Super-resolution microscopy methods and systems enhanced by dielectric microspheres or microcylinders used in combination with metallic nanostructures

Inventors

Astratov, Vasily N. • Limberopoulos, Nicholaos I. • URBAS, Augustine M.

Assignees

United States Department of the Air Force

Abstract

Methods and systems for the super-resolution imaging can make visible strongly subwavelength feature sizes (even below 100 nm) in the optical images of biomedical or any nanoscale structures. The main application of the proposed methods and systems is related to label-free imaging where biological or other objects are not stained with fluorescent dye molecules or with fluorophores. This label-free microscopy is more challenging as compared to fluorescent microscopy because of the poor optical contrast of images of objects with subwavelength dimensions. However, these methods and systems are also applicable to fluorescent imaging. Their use is extremely simple, and it is based on application of the microspheres or microcylinders or, alternatively, elastomeric slabs with embedded microspheres or microcylinders to the objects which are deposited on the surfaces covered with thin metallic layers or metallic nanostructures. The mechanism of imaging involved use of the plasmonic near-fields for illuminating the objects and virtual imaging of these objects through microspheres or microcylinders. These methods and systems do not require use of fragile probe tips and slow point-by-point scanning techniques. These methods and systems can be used in conjunction with any types of microscopes including upright, inverted, fluorescence, confocal, phase-contrast, total internal reflection and others. Scanning the samples can be performed using micromanipulation with individual spheres or cylinders or using translation of the slabs. These methods and systems are applicable to dry, wet and totally liquid-immersed samples and structures.

Core Innovation

The invention provides methods and systems for super-resolution imaging that enable visualization of nanoscale structures with feature sizes well below the classical diffraction limit, even down to below 100 nm. The main application is label-free imaging of biological or other objects without the use of fluorescent dyes or fluorophores, which poses challenges due to poor optical contrast of subwavelength-sized objects. These methods are also applicable to fluorescent microscopy. The approach utilizes dielectric microspheres or microcylinders placed adjacent to the sample, combined with surfaces covered by metallic layers or nanostructures that enhance plasmonic near-fields, thereby illuminating the objects for virtual magnified imaging.

The problem addressed is the difficulty in label-free optical microscopy to achieve high resolution and contrast for subwavelength objects without fluorescent labeling. Conventional techniques face limitations such as low contrast, slow point-by-point scanning, or fabrication complexity. Existing super-resolution methods often rely on fluorescent labels or fragile scanning probes. Plasmonic near-fields provide highly detailed spatial information but decay exponentially and require enhancement. Metallic nanostructures can generate enhanced plasmonic near-fields at selected illumination wavelengths that excite localized surface plasmon resonances or surface plasmon polaritons.

The solution involves placing dielectric microspheres or microcylinders in contact or near-contact with the objects on substrates coated with metallic nanostructures designed to enhance plasmonic near-fields. The microspheres create a magnified virtual image that can be observed by conventional far-field microscopes, thus preserving super-resolution features via magnification. The invention provides multiple embodiments including low-index spheres in air, high-index spheres in liquids, elastomeric slabs embedding spheres, and micromanipulatable spheres or slabs. Structured illumination using nanoplasmonic arrays can be combined to further increase resolution.

Claims Coverage

The patent includes two independent claims covering both a super-resolution optical imaging method and an imaging system. The main inventive features involve the combination of microstructures and metallic nanostructures adjacent to the sample to enhance plasmonic near-fields for improved imaging.

Overall, the claims cover a super-resolution imaging method and system combining dielectric microspheres or microcylinders positioned adjacent to the sample with metallic nanostructures engineered to enhance plasmonic near-fields, compatible with multiple microscope modalities, microstructure indices, and manipulation approaches, providing improved imaging beyond the diffraction limit.

Stated Advantages

Documented Applications