Selective dsDNA-templated formation of copper nanoparticles in solution

Construction of a Sensing Platform Based on DNA-Encoded Magnetic Beads and Copper Nanoclusters for Viral Gene Analysis with Target Recycling Amplification

The rapid and accurate monitoring of viral genes plays an important role in the area of disease diagnosis, biomedical research, and food safety. Herein, we successfully designed a sensing system that combined the technologies of target DNA recycling amplification, magnetic separation, and in situ formation of fluorescent copper nanoclusters (CuNCs) for viral DNA analysis. In the presence of target viral DNA (tDNA), a large quantity of output DNA (oDNA) was produced from hairpin DNA (hDNA) through an exonuclease III-assisted target recycling amplification strategy. Magnetic beads (MBs) labeled with capture DNA (cDNA) were hybridized with oDNA, and the partially complementary oDNA served as a bridge that could link AT-rich dsDNA on the surface of MBs, which led to a decrease of AT-rich dsDNA in solution after magnetic separation. On account of the lack of AT-rich dsDNA as a template in solution, in situ formation of fluorescent CuNCs was blocked, which resulted in a decrease in the fluorescence intensity at 590 nm. Therefore, taking advantage of one-step magnetic separation and in situ formation of CuNCs, the target viral DNA was sensitively and specifically detected in a linear range from 5 pM to 5 nM with a detection limit of 1 pM. The MB-based platform was not only reusable but also achieved magnetic separation, which could eliminate interferences in complex samples. The assay combining the MB-based probe with fluorescent CuNCs provided a universal, label-free, and reusable platform for viral DNA detection.

Dynamic metallization of spherical DNA via conformational transition into gold nanostructures with controlled sizes and shapes

Despite the reversible condensation properties of DNA, DNA metallization during controlled conformational transitions has been rarely investigated. We perform dynamic metallization of spherically condensed DNA nanoparticles (DNA NPs) via a globule-to-coil transition. A positively charged new Au³⁺ reagent is prepared via ligand-exchange of conventional complex Au³⁺ ions, which was used to synthesize spherically condensed DNA NPs simply based on the fundamental electrostatic and coordinative interactions between DNA and Au³⁺ions. Interestingly, the size of the Au³⁺-condensed DNA NPs (Au³⁺-DNA NPs) and the type of reducing agents lead to the formation of different Au nanostructures with unprecedented morphologies (cracked NPs, bowl-shaped NPs, and small NPs), owing to the controlled conformational changes in the Au³⁺-DNA NPs during metallization. The condensed DNA NPs play significant roles for Au nanostructures as (1) the dynamic template for the synthesis, (2) the reservoir and supply of Au³⁺ for the growth, and (3) the surface stabilizer. The synthesized Au nanostructures are remarkably stable against high ionic strength and exhibit catalytic activities and excellent SERS properties. This is the first study on the morphological control and concomitant dynamic metallization of spherically condensed DNA, proposing new synthetic routes for bioinorganic nanomaterials.

Self-Assembly of Precision Noble Metal Nanoclusters: Hierarchical Structural Complexity, Colloidal Superstructures, and Applications

Ligand protected noble metal nanoparticles are excellent building blocks for colloidal self-assembly. Metal nanoparticle self-assembly offers routes for a wide range of multifunctional nanomaterials with enhanced optoelectronic properties. The emergence of atomically precise monolayer thiol-protected noble metal nanoclusters has overcome numerous challenges such as uncontrolled aggregation, polydispersity, and directionalities faced in plasmonic nanoparticle self-assemblies. Because of their well-defined molecular compositions, enhanced stability, and diverse surface functionalities, nanoclusters offer an excellent platform for developing colloidal superstructures via the self-assembly driven by surface ligands and metal cores. More importantly, recent reports have also revealed the hierarchical structural complexity of several nanoclusters. In this review, the formulation and periodic self-assembly of different noble metal nanoclusters are focused upon. Further, self-assembly induced amplification of physicochemical properties, and their potential applications in molecular recognition, sensing, gas storage, device fabrication, bioimaging, therapeutics, and catalysis are discussed. The topics covered in this review are extensively associated with state-of-the-art achievements in the field of precision noble metal nanoclusters.

L-Histidine-DNA interaction: a strategy for the improvement of the fluorescence signal of poly(adenine) DNA-templated gold nanoclusters

An interesting phenomenon is described that the fluorescence signal of poly(adenine) (A) DNA-templated gold nanoclusters (AuNCs) is greatly improved in the presence of L-histidine by means of L-histidine-DNA interaction. The modified nanoclusters display strong fluorescence emission with excitation/emission maxima at 290/475 nm. The fluorescence quantum yield (QY) is improved from 1.9 to 6.5%. Fluorescence enhancement is mainly ascribed to the L-histidine-DNA interaction leading to conformational changes of the poly(A) DNA template, which offer a better microenvironment to protect AuNCs. The assay enables L-histidine to be determined with good sensitivity and a linear response that covers the 1 to 50 nM L-histidine concentration range with a 0.3 nM limit of detection. The proposed method has been applied to the determination of imidazole-containing drugs in pharmaceutical samples. A turn-on fluorescent method has been designed for the sensitive detection of L-histidine as well as imidazole-containing drugs on the basis of the L-histidine-DNA interaction.

