Radiofrequency-Multiplexed Fluorescence Imaging for Sub-Millisecond Resolution
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Solution Overview
Problem
Current fluorescence microscopy technologies are limited by their inability to achieve sub-millisecond time resolution, which hinders the capture of dynamic biochemical processes in live cells and high-throughput analysis in flow cytometry.
Innovation Solution
The FIRE (Fluorescence Imaging by Radiofrequency Multiplexed Excitation) system employs orthogonal frequency-domain multiplexing techniques for parallel pixel excitation and high-speed readout, utilizing acousto-optic deflectors and direct digital synthesis to enable MHz-equivalent pixel clock readout and phase-coherent digital lock-in detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional single-point laser scanning fluorescence microscopy is used, then spatial resolution is improved, but time resolution deteriorates (limited to approximately 30 frames per second)
Solution Approach 1:
The invention segments the excitation process by assigning distinct radiofrequency codes to different spatial locations (pixels) within the field of view. This allows simultaneous excitation of multiple pixels through frequency-division multiplexing, thereby increasing frame rate while maintaining spatial resolution. Each pixel's fluorescence signal is modulated at its assigned frequency, enabling parallel detection and subsequent digital demultiplexing to reconstruct the image.
Solution Approach 2:
The invention transitions from temporal scanning (sequential pixel-by-pixel excitation) to frequency-domain multiplexing. By adding the frequency dimension as an additional degree of freedom, multiple spatial locations can be excited and detected simultaneously without temporal sequencing, thus achieving high-speed imaging while preserving spatial resolution.
2Speed
If linescan or spinning disk confocal microscopes are used to increase frame rate, then time resolution is improved, but sensitivity deteriorates (limited by low electronic gain and optical throughput)
Solution Approach 1:
The invention replaces mechanical scanning systems (such as spinning disks or galvanometer mirrors) with a stationary optical system combined with radiofrequency multiplexed excitation. This eliminates mechanical throughput limitations and enables simultaneous excitation of the entire field of view, achieving high frame rates while maintaining high sensitivity through parallel photon collection from all pixels.
3Speed
If EMCCD or sCMOS cameras are used for high-speed imaging, then frame rate is improved, but sensitivity deteriorates (limited by readout time and electronic noise)
Solution Approach 1:
The invention introduces radiofrequency modulation as an intermediary between the fluorescence emission and the detector. By modulating each pixel's excitation at a distinct radiofrequency, the system enables frequency-selective detection that can reject out-of-band noise and interference. This allows the use of high-speed detectors while maintaining sensitivity through coherent signal extraction at the assigned frequencies.
4Productivity
If conventional imaging flow cytometry is used, then cell throughput is improved, but sensitivity deteriorates (limited to 5,000 cells per second)
Solution Approach 1:
The invention merges the capabilities of fluorescence microscopy with flow cytometry by implementing parallel excitation of multiple spatial positions. This allows simultaneous detection of multiple cells passing through the field of view, thereby increasing throughput while maintaining the sensitivity of fluorescence detection. The radiofrequency multiplexing enables discrimination of signals from different spatial locations even as cells flow through the system.
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
FIRE microscopy achieves high-speed fluorescence imaging with sub-millisecond time resolution, enabling the capture of previously unresolved dynamics in biology and allowing for high-throughput analysis of large cell populations.
Implementation Method 1
an acousto-optic deflector, driven by a comb of radiofrequencies produced by a direct digital synthesizer, produces multiple deflected optical beams, each with a distinct frequency shift
Implementation Method 2
Fluorescence emissions from the sample are detected by a photomultiplier tube
Implementation Method 3
Fluorescence imaging by radiofrequency-multiplexed excitation
Data Source
AI summary
Apparatus and methods for fluorescence imaging using radiofrequency multiplexed excitation. One apparatus splits an excitation laser beam into two arms of a Mach-Zehnder interferometer. The light in the first beam is frequency shifted by an acousto-optic deflector, which is driven by a phase-engineered radiofrequency comb designed to minimize peak-to-average power ratio. This RF comb generates multiple deflected optical beams possessing a range of output angles and frequency shifts. The second beam is shifted in frequency using an acousto-optic frequency shifter. After combining at a second beam splitter, the two beams are focused to a line on the sample using a conventional laser scanning microscope lens system. The acousto-optic deflectors frequency-encode the simultaneous excitation of an entire row of pixels, which enables detection and de-multiplexing of fluorescence images using a single photomultiplier tube and digital phase-coherent signal recovery techniques.