A label-free double-amplification system for sensitive detection of single-stranded DNA and thrombin by liquid chromatography-mass spectrometry

Immobilization-free electrochemical DNA sensor based on signal cascade amplification strategy

The development of convenient and efficient strategies without using complex nanomaterials or enzymes for signal amplification is very important for bioanalytical applications. Herein, a novel electrochemical DNA sensor was developed by harnessing the signal amplification efficiency of catalytic hairpin assembly (CHA) and a brand-new signal marker tetraferrocene. The prepared sensor had both ends of the probe H2 labeled with tetraferrocene; both ends have a large number of unhybridized T bases, which cause tetraferrocene to move closer to the electrode surface, generating a high-efficiency amplification signal. In the presence of target DNA, it induced strand exchange reactions promoting the formation of double-stranded DNA and recycling of target DNA. Under optimal conditions, the sensor showed a good linear correlation between the peak currents and logarithm of target DNA concentrations (ranging from 0.1 fM to 0.3125 pM) with a detection limit of 0.06 fM, which is obtained by a triple signal-to-noise ratio. Additionally, the prepared sensor possesses excellent selectivity, reproducibility, and stability, demonstrating efficient and stable DNA detection methodology.

Ce(III, IV)-MOF electrocatalyst as signal-amplifying tag for sensitive electrochemical aptasensing

Metal-organic frameworks (MOFs) as a new class of porous materials have attracted increasing attention in the field of biomimetic catalysis. This study firstly reports a mixed valence state Ce-MOF possessing intrinsic catalytic activity towards thionine (Thi), and its application in constructing an amplified electrochemical aptasensor for thrombin detection. As noticed, the novel catalytic process combines the advantages of 3D infinite extension of the Ce(III, IV)-MOF skeleton containing large amounts of catalytic sites and spontaneous recycling of the Ce(III)/Ce(IV) for electrochemical reduction of Thi, thereby presenting amplified electrochemical signals. To further improve the aptasensor performance, the high selectivity of proximity binding-induced DNA strand displacement and high efficiency of exonuclease III-assisted recycling amplification were incorporated into the assay. The aptasensor was employed to detect thrombin in complex serum samples, which shows high sensitivity, specificity, stability and reproducibility. This work offers an opportunity to develop MOF-based electrocatalyst as signal-amplifying tag for versatile bioassays and catalytic applications.

Bare magnetic nanoparticles as fluorescence quenchers for detection of thrombin

Rapid and sensitive detection of thrombin has very important significance in clinical diagnosis. In this work, bare magnetic iron oxide nanoparticles (magnetic nanoparticles) without any modification were used as fluorescence quenchers. In the absence of thrombin, a fluorescent dye (CY3) labeled thrombin aptamer (named CY3-aptamer) was adsorbed on the surface of magnetic nanoparticles through interaction between a phosphate backbone of the CY3-aptamer and hydroxyl groups on the bare magnetic nanoparticles in binding solution, leading to fluorescence quenching. Once thrombin was introduced, the CY3-aptamer formed a G-quartet structure and combined with thrombin, which resulted in the CY3-aptamer being separated from the magnetic nanoparticles and restoration of fluorescence. This proposed assay took advantage of binding affinity between the CY3-aptamer and thrombin for specificity, and bare magnetic nanoparticles for fluorescence quenching. The fluorescence signal had a good linear relationship with thrombin concentration in the range of 1-60 nM, and the limit of detection for thrombin was estimated as low as 0.5 nM. Furthermore, this method could be applied for other target detection using the corresponding fluorescence labeled aptamer.

Direct sequencing of a disulfide-linked peptide with electrospray ionization tandem mass spectrometry

Enhanced corona discharge was employed for in-spray dissociation of disulfide bonds, facilitating disulfide-containing peptide sequencing with ESI-MS/MS.