Thermally Stimulated Desorption Optical Fiber-Based Interrogation System: An Analysis of Graphene Oxide Layers’ Stability

Maria Raposo,Paulo António Ribeiro,Catarina Monteiro,Orlando Frazão,Susana Silva,Paulo Zagalo,Carlota Xavier

doi:10.3390/photonics8030070

Abstract

Thin graphene oxide (GO) film layers are being widely used as sensing layers in different types of electrical and optical sensor devices. GO layers are particularly popular because of their tuned interface reflectivity. The stability of GO layers is fundamental for sensor device reliability, particularly in complex aqueous environments such as wastewater. In this work, the stability of GO layers in layer-by-layer (LbL) films of polyethyleneimine (PEI) and GO was investigated. The results led to the following conclusions: PEI/GO films grow linearly with the number of bilayers as long as the adsorption time is kept constant; the adsorption kinetics of a GO layer follow the behavior of the adsorption of polyelectrolytes; and the interaction associated with the growth of these films is of the ionic type since the desorption activation energy has a value of 119 ± 17 kJ/mol. Therefore, it is possible to conclude that PEI/GO films are suitable for application in optical fiber sensor devices; most importantly, an optical fiber-based interrogation setup can easily be adapted to investigate in situ desorption via a thermally stimulated process. In addition, it is possible to draw inferences about film stability in solution in a fast, reliable way when compared with the traditional ones.

Highlights

Optical fiber-based sensors [1,2,3,4,5,6,7] ordinarily have fiber interfaces coated with different materials, namely organic materials or even functionalization with biologic molecules to enhance sensing features
This issue is of relevance for sensing traces of a component in complex media, for example when sensing in a complex liquid medium such as wastewater [8,9,10]. Another relevant aspect to consider for the sake of sensor device reliability is the stability of the coated layers in liquid media, because they might desorb from the fiber interface
This means that other experimental methods should be addressed, such as carrying out desorption measurements over optical fibers that have molecular layers previously adsorbed at each end or measuring light signals reflected through the fiber in an interrogation-like optical setup

Summary

Introduction

Optical fiber-based sensors [1,2,3,4,5,6,7] ordinarily have fiber interfaces coated with different materials, namely organic materials or even functionalization with biologic molecules to enhance sensing features This issue is of relevance for sensing traces of a component in complex media, for example when sensing in a complex liquid medium such as wastewater [8,9,10]. Conventional spectrophotometry is not easy to adapt for in situ measurements, and a quartz crystal microbalance is limited by crystal thermal coefficients This means that other experimental methods should be addressed, such as carrying out desorption measurements over optical fibers that have molecular layers previously adsorbed at each end or measuring light signals reflected through the fiber in an interrogation-like optical setup. This procedure allows in situ measurement of both adsorbed and desorbed amounts

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Discussion

Conclusion