Search

Stimuli-responsive hydrogel strain sensors that synergize the advantages of both soft-wet hydrogels and smart functional materials have attracted rapidly increasing interest for exploring the opportunities from material design principles to emerging applications in electronic skins, health monitors, and human-machine interfaces. Stimuli-responsive hydrogel strain sensors possess smart and on-demand ability to specifically recognize various external stimuli and convert them into strain-induced mechanical, thermal, optical, and electrical signals. This review presents an up-to-date summary over the past five years on hydrogel strain sensors from different aspects, including material designs, gelation/fabrication methods, stimuli-responsive principles, and sensing performance. Hydrogel strain sensors are classified into five major categories based on the nature of the stimuli, and representative examples from each category are carefully selected and discussed in terms of structures, response mechanisms, and potential medical applications. Finally, current challenges and future perspectives of hydrogel strain sensors are tentatively proposed to stimulate more and better research in this emerging field.

A novel and sensitive electrochemical sensor based on magnetic porous pseudo-carbon paste electrode (MPPCPE) for DNA detection was described in this study. The MPPCPE was fabricated by mixing polymethyl methacrylate (PMMA) microspheres, as template, graphite powders, as filler, pyrrole, as precursor of polymer and magnetic powder. It was demonstrated that the fabricated MPPCPE had more sensitivity for detecting DNA when compared with magnetic carbon paste electrode (MPCPE). Results from anodic stripping voltammetry (ASV) experiments showed that the Ag peak current versus concentration of complementary DNA at MPPCPE had two linear regions. The first region demonstrated linearity over a concentration range from 0.5 to 20 nM, with correlation coefficient of 0.992, while the second linear region had concentration of complementary DNA at 0.005 to 0.1 nM range, with correlation coefficient of 0.957. The detection limit was as low as 0.005 nM and the electrochemical sensor was easy to preserve for a long time, and had good reusability and stability.

A novel type of acetylcholine electrochemical biosensor was successfully fabricated by dropping beta-cyclodextrin solution, acetylcholinesterase solution and Nafion-methanol solution to the homemade nano-porous pseudo carbon paste electrode (nano-PPCPE) as working electrode, and then the electrochemical behavior of the as-prepared biosensor was studied through the acetylthiocholine iodide (ATChI). It was shown that the modified nano-PPCPE displays a high selectivity and sensitivity. The acetylcholine biosensor showed the linear range from 5 x 10(-6) M to 2 x 10(-4) M with the detection limit of 1.5 x 10(-7) M.

Using the nano-porous pseudo carbon paste electrode (Nano-PPCPE) as the working electrode, mixing L-glutamate oxidase (L-GLOD), catalase (Cat) and bovine serum albumin (BSA) with phosphate buffer (PB, pH = 7.4), followed by cross-linking with glutaraldehyde, a novel L-glutamate electrochemical biosensor was successfully formed. It was demonstrated that the modified nano-PPCPE exhibits a high selectivity and sensitivity in comparison with the modified CPE. The L-glutamate biosensor showed a linear range from 5 x 10(-7) M to 1 x 10(-5) M with the detection limit of 2.5 x 10(-7) M.

This paper gives an introduction of preparation and application of neurotransmitters-based bioelectrochemical microsensors/microelectrode with the help of nanotechnology, and illustrates various methods to measure neurotransmitter (including L-glutamate (Glu), acetylcholine, dopamine, etc.) microsensors/microelectrode and the prospects in the future of the sensors.

A novel and sensitive electrochemical sensor based on porous pseudo-carbon paste electrode (PPCPE) for paracetamol detection is described. It was demonstrated that PPCPE exhibits a high selectivity and sensitivity toward paracetamol in comparison with polypyrrole modified carbon paste electrode (PCPE), carbon nanotube modified carbon paste electrode (CNTPE) and carbon paste electrode (CPE), and a detection limit as low as 0.005 mM was obtained.

An electrochemical biosensor is fabricated for detecting albumin by self-assembling monolayer of 3-aminopropylmethyldiethoxysilane (APMDES) on the surface of glassy carbon electrode. The compact self-assembled monolayer is obtained when the self-assembling temperature is 303 K, the self-assembling time is 4 h and the concentration of APMDES is 3%. To detect albumin by means of the nanogold-promoted precipitation of silver with the optimal signal-to-noise ratio, the parameters to influence the detection current signals and the background current signals are investigated using anodic stripping voltammetry. The obtained optimal processing conditions are as follows: the gold labeling temperature is 298 K and the time is 30 min, the silver enhancement temperature is 303 K and the time is 8 min. Under the above conditions, different concentrations of BSA are detected by anodic stripping voltammetry. The results showed that the peak currents are linear to the concentration of albumin over the wide range from 0.5 to 0.05 ng/mL, and the detection limit is 0.02 ng/mL, the regress linear equation is I (microA)= 0.8254 + 1.4319 x C (ng/mL), R = 0.958, and the background current signals are smaller than 2.0 x 10(-7) A.