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An electrode modified with phytic acid (PA)-doped polypyrrole (PPy)/molybdenum disulfide (MoS2) nanocomposites for the simultaneous detection of Pb2+ and Cd2+ heavy metal ions in water. On the surface of MoS2 nanosheets PA-doped PPy/MoS2 nanomaterials were fabricated by in situ chemical oxidation polymerization. The PA-doped PPy network was uniformly covered the surface of MoS2 nanosheets which can improve stability of MoS2 and increase electrochemical active sites. The PA-doped PPy/MoS2-modified electrode demonstrated outstanding electrochemical performance compared to the PA-doped PPy and MoS2-modified electrodes. The PA-doped PPy/MoS2 has been proven to detect range of Pb2+ and Cd2+ between 10 and 300 μg/L. The limit of detection (LOD = 3σ/k) for Pb2+ was 1.78 μg/L and for Cd2+ was 2.03 μg/L. The PA-doped PPy/MoS2-modified electrode has good selectivity, reproducibility and stability. In practical tap water applications, good recoveries were achieved. This work illustrated a straightforward, helpful and high performing pathway within the areas of electrochemical detecting Pb2+ and Cd2+. [ABSTRACT FROM AUTHOR]

Ligation efficiency in a surface-based DNA click chemistry (CuAAC) reaction is extremely restricted by the orientation and density of probes arranged on a heterogeneous surface. Herein, we engineer DNA tetrahedral nanostructure (DTN)-corbelled click chemistry to trigger a hybridization chain reaction (HCR) assembling a large-scale of nanozymes for ratiometric fluorescence detection of DNA adenine methyltransferase (Dam). In this study, a DNA tetrahedron structure with an alkynyl modifying pendant DNA probe (Alk-DTN) is designed and assembled on a magnetic bead (MB) as a scaffold for click chemistry. When a CuO NP-encoded magnetic nanoparticle (CuO-MNP) substrate was methylated by Dam, CuO NPs were released and turned into a mass of Cu+. The Cu+ droves azido modifying lDNA (azide-lDNA) to connect with the Alk-DTN probe on the MB through the click reaction, forming an intact primer to initiate the HCR. The HCR product, a rigid structure double-stranded DNA, periodically assembles glucose oxidase mimicking gold nanoparticles (GNPs) into a large-scale of nanozymes for catalyzing the oxidation of glucose to H2O2. NH2-MIL-101 MOFs, a fluorescent indicator and a biomimetic catalyst, activated the product H2O2 to oxidize o-phenylenediamine (oPD) into visually detectable 2,3-diaminophenazine (DAP). The change of the signal ratio between DAP and NH2-MIL-101 is proportional to the methylation event corresponding to the MTase activity. In this study, the DTN enhances the efficiency of the surface-based DNA click reaction and maintains the catalytic activities of gold nanoparticle nanozymes due to the intrinsic nature of mechanical rigidity and well-controlled orientation and well-adjusted size. Large-scale assembly of nanozymes circumvents the loss of natural enzyme activity caused by chemical modification and greatly improves the amplification efficiency. The proposed biosensor displayed a low detection limit of 0.001 U mL−1 for Dam MTase due to multiple amplification and was effective in real samples and methylation inhibitor screening, providing a promising modular platform for bioanalysis. [ABSTRACT FROM AUTHOR]

Highly sensitive and reliable PEC detection of miRNAs still faces some challenges like the inaccuracy caused by coexisting interferences in the PEC system. Herein, we developed a split-type "turn-off" PEC biosensor based on spatially-extended 3D magnetic DNA nanodevices with high-order DNA amplifiers for sensitive detection of miRNAs in cancer cells. [ABSTRACT FROM AUTHOR]

Developing sensing platforms that simultaneously integrate high sensitivity and accuracy has been a promising but challenging task for the detection of protein biomarkers in clinical samples. Herein, we engineered an Au nanostar-based liquid phase interfacial ratiometric SERS platform with programmable entropy-driven DNA circuits to detect the protein biomarker Mucin 1 (MUC1) in clinical samples. [ABSTRACT FROM AUTHOR]

