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• A method of promoting the axial feature size of PPI-DLW is proposed. • A 3D hollow focus was generated using one beam without light field superposition. • Two-focus parallel scanning using 3D hollow focus was realized without hardware updating based on a classic method. • The isotropic 30 nm feature size was realized. • This work will improve the ability of PPI-DLW to fabricate arbitrary 3D structures. Peripheral-photoinhibition (PPI)-based direct laser writing (DLW) inspired by simulated emission depletion (STED) microscopy has improved the fabrication resolution of three-dimensional (3D) structures on the nano-scale. However, most previous studies have focused on the lateral feature size, neglecting axial-feature-size enhancement. This article proposes a novel method to simultaneously reduce the axial and lateral feature sizes of PPI-DLW. By employing a pseudo 3D hollow focus, a suspended nanowire with an isotropic 30-nm feature size was realized. Such an isotropic 3D hollow focus for photoinhibition is generated using a single beam instead of two-beam superposition, thus it does not increase the system complexity of a PPI-DIW system. Owing to the reduced feature size in all three dimensions and the low systematic complexity, the proposed method improves the capabilities of PPI-DLW for fabricating arbitrary 3D structures. [ABSTRACT FROM AUTHOR]