Switchable Fluorophore Anisotropy Readout for Slow Rotational Diffusion
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Solution Overview
Problem
Current methods for measuring rotational diffusion of large molecules in living cells are limited by the nanosecond-scale time-window of conventional time-resolved fluorescence anisotropy, which cannot distinguish molecular complexes based on their tumbling rates due to homo-fret interference and molecular size limitations.
Innovation Solution
A method and system using reversibly switchable fluorophores, activated by specific light pulses, to achieve long-lived photo-selected states for measuring polarization and anisotropy, enabling extended temporal windows beyond fluorescence lifetime through angular narrowing and photo-selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If conventional time-resolved fluorescence anisotropy is used to measure rotational diffusion, then measurement can be performed with standard fluorophores, but the time window is limited to nanosecond scale which cannot detect larger molecular complexes
Solution Approach 1:
The patent changes the key parameter of fluorescence lifetime by using long-lived fluorophores (microsecond to millisecond scale) instead of conventional nanosecond fluorophores. This parameter change extends the observable time window from nanoseconds to microseconds/milliseconds, enabling detection of rotational diffusion in larger molecular complexes that tumble too slowly to be distinguished from stationary within the conventional nanosecond time window.
Solution Approach 2:
The patent introduces an intermediary mechanism (reversible photo-selection) that allows controlled population of long-lived fluorescent states. By using light pulses to selectively populate long-lived fluorescent states with specific orientations, the system bridges the gap between short excitation pulses and long fluorescence lifetimes, enabling precise measurement of slow rotational diffusion.
2Duration of action of moving object
If reversibly switchable fluorophores with long-lived states are used to extend the time window, then larger molecules can be detected, but homo-FRET interference occurs
Solution Approach 1:
The patent extracts or removes the harmful homo-FRET interference by using reversible photo-selection to populate long-lived fluorescent states selectively. By controlling which molecules are in the fluorescent state through optical switching, the method isolates the signal from individual molecules or controlled populations, eliminating the homogeneous FRET interference that occurs when multiple fluorophores are simultaneously excited and energy transfers between them.
Solution Approach 2:
The patent employs periodic action through pulsed optical excitation and reversible switching sequences. By alternately switching fluorophores between dark and long-lived fluorescent states using timed light pulses, the system controls the temporal distribution of fluorescent molecules, allowing measurement of rotational diffusion while minimizing homo-FRET through controlled periodic population of fluorescent states.
3Measurement precision
If fluorescence anisotropy is used to measure rotational diffusion, then molecular orientation information can be obtained, but the method cannot distinguish slow tumbling of large complexes from stationary within nanosecond time window
Solution Approach 1:
The patent changes the timescale parameter from nanoseconds to microseconds/milliseconds by using long-lived fluorophores. This parameter change allows the measurement window to match the rotational diffusion timescale of larger molecular complexes, enabling distinction between slow tumbling and stationary states that are indistinguishable in conventional nanosecond TR-FA.
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 specificity and sensitivity in measuring rotational diffusion and molecular orientation of large molecules in vitro and in cells, allowing studies of molecular assemblies and interactions, such as drug-antigen interactions and viral maturation, with improved sensitivity and temporal resolution.
Implementation Method 1
applying of a first activation light pulse of a wavelength suitable for switching the reversibly switchable fluorophores into a long-lived photo-selected state
Implementation Method 2
applying of a read-out light pulse and detecting emission from the reversibly switchable fluorescent proteins
Implementation Method 3
Polarization and anisotropy of the reversibly switchable fluorophores in the long-lived photo-selected state are read out
Data Source
AI summary
A method for measuring polarization and anisotropy of fluorophores comprises activating reversibly switchable fluorophores in a sample. The activating comprises applying of a first activation light pulse of a wavelength suitable for switching the reversibly switchable fluorophores into a long-lived photo-selected state. Polarization and anisotropy of the reversibly switchable fluorophores in the long-lived photo-selected state are read out. The reading out in turn comprises applying of a read-out light pulse and detecting emission from the reversibly switchable fluorescent proteins. The first activation light pulse or the read-out light pulse comprises non-polarized light or circularly polarized light. The other one of the first activation light pulse and the read-out light pulse comprises linearly polarized light. A system for measuring polarization and anisotropy of fluorophores is also disclosed.