Recent advances in the synthesis and application of copper nanomaterials based on various DNA scaffolds

A label-free and rapid fluorometric strategy for microRNA detection using CRISPR-Cas12a coupled with copper nanoparticles

CRISPR-Cas12a with robust trans-cleavage activity were employed to mitigate background fluorescence signal, achieving sensitive detection of miRNA-21. The activation of trans-cleavage activity of Cas12a was achieved by utilizing cDNA as a trigger. Upon the presence of target miRNA-21, cDNA hybridizes with it forming a DNA/RNA double-stranded structure. Exonuclease III (ExoIII) facilitates the degradation of cDNA, releasing the target for subsequent cycles. Due to cDNA degradation, the trans-cleavage activity of Cas12a remains unactivated and does not disrupt the synthesis template of copper nanoparticles. Addition of Cu2+ and AA leads to the formation of highly fluorescent copper nanoparticles. Conversely, in absence of miRNA-21, intact cDNA activates trans-cleavage activity of Cas12a, resulting in degradation of the synthesis template and failure in synthesizing fluorescent copper nanoparticles. This method exhibits excellent selectivity with a low limit of detection (LOD) at 5 pM. Furthermore, we successfully applied this approach to determine miRNA-21 in cell lysates and human serum samples, providing a new approach for sensitive determination of biomarkers in biochemical research and disease diagnosis.

Recent trends and advancement in metal oxide nanoparticles for the degradation of dyes: synthesis, mechanism, types and its application

Synthetic dyes play a crucial role in our daily lives, especially in clothing, leather accessories, and furniture manufacturing. Unfortunately, these potentially carcinogenic substances are significantly impacting our water systems due to their widespread use. Dyes from various sources pose a serious environmental threat owing to their persistence and toxicity. Regulations underscore the urgency in addressing this problem. In response to this challenge, metal oxide nanoparticles such as titanium dioxide (TiO2), zinc oxide (ZnO), and iron oxide (Fe3O4) have emerged as intriguing options for dye degradation due to their unique characteristics and production methods. This paper aims to explore the types of nanoparticles suitable for dye degradation, various synthesis methods, and the properties of nanoparticles. The study elaborates on the photocatalytic and adsorption-desorption activities of metal oxide nanoparticles, elucidating their role in dye degradation and their application potential. Factors influencing degradation, including nanoparticle properties and environmental conditions, are discussed. Furthermore, the paper provides relevant case studies, practical applications in water treatment, and effluent treatment specifically in the textile sector. Challenges such as agglomeration, toxicity concerns, and cost-effectiveness are acknowledged. Future advancements in nanomaterial synthesis, their integration with other materials, and their impact on environmental regulations are potential areas for development. In conclusion, metal oxide nanoparticles possess immense potential in reducing dye pollution, and further research and development are essential to define their role in long-term environmental management.

A highly sensitive colorimetric DNA sensor for MicroRNA-155 detection: leveraging the peroxidase-like activity of copper nanoparticles in a double amplification strategy

A novel and highly sensitive colorimetric DNA sensor for determination of miRNA-155 at attomolar levelsis presented that combines the peroxidase-like activity of copper nanoparticles (CuNPs) with the hybridization chain reaction (HCR) . The utilization of CuNPs offers advantages such as strong interaction with double-stranded DNA, excellent molecular recognition, and mimic catalytic activity. Herein, a capture probe DNA (P1) was immobilized on carboxylated magnetic beads (MBs), allowing for amplified immobilization due to the 3D surface. Subsequently, the presence of the target microRNA-155 led to the formation of a sandwich structure (P2/microRNA-155/P1/MBs) when P2 was introduced to the modified P1/MBs. The HCR reaction was then triggered by adding H1 and H2 to create a super sandwich (H1/H2)n. Following this, Cu2+ ions were attracted to the negatively charged phosphate groups of the (H1/H2)n and reduced by ascorbic acid, resulting in the formation of CuNPs, which were embedded into the grooves of the (H1/H2)n. The peroxidase-like activity of CuNPs catalyzed the oxidation reaction of 3,3',5,5'-Tetramethylbenzidine (TMB), resulting in a distinct blue color measured at 630 nm. Under optimal conditions, the colorimetric biosensor exhibited a linear response to microRNA-155 concentrations ranging from 80 to 500 aM, with a detection limit of 22 aM, and discriminate against other microRNAs. It was also successfully applied to the determination of microRNA-155 levels in spiked human serum.

