Graphene Oxide Biosensors Based on Hybridization Chain Reaction Signal Amplification for Detecting Biomarkers of Radiation-Resistant Nasopharyngeal Carcinoma and Imaging in Living Cells

Spectrophotometric Detection of the BRCA1 Gene via Exponential Isothermal Amplification and Hybridization Chain Reaction of Surface-Bound Probes

In this work, we demonstrated an ultrasensitive approach with a dual-amplification strategy for DNA assay based on isothermal exponential amplification (EXPAR) and the hybridization chain reaction (HCR). In the presence of target DNA, the hairpin probe DNA (HP1) recognized and partially hybridized with the target DNA to form double-stranded structures containing the full recognition sequences for nicking endonuclease and then initiated EXPAR. Under the reaction of EXPAR, a large number of single-stranded DNA (ssDNA) was produced in the circle of nicking, polymerization, and strand displacement. The resulting ssDNA can bind to the surface-bound probe on the well of the microplate and trigger the hybridization chain reaction, resulting in the production of numerous double-stranded DNA concatamers with biotin labeling. In the presence of streptavidin-conjugated horseradish peroxidase (HRP), the amplified signal can be detected by a spectrophotometer via HRP-catalyzed substrate 3,3'5,5'-tetramethylbenzidine (TMB). This proposed dual-amplification method provides a detection limit of 74.48 aM, which also exhibits good linearity ranging from 0.1 fM to 100 pM.

Self-Assembly of DNA Tiles with G-Quadruplex DNAzyme Catalytic Activity for Sensing Applications

DNA tiles form through self-assembly of a small number of DNA strands that interact through basic repeated interactions, allowing the growth of nanoscale structures seeded by molecular inputs. If an approach for catalytic signal amplification can be integrated into the resultant nanostructure, then one can anticipate biosensing or diagnostic applications mediated by DNA tile self-assembly. Here, two-dimensional DNA tiles with split quadruplexes were designed as diagnostic tools for nucleic acid sensing without the use of protein enzymes. The presence of a target sequence leads to formation of extended microscale structures with arrayed multiple G-quadruplexes across the tile plane, with catalytic activity coupled to a colorimetric reporter. Such a mechanism has potential for low-cost signal amplification using unmodified DNA without the use of protein enzymes for biosensing.

Resolving the Heterogeneous Adsorption of Antibody Fragment on a 2D Layered Molybdenum Disulfide by Super-Resolution Imaging

The development of nanomaterials such as two-dimensional (2D) layered materials advanced applications in many fields, including biosensors format based on field-effect transistors. The unique physical and chemical properties of 2D layered materials enable the detection limit of biomolecules as low as ∼1 pg/mL. The majority of 2D layered materials contain different structural features and defects introduced in chemical synthesis and fabrication processing. These structural features have different physicochemical properties, causing heterogeneous adsorption of bioreceptors like antibodies, enzymes, etc. Understanding the correlation between the adsorption of bioreceptors and properties of structural features is essential for building highly efficient, sensitive biosensors based on 2D layered materials. Here, we utilize a single-molecule localization-based super-resolved fluorescence imaging method to unveil the inhomogeneous adsorption of antibody fragments on 2D layered molybdenum disulfide (MoS₂). The surface coverage of antibody fragments on MoS₂ thin flakes is quantitatively measured and compared at different structural features and different layer thicknesses. The methodology in the current work can be extended to study bioreceptor adsorption on other types of 2D layered materials and pave a way to improve biosensors' sensitivity based on defect engineering 2D layered materials.