Substrate Strand Research Articles

Hybridization chain reaction and DNAzyme-based dual signal amplification strategy for sensitive fluorescent sensing of aflatoxin B1 by using the pivot of triplex DNA

This work developed an enzyme-free fluorescent aptasensor for sensitive aflatoxin B1 (AFB1) detection based on a dual signal amplification strategy of hybridization chain reaction (HCR) and Zn2+-dependent DNAzyme. In the presence of AFB1, the aptamer specifically binds to the target, releasing the blocking DNA, which can initiate HCR between hairpin probes H1 and H2. With the addition of the substrate strand (Zn-Sub) and enzyme strand (Zn-Enz) of DNAzyme, HCR product can hybridize with Zn-Sub and Zn-Enz to form triplex DNA and Y-shaped structure together, which further activates the DNAzyme to cleave Zn-Sub. Then, two separated fragments of Zn-Sub respectively hybridize with the fluorescent probe and quencher probe, which results in a dramatic increase in the fluorescence intensity. The proposed aptasensor shows high sensitivity and selectivity for AFB1 detection with a detection limit of 0.22 nmol/L in a linear range of 0.4–16 nmol/L. Moreover, the fluorescent aptasensor exhibits acceptable applicability for detecting AFB1 in oil samples with satisfactory recoveries of 92.2–107.8%. Results are also in agreement with those of the ELISA method, indicating that the fluorescent sensing strategy has great potential applications in food safety control.

Reversible Ratiometric Electrochemiluminescence Biosensor Based on DNAzyme Regulated Resonance Energy Transfer for Myocardial miRNA Detection.

Myocardial miRNAs in peripheral blood are closely related to the pathogenic process of myocardial infarction. Rapid identification and accurate quantification of myocardial miRNAs are of great significance to clinical interventions for treating cardiovascular lesions. Therefore, a ratiometric electrochemiluminescence (ECL) biosensor integrating DNAzyme with a resonance energy transfer (RET) system was designed to detect myocardial miRNA. The dual-signal system was composed of rA marked substrate strand functionalized CdTe quantum dots (QDs) as reductive-oxidative (R-O) emitters and Cy5-labeled strand-functionalized Ru(bpy)32+-filled silica nanoparticles (RuSi NPs) as oxidative-reductive (O-R) emitters. In the presence of target miRNA, DNAzyme was activated to cut substrate strands on the CdTe QDs and release triggers for opening hairpin probes. Then, the Cy5 molecule-labeled hairpin DNA on the RuSi NPs was opened to introduce Cy5 molecules and RuSi NPs into the system. The R-O ECL was quenched by ECL-RET between CdTe QDs and Cy5 molecules and the O-R ECL was introduced by the RuSi NPs. In this way, based on the simultaneous changing of the ECL signal, the dual-potential dynamic signal ratiometric ECL sensing platform was developed. By measuring the ratio of O-R ECL signal to R-O ECL signal, the concentration of miRNA-499 was accurately quantified in the range of 10 fM to 10 nM, and the detection limit was as low as 2.44 fM (S/N = 3). This DNAzyme guided dual-potential ratiometric ECL method provides a sensitive and reliable method for myocardial miRNA detection, and it has great potential in clinical diagnosis and treatment.

Label-free DNAzyme for highly sensitive detection of multiple biomolecules in real samples through target-triggered catalytic cleavage reactions with auramine O's discriminated fluorescence emission.

