Fluorescent copper nanoparticles: recent advances in synthesis and applications for sensing metal ions

Recent Progress in Nanoparticles Based Sensors for the Detection of Mercury (II) Ions in Environmental and Biological Samples

To maintain a green and sustainable environment for human beings, rapid detection of potentially toxic heavy metals like mercury (Hg(II)) has attracted great attention. Recently, sensors have been designed which can selectively detect Hg(II) over other common available cations and give a naked eye or fluorometric response. In the last two decades, the trend is shifting from bulky organic chemosensors toward nanoparticles due to their rapid response, low cost, eco-friendly and easy synthesis. In this review, promising nanoparticles-based sensors for Hg(II) detection are discussed. The nano-sensors are functionalized with nucleotide or other suitable materials which coordinate with Hg(II) ions and give clear color or fluorescence change. The operational mechanisms are discussed focusing on its four basic types. The nanoparticles-based sensors are even able to detect Hg in three different oxidation states (Hg(II), Hg(I) and Hg(0)). Recently, the trend has been shifted from ordinary nanoparticles to magnetic nanoparticles to simultaneously detect and remove Hg(II) ions from environmental samples. Furthermore, the nano-sensors for Hg(II) are compared with each other and with the reported organic chemosensors.

Small Copper Nanoclusters Synthesized through Solid-State Reduction inside a Ring-Shaped Polyoxometalate Nanoreactor

Cu nanoclusters exhibit distinctive physicochemical properties and hold significant potential for multifaceted applications. Although Cu nanoclusters are synthesized by reacting Cu ions and reducing agents by covering their surfaces using organic protecting ligands or supporting them inside porous materials, the synthesis of surface-exposed Cu nanoclusters with a controlled number of Cu atoms remains challenging. This study presents a solid-state reduction method for the synthesis of Cu nanoclusters employing a ring-shaped polyoxometalate (POM) as a structurally defined and rigid molecular nanoreactor. Through the reduction of Cu2+ incorporated within the cavity of a ring-shaped POM using H2 at 140 °C, spectroscopic studies and single-crystal X-ray diffraction analysis revealed the formation of surface-exposed Cu nanoclusters with a defined number of Cu atoms within the cavities of POMs. Furthermore, the Cu nanoclusters underwent a reversible redox transformation within the cavity upon alternating the gas atmosphere (i.e., H2 or O2). These Cu nanoclusters produced active hydrogen species that can efficiently hydrogenate various functional groups such as alkenes, alkynes, carbonyls, and nitro groups using H2 as a reductant. We expect that this synthesis approach will facilitate the development of a wide variety of metal nanoclusters with high reactivity and unexplored properties.

A Novel Enhanced-Fluorescent Probe Based on DHLA-Stabilized Red-Emitting Copper Nanoclusters for Methimazole Detection Via Aggregation-Induced Emission Effect

Herein, an aqueous phase synthesis approach was presented for the fabrication of copper nanoclusters (Cu NCs) with aggregation-induced emission (AIE) property, utilizing lipoic acid and NaBH4 as ligands and reducing agent, respectively. The as-synthesized Cu NCs exhibit an average size of 3.0 ± 0.2 nm and demonstrate strong solid-state fluorescence upon excitation with UV light. However, when dissolved in water, no observable fluorescent emission is detected in the aqueous solution of Cu NCs. Remarkably, the addition of Methimazole induced a significant red fluorescence from the aqueous solution of Cu NCs. This unexpected phenomenon can be ascribed to the aggregation of negatively charged Cu NCs caused by electrostatic interaction with positively charged imidazole groups in Methimazole, resulting in enhanced fluorescence through AIE mechanism. Therefore, there exists an excellent linear correlation between the fluorescent intensities of Cu NCs aqueous solution and the concentration of Methimazole within a range of 0.1-1.5 mM with a low limit of detection of 82.2 µM. Importantly, the designed enhanced-fluorescent nanoprobe based on Cu NCs exhibits satisfactory performance in assaying commercially available Methimazole tablets, demonstrating its exceptional sensitivity, reliability, and accuracy.

Advances in Fluorescent Nanosensors for Detection of Vitamin B12

Vitamin B12 plays a significant role in maintaining human health. Deficiency or excess intake of vitamin B12 may cause some diseases. Therefore, it is significant to fabricate sensors for sensitive assay of vitamin B12. In the past few years, a variety of nanomaterials have been developed for the fluorescence detection of vitamin B12 in tablets, injection, human serum and food. In the review, the assay mechanisms of fluorescent nanomaterials for sensing vitamin B12 were first briefly discussed. And the progress of various nanomaterials for fluorescence detection of vitamin B12 were systematically summarized. Furthermore, the sensing performance of fluorescent nanosensors was compared with fluorescent probes. Lastly, the challenges and perspectives about the topic were presented.

Nanomaterials for Fluorescent Detection of Hemoglobin

Hemoglobin plays a vital role in a series of biological activities. Abnormal levels of hemoglobin in blood are associated with many clinical diseases. Therefore, development of simple and accurate methods for sensing hemoglobin is of considerable significance. The blowout advancement in nanotechnology has urged the use of different types of fluorescent nanomaterials for hemoglobin assay. The past decades have witnessed the rapid progress of fluorescent nanosensors for hemoglobin assay. In the review, the sensing principles of fluorescent nanomaterials for sensing hemoglobin were briefly discussed. The advances of fluorescent nanosensors for detection of hemoglobin were further highlighted. And the sensing performance of fluorescent nanosensors versus traditional detection approaches was compared. Finally, the challenges and future directions of fluorescent nanomaterials for detection of hemoglobin are discussed. The review will arouse much more attention to the construction of hemoglobin sensors and facilitate rapid development of fluorescent nanosensors of hemoglobin.

