Programmable DNA Nanomachine Integrated with Electrochemically Controlled Atom Transfer Radical Polymerization for Antibody Detection at Picomolar Level

The quantitative detection of antibodies is crucial for the diagnosis of infectious and autoimmune diseases, while the traditional methods experience high background signal noise and restricted signal gain. In this work, we have developed a highly efficient electrochemical biosensor by constructing a programmable DNA nanomachine integrated with electrochemically controlled atom transfer radical polymerization (eATRP). The sensor works by binding the target antidigoxin antibody (anti-Dig) to the epitope of the recognization probe, which then initiates the cascaded strand displacement reaction on a magnetic bead, leading to the capture of cupric oxide (CuO) nanoparticles through magnetic separation. After CuO was dissolved, the eATRP initiators were attached to the electrode based on the CuΙ-catalyzed azide-alkyne cycloaddition. The subsequent eATRP reaction results in the formation of long electroactive polymers (poly-FcMMA), producing an amplified current response for sensitive detection of anti-Dig. This method achieved a detection limit at clinically relevant picomolar concentration in human serum, offering a sensitive, convenient, and cost-effective tool for detecting various biomarkers in a wide range of applications.

Surface Plasmon Resonance-Enhanced CdS/FTO Heterojunction for Cu2+ Detection

Copper ion (Cu2+) pollution poses a serious threat to marine ecology and fisheries. However, the complexity of seawater and its interference factors make the online detection of Cu2+ quite challenging. To address this issue, we introduce the concept of the photo-assisted adjustment barrier effect into electrochemical detection, using it as a driving force to generate electrochemical responses. The Schottky barrier demonstrates a remarkable regulatory influence on the electrochemical response under photoexcitation, facilitating the response through Cu2+ adsorption. We developed a 4-MBA-AuNPs/CdS/FTO composite that serves as a sensitive platform for Cu2+ detection, achieving a detection limit of 70 nM. Notably, the photo-assisted adjustment of the barrier effect effectively counters the interference posed by ions in seawater, ensuring accurate detection. Furthermore, the sensor exhibits a promising recovery rate (99.62-104.9%) in real seawater samples, highlighting its practical applications. This innovative approach utilizing the photo-assisted adjustment barrier effect offers a promising path for developing electrochemical sensors that can withstand interference.

Porphyrin Functionalized Carbon Quantum Dots for Enhanced Electrochemiluminescence and Sensitive Detection of Cu2

Porphyrin (TMPyP) functionalized carbon quantum dots (CQDs-TMPyP), a novel and efficient carbon nanocomposite material, were developed as a novel luminescent material, which could be very useful for the sensitive detection of copper ions in the Cu²⁺ quenching luminescence of functionalized carbon quantum dots. Therefore, we constructed a sensitive "signal off" ECL biosensor for the detection of Cu²⁺. This sensor can sensitively respond to copper ions in the range of 10 nM to 10 μM, and the detection limit is 2.78 nM. At the same time, it has good selectivity and stability and a benign response in complex systems. With excellent properties, this proposed ECL biosensor provides an efficient and ultrasensitive method for Cu²⁺ detection.

Polydopamine nanoparticle-mediated, click chemistry triggered, microparticle-counting immunosensor for the sensitive detection of ochratoxin A

A rapid and accurate detection method is needed for the quantitation of ochratoxin A in agricultural products due to its high toxicity. A microparticle-counting immunosensor based on polydopamine nanoparticle-mediated click chemistry was established for the highly-sensitive detection of ochratoxin A. Polydopamine nanoparticles with good biocompatibility and a strong metal-chelating ability were synthesized and conjugated with the antibody. The Coupled compounds were then used as an immune carrier to change the Cu²⁺ concentration via an immuno-reaction. Some of the remaining Cu²⁺ ions were reduced to Cu⁺ ions, which caused azide-polystyrene microspheres and alkyne-polystyrene microspheres to aggregate via a Cu⁺ ion-mediated click reaction. Particle counting was used to distinguish changes in the sizes of the polystyrene microspheres from dispersed to aggregated to detect ochratoxin A. It showed a wide linear detection range of 0.5-800 ng/mL, and a detection limit of 0.2 ng/mL. This assay provides an attractive analytical tool for the accurate detection of trace targets in complex samples.

