Xiujun Fan

Immunosensors achieve highly selective detection through specific antigen–antibody recognition. However, their signal-amplification strategies, which are commonly based on natural enzymes or noble-metal nanomaterials, often suffer from poor stability, high cost, and susceptibility to matrix interference. Although nanozymes have emerged as promising alternatives, their heterogeneous active domains and poorly defined electronic structures often result in less controllable uncontrollable catalytic behavior. Single-atom nanozymes (SANs), featuring atomically dispersed active sites and tunable coordination/electronic structures, establish well-defined structure–activity relationships and provide a mechanistic link between atomic-scale active-site engineering and sensing performance through integration with immunorecognition interfaces. In this review, recent advances in SAN-enabled immunosensors are systematically summarized from the perspective of the structure–mechanism–application relationship. We discuss active-site engineering strategies, characterization techniques, and catalytic mechanisms that govern enzyme-mimicking activity, followed by representative signal-amplification pathways and sensing platforms across different detection modes. Emerging applications in clinical diagnostics and food and agricultural safety are highlighted. Finally, the key challenges toward practical translation and future perspectives, including AI-guided materials discovery, mechanism-guided design, multifunctional sensing systems, and real-world deployment, are discussed. This review aims to provide fundamental design principles for the rational development of next-generation high-performance single-atom immunosensors. Graphical Abstract

MOF-derived materials constitute a versatile family with diverse morphological features, and these derivatives have exhibited promising electrochemical performance when applied in supercapacitors.

The development of efficient and stable catalysts for scalable and sustainable hydrogen peroxide (H ₂ O ₂ ) electrosynthesis via two‐electron oxygen reduction reaction (2e‐ORR) is of great significance to replace the high‐pollution anthraquinone oxidation process. Herein, O/N dual‐coordinated silicon (Si) single‐atom catalysts (SACs) uniformly immobilized on N‐doped graphene (SiO ₃ ‐NC) are successfully synthesized using silicate as Si dopant via controllable solvothermal and nitridation processes. In the synthesize reaction, Si centers convert from Si–O ₃ planar triangle to unsymmetrical Si–O ₃ N ₁ tetrahedron, which effectively modify the electronic distribution of the carbon matrix, providing high‐density active sites for electrocatalytic H ₂ O ₂ production. SiO ₃ ‐NC catalysts achieve industrial‐relevant current densities for H ₂ O ₂ production with a record‐high productivity of 63.69 mol h ⁻¹ g _cat. ⁻¹ , while maintaining exceptional Faradaic efficiencies and stability. In situ spectroscopic studies and theoretical calculations uncover that the unsymmetrically Si–O ₃ N ₁ configuration acts as an active center, which affords near‐optimal binding strength for OOH* adsorption and accelerates the kinetics of H ₂ O ₂ formation, thus promoting 2e‐ORR process.

Ru-based catalysts manifest unparalleled hydrogen evolution reaction (HER) performance, but the hydrolysis of Ru species and the accumulation of corresponding reaction intermediates greatly limit HER activity and stability. Herein, Ru nanoparticle assemblies modified with single Mo atoms and supported on N-incorporated graphene (referred to as MoRu-NG) are compounded via hydrothermal and chemical vapor deposition (CVD) methods. The incorporation of single Mo atoms into Ru lattices modifies the local atomic milieu around Ru centers, significantly improving HER catalytic behavior and stability. More specifically, MoRu-NG achieves overpotentials of 53 mV and 28 mV at 10 mA cm⁻², with exceptional stability in acidic and alkaline seawater solutions, respectively. In MoRu-NG, Ru atoms have a special electronic structure and thus possess optimal hydrogen adsorption energy, which indicates that excellent HER activity mainly hinges upon Ru centers. To be specific, the d-electron orbitals of Ru atoms are close to half full, giving Ru atoms moderate bond energy for the assimilation and release of hydrogen, which is beneficial for the conversion of reaction intermediates. Moreover, the incorporation of single Mo atoms facilitates the formation of O and O’-bidentate ligands, significantly enhancing the structural stability of MoRu-NG in universal-pH seawater electrolysis. This work advances a feasible construction method of hexagonal octahedral configuration (Ru-O-Mo-N-C) and provides a route to synthesize an efficient and stable catalyst for electrocatalytic HER in universal-pH seawater.