Ligand "switching on" fluorescence of HIV-1 RNA-templated copper nanoclusters for ligand-RNA interaction assays

Ligand-RNA interaction assay provides the basis for developing new RNA-binding small molecules. In this study, fluorescent copper nanoclusters (CuNCs) were first prepared using two kinds of HIV-1 RNA targets, rev-responsive element (RRE) and transactivator response element (TAR) RNA, as new templates, and it was found that the fluorescence of the single RNA-templated CuNCs was negligible. Using neomycin as a model drug, the fluorescence could be augmented (approximately 6 times) for the neomycin/RNA-templated CuNCs. Thus, a novel method was developed for ligand-RNA interactions by observing the fluorescence changes in CuNCs prepared using RNA before and after the addition of ligands. The preparation parameters of neomycin/RNA-CuNCs were optimized. The as-prepared CuNCs were characterized using UV-vis spectroscopy, fluorescence spectroscopy, and high-resolution transmission electron microscope. Circular dichroism spectral analysis showed that RRE and TAR were inclined to form a double-stranded structure after interaction with neomycin, which was more conducive to the formation of CuNCs. The interactions of neomycin and three test drugs (amikacin, gentamicin, and tobramycin) with RNA were investigated using the proposed method, and the binding constants and number of binding sites were obtained through theoretical calculations. This study provides a novel approach for ligand-RNA interaction assays.

Development of Copper Nanoclusters-Based Turn-Off Nanosensor for Fluorescence Detection of Two Pyrethroid Pesticides (Cypermethrin and Lambda-Cyhalothrin)

Fluorescent copper nanoclusters (Cu NCs) were synthesized by using Withania somnifera (W. somnifera) plant extract as a biotemplate. Aqueous dispersion of W. somnifera-Cu NCs displays intense emission peak at 458 nm upon excitation at 350 nm. This fluorescence emission was utilized for the detection of two pyrethroid pesticides (cypermethrin and lambda-cyhalothrin) via "turn-off" mechanism. Upon the addition of two pyrethiod pesticides independently, the fluorescence emission of W. somnifera-Cu NCs was gradually decreased with increasing concentrations of both pesticides. It was noticed that the decrease in emission intensity at 458 nm was linearly dependent on the logarithm of both pesticides concentrations in the ranges of 0.01-100 μM and of 0.05-100 μM for cypermethrin and lambda-cyhalothrin, respectively. Consequently, the limits of detection were found to be 27.06 and 23.28 nM for cypermethrin and lambda-cyhalothrin, respectively. The as-fabricated W. somnifera-Cu NCs acted as a facile sensor for the analyses of cypermethrin and lambda-cyhalothrin in vegetables (tomato and bottle gourd), which demonstrates that it could be used as portable sensing platform for assaying of two pyrethroid pesticides in food samples.

Nanomaterials for fluorescent detection of vitamin B2: A review

Vitamin B2 plays vital roles in maintaining human health. It is of tremendous significance to construct sensitive sensors of VB2. In this review, we first briefly presented the sensing mechanisms of fluorescent nanomaterials for sensing VB2. Subsequently, the advances of nanomaterials for fluorescent determination of VB2 were highlighted. And sensing performance of traditional approaches and fluorescent nanosensors was further compared. In last section, the challenges and perspectives concerning the topic were discussed.

Highly Stable Fluorescent-Traffic-Light Sensor for Point-of-Care Detection of Tetracycline

Fluorescent point-of-care (POC) sensors have found great utility in fields like clinical diagnosis, food testing, and environmental monitoring. Herein, we developed a highly stable POC sensor that enabled the visual detection of tetracycline (TC) in a distinct fluorescent-traffic-light manner. In the sensor, a composite material of copper nanoclusters and metal-organic framework (CuNCs@MOF-5) prepared with a facile one-pot synthetic strategy was employed as the core element for target recognition and signal transduction. As evidenced by experiments, the as-prepared CuNCs@MOF-5 exhibited significantly improved fluorescence properties in terms of emission enhancement (about 28-fold) and stability improvement (over 110 days) compared to the CuNCs without confining and protection by MOF-5. More importantly, it was found that TC could uniquely interact with Zn(II) to trigger the disassembly of CuNCs@MOF-5, resulting in green fluorescence emission from the TC-Zn(II) complex and red fluorescence weakening of CuNCs. On the basis of this finding, a simple and stable sensor was proposed for POC detection of TC, which demonstrated high sensitivity, selectivity, and reproducibility. In addition to homogeneous visual detection in a 96-well plate, a CuNCs@MOF-5-contained agarose gel array was easily fabricated to achieve direct detection of TC in milk without any pretreatment, thanks to the size-sieving effect of the gel. Moreover, a test paper array was also put forward for low-cost TC detection, which indicates the extensibility and practicability of this sensing strategy.

