DNA-Based Molecular Machines: Controlling Mechanisms and Biosensing Applications.

The rise of DNA nanotechnology has driven the development of DNA-based molecular machines, which are capable of performing specific operations and tasks at the nanoscale. Benefitting from the programmability of DNA molecules and the predictability of DNA hybridization and strand displacement, DNA-based molecular machines can be designed with various structures and dynamic behaviors and have been implemented for wide applications in the field of biosensing due to their unique advantages. This review summarizes the reported controlling mechanisms of DNA-based molecular machines and introduces biosensing applications of DNA-based molecular machines in amplified detection, multiplex detection, real-time monitoring, spatial recognition detection, and single-molecule detection of biomarkers. The challenges and future directions of DNA-based molecular machines in biosensing are also discussed.

Membrane-anchored DNA nanojunctions enable closer antigen-presenting cell-T-cell contact in elevated T-cell receptor triggering.

How the engagement of a T-cell receptor to antigenic peptide-loaded major histocompatibility complex on antigen-presenting cells (APCs) initiates intracellular signalling cascades in T cells is not well understood. In particular, the dimension of the cellular contact zone is regarded as a determinant, but its influence remains controversial. This is due to the need for appropriate strategies for manipulating intermembrane spacing between the APC-T-cell interfaces without involving protein modification. Here we describe a membrane-anchored DNA nanojunction with distinct sizes to extend, maintain and shorten the APC-T-cell interface down to 10 nm. Our results suggest that the axial distance of the contact zone is critical in T-cell activation, presumably by modulating protein reorganization and mechanical force. Notably, we observe the promotion of T-cell signalling by shortening the intermembrane distance.

A novel ratiometric fluorescence nanoprobe for sensitive determination of uric acid based on CD@ZIF-CuNC nanocomposites.

A novel ratiometric fluorescence nanoprobe based on carbon dots (CDs) and Cu nanoclusters (CuNCs) was designed for the label-free determination of uric acid (UA). The metal-organic framework (MOF) encapsulated CuNCs (ZIF-CuNC), and nitrogen-doped CDs can self-assemble into well-defined spherical nanocomposites (CD@ZIF-CuNC) due to physical adsorption. Under the excitation wavelength of 360 nm, the CD@ZIF-CuNC nanocomposites exhibit two evident intrinsic emissions peaked at 460 nm (CDs) and 620 nm (ZIF-CuNC), respectively. In the presence of H2O2, the fluorescence of CD@ZIF-CuNC at 620 nm is quenched remarkably within 1 min, while little effect on the emission at 460 nm is observed. Therefore, taking the fluorescence at 620 nm as the report signal and 460 nm as the reference signal, ratiometric quantitative determination of H2O2 was achieved with a linear range of 1-100 µM and a detection limit of 0.30 µM. The CD@ZIF-CuNC nanoprobe was successfully applied to the determination of UA that is catalyzed by uricase to produce H2O2, obtaining the linear range of 1-30 µM and the detection limit of 0.33 µM. Eventually, this strategy has been successfully applied to the determination of UA in human urine samples. A novel and convenient CDs@ZIF-CuNCs-based nanoplatform was constructed for sensitive ratiometric fluorescence determination of UA.

Hg2+-mediated stabilization of G-triplex based molecular beacon for label-free fluorescence detection of Hg2+, reduced glutathione, and glutathione reductase activity.

G-triplexes have been reported recently with the similar function to G-quadruplex that can combine with thioflavin T (ThT) and emit strong fluorescence but easier to be controlled and excited. In this work, we report an Hg2+-mediated stabilization of G-triplex based functional molecular beacon (G3TMB) sensing system for the label-free detection of Hg2+, reduced glutathione (GSH), and glutathione reductase (GR) activity. In the presence of Hg2+, the extended G-triplex sequence containing the "T" bases can form a stable hairpin structure due to the strong interactions of "T-Hg2+-T", resulting in the locking of G-tracts in the stem of the G3TMB effectively. However, the hairpin structure of the G3TMB can be opened by the introduction of GSH through the stronger "GSH-Hg2+" interaction. Therefore, by employing the fact that GR can catalyze the reduction of oxidized glutathione (GSSG) into GSH, this concept can be applied to fluorescence "off-on" detection of GR activity, with a linear range of 0.02-30 mU/mL and detection limit of 0.01 mU/mL. This work may expand a new perspective of G-triplex based functional molecular beacon as the label-free fluorescent probes in the detection of small biomolecule and enzyme activity.