Electrochemical aptasensor based on DNA-templated copper nanoparticles and RecJf exonuclease-assisted target recycling for lipopolysaccharide detection.

An electrochemical aptasensor for detecting lipopolysaccharides (LPS) was fabricated based on DNA-templated copper nanoparticles (DNA-CuNPs) and RecJf exonuclease-assisted target recycling. The DNA-CuNPs were synthesized on a double-stranded DNA template generated through the hybridization of the LPS aptamer and its complementary chain (cDNA). In the absence of LPS, the CuNPs were synthesized on DNA double-strands, and a strong readout corresponding to the CuNPs was achieved at 0.10 V (vs. SCE). In the presence of LPS, the fabricated aptamer could detach from the DNA double-strand to form a complex with LPS, disrupting the template for the synthesis of CuNPs on the electrode. Meanwhile, RecJf exonuclease could hydrolyze the cDNA together with this single-stranded aptamer, releasing the LPS for the next round of aptamer binding, thereby enabling target recycling amplification. As a result, the electrochemical signal decreased and could be used to indicate the LPS content. The fabricated electrochemical aptasensor exhibited an extensive dynamic working range of 0.01 pg mL-1 to 100 ng mL-1, and its detection limit was 6.8 fg mL-1. The aptasensor also exhibited high selectivity and excellent reproducibility. Moreover, the proposed aptasensor could be used in practical applications for the detection of LPS in human serum samples.

Recent progress in liquid metal printing and its applications.

This paper focuses on the latest research printing technology and broad application for flexible liquid metal (LM) materials. Through the newest template printing method, centrifugal force assisted method, pen lithography technology, and laser method, the precision of liquid metal printing on the devices was improved to 10 nm. The development of novel liquid metal inks, such as PVA-LM ink and ethanol/PDMS/LM double emulsion ink, have further enhanced the recovery, rapid printing, high conductivity, and strain resistance. At the same time, liquid metals also show promise in the application of biochemical sensors, photocatalysts, composite materials, driving machines, and electrode materials. Liquid metals have been applied to biomedical, pressure/gas, and electrochemical sensors. The sensitivity, biostability, and electrochemical performance of these LM sensors were improved rapidly. They could continue to be used in healthy respiratory, heartbeat monitoring, and dopamine detection. Meanwhile, the applications of liquid metal droplets in catalytic-assisted MoS2 deposition, catalytic growth of two-dimensional (2D) lamellar, catalytic free radical polymerization, catalytic hydrogen absorption/dehydrogenation, photo/electrocatalysis, and other fields were also summarized. Through improving liquid metal composites, magnetic, thermal, electrical, and tensile enhancement alloys, and shape memory alloys with excellent properties could also be prepared. Finally, the applications of liquid metal in micro-motors, intelligent robot feet, nanorobots, self-actuation, and electrode materials were also summarized. This paper comprehensively summarizes the practical application of liquid metals in different fields, which helps understand LMs development trends, and lays a foundation for subsequent research.

A dual-mode of electrochemical-colorimetric biosensing platform for kanamycin detection based on self-sacrifice beacon and magnetic separation technique.

In this work, iron-based metal organic frameworks (Fe-MOF) are used as a self-sacrifice beacon to produce Prussian blue (PB). Then, a dual-mode electrochemical-colorimetric biosensing platform for kanamycin (KAN) detection is established considering the prominent redox activity and blue color of PB. CoFe2O4 magnetic nanobeads (CoFe2O4 MBs) are employed for immobilization and separation of the signal beacon in the complex matrix, and the combination between CoFe2O4 MBs and magnetic electrodes simplifies the electrochemical testing process. The linear range of the electrochemical mode is 0.1 nM-1.0 µM with a detection limit of 39 pM, and that of the colorimetric mode is 10 nM-2.0 µM with a detection limit of 3.6 nM. Furthermore, the dual-mode strategy shows satisfactory specificity and enhanced applicability for KAN detection in real samples. Compared with known dual-mode determination methods, the proposed design employs the same reaction to produce two signal output modes, thus eliminating the effect of different reactive pathways on the outcome and in turn promoting greater accuracy.