A universal enzyme strand (E-DNA) recyclable L-histidine (L-His), melamine (MA), and cisplatin (CP) biosensor was fabricated on the basis of a target-specific RNA-cleaving DNAzyme with specific auramine O (AuO) dye instead of thioflavin T. In this strategy, the substrate strand (S-DNA) of the RNA-cleaving site was constructed as an intramolecular stem-loop structure, and a GT-rich sequence was imprisoned in the double-stranded stem which inhibits the formation of stable G-quadruplex (G4cpx) with AuO. The presence of L-His initiates a catalytic reaction for cleaving the RNA site of the S-DNA hydrolytically releasing the GT-rich portion, which subsequently combines with AuO and forms a G4cpx for enhanced fluorescent signal. The subsequent addition of MA uncoils the G4cpx to form T-MA-T dsDNA, or addition of CP unwound the G4cpx to form CP-DNA leading to an intensive decrease of AuO emission. Remarkably, the liberated L-His can ultimately cause several rounds of cleavage, and the liberated E-DNA can catalyze the subsequent reaction with the other S-DNA. The use of L-His and E-DNA repeatedly induces S-DNA cleavage and intensifies the emission signal. The results show that the proposed biosensor is extremely sensitive to L-His, MA, and CP with a detection limit of 0.98, 10, and 3.4nM respectively. To the best of our knowledge, the utilization of AuO as the G4cpx inducer and stabilizer for L-His, MA, and CP detection in real milk and urine samples has never been reported.

Signal-on fluorescent strategy based on RNA cleavage-inhibited catalytic hairpin assembly and photo-induced electron transfer for Pb2+ detection

A signal-on fluorescence biosensing strategy was developed by integrating GR-5 DNAzyme, catalytic hairpin assembly (CHA), photo-induced electron transfer (PET) between G-quadruplex (G4)/hemin DNAzyme and fluorophore. An oligonucleotide (cGRE), complementary to the enzyme strand (GRE), was applied to facilitate the separation of substrate strand (GRS) from GR-5 DNAzyme. The separated GRS acted as a trigger to initiate the CHA process and the formation of G4/hemin DNAzyme, resulting in the fluorescence quenching via PET. The Pb2+-responsive cleavage of GRS led to the suppression of the occurrence of CHA and the generation of G4/hemin DNAzyme, yielding the enhancement of the fluorescence. This DNAzymes-CHA-PET Pb2+ assay can be carried out in a single tube, endowed with the obvious advantages of facile design, simple procedure and excellent specificity. The quantitative determination of Pb2+ was achieved in a broad range of 0.1–150 ng mL−1 with the detection limit of 0.03 ng mL−1. This strategy was successfully applied to the analysis of standard reference materials (drinking water), spiked water and fish samples. The ingenious design proposed herein provides a new method for routine screening of heavy metals, and also opens up new avenues for the development and application of PET biosensors based on G4/hemin DNAzyme.

DNAzyme-based biosensor for sub ppb lead ions detection using porous silicon Fabry-Pérot interferometer

Herein, we present an optical sensing approach based on nanostructured porous silicon (PSi) Fabry-Pérot interferometers for real-time monitoring of lead (Pb2+) contaminants using DNAzyme, a synthetic DNA sequence with a functional catalytic region. The latter cleaved the complementary DNA/RNA substrate strand in the presence of Pb2+, which resulted in a decrease in the average refractive index of the total porous void. The interfacial optical contrast was enhanced by coupling silica nanoparticles to the complementary strand, thus improving the interferometer’s inherent performance. The catalytic activity of the DNAzyme-modified platform was monitored in real-time using reflective interferometric Fourier transform spectroscopy. The optimized conditions offered means for accurate, rapid (~20 min) and precise detection of Pb2+ in the range of 0.1–25 ppb with a detection limit of 0.49 ppb (2.4 nM). Sufficient selectivity and specificity were attained against other commonly known metallic pollutants in water sources. Finally, the practical applicability of the biosensor’s performance was demonstrated using real samples, such as ground, irrigation, tap water and even plasma, while depicting satisfactory recovery values of 94–103% in compliance with the ICP-MS approach. Overall, the developed sensing platform coupled to optical signal amplification can be easily redesigned for targeting other metal pollutants posing risks to water sources and the environment.