Cu(I)-thioether coordination complexes based on a chiral cyclic β-amino acid ligand

Coordination complexes, particularly metalloproteins, highlight the significance of metal-sulfur bonds in biological processes. Their unique attributes inspire efforts to synthetically reproduce these intricate metal-sulfur motifs. Here, we investigate the synthesis and characterization of copper(I)-thioether coordination complexes derived from copper(I) halides and the chiral cyclic β-amino acid trans-4-aminotetrahydrothiophene-3-carboxylic acid (ATTC), which present distinctive structural properties and ligand-to-metal ratios. By incorporating ATTC as the ligand, we generated complexes that feature a unique chiral conformation and the capacity for hydrogen bonding, facilitating the formation of distinct geometric structures. Through spectroscopic analyses and density functional theory (DFT) calculations, we studied the complexes' optical properties, including their emission bands and variable second-harmonic generation (SHG) efficiencies, which vary based on the halide used. Our findings underscore the potential of the ATTC ligand in creating unusual coordination complexes and pave the way for further investigations into their potential applications, particularly within materials science.

Label-free and low-background FEN1 sensing based on cleavage-induced ligation of bifunctional dumbbell DNA and in-situ signal readout

Flap endonuclease 1 (FEN1) is overexpressed in various types of human tumor cells and has been recognized as a promising biomarker for cancer diagnosis in recent years. In this work, a label-free fluorescent nanosensor for FEN1 detection was developed based on cleavage-induced ligation of bifunctional dumbbell DNA and in-situ signal readout by copper nanoparticles (CuNPs). The dumbbell DNA was rationally designed with a FEN1 cleavable 5' flap for target recognition and AT-riched stem-loop template for CuNPs formation. In the presence of FEN1, 5' overhanging DNA flap of dumbbell DNA was effectively removed to form a linkable nick site. After the ligation by T4 DNA ligase, the dumbbell DNA changed to exonuclease-resisted closed structure which enabled in-situ generation of fluorescent CuNPs that served as signal source for target quantification. The low background attributed to synergic digestion by exonucleases facilitated the highly sensitive detection of FEN1 with limit of detection of 0.007 U/mL. Additionally, the sensor was extended to the assay of FEN1 inhibitor (aurintricarboxylic acid) with reasonable results. Last but not least, the normal cells and tumor cells were distinguished unambiguously by this sensor according to the detected concentration difference of cellular FEN1, which indicates the robustness and practicability of this nanosensor.

Nanomaterials for fluorescent assay of bilirubin

The accumulation of bilirubin in blood is associated with many diseases. Sensitive and accurate detection of bilirubin is of great significance for personal health care. The rapid development of fluorescent nanomaterials promotes rapid development in the bilirubin assay. In this review, traditional methods for detection of bilirubin are briefly presented to compare with fluorescent nanosensors. Subsequently, the recent progress of different types of fluorescent nanomaterials for determination of bilirubin is summarized. Further, the performance of fluorescent nanosensors and conventional techniques for sensing bilirubin are compared. To this end, the challenges and prospects concerning the topics are discussed. This review will provide some introductory knowledge for researchers to understand the status and importance of fluorescent nanosensors for sensing bilirubin.

Determination of trypsin using protamine mediated fluorescent enhancement of DNA templated Au nanoclusters

A fluorescent method is described for trypsin determination through the strong electrostatic interactions between cationic polyelectrolytes and single-stranded DNA (ssDNA) templated Au nanoclusters (AuNCs). The ssDNA-AuNCs display improved fluorescence emission with excitation/emission maxima at 280/475 nm after being incorporated with poly(diallyldimethylammonium chloride) (PDDA). Fluorescent enhancement is mainly attributed to the electrostatic interactions occurring  between PDDA and ssDNA templates. This can make the conformation of the ssDNA templates to change. Thus, it offers a better microenvironment for stabilizing and protecting ssDNA-AuNCs, and results in fluorescence emission enhancement. By using protamine as a model, the method is employed for the determination of trypsin. The assay enables trypsin to be determined with good sensitivity and a linear response ranging from 5 ng⋅mL^-1 to 60 ng⋅mL^-1 with a 1.5 ng⋅mL^-1 limit of detection. It is also extended to determine  the trypsin contents in human's serum samples with recoveries between 98.7% and 103.5% with relative standard deviations (RSDs) between 3.5% and 4.8%. A novel fluorescent strategy has been developed for of trypsin determination by using protamine mediated fluorescent enhancement of DNA templated Au nanoclusters.

Preparation of a Red-Emitting, Chitosan-Stabilized Copper Nanocluster Composite and Its Application as a Hydrogen Peroxide Detection Probe in the Analysis of Water Samples

Hydrogen peroxide (H₂O₂) is an important reactive oxygen species that mediates a variety of physiological functions in biological processes, and it is an essential mediator in food, pharmaceutical, and environmental analysis. However, H₂O₂ can be dangerous and toxic at certain concentrations. It is crucial to detect the concentration of H₂O₂ in the environment for human health and environmental protection. Herein, we prepared the red-emitting copper nanoclusters (Cu NCs) by a one-step method, with lipoic acid (LA) and sodium borohydride as protective ligands and reducing agents, respectively, moreover, adding chitosan (CS) to wrap LA-Cu NCs. The as-prepared LA-Cu NCs@CS have stronger fluorescence than LA-Cu NCs. We found that the presence of H₂O₂ causes the fluorescence of LA-Cu NCs@CS to be strongly quenched. Based on this, a fluorescent probe based on LA-Cu NCs@CS was constructed for the detection of H₂O₂ with a limit of detection of 47 nM. The results from this research not only illustrate that the as--developed fluorescent probe exhibits good selectivity and high sensitivity to H₂O₂ in environmental water samples but also propose a novel strategy to prepare red-emitting copper nanoclusters (Cu NCs) by a one-step method.