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.

Strategy of functional nucleic acids-mediated isothermal amplification for detection of foodborne microbial contaminants: A review

Foodborne microbial contamination (FMC) is the leading cause of food poisoning and foodborne illness. The foodborne microbial detection methods based on isothermal amplification have high sensitivity and short detection time, and functional nucleic acids (FNAs) could extend the detectable object of isothermal amplification to mycotoxins. Therefore, the strategy of FNAs-mediated isothermal amplification has been emergingly applied in biosensors for foodborne microbial contaminants detection, making biosensors more sensitive with lower cost and less dependent on nanomaterials for signal output. Here, the mechanism of six isothermal amplification technologies and their application in detecting FMC is firstly introduced. Then the strategy of FNAs-mediated isothermal amplification is systematically discussed from perspectives of FNAs' versatility including recognition elements (Aptamer, DNAzyme), programming tools (DNA tweezer, DNA walker and CRISPR-Cas) and signal units (G-quadruplex, FNAs-based nanomaterials). Finally, challenges and prospects are presented in terms of addressing the issue of nonspecific amplification reaction, developing better FNAs-based sensing elements and eliminating food matrix effects.

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.

Monitoring leaching of Cd2+ from cadmium-based quantum dots by an Cd aptamer fluorescence sensor

Quantum Dots (QDs) have been demonstrated with outstanding optical properties and thus been widely used in many biological and biomedical studies. However, previous studies have shown that QDs can cause cell toxicity, mainly attributable to the leached Cd2+. Therefore, identifying the leaching kinetics is very important to understand QD biosafety and cytotoxicity. Toward this goal, instrumental analyses such as inductively coupled plasma mass spectrometry (ICP-MS) have been used, which are time-consuming, costly and do not provide real-time or spatial information. To overcome these limitations, we report herein a fast and cost-effective fluorescence sensor based a Cd2+-specific aptamer for real-time monitoring the rapid leaching kinetics of QDs in vitro and in living cells. The sensor shows high specificity towards Cd2+ and is able to measure the Cd2+ leached either from water-dispersed CdTe QDs or two-layered CdSe/CdS QDs. The sensor is then used to study the stability of these two types of QDs under conditions to mimic cellular pH and temperature and the results from the sensor are similar to those obtained from ICP-MS. Finally, the sensor is able to monitor the leaching of Cd2+ from QDs in HeLa cells. The fluorescence aptamer sensor described in this study may find many applications as a tool for understanding biosafety of numerous other Cd-based QDs, including leaching kinetics and toxicity mechanisms in living systems.

Fast detection, a precise and sensitive diagnostic agent for breast cancer

Background

Breast cancer targeting diagnostic agent with effective imaging ability is important in guiding plan formulation, prediction, and curative effect evaluation of tumors in clinic. A tumor-targeting nanoprobe based on the functional and programmable Liquid–Liquid phase separation of AS1411 promoted by Ru(II) complex RuPEP may develop into a potential phosphorescence probe to detect breast cancer cells, where AS1411 act as a tumor-targeting guidance moiety to distinguish tumor cells from normal cells and RuPEP act as a light-emitting element to highlight breast cancer cells.

Methods

Here we designed and constructed a nanoprobe AS1411@RuPEP, and the physicochemical and biochemical properties were characterized by TEM, AFM and EDS. The breast cancer targeting diagnostic capacity was evaluated by normal/tumor cell co-culture assay, tumor cells targeting tracking in xenograft model and cancerous area selectively distinguishing in human patient tissue.

Results

Further studies indicated that the nanoprobe exhibits excellent tumor-targeting imaging ability in vitro and in vivo by effectively recognize the over-expressed nucleolin (NCL) on the breast cancer cells membrane. Intriguingly, we discovered that the selectively enrichment of nanoprobe particles in tumor cells is related to ATP-dependent NCL transport processes that rely on the AS1411 component of nanoprobe to recognize NCL. Furthermore, preferential accumulation of nanoprobe is clearly differentiating the human breast cancer tissue surrounding non-cancerous tissue in histological analysis.

