Digital Holographic Microscope Using Frustrated Total Internal Reflection
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Solution Overview
Problem
Current techniques for imaging cell-substrate interfaces, such as TIRFM and IRM, provide limited quantitative information on cellular membrane morphology and are unable to generate accurate, quantitative surface profile images of live cellular membranes, hindering the understanding of cellular motion and processes like cell migration.
Innovation Solution
Digital holographic microscopy utilizing frustrated total internal reflection (fTIR) to generate holographic interference patterns, which are then numerically reconstructed to provide precise phase profiles of the cell-substrate interface, allowing for nanometric precision in optical thickness variation measurements and imaging over arbitrary distances and orientations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If TIRFM is used to image cell-substrate contacts, then signal-to-noise ratio is dramatically increased, but information on cellular membrane surface morphology is largely absent
Solution Approach 1:
The patent combines TIRFM's evanescent field excitation with digital holographic microscopy to create a system that simultaneously achieves high signal-to-noise ratio at the interface and quantitative phase imaging capability. The holographic interferometer records both amplitude and phase information, merging the advantages of TIRFM's optical sectioning with holography's quantitative surface profiling.
Solution Approach 2:
The imaging system is designed to perform multiple functions: it provides both the high-contrast interface imaging of TIRFM and the quantitative phase information of holographic microscopy. The system can simultaneously image protein dynamics and membrane surface morphology, making it a multi-functional tool for cellular interface studies.
2Measurement precision
If IRM is used to estimate interface thickness profile, then qualitative interpretation of surface profile is possible, but the interference image is complicated by reflection image of cell body and contents
Solution Approach 1:
The patent extracts only the relevant interface information by using the evanescent field's exponential decay characteristic. The TIRFM component selectively excites fluorophores within ~100 nm of the coverslip surface, effectively filtering out reflections from deeper cell body structures. The holographic component records phase information specifically from the interface region, separating it from complicating background reflections.
Solution Approach 2:
The system applies local quality by creating an evanescent field that is highly localized to the immediate interface region. The exponential decay of the evanescent wave ensures that only structures very close to the coverslip (within the penetration depth) are imaged, providing localized high-resolution information about the cell-substrate interface while ignoring distant cellular structures.
3Ease of operation
If conventional microscopy is used for real-space imaging, then direct visualization is achieved, but magnification of hologram in real space is mostly impractical
Solution Approach 1:
The patent replaces mechanical magnification with computational reconstruction. Instead of using complex optical magnification systems to enlarge holograms in real space, the invention uses digital signal processing and numerical reconstruction algorithms to achieve high-resolution images from the recorded holographic data, eliminating the need for practical mechanical magnification of the hologram itself.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables high-resolution, quantitative imaging of cellular surface profiles with enhanced signal-to-noise ratio and minimal light intensity requirements, overcoming the limitations of TIRFM and IRM by providing detailed insights into cellular motion and membrane morphology.
Implementation Method 1
TIRFM uses a higher-index medium n1, and a lower-index medium n2 to reflect incident light back into the first medium. The light does not propagate into the second medium, except for an evanescent wave field, whose amplitude decays exponentially over a distance a fraction of a wavelength ( ̃λ/3).
Implementation Method 2
the holographic interference between the object and reference fields is created optically and recorded electronically by a CCD camera
Data Source
AI summary
The present invention provides for a digital holographic microscope using a holographic interferometer and incorporating a TIR sample mount and microscopic imaging optics. The microscope uses phase shifting from frustrated internal reflection within a prism to measure nanometric distances. The invention also provides for a numerical reconstruction algorithm of an inclined surface of the object/prism.