Surface-enhanced Raman spectroscopy for the characterization of Vaccinium myrtillus L. bilberries of the Baltic\u2013Nordic regions

Lina Traksele,Valentinas Snitka

doi:10.1007/s00217-021-03887-8

Abstract

In this study, an investigation of the wild bilberries (Vaccinium myrtillus L.) of the different Baltic–Nordic regions using surface-enhanced Raman spectroscopy (SERS) combined with principal component analysis (PCA) is presented. The bilberries were collected in Lithuania, Latvia, Finland and Norway. The set of the SERS spectra of the berry extracts (pH ~ 4) were recorded on the silver nanoparticles based SERS substrates. The SERS spectra of the extracts were acquired using 532 nm laser as an excitation source. The morphology of the SERS substrates was evaluated by scanning electron microscopy (SEM) and the presence of the silver nanoparticles was confirmed by the energy-dispersive X-ray spectroscopy (EDX). The enhancement factor (EF) of the silver SERS substrates was found to be 105. It has been shown that a strong fluorescence background, associated with the phenolic compounds found in bilberries, can be subtracted due to the fluorescence-quenching properties of the silver nanoparticles. Therefore, an application of the SERS technique allowed to observe the characteristic peaks of the bilberries and the PCA tool enabled to evaluate the spectral variation across the entire SERS data set. The results presented in this paper show that the SERS technique coupled with PCA chemometric analysis might serve as a complementary method that allows to identify the country of origin of the bilberries based on the spectral differences.

Highlights

Over the past decade, Raman spectroscopy and SERS began to compete intensively with traditional food research methods such as high-performance liquid chromatography (HPLC), gas chromatography (GS) and enzyme-linked immunosorbent assay (ELISA) [1, 2]
We focus on the application of the SERS technique for the investigation of the wild bilberries naturally growing in the different Baltic–Nordic regions
Raman spectroscopy is a non-sensitive technique related to a weak scattering because only one of a million photons are scattered in-elastically

Summary

Introduction

Raman spectroscopy and SERS began to compete intensively with traditional food research methods such as high-performance liquid chromatography (HPLC), gas chromatography (GS) and enzyme-linked immunosorbent assay (ELISA) [1, 2]. One of the main reasons for such competition is the potential of the SERS to provide the diverse information about the chemical composition of the materials with high sensitivity and specificity. Such capabilities make SERS technique attractive for the detection of molecular traces in various food matrixes leading to the level control of food quality and safety. SERS technique allows to obtain a complex spectra that consist of common molecular vibrations of all the sample’s compounds at the same time This is important for the initial qualitative assessment of raw materials and products, as the overall spectra reflects the molecular fingerprints of toxic substances such as mycotoxins [14]. A chemically specific SERS tool provides an opportunity to observe the delicate changes of the molecular structure of flavonoids (i.e., anthocyanin) [15,16,17]

Methods

Results

Conclusion