Unraveling a Concerted Proton-Coupled Electron Transfer Pathway in Atomically Precise Gold Nanoclusters.

Metal nanoclusters (MNCs) represent a promising class of materials for catalytic carbon dioxide and proton reduction as well as dihydrogen oxidation. In such reactions, multiple proton-coupled electron transfer (PCET) processes are typically involved, and the current understanding of PCET mechanisms in MNCs has primarily focused on the sequential transfer mode. However, a concerted transfer pathway, i.e., concerted electron-proton transfer (CEPT), despite its potential for a higher catalytic rate and lower reaction barrier, still lacks comprehensive elucidation. Herein, we introduce an experimental paradigm to test the feasibility of the CEPT process in MNCs, by employing Au18(SR)14 (SR denotes thiolate ligand), Au22(SR)18, and Au25(SR)18- as model clusters. Detailed investigations indicate that the photoinduced PCET reactions in the designed system proceed via an CEPT pathway. Furthermore, the rate constants of gold nanoclusters (AuNCs) have been found to be correlated with both the size of the cluster and the flexibility of the Au-S framework. This newly identified PCET behavior in AuNCs is prominently different from that observed in semiconductor quantum dots and plasmonic metal nanoparticles. Our findings are of crucial importance for unveiling the catalytic mechanisms of quantum-confined metal nanomaterials and for the future rational design of more efficient catalysts.

First Report of Powdery Mildew Caused by Podosphaera fuliginea on Veronica spicata in China.

Veronica spicata L. (syn. Pseudolysimachion spicatum Opiz), Plantaginaceae, is a perennial herb and frequently cultivated in gardens as an ornamental plant in China. In June 2017, powdery mildew infections were observed on V. spicata in Jingyuetan National Forest Park (43.80°N, 125.46°E), Changchun, China. A voucher specimen was deposited in the Herbarium of Mycology of Jilin Agricultural University under the accession no. HMJAU-PM91763. The incidence of the disease on leaves and stems was about 30 to 50%. The disease initially appeared as thin white colonies, which subsequently developed into dense effuse white colonies on the plant. Hyphae were flexuous to straight, septate, 3.0 to 8.0 µm wide. Hyphal appressoria were indistinct or nipple-shaped, solitary. Conidiophores (n=30) arise from the upper surface of hyphal mother cells, erect to straight, 133.4 to 176.2 × 7.8 to 10.7 µm. Foot-cells (n=40) were cylindrical, straight or slightly flexuous, 39.1 to 78.5 × 7.4 to 9.7 µm, and followed by 1 to 3 short cells. Conidia (n=45) were catenescent, ellipsoid, oval, or doliiform, with fibrosin bodies, 17.8 to 27.8 × 12.2 to 17.4 µm, length/width ratio 1.3 to 2.1. Germ tubes were produced at the subterminal to lateral part of conidia, straight or sinuous, without a distinct terminal appressorium. The sexual morph was not observed in the collected samples. The morphological characteristics of the asexual morph were consistent with Podosphaera fuliginea (Schltdl.) U. Braun & S. Takam. (Braun and Cook 2012). To confirm the identification, the complete internal transcribed spacer (ITS) region and partial 28S rRNA gene sequences of the pathogen were amplified by semi-nested PCR with the primers ITS5/P3 followed by ITS5/ITS4, and LSU1/TW14 followed by LSU1/LSU2, respectively. The sequences of 566 bp ITS (MF543026) and 609 bp 28S rDNA (MF543027) were obtained and showed 100% identity with P. fuliginea (AB046986, ON073893) on V. spicata from USA (Hirata et al. 2000). Based on the morphological and molecular characteristics, the fungus was identified as P. fuliginea. To perform pathogenicity assays, three healthy annual plants of P. spicatum were inoculated by gently pressing a diseased leaf onto the leaves, with three non-inoculated plants as controls. All plants were placed in a greenhouse at 21 to 29 °C, 60% relative humidity, with 16 h/8 h light/dark cycle. Nine days after inoculation, typical powdery mildew colonies started to appear on the inoculated plants, while the control plants remained symptomless. The morphology of the fungus on the inoculated leaves was identical to that observed on the originally diseased leaves. Powdery mildews on V. spicata (P. spicatum) were previously referred to as Erysiphe (Golovinomyces) orontii in Italy (Garibaldi et al. 2006) and Sphaerotheca (Podosphaera) fuliginea in many countries, such as Poland, Russia, Switzerland, Wisconsin, Ukraine, etc. (Amano 1986; Braun and Cook 2012; Farr and Rossman 2022; Heluta et al. 2011). To our knowledge, this is the first record of P. fuliginea on V. spicata from China and the first report of this species at all. The results of this study provide important information for horticultural management and plant protection in China. Acknowledgements This work was supported by the National Natural Science Foundation of China (31970019, 31670022). References: Amano, K. 1986. Host range and geographical distribution of the powdery mildew fungi. Japan Scientific Societies Press, Tokyo. Braun, U., and Cook, R. T. A. 2012. Taxonomic Manual of The Erysiphales (Powdery Mildews) CBS Biodiversity Series 11. CBS-KNAW Fungal Biodiversity Centre, Utrecht, the Netherlands. Farr, D. F., and Rossman, A. Y. 2022. Fungal Databases. Syst. Mycol. Microbiol. Lab., USDA-ARS. https://nt.ars-grin.gov/fungaldatabases Garibaldi, A., et al. 2006. Plant Dis. 90:831. https://doi.org/10.1094/PD-90-0831C Heluta, V. P., et al. 2011. Ukr. Botan. Journ. 68:585. Hirata, T., et al. 2000. Can. J. Bot. 78:1521. https://doi.org/10.1139/b00-124.