Two diphosphine-protected superatom gold selenido nanoclusters, [Au8Se2(dppm)4]2+(SD/Au8a, dppm = Ph2PCH2PPh2) and [Au8Se2(dppe)4]2+(SD/Au8b, dppe = Ph2P(CH2)2PPh2), were obtained by the reduction of [Au(SMe2)Cl] in the presence of Ph3PSe as the selenium ion releasing agents. Both can be regarded as "superatoms" with 1S2 configuration based on the spherical Jellium model. Despite the same metal-ligand binding motifs on the surface and the intrinsic C2 molecular symmetry, the configurations of Au8Se2 kernels in them are different in terms of Au-Au bonded metallic frameworks. SD/Au8a displays a heart-shaped [core + exo] type structure (Au4 tetrahedron core + two exo Au2Se units), whereas the two exo Au2Se counterparts in SD/Au8b are additionally locked by an obvious Au-Au bond, forming a distorted hexagonal Au6 ring with two capping AuSe units appended above and below it. Consequently, they showed different photophysical properties as reflected by their electronic absorption and emission spectra. Especially, both SD/Au8a and SD/Au8b exhibit blue-shifted thermochromic luminescence upon cooling from 293 to 83 K but the latter exhibits anomalous emission intensity evolution trends due to the occurrence of temperature-induced phase transition as revealed by varied-temperature crystallographic analyses. This work not only clearly illustrates the significance of ligands on tuning the kernel structure but also provides two rarely comparable examples for better understanding of the structure-property relationship of gold nanoclusters. [ABSTRACT FROM AUTHOR]

Summary: The present study is aimed to evaluate the effect of three different drying methods, including shade drying (SD), freeze drying (FD) and hot air dying (HAD), on the chemical components, antioxidant and cytoprotective activities of aqueous‐methanol extracts from A. fragrans leaves. The total phenolic and flavonoid content were determined by spectroscopic methods, whereas the chemical profile of different extracts was determined by ultra‐high‐performance liquid chromatography coupled with a tandem mass spectrometry (UHPLC‐MS/MS). A total of thirteen compounds were characterised and 9 phenolic compounds have been quantified. Two dihydrochalcone glycosides named confusoside and vacciniifolin were found to be the most abundant phenolic compounds in the SD extract of A. fragrans leaves, which also showed the strongest antioxidant and cytoprotective activities. The results showed that shade drying is an efficient method for preserving the chemical constituents and maintaining the antioxidant and cytoprotective activities of A. fragrans leaves. [ABSTRACT FROM AUTHOR]

DBP, one of the phthalic acid esters (PAEs), is known as an endocrine disruptor and is toxic to humans in abnormal concentrations. Here, a high-density and ordered SERS substrate based on the self-assembly of triangular Ag nanoplate (TAgNP) arrays is developed for DBP detection. Benefiting from the ordered arrangement and sharp corners of TAgNPS, the arrays can provide sufficient and uniform hotspots for reproducible and highly active SERS effects. Using Rhodamine 6G (R6G) as a reporter molecule, the SERS enhancement factor (EF) of the TAgNP arrays was found to be as high as 1.2 × 107 and the relative standard deviation was 6.56%. As a trial for practical applications, the TAgNP array substrates were used for the detection of dibutyl phthalate (DBP) in edible oils. In this assay, edible oil samples were added to hexane as an organic phase for the formation of the TAgNP arrays, which caused DBP to be loaded at hotspots. DBP in edible oils could be identified at concentrations as low as 10−7 M. This SERS substrate based on the TAgNP arrays has great potential applications in the high sensitivity and reproducible detection of contaminants in food. [ABSTRACT FROM AUTHOR]

In the electrochemiluminescence (ECL) field, most reported luminophores were focused on high-triggering potential and short wavelength, which was adverse for the ECL theory study and application at low potentials. Perylene diimide derivatives could emit near-infrared (NIR) ECL at low-triggering potential; however, they are always highly aggregated into a microrod structure and stacked together, which largely limited their application in biological fields such as bio-sensing and bio-imaging. To overcome these obstacles, we designed a novel perylene diimide molecule, namely N,N′-dicaproate sodium-3,4,9,10-perylenedicarboximide (PDI-COONa). This molecule self-assembled into a two-dimensional network nanostructure, which largely decreased the aggregation degree of PDI molecules and provided solid bases for designing lowly-aggregated PDI molecules. Also, the formed nanoluminophore produced strong emission at −0.26 V with an NIR wavelength 700 nm, which should be due to the excited J-type PDI-COO− dimers. Moreover, this network nanoluminophore well-dispersed on graphene oxide (GO) as an ECL nanomaterial to label secondary antibodies and fabricate a sandwiched immunosensor for alpha-fetoprotein (AFP) detection between 0 and −0.6 V. This immunosensor showed a wider linear response for AFP ranging from 0.1 fg mL−1 to 1 μg mL−1 with a low detection limit 0.0353 fg mL−1 compared with other immunosensors based on PDI microrod-modified GO ECL materials. The fabricated immunosensor also showed good feasibility in human serum samples. [ABSTRACT FROM AUTHOR]