Construction of a target-triggered DNAzyme motor for electrochemical detection of multiple DNA glycosylases

DNA repair enzymes are responsible for the repair of DNA lesions and are important disease biomarkers. Herein, we construct a target-triggered DNAzyme motor for electrochemical detection of multiple DNA glycosylases based on the DNAzyme motor-driven encoding of different electrochemical molecules. This assay involves two hairpin probes for sensing uracil DNA glycosylase (UDG) and human alkyladenine DNA glycosylase (hAAG), a AuNPs@locked DNAzyme motor which contains the locking strands and the Mg2+/Pb2+ DNAzyme strands, and a magnetic bead track which contains MB/Fc-labelled Mg2+/Pb2+ substrate strands. When UDG and hAAG are present, they can cleave the corresponding hairpin DNA probes to release two single-stranded DNAs (ssDNAs) which can hybridize with the locking strands to induce the liberation of Mg2+/Pb2+ DNAzyme strands from the AuNPs@DNAzyme motor. The subsequent hybridization of Mg2+/Pb2+ DNAzyme strands with their corresponding substrate strands results in the cleavage of Mg2+/Pb2+ substrate strands and the simultaneous release of MB/Fc-labelled ssDNAs from magnetic bead. The released MB/Fc labels can be electrochemically detected for accurate quantification of UDG/hAAG. This target-triggered DNAzyme motor exhibits high sensitivity and good specificity with the capability of simultaneously measuring multiple DNA glycosylases in HeLa cells and screening the potential inhibitors.

Toehold-Mediated Cascade Catalytic Assembly for Mycotoxin Detection and Its Logic Applications.

In this work, an enzyme-free biosensor is reported for mycotoxin detection based on a toehold-mediated catalytic hairpin assembly (CHA) and a DNAzyme-cascaded hydrolysis reaction. In the presence of a mycotoxin, the recognition between an aptamer and the mycotoxin releases the trigger DNA. The trigger DNA initiates the toehold-mediated CHA, generating large amounts of partial duplex B/C with four toeholds, which can be used to assemble the DNAzyme-cascaded hydrolysis reaction. Furthermore, through a collaborative autoassembly reaction among the B/C duplex, DNA1, and DNA2, supramolecular nanostructures corresponding to Mg2+-dependent DNAzymes can be formed. With the incubation of Mg2+, the dual-modified (TAMRA/BHQ2) substrate strand DNA2 will be cleaved into two fragments, yielding a high TAMRA fluorescence signal for mycotoxin testing. Under optimal conditions, the sensing system was ultrasensitive and showed low detection limits of 0.2 pM for ochratoxin A (OTA), 0.13 pM for aflatoxin B1 (AFB1), and 0.17 pM for zearalenone (ZEN). The mycotoxin aptasensor also exhibited high selectivity and was successfully applied for the quantitative analysis of OTA, AFB1, and ZEN in wine samples. Due to the advantages of flexibility and versatility, this mycotoxin platform was used to fabricate several concatenated logic gates including "AND-INHIBIT", "INHIBIT-OR", "OR-AND", and "OR-INHIBIT" logic biocomputings. Such multiple functions of the logic system provided a universal sensing strategy for the intelligent detection of multiplex mycotoxins, demonstrating considerable potential in food safety and environmental monitoring.

Smartphone-assisted colorimetric biosensor for on-site detection of Cr3+ ion analysis

A simple and low-cost biosensor has been established for the detection of Cr3+ ion by using the image processing function of the smartphone. In the presence of Cr3+ ion, its dependent DNAzyme can specifically cleave the substrate strand, resulting in the release of ligation probe, which will trigger hyperbranched rolling circle amplification (HRCA) to produce hydrogen ions, causing the color change of the solution containing cresol red. A free APP named "Pixel Picker" has been further used to measure the RGB values. It can be well found that the R/G values correlate with Cr3+ ion concentrations with a linear detection range of 0.5 μM–500 μM and a lowest detection limit of 0.12 μM. In addition, the proposed biosensor has been successfully applied to determine Cr3+ ions in various milks. In a word, the constructed smartphone-assisted colorimetric biosensor has the advantages of simplicity, low cost, high specificity and anti-interference ability.

Target-Activated, Light-Actuated Three-Dimensional DNA Walker Nanomachine for Amplified miRNA Detection.