Catalytic hairpin assembly-based electrochemical biosensor with tandem signal amplification for sensitive microRNA assay

We demonstrate for the first time the construction of a low background electrochemical biosensor with tandem signal amplification for sensitive microRNA assay based on target-activated catalytic hairpin assembly (CHA) of heteroduplex-templated copper nanoparticles. This electrochemical biosensor exhibits high sensitivity, good specificity, single-base mismatch discrimination capability, excellent stability and reproducibility, and it can sensitively detect microRNA in cancer cells.

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.

Functional Nucleic Acid Nanomaterials: Development, Properties, and Applications

Functional nucleic acid (FNA) nanotechnology is an interdisciplinary field between nucleic acid biochemistry and nanotechnology that focuses on the study of interactions between FNAs and nanomaterials and explores the particular advantages and applications of FNA nanomaterials. With the goal of building the next-generation biomaterials that combine the advantages of FNAs and nanomaterials, the interactions between FNAs and nanomaterials as well as FNA self-assembly technologies have established themselves as hot research areas, where the target recognition, response, and self-assembly ability, combined with the plasmon properties, stability, stimuli-response, and delivery potential of various nanomaterials can give rise to a variety of novel fascinating applications. As research on the structural and functional group features of FNAs and nanomaterials rapidly develops, many laboratories have reported numerous methods to construct FNA nanomaterials. In this Review, we first introduce some widely used FNAs and nanomaterials along with their classification, structure, and application features. Then we discuss the most successful methods employing FNAs and nanomaterials as elements for creating advanced FNA nanomaterials. Finally, we review the extensive applications of FNA nanomaterials in bioimaging, biosensing, biomedicine, and other important fields, with their own advantages and drawbacks, and provide our perspective about the issues and developing trends in FNA nanotechnology.

Fluorescence resonance energy transfer using DNA-templated copper nanoparticles for ratiometric detection of microRNAs

We examined the effectiveness of a ratiometric method using DNA-templated copper nanoparticles, which can function as a probe for fluorescence resonance energy transfer. This method in combination with PCR successfully detected the target microRNA, which corresponded well with the results obtained by quantitative reverse transcription PCR.

Recent advances in templated synthesis of metal nanoclusters and their applications in biosensing, bioimaging and theranostics

As a kind of promising nanomaterials, metal nanoclusters (MNCs) generally composed of several to hundreds of metal atoms have received increasing interest owing to their unique properties, such as ultrasmall size (<2 nm), fascinating physical and chemical properties, and so on. Recently, template-assisted synthesis of MNCs (e.g., Au, Ag, Cu, Pt and Cd) has attracted extensive attention in biological fields. Up to now, various templates (e.g., dendrimers, polymers, DNAs, proteins and peptides) with different configurations and spaces have been applied to prepare MNCs with the advantages of facile preparation, controllable size, good water-solubility and biocompatibility. Herein, we focus on the recent advances in the template-assisted synthesis of MNCs, including the templates used to synthesize MNCs, and their applications in biosensing, bioimaging, and disease theranostics. Finally, the challenges and future perspectives of template-assisted synthesized MNCs are highlighted. We believe that this review could not only arouse more interest in MNCs but also promote their further development and applications by presenting the recent advances in this area to researchers from various fields, such as chemistry, material science, physiology, biomedicine, and so on.

dsDNA-templated fluorescent copper nanoparticles for the detection of lipopolysaccharides

The introduction of lipopolysaccharides (LPS) or endotoxins that originate from Gram-negative bacteria into the human blood stream induces a severe immune response that can lead to septic shock, and even death. Hence, the accurate detection of LPS is of great importance in the medical and pharmaceutical sectors. This paper proposes a novel label-free fluorescence assay for the detection of LPS utilizing aptamers and the interference synthesis of dsDNA-templated copper nanoparticles. The assay can be performed at room temperature and does not require expensive reagents. The proposed assay has a limit of detection of 0.95 ng ml-1 of LPS, and the fluorescence emission from the copper nanoparticles was found to vary linearly with the concentration of LPS over a wide range (1 to 105 ng ml-1) with R2 = 0.9877.

Fabrication of multiple molecular logic gates made of fluorescent DNA-templated Au nanoclusters

A universal platform of label-free multiple molecular logic gates have been constructed by taking the advantage of DNA-AuNCs.

The spatial organization of trace silver atoms on a DNA template

DNA with programmable information can be used to encode the spatial organization of silver atoms. Based on the primary structures of a DNA template containing a controllable base arrangement and number, the surrounding environment and cluster together can induce the folding of the DNA template into an appropriate secondary structure for forming AgNCs with different fluorescence emissions, such as i-motif, G-quadruplex, dimeric template, triplex, monomeric or dimeric C-loop, emitter pair, and G-enhancer/template conjugate. Stimuli can induce the dynamic structural transformation of the DNA template with a recognition site for favourably or unfavourably forming AgNCs, along with varied fluorescence intensities and colours. The array of several or more of the same and different clusters can be performed on simple and complex nanostructures, while maintaining their original properties. By sorting out this review, we systematically conclude the link between the performance of AgNCs and the secondary structure of the DNA template, and summarize the precise arrangement of nanoclusters on DNA nanotechnology. This clear review on the origin and controllability of AgNCs based on the secondary structure of the DNA template is beneficial for exploring the new probe and optical devices.