Encapsulation and Release of Recognition Probes Based on a Rigid Three-Dimensional DNA "Nanosafe-box" for Construction of a Electrochemical Biosensor.

Herein a rigid three-dimensional (3D) DNA "nanosafe-box" (DNB) for encapsulation and release of a recognition probe (N3) is designed to construct an electrochemical biosensor with the use of electroactive two-dimensional metal-organic framework (2D MOF) nanosheets as signal tags for ultrasensitive detection of mercury ion (Hg2+). Initially, N3 is locked in the 3D cavity of DNB by blocker DNA. After addition of target Hg2+, exonuclease III (Exo-III) digestion is initiated to the liberate DNA "key" (K); thereby, the free K triggers a strand displacement reaction for exposing the prelocked N3 to successfully ligate dibenzocyclooctyne (DBCO)-tagged anchor via metal-catalyst-free click chemistry, in which amounts of 2D MOF nanosheets containing Co(II) as electron mediator are introduced accompanied by significant electrochemical response. Compared with traditional linear or stem-loop DNA nanostructure, the well-designed 3D DNB possesses remarkably enhanced mechanical rigidity and structural stability, resulting in improved accessibility of probes and increased loading amounts of signal tags. More importantly, by this way of encapsulation and release of recognition probes, the background signal is decreased dramatically, leading to increased sensitivity of the proposed biosensor. Consequently, this electrochemical biosensor exhibits outstanding analytical performance for Hg2+ detection with a low detection limit of 33 fM and dynamic linear range of 0.1 pM to 10 nM. This strategy offers an ingenious method for detection of metal ions and biomarkers, possessing potential applications in environmental tests and clinical diagnosis.

An electroanalytical platform for nereistoxin-related insecticide detection based on DNA conformational switching and exonuclease III assisted target recycling.

In this work, an electroanalytical platform for nereistoxin (NRT)-related insecticide detection is proposed on the basis of NRT induced DNA conformational switching and exonuclease III (Exo III) assisted target recycling. NRT-related insecticides were first hydrolyzed and converted into NRT with two thiol groups (-SH). Then, a cytosine-Ag+-cytosine (C-Ag+-C) mismatched base pair was adopted to induce a blunt-ended hairpin configuration of HP DNA. In the presence of converted NRT, it could take up Ag+ from HP DNA to change its conformation from a hairpin to single-stranded structure (HP ssDNA). Thereafter, the obtained HP ssDNA was further hybridized with an H1 hairpin probe on the electrode surface to trigger the Exo III cleavage process, releasing HP ssDNA for recycling leaving the G-quadruplex fragment of H1, which was used for hemin/G-quadruplex complex formation. The reversible redox reaction of Fe(iii)/Fe(ii) of hemin gave a remarkable electrochemical response for quantitative determination of the NRT-related insecticides. As an analytical model, a low detection limit of 3.9 ng L-1 and a wide linear range of 0.01-1500 µg L-1 with excellent selectivity were achieved for cartap detection. The proposed method also displayed great applicability for cartap detection in agricultural products.

Click Chemistry Reaction-Triggered 3D DNA Walking Machine for Sensitive Electrochemical Detection of Copper Ion.

Herein, for the first time, we engineered click chemistry reaction to trigger a 3D DNA walking machine for ultrasensitive electrochemical detection of copper ion (Cu2+), which provided a convenient access to overcome the shortcomings of poor selectivity and limited amplification efficiency in traditional determination of Cu2+. Click chemistry reaction drove azido-S2 to bind with alkynyl-S1 for the formation of a walker probe on aminated magnetic polystyrene microsphere@gold nanoparticles (PSC@Au), which opened the hairpin-locked DNAzyme. In the presence of magnesium ion (Mg2+), the unlocked DNAzyme was activated to cleave the self-strand at the facing ribonucleotide site, accompanied by the release of product DNA (S3) and the walker probe. Therefore, the walker probe was able to open the adjacent hairpin-locked DNAzyme strand and then be released by DNAzyme cleavage along the PSC@Au-DNAzyme track. Eventually, the liberated single-strand S3 induced catalytic hairpin assembly (CHA) recycling, resulting in the capture of a large number of methylene blue-tagged hairpin DNA (MB-H2) on the sensor surface and significant electrochemical responses. By coupling click chemistry reaction with the dual-amplification strategy of the 3D DNA walking machine and CHA recycling, the proposed biosensor not only demonstrated high accuracy and selectivity for Cu2+ detection in real samples but also showed excellent performance for Cu2+ detection with a wide linear range of 1.0 pM to 500 nM and low detection limit of 0.33 pM. Moreover, this elaborated biosensor could be readily expanded to Mg2+ detection with a constant concentration of Cu2+, which paves a new way to apply the 3D DNA walking machine in various ion sensings.

