An optical fiber sensor for Hg²⁺ detection based on the LSPR of silver and gold nanoparticles embedded in a polymeric matrix as an effective sensing material

In this work, an optical fiber sensor based on the Localized Surface Plasmon Resonance (LSPR) phenomenon is presented as a powerful tool for the detection of heavy metals (Hg²⁺) in the field of environmental applications [1], [2]. The resultant sensing film has been fabricated using a nanofabrication process, known as Layer-by-Layer Embedding (LbL-E) technique [3], which makes possible a successful immobilization of metallic nanoparticles into a polymeric matrix. In this sense, both silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) have been synthesized using a synthetic chemical protocol as a function of a strict control of three main parameters such as polyelectrolyte concentration, loading agent and reducing agent, respectively. The use of metallic nanostructures as sensing materials is of great interest because well-located absorption peaks associated to their LSPR are obtained at 420 nm (AgNPs) and 530 nm (AuNPs), respectively [4]. Both plasmonic peaks provide a stable real-time references that can be extracted from the spectral response of the optical fiber sensor, giving a reliable monitoring of the Hg²⁺ concentration. An exhaustive study about the most appropriate deposition parameters (mostly pH and thickness) has been evaluated in order to obtain a more detailed analysis of the sensing spectral response. To sum up, this is the first time that an optical fiber sensor based on two different LSPR sensing signals has been presented for Hg²⁺ detection in the bibliography.

[1] X. Zhong, L. Ma G. Yin, M. Gan, and Y.Wei, “Hg²⁺ Optical Fiber Sensor Based on LSPR with PDDA Templated AuNPs and CS/PAA Bilayers,” Applied Sciences, vol. 10, no. 14, 2020.

[2] M. E. Martínez-Hernández, J. Goicoechea, and F. J. Arregui, “Hg²⁺ optical fiber sensor based on LSPR generated by gold nanoparticles embedded in LBL nano-assembled coatings,” Sensors (Switzerland), vol. 19, no. 22, 2019.

[3] P. J. Rivero, J. Goicoechea, I. R. Matias, and F. J. Arregui, “A comparative study of two different approaches for the incorporation of silver nanoparticles into layer-by-layer films,” Nanoscale Res. Lett., vol. 9, no. 1, pp. 1–11, 2014.

[4] J. Goicoechea, P. J. Rivero, S. Sada, and F. J. Arregui, “Self-Referenced Optical Fiber Sensor for Hydrogen Peroxide Detection based on LSPR of Metallic Nanoparticles in Layer-by-Layer Films,” Sensors, vol. 19, no. 18, p. 3872, 2019.