A Novel Truncated DNAzyme Modified Paper Analytical Device for Point-of-Care Test of Copper Ions in Natural Waters

On-site determination of trace copper ions in natural waters is of great significance to environmental monitoring, and how to develop accurate and specific point-of-care test methods is one critical issue. In the study, a paper-based analytical device (PAD) being modified with a new truncated DNAzyme (CLICK-T, which was derived from a reported DNAzyme-CLICK-17) was developed for Cu ions detection. The detection mechanism was based on Cu(II)-catalyzed azide-alkyne cycloaddition (Cu(II)AAC) reaction. It can directly conduct on-site analysis of Cu(II) ions based on fluorescent signals detected using a mobile phone. In the assay, the CLICK-T was firstly modified on the PADs. Then, water samples containing Cu ions mixed with 3-azido-7-hydroxycoumarin and 3-butyn-1-ol were instantly dripped on PADs and incubated for 20 min. Finally, the PADs were excited at 365 nm and emitted fluorescence which could be analyzed on site using smart phones. The Cu(II) concentration could be quantified through RGB analysis with the aid of iPhone APP software. The limit of detection is 0.1 µM by the naked eye due to the fact that CLICK-T exhibited a good catalytic effect on Cu(II)AAC. The Cu(II) concentration could also be directly detected without using reductant, such as ascorbic acid, which is prone to be oxidized in air. This simplifies the PDA detection process improves its efficiency. The PAD is convenient for the on-site analysis of Cu ions in natural waters.

Fluorescent and colorimetric assay for determination of Cu(II) and Hg(II) using AuNPs reduced and wrapped by carbon dots

To improve the accuracy and specificity of visual sensors for detecting Cu(II) and Hg(II), a fluorescent and colorimetric dual-modal sensor based on Au nanoparticles (AuNPs) prepared by using carbon dots (CDs) was designed. If a sensor is to be applied for the detection of targets in different environmental backgrounds, it needs to have high stability against heat, pH, and salt. To this end, CD-wrapped AuNP probes were fabricated by the in situ reaction of chloroauric acid and reductive CDs. The reductive CDs were prepared with hyperbranched polyethyleneimine (HPEI) as a carbon source. HPEI-CDs not only acted as a reducing agent but also as an excellent stabilizer in the preparation and detection application of the AuNPs. Based on multiple signal responses, including color, UV-Vis absorption, and fluorescence intensity, the HPEI-CD/AuNP nanosensor was used to realize the detection of Cu²⁺ and Hg²⁺ in the linear range 9.0×10^-10-9.0×10^-4 M and 9.0×10^-7-9.0×10^-5 M with low detection limits of 75.6 nM and 281 nM, respectively. In tap water analysis, the recovery of Cu²⁺ and Hg²⁺ by fluorescent range from 109.98-113.31% and 100.65-100.81%, and the RSD values were 0.1159-1.6317% and 3.2-5.4%, respectively. The recovery of Cu²⁺ and Hg²⁺ by colorimetric detection were 99.72-100.14% and 99.88-100.12%, and RSD values were 0.6527-0.6842% and 0.4400-0.8386%, respectively. Importantly, this sensor was applied to the accurate and sensitive detection of Cu²⁺ and Hg²⁺ in tap water and sea water. The multimode readout nanosensor exhibited strong potential for achieving simultaneous detection of two different heavy metal ions in practical applications. The novel multi-mode readout carbon dots/AuNPs sensor for Cu²⁺ and Hg²⁺ detectionshowed high sensitivity and selectivity.

