Plasmonic Nano-aperture Label-free Imaging for Nano-Biosensing

Label-free observation of transparent nanoparticles by far-field optical microscopy faces fundamental challenges in resolution and detection sensitivity. They are difficult to detect because their ability to scatter light drastically diminishes with decreasing size. Among various imaging techniques, those based on propagating surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) have shown promise and respective limitations. In this paper, we demonstrate ultra near-field index modulated PlAsmonic NanQ-apeRture 1Abel-free iMAging (PANORAMA) that addresses existing issues for both SPR and LSPR imaging techniques [1]–[2]. On one hand, PANORAMA can produce diffraction-limited lateral resolution free of the smearing effect in SPR imaging. PANORAMA also has higher surface sensitivity. With dynamic imaging, PANORAMA can produce localization-based super-resolution using time-gating. PANORAMA addresses the sparse sampling issue in LSPR imaging by achieving dense sampling with a large imaging fill factor. The bright-field approach also provides much higher light throughput compared to dark-field microscopy, empowering higher imaging speed. Its system configuration is identical to a standard bright-field microscope using a trans-illumination tungsten-halogen lamp and a camera without the need for laser, LED, or interferometric detection. Therefore, PANORAMA is readily implementable on any existing commercial microscopes.