Immobilized-free miniaturized electrochemical sensing system for Pb2+ detection based on dual Pb2+-DNAzyme assistant feedback amplification strategy.

We presented a novel dual-DNAzyme feedback amplification (DDFA) strategy for Pb2+ detection based on a micropipette tip-based miniaturized homogeneous electrochemical device. The DDFA system involves two rolling circle amplification (RCA) processes in which two circular DNA templates (C1 and C2) have been designed with a Pb2+-DNAzyme sequence (8-17 DNAzyme, anti-GR-5 DNAzyme) and an antisense sequence of G-quadruplex. And a linear DNA (L-DNA), which consists of a primer sequence and a Pb2+-DNAzyme substrate sequence, could hybridize with C1 and C2 to form two DNA complexes. In presence of Pb2+, the Pb2+-DNAzyme exhibited excellent cleavage specificity toward the substrate sequence in L-DNA, leaving primer sequence to trigger two paths of RCA process and finally resulting in massive long nanosolo DNA strands with reduplicated G-quadruplex sequences. And then, methylene blue (MB) could selectively intercalate into G-quadruplex to reduce the free MB concentration in the solution. Thereafter, a carbon fiber microelectrode-based miniaturized electrochemical device was constructed to record the decrease of electrochemical signal due to the much lower diffusion rate of MB/G-quadruplex complex than that of free MB. Therefore, the concentration of Pb2+ could be correctively and sensitively determined in a homogeneous solution by combining DDFA with miniaturized electrochemical device. This protocol not only exhibited high selectivity and sensitivity toward Pb2+ with a detection limit of 0.048 pM, but also reduced sample volume to 10 µL. In addition, this sensing system has been successfully applied to Pb2+ detection in Yangtze River with desirable quantitative manners, which matched well with the atomic absorption spectrometry (AAS).

Highly sensitive impedimetric biosensor for Hg2+ detection based on manganese porphyrin-decorated DNA network for precipitation polymerization.

In this work, a highly sensitive impedimetric biosensor was developed for mercuric ion (Hg2+) detection. The biosensor design was based on Hg2+-triggered exonuclease III (Exo III) cleavage for target recycling and DNAzyme-mediated catalytic for precipitation polymerization. Hg2+ induced thymine-thymine (T-T) mismatches were used to trigger the Exo III-catalyzed target recycling and produce free single-stranded DNA (defined as M). The outputted M then assisted the in formation of a DNA network on electrode surface to efficiently immobilize the porphyrin manganese (MnTmPyP). The formed MnTMPyP-double-stranded DNA (MnTmPyP-dsDNA) complex exhibited peroxidase-like activity capable of catalyzing a 3,3-diaminobenzidine (DAB) oxidation reaction, which produced an insoluble precipitate on the electrode surface. This reaction significantly enhanced the resistance signal for the quantitative determination of Hg2+. Under optimal conditions, the impedimetric biosensor exhibited a wide dynamic working range of 0.005 nM-100 nM with a detection limit of 1.47 pM. This platform also demonstrated good reproducibility and selectivity, offering a promising avenue for the detection of other molecules.

Converting pyrophosphate generated during loop mediated isothermal amplification to ATP: Application to electrochemical detection of Nosema bombycis genomic DNA PTP1.

