Ultrasensitive electrochemical biosensing platform based on spherical silicon dioxide/molybdenum selenide nanohybrids and triggered Hybridization Chain Reaction

Ultrasensitive and label-free electrochemical aptasensor of kanamycin coupling with hybridization chain reaction and strand-displacement amplification

This work reports the proof-of-concept of an ultrasensitive label-free electrochemical aptasensor for Kanamycin (Kana) detection coupling strand-displacement amplification (SDA) with hybridization chain reaction (HCR). In the presence of target Kana, the analyte triggers conformational change of hairpin HP1 (HP1) and two-staged SDA to produce short single-stranded DNA (S1) with the aid of KF polymerase and nicking endonuclease. Meanwhile, the as-produced S1 hybridizes with the immobilized hairpin HP2 (HP2) on the electrode to open the hairpin, thereby resulting in the formation of DNA duplex. Thereafter, DNA duplex is selectively digested by Exo III accompanying S1 recycling. The residual single-stranded probe (S2) on the electrode opens another two hairpins in sequence and propagates a chain reaction of hybridization events between two alternating hairpins (H1 and H2) to form a long nicked double-helix. Upon addition of redox-active methylene blue (MB), numerous indicators are intercalated into the grooves of double-helix DNA polymers, each of which produces an electrochemical signal within the applied potentials. Under optimum conditions, the SDA/HCR-based electrochemical aptasensor exhibits a high sensitivity for detection of Kana down to 36 fM with a linear range from 0.05 to 200 pM. Additionally, the as-prepared aptasensor is successfully employed to determinate the Kana in animal derived food (milk). With the advantages of high sensitivity, label-free strategy and excellent selectivity, the developed aptasensor possesses great potential application value in food-safety analysis field.

Cost-effective three dimensional Ag/polymer dyes/graphene-carbon spheres hybrids for high performance nonenzymatic sensor and its application in living cell H2O2 detection

We describe a facile method to synthesize a new type of catalyst by electrodepositing Ag nanocrystals (AgNCs) on the different polymer dyes, Poly (methylene blue) (PMB) or Poly (4-(2-Pyridylazo)-Resorcinol) (PAR) modified graphene‑carbon spheres (GS) hybrids. The self-assembled GS take dual advantages of carbon spheres and graphene. Carbon spheres acts as nano-spacers prevent the aggregation of graphene and guarantee the fast electron transfer of GS. Secondly, polymerized dyes used here are beneficial for AgNCs growing as a linker. The effects of dyes on the growth habits, morphologies and catalytic properties for AgNCs were investigated. A novel electrochemical nonenzymatic sensor for hydrogen peroxide (H₂O₂) detection is fabricated based on the Ag/Polymer dyes/GS ternary composites modified glass carbon electrode (GCE) for the first time. It was found that the proposed electrodes, especially for Ag/PMB/GS/GCE, displayed a peculiar electrocatalytic activity towards H₂O₂ reduction synergistically as compared to Ag/PAR/GS/GCE or Ag/GS/GCE alone. Ag/PMB/GS/GCE showed a linear response over the H₂O₂ concentration range of 0.5 to 1112 μM. The detection limit and sensitivity is 0.15 μM and 400 μA mM^-1 cm^-2, respectively. These outstanding results enable the practical application of Ag/PMB/GS/GCE for the H₂O₂ tracking released from MCF-7 (human breast cancer cells) with satisfactory results.

Ultrasensitive supersandwich-type biosensor for enzyme-free amplified microRNA detection based on N-doped graphene/Au nanoparticles and hemin/G-quadruplexes

A simple, enzyme-free supersandwich-type biosensor is fabricated for the ultrasensitive detection of microRNAs (miRNAs) using N-doped graphene/Au nanoparticles (NG-AuNPs) and hemin/G-quadruplexes. In the proposed strategy, AuNPs are deposited on the surface of a MoSe₂ modified electrode to immobilize the thiol-modified hairpin probe through the strong Au-S bond. When the target miRNA is added, capture DNA hybridizes with it and unfolds its stem-and-loop structure. The NG-AuNP hybrids are the main amplification element and are modified by hybridization with assistance DNA and the terminus of capture DNA, resulting in the formation of the supersandwich structure. The assistance DNA is embedded into the hemin/G-quadruplex complexes in the presence of hemin and K⁺ to provide an exceptional current signal for the detection of miRNAs. Under the optimized experimental conditions, a detection limit of 0.17 fM is obtained with a linear range of 10 fM-1 nM. In addition, the present biosensor shows outstanding selectivity towards mismatched miRNAs. This biosensor platform successfully realized the combination of the signal amplification technique with the supersandwich structure, providing a promising approach for the detection of miRNA-21 in practical applications.