In electrochemiluminescence (ECL) field, screening luminophores, especially potential-resolved luminophores with the same parent chromophore, is essential for the development of fundamental theory study and accurate assay application such as ratiometric assay in biomedical research and clinical diagnosis. In this work, we developed a luminophore, reported a pair of potential-resolved luminophores with perylene as chromophore, and fabricated a dual-potential ECL ratiometric immunosensor. Luminophore chlorine-substituted perylene dianhydride (PTCDA-Cl4) was reported to produce strong ECL at −1.2 V with a wavelength at 630 nm. The ECL mechanism was interpreted with excited J-type PTCDA-Cl4 dimers. PTCDA-Cl4 and perylene diimide exhibited potential-resolved ECL features with K2S2O8 as a coreactant between 0 and −1.2 V, which were used to integrate gold nanoparticles for fabricating dual-potential ECL ratiometric immunosensors to detect α-fetoprotein (AFP). The biosensor showed good linear response for AFP from 10 fg mL–1 to 100 pg mL–1 with a detection limit of 3.33 fg mL–1. The biosensor also showed good application in real sample detection. [ABSTRACT FROM AUTHOR]

Developing convenient and sensitive detection methods for antibiotic residues in food is beneficial for ensuring food quality and human health. The tough challenges that limit the development of sensitive, quantitative, portable, on-the-spot antibiotic detectors are the lack of simple and effective target recognition and signal amplification strategies, and direct digital quantification. Herein, we developed a visual digital quantitative aptasensor, based on a binding-induced 3-D DNA nanomachine signal probe, for the simple and sensitive, on-the-spot detection of antibiotics. [ABSTRACT FROM AUTHOR]

The tough challenges for the sensitive and accurate detection of circulating miRNAs (cmiRNAs) in the peripheral blood are low abundance, and high interference from environmental or background factors or other molecules. Here, we developed a double-signal mode based on metal–organic framework coupled cascaded nucleic acid circuits for the accurate and sensitive detection of serum circulating miRNAs. [ABSTRACT FROM AUTHOR]

The tough challenges for the convenient and quantitative determination of circulating miRNAs (cmiRNAs) in the peripheral blood are low abundance, high interference and lack of direct digital readout. Here, we developed dual-enhanced magnetobiosensors based on cascaded nucleic acid circuits, which integrate catalyzed hairpin assembly (CHA) with the hybridization chain reaction (HCR), for sensitive, portable and digital quantitative detection of circulating miRNAs in serum by a personal glucose meter (PGM). [ABSTRACT FROM AUTHOR]

Simultaneous detection of different types of cancer biomarkers (nucleic acids and proteins) could facilitate early diagnosis of cancer and clinical treatment. Herein, a simultaneous detection platform of proteins and nucleic acids has been developed using a single substrate probe combining a label-free and background-eliminated fluorescence assay. Telomerase and telomerase RNA (TR) were chosen as the models. The molecular beacon (dU-BIO-HP) that contains deoxyuridine/biotin in its side arm, a TR recognition sequence in the loop and a telomerase substrate primer at the stem end was ingeniously designed. In the presence of telomerase, the stem of dU-BIO-HP is elongated by the addition of telomere repeats complementary to the assistant DNA. Furthermore, the formed dsDNA performed as engaging primers to initiate a SDA reaction, generating abundant G-quadruplex monomers. Similarly, on TR, the hybridization between TR and dU-BIO-HP can open its stem, triggering another SDA reaction, producing abundant short ssDNAs. With the G-quadruplex binding with ZnPPIX and ssDNA binding with SG for specific fluorescence responses, the label-free multiple detection can be achieved. In our strategy, the deoxyuridine of dU-BIO-HP acts as a barrier to block the DNA extension due to its strong inhibitory effects on DNA polymerase activity and to make sure that the two SDA reactions occurred independently. The biotin of dU-BIO-HP enables the reduction of the background from the binding between SG, ZnPPIX and dU-BIO-HP through streptavidin–biotin interaction. This method showed an excellent sensitivity with telomerase and TR detection limit of 2.18 HeLa cells per mL and 0.16 × 10−12 M, respectively. Furthermore, the telomerase and TR in different cell lines have been evaluated as powerful tools for biomedical research and clinical diagnosis. [ABSTRACT FROM AUTHOR]

