•AGR2 detection was realized based on HCR for the first time;•AGR2 detection was realized firstly using the fluorescence quenching of AuNPs;•A low detection limit of 2.65 pM was obtained for AGR2 detection;•The sensor is highly specific to AGR2 due to the application of aptamer;•Satisfactory results were obtained for AGR2 detection in real samples.An ultrasensitive and enzyme-free sensing platform was designed for sensitive detection of anterior gradient homolog 2 (AGR2) based on the fluorescence quenching of gold nanoparticles (AuNPs) coupled with hybridization chain reaction (HCR) amplification. To construct the sensor, two fluorophore labeled hairpin probes (HP1 and HP2) that contained the sticky tails were designed, and AGR2 aptamer was used as an initiator for the happen of HCR between HP1 and HP2 to form a long nicked dsDNA duplex. Such DNA duplex could not adsorb onto the surface of AuNPs, and a strong fluorescence signal appeared due to the label of HP1 and HP2 with fluorophore. In the presence of AGR2, AGR2 aptamer would specifically recognize with it and accordingly could not trigger the happen of HCR. As a result, the sticky tails of HP1 and HP2 would adsorb onto the surface of AuNPs to bring the fluorophore into the close proximity of the AuNPs, and lead to the quenching of the fluorescence signal. By using such method, AGR2 could be sensitively detected in the range of 5.0 pM–1.0 nM based on monitoring the decrease of the fluorescence signal. Importantly, the assay could realize the detection of AGR2 effectively in diluted human serum samples.

•4 nm of (+)AuNPs were introduced to enlarge the electrode surface for the first time.•MB can directly interact with ssDNA or dsDNA, making such method simple to operate.•A low detection limit of 372 fM was obtained for PTK detection due to (+)AuNPs amplification.•The proposed method is highly specific to PTK7 due to the application of sgc8 aptamer.•Satisfactory results were obtained for PTK7 detection in cellular debris.We present here an ultrasensitive and simple strategy for protein tyrosine kinase-7 (PTK7) detection based on the recognition-induced structure change of sgc8 aptamer, and the signal change of methylene blue (MB) that interacted with sandwiched DNA complex. To construct such a sensor, an homogeneous nano-surface was formed firstly on the glass carbon electrode (GCE) by using negatively charged Nafion (Nf) as the inner layer and positively charged gold nanoparticles ((+)AuNPs) as the outer layer, followed by the immobilization of sgc8 aptamer based on Au–S bond. In the presence of helper probe (HP), sandwiched DNA complex was formed between the sgc8 aptamer and the DNA modified gold nanoparticle probe (DNA-AuNPs). Then, a strong current signal was produced due to the capture of abundant MB molecules by both the sandwiched DNA complex and the multiple DNAs that modified on AuNPs surface. However, the specific binding of sgc8 aptamer with PNK7 would trigger a structure transition of it, and directly prevented the following formation of sandwiched structure and the capture of MB. Thus, PTK7 detection could be realized based on monitoring the signal reduction of MB upon incubation of sgc8 aptamer with PTK7. Under optimal conditions, a low detection limit of 372 fM was obtained for PNK7 detection. Due to the employment of sgc8 aptamer, the proposed biosensor exhibited high selectivity to PNK7. Moreover, satisfactory results were obtained when the proposed method was applied for PNK7 detection in cellular debris.

•Hybridization chain reaction was used for dsDNA recognition for the first time.•(+)AuNPs were electrostatically adsorbed onto the negatively charged surface of double-helix.•A low detection limit was obtained based on the dual signal amplification of HCR and (+)AuNPs.•dsDNA could be realized under neutral pH environment in the presence of Ag+.•The proposed method showed good sequence specificity for dsDNA recognition.Enhanced sequence-specific recognition of double-stranded DNA (dsDNA) was realized by using hybridization chain reaction (HCR) and positively charged gold nanoparticles ((+)AuNPs) dual signal amplification. To construct such a sensor, capture probe was initially assembled onto gold electrode surface. Upon addition of dsDNA, sandwiched DNA complex was formed between the capture probe and the detection probe, then another exposed part of the detection probe opened two alternating DNA hairpins (H1 and H2) in turn and initiated HCR to form a double-helix. Meantime, (+)AuNPs were electrostatically adsorbed onto such double-helix to amplify the electrochemical signal. Upon optimal conditions, the electronic signals of ferrocene (Fc) that modified on H1 and H2 increased linearly with increasing dsDNA concentration over the range from 15 pM to 1.0 nM, with a detection limit of 2.6 pM. Moreover, the proposed method showed good sequence specificity for dsDNA recognition.

