Silver nanoparticles deposited carbon microspheres nanozyme with enhanced peroxidase-like catalysis for colorimetric detection of Hg2+ in seafood

Novel methods for high-performance detection of Hg²⁺ in seafood are critical for ensuring food safety and human health. Herein, Ag nanoparticles (Ag NPs) were successfully deposited on carbon microspheres (CMs) to form Ag NPs-CMs nanocomplex. The proposed Ag NPs-CMs could oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidation state TMB (oxTMB) in the presence of hydrogen peroxide (H₂O₂) and had a significant UV-vis absorption peak at 652 nm. The excellent peroxidase-like activity was attributed to the increased electrostatic attraction of CMs and the catalytic synergistic effect. After adding Hg²⁺, the catalytic activity of Ag NPs-CMs was specifically enhanced and the Michaelis-Menten constant (K_m) decreased from 0.067 to 0.052 mmol/L due to the formation of Ag-Hg amalgam which produced more superoxide anions (O₂^•-) and hydroxyl radicals (•OH). The linear response ranges for Hg²⁺ were 2~833 nmol/L and 2.5~40 μmol/L, with the low detection limit of 1.10 nmol/L. This method was applied to detect Hg²⁺ in seafood with satisfactory recoveries of 95.65~106.56%. A hydrogel kit was designed for portable detection of Hg²⁺, and the response range was 0.5~5 μmol/L. This work provides a reliable method for visual Hg²⁺ detection in seafood as well as a feasible strategy for the design of high-performance nanozymes.

Room-Temperature One-Step Synthesis of Silver/Reduced Graphene Oxide Nanocomposites as an Excellent Microwave Absorber

The present study is focused on room-temperature synthesis carried out by reduction of an aqueous silver nitrate (AgNO₃) and AgNO₃/graphene oxide (GO) dispersion using a low-cost commercial Fehling B solution in one step to form silver quantum dots (Ag QDs) and their Ag/reduced graphene oxide (Ag/RGO) nanocomposites and their characterization. The crystallinity, surface chemistry, structural, and morphological studies indicated the formation of crystalline small-sized quasispherical-functionalized Ag particles distributed uniformly on the surface of RGO. The conductivity measurements further showed an improvement in the conductivity of Ag/RGO nanocomposites as compared to neat Ag QDs. Our findings showed that Ag/RGO nanocomposites prepared by using 0.055 wt % of GO exhibited a total enhanced electromagnetic interference (EMI)-shielding efficiency (SE_T) of ∼39.2-42.3 dB (2-8 GHz) with a maximum value of ∼43.8 dB at 7. 5 GHz due to conduction loss, an interconnected conducting network, and a synergistic effect, and it followed an absorption mechanism. Furthermore, this superior absorption-dominated shielding conferred reflection loss (R_L) in the range of -79 to -82.5 dB with a R_L minima of -88 dB at 7.5 GHz, considering an effective absorption bandwidth of ∼6 GHz with 99.9% absorptivity. It is anticipated that Ag/RGO nanocomposites prepared in one step at room temperature could find potential EMI-shielding applications.

Hierarchical Porous Film with Layer-by-Layer Assembly of 2D Copper Nanosheets for Ultimate Electromagnetic Interference Shielding

The emergence of technologies, such as 5G telecommunication, electric vehicles, and wearable electronics, has prompted demand for ultrahigh-performance and cost-effective shielding materials to protect against both the potentially harmful effects of electromagnetic interference (EMI) on human health and electronic device operation. Here, we report hierarchical porous Cu foils via an assembly of single-crystalline, nanometer-thick, and micrometer-long copper nanosheets and their use in EMI shielding. Layer-by-layer assembly of Cu nanosheets enabled the formation of a hierarchically structured porous Cu film with features such as multilayer stacking; two-dimensional networking; and a layered, sheetlike void architecture. The hierarchical-structured porous Cu foil exhibited outstanding EMI shielding performance compared to the same thickness of dense copper and other materials, exhibiting EMI shielding effectiveness (SE) values of 100 and 60.7 dB at thicknesses of 15 and 1.6 μm, respectively. In addition, the EMI SE of the hierarchical porous Cu film was maintained up to 18 months under ambient conditions at room temperature and showed negligible changes after thermal annealing at 200 °C for 1 h. These findings suggest that Cu nanosheets and their layer-by-layer assembly are one of the promising EMI shielding technologies for practical electronic applications.