The development of facile and sensitive miRNA quantitative detection methods is a central challenge for the early diagnosis of miRNA-related diseases. Herein, we propose a strategy for a liposome-encoded magnetic bead-based DNA toehold-mediated DNA circuit for the simple and sensitive detection of miRNA based on a toehold-mediated circular strand displacement reaction (TCSDR) coupled with a personal glucometer (PGM ). In this strategy, a glucoamylase-encapsulated liposomes (GELs)-encoded magnetic bead (GELs-MB) probe is designed to integrate target binding, magnetic separation, and signal response. Upon sensing the target miRNA-21, a GELs-MB probe-based toehold-mediated circular strand displacement reaction (TCSDR) was initiated with the help of fuel-DNA, constructing a DNA circuit system, and realizing target recycling amplification and the disassembly of the liposomes. The disassembled liposomes were finally removed via magnetic separation, and the encapsulated glucoamylase was liberated to catalyze amylose hydrolysis with multiple turnovers to glucose for a PGM readout. Benefiting from target recycling amplification initiated by the toehold-mediated DNA circuit and the liposome multiple-label amplification, a small quantity of target miRNA-21 can be transformed into a large glucose signal. The strategy realized the quantification of miRNA-21 down to a level of 0.7 fM without enzymatic amplification or precise instrumentation. Moreover, the high-density GELs-MB probe allows the sensitive detection of miRNA-21 to be accomplished within 1.5 h. Furthermore, this strategy exhibits the advantages of specificity and simplicity, since a toehold-mediated strand displacement reaction, magnetic separation and portable PGM were used. Importantly, this strategy has been demonstrated to allow the high-confidence quantification of miRNA. Therefore, with the advantages of low cost, ease of use, portability, and sensitivity, the reported method holds great potential for the early diagnosis of miRNA-related diseases. [ABSTRACT FROM AUTHOR]

Development of a reliable and facile telomerase activity assay with high specificity and sensitivity is a central challenge to make telomerase testing a routine part of medical care with respect to cancer. Herein, we propose a point-of-care (POC) assay of telomerase activity based on multi-code magnetic beads initiated by DNAzyme-mediated double-cycling amplification coupling with a glucometer. A designed DNAzyme-based telomerase substrate prime (DTSP) probe consists of three regions (AXB) for a DNAzyme catalytic sequence, poly-thymine (poly-T) linker and telomere primer sequence. In the presence of telomerase, telomerase elongates the primer site on the DTSP probe. Subsequent addition of the PbII cofactor activates the DNAzyme, which cleaves the elongated fragment at the RNA site, and releases the DTSP probe for repetitive cycling and the elongated fragment. The cleaved fragment as a trigger then continuously triggers the cyclic strand displacement reaction (CSDR) between MB-H1 and invertase-H2, constructing the second cycling and forming the MB-H1/invertase-H2 duplex. Owing to the double-cycling amplification, numerous invertases were coded onto the surface of MBs. After magnetic separation, the enriched multi-code MB catalytically hydrolyzes the sucrose substrate with multiple turnovers, generating a large amount of glucose for quantitative readout by personal glucose meters (PGM). Benefiting from the double-cycling amplification and magnetic separation, a high signal-to-background ratio was achieved, and the point-of-care assay realizes sensitive telomerase activity detection down to 5 HeLa cells with a significantly enhanced dynamic range without the need for enzymatic amplification. The designed DTSP probe highly ensured the specificity and reliability due to the high dependence of DNAzyme on the metal ion cofactor. Moreover, this method can be applied for the screening of telomerase inhibitors and the discrimination of cancer cells from normal cells. With the ability of simple operation, outstanding sensitivity, and excellent selectivity, this method offers a convenient and specific POCT strategy for telomerase activity detection, holding great potential in clinical diagnosis and drug discovery. [ABSTRACT FROM AUTHOR]