Efficient Editing of Silver Nanoclusters by Changing Simply One Cytosine in a DNA Template

DNA with genetic information was edited to regulate and repair the structure and function of a protein. In DNA nanotechnology, DNA with programmable information can be designed to edit the fluorescence intensity and emissive colors of DNA-stabilized silver nanoclusters (DNA/AgNCs). By introducing and moving one cytosine in the spacer of the emitter domain, we have built up a simple strategy to regulate the excitation and emission wavelengths of AgNCs. When replacing thymine in the spacer of the emitter with one cytosine, the expected excitation and emission change do not occur. However, after moving the introduced cytosine, DNA templates produce AgNCs with extremely different excitation and emission wavelengths from those of the initial template, leading to a template for near-infrared (NIR) emissive species with the highest fluorescence intensity. The formation of AgNCs induces the DNA template into condensed secondary structure based on an altered migration rate in PAGE. The simple strategy of moving one cytosine in a spacer in the emitter domain can enrich the library of templates for synthesizing diverse DNA/AgNCs and has great potential in bioimaging and probe design.

A turn-on fluorescence strategy for biothiols determination by blocking Hg(II)-mediated fluorescence quenching of adenine-rich DNA-templated gold nanoclusters

Fluorescent adenine (A)-rich DNA-templated gold nanoclusters were demonstrated to be a novel probe for determination of biothiols (including cysteine, glutathione, and homocysteine). Fluorescence intensity of adenine-rich DNA-templated gold nanoclusters could be greatly quenched by Hg(II) ions through the formation of a gold nanoclusters-Hg(II) system. When biothiols (cysteine as the model) were introduced into the system, the fluorescence intensity recovered due to the formation of a more stable Hg(II)-thiol coordination complex using Hg-S metal-ligand bonds, which inhibited the Hg(II)-mediated fluorescence quenching of adenine-rich DNA-templated gold nanoclusters. Based on this fluorescence phenomenon, an on-off-on fluorescence strategy was designed for the sensitive determination of biothiols. The method allowed sensitive detection of cysteine with a linear detection range from 100 nM to 5 μM and a limit of detection of 30 nM. Additionally, the assay can be applied for detection of biothiol levels in human plasma samples. Therefore, it can provide a simple and rapid fluorescent platform for biothiol detection.

Single-strand DNA-scaffolded copper nanoclusters for the determination of inorganic pyrophosphatase activity and screening of its inhibitor

A fluorescence method for the determination of inorganic pyrophosphatase (PPase) activity has been established based on copper nanoclusters (CuNCs). The polythymine of 40 mer (T40) acts as a template for the reduction reaction from Cu²⁺ to Cu⁰ by ascorbic acid (AA). This reaction leads to the formation of fluorescent CuNCs with excitation/emission peaks at 340/640 nm. However, the higher binding affinity between inorganic pyrophosphate (PPi) and Cu²⁺ hinders the effective formation of CuNCs. This shows low fluorescence intensity. PPase catalyzes the hydrolysis of PPi into Pi during which free Cu²⁺ ions are produced. This facilitates the formation of fluorescent CuNCs. Thus, the fluorescence intensity was restored. The fluorescence enhancement of the system has a linear relationship with PPase activity in the range 0.3 to 20 mU·mL^-1, and the detection limit is0.2 mU·mL^-1. The relative intensity (I/I₀) at 640 nm for the analytical solution versus system is also employed to screen the inhibitor for PPase with high efficiency. Graphical abstract Schematic representation of a fluorescent assay for the determination of inorganic pyrophosphatase activity and screening its inhibitor based on single-strand polythymine-scaffolded copper nanoclusters.

A novel fluorescent nanoprobe that based on poly(thymine) single strand DNA-templated copper nanocluster for the detection of hydrogen peroxide

In this paper, a label-free fluorescence nanoprobe is constructed based on poly(thymine) single strand DNA-templated Copper nanocluster (denote as: T-CuNCs) for the detection of hydrogen peroxide. In the assay, the fluorescent T-CuNCs will generate though the reaction of Cu²⁺, poly(thymine) and sodium ascorbate. However, the hydroxyl radical (^.OH) will generated in the presence of H₂O₂, which is able to induced the oxidative lesions of poly(thymine) single chain DNA and lead to the poly(thymine) being splitted into shorter or single oligonucleotide fragments and lose the ability to template the fluorescent T-CuNCs again. Therefore, H₂O₂ can be detected by monitoring the fluorescence strength change of T-CuNCs. The experimental results show that the fluorescence intensity change of T-CuNCs has fantastic linearity versus H₂O₂ concentration in the range of 1-30 μM (R² = 0.9947) and 30-80 μM (R² = 0.9972) with the limit of detection (LOD) as low as 0.5 μM (S/N = 3). More important, the fluorescent nanoprobe was also successfully utilized on the detection of H₂O₂ in serum samples. Therefore, a label-free, costless and effective fluorescence method has been established for the detection of H₂O₂, the intrinsic properties of the nanoprobe endow its more potential applications in chemical and biological study.