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.

Ion-Imprinted Polymer Modified with Carbon Quantum Dots as a Highly Sensitive Copper(II) Ion Probe

Fluorescence analysis technology and ion imprinting technology are combined to prepare a copper ion fluorescence sensor. Carbon quantum dots (CQDs), with a quantum yield of 79%, were synthesized by a hydrothermal process using citric acid as the carbon source. The prepared CQDs, acting as the fluorophore, were grafted onto the surface of an SBA-15 mesoporous molecular sieve by an amidation reaction. Then, the fluorescent sensor CQDs@Cu-IIP was prepared using a surface imprinting technique with the modified SBA-15 as the substrate, copper ions as a template, tetraethoxysilane as the crosslinker, and 3-aminopropyl-3-ethoxysilane as the functional monomers. The sensor showed strong fluorescence from CQDs and high selectivity due to the presence of Cu(II)-IIP. After the detection conditions were optimized, the fluorescence intensity of the sensor had good linearity with Cu(II) concentration in a linear range of 0.25-2 mg/L and 3-10 mg/L. This CQDs@Cu-IIP was applied to the determination of traces Cu(II) in real water samples and good recoveries of 99.29-105.42% were obtained. The present study provides a general strategy for fabricating materials based on CQDs for selective fluorescence detection of heavy metals.

Supramolecular Template-Directed In Situ Click Chemistry: A Bioinspired Approach to Synthesize G-Quadruplex DNA Ligands

The assembly of guanosine and boronic acids produces anionic hydrogels (G-B hydrogels) that mimic the topology of the DNA G-quadruplex. We herein demonstrate an unconventional approach of using the G-B hydrogel as a supramolecular template that assembles the irreversible formation of DNA G-quadruplex-selective 1,4-triazole ligands from a pool of alkyne-azide building blocks. These generated ligands could also stabilize and strengthen the gel assembly.

Click chemistry as a tool in biosensing systems for sensitive copper detection

Copper detection for diagnostic purposes is an appealing field due to the important biological role copper plays as a trace metal. A convenient strategy for sensing copper is to utilize its catalytic ability. Therefore, this review summarizes approaches for copper determination by Cu^I-catalyzed azide/alkyne cycloaddition (CuAAC). The concept was introduced in 2006 and all contributions made up to the middle of 2020 are covered in this review. The issue is divided into three categories: electrochemical, visual, and fluorescence-based methods. The advantages, as well as the disadvantages, of every group, are discussed in detail. The methodology which allows for the determination of copper content in water and human biological samples from 5 s up to 48 h without complex instrumentation are discussed. The reported range of limit of detection (LOD) was 0.38 aM-20 μM, with 1-10 nM being the typical range. The most successful strategies involved using DNA chains or enzymes in the sensing systems.

A novel imidazole derived colorimetric and fluorometric chemosensor for bifunctional detection of copper (II) and sulphide ions in environmental water samples

Herein, a novel "ON-OFF" colorimetric and fluorometric chemosensor; 1N-allyl-2-(2, 5-dimethoxyphenyl)-4, 5-diphenyl-1H-imidazole (ADPPI), was constructed for sequential determination of Cu²⁺ and S^2- ions in aqueous media. The interaction between chemosensor ADPPI and different metal cations was investigated using UV-VIS and fluorimetric spectroscopy. ADPPI showed a favorable and good interaction with Cu²⁺ ions producing blue colored solution peaked at 610 nm with blue fluorescence at λ_em. = 447 nm. The produced complex between Cu²⁺ ions and ADPPI can be used as a cascade probe for detection of S^2- ions. The detection limits (LODs) were 1.01 nM and 1.25 μM for Cu²⁺ and S^2- ions, respectively (the lowest between the family of colorimetric and fluorometric chemosensors). To further increase the applicability of the proposed method, Cu²⁺ and S^2- ions concentrations were measured in environmental water samples.