Traditionally, genomic DNA detection is relay on a rigorous DNA amplification process, which always accompanied with complicated gel electrophoresis or expensive fluorescence detection methods. In this work, we have translated genomic DNA detection into adenosine triphosphate (ATP) test based on a split aptamer-based electrochemical sandwich assay. The key characteristic of our method are list as follows: first, nucleic acid amplification of the target gene was performed by the use of a loop mediated isothermal amplification (LAMP) process. The pyrophosphate (PPi), which released as the byproduct during the LAMP reaction, were further converted into ATP in the presence of adenosine 5'-phosphosulfate (APS) and ATP sulfurylase. Thereafter, the converted ATP was detected by constructing an electrochemical sandwich aptasensor. With such design, the conversion from the difficult detecting target (genomic DNA) into a convenient measured object (ATP) has been achieved. This proposed strategy was highly sensitive for Nosema bombycis genomic DNA PTP1 detection with a detection limit as low as 0.47 fg/µL and a linear range from 0.001pg/µL to 50ng/µL. And we supposed that this novel target conversion electroanalytical strategy established a universal approach for quantitative analysis of any other kinds of nucleic acid in assistance of nucleic acid polymerization reaction.

Highly effective target converting strategy for ultrasensitive electrochemical assay of Hg2.

An electrochemical sensing system based on a highly effective mercuric ion (Hg2+) converting strategy and rolling circle amplification (RCA) is developed for the ultrasensitive detection of Hg2+. The Hg2+ converting strategy is implemented based on Hg2+ specific recognition thymine-Hg2+-thymine (T-Hg2+-T)-induced DNA strand displacement. First, polystyrene magnetic microspheres coated by AuNPs (Au@PSC) as a magnetic separator were labeled with ssDNA D1 (thymine-rich) and S1/D2 DNA duplex (guanine-rich S1). In the presence of Hg2+ and long ssDNA D3 (thymine-rich at the 5' end), the formation of a stable T-Hg2+-T structure between D2 and D3 pushes S1 out from the S1/D2 DNA duplex, realizing the conversion of input target Hg2+ into output S1. Thus, the total amount of output S1 is proportional to the amount of input Hg2+. Thereafter, the output S1 serves as the primer to perform RCA to obtain long guanine-rich ssDNA, which could be further hybridized with the capture DNA on the electrode surface. Subsequently, methylene blue (MB) as an electron mediator interacts with the ssDNA polymers via electrostatic binding to produce a detection signal. The electrochemical biosensor exhibits a wide linear range of 1 pM to 1 µM with a low detection limit of 0.684 pM. Importantly, this sensor can be successfully applied in water samples with good accuracy and excellent recovery, which indicates its potential for Hg2+ detection in the environment.

An electrochemical impedance biosensor for Hg2+ detection based on DNA hydrogel by coupling with DNAzyme-assisted target recycling and hybridization chain reaction.

In this work, an electrochemical impedance biosensor for high sensitive detection of Hg2+ was presented by coupling with Hg2+-induced activation of Mg2+-specific DNAzyme (Mg2+-DNAzyme) for target cycling and hybridization chain reaction (HCR) assembled DNA hydrogel for signal amplification. Firstly, we synthesized two different copolymer chains P1 and P2 by modifying hairpin DNA H3 and H4 with acrylamide polymer, respectively. Subsequently, Hg2+ was served as trigger to activate the Mg2+-DNAzyme for selectively cleavage ribonucleobase-modified substrate in the presence of Mg2+. The partial substrate strand could dissociate from DNAzyme structure, and hybridize with capture probe H1 to expose its concealed sequence for further hybridization. With the help of the exposed sequence, the HCR between hairpin DNA H3 and H4 in P1 and P2 was initiated, and assembled a layer of DNA cross-linked hydrogel on the electrode surface. The formed non-conductive DNA hydrogel film could greatly hinder the interfacial electronic transfer which provided a possibility for us to construct a high sensitive impedance biosensor for Hg2+ detection. Under the optimal conditions, the impedance biosensor showed an excellent sensitivity and selectivity toward Hg2+ in a concentration range of 0.1pM - 10nM with a detection limit of 0.042pM Moreover, the real sample analysis reveal that the proposed biosensor is capable of discriminating Hg2+ ions in reliable and quantitative manners, indicating this method has a promising potential for preliminary application in routine tests.