The asexual morph and molecular phylogeny of endemic Phyllactinia verruculosa on Indigofera tinctoria.

Phyllactinia verruculosa is a powdery mildew species (Erysiphaceae, tribe Phyllactinieae) so far only known from its type material collected in China on Indigofera scabrida in 1992, which only comprised the sexual morph. Two asexual morph samples were observed, one was collected on I. tinctoria on the campus of Guizhou University, Guiyang, China, and another one, on I. scabrida, was borrowed from Kunming Institute of Botany, Chinese Academy of Sciences. The anamorphic characters were observed, described and illustrated. The phylogenetic analysis of the combination of internal transcribed spacer regions (ITS) and 28S rDNA sequences showed that Ph. verruculosa is phylogenetically distantly related from other Phyllactinia species. To our knowledge, this is the first record of the asexual morph and first ITS+28S sequences for Ph. verruculosa, and I. tinctoria is a new host record for this species.

Genetic Factors Underlying Single Fiber Quality in A-Genome Donor Asian Cotton (Gossypium arboreum).

The study of A-genome Asian cotton as a potential fiber donor in Gossypium species may offer an enhanced understanding of complex genetics and novel players related to fiber quality traits. Assessment of individual fibers providing classified fiber quality information to the textile industry is Advanced Fiber Information System (AFIS) in the recent technological era. Keeping the scenario, a diverse collection of 215 Asiatic cotton accessions were evaluated across three agro-ecological zones of China. Genome-Wide Association Studies (GWAS) was performed to detect association signals related to 17 AFIS fiber quality traits grouped into four categories viz: NEPs, fiber length, maturity, and fineness. Significant correlations were found within as well as among different categories of various traits related to fiber quality. Fiber fineness has shown a strong correlation to all other categories, whereas these categories are shown interrelationships via fiber-fineness. A total of 7,429 SNPs were found in association with 17 investigated traits, of which 177 were selected as lead SNPs. In the vicinity of these lead SNPs, 56 differentially expressed genes in various tissues/development stages were identified as candidate genes. This compendium connecting trait-SNP-genes may allow further prioritization of genes in GWAS loci to enable mechanistic studies. These identified quantitative trait nucleotides (QTNs) may prove helpful in fiber quality improvement in Asian cotton through marker-assisted breeding as well as in reviving eroded genetic factors of G. hirsutum via introgression breeding.