Highly Selective Fluorimetric Turn-Off Detection of Copper(II) by Two Different Mechanisms in Calix[4]arene-Based Chemosensors and Chemodosimeters

Isoxazolo-pyrene tethered calix[4]arenes selectively detect copper(II) ions without interference from related perchlorate ions. The fluorescence emission of the probes, synthesised by nitrile oxide alkyne cycloaddition, and characterised by spectroscopic and crystallographic data, is rapidly reduced by Cu(II) ions. Detection limits are in the micromolar or sub-micromolar range (0.3-3.6 μM) based on a 1 : 1 sensor:analyte interaction. Voltammetric behaviour and ¹ H NMR data provide new insights into the sensing mechanism which is dependent on the calixarene substitution pattern. When the calixarene lower rim is fully substituted, Cu(II) detection occurs through a traditional chelation mechanism. In contrast, for calixarenes 1,3-disubstituted on the lower rim, detection takes place through a chemodosimetric redox reaction. The isolation of a calix[4]diquinone from the reaction with excess Cu(ClO₄ )₂ provides confirmation that the sensor-analyte interaction culminates in irreversible sensor oxidation.

A unimolecular DNA fluorescent probe for determination of copper ions based on click chemistry

A homogenous fluorescence method was constructed for Cu²⁺ detection by employing DNA-templated click chemistry and exonuclease reaction. In this strategy, a dumbbell shaped DNA probe, which contained an alkyne group and an azide group at its ends, was designed as the template for the click chemistry reaction, and also the signal probe. In the absence of Cu²⁺, the DNA probe was digested into small oligonucleotide fragments by exonuclease, resulting in a low fluorescence background. However, this DNA probe can be sealed at its two ends by Cu²⁺-induced click chemistry ligation in the presence of Cu²⁺. This closed structure of DNA would remain stable after addition of exonuclease, and could then be stained by SYBR Green I. A strong fluorescence signal was observed, which was related to the concentration of Cu²⁺. This assay showed high selectivity and reached the detection limit of 39 nM. Moreover, the proposed strategy exhibited satisfactory detection results in real complex sample analysis, and has promising application in environmental monitoring and food safety.

A homogenous fluorescence method was constructed for Cu²⁺ detection by employing DNA-templated click chemistry and exonuclease reaction.

Nanopore-Based Strategy for Sensing of Copper(II) Ion and Real-Time Monitoring of a Click Reaction

A straightforward yet efficient, nanopore-based strategy that enables the sensitive detection of copper(II) ion (Cu²⁺) and real-time monitoring of a click reaction is provided. Two single-stranded DNAs (ssDNAs) are designed to act as the preprobes, one being modified with an azide and the other an alkyne. The presence of Cu²⁺ induces the ligation of two ssDNAs via click reaction, leading to the formation of a forked DNA which can quantitatively generate characteristic current signatures when interacts with α-hemolysin (α-HL) nanopore. The assay facilitates a highly selective and sensitive measurement of Cu²⁺ without the need for labels or signal amplification. More importantly, this nanopore platform exhibits excellent performance in real-time monitoring of a copper(I) ion (Cu⁺)-catalyzed click reaction at the single-molecule level, by recording the current signals of the forked DNA generated by click chemistry. The proposed strategy is believed to play an important role in both nanopore sensing and characterization of chemistry reactions, especially coupling reactions.

Tailored therapeutics based on 1,2,3-1H-triazoles: a mini review

Contemporary drug discovery approaches rely on library synthesis coupled with combinatorial methods and high-throughput screening to identify leads. However, due to the multitude of components involved, a majority of optimization techniques face persistent challenges related to the efficiency of synthetic processes and the purity of compound libraries. These methods have recently found an upgradation as fragment-based approaches for target-guided synthesis of lead molecules with active involvement of their biological target. The click chemistry approach serves as a promising tool for tailoring the therapeutically relevant biomolecules of interest, improving their bioavailability and bioactivity and redirecting them as efficacious drugs. 1,2,3-1H-Triazole nucleus, being a planar and biologically acceptable scaffold, plays a crucial role in the design of biomolecular mimetics and tailor-made molecules with therapeutic relevance. This versatile scaffold also forms an integral part of the current fragment-based approaches for drug design, kinetic target guided synthesis and bioorthogonal methodologies.