Accurate analysis of microRNA (miRNA) is promising for elucidation of cancer processes and therapeutic effects. In this study, we reported a new target-activated, light-actuated three-dimensional (3D) DNA walker on gold nanoparticles for sensitive detection of miRNA using pyrene-incorporated DNAzyme analogues. In this design, the target miRNA activated the 3D DNA walker system to releases the walking arm. Then, under ultraviolet light irradiation, the pyrene DNAzyme on the walking arm would consecutively cleave the disulfide bonds of substrate strands and recover the fluorescence signal, thus achieving the amplified miRNA detection. The sophisticated design of the light-actuated 3D DNA walker was systematically investigated. Furthermore, this strategy could also be employed for miRNA analysis in serum samples with satisfactory reproducibility. Notably, the proposed light-actuated 3D DNA walker-based technique eliminated the need of enzymes, cofactors, and RNA backbones, thereby significantly improving the stability and efficiency. Overall, the light-actuated 3D DNA walker-based strategy enabled facile, sensitive, and specific detection of miRNA and provided new perspectives in diagnostics.

Disassembly of DNA origami dimers controlled by programmable polymerase primers.

Dynamic regulation of DNA origami nanostructures is important for the fabrication of intelligent DNA nanodevices. Toehold-mediated strand displacement is a common regulation strategy, which utilizes trigger strands to assemble and disassemble nanostructures. Such trigger strands are required to be completely complementary to the corresponding substrate strands, which strictly demands orthogonality and accuracy of the sequence design. Herein, we present a disassembly strategy of DNA origami dimers based on polymerase-triggered strand displacement, where the polymerase primers, as the trigger strands, were only partially complementary to the toehold region of the substrate strands. To demonstrate the programmability of trigger strands, we utilized primers with different sequence combination patterns to disassemble DNA origami dimers. The statistical summary of AFM images and fluorescence curves proved the feasibility of the new strategy. The utilization of polymerase-triggered strand displacement on the disassembly of DNA origami structures enriches the toolbox for the dynamic regulation of DNA nanostructures.

Toehold-mediated strand displacement coupled with single nanoparticle dark-field microscopy imaging for ultrasensitive biosensing.

Highly sensitive detection of biomarkers is essential for disease prevention and early diagnosis. Herein, a highly sensitive strategy was proposed for microRNA-21 (miRNA-21) detection by the incorporation of programmable toehold-mediated strand displacement (TMSD) and dark-field microscopy imaging. Firstly, efficient and specific TSMD was carried out via hybridization between the substrate strand (Sub) and two short probe strands (P1, P2). Then, miRNA-21 could specifically hybridize with Sub due to the toehold that existed on its tail, which triggered the amplification with the help of the assist strands, and forming a large number of Sub-assist double-stranded DNA (dsDNA). This process realized the targeted highly specific recognition of miRNA-21 and the amplification of the trace target to high-output dsDNA. Additionally, as glucose oxidase (Gox) was modified on the end of the assist strands in advance, hydrogen peroxide was generated after adding glucose to the system, which further etched gold-silver core-shell nanocubes (Au@Ag NCs). As a result, the size of Au@Ag NCs decreased and the scattering intensity reduced simultaneously. The scattering intensity reduction value of Au@Ag NCs has a linear relationship with miRNA-21 concentration in the range of 1.0 to 100.0 fM with a limit of detection of 1.0 fM. Finally, the proposed method has been successfully demonstrated for the determination of miRNA-21 in lung cancer cell A549 lysate.

Tetrahedron-Based Constitutional Dynamic Network for COVID-19 or Other Coronaviruses Diagnostics and Its Logic Gate Applications.