A label-free electrochemical biosensor for microRNA detection based on catalytic hairpin assembly and in situ formation of molybdophosphate.

A label-free electrochemical biosensor for sensitive detection of miRNA-155 was presented by coupling enzyme-catalyzed in situ generation of electronic mediator for signal introduction with catalytic hairpin assembly (CHA) induced target recycling amplification strategy. In this work, alkaline phosphatase (ALP) was adopted to hydrolyze inactive substrate 1-naphthyl phosphate (NPP) to produce phosphate ion (PO43-), which could further react with acidic molybdate to form abundant molybdophosphate anion (PMo12O403-) on the surface of electrode. The produced PMo12O403- could directly generate a strong and stable electrochemical signal for quantitative detection of targets. In addition, CHA induced the cyclic reuse of the target was also employed as an effective strategy for improving the sensitivity of biosensor. This electrochemical method for miRNA-155 detection had achieved a good linear relationship ranging from 10fM to 1nM with a detection limit of 1.64fM. With this assay successfully applied in tumor cell lysates, it holds great potential for early cancer diagnosis by employing miRNA as the effective biomarker.

Ultrasensitive Lipopolysaccharides Detection Based on Doxorubicin Conjugated N-(Aminobutyl)-N-(ethylisoluminol) as Electrochemiluminescence Indicator and Self-Assembled Tetrahedron DNA Dendrimers as Nanocarriers.

The preparation of self-assembled DNA nanostructure with different sizes and shapes has been one of the most promising research areas in recent years, while the application of these DNA nanostructures in biosensors is far from fully developed. Here, we presented a novel carrier system to construct an electrochemiluminescence (ECL) aptasensor for ultrasensitive determination of lipopolysaccharides (LPS) on the basis of self-assembled tetrahedron DNA dendrimers. Doxorubicin (Dox), a well-known intercalator of double stranded DNA (dsDNA), was conjugated with the ECL luminophore of N-(aminobutyl)-N-(ethylisoluminol) (ABEI) to form a new type of ECL indicators (Dox-ABEI), which could noncovalently attach to dsDNA through intercalation. Based on this property, self-assembled tetrahedron DNA dendrimers were employed as an efficient nanocarrier to achieve a high loading efficiency for Dox-ABEI with significantly amplified ECL signal output. Streptavidin (SA) and biotin, a typical ligand-receptor pair, has been chosen to anchor the tetrahedron DNA dendrimers on the electrode surface. Moreover, by converting LPS content into DNA output, catalyzed hairpin assembly (CHA) target recycling signal amplification strategy was also adopted to enhance the sensitivity of the ECL aptasensor. With combining the loading power of the tetrahedron DNA dendrimers for ECL indicators, the inherent high sensitivity of ECL technique and target recycling for signal amplification, the proposed strategy showed a detection limit of 0.18 fg/mL for LPS.

Metal Organic Frameworks Combining CoFe2O4 Magnetic Nanoparticles as Highly Efficient SERS Sensing Platform for Ultrasensitive Detection of N-Terminal Pro-Brain Natriuretic Peptide.

N-terminal pro-brain natriuretic peptide (NT-proBNP) has been demonstrated to be a sensitive and specific biomarker for heart failure (HF). Surface-enhanced Raman spectroscopy (SERS) technology can be used to accurately detect NT-proBNP at an early stage for its advantages of high sensitivity, less wastage and time consumption. In this work, we have demonstrated a new SERS-based immunosensor for ultrasensitive analysis of NT-proBNP by using metal-organic frameworks (MOFs)@Au tetrapods (AuTPs) immobilized toluidine blue as SERS tag. Here, MOFs@AuTPs complexes were utilized to immobilize antibody and Raman probe for their excellent characteristics of high porosity, large surface area, and good biocompatibility which can obviously enhance the fixing amount of biomolecule. To simplify the experimental operation and improve the uniformity of the substrate, Au nanoparticles functionalized CoFe2O4 magnetic nanospheres (CoFe2O4@AuNPs) were further prepared to assemble primary antibody. Through sandwiched antibody-antigen interactions, the immunosensor can produce a strong SERS signal to detect NT-proBNP fast and effectively. With such design, the proposed immunosensor can achieve a large dynamic range of 6 orders of magnitude from 1 fg mL(-1) to 1 ng mL(-1) with a detection limit of 0.75 fg mL(-1). And this newly designed amplification strategy holds high probability for ultrasensitive immunoassay of NT-proBNP.