A turn-on fluorescent BOPHY probe for Cu2+ ion detection

A novel D–π–A type fluorine–boron compound BOPHY-PTZ was synthesized and employed as a “turn on” fluorescent probe for the sensitive detection of Cu²⁺ ions.

Signal-Amplified Lateral Flow Test Strip for Visual Detection of Cu2

A signal-amplified lateral flow test strip (SA-LFTS) for the detection of Cu2+ in aqueous solution was constructed based on Cu+-catalyzed click chemistry and hybridization of single-stranded DNA (ssDNA). Alkyne and azide modified ssDNA acted as specific elements for Cu2+ recognition, and a chemical ligation product formed through Cu+-catalyzed alkyne-azide cycloaddition. Hybridization of ssDNA-labeled gold nanoparticles resulted in high sensitivity, and the output signal could be observed directly by the naked eye. Using the developed SA-LFTS under optimal conditions, Cu2+ could be detected rapidly with limit of detections of 5 nM and 4.2 nM by visual observation and quantitative analysis, respectively. The sensitivity (i.e. the visual limit of detection) of the SA-LFTS was 80-times higher than that of traditional LFTS. The SA-LFTS was applied to the determination of Cu2+ in municipal water and river water samples with the results showing good recovery and accuracy. The developed test strip is promising for point-of-care applications and detection of Cu2+ in the field.

Sensitive detection of mercury and copper ions by fluorescent DNA/Ag nanoclusters in guanine-rich DNA hybridization

In this work, we designed a new fluorescent oligonucleotides-stabilized silver nanoclusters (DNA/AgNCs) probe for sensitive detection of mercury and copper ions. This probe contains two tailored DNA sequence. One is a signal probe contains a cytosine-rich sequence template for AgNCs synthesis and link sequence at both ends. The other is a guanine-rich sequence for signal enhancement and link sequence complementary to the link sequence of the signal probe. After hybridization, the fluorescence of hybridized double-strand DNA/AgNCs is 200-fold enhanced based on the fluorescence enhancement effect of DNA/AgNCs in proximity of guanine-rich DNA sequence. The double-strand DNA/AgNCs probe is brighter and stable than that of single-strand DNA/AgNCs, and more importantly, can be used as novel fluorescent probes for detecting mercury and copper ions. Mercury and copper ions in the range of 6.0-160.0 and 6-240 nM, can be linearly detected with the detection limits of 2.1 and 3.4 nM, respectively. Our results indicated that the analytical parameters of the method for mercury and copper ions detection are much better than which using a single-strand DNA/AgNCs.

New insights into the kinetic target-guided synthesis of protein ligands

This review describes the recent applications of the kinetic target guided synthesis and highlights the new advances of this strategy.

Click chemistry-mediated catalytic hairpin self-assembly for amplified and sensitive fluorescence detection of Cu2+in human serum

Cu⁺-mediated click ligation of DNA leads to catalytic self-assembly of hairpins and amplified fluorescent signals for sensitive detection of Cu²⁺.

A fluorescence turn-on detection of copper(II) based on the template-dependent click ligation of oligonucleotides

In this work, a fluorescence turn-on method for copper(II) detection is reported. A molecular beacon (MB) was designed as a template. Cu(2+) was reduced to Cu(+) in the presence of a reductant (ascorbic acid). Two short single-stranded oligonucleotides one was labeled with a 5'-alkyne and the other with 3'-azide group, proceeded a template-dependent chemical ligation through the Cu(I)-catalyzed azide-alkyne cycloaddition. The newly generated click-ligated long chain oligonucleotide, which was complementary to the MB, opened the MB hairpin structure and resulted in a turn on fluorescence. The increase in fluorescence intensity is directly proportional to the amount of Cu(2+) added to the assay solution. The present assay is quite sensitive and allows the detection of 2 nM Cu(2+). The described assay also exhibits high selectivity over other metal ions.