Considering the large-scale outbreak of the coronavirus, it is essential to develop a versatile sensing system for different coronaviruses diagnostics, such as COVID-19, severe acute respiratory syndrome-related coronavirus (SARS-CoV), and bat SARS-like coronavirus (Bat-SL-CoVZC45). In this work, a tetrahedron-based constitutional dynamic network was built as the sensing platform for coronavirus detection. Four different DNA probes were used to construct the tetrahedron structure. DNAzyme and the fluorophore modified substrate strand were used to generate different fluorescence signals, which can be used to distinguish different coronaviruses. The coronavirus biosensor shows a high sensitivity for COVID-19, Bat-SL-CoVZC45, and SARS-CoV detection, with detection limits of 2.5, 3.1, and 2.9 fM, respectively. Also, the platform is robust, and the possible interference from clinical samples was negligible. Using different coronaviruses as inputs, we have fabricated several concatenated logic gates, such as "AND-OR", "INHIBIT-AND", "AND-AND-AND", and "AND-INHIBIT". Importantly, our logic system can also be used to identify SARS-CoV-2 Delta and Lambda variants in the logic operations. Due to the unique advantages of high sensitivity and selectivity, multiple logic biocomputing capabilities, and multireadout mode, this flexible sensing system provides a versatile sensing strategy for intelligent diagnostics of different coronaviruses with low false-negative rates.

Simple and sensitive lead ion detection based on difference of gold monomer ratio using dark field microscope as readout system

Small amount of lead ions (Pb2+) can cause great harm to human health, it is important to develop some simple but sensitive methods to detect Pb2+ quickly and accurately. In this study, a sensitive method has been developed for Pb2+ detection based on the difference of gold monomer ratio using a dark field microscope (DFM) as readout system. The proposed method employed single-particle gold nanoparticles (AuNPs) and 8–17 DNAzyme as signal converter and identification unit, respectively. The 8–17 DNAzyme consists of a catalytic strand and a substrate strand, the 5′ end of the two strands are modified with sulfhydryl groups. The 8–17 DNAzyme is firmly modified on the surface of AuNPs (50 nm, AuNPs1) in advance, in the absence of Pb2+, AuNP aggregation is occurred by adding AuNPs (20 nm, AuNPs2) as they can interact with the other end of the dsDNA. In the presence of Pb2+, due to the specific cleavage of the substrate chain by Pb2+, another –SH leaves away from AuNPs1, the aggregation of AuNPs cannot be occurred. AuNP aggregates can be easily distinguished from the monomers under DFM because the aggregation can induce green-to-yellow scattering color changing, and the monomer ratio summarized by Image J can be used for quantitative analysis. The linear response range is 0.1–100.0 pM with a detection limit of 0.075 pM. The proposed method has been applied to detect Pb2+ in lake water and human blood serum samples with satisfied results.

Highly Sensitive and Selective Copper (II)-Catalyzed Dual-DNAzyme Colorimetric Biosensor Based on Exonuclease III-Mediated Cyclical Assembly

“Cu-DNAzyme” and “G4-DNAzyme” were used to develop a “turn-off” dual-DNAzyme colorimetric biosensor, which could be used to detect Cu2+ by employing exonuclease III-mediated cyclical assembly (EMCA). EMCA was based on the cleavage activity of Cu2+ to transfer the linkage sequences of the substrate strand and enzyme strand into the transition sequence. The horseradish peroxidase (HRP)-mimicking activity of the G4-DNAzyme was lost after binding with the complementary transition sequence and was hydrolyzed by Exo III. These results demonstrate that the proposed colorimetric biosensor was an effective method for ultradetection of trace metals in a high original signal background. Due to the high sensitivity of the biosensor, the limit of detection (LOD) of Cu2+ is 0.16 nM. This design offers a general purpose platform that could be applied for the detection of any metal ion target through adjustment of metal-dependent DNA-cleaving DNAzymes, which is of great significance for the rapid determination of food safety.