Water-soluble luminescent copper nanoclusters as a fluorescent quenching probe for the detection of rutin and quercetin based on the inner filter effect

In the present study, we proposed a simple, sensitive and selective fluorescence method for the detection of rutin (Rut) and quercetin (Que) based on the inner filter effect (IFE) utilizing water- soluble cysteine-stabilized copper nanoclusters (Cys-CuNCs) as a fluorescent probe. The Cys-CuNCs were successfully synthesized and characterized using UV-visible absorption, emission, Fourier-transform infrared (FT-IR) spectroscopy, fluorescence lifetime, high resolution transmission electron microscopy (HR-TEM) and zeta potential measurements. Cys-CuNCs exhibited bluish-green luminescence under UV light with characteristic emission maxima at 486 nm. Cys-CuNCs was successfully exploited as fluorescent probes for the detection of Rut/Que. The addition of increasing concentrations of Rut/Que led to a gradual decrease in the emission intensity of Cys-CuNCs. The decrease in Cys-CuNC emission intensities were attributed to the strong IFE and static quenching mechanism. The calculated limit of detection values for Rut and Que were as low as 0.021 μM and 0.035 μM, respectively. The Cys-CuNCs sensing probe exhibited excellent selectivity in the presence of other potential interfering compounds. Furthermore, the present method was successfully applied to the analysis of both Rut and Que in biological samples.

DNA functionalized metal and metal oxide nanoparticles: principles and recent advances in food safety detection

The frequent occurrence of food safety incidents has given rise to unprecedented concern about food contamination issues for both consumers and the industry. Various contaminations in food pose serious threats to food safety and human health. Many detection methods were studied to address the challenge. Recently, biosensors relying on deoxyribonucleic acid (DNA)-functionalized nanoparticles have been developed as an efficient and effective detection method. In the current review, the strategies for DNA assembly metal and metal oxide nanoparticles are elaborated, recent applications of the sensors based on DNA-functionalized nanoparticles in food contaminant detection are discussed. Pathogenic bacteria, heavy metal ions, mycotoxins, antibiotics, and pesticides are covered as food contaminants. Additionally, limitations and future trends of functionalized nanoparticles-based technology are also presented. The current review indicates that DNA-functionalized metal and metal oxide nanoparticles are a novel nanomaterial with unique biological and physical properties for developing electrochemical, fluorescent, colourimetric and surface-enhanced Raman spectroscopy (SERS) sensors, etc. Compared with conventional detection techniques, DNA-functionalized metal and metal oxide nanoparticles have considerable advantages with high accuracy, high specificity, micro-intelligence, and low cost. Nevertheless, the stability of these sensors and the limitations of real-time detection are still under discussion. Therefore, more tolerant, portable, and rapid DNA sensors should be developed to better the real-time monitoring of harmful contaminants.

Fluorescent detection of Cu (II) ions based on DNAzymatic cascaded cyclic amplification

A fluorescent biosensor based on the cascaded cyclic amplification-lighted copper nanoparticles has been developed, optimized, and validated. In the double-modular cascaded cyclic amplification, a DNAzymatic cyclic amplification unit transforms metal ion signal to specific DNA sequences, and a linear/exponential integrated amplification unit converts as-prepared DNA codes to identical thymine (T)-rich DNA templates. T-rich scaffolds can induce the generation of red fluorescent copper nanoparticles, with fluorescence emission at 625 nm upon the excitation at 340 nm, as signal vehicles for quantitative detection of metal ions. Copper ions, selected as the model target, could be detected in a wide linear range from 10 to 10⁴ nM depending on the increased fluorescent intensity, and the detection limit is 5.6 ± 0.52 nM (n = 3) within 40 min, which is 4 orders of magnitude lower than the limits set in drinking water. In the detection of Cu²⁺ in real tap and lake water, the results between inductively coupled plasma mass spectrometry (ICP-MS) and our proposed biosensor were consistent, illustrating the practicability of the fabricated method. In summary, the established fluorescent biosensor compensates the deficiency of immunoassays failing to analyze metal ions, broadens ranges of biomarkers responding to cleaved DNAzymes, provides an open platform sensing different metal ions, and meets the increasing need for the ultrasensitive detection in the field of food safety, environmental monitoring, and medical diagnosis.

A Label-Free Fluorescent Sensor Based on the Formation of Poly(thymine)-Templated Copper Nanoparticles for the Sensitive and Selective Detection of MicroRNA from Cancer Cells

In this work, a simple and label-free fluorescence “off” to “on” platform was designed for the sensitive and selective detection of microRNA (miRNA) in cancer cells. This method utilized a padlock DNA-based rolling circle amplification (P-RCA) to synthesize fluorescent poly(thymine) (PolyT) which acted as a template for the synthesis of copper nanoparticles (CuNPs) within 10 minutes under mild conditions. While the repeated PolyT sequence was used as the template for CuNP synthesis, other non-PolyT parts (single strand-DNAs without the capacity to act as the template for CuNP formation) served as “smart glues” or rigid linkers to build complex nanostructures. Under the excitation wavelength of 340 nm, the synthesized CuNPs emitted strong red fluorescence effectively at 620 nm. To demonstrate the use of this method as a universal biosensor platform, lethal-7a (let-7a) miRNA was chosen as the standard target. This sensor could achieve highly sensitive and selective detection of miRNA in the presence of other homologous analogues for the combination of P-RCA with the fluorescent copper nanoparticle. Overall, this novel label-free method holds great potential in the sensitive detection of miRNA with high specificity in real samples.

