determination of a phenolic food additive using protein capped gold nanoclusters: a dual in-line fluorometric and colorimetric sensing probe

The application of red luminescence BSA-AuNCs towards the selective determination of food additive tert-butylhydroquinone (TBHQ) was demonstrated by both fluorometric and colorimetric methods.

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.

Progressive aggregation-induced emission strategy for imaging of aluminum ions in cellular microenvironment

A progressive aggregation-induced emission (AIE) strategy is established based on two diverse stimulus-responsive patterns of copper nanoclusters (CuNCs) for imaging of aluminum ions (Al³⁺) in cellular microenvironment. The non-emissive CuNCs were facilely synthesized with l-glutathione (GSH) as both stabilizing agent and reducing agent, and demonstrated the excellent AIE characteristics in the ethanol/water mixture. Moreover, the dispersed CuNCs can be aggregated to give the AIE behavior in aqueous solutions by reducing the pH value, and could be further aggregated with 94-fold reinforce by introducing Al³⁺ ascribe to the strong coordination ability between Al³⁺ and the functional groups of GSH, demonstrating the progressive AIE process. Under endocytosis, the progressive AIE strategy can be employed to distinguish the Al³⁺ in the locations of lysosome against other organelles due to the acidic microenvironment of lysosome. The progressive AIE advantages of CuNCs provide a new concept for signal transduction, and have the promising applications in decoding the functions of intracellular biomolecules.

Highly Selective Detection of Metronidazole by Self-Assembly via 0D/2D N-C QDs/g-C3N4 Nanocomposites Through FRET Mechanism

A 0D/2D (0-dimensional/2-dimensional) nanostructure was designed by self-assembly of N-C QDs and carboxylated g-C3N4 nanosheets and used as a fluorescence resonance energy transfer (FRET) fluorescent sensor. The N-C QDs/g-C3N4 nanosheets were synthesized via the amino group on the N-C QD surface and the -COOH of the carboxylated g-C3N4 nanosheets. The mechanism of detection of metronidazole (MNZ) by N-C QDs/g-C3N4 nanocomposites is based on FRET between negatively charged N-QDs and positively charged carboxylated g-C3N4 nanoparticles. N-C QDs/g-C3N4 nanostructures displayed good responses for the detection of MNZ at normal temperature and pressure. The decrease in the fluorescence intensity showed a good linear relationship to MNZ concentration within 0-2.6 × 10-5 mol/L, and the detection limit was 0.66 μM. The novel FRET sensor will have a great potential in clinical analysis and biological studies.

Development of Copper Nanoclusters for In Vitro and In Vivo Theranostic Applications

Theranostics refers to the incorporation of therapeutic and diagnostic functions into one material system. An important class of nanomaterials exploited for theranostics is metal nanoclusters (NCs). In contrast to gold and silver NCs, copper is an essential trace element for humans. It can be more easily removed from the body. This, along with the low cost of copper that offers potential large-scale nanotechnology applications, means that copper NCs have attracted great interest in recent years. The latest advances in the design, synthesis, surface engineering, and applications of copper NCs in disease diagnosis, monitoring, and treatment are reviewed. Strategies to control and enhance the emission of copper NCs are considered. With this synopsis of the up-to-date development of copper NCs as theranostic agents, it is hoped that insights and directions for translating current advances from the laboratory to the clinic can be further advanced and accelerated.

Host–guest recognition-regulated aggregation-induced emission for in situ imaging of MUC1 protein

A host–guest recognition regulated aggregation-induced emission strategy is developed based on cyclodextrin-functionalized copper nanoclusters for long-term imaging of protein.

Aggregation-induced emission enhancement of adenosine monophosphate-capped bimetallic nanoclusters by aluminum(III) ions, and its application to the fluorometric determination of cysteine

The fluorescence of adenosine monophosphate-capped bimetallic gold and silver nanoclusters (type AuAgNC@AMP) is strongly enhanced and blue shifted in the presence of Al(III). As confirmed by transmission electron microscopy, the AuAgNC nanodots are converted to larger assembled spheres of type AuAgNC-Al(III). The fluorescence enhancement is attributed to aggregation-induced emission enhancement (AIEE). The fluorescence of the AuAgNC-Al(III) assembly (with excitation and emission maxima at 340 and 540 nm) is quenched by cysteine (Cys). The effect was applied to the fluorometric determination of Cys. The assay works in the 1.0 to 16.0 μM Cys concentration range and has a 50 nM limit of detection. The method was successfully applied to analyze Cys-spiked mineral waters and serum. The quenching mechanism is explored in depth. It is attributed to the partial replacement of AMP by Cys at the surface of the AuAgNC and alteration of the assembly structure from large spherical particles to a strip shape. Graphical abstractSchematic representation of the fluorescence enhancement of bimetallic nanoclusters capped with adenosine monophosphate by using Al(III), and its application in selective and sensitive determination of cysteine via ligand replacement and reassembly.

pH-induced aggregation of hydrophilic carbon dots for fluorescence detection of acidic amino acid and intracellular pH imaging

Intracellular pH level plays an important role in physiological and pathological processes. The development of nanoprobes for detecting in vivo pH levels is especially important for early diagnosis of disease. Therefore, we develop a hydrophilic carbon points (CDs) using quercetin and ethylenediamine as precursors to monitor intracellular pH. Under optimized conditions, the prepared CDs not only have uniform particle size and morphology, but also possess strong green fluorescence, photostability, and photoreversibility in water medium. The CDs exhibit pH-sensitive fluorescence effect under acidic and alkaline conditions, which is used to achieve "off-on-off" detection pH (from 3.5 to 13.5). Meanwhile, the pH-dependent mechanism is further investigated and explained, which is the fluorescence quenching caused by the pH-induced aggregation. Based on the pH-sensitive characteristics of CDs, it has been applied to the detection of aspartic acid and glutamic acid. More importantly, when applied to live cells, the pH-probe exhibits low cytotoxicity and high sensitivity, and is successfully used in intracellular pH fluorescence imaging. Consequently, this nanoprobe is expected to be used for real-time monitoring of intracellular pH level.

