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High-speed chip-based nanoscopy to discover real-time sub-cellular dynamics

Final Report Summary - NANOSCOPY (High-speed chip-based nanoscopy to discover real-time sub-cellular dynamics)

The invention of super-resolution optical microscopy, commonly referred as optical nanoscopy has enabled the researchers to visualize nanoscale bio-system inside a living cell. This invention was credited with Nobel Prize in Chemistry in 2014. Although, the invention of optical nanoscopy is bound to positively influence several domains such as life science, medical biology and cell biology; its true impact is hindered as present-day optical nanoscopes are costly (0.5-1 M€), complex and lack multi-modality operations. To-date, all of advanced optical nanoscope techniques use bulk optical components to generate and deliver light illumination patterns, and costly opto-mechanical components to steer the illumination pattern. This approach is prone to misalignment and therefore successful implementation requires well-calibrated optics hosted in a stable and mechanically rigid platform. This increases their cost and complexity.

In my ERC grant, I proposed to develop on-chip optical nanoscopy by harnessing integrated photonics and nanotechnology. The main idea consists in taking the generation, the steering and the delivery of the entire laser illumination pattern from the optical microscope and transfer it to the photonic-chip, consisting of an array of optical waveguides. The biological samples are placed on top of an optical waveguide and is illuminated by the evanescent field present on top of the waveguide surface. Integrated optical waveguides enables shaping of the laser illumination field as required for respective imaging techniques. The rationale is that photonic-chip offer great miniaturization of entire beam shaping that is required for different optical nanoscopy methodologies and that can be barely engineered with conventional far-field optics.

Within my ERC project, I have demonstrated different optical nanoscopy methodology using an integrated photonic chip: a) on-chip single molecule localization based super-resolution microscopy (dSTORM), b) on-chip fluctuating light intensity based optical nanoscopy (ESI, MUSICAL, SRRF) and c) on-chip structured illumination microscopy (SIM). The photonic-chip that generates and delivers the entire illumination can be retrofitted with any standard microscopy enabling it to acquire super-resolved images. Furthermore, besides being compact and affordable, I have demonstrated that chip-based nanoscopy has surpassed the technical capabilities of present day nanoscopy solution, in terms of field of view imaged (applicable on-chip single molecule localization microscopy) and the achievable resolution (applicable for on-chip SIM). On-chip dSTORM has shown the capabilities of acquiring 100X larger areas than otherwise possible; while on-chip SIM has shown to extend the resolution of present-day SIM by 30%. The ERC project has demonstrated the proof-of-principle of multi-modal optical imaging tools within a “single photonic chip” and with “any standard microscope”.

It was also demonstrated that by using high-refractive index waveguide material, such as silicon nitride and tantalum pentoxide it is possible to generate high-intensity on top of the waveguide chip to enable on-chip nanoscopy. The use of high-refractive index material also helps in enhancing the resolution of different on-chip nanoscopy methodology. While, choosing the waveguide material for on-chip nanoscopy, care must be taken to avoid background auto-fluorescence originating from the waveguide material, which increase rapidly with the short wavelengths, most noticeable between 400-500 nm.

The successful implementation of chip-based multi-modality optical nanoscopy has opened a new and a niche area of research activities in the field of on-chip optical nanoscopy. This project has opened new research and exploitation activates related towards on-chip optical nanoscopy. Two patent applications protecting the inventions of a) on-chip single molecule localization microscopy (such as dSTORM, PALM, etc) and b) on-chip SIM have been submitted.