With the development of DNA nanotechnology, DNA has been widely used to construct a variety of nanomachines. Among them, a DNA walker is a unique nanomachine that can move continuously along a specific orbit to fulfill diverse functions. In this paper, a dual signal amplification electrochemical biosensor based on a DNA walker and DNA nanoflowers is constructed for high sensitivity detection of Staphylococcus aureus (S. aureus). Two groups of double-stranded DNA are modified on the surface of a gold electrode. The binding of S. aureus with its aptamer induces the disintegration of the long double strands and releases the DNA walker. With the help of exonuclease III (Exo III), the DNA walker moves along the electrode surface and continuously hydrolyzes the anchored short double strands. The introduction of a specially customized circular DNA and phi29 DNA polymerase initiates the rolling circle amplification (RCA) reaction. DNA nanoflowers are formed at high local concentration of DNA in the solution, which provide binding sites for electroactive methylene blue (MB) and thus produce intense signal. Under the best conditions, the current response is linearly related to the logarithm of the concentration of S. aureus ranging from 60 to 6 × 107 CFU/mL, and the detection limit is 9 CFU/mL. In addition, the proposed biosensor has achieved satisfactory results in the detection of actual water samples and diluted honey samples, which confirm the practicability of the biosensor and its application potential in environmental monitoring and food safety.
Direct electrochemical behavior of lactoperoxidase(LPO) was firstly obtained by employing a concanavalin A(Con A) and lactoperoxidase co-modified gold electrode.Then the electrocatalytic activity of LPO toward hydrogen peroxide(H2O2) and the influence of nitric oxide(NO) on the electrocatalytic activity of LPO were investigated.With the aid of Con A,LPO displayed a pair of quasi-reversible redox peaks in pH 7.4 phosphate buffer solution with a formal redox potential of-190 mV in cyclic voltammogram(CV) and showed typical thin-layer electrochemical behavior.The co-modified electrode exhibited electrocatalytic activity toward the reduction of H2O2,which was utilized to fabricate a H2O2 biosensor with the detection range of 2.0×10-5-4.0×10-3 mol/L.The experimental result also proved that NO showed a suppressive effect on the reduction of H2O2 at the concentration of micro-molar level.
Soft robotic grippers are widely used in different industrial applications since they show great advantages in the adaptable grasping of objects with irregular shapes. However, as many soft grippers have a monolithic structure and gain their motion from the elastic deformation, it is difficult to use the conventional rigid-body mechanism theory to synthesize the shape of the soft grippers. To cope with this problem, the topology optimization is frequently employed as synthesis method since it can achieve automatic design of continuum-structure mechanisms. In this paper, we propose a novel 3D topology optimization framework in MATLAB to achieve automatic design of soft robotic grippers. Two design examples are also presented to illustrate the automatic synthesis process. Experimental tests have shown that the 3D topology optimized grippers in the example can successfully grasp objects with different shapes. In future work, the proposed framework can be further developed to synthesize soft robotic grippers with different actuation mechanisms and task-specific grasping behaviors.
Kanamycin is detected based on the conformational change of the aptamer attached to the electrode surface and the corresponding SWV current change in [Fe(CN)6]3−/4−solution.
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