One Crop Disease, How Many Pathogens? Podosphaera xanthii and Erysiphe vignae sp. nov. Identified as the Two Species that Cause Powdery Mildew of Mungbean (Vigna radiata) and Black Gram (V. mungo) in Australia.

Powdery mildew is a significant threat to mungbean (Vigna radiata) and black gram (V. mungo) production across Australia and overseas. Although they have been present in Australia for at least six decades and are easily recognized in the field, the precise identification of the pathogens causing this disease has remained unclear. Our goal was to identify the powdery mildew species infecting mungbean, black gram, and wild mungbean (V. radiata ssp. sublobata) in Australia. The internal transcribed spacer (ITS) and large subunit sequences of the ribosomal DNA and/or morphology of 57 Australian specimens were examined. Mungbean and black gram were infected by two species: Podosphaera xanthii and a newly recognized taxon, Erysiphe vignae sp. nov. Wild mungbean was infected only with P. xanthii. Mungbean and black gram powdery mildew ITS sequences from China, India, and Taiwan revealed the presence of only P. xanthii on these crops despite controversial reports of an Erysiphe species on both crops in India. Sequence analyses indicated that the closest relative of E. vignae is E. diffusa, which infects soybean (Glycine max) and other plants. E. vignae did not infect soybean in cross-inoculation tests. In turn, E. diffusa from soybean infected black gram and provoked hypersensitive response in mungbean. The recognition of a second species, E. vignae, as another causal agent of mungbean and black gram powdery mildew in Australia may complicate plant breeding efforts and control of the disease with fungicide applications.

A Simple Colorimetric Assay for Sensitive Cu2+ Detection Based on the Glutathione-Mediated Etching of MnO2 Nanosheets.

In this paper, we developed a quick, economical and sensitive colorimetric strategy for copper ions (Cu2+) quantification via the redox response of MnO2 nanosheets with glutathione (GSH). This reaction consumed MnO2 nanosheets, which acted as a catalyst for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product (oxTMB). In the presence of Cu2+, the GSH was catalyzed to GSSG (oxidized glutathione), and the solution changed from colorless to deep blue. Under the optimum conditions, the absorption signal of the oxidized product (oxTMB) became proportional to Cu2+ concentration in the range from 10 to 300 nM with a detection limit of 6.9 nM. This detection system showed high specificity for Cu2+. Moreover, the system has been efficaciously implemented for Cu2+ detection in actual tap water samples. The layered-nanostructures of MnO2 nanosheets make it possess high chemical and thermal stability. TMB can be quickly oxidized within 10 min by the catalyzing of MnO2 nanosheets with high oxidase-like activity. There is no need of expensive reagents, additional H2O2 and complicated modification processes during the colorimetric assay. Therefore, the strategy primarily based on MnO2 nanosheets is promising for real-time, rapid and highly sensitive detection of Cu2+ under practical conditions.

Multi-locus phylogeny and taxonomy of an unresolved, heterogeneous species complex within the genus Golovinomyces (Ascomycota, Erysiphales), including G. ambrosiae, G. circumfusus and G. spadiceus.