Cu Nanoparticle-Based Solution and Paper Strips for Colorimetric and Visual Detection of Heavy Metal Ions

The intrinsic toxicity of heavy metal ions to human health or other species calls for the need to develop an analytical tool for the easy and rapid detection of these ions based on inexpensive and stable nanomaterials. This article describes the potential utility of stable Cu nanoparticles (CuNPs) in the detection of toxic metal ions by solution and paper strip-based methods. For this, first, a dodecyl sulfate ion-stabilized CuNP (DS-CuNP) colloid was synthesized by a chemical reduction method. This was followed by treating the dispersion with heavy metal ions and monitoring the spectral change by spectrophotometric and colorimetric techniques. Among a host of metal ions, Hg²⁺, Cd²⁺, and Pb²⁺ have been found to significantly affect the surface plasmon resonance band of CuNPs by concomitantly altering the color of its solution. Notably, the brownish color of CuNP solution changed readily to milky white in the presence of Hg²⁺. Furthermore, the fabricated brownish-yellow test paper strips containing DS-CuNPs transformed to a prominent white color in the presence of a few drops of Hg²⁺ solution. This change in color of the paper strips could be visually detected by the naked eye. The experiments involving the detection of the various ions were carried out by optimizing the experimental conditions qualitatively as well as quantitatively. The limit of detection of the analytes (metal ions) has been found to be 10 μM. Routine analytical techniques like UV-vis spectroscopy, dynamic light scattering, transmission electron microscopy, and Fourier transform infrared spectroscopy formed part of the experiments.

Development of a paper printed colorimetric sensor based on Cu-Curcumin nanoparticles for evolving point-of-care clinical diagnosis of sodium

The homeostatic control of Sodium (Na⁺) ion in the human body assumes paramount relevance owing to its physiological importance. Any deviation from the normal level causes serious health problems like hypernatremia, hyponatremia, stroke, kidney problems etc. Therefore, quantification of Na⁺ levels in body fluids has significant diagnostic and prognostic importance. However, interfering ions like Potassium ion (K⁺) is the major hurdle in sodium detection. In this work, we synthesized the clusters of 3-9 nm-sized highly stable and pure Copper nanoparticles surface functionalised with curcumin, through chemical reduction method. Each cluster of particles is encapsulated in a curcumin layer which is clearly visible in TEM images. The results show that these curcumin functionalized Cu NPs (CuC) are highly selective to the colorimetric detection of Na⁺. The ions like K⁺, Mg²⁺ and Zn²⁺ did not interfere with the Na⁺ in this sensing technique. Low-cost paper-based sensor strips are fabricated and calibrated for the sensing of sodium in the physiological range and shade cards were developed as a calorimetric guide for estimation of Na⁺ which makes them ideal point of care diagnostic platform. We demonstrate that the proposed CuC paper strip can be used for detecting Na⁺ concentration within the whole physiological range in both blood serum and urine.

Nanomaterials for fluorescent detection of curcumin

Owing to the attractive biological and pharmacological activities, sensitive and selective detection of curcumin is of great significance. Nanomaterials possessing unique optical properties exhibit potential applications in the fluorescent detection of curcumin. This review first discussed the detection strategies of fluorescent nanosensors. In the subsequent section, we highlighted the recent advances of different nanomaterials for fluorescent detection of curcumin, including semiconductor QDs, lanthanide upconversion nanoparticles, fluorescent metal nanoclusters, and carbon quantum dots. And we further provided the merits of fluorescent nanosensors for curcumin. Lastly, the challenges and further directions were presented.

Ultrasmall Luminescent Metal Nanoparticles: Surface Engineering Strategies for Biological Targeting and Imaging

In the past decade, ultrasmall luminescent metal nanoparticles (ULMNPs, d < 3 nm) have achieved rapid progress in addressing many challenges in the healthcare field because of their excellent physicochemical properties and biological behaviors. With the sharp shrinking size of large plasmonic metal nanoparticles (PMNPs), the contributions from the surface characteristics increase significantly, which brings both opportunities and challenges in the application-driven surface engineering of ULMNPs toward advanced biological applications. Here, the systematic advancements in the biological applications of ULMNPs from bioimaging to theranostics are summarized with emphasis on the versatile surface engineering strategies in the regulation of biological targeting and imaging performance. The efforts in the surface functionalization strategies of ULMNPs for enhanced disease targeting abilities are first discussed. Thereafter, self-assembly strategies of ULMNPs for fabricating multifunctional nanostructures for multimodal imaging and nanomedicine are discussed. Further, surface engineering strategies of ratiometric ULMNPs to enhance the imaging stability to address the imaging challenges in complicated bioenvironments are summarized. Finally, the phototoxicity of ULMNPs and future perspectives are also reviewed, which are expected to provide a fundamental understanding of the physicochemical properties and biological behaviors of ULMNPs to accelerate their future clinical applications in healthcare.

