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We report the search results of light dark matter through its interactions with shell electrons and nuclei, using the commissioning data from the PandaX-4T liquid xenon detector. Low energy events are selected to have an ionization-only signal between 60 to 200 photoelectrons, corresponding to a mean nuclear recoil energy from 0.77 to 2.54 keV and electronic recoil energy from 0.07 to 0.23 keV. With an effective exposure of 0.55  tonne·year, we set the most stringent limits within a mass range from 40  MeV/c^{2} to 10  GeV/c^{2} for pointlike dark matter-electron interaction, 100  MeV/c^{2} to 10  GeV/c^{2} for dark matter-electron interaction via a light mediator, and 3.2 to 4  GeV/c^{2} for dark matter-nucleon spin-independent interaction. For DM interaction with electrons, our limits are closing in on the parameter space predicted by the freeze-in and freeze-out mechanisms in the early Universe.

Two-dimensional (2D) metal-organic framework (MOF) nanosheets emerging as a new member of the 2D family have received significant research interest in recent years. Herein, we have successfully synthesized 2D copper-based MOF nanosheets with bimetallic anchorage using a facile two-step process at room temperature and ambient pressure, denoted as Cu(HBTC)-1/Fe 3 O 4 -AuNPs nanosheets. The as-synthesized 2D bimetallic MOF nanosheets displayed enhanced peroxidase-like activity with relatively high catalytic velocity and affinity for substrates compared with previously reported peroxidase mimics. Furthermore, their intrinsic peroxidase-like catalytic activity could be flexibly regulated by single-stranded DNA (ssDNA), exhibiting the enhancement of 3,3',5,5'-tetramethylbenzidine (TMB) oxidation or inhibition of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt (ABTS) oxidation due to the adsorption of ssDNA via π-π stacking. Accordingly, on the basis of their peroxidase-like activity, our prepared 2D bimetallic immobilized MOF nanosheets achieved ultra-sensitive detection of H 2 O 2 with a linear range of 2.86 to 71.43 nM, and comparable detection performance for glucose with a linear range of 12.86 to 257.14 μM. By means of their controllable peroxidase-like activity, a versatile colorimetric sensing platform was developed which realized the detection of sulfadimethoxine (SDM) with a linear range of 3.57 to 357.14 μg L -1 and the limit of detection (LOD) of 1.70 μg L -1 . With the multiplexed performance for detecting various targets, our as-synthesized bimetallic MOF nanosheets hold great promise for applications in environmental monitoring, as well as bioassays by virtue of their good biocompatibility.