BACKGROUND: Previous phylogenetic analyses of species within the genus Golovinomyces (Ascomycota, Erysiphales), based on ITS and 28S rDNA sequence data, revealed a co-evolutionary relationship between powdery mildew species and hosts of certain tribes of the plant family Asteraceae. Golovinomyces growing on host plants belonging to the Heliantheae formed a single lineage, comprised of a morphologically differentiated complex of species, which included G. ambrosiae, G. circumfusus, and G. spadiceus. However, the lineage also encompassed sequences retrieved from Golovinomyces specimens on other Asteraceae tribes as well as other plant families, suggesting the involvement of a plurivorous species. A multilocus phylogenetic examination of this complex, using ITS, 28S, IGS (intergenic spacer), TUB2 (beta-tubulin), and CHS1 (chitin synthase I) sequence data was carried out to clarify the discrepancies between ITS and 28S rDNA sequence data and morphological differences. Furthermore, the circumscription of species and their host ranges were emended. RESULTS: The phylogenetic and morphological analyses conducted in this study revealed three distinct species named, viz., (1) G. ambrosiae emend. (including G. spadiceus), a plurivorous species that occurs on a multitude of hosts including, Ambrosia spp., multiple species of the Heliantheae and plant species of other tribes of Asteraceae including the Asian species of Eupatorium; (2) G. latisporus comb. nov. (≡ Oidium latisporum), the closely related, but morphologically distinct species confined to hosts of the Heliantheae genera Helianthus, Zinnia, and most likely Rudbeckia; and (3) G. circumfusus confined to Eupatorium cannabinum in Europe. CONCLUSIONS: The present results provide strong evidence that the combination of multi-locus phylogeny and morphological analysis is an effective way to identify species in the genus Golovinomyces.

QTL analysis and candidate gene identification for plant height in cotton based on an interspecific backcross inbred line population of Gossypium hirsutum × Gossypium barbadense.

KEY MESSAGE: We constructed the first high-quality and high-density genetic linkage map for an interspecific BIL population in cotton by specific-locus amplified fragment sequencing for QTL mapping. A novel gene GhPIN3 for plant height was identified in cotton. Ideal plant height (PH) is important for improving lint yield and mechanized harvesting in cotton. Most published genetic studies on cotton have focused on fibre yield and quality traits rather than PH. To facilitate the understanding of the genetic basis in PH, an interspecific backcross inbred line (BIL) population of 250 lines derived from upland cotton (Gossypium hirsutum L.) CRI36 and Egyptian cotton (G. barbadense L.) Hai7124 was used to construct a high-density genetic linkage map for quantitative trait locus (QTL) mapping. The high-density genetic map harboured 7,709 genotyping-by-sequencing (GBS)-based single nucleotide polymorphism (SNP) markers that covered 3,433.24 cM with a mean marker interval of 0.67 cM. In total, ten PH QTLs were identified and each explained 4.27-14.92% of the phenotypic variation, four of which were stable as they were mapped in at least two tests or based on best linear unbiased prediction in seven field tests. Based on functional annotation of orthologues in Arabidopsis and transcriptome data for the genes within the stable QTL regions, GhPIN3 encoding for the hormone auxin efflux carrier protein was identified as a candidate gene located in the stable QTL qPH-Dt1-1 region. A qRT-PCR analysis showed that the expression level of GhPIN3 in apical tissues was significantly higher in four short-statured cotton genotypes than that in four tall-statured cotton genotypes. Virus-induced gene silencing cotton has significantly increased PH when the expression of the GhPIN3 gene was suppressed.

A Fluorescence Inner-Filter Effect Based Sensing Platform for Turn-On Detection of Glutathione in Human Serum.

A novel turn-on fluorescence assay was developed for the rapid detection of glutathione (GSH) based on the inner-filter effect (IFE) and redox reaction. Molybdenum disulfide quantum dots (MoS2 QDs), which have stable fluorescent properties, were synthesized with hydrothermal method. Manganese dioxide nanosheets (MnO2 NSs) were prepared by exfoliating the bulk δ-MnO2 material in bovine serum albumin (BSA) aqueous solution. The morphology structures of the prepared nanoparticles were characterized by transmission electron microscope (TEM). Studies have shown that the fluorescence of MoS2 QDs could be quenched in the presence of MnO2 NSs as a result of the IFE, and is recovered after the addition of GSH to dissolve the MnO2 NSs. The fluorescence intensity showed a good linear relationship with the GSH concentration in the range 20⁻2500 µM, the limit of detection was 1.0 µM. The detection method was applied to the analysis of GSH in human serum samples. This simple, rapid, and cost-effective method has great potential in analyzing GSH and in disease diagnosis.