Ratiometric fluorescence determination of chlortetracycline based on the aggregation of copper nanoclusters triggered by aluminum ion

The aggregation-induced emission (AIE) characteristic of copper nanoclusters (CuNC) was for the first time used to construct a ratiometric fluorescence probe (CuNC-Al³⁺) for detection of chlortetracycline (CTC). Aluminum ion (Al³⁺) can aggregate free CuNC and make it emit a bright and stable red fluorescence. A slight excess of Al³⁺ in CuNC-Al³⁺ solution can form a CTC-Al³⁺ complex to limit the conformational rotation of CTC molecule and enhance CTC fluorescence. So, the red fluorescence of CuNC-Al³⁺ probe and the enhanced CTC fluorescence are used as a reference signal and a response signal to detect CTC, respectively. The method developed shows a good linear relationship between the CTC concentration and the fluorescence intensity ratio (I₄₉₅/I₅₇₅) in the range 0.1-3.0 µM, and the detection limit is 25.3 nM (S/N = 3). In addition, the fluorescent color of CuNC-Al³⁺ probe changes from red to yellow-green as the concentration of CTC increases. Based on this observation, a fluorescent test paper has also been fabricated. Schematic illustration of Al³⁺ inducing CuNC to produce AIE performance and detecting CTC.

A versatile fluorescent nanobeacon lighted by DNA-templated copper nanoparticles and the application in isothermal amplification detection

In this work, an environmentally-friendly and versatile nanobeacon was constructed by utilizing DNA-templated copper nanoparticles (CuNPs) as fluorescence signal source. As the key component of the nanobeacon, a hairpin DNA was designed to contain four segments: two segments for CuNPs template sequence, a target recognition segment and a blocking segment. At room temperature, the target recognition segment partly hybridizes with the blocking segment and thus prohibits the formation of double stranded DNA template, so that no CuNPs can be generated on the hairpin DNA. While a target is introduced, the specific binding of target with recognition sequence triggers off the conformational transformation of the hairpin DNA, which contributes to the formation of the CuNPs template. As a result, the in-situ generation of CuNPs gives birth to the fluorescence signal readout that can be used to identify the target. By reasonably varying the recognition sequence within hairpin DNA, a series of nanobeacons in response to corresponding targets, such as DNA, microRNA, thrombin, and ATP, were put forward with satisfactory sensitivity and selectivity. Moreover, this nanobeacon was also integrated with the strategy of enzyme-assisted target-recycling to realize signal amplification and ultrasensitive detection, which further demonstrated the versatility of the nanobeacon. This novel nanobeacon is expected to be a promising alternative to classical dye-labeled molecular beacon and provide new perspective on ultrasensitive fluorescence sensing.

Synthetic Tunability and Biophysical Basis for Fabricating Highly Fluorescent and Stable DNA Copper Nanoclusters

The real motivation in the present work is to tune the synthesis variables that can result in a highly fluorescent and stable DNA copper nanocluster (CuNC) and also to understand the intricate mechanism behind this process. Here, carefully optimized concentrations of various reactants enabled the creation of a DNA-encapsulated CuNC for AT-DNA, displaying a size of <1.0 nm as confirmed by transmission electron microscopy and dynamic light scattering. The extremely small size of the AT-DNACuNC supports the discrete electronic transitions, also characterized by an exceptionally strong negative circular dichroism (CD) band around 350 nm, whose intensity is well correlated with the observed strong fluorescence emission intensity. This remarkably strong CD can open new applications in the detection and quantification of a specific DNACuNC. Further, time-dependent fluorescence analysis suggested stronger photostabilization of these DNACuNCs. The simulation study, based on Cu ion distribution, explained how AT-DNA is a better candidate for NC formation than GC-DNA. In conclusion, the better-tuned synthesis procedure has resulted in a highly compact, well-defined three-dimensional conformation that promotes a more favorable microenvironment to sequester a DNA-based CuNC with high brightness and outstanding photostability.

Self-Assembly of Amphiphilic Copper Nanoclusters Driven by Cationic Surfactants

Amphiphilicity is an excellent physicochemical property, which is yet to be explored from traditional surfactants to nanoparticles. This article shows that the amphiphilicity of copper nanoclusters (CuNCs) can be readily tuned by electrostatic interactions with cationic surfactants and cetyltrimethylammonium cations (CTA⁺) with counterions Br^-, Cl^-, and C₇H₈O₃S^-. Due to the role of surface ligands, the complexes of glutathione-capped CuNCs (GSH-CuNCs) and the surfactants exhibit good amphiphilicity, which enables them to self-assemble like a molecular amphiphile. This could significantly increase the utility of metal nanoclusters in basic and applied research. As the concentration of the surfactant changes, the aggregates change from nanoparticles to network-like structures. After the formation of supramolecular self-assemblies by hydrophobic interactions, the enhancement of fluorescence intensity was observed, which can be ascribed to the suppression of intramolecular vibrations based on aggregation-induced emission (AIE) and combined with the compactness of GSH-CuNCs in self-assemblies. Our study provides a facile way to generate solid fluorescent materials with excellent fluorescence performance, which may find applications in light-emitting diodes (LEDs).

