An Affordable Shifted-Excitation Raman Difference Spectroscopy (SERDS) Setup: Construction, Noise Analysis, and Detection Limits
- 1Department of Chemistry, University of Illinois Urbana-Champaign, 600 S Mathews Ave., Urbana, Illinois, 61801
Abstract
Shifted-excitation Raman difference spectroscopy (SERDS) is an effective method for suppressing fluorescence backgrounds in Raman spectroscopy but often requires expensive instrumentation for the generation of two excitation beams. In this work, we constructed an affordable SERDS instrument using an inexpensive laser pointer together with standard optical components. A diffraction grating and two mechanical slits were used to generate two excitation beams with linewidths below 0.25 nm from the laser pointer. Cyclohexane was first used as a benchmark molecule for data acquisition and analysis processes. The instrument performance was then examined using ethanol samples containing different concentrations of methylene blue (MB), where SERDS spectra were compared with asymmetric least-squares (ALS) baseline corrected spectra. For ethanol contaminated with 1×10-8 M MB, the SERDS spectrum achieved a signal-to-noise ratio (S/N) of 53 at a fluorescence/Raman ratio (FL/Raman) of 18:1, whereas the corresponding ALS baseline-corrected spectrum had a S/N of only 25. The improvement provided by SERDS was reflected not only in the higher S/N but also in its ability to suppress Raman-like artifacts that remained after ALS baseline correction. The effects of the FL/Raman value, scan number, integration time, and the intensity ratio between the two excitation beams were also investigated to understand the major sources of noise and practical methods for improving spectral quality. Finally, the instrument was used to measure the Raman spectrum of anthraquinone-2,7-disulfonic acid disodium salt (2,7-AQDS), a highly fluorescent molecule where conventional ALS correction method failed. This experiment introduces students to optical alignment, SERDS instrumentation, spectral processing, and noise analysis, offering an accessible, hands-on laboratory exercise for teaching fluorescence suppression techniques.
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BibTeX
@misc{qian2026affordable,
title = {{An Affordable Shifted-Excitation Raman Difference Spectroscopy (SERDS) Setup: Construction, Noise Analysis, and Detection Limits}},
author = {Peisen Qian and Brandon Rasmussen and Joaquín Rodríguez-López and Josh Vura-Weis},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010360/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010360/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - An Affordable Shifted-Excitation Raman Difference Spectroscopy (SERDS) Setup: Construction, Noise Analysis, and Detection Limits
AU - Peisen Qian
AU - Brandon Rasmussen
AU - Joaquín Rodríguez-López
AU - Josh Vura-Weis
PY - 2026
DA - 2026/10/13
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010360/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010360/v1
AB - Shifted-excitation Raman difference spectroscopy (SERDS) is an effective method for suppressing fluorescence backgrounds in Raman spectroscopy but often requires expensive instrumentation for the generation of two excitation beams. In this work, we constructed an affordable SERDS instrument using an inexpensive laser pointer together with standard optical components. A diffraction grating and two mechanical slits were used to generate two excitation beams with linewidths below 0.25 nm from the laser pointer. Cyclohexane was first used as a benchmark molecule for data acquisition and analysis processes. The instrument performance was then examined using ethanol samples containing different concentrations of methylene blue (MB), where SERDS spectra were compared with asymmetric least-squares (ALS) baseline corrected spectra. For ethanol contaminated with 1×10-8 M MB, the SERDS spectrum achieved a signal-to-noise ratio (S/N) of 53 at a fluorescence/Raman ratio (FL/Raman) of 18:1, whereas the corresponding ALS baseline-corrected spectrum had a S/N of only 25. The improvement provided by SERDS was reflected not only in the higher S/N but also in its ability to suppress Raman-like artifacts that remained after ALS baseline correction. The effects of the FL/Raman value, scan number, integration time, and the intensity ratio between the two excitation beams were also investigated to understand the major sources of noise and practical methods for improving spectral quality. Finally, the instrument was used to measure the Raman spectrum of anthraquinone-2,7-disulfonic acid disodium salt (2,7-AQDS), a highly fluorescent molecule where conventional ALS correction method failed. This experiment introduces students to optical alignment, SERDS instrumentation, spectral processing, and noise analysis, offering an accessible, hands-on laboratory exercise for teaching fluorescence suppression techniques.
ER -