Versatile fluorescence detection of T4 PNK and mRNA based on unique DNA nanomachine amplification.

The development of DNA nanomachines provides a new strategy for the detection of tumor markers. In this work, an intelligent three-dimensional (3D) DNA walking machine with polynucleotide kinase (PNK) activator was designed, which was coupled with unique nanomachine formed by DNA nanowire cascade amplification reaction for versatile fluorescence detection of T4 PNK activity and messenger RNA (mRNA). When PNK exists, the free DNA walker was formed by hydrolysis cleavage of exonuclease, then the fluorophore-labeled report probe on the Au nanoparticles (NPs) was sheared during cycling cleavage reaction, thus the fluorescence signal was recovered for detection of PNK. Moreover, the DNA nanowires were produced by rolling ring amplification, then target mRNA sequentially initiated interval hybridization of hairpin probes through DNA nanowire, thus realizing DNA cascade reaction (DCR) with high "on" signal of DNA nanomachine for mRNA assay. This developed novel fluorescence nanomachine reported a new assay method with promising application for versatile targets and showed great potential for molecular-target therapies, and clinic diagnostics.

Photoelectrochemical biosensing platform based on in situ generated ultrathin covalent organic framework film and AgInS2 QDs for dual target detection of HIV and CEA.

In this work, a new photoelectrochemical (PEC) biosensing platform based on an ordered two-dimensional (2D) ultrathin covalent organic framework (COF) film and AgInS2 quantum dots (QDs) has been developed to enable dual-target detection of HIV and CEA. The porous COF film was firstly in situ generated on ITO, displaying super-stable and intense photocurrent with excellent repeatability. Moreover, an effective PEC quenching probe was specifically designed by loading large number of AgInS2 QDs on Au nanoparticles (NPs). After target HIV-induced cyclic amplification process to generate abundant DNA S0, the Au NPs-AgInS2 QDs probe was binded to the COF film through DNA hybridization, enabling PEC signal of the COF film to turn "off" for ultra-sensitive detection of HIV. Furthermore, when CEA as the second target specifically binded to its aptamer, the Au NPs-AgInS2 QDs quenching probe was released, achieving PEC signal "on" of the T-DA COF film for ultra-sensitive detection of CEA. This work opened a unique 2-D COF film-based PEC biosensing platform with excellent signal for rapid detection of dual targets, which can effectively avoid false positives and negatives and shows promising application for early prevention and detection of cancer diseases.

Target-switchable DNA hydrogels coupled with a Bi2Sn2O7/Bi2S3 heterojunction based on in situ anion exchange for the "signal-on" photoelectrochemical detection of DNA.

In this paper, a novel photoelectrochemical (PEC) "signal-on" biosensor based on a Bi2Sn2O7/Bi2S3 heterojunctioncoupled with target-switchable DNA hydrogels is reported for the ultrasensitive detection of P53 gene DNA. For the first time, sulfide ions are discovered to display an excellent PEC sensitization effect on Bi2Sn2O7 material by forming the Bi2Sn2O7/Bi2S3 heterojunction. The sensitization amplitude increased by 63 times, and the photocurrent polarity switched from cathodic to anodic. When the target DNA-induced-cycling amplification process produced a mass of product chains (PD), PD was introduced into the target-switchable DNA hydrogels to quantitatively release sulfide ions, which were further introduced to the Bi2Sn2O7-modified PEC platform and resulted in an enormous enhancement of the PEC signal due to the significant sensitization effect of sulfide ions on Bi2Sn2O7via an anion-exchange reaction. The corresponding PEC signal change of the Bi2Sn2O7/Bi2S3 platform was used for the detection of target DNA. This biosensing strategy opens up a novel sulfide ion-sensitized PEC platform and exhibits excellent analytical performance with a wide linear range (100 fM-10 nM), which has broad application prospects in bioanalysis and clinical diagnosis.