In situ STEM study on the morphological evolution of copper-based nanoparticles during high-temperature redox reactions

Despite the broad relevance of copper nanoparticles in industrial applications, the fundamental understanding of oxidation and reduction of copper at the nanoscale is still a matter of debate and remains within the realm of bulk or thin film-based systems. Moreover, the reported studies on nanoparticles vary widely in terms of experimental parameters and are predominantly carried out using either ex situ observation or environmental transmission electron microscopy in a gaseous atmosphere at low pressure. Hence, dedicated studies in regards to the morphological transformations and structural transitions of copper-based nanoparticles at a wider range of temperatures and under industrially relevant pressure would provide valuable insights to improve the application-specific material design. In this paper, copper nanoparticles are studied using in situ Scanning Transmission Electron Microscopy to discern the transformation of the nanoparticles induced by oxidative and reductive environments at high temperatures. The nanoparticles were subjected to a temperature of 150 °C to 900 °C at 0.5 atm partial pressure of the reactive gas, which resulted in different modes of copper mobility both within the individual nanoparticles and on the surface of the support. Oxidation at an incremental temperature revealed the dependency of the nanoparticles' morphological evolution on their initial size as well as reaction temperature. After the formation of an initial thin layer of oxide, the nanoparticles evolved to form hollow oxide shells. The kinetics of formation of hollow particles were simulated using a reaction-diffusion model to determine the activation energy of diffusion and temperature-dependent diffusion coefficient of copper in copper oxide. Upon further temperature increase, the hollow shell collapsed to form compact and facetted nanoparticles. Reduction of copper oxide was carried out at different temperatures starting from various oxide phase morphologies. A reduction mechanism is proposed based on the dynamic of the reduction-induced fragmentation of the oxide phase. In a broader perspective, this study offers insights into the mobility of the copper phase during its oxidation-reduction process in terms of microstructural evolution as a function of nanoparticle size, reaction gas, and temperature.

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.

Copper Oxide Nanoparticles Alter Serum Biochemical Indices, Induce Histopathological Alterations, and Modulate Transcription of Cytokines, HSP70, and Oxidative Stress Genes in Oreochromis niloticus

In the present study, fish were exposed to sub-lethal doses of CuONPs (68.92 ± 3.49 nm) (10 mg/L, 20 mg/L, and 50 mg/L) for a long exposure period (25 days). Compared to the control group (0.0 mg/L CuONPs), a significant dose-dependent elevation in blood urea and creatinine values, serum alanine transaminase, aspartate transaminase, and alkaline phosphatase enzyme activities were evident in CuONPs-exposed groups (p < 0.05). Fish exposure to 50 mg/L CuONPs significantly upregulated the transcription of pro-inflammatory cytokines (tumor necrosis factor-alpha, interleukin-1beta, interleukin 12, and interleukin 8), heat shock protein 70, apoptosis-related gene (caspase 3), and oxidative stress-related (superoxide dismutase, catalase, and glutathione peroxidase) genes in liver and gills of the exposed fish in comparison with those in the control group (p < 0.05). Moreover, varying histopathological injuries were noticed in the hepatopancreatic tissues, posterior kidneys, and gills of fish groups correlated to the tested exposure dose of CuONPs. In summary, our results provide new insights and helpful information for better understanding the mechanisms of CuONPs toxicity in Nile tilapia at hematological, molecular levels, and tissue levels.

A fluorescence strategy for monitoring α-glucosidase activity and screening its inhibitors from Chinese herbal medicines based on Cu nanoclusters with aggregation-induced emission

Herein, the self-assembly of 1-dodecanethiol-capped Cu nanoclusters (DT-Cu NCs) is obtained by annealing of dibenzyl ether solution of nanoclusters. These aggregates are composed of small clusters and emit a high level of aggregation-induced emission (AIE) in water. Based on the quenching effect of 4-nitrophenol (4-NP) on DT-Cu NCs, a fluorescence strategy is developed to monitor α-glucosidase (α-Glu) activity and screen its inhibitors from Chinese herbal medicines. 4-Nitrophenyl-α-D-glucopyranoside (NGP) is selected as the substrate, which is further hydrolyzed to yield 4-NP through the catalysis of α-Glu. The quenching efficiency is positively correlated to the concentration of α-Glu. Furthermore, the inhibitory effects of the extracts from four Chinese herbal medicines (i.e., the rind of Punica granatum L., Momordica grosvenorii Swingle., Crataegus pinnatifida Bge., and Lycium barbarum L.) on the α-Glu activity have been studied. The IC₅₀ values of extracts from the rind of Punica granatum L. and Momordica grosvenorii Swingle are 0.23 and 0.37 g/L, respectively, so they show obvious inhibitory effects on α-Glu. The extracts of Crataegus pinnatifida Bge. and Lycium barbarum L. exhibit relatively weak inhibitory effects. Hence, the proposed strategy can be applicable for screening α-Glu inhibitors from Chinese herbal medicines. Last but not the least, by immobilizing DT-Cu NCs into agarose hydrogels in polyethylene tubes, a visual device is fabricated to screen α-Glu inhibitors with high throughput and sensitivity.

Probing the Interaction of Bovine Serum Albumin with Copper Nanoclusters: Realization of Binding Pathway Different from Protein Corona

With an aim to understand the interaction mechanism of bovine serum albumin (BSA) with copper nanoclusters (CuNCs), three different types CuNCs having chemically different surface ligands, namely, tannic acid (TA), chitosan, and cysteine (Cys), have been fabricated, and investigations are carried out in the absence and presence of protein (BSA) at ensemble-averaged and single-molecule levels. The CuNCs, capped with different surface ligands, are consciously chosen so that the role of surface ligands in the overall protein-NCs interactions is clearly understood, but, more importantly, to find whether these CuNCs can interact with protein in a new pathway without forming the "protein corona", which otherwise has been observed in relatively larger nanoparticles when they are exposed to biological fluids. Analysis of the data obtained from fluorescence, ζ-potential, and ITC measurements has clearly indicated that the BSA protein in the presence of CuNCs does not attain the binding stoichiometry (BSA/CuNCs > 1) that is required for the formation of "protein corona". This conclusion is further substantiated by the outcome of the fluorescence correlation spectroscopy (FCS) study. Further analysis of data and thermodynamic calculations have revealed that the surface ligands of the CuNCs play an important role in the protein-NCs binding events, and they can alter the mode and thermodynamics of the process. Specifically, the data have demonstrated that the binding of BSA with TA-CuNCs and Chitosan-CuNCs follows two types of binding modes; however, the same with Cys-CuNCs goes through only one type of binding mode. Circular dichroism (CD) measurements have indicated that the basic structure of BSA remains almost unaltered in the presence of CuNCs. The outcome of the present study is expected to encourage and enable better application of NCs in biological applications.