Wavelength-resolved simultaneous photoelectrochemical bifunctional sensor on single interface: A newly in vitro approach for multiplexed DNA monitoring in cancer cells.

Currently, the photoelectrochemical (PEC) strategies can just achieve single analyte detection on a single interface with limited detection efficiency. It is highly valuable but full of challenge to develop a PEC biosensor for multiple analytes evaluation on a single interface. For this point, the wavelength-selective photoactive materials, which could generate separated photocurrents under excitation lights with certain wavelengths, were mainly important to overcome this challenge. Herein, these wavelength-selective photoactive materials were successfully synthesized and served as signal indicators to construct a novel PEC biosensor for multiple analytes evaluation on a single interface for the first time. Moreover, an enzyme-assisted target recycling amplification strategy was introduced for ultrasensitive monitoring. As a result, the proposed PEC biosensor showed excellent analytical performance for both oral cancer (ORVOA 1) gene and p53 gene down to attomolar level. In addition, the fabricated PEC biosensor was employed to evaluate ORVOA 1 gene and p53 gene in Hela cells. This assay has laid the foundation for fabrication of simple, ultrasensitive and economical PEC diagnostic devices to detect multiple analytes in cells, which paved a new avenue for early diagnosis of cancer with higher efficiency and accuracy.

Novel multifunctionalized peryleneteracarboxylic/amine supramolecules for electrochemical assay.

In this work, a series of novel multifunctionalized peryleneteracarboxylic supramolecules were synthesized based on hydrogen bonding interactions between 3,4,9,10-perylenetetracarboxylic acid (PTCA) and amines, which possess large specific surface area, good membrane-forming properties and high stability. Importantly, an interesting phenomenon was found in that these series of supramolecules could conciliate disorderly redox peaks of PTCA and result in a pair of well-defined redox peaks, which were able to act as redox carriers for charge-generation and electron-transportion. And the probable mechanism for this phenomenon was discussed for the first time in detail through the integration of theoretical with practical research. To further reveal the advantages of these novel multifunctionalized supramolecule nanomaterials, PTCA/triethylamine (PTCA/TEA) was chosen as the best candidate for a redox carrier to participate in a "signal-on" aptasensor for thrombin (TB) detection by employing Fe3O4 magnetic beads (MBs) as a good enzyme mimic to catalyze the PTCA/TEA for signal amplification. As a result, a wide linear detection range of 0.0001-50 nM is acquired with a relatively low detection limit of 0.05 pM. And the proposed aptasensor exhibited good specificity and acceptable reproducibility and stability. After all, the explorations between PTCA and amines would set up a meaningful basis in seeking multifunctionalized supramolecule nanomaterials based on PTCA for extending the application of PTCA in a wider range of fields, and exploring the essential reason for the referred peculiar phenomenon for PTCA.

A multifunctional hemin@metal-organic framework and its application to construct an electrochemical aptasensor for thrombin detection.