Handheld fluorometer for in-situ melamine detection via interference synthesis of dsDNA-templated copper nanoparticles

Fluorescent copper nanoparticles templated by dsDNA have gained significant research interest as they are inexpensive and easy to synthesize, and have found applications in the detection of a wide range of analytes. The presence of the analyte in the reaction mixture interferes with the synthesis of the copper nanoparticles and the subsequent drop in fluorescence can be correlated to the concentration of the analyte present in the solution. Analyte detection using copper nanoparticle-based assays is amenable for in-situ applications as the test does not require expensive reagents and can be performed at room temperature. However, expensive and sophisticated detection systems are required for the detection of copper nanoparticles due to the low fluorescence emission signal from these nanoparticles. This restricts the use of the technology to centralized labs. Utilizing a recently developed chemical technique for fluorescence enhancement, this paper presents the first report of a handheld fluorometer capable of detecting DNA-templated copper nanoparticles. The fluorometer is portable and constructed with low-cost, off-the-shelf components like a UV-LED and a PIN photodiode. The performance of the developed system is demonstrated through the detection of melamine in milk samples via the interference synthesis of copper nanoparticles. Melamine is an adulterant used in dairy products that is harmful to human health if present in levels above 1 ppm. The developed system is capable of detecting up to 0.1 ppm of melamine in milk samples with a linear relationship observed between the detector output and concentration of melamine in the range from 0.1 ppm to 100 ppm (R² = 0.9979).

AS1411-Templated Fluorescent Cu Nanomaterial’s Synthesis and Its Application to Detecting Melamine

Herein, we report a novel approach to AS1411-templated formation of fluorescent copper nanomaterials and their application to melamine detection. Fluorescent copper nanomaterials were formed at room temperature by using AS1411 as a template and ascorbic acid as reductant. However, the fluorescence intensity decreased obviously in the presence of melamine. Under the optimized conditions, the quenching fluorescence intensities of copper nanomaterials showed a good linear relationship with the concentration of melamine in the range of 50 μmol/L–120 μmol/L, and the correlation coefficient was 0.9823. In addition, the method was successfully applied in the detection of melamine in milk samples. This method was cost-effective and convenient without any labels or complicated operations. Thus, this work successfully develops the capping AS1411 scaffolds of copper nanomaterials detection of melamine.

DNA Nanoribbon-Templated Self-Assembly of Ultrasmall Fluorescent Copper Nanoclusters with Enhanced Luminescence

Fluorescent copper nanoclusters (CuNCs) have been widely used in chemical sensors, biological imaging, and light-emitting devices. However, individual fluorescent CuNCs have limitations in their capabilities arising from poor photostability and weak emission intensities. As one kind of aggregation-induced emission luminogen (AIEgen), the formation of aggregates with high compactness and good order can efficiently improve the emission intensity, stability, and tunability of CuNCs. Here, DNA nanoribbons, containing multiple specific binding sites, serve as a template for in situ synthesis and assembly of ultrasmall CuNCs (0.6 nm). These CuNC self-assemblies exhibit enhanced luminescence and excellent fluorescence stability because of tight and ordered arrangement through DNA nanoribbons templating. Furthermore, the stable and bright CuNC assemblies are demonstrated in the high-sensitivity detection and intracellular fluorescence imaging of biothiols.

Capping 1,3-propanedithiol to boost the antibacterial activity of protein-templated copper nanoclusters

We have prepared copper nanoclusters (Cu NCs) in the presence of bovine serum albumin (BSA) and 1,3-propanedithiol (PDT). The PDT/BSA-Cu NCs possess great activities against different types of bacteria, including non-multidrug-resistant bacteria (Escherichia coli, Salmonella Enteritidis, Pseudomonas aeruginosa, and Staphylococcus aureus) and multidrug-resistant bacteria (methicillin-resistant S. aureus). Their minimal inhibitory concentration (MIC) values are at least 242-fold and 10-fold lower than that of the free PDT and BSA-Cu NCs, respectively. The PDT/BSA-Cu NCs are strongly bound to the bacterial membrane, in which they induce the generation of ascorbyl (Asc) and perhydroxyl (HOO) radicals that result in disruption of their membrane integrity. At a concentration of 100-fold higher than their MIC for Escherichia coli, the PDT/BSA-Cu NCs exhibit negligible cytotoxicity towards the tested mammalian cells and show insignificant hemolysis. We have further demonstrated that low-cost PDT/BSA-Cu NCs-coated carbon fiber fabrics (CFFs) are effective against antibacterial growth, showing their great potential for antifouling applications.