AIE-based fluorescent sensors for low concentration toxic ion detection in water

Ions, including anions and heavy metals, are extremely toxic and easily accumulate in the human body, threatening the health of humans and even causing human death at low concentrations. It is therefore necessary to detect these toxic ions in low concentrations in water. Fluorescent sensing is a good method for detecting these ions, but some conventional dyes often exhibit an aggregation caused quench (ACQ) effect in their solid state, limiting their large-scale application. Fluorescent probes based on aggregation-induced emission (AIE) properties have received significant attention due to their high fluorescence quantum yields in their nano aggragated states, easy fabrication, use of moderate conditions, and selevtive recognization of organic/inorganic compounds in water with obvious changes in fluorescence. We surmarize the recent advances of AIE-based sensors for low concentration toxic ion detection in water. The detection probes can be divided into three categories: chemical reaction types, chemical interaction types and physical interaction types. Chemical reaction types utilize nucleophilic addition and coordination reaction, while chemical interaction types rely on hydrogen bonding and anion-π interactions. The physical interaction types are composed of electrostatic attractions. We finally comment on the challenges and outlook of AIE-active sensors.

Peptide-Engineered Fluorescent Nanomaterials: Structure Design, Function Tailoring, and Biomedical Applications

Fluorescent nanomaterials have exhibited promising applications in biomedical and tissue engineering fields. To improve the properties and expand bioapplications of fluorescent nanomaterials, various functionalization and biomodification strategies have been utilized to engineer the structure and function of fluorescent nanomaterials. Due to their high biocompatibility, satisfied bioactivity, unique biomimetic function, easy structural tailoring, and controlled self-assembly ability, supramolecular peptides are widely used as versatile modification agents and nanoscale building blocks for engineering fluorescent nanomaterials. In this work, recent advance in the synthesis, structure, function, and biomedical applications of peptide-engineered fluorescent nanomaterials is presented. Firstly, the types of different fluorescent nanomaterials are introduced. Then, potential strategies for the preparation of peptide-engineered fluorescent nanomaterials via templated synthesis, bioinspired conjugation, and peptide assembly-assisted synthesis are discussed. After that, the unique structure and functions through the peptide conjugation with fluorescent nanomaterials are demonstrated. Finally, the biomedical applications of peptide-engineered fluorescent nanomaterials in bioimaging, disease diagnostics and therapy, drug delivery, tissue engineering, antimicrobial test, and biosensing are presented and discussed in detail. It is helpful for readers to understand the peptide-based conjugation and bioinspired synthesis of fluorescent nanomaterials, and to design and synthesize novel hybrid bionanomaterials with special structures and improved functions for advanced applications.

Design of experiments a powerful tool to improve the selectivity of copper antimony sulfide nanoparticles synthesis

Design of experiments to find the main factors governing phase compositions and nanoparticle size.

Highly Stable Pyrimidine Based Luminescent Copper Nanoclusters with Superoxide Dismutase Mimetic and Nitric Oxide Releasing Activity

Copper nanoclusters (CuNCs) are emerging as an interesting class of materials for various biomedical applications. In this work, we have designed highly stable nucleobase-capped luminescent CuNCs and studied the effect of substituents on the cluster composition and photophysical properties. The NCs exhibit exceptional stability in ambient atmosphere and show significant variation in the emission properties with a change in position of substituents on the ligand, thiouracil. This study represents the first example of a nanocluster that functionally mimics the activity of a major antioxidant enzyme, superoxide dismutase (SOD). In addition to their enzyme-mimetic activity, the CuNCs evince controlled release of nitric oxide (NO), a key gaseous molecule of endothelial system from S-nitrosothiol, S-nitrosoglutathione (GSNO). Further, to a greater significance, these luminescent CuNCs are readily taken up by the mammalian cells and exhibit low toxicity. The superoxide dismutase and NO releasing activity of the fluorescent, biocompatible copper nanoclusters suggest their potential application in both therapeutics and bioimaging.

Bright fluorescent nucleic acid detection with CRISPR-Cas12a and poly(thymine) templated copper nanoparticles

Fluorescence-based diagnostic tools are attractive and versatile tests with multiple advantages: ease of use, sensitivity and rapid results. The advent of CRISPR-Cas technology has created new avenues for the development of diagnostic testing tools. In this study, by effectively combining the specific functions of two enzymes, CRISPR-Cas12a and terminal deoxynucleotidyl transferase (TdT), we developed a DNA detection assay that generates copper nanoparticles (CuNPs) that are easily visible to the naked eye under UV-light; we named this detection assay Cas12a Activated Nuclease poly-T Reporter Illuminating Particles (CANTRIP). Upon specific target DNA recognition by Cas12a, single-stranded DNA (ssDNA) reporter oligos with blocked 3'-ends are cut into smaller ssDNA fragments, thereby generating neo 3'-hydroxyl moieties. TdT subsequently elongates these newly formed ssDNA fragments, incorporating only dTTP nucleotides, and these poly(thymine)-tails subsequently function as scaffolds for the formation of CuNPs. These CuNPs produce a bright fluorescent signal upon UV excitation, and thus, this bright orange signal indicates the presence of target DNA, which in this proof-of-concept study consisted of anthrax lethal factor plasmid DNA. CANTRIP, which combines two detection platforms consisting of CRISPR-Cas12a and fluorescent CuNPs into a single reaction, appears to be a robust, low-cost and simple diagnostic tool.