Glucose is directly related to brain activity and to diabetes. Therefore, developing a rapid and sensitive method for glucose detection is essential. Here, label-free glucose detection at attomole levels was realized by detecting the average diameter change of gold nanoparticles (AuNPs) utilizing dynamic light scattering (DLS). Single-strand DNA (ssDNA) adsorbed into the AuNPs’ surfaces and prevented them from aggregating in solution that contained NaCl. However, ssDNA cleaved onto ssDNA fragments upon addition of glucose, and these fragments could not adsorb onto the AuNPs’ surfaces. Therefore, in high-salt solution, AuNPs would aggregate and their average diameter would increase. Based on monitoring the average diameter of AuNPs with DLS, glucose could be detected in the range from 15 pmol/L to 2.0 nmol/L, with a detection limit of 8.3 pmol/L. Satisfactory results were also obtained when the proposed method was applied in human serum glucose detection.

•The recognition of dsDNA could be realized under neutral pH environment.•The proposed method was sensitive with a detection limit of 275 pM.•The proposed method has good sequence-specificity as well.Direct recognition of double-stranded DNA (dsDNA) was crucial to disease diagnosis and gene therapy, because DNA in its natural state is double stranded. Here, a novel sensor for the sequence-specific recognition of dsDNA was developed based on the structure change of ferrocene (Fc) redox probe modified molecular beacon (MB). For constructing such a sensor, gold nanoparticles (AuNPs) were initially electrochemical-deposited onto glass carbon electrode (GCE) surface to immobilize thiolated MB in their folded states with Au–S bond. Hybridization of MB with target dsDNA induced the formation of parallel triplex DNA and opened the stem-loop structure of it, which resulted in the redox probe (Fc) away from the electrode and triggered the decrease of current signals. Under optimal conditions, dsDNA detection could be realized in the range from 350 pM to 25 nM, with a detection limit of 275 pM. Moreover, the proposed method has good sequence-specificity for target dsDNA compared with single base pair mismatch and two base pairs mismatches.

A sensitive sensor for the detection of glucose was developed with several merits:•Hybridization chain reaction was used for glucose recognition firstly.•(+) AuNPs were adsorbed onto the negatively charged surface of double-helix firstly.•A low detection limit was obtained based on the dual signal amplification of HCR and (+) AuNPs.•Satisfactory result was obtained in glucose detection of human serums by using the sensor.Ultrasensitive electrochemical method was established for glucose detection coupling hybridization chain reaction (HCR) and positively charged gold nanoparticles ((+)AuNPs) dual signal amplification. Molecular beacon (MB) was initially assembled onto gold electrode surface in their folded states. Hybridization of MB with detection probe opened the stem-loop structure of it, then another exposed part of it opened two ferrocene (Fc) modified DNA hairpins (H1 and H2) and induced HCR, which produced a strong current signal due to the formation of numerous Fc on such double-helix. Meantime, (+)AuNPs were electrostatically adsorbed onto such double-helix to amplify electrochemical signal. However, if the detection probe was incubated with the mixture of glucose, glucose oxidase (GOD) and Fe2+ firstly, it would be cleaved into DNA fragments and could not open the stem-loop structure of MB, accordingly resulted in no HCR happen and (+)AuNPs adsorption. Upon optimal conditions, a low detection limit of 21 pM for glucose detection was obtained. Moreover, the practicability of the assay in glucose detection of human serums was studied as well.Download high-res image (190KB)Download full-size image

•O-chitosan nanoparticles dramatically decreased the mycelium growth of V. dahlia.•The spore germination rate and dispersion state was changed with nanoparticles-treated.•Electron microscopy measurements demonstrated degenerative alterations of V. dahlia.•O-chitosan nanoparticles were internalized by spores and mycelium.•The increase of release of intracellular components and decrease of cellular protein evidenced the damaged membranes.Verticillium dahliae, which causes wilting in over 300 woody and herbaceous plant species, is a representative of fungal plant diseases for which effective controls are still needed. In this study, the antifungal action of oleoyl-chitosan nanoparticles was investigated against V. dahliae. Media containing oleoyl-chitosan nanoparticles dramatically decreased the mycelium growth. The highest antifungal indexes were observed on media amended with 2 mg/mL nanoparticles. Optical microscopy showed that spore germination and hyphae morphology were affected. Scanning electron microscopy and transmission electron microscopy demonstrated degenerative alterations including crumpled hyphae and spores, thickened cell walls, disappeared membranous organelles, massive vacuolation of the cytoplasm, and cell wall-plasmalemma separation. Fluorescence microscopy showed that nanoparticles were internalized by fungal cells. The sharp increase in the release of intracellular components and decrease of total cellular protein concentration demonstrated damaged cell membranes. Overall, the results indicate that oleoyl-chitosan nanoparticles have the potential to control phytopathogens in agriculture.