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Chemosensors
Volume 13
Issue 2
10.3390/chemosensors13020033
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This is an early access version, the complete PDF, HTML, and XML versions will be available soon.
Article

Stretching the Limits of Refractometric Sensing in Water Using Whispering-Gallery-Mode Resonators

by
Kevin Soler-Carracedo
1,*,
Antonia Ruiz
2,3,
Susana Ríos
2,
Sergio de Armas-Rillo
2,
Leopoldo L. Martín
2,3,
Martin Hohmann
4,5,
Inocencio R. Martín
2,6 and
Fernando Lahoz
2,3,*
1
Faculty of Chemistry, Adam Mickiewicz University, Uniwersytetu Poznańskiego 8, 61-614 Poznań, Poland
2
Departamento de Física, Universidad de La Laguna, Apdo. 456, E-38200 San Cristóbal de La Laguna, Spain
3
Instituto de Estudios Avanzados en Atómica, Molecular y Fotónica (IUDEA), Universidad de La Laguna, E-38200 San Cristóbal de La Laguna, Spain
4
Institute of Photonic Technologies (LPT), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Konrad-Zuse-Straße 3/5, 91052 Erlangen, Germany
5
Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Paul-Gordan-Straße 6, 91052 Erlangen, Germany
6
Instituto de Materiales y Nanotecnología (IMN), Universidad de La Laguna, E-38200 San Cristóbal de La Laguna, Spain
*
Authors to whom correspondence should be addressed.
Chemosensors 2025, 13(2), 33; https://doi.org/10.3390/chemosensors13020033
Submission received: 18 December 2024 / Revised: 14 January 2025 / Accepted: 22 January 2025 / Published: 24 January 2025
(This article belongs to the Special Issue Sensors for Food Testing, Environmental Analysis, and Medical Diagnostics)
Versions Notes

Abstract

A novel application of microresonators for refractometric sensing in aqueous media is presented. To carry out this approach, microspheres of different materials and sizes were fabricated and doped with Nd3+ ions. Under 532 nm excitation, the microspheres presented typical NIR Nd3+ emission bands with superimposed sharp peaks, related to the Whispering Gallery Modes (WGMs), due to the geometry of the microspheres. When the microspheres were submerged in water with increasing concentrations of glycerol, spectral shifts for the WGMs were observed as a function of the glycerol concentration. These spectral shifts were studied and calibrated for three different microspheres and validated with the theoretical shifts, obtained by solving the Helmholtz equations for the electromagnetic field, considering the geometry of the system, and also by calculating the extinction cross-section. WGM shifts strongly depend on the diameter of the microspheres and their refractive index (RI) difference compared with the external medium, and are greater for decreasing values of the diameter and lower values of RI difference. Experimental sensitivities ranging from 2.18 to 113.36 nm/RIU (refractive index unit) were obtained for different microspheres. Furthermore, reproducibility measurements were carried out, leading to a repeatability of 2.3 pm and a limit of detection of 5 × 10−4 RIU. The proposed sensors, taking advantage of confocal microscopy for excitation and detection, offer a robust, reliable, and contactless alternative for environmental water analysis.
Keywords: lanthanides; optofluidics; optical resonators; WGM; refractive index sensor; microspheres lanthanides; optofluidics; optical resonators; WGM; refractive index sensor; microspheres

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MDPI and ACS Style

Soler-Carracedo, K.; Ruiz, A.; Ríos, S.; de Armas-Rillo, S.; Martín, L.L.; Hohmann, M.; Martín, I.R.; Lahoz, F. Stretching the Limits of Refractometric Sensing in Water Using Whispering-Gallery-Mode Resonators. Chemosensors 2025, 13, 33. https://doi.org/10.3390/chemosensors13020033

AMA Style

Soler-Carracedo K, Ruiz A, Ríos S, de Armas-Rillo S, Martín LL, Hohmann M, Martín IR, Lahoz F. Stretching the Limits of Refractometric Sensing in Water Using Whispering-Gallery-Mode Resonators. Chemosensors. 2025; 13(2):33. https://doi.org/10.3390/chemosensors13020033

Chicago/Turabian Style

Soler-Carracedo, Kevin, Antonia Ruiz, Susana Ríos, Sergio de Armas-Rillo, Leopoldo L. Martín, Martin Hohmann, Inocencio R. Martín, and Fernando Lahoz. 2025. "Stretching the Limits of Refractometric Sensing in Water Using Whispering-Gallery-Mode Resonators" Chemosensors 13, no. 2: 33. https://doi.org/10.3390/chemosensors13020033

APA Style

Soler-Carracedo, K., Ruiz, A., Ríos, S., de Armas-Rillo, S., Martín, L. L., Hohmann, M., Martín, I. R., & Lahoz, F. (2025). Stretching the Limits of Refractometric Sensing in Water Using Whispering-Gallery-Mode Resonators. Chemosensors, 13(2), 33. https://doi.org/10.3390/chemosensors13020033

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