Developing ion‐selective membranes with anti‐biofouling property and biocompatibility is highly crucial in harvesting osmotic energy in natural environments and for future biomimetic applications. However, the exploration of membranes with these properties in osmotic energy conversion remain largely unaddressed. Herein, a tough zwitterionic gradient double‐network hydrogel membrane (ZGDHM) with excellent biofouling resistance and cytocompatibility for sustainable osmotic energy harvesting is demonstrated. The ZGDHM, composed of negatively charged 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS) as the first scaffold network and zwitterionic sulfobetaine acrylamide (SBAA) as the second network, is prepared by a two‐step photopolymerization, thus creating continuous gradient double‐network nanoarchitecture and then remarkably enhanced mechanical properties. As verified by the experiments and simulations, the gradient nanoarchitecture endows the hydrogel membrane with apparent ionic diode effect and space‐charge‐governed transport property, thus facilitating directional ion transport. Consequently, the ZGDHM can achieve a power density of 5.44 W m−2 by mixing artificial seawater and river water, surpassing the commercial benchmark. Most importantly, the output power can be promoted to an unprecedented value of 49.6 W m−2 at the mixing of salt‐lake water and river water, nearly doubling up most of the existing nanofluidic membranes. This study paves a new avenue toward developing ultrahigh‐performance osmotic energy harvesters for biomimetic applications.

Mercury ion (Hg 2+ ) is extremely toxic even at very low concentrations and its detection mainly relies on bulky and high-cost analytical instruments. Here, we introduce a fast and ultrasensitive biosensing method developed by the integration of fiber optic particle plasmon resonance and a highly selective molecular beacon with a stem-loop DNA structure immobilized on the unclad surface of an optical fiber. In the presence of Hg 2+ ions and a free assisting DNA probe, the stem-loop opens and forms thymine−Hg 2+ −thymine complexes. A DNA reporting probe conjugated to gold nanoparticles is used as a label to interrogate the recognition event by binding with the terminal DNA binding domain of the opened stem-loop. The method provides a wide linear range of at least 5 orders from 10 −14 to 10 −9 M and an extremely low detection limit of 4.37 fM (0.876 ppq). It takes less than 15 min to analyze the concentration of Hg 2+ ions in aqueous samples. The method is desirable for point-of-use applications because of its low-cost instrumentation and sensor chips, easy operation, and portability.

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