Smoothing and differentiation of data by Tikhonov and fractional derivative tools, applied to surface-enhanced Raman scattering (SERS) spectra of crystal violet dye

TL;DR

This paper introduces an enhanced Tikhonov regularization method incorporating fractional derivatives to effectively denoise Raman spectra, especially SERS data, without compromising molecular signal fidelity.

Contribution

It proposes a novel Tikhonov-based filtering approach using fractional derivatives as a control parameter, improving noise removal in Raman spectral data.

Findings

Successfully denoised simulated data and SERS spectra of crystal violet dye.

Preserved molecular signal integrity while reducing noise.

Enhanced spectral analysis accuracy in Raman spectroscopy.

Abstract

All signals obtained as instrumental response of analytical apparatus are affected by noise, as in Raman spectroscopy. Whereas Raman scattering is an inherently weak process, the noise background can lead to misinterpretations. Although surface amplification of the Raman signal using metallic nanoparticles has been a strategy employed to partially solve the signal-to-noise problem, the pre-processing of Raman spectral data through the use of mathematical filters has become an integral part of Raman spectroscopy analysis. In this paper, a Tikhonov modified method to remove random noise in experimental data is presented. In order to refine and improve the Tikhonov method as filter, the proposed method includes Euclidean norm of the fractional-order derivative of the solution as an additional criterion in Tikhonov function. In the strategy used here, the solution depends on the regularization parameter, $\lambda$, and on the fractional derivative order, $\alpha$. As will be demonstrated, with the algorithm presented here, it is possible to obtain a noise free spectrum without affecting the fidelity of the molecular signal. In this alternative, the fractional derivative works as a fine control parameter for the usual Tikhonov method. The proposed method was applied to simulated data and to surface-enhanced Raman scattering (SERS) spectra of crystal violet dye in Ag nanoparticles colloidal dispersion.