A colorimetric mercury(II) assay based on the Hg(II)-stimulated peroxidase mimicking activity of a nanocomposite prepared from graphitic carbon nitride and gold nanoparticles.

A one-step reduction method was used for the preparation of stable graphitic carbon nitride-gold nanoparticles (g-C3N4-Au) nanocomposites from ultrathin g-C3N4 nanosheets and chloroauric acid by using NaBH4 as a reducing agent under ultrasonication. The nanocomposites were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, UV-Vis absorption and fluorescence spectroscopy etc. The results revealed that the gold nanoparticles (AuNPs) are uniformly formed on the g-C3N4 nanosheets. It is found that the peroxidase-like catalytic activity of this nanocomposite for the oxidation of 3,3',5,5'-tetramethylbenzidine by H2O2 to form a blue-colored product is strongly enhanced in the presence of Hg(II). Based on this phenomenon, a sensitive "turn-on" colorimetric assay for Hg(II) was developed that works at physiological pH values. Under optimal conditions, the absorption signal at 652 nm increases linearly with Hg(II) concentration in the range from 5 to 500 nM. A detection limit as low as 3.0 nM was achieved. This assay has excellent selectivity over other metal ions. It was successfully applied to the determination of Hg(II) in real water samples. The method is cost-effective, rapid, and allows for visual detection. Graphical abstract The nanocomposite composed of graphitic carbon nitride (g-C3N4) and gold nanoparticles (g-C3N4-AuNPs) can catalyze tetramethylbenzidine (TMB) oxidation by H2O2 to produce light-blue product (oxTMB). The peroxidase-like activity of g-C3N4-AuNPs can be greatly enhanced by Hg2+, thus increases the amount of the blue product formed.

Ultrasensitive colorimetric determination of silver(I) based on the peroxidase mimicking activity of a hybrid material composed of graphitic carbon nitride and platinum nanoparticles.

A hybrid material composed of graphitic carbon nitride (g-C3N4) and platinum nanoparticles (PtNPs) with peroxidase mimicking activity was used to design a rapid, sensitive and low-cost colorimetric method for the determination of Ag(I). The g-C3N4-PtNPs hybrid was synthesized by reduction of chloroplatinic acid using sodium borohydride under ultrasonication and in the presence of g-C3N4. The hybrid can catalyze the oxidation 3,3',5,5'-tetramethylbenzidine (TMB) to produce a blue-colored product with an absorption maximum at 652 nm. On addition of Ag(I) and in the presence of citric acid, it will be reduced to form Ag(0) under the catalytic action of PtNPs. Ag(0) is then adsorbed on the surface of the g-C3N4-PtNPs. This results in the inhibition of the enzyme mimetic activity of the hybrid. Hence, less blue product will be formed from TMB. Under optimum conditions, Ag(I) can be quantified in the 0.05-5.0 nM concentration range with a 22 pM detection limit. This assay is rapid and reliable and was applied to the determination of Ag(I) in spiked real water samples. Graphical abstract A hybrid nanomaterial consisting of graphitic carbon nitride and platinum nanoparticles (g-C3N4-PtNPs) can catalyze the oxidation of tetramethylbenzidine (TMB) to produce a blue-colored product (TMBox). The enzyme mimetic activity of the hybrid is inhibited by Ag+, thereby decreasing the generation of blue product from TMB.

Physicochemical and functional properties of protein isolate obtained from cottonseed meal.

To investigate the effect of preparation methods of cottonseed meals on protein properties, the physicochemical and functional properties of proteins isolated from hot-pressed solvent extraction cottonseed meal (HCM), cold-pressed solvent extraction cottonseed meal (CCM) and subcritical fluid extraction cottonseed meal (SCM) were investigated. Cottonseed proteins had two major bands (at about 45 and 50kD), two X-ray diffraction peaks (8.5° and 19.5°) and one endothermic peak (94.31°C-97.72°C). Proteins of HCM showed relatively more ß-sheet (38.3%-40.5%), and less ß-turn (22.2%-25.8%) and α-helix (15.8%-19.5%), indicating the presence of highly denatured protein molecules. Proteins of CCM and SCM exhibited high water/oil absorption capacity, emulsifying abilities, surface hydrophobicity and fluorescence intensity, suggesting that the proteins have potential as functional ingredients in the food industry.

