Cylindrical Illumination Confocal Spectroscopy for Single Molecule Detection
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Solution Overview
Problem
Current single molecule detection (SMD) systems face limitations in accuracy, throughput, and practical applicability due to a diffraction-limited observation volume that results in low mass detection efficiency and variability in molecular trajectory, leading to inefficient detection of rare biomolecules.
Innovation Solution
A cylindrical illumination confocal spectroscopy system that uses a sheet-like observation volume expanded in one dimension to span the cross-section of a microchannel, with a microfabricated rectangular aperture to ensure uniform illumination and detection across the channel, enhancing mass detection efficiency and reducing variability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a diffraction-limited observation volume is used in standard SMD, then high signal-to-noise ratio detection is achieved, but mass detection efficiency deteriorates to 1% or less
Solution Approach 1:
The patent transforms the traditional three-dimensional diffraction-limited observation volume into a two-dimensional sheet-like observation volume by expanding it in one dimension (the lateral dimension perpendicular to the flow direction) while maintaining confinement in the other dimensions. This dimensional transformation allows the observation volume to span the entire cross-section of the microchannel, thereby detecting all molecules that pass through the channel while preserving the confocal detection advantages.
2Measurement precision
If a small diffraction-limited observation volume is used, then background suppression is improved, but detection uniformity deteriorates due to molecular trajectory variability
Solution Approach 1:
By expanding the observation volume in the lateral dimension to match the channel width, the patent ensures that molecules regardless of their transverse position or trajectory within the channel all pass through the detection region. This eliminates the variability caused by different molecular trajectories while maintaining confocal detection capabilities through the sheet-like geometry.
Solution Approach 2:
The sheet-like observation volume creates a uniform detection region where illumination and detection are homogeneous across the channel cross-section. This homogeneity ensures that all molecules experience similar detection conditions, leading to consistent burst parameters and improved detection uniformity.
3Productivity
If the observation volume is expanded to increase mass detection efficiency, then throughput is improved, but signal-to-noise ratio deteriorates
Solution Approach 1:
The patent achieves observation volume expansion solely in the lateral dimension (perpendicular to flow) rather than expanding in all three dimensions. This selective expansion increases the detection efficiency by spanning the channel cross-section while maintaining a thin profile in the flow direction, thereby preserving the confocal signal-to-noise ratio.
Solution Approach 2:
The observation volume has different characteristics in different dimensions: it is expanded and uniform in the lateral dimension to ensure all molecules are detected, but remains confined and diffraction-limited in the axial dimension to maintain signal-to-noise ratio. This anisotropic structure optimizes both detection efficiency and signal quality.
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
The system achieves near 100% mass detection efficiency and high uniformity in burst rate and height, making it more accurate and robust for quantifying single molecules, while maintaining sensitivity and ease of integration with microfluidic systems.
Implementation Method 1
The illumination system includes a beam-shaping lens unit constructed and arranged to provide a substantially planar illumination beam that subtends across, and is longer than, a lateral dimension of the fluid channel, the substantially planar illumination beam having a diffraction limited thickness
Implementation Method 2
an objective lens unit arranged proximate the fluidic device, an illumination system in optical communication with the objective lens unit to provide light to illuminate a sample through the objective lens unit
Implementation Method 3
The detection system comprises an aperture stop defining a substantially rectangular aperture having a longitudinal dimension and a transverse dimension. The aperture stop is arranged so that the substantially rectangular aperture is confocal with an illuminated portion of the fluid channel such that the transverse dimension of the substantially rectangular aperture substantially subtends the lateral dimension of the fluid channel without extending substantially beyond the fluid channel and allows light to pass from only a uniform excitation region while occluding light from outside the uniform excitation region
Implementation Method 4
SMD allows the study of molecular properties without the bias of ensemble averaging. Although methods using scanning probe, resonant, and electrical sensors are being developed, it can also be performed using confocal spectroscopy, an optical detection method in which a collimated laser beam is focused into a diffraction-limited spot about 1 femtoliter in volume and used to excite single fluorescent molecules
Data Source
AI summary
A cylindrical illumination confocal spectroscopy system has a fluidic device having a fluid channel defined therein, an objective lens unit arranged proximate the fluidic device, an illumination system in optical communication with the objective lens unit to provide light to illuminate a sample through the objective lens unit, and a detection system in optical communication with the objective lens unit to receive at least a portion of light that passes through the objective lens unit from the sample. The illumination system includes a beam-shaping lens unit constructed and arranged to provide a substantially planar illumination beam that subtends across, and is longer than, a lateral dimension of the fluid channel.