A novel electrochemical cytosensor for selective and highly sensitive detection of cancer cells using binding-induced dual catalytic hairpin assembly

Rare cancer cells in body fluid could be useful biomarkers for noninvasive diagnosis of cancer. However, detection of these rare cells is currently challenging. In this work, a binding-induced dual catalytic hairpin assembly (DCHA) electrochemical cytosensor was developed for highly selective and sensitive detection of cancer cells. The fuel probe, released by hybridization between the capture probe and catalytic hairpin assembly (CHA) products of target cell-responsive reaction, initiated dual CHA recycling, leading to multiple CHA products. Furthermore, the hybridization between fuel probe and capture probe decreased non-specific CHA products, improving the signal-to-noise ratio and detection sensitivity. Under the optimal conditions, the developed cytosensor was able to detect cells down to 30 cells mL^-1 (S/N = 3) with a linear range from 50 to 100,000 cells mL^-1 and was capable of distinguishing target cells from normal cells in clinical blood samples.

Recent advances in signal amplification strategy based on oligonucleotide and nanomaterials for microRNA detection-a review

MicroRNAs (MiRNAs) play multiple crucial regulating roles in cell which can regulate one third of protein-coding genes. MiRNAs participate in the developmental and physiological processes of human body, while their aberrant adjustment will be more likely to trigger diseases such as cancers, kidney disease, central nervous system diseases, cardiovascular diseases, diabetes, viral infections and so on. What's worse, for the detection of miRNAs, their small size, high sequence similarity, low abundance and difficult extraction from cells impose great challenges in the analysis. Hence, it's necessary to fabricate accurate and sensitive biosensing platform for miRNAs detection. Up to now, researchers have developed many signal-amplification strategies for miRNAs detection, including hybridization chain reaction, nuclease amplification, rolling circle amplification, catalyzed hairpin assembly amplification and nanomaterials based amplification. These methods are typical, feasible and frequently used. In this review, we retrospect recent advances in signal amplification strategies for detecting miRNAs and point out the pros and cons of them. Furthermore, further prospects and promising developments of the signal-amplification strategies for detecting miRNAs are proposed.

Binding-induced DNA walker for signal amplification in highly selective electrochemical detection of protein

A binding-induced DNA walker-assisted signal amplification was developed for highly selective electrochemical detection of protein. Firstly, the track of DNA walker was constructed by self-assembly of the high density ferrocene (Fc)-labeled anchor DNA and aptamer 1 on the gold electrode surface. Sequentially, a long swing-arm chain containing aptamer 2 and walking strand DNA was introduced onto gold electrode through aptamers-target specific recognition, and thus initiated walker strand sequences to hybridize with anchor DNA. Then, the DNA walker was activated by the stepwise cleavage of the hybridized anchor DNA by nicking endonuclease to release multiple Fc molecules for signal amplification. Taking thrombin as the model target, the Fc-generated electrochemical signal decreased linearly with logarithm value of thrombin concentration ranging from 10pM to 100nM with a detection limit of 2.5pM under the optimal conditions. By integrating the specific recognition of aptamers to target with the enzymatic cleavage of nicking endonuclease, the aptasensor showed the high selectivity. The binding-induced DNA walker provides a promising strategy for signal amplification in electrochemical biosensor, and has the extensive applications in sensitive and selective detection of the various targets.

PEGylated molybdenum dichalcogenide (PEG-MoS2) nanosheets with enhanced peroxidase-like activity for the colorimetric detection of H2O2

Colorimetric detection of H₂O₂ using biocompatible and dispersible PEG-MoS₂ nanosheets with enhanced peroxidase-like catalytic activity.

A sandwich-type electrochemical biosensor for alpha-fetoprotein based on Au nanoparticles decorating a hollow molybdenum disulfide microbox coupled with a hybridization chain reaction

In this work, a sensitive sandwich-type biosensor for detecting alpha-fetoprotein (AFP) is developed by using a target-triggered hybridization chain reaction strategy.

Molybdenum disulfide sphere-based electrochemical aptasensors for protein detection

In this work, we report the development of an ultrasensitive sandwich-type electrochemical aptasensor for protein detection.