Advancements in the mechanistic understanding of the copper-catalyzed azide-alkyne cycloaddition

The copper-catalyzed azide-alkyne cycloaddition (CuAAC) is one of the most broadly applicable and easy-to-handle reactions in the arsenal of organic chemistry. However, the mechanistic understanding of this reaction has lagged behind the plethora of its applications for a long time. As reagent mixtures of copper salts and additives are commonly used in CuAAC reactions, the structure of the catalytically active species itself has remained subject to speculation, which can be attributed to the multifaceted aggregation chemistry of copper(I) alkyne and acetylide complexes. Following an introductory section on common catalyst systems in CuAAC reactions, this review will highlight experimental and computational studies from early proposals to very recent and more sophisticated investigations, which deliver more detailed insights into the CuAAC's catalytic cycle and the species involved. As diverging mechanistic views are presented in articles, books and online resources, we intend to present the research efforts in this field during the past decade and finally give an up-to-date picture of the currently accepted dinuclear mechanism of CuAAC. Additionally, we hope to inspire research efforts on the development of molecularly defined copper(I) catalysts with defined structural characteristics, whose main advantage in contrast to the regularly used precatalyst reagent mixtures is twofold: on the one hand, the characteristics of molecularly defined, well soluble catalysts can be tuned according to the particular requirements of the experiment; on the other hand, the understanding of the CuAAC reaction mechanism can be further advanced by kinetic studies and the isolation and characterization of key intermediates.

Toehold-mediated nonenzymatic DNA strand displacement as a platform for DNA genotyping

Toehold-mediated DNA strand displacement provides unique advantages in the construction and manipulation of multidimensional DNA nanostructures as well as nucleic acid sequence analysis. We demonstrate a step change in the use of toehold-mediated DNA strand displacement reactions, where a double-stranded DNA duplex, containing a single-stranded toehold domain, enzymatically generated and then treated as a molecular target for analysis. The approach was successfully implemented for human DNA genotyping, such as gender identification where the amelogenin gene was used as a model target system, and detecting single nucleotide polymorphisms of human mitochondrial DNA. Kinetics of the strand displacement was monitored by the quenched Förster resonance energy transfer effect.

A molecular beacon and graphene oxide-based fluorescent biosensor for Cu(2+) detection

In this work, we report a "turn-on" fluorescent strategy for the direct detection of Cu(2+) in solutions using molecular beacons (MBs) and graphene oxide (GO). MBs are special single-stranded DNA and carry fluorescence sources. GO is a new nanomaterial having remarkable physical properties. In the sensing system, GO was used as an efficient fluorescence quencher upon the adsorption of MBs, which reduced the background signal and made the detection method highly sensitive. In the presence of Cu(2+), the MBs were cut into short pieces and released by the GO, leading to fluorescence restoration. The detection limit of the sensing strategy was ∼50nM, which is sufficiently sensitive for practical applications. The sensing method also exhibited high selectivity in testing samples containing other metal ions. The application of the method for drinking water is demonstrated.

A fluorescence "turn-on" chemodosimeter for Cu2+ in aqueous solution based on the ion promoted oxidation

We developed a novel method for Cu(2+) detection based on the ion promoted oxidation reaction. Chemodosimeter L (weak fluorescence) can be oxidized into 3-benzothiazoly-7-N,N-diethylaminocoumarin (strong green fluorescence, coumarin 6) by Cu(2+) with high selectivity and sensitivity in HEPES (10 mM, pH = 7.4) buffer containing 50% (v/v) water-CH(3)CN solution.