Functionalized Copper Nanoclusters-Based Fluorescent Probe with Aggregation-Induced Emission Property for Selective Detection of Sulfide Ions in Food Additives

In this paper, a novel and facile synthetic method of 3-mercaptopropionic acid functionalized copper nanoclusters with aggregation-induced emission (AIE) induced by Cu²⁺ (Cu²⁺@MPA-Cu NCs) was developed by a one-pot reaction as a fluorescent probe for the detection of sulfide ion (S^2-). The prepared Cu²⁺@MPA-Cu NCs behaved as aggregated clusters and had strong pink fluorescence under 365 nm UV light with excellent fluorescence emission at 610 nm. The quantum yield increased from 0.56% to 4.8% before and after Cu²⁺ added. The presence of S^2- would strongly bind to Cu²⁺, which caused the structure of the aggregated Cu²⁺@MPA-Cu NCs to be destroyed and then the fluorescence quenched. On the basis of this principle, a fluorescent probe was constructed for the detection of S^2- with a very good linearity in the range 0-600 μM (R² = 0.9843) and a detection limit of 26.3 nM. Finally, the nanohybrids were successfully demonstrated for the application in the selective detection of S^2- in food additives. This study essentially paved a new avenue for effectively developing an easy sensor platform for S^2- measurements in food additives.

Applications of fluorescent materials in the detection of alkaline phosphatase activity

Alkaline phosphatase (ALP) is important in the diagnosis of many diseases. Because ALP is used to detect biomarkers for many diseases, many researchers conduct investigations to develop ALP detection strategies. The use of fluorescent material has attracted attention because of the technique's high sensitivity and the low sample volume required. Herein, we review and discuss the working mechanisms and advantages of four main categories:DNA fluorescent probes, molecular fluorescent probes, chemical coordination-based probes, and nanoparticle probes. Development prospects and trends are also discussed.

Novel synthesis of orange-red emitting copper nanoclusters stabilized by methionine as a fluorescent probe for norfloxacin sensing

In the present work, we report a novel chemical approach for the synthesis of orange-red emitting copper nanoclusters (Cu NCs) using L-methionine as stabilizing agent at room temperature for the first time. The synthetic route is facile, economical and viable. The methionine stabilized copper nanoclusters (Cu NCs/Met) were thoroughly characterized by TEM, FT-IR, XPS, UV-Vis, steady state and transient fluorescence spectroscopy. The results show the synthesized Cu NCs/Met with a fluorescence quantum yield of 4.37% possessed high stability and excellent optical features such as large Stokes shift and long fluorescence lifetime (8.3 μs). Significantly, the fluorescence intensity of Cu NCs/Met could be efficiently quenched by norfloxacin (NOR) pharmaceutical. A fast and cost-effective NOR sensor was proposed employing Cu NCs/Met as the fluorescent nanoprobe, and the quenching mechanisms were attributed to inner filter effect and agglomeration-induced quenching. The developed sensor exhibited a high sensitivity and selectivity towards NOR in a wide linear range from 0.05 to 250 μM with a detection limit as low as 17 nM. Moreover, the practicability of the developed NOR sensor for real sample assay was validated with satisfactory recoveries, indicating this sensing platform with great potential for label-free pharmaceutical detection in complex systems.

Detection Methods and Research Progress of Human Serum Albumin

Human serum albumin (HSA) is a biological macromolecule with important physiological functions; abnormal HSA levels are associated with coronary heart disease, multiple myeloma, diabetes, nephropathy, neurometabolic disorders, liver cirrhosis and other diseases. Therefore, accurate and quantitative detection of HAS have extremely important research and application value in biological science, molecular biology, clinical medicine and other fields. As for the detection method of HSA, dye-binding method and immune method are the first to be used, and have been applied in clinical detection. In recent years, many new detection technologies have emerged, such as fluorescent probe detection method, nano-materials for HSA detection, biosensor and so on. Although there are many methods developed recently to detect HSA, comprehensive reviews for HSA detection methods are still rare. Thus, writing this review to fill in the blank is in need. In order to highlight the recent progress in the field of HSA detection, in this review, the methods used to detect HSA are summarized and sorted, the advantages and disadvantages of these detection methods are also listed, then the research progress of small molecular fluorescence probe method is emphatically introduced in this paper. Then, we briefly discussed the challenges and future development directions in this field.

Developing fluorescent copper nanoclusters: Synthesis, properties, and applications

Metal nanoclusters exhibit strong fluorescence emission, providing immense potential for developments in biological labeling and imaging. Copper nanoclusters in particular, due to their unique optical properties such as molecular-like absorption and strong luminescence, represent a novel fluorescent nanomaterial for sensing and bioimaging applications. This review describes research progress on Cu nanoclusters in recent years, investigating the synthesis techniques, their properties, and their promising applications. A concluding summary provides an outlook on the future research challenges for Cu nanoclusters and their corresponding synthesis techniques.