stimulated bilayer DNA hybrid hydrogel film actuator is further constructed and exhibits excellent actuation behaviors. Thanks to the micrometer-scale thickness of the films, these actuators exhibit a high degree of macroscopic and reversible shape deformations at high speed, which may find use in future smart biosensing and biomedical applications.

Scheme 1. Schematic illustration of the construction of DOX-loaded MXene-DNA hydrogel and its application as a NIR-responsive injectable platform for the photothermal-chemo synergistic treatment of tumor.

Programmable stimuli‐responsive materials have great potential in biosensing and biomedical applications. However, the slow response of DNA hydrogels to biological targets, especially bio‐macromolecules, i.e., proteins, due to the slow mass transfer within hydrogel matrices, as well as poor mechanical strength, severely hinders their extensive applications. Herein, the construction of hierarchically structured DNA hydrogels exhibiting significantly enhanced responsive and mechanical properties via a facile cryostructuration process is demonstrated. During the cryostructuration, interconnected macropores that can function as the channels for the migration of bio‐macromolecular substances, i.e., enzymes, are formed with the generated ice crystals as templates; meanwhile, densely crosslinked networks between the macropores are formed by the concentrated monomers localized in the unfrozen zones of the gelation system, leading to higher strength of the gel matrices. By programming the sequences of the DNA crosslinkers, two model hydrogels composed of enzyme‐responsive DNA structures and catalytic DNA crosslinking structures that can collaborate with enzymes to form biocatalytic cascades are constructed, and, in both systems, the hierarchically structured DNA hydrogels exhibit significantly enhanced responsive properties and mechanical strengths compared with typical DNA hydrogels. Moreover, the introduction of thermosensitive polymers can further endow the system with thermally switchable responsive properties.

In addition to their roles as revolutionary genome engineering tools, CRISPR-Cas systems are also highly promising candidates in the construction of biosensing systems and diagnostic devices, which have attracted significant attention recently. However, the CRISPR-Cas system cannot be directly applied in the sensing of non-nucleic acid targets, and the needs of synthesizing and storing different vulnerable guide RNA for different targets also increase the application and storage costs of relevant biosensing systems, and therefore restrict their widespread applications. To tackle these barriers, in this work, a versatile CRISPR-Cas12a-based biosensing platform was developed through the introduction of an enzyme-free and robust DNA reaction network, the entropy-driven dynamic DNA network. By programming the sequences of the system, the entropy-driven catalysis-based dynamic DNA network can respond to different types of targets, such as nucleic acids or proteins, and then activate the CRISPR-Cas12a to generate amplified signals. As a proof of concept, both nucleic acid targets (a DNA target with random sequence, T, and an RNA target, microRNA-21 (miR-21)) and a non-nucleic acid target (a protein target, thrombin) were chosen as model analytes to address the feasibility of the designed sensing platform, with detection limits at the pM level for the nucleic acid analytes (7.4 pM for the DNA target T and 25.5 pM for miR-21) and 0.4 nM for thrombin. In addition, the detection of miR-21 or thrombin in human serum samples further demonstrated the applicability of the proposed biosensing platform in real sample analysis.

Although smart hydrogels hold great promise in biosensing and biomedical applications, their response to external stimuli is governed by the passive diffusion‐dependent substance transport between hydrogels and environments and within the 3D hydrogel matrices, resulting in slow response to biomacromolecules and limiting their extensive applications. Herein, inspired by the respiration systems of organisms, an active strategy to achieve highly efficient biomolecular substance transport through the thermo‐stimulated “inhalation–exhalation” cycles of hydrogel matrices is demonstrated. The cryo‐structured poly(N‐isopropylacrylamide) (pNIPAM)–DNA hydrogels, composed of functional DNA‐tethered pNIPAM networks and free‐water‐containing macroporous channels, exhibit thermally triggered fast and reversible shrinking/swelling cycles with high‐volume changes, which drive the formation of dynamic water stream to accelerate the intake of external substances and expelling of endogenous substances, thus promoting the functional properties of hydrogel systems. Demonstrated by catalytic DNAzyme and CRISPR‐Cas12a‐incorporating hydrogels, significantly enhanced catalytic efficiency with up to 280% and 390% is achieved, upon the introduction of active “inhalation–exhalation” cycles, respectively. Moreover, remotely near‐infrared (NIR)‐triggering of “inhalation–exhalation” cycles is achieved after the introduction of NIR‐responsive MXene nanosheets into the hydrogel matrix. These hydrogel systems with enhanced substance transport and transformation properties hold promise in the development of more effective biosensing and therapeutic systems.