Dual CHA-mediated high-efficient formation of a tripedal DNA walker for constructing a novel proteinase-free dual-mode biosensing strategy

DNA walkers have been recognized as a type of powerful signal amplification tool for biosensors, but how to adopt a proper strategy to increase their amplification efficiency is still highly desirable. Herein we design a dual-catalytic hairpin assembly (CHA)-mediated strategy for the high-efficient formation of a tripedal Mg2+-dependent DNAzyme (MNAzyme)-DNA walker, and thus develop a novel proteinase-free dual-mode biosensing method for the kanamycin (Kana) antibiotic assay. The first CHA is initiated by a target-biorecognition reaction, which can produce the DNA walker and also induce the target recycling. The second CHA is initiated by a special base sequence designed as a one-half substrate of the MNAzyme. Upon the first CHA-triggered DNA walking at a magnetic bead (MB) track, this “pseudo-target” sequence can be released to induce another CHA-cycle for the formation of the same DNA walker. Meanwhile, the other one-half substrate strand exposed on the MB surface will trigger the quantitative hybridization chain reaction (HCR)-assembly of a G-quadruplex DNAzyme (G-DNAzyme)-enriched double-stranded DNA polymer. So the enzymatic reaction of G-DNAzymes enabled the convenient colorimetric and photoelectrochemical dual-mode signal transduction of the method. Due to the dual-CHA facilitation to the tripedal and three-dimensional DNA walking and synergetic signal amplification of HCR, this method exhibits very low detection limits of 9.4 and 0.55 fg mL−1, respectively. In combination with its wide linear range, automated manipulation, and excellent selectivity, repeatability and reliability, the proposed method is expected to be used for the convenient semiquantitative screening and accurate determination of possible antibiotic residues in complicated matrices.

LAMP-H+-responsive electrochemical ratiometric biosensor with minimized background signal for highly sensitive assay of specific short-stranded DNA

Herein, the sequence-specific short-stranded biomarker DNA (hDNA, 21-nt) is acted as targeting out-primer to implement the loop-mediated isothermal amplification for releasing hydrogen ions (LAMP-H+). Using LAMP-H+ as signaling transducer, we report a highly sensitive electrochemical ratiometric biosensor for hDNA with minimized background signal, which is achieved via magnetic separation using AuNPs-modified Fe3O4 (Au@Fe3O4) as micro-reactor. In Au@Fe3O4, a double-stranded complex of a pH-responsible strand (I*) and a substrate strand (S*) is bound via Au–N bonds, where the treatment with LAMP-H+ leads to I* folding into i-motif conformation and S* dehybridization. The S* further hybridizes a catalytic strand (C*) to assemble Mg2+-DNAzymes that are cleaved by Mg2+, releasing C* for repeated formation and robust nicking of Mg2+-DNAzymes. The resultant output fuel strands (F*) are introduced in a modified electrode to drive the strand displacement of two hairpins individually labeled with two electron mediators. Through F*-mediated recycled amplification, the ratio of their electrochemical currents changed in opposite is highly sensitive to the varied hDNA down to 2.1 fM. By integrating LAMP-H+-stimulated i-motif switching with Mg2+-DNAzyme cleavage, this logic transduction of LAMP-H+(i-motif/Mg2+-DNAzyme)F* efficiently minimizes the inherent background of traditional LAMP-based assays. Resultantly, our electrochemical ratiometric strategy would be applicable to diverse short-stranded DNAs or even RNAs as targeting primers of LAMP.

Probing and modulating the interactions of the DNAzyme with DNA-functionalized nanoparticles

DNA-functionalized gold nanoparticles are one of the most versatile bionanomaterials for biomedical and clinical diagnosis. Herein, we discovered that the performance of DNAzyme cleaving the substrate is highly related to its length. This intriguing phenomenon only appears at the interfaces of DNA-functionalized gold nanoparticles. We systematically investigated the causes of this phenomenon. We conjectured that the DNAzyme with extended nucleotides that do not match its substrate strand is vulnerable to non-specific adsorption, electrostatic repulsion, and steric hindrance. Based on our improved understanding of this phenomenon, we have successfully developed a highly sensitive and specific amplifiable biosensor to detect human apurinic/apyrimidinic endonuclease 1.

