Sensing of iron(III)-biomolecules by surfactant-free fluorescent copper nanoclusters

Two-dimensional oxygen-deficient ZnO1-x nanosheet as a highly selective and sensitive fluorescence probe for ferritin detection: the electron transfer biosensor (ETBS)

Iron proteins are of great scientific interest due to their importance as an excellent biomarker for human diseases. Ferritin (Fe3+), being an iron-rich blood protein, is related to various diseases like anemia and cancer. For the first time, we have developed a highly sensitive and selective ferritin biosensor based on fluorescent oxygen-deficient zinc oxide nanosheets through hydrothermal and probe-ultrasonication combined methods. The fluorescence study showed an intense bluish-green fluorescence at λex = 370 nm, after optimization at different excitation wavelengths. In addition, the fluorescence of ZnO1-x nanosheets can be efficiently quenched due to electron transfer reactions in order to achieve quantification analysis. The limit of detection (LOD) was calculated to be 0.015 nM (7.2 ng mL-1) with high linearity (R2 = 0.9930). In addition, the real-world application of the proposed biosensor has been performed on human blood serum samples in the presence of various interfering analytes showing high selectivity and sensitivity with a regression value R2 = 0.9980 indicating the current approach is an excellent biosensor platform.

Construction of nanohybrid Tb@CDs/GSH-CuNCs as a ratiometric probe to detect phosphate anion based on aggregation-induced emission and FRET mechanism

The simple preparation of a nanohybrid of terbium-doped carbon dots/glutathione-capped copper nanoclusters (Tb@CDs/GSH-CuNCs) was for the first time developed for ratiometric detection of phosphate anion (Pi). Blue-emission of Tb@CDs can trigger non-luminescence of GSH-CuNCs for aggregation-induced emission (AIE) performance due to the strong reserved coordination capacity of Tb3+. Thus, Tb@CDs/GSH-CuNCs rapidly generated dual-emission signals at 630 nm and 545 nm by directly mixing the two individual materials via the AIE effect, alongside fluorescence resonance energy transfer (FRET) process. However, by the introduction of Pi, both AIE and FRET processes were blocked because of the stronger binding affinity of Tb3+ and Pi than that of Tb3+ and -COOH on Tb@CDs, thus realizing successful ratiometric detection of Pi. The linear concentration range was 0-16 μM, with the limit of detection (LOD) of 0.32 μM. The proposed method provided new ideas for designing nanohybrid of CDs and nanoclusters (MNCs) as ratiometric fluorescent probes for analytical applications.

Aggregates-based fluorescence sensing technology for food hazard detection: Principles, improvement strategies, and applications

Aggregates often exhibit modified or completely new properties compared with their molecular elements, making them an extraordinarily advantageous form of materials. The fluorescence signal change characteristics resulting from molecular aggregation endow aggregates with high sensitivity and broad applicability. In molecular aggregates, the photoluminescence properties at the molecular level can be annihilated or elevated, leading to aggregation-causing quenching (ACQ) or aggregation-induced emission (AIE) effects. This change in photoluminescence properties can be intelligently introduced in food hazard detection. Recognition units can combine with the aggregate-based sensor by joining the aggregation process, endowing the sensor with the high specificity of analytes (such as mycotoxins, pathogens, and complex organic molecules). In this review, aggregation mechanisms, structural characteristics of fluorescent materials (including ACQ/AIE-activated), and their applications in food hazard detection (with/without recognition units) are summarized. Because the design of aggregate-based sensors may be influenced by the properties of their components, the sensing mechanisms of different fluorescent materials were described separately. Details of fluorescent materials, including conventional organic dyes, carbon nanomaterials, quantum dots, polymers and polymer-based nanostructures and metal nanoclusters, and recognition units, such as aptamer, antibody, molecular imprinting, and host-guest recognition, are discussed. In addition, future trends of developing aggregate-based fluorescence sensing technology in monitoring food hazards are also proposed.