Exonuclease III-assisted signal amplification strategy for sensitive fluorescence detection of polynucleotide kinase based on poly(thymine)-templated copper nanoparticles

A sensitive and label-free fluorometric method has been developed for the determination of polynucleotide kinase (PNK) activity, by employing exonuclease III (Exo III)-assisted cyclic signal amplification and poly(thymine)-templated copper nanoparticles (polyT-CuNPs). In the presence of PNK, cDNA with 5'-hydroxyl termini was phosphorylated and then hybridized with tDNA to form the cDNA/tDNA duplex, which subsequently triggered the λ exonuclease cleavage reaction, eventually resulting in the release of tDNA. The released tDNA could unfold the hairpin structure of HP DNA to generate partially complementary duplex (tDNA/HP DNA), wherein the HP DNA possessed T-rich sequences (T30) and tDNA recognition sequence. With the help of Exo III digestion, the tDNA was able to initiate the cycle for the generation of T-rich sequences, the template for the formation of fluorescent CuNPs. Conversely, the cDNA could not be cleaved by λ exonuclease without PNK and individual HP DNA could not be hydrolyzed by Exo III. The T-rich sequence was caged in HP DNA, resulting in a weak fluorescence signal. Under optimized conditions, the fluorescence intensity was linearly correlated to a concentration range of 0.001 to 1 U mL-1 with a low detection limit of 2 × 10-4 U mL-1. Considering the intriguing analytical performance, this approach could be explored to screen T4 PNK inhibitors and hold promising applications in drug discovery and disease therapy.

Molecular inversion probe-rolling circle amplification with single-strand poly-T luminescent copper nanoclusters for fluorescent detection of single-nucleotide variant of SMN gene in diagnosis of spinal muscular atrophy

In this study, a simple fluorescent detection of survival motor neuron gene (SMN) in diagnosis of spinal muscular atrophy (SMA) based on nucleic acid amplification test and the poly-T luminescent copper nanoclusters (CuNCs) was established. SMA is a severely genetic diseases to cause infant death in clinical, and detection of SMN gene is a powerful tool for pre- and postnatal diagnosis of this disease. This study utilized the molecular inversion probe for recognition of nucleotide variant between SMN1 (c.840 C) and SMN2 (c.840 C  >  T) genes, and rolling circle amplification with a universal primer for production of poly-T single-strand DNA. Finally, the fluorescent CuNCs were formed on the poly-T single-strand DNA template with addition of CuSO₄ and sodium ascorbate. The fluorescence of CuNCs was only detected in the samples with the presence of SMN1 gene controlling the disease of SMA. After optimization of experimental conditions, this highly efficient method was performed under 50 °C for DNA ligation temperature by using 2U Ampligase, 3 h for rolling circle amplification, and the formation of the CuNCs by mixing 500 μM Cu²⁺ and 4 mM sodium ascorbate. Additionally, this highly efficient method was successfully applied for 65 clinical DNA samples, including 4 SMA patients, 4 carriers and 57 wild individuals. This label-free detection strategy has the own potential to not only be a general method for detection of SMN1 gene in diagnosis of SMA disease, but also served as a tool for detection of other single nucleotide polymorphisms or nucleotide variants in genetic analysis through designing the different sensing probes.

Sensitivity Comparison of Refractive Index Transducer Optical Fiber Based on Surface Plasmon Resonance Using Ag, Cu, and Bimetallic Ag-Cu Layer

A single-mode optical fiber sensor uses surface plasmon resonance (SPR) with a bimetallic silver-copper (Ag-Cu) coating compared to a single layer of Ag and Cu itself. Bimetallic Ag-Cu sensors are constructed by simple fabrication on a side-polished optical fiber, followed by an electron beam evaporation of Ag and Cu films. For this investigation, the thickness of the single Ag layer was set to 30 nm and the single Cu layer was set to 30 nm; whereas for the bimetallic combined Ag-Cu layer the thickness of Ag was 7 nm and Cu 23 nm. The sensor performance was analyzed and compared experimentally and numerically using the COMSOL Multiphysics. A white light source was used with a broad optical bandwidth to provide a range of wavelengths to the optical fiber. The characteristics of the thin layers of Ag, Cu, and Ag-Cu as alcohol sensors were evaluated. We found that Cu was the most sensitive metallic layer compared to the Ag and the bimetallic Ag-Cu layers. For a 100% alcohol concentration, Cu showed a sensitivity of 425 nm/RIU followed by the bimetallic Ag-Cu layer with 108.33 nm/RIU, whereas the Ag layer was not detected. Interestingly, sensitivity reached saturation beyond the 20 nm thick layer of Ag. This shows that the Cu and the bimetallic Ag-Cu layers are suitable for an alcohol-based optical sensor.

Enzyme-free amplified detection of miRNA based on target-catalyzed hairpin assembly and DNA-stabilized fluorescent silver nanoclusters

A simple, cost-effective, sensitive, and selective strategy was developed for microRNA analysis using target-catalyzed hairpin assembly and fluorescent silver nanoclusters.

Nano-fluorescent probes based on DNA-templated copper nanoclusters for fast sensing of thiocyanate

A fast and label-free fluorescent sensor was developed to determine SCN⁻via inhibiting the formation of DNA-templated copper nanoclusters (CuNCs).

