On-chip light-scattering enhancement enables high performance single-particle tracking under conventional bright-field microscope

Scattering-based single-particle tracking (S-SPT) has opened new avenues for highly sensitive label-free detection and characterization of nanoscopic objects, making it particularly attractive for various analytical applications. However, a long-standing issue hindering its widespread applicability is its high technical demands on optical systems. The most promising solution entails implementing on-chip light-scattering enhancement, but the existing field-enhancement technology fails as their highly localized field is insufficient to cover the three-dimensional trajectory of particles within the interrogation time. Here, we present a straightforward and robust on-chip microlens-based strategy for light-scattering enhancement, providing an enhancement range ten times greater than that of near-field optical techniques. These properties are attributed to the increased long-range optical fields and complex composite interactions between two closely spaced structures. Thanks to this strategy, we demonstrate that high-performance S-SPT can be achieved, for the first time, under a conventional bright-field microscope with illumination powers over 1,000 times lower than typically required. This significantly reduces the technical demands of S-SPT, representing a significant step forward in facilitating its practical application in biophotonics, biosensors, diagnostics, and other fields.