Multispectral Raman Spectroscopy for Flowing Samples
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Solution Overview
Problem
Conventional Raman spectroscopy setups are inadequate for analyzing moving samples due to difficulties in tracking excitation and detection of scattered radiation, leading to impaired signal quality and inability to record complete Raman spectra within short measurement times, especially in flow cytometry applications.
Innovation Solution
An optical system with a multispectral excitation source emitting monochromatic radiation at multiple wavelengths along a common beam axis, combined with an elongate flow-through region and a detection device for wavelength-selective filtering, allows for the examination of moving sample elements by irradiating excitation radiation at multiple positions and detecting scattered radiation at different wavelengths, reducing measurement times and enabling compact, robust setups.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional Raman spectroscopy setups are used to analyze moving samples, then excitation and detection can be performed, but signal quality is impaired and complete Raman spectra cannot be recorded within short measurement times
Solution Approach 1:
The system segments the spectrum detection process by using multiple detection channels, each equipped with specific filter combinations tuned to detect different spectral regions simultaneously. This allows parallel detection of multiple wavelength ranges, enabling complete spectral acquisition within the short measurement time window of flowing samples while maintaining signal quality through dedicated detection paths for each spectral region
Solution Approach 2:
The invention transitions from sequential spectral scanning to simultaneous multi-wavelength detection by adding a spectral dimension to the detection process. Multiple detection channels operate in parallel at different wavelength ranges, effectively converting a time-based sequential measurement approach into a spatially parallel approach, thereby achieving both high measurement speed and complete spectral coverage
2Measurement precision
If stationary samples are used for Raman spectroscopy, then measurement background can be suppressed by integrating over long measurement periods, but the setup cannot track moving samples
Solution Approach 1:
The system employs periodic modulation of the excitation light source at specific frequencies, which allows the Raman signal to be distinguished from the continuous background fluorescence through frequency-based filtering. This periodic excitation approach enables background suppression even with moving samples by locking onto the modulated signal frequency, eliminating the need for long integration periods on stationary samples
Solution Approach 2:
The invention replaces the mechanical tracking system (moving mirrors or stages to follow sample position) with an optical field-based approach where the excitation and detection are configured to illuminate and collect signals from a defined measurement volume in the flow path. The system uses flow cytometry principles where samples pass through a fixed measurement zone, eliminating mechanical tracking while maintaining measurement capability on moving samples
3Measurement precision
If conventional spectrometers are used for continuous Raman spectrum recording, then complete spectra can be obtained, but integration and measurement times are too long for moving samples
Solution Approach 1:
The detection system is segmented into multiple parallel channels, each detecting a specific wavelength range simultaneously. This segmentation allows the complete spectrum to be reconstructed from multiple simultaneous measurements rather than sequential scanning, reducing the measurement time from seconds to microseconds while maintaining full spectral coverage
Solution Approach 2:
The invention merges multiple detection channels with different filter combinations into a single integrated detection system. Each channel detects a portion of the spectrum simultaneously, and the signals are combined to form a complete Raman spectrum. This merging of parallel detection paths achieves both spectral completeness and rapid measurement times suitable for flowing samples
4Productivity
If flow cytometry is used for particle analysis, then individual sample elements can be examined, but Raman spectra cannot be recorded due to short observation time
Solution Approach 1:
The excitation source is modulated periodically, allowing the Raman signal to be detected through synchronous detection techniques that filter out the much stronger continuous fluorescence background. This periodic excitation enables Raman spectroscopy in the flow cytometry context by creating a time-resolved signal that can be extracted from the rapid flow environment
Solution Approach 2:
The detection system is divided into multiple channels with specific filter sets optimized for different spectral regions, allowing simultaneous detection of multiple Raman lines. This segmentation enables complete spectral acquisition during the brief observation time of flowing particles by capturing different spectral components in parallel rather than sequentially
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
This approach enables rapid recording of Raman spectra from moving samples without complex setups, using inexpensive components, and provides precise intensity measurements of Raman lines, overcoming the limitations of conventional Raman spectroscopy in flow cytometry and other applications.
Implementation Method 1
a laser device that can be switched on and off between at least two different wavelengths and that emits along a common beam axis
Implementation Method 2
inelastically scattered by the sample. The scattered excitation radiation can then be collected using a suitable spectroscopy arrangement and examined spectrally
Implementation Method 3
a detection device for wavelength-selective filtering and detection of at least part of the scattered radiation
Data Source
Figure 1A
Figure 1B~1C
Figure 2
AI summary
The invention relates to an optical system and a method for spectroscopy. The optical system (100) according to the invention is particularly suitable for Raman spectroscopy and comprises a multispectral excitation source (10) configured to successively emit monochromatic excitation radiation (12, 14) at at least two different excitation wavelengths (λ1, λ2) along a common beam axis (O); an elongated flow section (30) with a longitudinal axis (L) configured to guide a particle stream along the longitudinal axis (L); and an excitation beam path configured to direct the monochromatic excitation radiation (12, 14) into the flow section (30) at a first position (A) and a second position (B), wherein the first position (A) and the second position (B) are located in the flow section (30) and the first position (A) is spaced (Δz) apart from the second position (B).and a detection device (50, 52, 52', 60, 60') configured to selectively filter and detect at least a portion of radiation scattered from the first position (A) at a first filter wavelength (f1) and to selectively filter and detect at least a portion of radiation scattered from the second position (B) at a second filter wavelength (f2).