A Simple Assay for Ultrasensitive Colorimetric Detection of Ag⁺ at Picomolar Levels Using Platinum Nanoparticles.

In this work, uniformly-dispersed platinum nanoparticles (PtNPs) were synthesized by a simple chemical reduction method, in which citric acid and sodium borohydride acted as a stabilizer and reducer, respectively. An ultrasensitive colorimetric sensor for the facile and rapid detection of Ag⁺ ions was constructed based on the peroxidase mimetic activities of the obtained PtNPs, which can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 to produce colored products. The introduced Ag⁺ would be reduced to Ag° by the capped citric acid, and the deposition of Ag° on the PtNPs surface, can effectively inhibit the peroxidase-mimetic activity of PtNPs. Through measuring the maximum absorption signal of oxidized TMB at 652 nm, ultra-low detection limits (7.8 pM) of Ag⁺ can be reached. In addition to such high sensitivity, the colorimetric assay also displays excellent selectivity for other ions of interest and shows great potential for the detection of Ag⁺ in real water samples.

Graphitic carbon nitride supported platinum nanocomposites for rapid and sensitive colorimetric detection of mercury ions.

In this study, graphitic carbon nitride supported platinum nanocomposites (g-C3N4/PtNPs) have been synthesized for the first time by an ultrasonic-assisted chemical reduction method. By using g-C3N4 as the stabilizer, Pt ions could be reduced to PtNPs by NaBH4 and uniformly deposited on the surface of g-C3N4. The resulting g-C3N4/PtNPs exhibited enhanced catalytic activity for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) compared to that of g-C3N4 or PtNPs alone. After interaction with Hg2+, the catalytic activity of g-C3N4/PtNPs was effectively inhibited due to the formation of HgPt amalgam. On the basis of this effect, a novel label free colorimetric sensor has been developed for sensitive detection of Hg2+ through the g-C3N4/PtNPs mediated catalytic reaction. A detection limit as low as 1.23 nM was achieved. This assay also exhibited excellent selectivity toward Hg2+ over other metal ions. In addition, it was successfully applied to the determination of Hg2+ in real water samples. In view of the advantages, such as simple operation, cost-effective, rapid response and naked-eye observation, the developed colorimetric sensor hold great potential for the detection of toxic Hg2+ in environmental and biological samples.

A novel sensitive colorimetric sensor for Cu2+ based on in situ formation of fluorescent quantum dots with photocatalytic activity.

This work demonstrates the use of quantum dots (QDs) with photocatalytic activity as a sensitive, inexpensive and rapid colorimetric platform for Cu2+ sensing. Based on the simple thiol compound mediated QDs growing method, CdS QDs can be quickly formed in situ, which possess excellent photocatalytic ability for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to produce a colored product under light irradiation. Cu2+ can catalyze the oxidation of sulfhydryl groups in glutathione (GSH) which act as a stabilizer for CdS QDs. In the presence of Cu2+, GSH is oxidized and loss the stabilization ability for the growth of CdS QDs, thus resulting in the decrease of the absorbance. Under optimum conditions, as low as 5.3nM Cu2+ can be detected. This sensing system is simple, reliable and holds great potential to provide a new general platform for ultrasensitive monitoring of a variety of analytes.

A novel label-free and sensitive electrochemical biosensor for Hg2+ based on ligase-mediated formation of DNAzyme.