Ru-based catalysts manifest unparalleled hydrogen evolution reaction (HER) performance, but the hydrolysis of Ru species and the accumulation of corresponding reaction intermediates greatly limit HER activity and stability. Herein, Mo single atoms modified Ru nanoparticles assemblies supported on N-incorporated graphene (referred to as MoRu-NG) are compounded via hydrothermal and chemical vapor deposition methods (CVD). The incorporation of Mo single atoms into Ru lattices modifies the local atomic milieu around Ru centers, significantly improving HER catalytic behavior and stability. More specifically, MoRu-NG achieves the overpotential of 53 mV and 28 mV at 10 mA cm–2 with exceptional stability in acidic and alkaline seawater solutions, respectively. In MoRu-NG, Ru atoms have special electronic structure and thus possess optimal hydrogen adsorption energy, which indicates that the excellent HER activity mainly hinges upon Ru centers. To be specific, the d-electron orbitals of Ru atoms are close to half full, giving Ru atoms moderate bond energy for the assimilation and release of hydrogen, which is beneficial for the conversion of reaction intermediates. Moreover, the incorporation of Mo single atoms facilitates the formation of O, O'-bidentate ligands, significantly enhancing the structural stability of MoRu-NG in pH-universal seawater electrolysis. This work advances a feasible construction method of hexagonal octahedral configuration (Ru–O–Mo–N–C) and provides a route to synthesize the efficient and stable catalyst for electrocatalytic HER in pH-universal seawater.

Cobalt-nitrogen-carbon (Co-N-C) catalysts with a CoN₄ structure exhibit great potential for oxygen reduction reaction (ORR), but the imperfect adsorption energy toward oxygen species greatly limits their reduction efficiency and practical application potential. Here, F-coordinated Co-N-C catalysts with square-pyramidal CoN₄-F₁ configuration are successfully synthesized using F atoms to regulate the axial coordination of Co centers via hydrothermal and chemical vapor deposition methods. During the synthesis process, the geometry structure of the Co atom converts from six-coordinated Co-F₆ to square-pyramidal CoN₄-F₁ in the coordinatively unsaturated state, which provides an open binding site for the O₂. The introduction of axial F atoms into the CoN₄ plane alters the local atomic environment around Co, significantly improving the ORR activity and Zn-air batteries performance. In situ spectroscopy proves that CoN₄-F₁ sites strongly combine with the OOH* intermediate and facilitate the splitting of O-O bond, making OOH* readily decompose into O* and OH* via a dissociative pathway. Theoretical calculations confirm that the axial F atom effectively reduces the electronic density of the Co centers and facilitates the desorption of the OH* intermediate, efficiently accelerating the overall ORR kinetics. This work advances a feasible synthesis mechanism of axial ligands and provides a route to construct efficient high-coordination catalysts.

Developing efficient metal‐free catalysts to directly synthesize hydrogen peroxide (H₂O₂) through a 2‐electron (2e) oxygen reduction reaction (ORR) is crucial for substituting the traditional energy‐intensive anthraquinone process. Here, in‐plane topological defects enriched graphene with pentagon‐S and pyrrolic‐N coordination (SNC) is synthesized via the process of hydrothermal and nitridation. In SNC, pentagon‐S and pyrrolic‐N originating from thiourea precursor are covalently grafted onto the basal plane of the graphene framework, building unsymmetrical dumbbell‐like S─C─N motifs, which effectively modulates atomic and electronic structures of graphene. The SNC catalyst delivers ultrahigh H₂O₂ productivity of 8.1, 7.3, and 3.9 mol g_catalyst⁻¹ h⁻¹ in alkaline, neutral, and acidic electrolytes, respectively, together with long‐term operational stability in pH‐universal electrolytes, outperforming most reported carbon catalysts. Theoretical calculations further unveil that defective S─C─N motifs efficiently optimize the binding strength to OOH^* intermediate and substantially diminish the kinetic barrier for reducing O₂ to H₂O₂, thereby promoting the intrinsic activity of 2e‐ORR.

Developing efficient and robust hydrogen evolution reaction (HER) catalysts for scalable and sustainable hydrogen production through electrochemical water splitting is strategic and challenging. Herein, heterogeneous Mo ₈ O ₂₆ ‐NbN _x O _y supported on N‐doped graphene (defined as Mo ₈ O ₂₆ ‐NbN _x O _y /NG) is synthesized by controllable hydrothermal reaction and nitridation process. The O‐exposed Mo ₈ O ₂₆ clusters covalently confined on NbN _x O _y nanodomains provide a distinctive interface configuration and appropriate electronic structure, where fully exposed multiple active sites give excellent HER performance beyond commercial Pt/C catalyst in pH‐universal electrolytes. Theoretical studies reveal that the Mo ₈ O ₂₆ ‐NbN _x O _y interface with electronic reconstruction affords near‐optimal hydrogen adsorption energy and enhanced initial H ₂ O adsorption. Furthermore, the terminal O atoms in Mo ₈ O ₂₆ clusters cooperate with Nb atoms to promote the initial H ₂ O adsorption, and subsequently reduce the H ₂ O dissociation energy, accelerating the entire HER kinetics.