Conclusion

This study produce a potent nanoprobe can be used as a convenient tool to highlight and distinguish tumor cells in vivo, and indicate the tumorous grading and staging in human breast cancer patient pathological section, which provides an effective way for breast cancer diagnostic imaging by targeting recognize NCL.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02393-3.

Copper nanoclusters on specific-primer PCR fragments with magnetic capture for the label-free fluorescent sensing of the T315I single nucleotide variant in the BCR–ABL1 gene

A simple and facile strategy using the all or none formation of dsDNA-templated copper nanoclusters on specific-primer PCR fragments was designed to fluorescently identify the T315I single nucleotide variant on the BCR–ABL1 gene.

Stable Luminescent Poly(Allylaminehydrochloride)-Templated Copper Nanoclusters for Selectively Turn-Off Sensing of Deferasirox in β-Thalassemia Plasma

Highly stable and facile one-pot copper nanoclusters (Cu NCs) coated with poly(allylamine hydrochloride) (PAH) have been synthesized for selectively sensing deferasirox (DFX) in β-thalassemia plasma. DFX is an important drug used for treating iron overloading in β-thalassemia, but needs to be monitored due to certain toxicity. In this study, the PAH-Cu NCs showed highly stable fluorescence with emission wavelengths at 450 nm. The DFX specifically interacted with the copper nanocluster to turn off the fluorescence of the PAH-Cu NCs, and could be selectively quantified through the fluorescence quenching effect. The linear range of DFX in plasma analyzed by PAH-Cu NCs was 1.0-100.0 µg/mL (r = 0.985). The relative standard deviation (RSD) and relative error (RE) were lower than 6.51% and 7.57%, respectively, showing excellent reproducibility of PAH-Cu NCs for sensing DFX in plasma. This method was also successfully applied for an analysis of three clinical plasma samples from β-thalassemia patients taking DFX. The data presented high similarity with that obtained through a capillary electrophoresis method. According to the results, the PAH-Cu NCs could be used as a tool for clinically sensing DFX in human plasma for clinical surveys.

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.

Advances in Applications of Molecular Logic Gates

Logic gates are devices that can perform Boolean logic operations and are the basic components of integrated circuits for information processing and storage. In recent years, molecular logic gates are gradually replacing traditional silicon-based electronic computers with their significant advantages and are used in research in water quality monitoring, heavy metal ion detection, disease diagnosis and treatment, food safety detection, and biological sensors. Logic gates at the molecular level have broad development prospects and huge development potential. In this review, the development and application of logic gates in various fields are used as the entry point to discuss the research progress of logic gates and logic circuits. At the same time, the application of logic gates in quite a few emerging fields is briefly summarized and predicted.

DNA dendrimer-templated copper nanoparticles: self-assembly, aggregation-induced emission enhancement and sensing of lead ions

Copper nanomaterials based on DNA scaffold (DNA-Cu NMs) are becoming a novel fluorescent material, but it is still challenging to obtain highly fluorescent DNA-Cu NMs with excellent stability. In this work, we report a kind of copper nano-assemblies (Cu NASs) with aggregation-induced emission enhancement (AIEE) property using DNA dendrimers with sticky end as template. The sticky end of the DNA dendrimers induced the formation of much bigger Cu NASs with average size ranging from 131 to 264 nm, depending on the length of the DNA dendrimer sticky end from 6 bases to 27 bases. Compared with complete complementary DNA dendrimer, nearly 6-fold fluorescence enhancement was achieved using DNA dendrimer with 27 bases sticky end. Moreover, the DNA dendrimer-Cu NASs demonstrated excellent stability in serum and could be rapidly quenched by Pb²⁺ ions. Based on the above property, highly sensitive and selective fluorescent detection of Pb²⁺ ions was possible with a linear range of 2.0-100 nM and a detection limit of 0.75 nM. Due to the sensitive and rapid response to Pb²⁺ as well as excellent stability in complex matrix, the proposed fluorescent Cu NASs demonstrated high potential as an excellent fluorescent probe for Pb²⁺ in complex matrix.