An “on-off” signal-switchable electrochemiluminescence biosensor for ultrasensitive detection of dual microRNAs based on DNAzyme-powered DNA walker

Herein, an “on-off” signal-switchable electrochemiluminescence (ECL) biosensor for dual miRNAs (miRNA-21 and miRNA-155) detection was constructed based on carbon dots (CDs)-labeled DNA walker, which can effectively avoid problems of the signal overlap or limited available labels that general exist in multiplex assays. In the presence of miRNA-21, the CDs-DNA walker were captured on the electrode via nucleic acid hybridization, producing a strong ECL signal corresponding to miRNA-21 (signal on). For miRNA-155, the biosensor was pre-incubated with CDs-DNA walker and assistant DNA (DNA-21). Target miRNA-155 could trigger metal ion-dependent DNAzyme cleavage. With the assistance of Mn2+, the substrate strands were cleaved and CDs detached from the electrode, resulting in a reduced ECL signal (signal off). The interference of miRNA-21 was eliminated because no more CDs-DNA walker was added. As a result, benefiting from the signal amplification offered by the CDs-DNA walker and the inherent properties of ECL technique, this biosensor achieved low detection limits of 33 fM for miRNA-21 and 33 aM for miRNA-155. This paper also demonstrates the biosensor’s bioanalytical application for multiplex detection of miRNA-21/155 in human serum samples and the total RNA extraction solution from the human cancer cell lines.

Dual-signal amplification electrochemical sensing for the sensitive detection of uranyl ion based on gold nanoparticles and hybridization chain reaction-assisted synthesis of silver nanoclusters

Herein, a dual-signal amplification electrochemical sensing has been proposed for the ultrasensitive detection of uranyl ions (UO22+) by integration of gold nanoparticles (AuNPs) and hybridization chain reaction (HCR)-assisted synthesis of silver nanoclusters (AgNCs). In this sensing platform, AuNPs are used as an ideal signal amplification carrier, aiming at increasing the loads of UO22+-specific DNAzyme on the gold electrode. In the presence of UO22+, UO22+-specific DNAzyme can be activated, leading to the cleavage of substrate strands (S-DNA). Then, HCR is triggered to produce long dsDNA through hybridization the probe with the ssDNA on the electrode surface. As a result, an amplified electrochemical response can be detected by inserting a large amount of AgNCs generated in situ using dsDNA as template. Featured with amplification efficiency, good specificity and high sensitivity, the strategy could quantitatively detect UO22+ down to 6.2 pM with a linear calibration range from 20 pM to 5000 pM. The proposed sensing platform has been also successfully demonstrated the practical application of detecting UO22+, indicating that the developed method has the potential applications and can open up a new avenue for highly sensitive detection of UO22+ in environmental monitoring.

Electrochemical aptasensor based on gold modified thiol graphene as sensing platform and gold-palladium modified zirconium metal-organic frameworks nanozyme as signal enhancer for ultrasensitive detection of mercury ions

Gold modified thiol graphene (Au@HS-rGO) was prepared and applied as sensing platform for constructing the electrochemical aptasensor. While gold-palladium modified zirconium metal-organic frameworks (AuPd@UiO-67) nanozyme was employed as signal enhancer for detecting mercury ions (Hg2+) sensitively. Herein, gold nanoparticles (Au NPs) were modified on HS-rGO to form the thin Au@HS-rGO layer. Then the substrate strand (Apt1) was modified on the platform through Au-S bond. The signal strand (Apt2) was further decorated on the platform in the presence of Hg2+. Herein, the Apt2 was labeled with AuPd@UiO-67 nanozyme, which exhibited catalase-like properties to catalyze H2O2, thereby generating the electrical signal. With the concentration of Hg2+ increased, the amount of modified Apt2-AuPd@UiO-67 increased, leading to the rise of current response. Since the current responses were linear with concentration of Hg2+, the detection of Hg2+ can be achieved. Under the optimum conditions, the prepared electrochemical aptasensor exhibited wide linear range from 1.0 nmol/L to 1.0 mmol/L, along with a low detection limit of 0.16 nmol/L. Moreover, the electrochemical aptasensor showed excellent selectivity, reproducibility and stability, together with superior performance in actual water sample analysis. Therefore, this proposed electrochemical aptasensor may have promising applications and provide references for environmental monitoring and management.