Photo induced chemical modification of surface ligands for aggregation and luminescence modulation of copper nanoclusters in the presence of oxygen

Surface modification of nanoparticles has been a popular approach to tailor the properties of nanoparticles. Herein we report the unprecedented photo oxidation of cysteine moeties on the surface of copper nanoclusters (Cu NCs) leading to aggregation of Cu NCs, which further led to quenching of luminescence of the latter. Upon illumination of a dispersion of Cu NCs at 365 nm wavelength light, the luminescence of Cu NCs was completely quenched. Furthermore, the extent of luminescence quenching of Cu NCs upon photo illumination could be tuned by varying the area of exposure of light. Confirmation of photooxidation of cysteine molecules was made through Fourier transformed infrared (FTIR) studies, while the formation of submicron sized aggregates of Cu NCs as a result of photo oxidation of cysteine stabilizing the nanoclusters was evinced through transmission electron microscopy (TEM). The study embodied herein opens up new avenues for the tailoring of the chemical and optical properties of metal nanoclusters through chemical transformation of surface ligand moieties, which is envisioned to emerge as a powerful strategy for broadening the application potential of metal nanoclusters.

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.

Fluorometric detection of sulfate-reducing bacteria via the aggregation-induced emission of glutathione-gold(I) complexes

It is reported that gold(I)-thiolate complexes can display aggregation-induced emission (AIE) similar to organic fluorogens. On addition of lead(II) to glutathione-gold(I) complexes, a supermolecular structure of type GSH-Au(I)-Pb(II) is formed through strong coordination between Pb(II) and GSH. Its fluorescence is quenched by sulfide due to the formation of PbS which destroys the GSH-Au(I)-Pb(II) complex. The finding was used to design a method for fluorometric detection of sulfate-reducing bacteria (SRB) which produce sulfide. The time needed to reduce fluorescence to 10% of its initial intensity linearly dependent on the logarithm of the SRB concentrations in the ranging from 10 to 1 × 10^7 cfu mL^-1. The assay time is also reduced down to 4 days even if the SRB concentration is as low as 10 cfu mL^-1. Graphical abstract Schematic presentation of aggregation-induced emission (AIE)-active GSH-Au(I) complexes based fluorescence detection of SRB. The GSH-Au(I) complexes turn into aggregation and display strong emissive property in the presence of Pb²⁺. Then the fluorescence of GSH-Au(I)-Pb(II) complexes can be quenched by S^2- generated by SRB.

A signal-on nanobiosensor for VEGF165 detection based on supraparticle copper nanoclusters formed on bivalent aptamer

In this study, a signal-on nanobiosensor based on bivalent aptamer-Cu nanocluster was designed and optimized for specific and sensitive detection of VEGF₁₆₅. The VEGF₁₆₅ is known as a promising biomarker in different diseases such as cancer in the angiogenic stage. Detection and quantification of VEGF₁₆₅ is a crucial step in diagnosis and monitoring the treatment plan. The represented nanostructure consists of multimerized VEGF₁₆₅ aptamer joint with ssDNA based linker in the middle and poly thymine sequences on both 3' and 5' ends as a template for Cu-nanocluster supraparticle formation. This self-assembled structure leads to accurate controlling of aggregation in the presence of VEGF₁₆₅. This study is the first report for Cu nanocluster nucleation on ploy thymine tails of ssDNA which performed in two reduction steps to form stable CuNC supraparticle. The sensing strategy was designed based on the target-induced structure switching mode of the aptamer. In the presence of VEGF₁₆₅, due to self-assembly induced emission and aggregation-induced emission phenomena this nanostructure depicted the visible wavelength shift and enhancement in the fluorescence emission intensity. Also, the results of the analytical performance of this nanobiosensor indicated the LOD of 12 pM which revealed high rate sensitivity. This aptasensor exhibited stability and decent response linearity range (10-800 pM, R² = 0.9943). The selectivity and specificity assessment showed high discriminant capability in the real serum sample. In conclusion, this signal-on nanobiosensor provides a facile, sensitive and reliable assay for clinical monitoring of the VEGF₁₆₅ concentration in serum without further sample preparation.

Synthesis of novel luminescent copper nanoclusters with substituent driven self-assembly and aggregation induced emission (AIE)

We demonstrate a novel strategy to synthesize highly stable and luminescent mercaptoimidazole-capped copper nanoclusters (CuNCs). Simple modification of substituents on the mercaptoimidazole ligand dictates the self-assembly and photophysical properties of the clusters.

Engineering the Self-Assembly Induced Emission of Copper Nanoclusters as 3D Nanomaterials with Mesoporous Sphere Structures by the Crosslinking of Ce3

Aggregation-induced emission has provided fluorescence enhancement strategies for metal nanoclusters. However, the morphology of the aggregated nanoclusters tended to be irregular due to the random aggregated route, which would result in the formation of an unstable product. Herein, copper nanoclusters were directly synthesized by using l-cysteine as both the reducing and protection ligand. Initially, the structure of the product was irregular. Furthermore, Ce3+ was introduced to re-arrange the aggregates through a crosslinking avenue. It was interesting to find that well-ordered three-dimensional nanomaterials with mesoporous sphere structures were obtained after re-aggregation. On the basis of the stability test at a relatively high temperature and the light-emitting diode fabrication investigation, it revealed that the regulated product demonstrated more promising stability and color purity for practical applications than the random aggregated product with irregular structures.