Wafer‐Scale Deterministic Fabrication of Axis‐Ratio–Engineered Silicon Nanoparticles for On‐Resonance Electric–Magnetic Dipole Interference

High-index dielectric nanoparticles support coexisting electric and magnetic dipole resonances whose interference governs directional scattering. Achieving reproducible control of this interference has remained challenging. Here, we report a wafer-scale top-down fabrication strategy that yields silicon nanoparticles with exceptional uniformity (coefficient of variation 1.7%-2.4%), enabling deterministic axis-ratio (AR) tuning as a design parameter. By defining pillar geometry and precisely controlling annealing and oxidation, we tune dipolar mode overlap to realize on-resonance Kerker-type forward scattering with a forward-to-backward ratio of 12.5, which is among the highest reported for single silicon nanoparticles under comparable substrate-supported finite-NA measurement geometries. At the optimized AR = 2.1, this near-Kerker condition enables ultrasensitive refractometric sensing and label-free monitoring of protein-corona formation in serum, achieving a resolution of ~10⁻⁴ refractive-index units per 1% fetal bovine serum (FBS). These results establish AR engineering as a deterministic route to tailor electric-magnetic interference, linking wafer-scale fabrication precision with single-particle optical control and quantitative bio-interfacial sensing.