Ce3+-induced Fluorescence Amplification of Copper Nanoclusters Based on Aggregation-induced Emission for Specific Sensing 2,6-pyridine Dicarboxylic Acid

A straightforward, cost-effective and biocompatible reduction approach was applied to fabricate soluble but non-luminous glutathione-stabilized copper nanocluster (GSH-CuNCs). Surprisingly, as high as 1 × 10³ times fluorescence enhancement was acquired when Ce³⁺ was injected at an extremely low concentration of only 18 µM. Ce³⁺ outperformed other rare-earth metal ions in terms of inducing fluorescence amplification of the non-luminous GSH-CuNCs. Furthermore, Ce³⁺ was employed as inducer for aggregation-induce emission (AIE) effect as well as reactant to coordinate with target of 2,6-pyridine dicarboxylic acid (DPA) due to the stronger coordination ability between Ce³⁺ and DPA than that of Ce³⁺ and GSH. As a result, the Ce³⁺/GSH-CuNCs ensemble was developed as a novel sensor to detect DPA in the "on-off" mode. When DPA was introduced into the sensor, Ce³⁺ failed to interact with GSH and detached from the surface of GSH-CuNCs, leading to fluorescence quenching. In addition, static quenching process and internal filtration effect (IFE) between Ce³⁺/GSH-CuNCs and DPA were also responsible for fluorescence quenching effect. A good linear relationship was obtained from 0.3 µM to 18 µM, with a limit of detection (LOD) of 0.19 µM. The as-proposed probe displayed high specificity to DPA and provided a simple, fast rapid and cheap method for construction this type of ensemble sensors to detect other targets.

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.

Iron(III) Complex-Functionalized Gold Nanocomposite as a Strategic Tool for Targeted Photochemotherapy in Red Light

Iron(III)-phenolate/carboxylate complexes exhibiting photoredox chemistry and photoactivated reactive oxygen species (ROS) generation at their ligand-to-metal charge-transfer (LMCT) bands have emerged as potential strategic tools for photoactivated chemotherapy. Herein, the synthesis, in-depth characterization, photochemical assays, and remarkable red light-induced photocytotoxicities in adenocarcinomic human immortalized human keratinocytes (HaCaT) and alveolar basal epithelial (A549) cells of iron(III)-phenolate/carboxylate complex of molecular formula, [Fe(L¹)(L²)] (1), where L¹ is bis(3,5 di-tert-butyl-2-hydroxybenzyl)glycine and L² is 5-(1,2-dithiolan-3-yl)-N-(1,10-phenanthroline-5-yl)pentanamide, and the gold nanocomposite functionalized with complex 1 (1-AuNPs) are reported. There was a significant red shift in the UV-visible absorption band on functionalization of complex 1 to the gold nanoparticles (λ_max: 573 nm, 1; λ_max: 660 nm, 1-AuNPs), rendering the nanocomposite an ideal candidate for photochemotherapeutic applications. The notable findings in our present studies are (i) the remarkable cytotoxicity of the nanocomposite (1-AuNPs) to A549 (IC₅₀: 0.006 μM) and HaCaT (IC₅₀: 0.0075 μM) cells in red light (600-720 nm, 30 J/cm²) while almost nontoxic (IC₅₀ > 500 μg/mL, 0.053 μM) in the dark, (ii) the nontoxicity of 1-AuNPs to normal human diploid fibroblasts (WI-38) or human peripheral lung epithelial (HPL1D) cells (IC₅₀ > 500 μg/mL, 0.053 μM) both in the dark and red light signifying the target-specific anticancer activity of the nanocomposite, (iii) localization of 1-AuNPs in mitochondria and partly nucleus, (iv) remarkable red light-induced generation of reactive oxygen species (ROS: ¹O₂, ^•OH) in vitro, (v) disruption of the mitochondrial membrane due to enhanced oxidative stress, and (vi) caspase 3/7-dependent apoptosis. A similar cytotoxic profile of complex 1 was another key finding of our studies. Overall, our current investigations show a new red light-absorbing iron(III)-phenolate/carboxylate complex-functionalized gold nanocomposite (1-AuNPs) as the emerging next-generation iron-based photochemotherapeutic agent for targeted cancer treatment modality.

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.

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.