A new type of multifunctional metal-organic framework (MOF) has been synthesized by encapsulating hemin into the nano-sized Fe-MIL-88 MOFs (hemin@MOFs) and first applied in an electrochemical aptasensor to detect thrombin (TB) with the aid of an enzyme for signal amplification. The gold nanoparticle functionalized hemin@MOFs (Au/hemin@MOFs) have not only simultaneously served as redox mediators and solid electrocatalysts, but have also been utilized as an ideal loading platform to immobilize a large number of biomolecules. In this aptasensor, Au/hemin@MOFs conjugated with glucose oxidase (GOD) and thrombin binding aptamer (TBA II) were used as the secondary aptamer bioconjugates (Au/hemin@MOF-TBA II-GOD bioconjugates), and TB was sandwiched between Au/hemin@MOF-TBA II-GOD bioconjugates and the amino-terminated TBA I which was self-assembled on the gold nanoparticle (AuNP) modified electrode. The GOD could oxidize glucose into gluconic acid accompanied by the generation of H2O2. The generated H2O2 on the electrode surface was further electrocatalyzed by hemin@MOFs to amplify the electrochemical signal of hemin contained in hemin@MOFs. Therefore, the synthesized hemin@MOFs represented a new paradigm for multifunctional materials since it combined three different functions including serving as catalysts, redox mediators and loading platforms within a single material. With such an ingenious design, a wide linear range of 0.0001 nM to 30 nM was acquired with a relatively low detection limit of 0.068 pM for TB detection.

Tracing Phosphate Ions Generated during Loop-Mediated Isothermal Amplification for Electrochemical Detection of Nosema bombycis Genomic DNA PTP1.

Traditionally, amplified DNA detection in a loop-mediated isothermal amplification (LAMP) was carried out in a complicated gel electrophoresis or with expensive fluorescence-based methods. Here, instead of direct detection that relies on amplified DNA, the indirect detection based on tracing phosphate ions (Pi) generated during LAMP by using an electrochemical method has been proposed for sensitive nucleic acid detection. Pyrophosphate (PPi) as the byproduct of nucleic acid polymerization reaction in LAMP was hydrolyzed into Pi by the preaddition of thermostable inorganic pyrophosphatase (PPase). Thus, the total amount of Pi in the LAMP-amplified sample was proportional to the amount of starting DNA templates. The obtained Pi could then react with acidic molybdate to form the molybdophosphate precipitates on the electrode surface, which serve as redox mediators to give a readily measurable electrochemical signal. The practicality of this strategy has been further demonstrated by employing it for sensitive and accurate quantification of Nosema bombycis genomic DNA PTP1. The electrochemical method allowed the quantitative analysis for target genomic DNA with a detection limit of 17 fg/µL. Thus, we suppose that the novel method proposed in this work with superior sensitivity and specificity, as well as the simple feature, can be easily established for quantitative analysis of many other kinds of nucleic acids in the assistance of LAMP.

Electrochemical Peptide Biosensor Based on in Situ Silver Deposition for Detection of Prostate Specific Antigen.

In this work, we have demonstrated a novel electrochemical method based on target-induced cleavage of a specific peptide for sensitive analysis of prostate specific antigen (PSA) by using silver enhancement. First, multiwalled carbon nanotubes/poly(amidoamine) dendrimers (MWCNTs-PAMAM) nanohybrids were assembled on the electrode to bind the peptide. Subsequently, dithiobis(succinimidylpropionate) (DSP)@Au@SiO2 was prepared as a tracing tag and covalent bond with the peptides via the inherent interaction between DSP and the amino of peptide. In the presence of PSA, the peptide was specifically recognized and cleaved, resulting in the loss of the tracing tag in electrode surface. Thereafter, silver enhancement was performed on the left DSP@Au@SiO2 nanohybrids. The electrochemical stripping signal of the deposited silver was used to monitor this process. Under optimal conditions, the proposed biosensor achieved a wide line from 0.001 to 30 ng mL(-1) with a detection limit of 0.7 pg mL(-1). This work demonstrated the combination of the direct transduction of peptide cleavage events with the highly sensitive silver enhancement method, providing a promising effective strategy for PSA detection.

3,4,9,10-Perylenetetracarboxylic acid/o-phenylenediamine nanomaterials as novel redox probes for electrochemical aptasensor systems based on an Fe3O4 magnetic bead as a nonenzymatic catalyst.

A novel redox probe 3,4,9,10-perylenetetracarboxylic acid/o-phenylenediamine (PTCA/OPD) with well-defined redox peaks caused by the synergistic action between them was demonstrated via theoretical and practical research, and applied in an electrochemical aptasensor to detect thrombin (TB) based on an Fe3O4 magnetic bead (MB) as a nonenzymatic catalyst.