Multi-excitation Raman spectroscopy technique for fluorescence rejection

Area of Science:

• Spectroscopy
• Analytical Chemistry
• Physical Chemistry

Background:

• Fluorescence often overwhelms weak Raman signals in spectroscopy.
• Existing methods like Shifted Excitation Raman Difference Spectroscopy (SERDS) offer partial solutions.
• A need exists for robust methods to isolate Raman signals from complex backgrounds.

Purpose of the Study:

• To develop and validate a multi-excitation Raman spectroscopy technique for effective fluorescence background removal.
• To improve the signal-to-noise ratio (SNR) in Raman spectroscopy of fluorescent samples.
• To compare the efficacy of multi-excitation methods against traditional background subtraction techniques.

Main Methods:

• Sequential acquisition of Raman spectra using multiple, slightly shifted excitation frequencies.
• Application of an Expectation-Maximization algorithm to deconvolve Raman and fluorescence signals.
• Validation through both computational simulations and experimental measurements.

Main Results:

• The multi-excitation approach effectively filters out fluorescence, isolating the Raman signal.
• Increasing the number of excitation frequencies enhances the algorithm's efficacy and SNR.
• The technique demonstrates superior performance over non-iterative methods like polynomial background subtraction in highly fluorescent scenarios.

Conclusions:

• Multi-excitation Raman spectroscopy provides a powerful tool for analyzing samples with significant fluorescence.
• The Expectation-Maximization algorithm effectively estimates Raman and fluorescence components.
• This method offers a significant advancement for Raman spectroscopy in complex biological and material science applications.