Nanoparticles as Emerging Labels in Electrochemical Immunosensors

This review shows recent trends in the use of nanoparticles as labels for electrochemical immunosensing applications. Some general considerations on the principles of both the direct detection based on redox properties and indirect detection through electrocatalytic properties, before focusing on the applications for mainly proteins detection, are given. Emerging use as blocking tags in nanochannels-based immunosensing systems is also covered in this review. Finally, aspects related to the analytical performance of the developed devices together with prospects for future improvements and applications are discussed.

Fluorescent Double-Stranded DNA-Templated Copper Nanoprobes for Rapid Diagnosis of Tuberculosis

In this work, we investigate highly sensitive fluorescent Cu nanoparticles for use as rapid and specific nucleic acid amplification nanoprobes (NPs) for the diagnosis of tuberculosis. After applying polymerase chain reaction (PCR) to a tuberculosis (TB) sample, we demonstrate that the presence of the targeted IS6110 DNA sequence of TB can be easily and directly detected through the in situ formation of DNA-templated fluorescent Cu NPs and subsequently quantified using only a smartphone. Compared to traditional DNA analysis, this sensing platform does not require purification steps and eliminates the need for electrophoresis to confirm the PCR results. After optimization, this dsDNA-Cu NP-PCR method has the ability to analyze clinical TB nucleic acid samples at a detection limit of 5 fg/μL, and the fluorescent signal can be distinguished in only ∼3 min after the DNA has been amplified. Moreover, with the combination of smartphone-assisted imaging analysis, we can further reduce the instrument size/cost and enhance the portability. In this manner, we are able to eliminate the need for a fluorescent spectrophotometer to measure the clinical sample. These results demonstrate this platform's practical applicability, combining a smartphone and on-site analysis while retaining the detection performance, making it suitable for clinical DNA applications in resource-limited regions of the world.

DNA-Templated Fluorescent Nanoclusters for Metal Ions Detection

DNA-templated fluorescent nanoclusters (NCs) have attracted increasing research interest on account of their prominent features, such as DNA sequence-dependent fluorescence, easy functionalization, wide availability, water solubility, and excellent biocompatibility. Coupling DNA templates with complementary DNA, aptamers, G-quadruplex, and so on has generated a large number of sensors. Additionally, the preparation and applications of DNA-templated fluorescent NCs in these sensing have been widely studied. This review firstly focuses on the properties of DNA-templated fluorescent NCs, and the synthesis of DNA-templated fluorescent NCs with different metals is then discussed. In the third part, we mainly introduce the applications of DNA-templated fluorescent NCs for sensing metal ions. At last, we further discuss the future perspectives of DNA-templated fluorescent NCs in the synthesis and sensing metal ions in the environmental and biological fields.

Recent progress in copper nanocluster-based fluorescent probing: a review

Copper nanoclusters (CuNCs) are an attractive alternative to other metal nanoclusters. The synthesis of CuNCs is highly efficient and fast, with low-cost and without any complicated manipulation. Because of their tunable fluorescence and low toxicity, CuNCs have been highly exploited for biochemical sensing. This review (with 172 refs.) summarizes the progress that has been made in the field in the past years. Following an introduction into the fundamentals of CuNCs, the review first focuses on synthetic methods and the fluorescence properties of CuNCs (with subsections on the use of proteins, peptides, DNA and other molecules as templates). This is followed by a section on the use of CuNCs in fluorometric assays, with subsections on the detection of small molecules, proteins, nucleic acids, various other biomolecules including drugs, and of pH values. A further large chapter summarizes the work related to environmental analyses, specifically on determination of metal ions, anions and pollutants. Graphical abstract Schematic representation of the synthesis and potential applications of copper nanocluster (CuNCs) in biochemical analysis, emphatically reflected in some vital areas such as small molecule analysis, biomacromolecule monitoring, cell imaging, ions detection, toxic pollutant, etc.

In situ formation of DNA-templated copper nanoparticles as fluorescent indicator for hydroxylamine detection

Herein, we develop a facile method for selective and sensitive detection of hydroxylamine (HA) based on the in situ formation of DNA templated copper nanoparticles (DNA-CuNPs) as fluorescent probes. It is firstly found that HA as a reducing agent can play a key role in the in situ formation of fluorescent DNA-CuNPs. This special optical property of DNA-CuNPs with (λ ex = 340 nm, λ em = 588 nm) with a mega-Stokes shifting (248 nm) makes it applicable for the turn-on detection of HA. In addition, this fluorescent method has several advantages such as being simple, rapid, and environmentally friendly, because it avoids the traditional organic dye molecules and complex procedures. Under optimized conditions, this platform achieves a fluorescent response for HA with a detection limit of 0.022 mM. Especially, successful detection capability in tap waters and ground waters exhibits its potential to be general method.