Ultrasensitive and turn-on homogeneous Hg2+ sensing based on a target-triggered isothermal cycling reaction and dsDNA-templated copper nanoparticles

In this work, an ultrasensitive and turn-on sensor for homogeneous Hg2+ detection has been constructed based on a target-triggered isothermal cycling reaction and rapid label-free signal output with dsDNA-templated copper nanoparticles (CuNPs). As the key component of the sensor, a hairpin DNA without any labels was designed to contain different functional sequence segments and to resist digestion by exonuclease due to the protruding 3'-terminus. In the presence of Hg2+, the formation of a T-Hg2+-T structure turned the protruding 3'-terminus of the hairpin DNA to a blunt end that could be efficiently digested by Exo III, accompanied by Hg2+ release, followed by another digestion cycle. Hence, the Hg2+-triggered isothermal cycling reaction accumulated numerous dsDNA templates that facilitated fluorescent CuNP generation and finally output an amplified signal used to identify the target. This protocol is capable of Hg2+ sensing in a concentration range of 5 orders of magnitude with a detection limit down to 3.9 pM. The as-constructed sensor also revealed high selectivity, as well as satisfactory results in recovery experiments of Hg2+ detection in real water samples.

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.

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.

Carbon Dots-Based Logic Gates

Carbon dots (CDs)-based logic gates are smart nanoprobes that can respond to various analytes such as metal cations, anions, amino acids, pesticides, antioxidants, etc. Most of these logic gates are based on fluorescence techniques because they are inexpensive, give an instant response, and highly sensitive. Computations based on molecular logic can lead to advancement in modern science. This review focuses on different logic functions based on the sensing abilities of CDs and their synthesis. We also discuss the sensing mechanism of these logic gates and bring different types of possible logic operations. This review envisions that CDs-based logic gates have a promising future in computing nanodevices. In addition, we cover the advancement in CDs-based logic gates with the focus of understanding the fundamentals of how CDs have the potential for performing various logic functions depending upon their different categories.

Highly specific nuclear labeling via in situ formation of fluorescent copper nanoparticles

When imaging cells, nuclear counterstaining is imperative; however, many commercial nuclear-staining dyes based on nucleic acid intercalation result in nonspecific signals in the cytoplasm. Here, we propose a new strategy that stains the nucleus with high specificity by in situ formation of DNA-templated copper nanoparticles (CuNPs). We demonstrated that genomic DNA in the nucleus enabled rapid formation of highly fluorescent CuNPs immediately following addition of a copper ion source and ascorbate as a reducing agent. Moreover, we found that RNA and mitochondrial DNA, largely responsible for nonspecific cytoplasmic signals from commercial nuclear-staining dyes, did not mediate the formation of the highly fluorescent CuNPs, resulting in highly specific nuclear staining at a reduced cost relative to commercially available methods. Furthermore, we verified the compatibility of the proposed method with other fluorescence-labeling techniques. These results demonstrated the efficacy of this method and its promise as a powerful tool for cell imaging.

The Fluorescent Palette of DNA-Templated Silver Nanoclusters for Biological Applications

Recently years have witnessed a surge in application of DNA-AgNCs in optics, catalysis, sensing, and biomedicine. DNA-templated silver nanoclusters (DNA-AgNCs), as emerging fluorophores, display superior optical performance since their size is close to the Fermi wavelength. DNA-AgNCs possess unique features, including high fluorescence quantum yields and stability, biocompatibility, facile synthesis, and low toxicity, which are requisite for fluorescent probes. The fluorescent emission of DNA-AgNCs can cover the violet to near-infrared (NIR) region by varying the DNA sequences, lengths, and structures or by modifying the environmental factors (such as buffer, pH, metal ions, macromolecular polymers, and small molecules). In view of the above excellent properties, we overview the DNA-AgNCs from the viewpoints of synthesis and fluorescence properties, and summarized its biological applications of fluorescence sensing and imaging.

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.