A novel label-free electrochemical biosensor for the detection of Hg2+ based on ligase mediated creation of G-quadruplex-hemin DNAzyme has been developed. Firstly, Cp probe was immobilized on the gold electrode surface through Au-SH bond. In the presence of Hg2+, Cp and Ap probes were partly hybridized with the LJ probe respectively through the specific T-Hg2+-T interaction. Then, the adjacent 3'-OH terminal of Cp will link with the 5'-PO4 terminal of Ap to form a G-rich DNA at the function of T4-ligase. After interaction with hemin, the G-rich DNA can form a G-quadruplex-hemin HRP-mimicking DNAzyme. Through measuring the current change caused by DNAzyme-catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine(TMB), sensitive detection of Hg2+ can be achieved. The proposed sensor is simple, sensitive and selective, without the need of complicated labeling process, thus holds great potential for routine analysis of Hg2+ in environmental and biological samples.

A novel colorimetric assay for rapid detection of cysteine and Hg²âº based on gold clusters.

Inhibition and recovery of the catalytic activity of bovine serum albumin-capped gold nanoclusters (BSA-AuNCs) is observed for the first time by introduction of cysteine and Hg(2+). The prepared BSA-AuNCs possess highly intrinsic peroxidase-like activity. It can catalyze the oxidation of 3, 3, 5, 5-tetramethylbenzidine by H2O2 to produce a blue colored product. Based on this phenomenon, a new colorimetric assay for rapid, selective and sensitive detection of cysteine and Hg(2+) in aqueous solution has been demonstrated. The interaction process between target molecule and BSA-AuNCs is very fast, so that the whole test can be completed within ten minutes. Moreover, the fabricated colorimetric sensor is simple and cost-effective, without the need of nucleic acid based recognition element and complicated washing, separation and labeling process, thus holds great promise for routine analysis of cysteine and Hg(2+) in real samples.

A novel colorimetric sensor for Hg(2+) based on hybridization chain reaction and silver nanowire amplification.

Through the silver ion catalysis to form colored KMnO4, and combined with the DNA hybridization chain reaction and silver nanowire for signal amplification, a highly sensitive and selective colorimetric sensor has been developed for the detection of Hg(2+).

A novel label-free electrochemical sensor for Hg2+ based on the catalytic formation of metal nanoparticle.

A novel label-free electrochemical sensor has been developed for the highly sensitive and selective detection of Hg(2+). Hg(2+) were first captured on the modified electrode surface through the specific thymine-Hg(2+)-thymine (T-Hg(2+)-T) coordination and then through the catalytic HAuCl4/NH2OH reaction for the formation of gold nanoparticles (AuNPs) as signal reporter. The formed AuNPs could be directly detected by stripping voltammetry. By the introduction of graphene to accelerate electron transfer and amplify the electrochemical signal, a detection limit as low as 0.06 nM could be obtained for Hg(2+). Compared with the traditional metal nanoparticles (NPs)-based method, this sensor avoids the labeling of the DNA probe with NP tags, only one unlabeled T-rich DNA sequence was needed, which greatly reduced the cost and simplified the sensing procedure.

The three-way junction DNAzyme based probe for label-free colorimetric detection of DNA.

A novel three-way junction DNAzyme based probe has been designed for the colorimetric sensing of target DNA. Specifically, a DNAzyme-linked hairpin DNA is used as a signal probe. In the presence of target DNA, the signal probe, assistant probe and target DNA can hybridize with each other, resulting in the formation of a three-way junction DNA. At the same time, the signal probe is opened and the DNAzyme sequence in the signal probe is dehybridized. Subsequently, in the presence of hemin, the DNAzyme sequence forms a G-quadruplex-hemin complex, which catalyzes oxidation of 2, 2'-azinobis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) by H(2)O(2) to the colored ABTS(.-)radical. The significant color changes can be distinguished visually. By the combination of the hairpin probe and the three-way junction DNA probe, the proposed sensor exhibits high recognition property for single-nucleotide polymorphisms (SNPs). This sensor allows the detection of target DNA at a concentration as low as 0.25 nmol L(-1). The proposed sensor is easy to fabricate, which avoids the tedious and expensive labeling procedures, and exhibits high selectivity against single-base mismatched DNA.