Multifunctional CuO nanoparticles with cytotoxic effects on KYSE30 esophageal cancer cells, antimicrobial and heavy metal sensing activities

In this work, fluorescent copper oxide nanoparticles (CuO NPs) were green synthesized using viable cells, cell lysate supernatant (CLS) and protein extracts of luminescent Vibrio sp. VLC. Biogenic CuO NPs were then characterized by XRD, FTIR, UV/Vis spectroscopy, TEM, DLS, and PL spectroscopy. Results showed that CLS method was more efficient for CuO NPs production, therefore CuO NPs synthesized by this method from copper sulfate (CuO NPs-1) and/or copper nitrate (CuO NPs-2) were used for further studies. The crystallite size of polydispersed CuO NPs-1 and CuO NPs-2 were about 8.83 and 8.77 nm, respectively indicating their suitability for biological applications. Antibacterial activity of CuO NPs was determined using broth microdilution, well diffusion agar, and time-kill curves methods. Both CuO NP-1 and CuO NP-2 inhibited bacterial growth at the minimum inhibitory concentration (MIC) of 625 mg/L except St. mutants (MIC = 1250 mg/L). Emission of fluorescent light from the surface of NPs was increased when exposed to Cd²⁺, As²⁺ and Hg²⁺ ions but decreased by Pb²⁺ ions. Results showed that CuO NP-1 had anticancer properties against KYSE30 esophageal cancer cell line (IC₅₀ = 13.96 mg/L) while no higher cytotoxic effects were observed on Human Dermal Fibroblasts (HDF) (IC₅₀ = 48.88 mg/L).

Sensitive CVG-AFS/ICP-MS label-free nucleic acid and protein assays based on a selective cation exchange reaction and simple filtration separation

Nowadays, label-free atomic spectrometric bioassays are attracting great research interest because of their advantages of low cost, simple design and operation, etc. Herein, a novel and simple chemical vapor generation-atomic fluorescence spectrometry (CVG-AFS)/inductively coupled plasma-mass spectrometry (ICP-MS) label-free detection method is presented for highly sensitive and selective assay of DNA and proteins. This work mainly combined a phenomenon that CdTe quantum dots (QDs) can be used to selectively differentiate free Hg2+ and the T-Hg2+-T complex, with the use of simple membrane filtration separation to improve the performance of the label-free bioassay methods. Upon hybridization with the DNA/protein (carcinoembryonic antigen, CEA) target, the T-Hg2+-T hairpin structure was opened and Hg2+ was released; this initiated the cation exchange reaction between Hg2+ and CdTe QDs which released Cd2+ simultaneously. Subsequently, the free Cd2+ was separated by the filtration membrane without separating the CdTe QDs, which could then be separated from the sample matrices for the CVG-AFS/ICP-MS assay. Under the optimal conditions, this method possessed high sensitivity for DNA and CEA determination with limits of detection (LODs) of 0.2 nM and 0.2 ng mL-1, and linear dynamic ranges of 1-160 nM and 0.5-20 ng mL-1, respectively, and exhibited excellent DNA sequence specificity and protein selectivity. This method preserves the advantages of the label-free atomic spectrometric bioassay, and combined with the selective cation exchange reaction and simple filtration separation to improve the performance.

Synthesis of DNA-templated copper nanoparticles with enhanced fluorescence stability for cellular imaging

Fluorescence of DNA-templated copper nanoparticles (DNA-CuNPs) is not stable over time which limits applications in cellular imaging. This is due to the presence of oxygen during synthesis which oxidizes Cu(0) to Cu(II) and also produces the free hydroxyl radical. The authors have prepared DNA-CuNPs with enhanced temporal stability of fluorescence by optimizing the reaction conditions so as to minimize the deleterious effects of oxygen. The operational lifetime of DNA-CuNPs was increased from 25 min to 200 min. Fluorescence spectra of DNA-CuNPs in optimized condition show an emission peak at 650 nm when excited at 340 nm. DNA-CuNPs synthesized in this manner were used for cell imaging. As a proof of concept, the nucleus of a human colon cell line (HCT116) was stained. The method does not involve any chemicals other that copper sulfate and ascorbate. This new approach for generating DNA-CuNPs improves imaging of biological processes and provides a basis for developing other types of DNA-templated nanomaterials. Graphical abstract Schematic presentation of the formation of fluorescent DNA-templated copper nanoparticles (DNA-CuNPs). A large amount of ascorbate provides long operational lifetime for cellular imaging under the condition exposed to oxygen. *Asc^- and **DHA stand for ascorbate and dehydroascorbic acid.

Remote control of charge transport and chiral induction along a DNA-metallohelicate

Herein we present a new strategy to achieve chiral induction and redox switching along the backbone of metallohelicate architectures, wherein a DNA duplex directs the handedness and charge transport properties of a metal-organic assembly more than 60 bonds away (a distance of >10 nm). The quantitative and site-specific binding of copper(i) ions to DNA-templated coordination sites imparts enhanced thermodynamic stability to the assembly, while the DNA duplex transfers its natural right-handed helicity to the proximal and distal metal centers of the helicates. When copper(ii) ions are employed instead of copper(i) ions, spontaneous DNA-mediated reduction occurs, which we propose is followed by a slower change in coordination environment (from pentacoordinate CuII to tetrahedral CuI) to generate copper(i) helicates. We demonstrate that the reduction of the adjacent and distal bis-phenanthroline sites is dependent on their proximity to DNA guanine bases (which act as the electron source). The kinetics of helical charge transport can thus be tuned based on guanine-CuII separation, resulting in a sequence- and distance-dependent redox switch that transfers electronic information from DNA to multiple linearly-arranged metal centers.