A Novel Polyaniline Nanofiber Combined with Toluidine Blue as a Sensitive Detection Platform for Lignin by Raman Spectroscopy

Hui Zhang,Jing Li,Liang Zhou,Shengquan Liu

doi:10.1155/2021/9910553

Abstract

Raman spectroscopy is widely applied in wood science because of its features of being nondestructive, rapidity, and high resolution. However, Raman scattering is weak, and the Raman signal is easily disturbed by autofluorescence arising from endogenous fluorescent molecules in biological tissue. In this work, a sensitive lignin detection platform was fabricated by a composite with a polyaniline (PANI) nanofiber and toluidine blue (TB) under the excitation of visible light. In this platform, TB acts as a specific marker for lignin, and a PANI nanofiber was used as a reinforcing reagent to improve the Raman intensity of TB. When wood slice is impregnated with TB/PANI, the lignin in wood can be precisely labeled with the TB, and the Raman intensity of TB had a threefold increase at 532 nm excitation. This TB/PANI detection platform is expected to make a significant contribution in qualitative and quantitative analysis of lignin to avoid autofluorescence in various lignin-based biosciences.

Highlights

Lignin is a major component of the cell wall in wood; the content of lignin has a significant effect on wood performance; for example, lignin in plant fibers is generally regarded as undesirable by the pulp and paper industry, but the high concentration of lignin in the middle lamella between cells in wood is regarded as a positive benefit; the determination of lignin quantity is very important in wood science [1]
The X-ray diffraction (XRD) pattern of the PANI exhibits major reflection peaks at 2θ = 27°, and similar peak appeared in the sample of Toluidine blue (TB)/PANI
These observations suggest that the chemical mechanism (CM) dominates over the surface-enhanced effect in this study, charge transfer can occur between PANI and TB, and the similarity of the chemical structure between PANI and TB may be another factor contributing to the Raman enhancement

Summary

Introduction

Lignin is a major component of the cell wall in wood; the content of lignin has a significant effect on wood performance; for example, lignin in plant fibers is generally regarded as undesirable by the pulp and paper industry, but the high concentration of lignin in the middle lamella between cells in wood is regarded as a positive benefit; the determination of lignin quantity is very important in wood science [1]. The structural characterizations of lignin and the chemical transformations of lignin have been studied by using a confocal Raman microscope [8] This is not often achieved in practice when using UV/visible laser excitation to measure biomass as the autofluorescence arises from endogenous fluorescent molecules in biological tissues which makes it difficult to obtain Raman spectra with an acceptable signal-to-noise ratio [9]. In the presence of target lignin, it would be labeled with TB and a powerful Raman signal was obtained by the approach between PANI and TB at the excitation wavelengths of 532 nm This TB/PANIA platform had high specificity and sensitivity and can quantitatively detect lignin to avoid autofluorescence stimulated by the visible range light. The strategy of this detection system is shown in Scheme 1. This system has characteristics of simple preparation process, low cost, and being nondestructive and may be an effective detection method for lignin-based materials

Experiment

Results and Discussion

Conclusions

Conflicts of Interest