Highly stable folic acid functionalized copper-nanocluster/silica nanoparticles for selective targeting of cancer cells

In this paper, we present a novel strategy to construct folic acid functionalized conjugated Cu nanoclusters (CuNCs) and silica (SiO₂) nanocomposites for targeted detection of cancer cells. First of all, BSA capped CuNCs were encapsulated into a SiO₂ matrix. The resulting CuNCs@SiO₂ nanoparticles showed bright red fluorescence with an enhanced photoluminescence quantum yield compared with free CuNCs, as well as improved stability in a complex biological environment owning to the protection of the SiO₂ matrix. Upon attachment of folic acid via the poly-l-lysine conjugates (PLL-FA) on the surface of CuNCs@SiO₂ driven by electrostatic interaction, the as-prepared CuNCs@SiO₂/PLL-FA nanocomposites are capable of selectively recognizing folate receptor (FR) over-expressed cancer cells rather than FR-negative cells. The cell viability assay proved the low biotoxicity of CuNCs@SiO₂/PLL-FA nanocomposites toward living cells and the in vitro cellular imaging assay results demonstrated their selective endocytosis of FR-positive cells (KB cells), bringing about red fluorescence labeling within the cells. Intriguingly, our strategy provides a novel route to synthesize functional CuNCs@SiO₂/PLL-FA nanocomposites equipped with superior fluorescence properties, high stability against external stimuli and good biocompatibility, and have great application potential in bioimaging imaging and targeted cell detection.

Folic acid functionalized CuNCs@SiO₂ nanocomposites with superior fluorescence properties, high stability and good biocompatibility for targeted cell imaging.

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.

Target-induced in-situ formation of fluorescent DNA-templated copper nanoparticles by a catalytic hairpin assembly: application to the determination of DNA and thrombin

A fluorometric method is described for nucleic acid signal amplification through target-induced catalytic hairpin assembly with DNA-templated copper nanoparticles (Cu NPs). The toehold-mediated self-assembly of three metastable hairpins is triggered in presence of target DNA. This leads to the formation of a three-way junction structure with protruding mononucleotides at the 3' terminus. The target DNA is released from the formed branched structure and triggers another assembly cycle. As a result, plenty of branched DNA becomes available for the synthesis of Cu NPs which have fluorescence excitation/emission maxima at 340/590 nm. At the same time, the branched structure protects the Cu NPs from digestion by exonuclease III. The unreacted hairpins are digested by exonuclease III, and this warrants a lower background signal. The method can detect ssDNA (24 nt) at low concentration (44 pM) and is selective over single-nucleotide polymorphism. On addition of an aptamer, the strategy can also be applied to the quantitation of thrombin at levels as low as 0.9 nM. Graphical abstractSchematic representation of target-induced catalytic hairpin assembly to form branched DNA template for the in situ synthesis of fluorescent Cu nanoparticles.

Label-free detection of miRNA cancer markers based on terminal deoxynucleotidyl transferase-induced copper nanoclusters

The variations in microRNA (miRNA) expression levels can be useful biomarkers for the diagnosis of different cancers. In this work, a label-free and sensitive fluorescent method for detection of miRNA-21 is described based on duplex-specific nuclease (DSN) assist target recycling and terminal deoxynucleotidyl transferase (TdT) induced copper nanoclusters (CuNCs). In the absence of target, the 3'-phosphorylated probe DNA cannot be hydrolyzed by DSN and extended by TdT, and failed to synthesizing fluorescent CuNCs. However, the target miRNA-21 can caused the digestion of probe DNA with DSN, releasing primer DNA with 3'-OH. After that, the primer DNA can forms long poly T with the assistance of TdT, leading to synthesize high fluorescent CuNCs. The fluorescence change of CuNCs can be used to identify the concentration of target miRNA-21. Under optimal experimental conditions, this strategy could quantitatively detect miRNA-21 down to 18.7 pM. We have also demonstrated the practical application of our proposed method for monitoring miRNA-21 expression levels in cancer cells. Moreover, this method show good specificity for miRNA-21 detection due to the strong preference of DSN for cutting perfectly matched DNA/RNA duplex, which holds great potential for highly specific quantification of biomarkers in bioanalysis and clinical diagnosis.