PH-sensitive optical micro-resonator based on PAA/PVA gel swelling

Médéric Loyez, Maxwell Adolphson, Jie Liao, Sanskar Thakur, Lan Yang

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

2 Scopus citations


A pH sensor can help understand chemical conditions of solutions, such as precise cell culture medium monitoring in real time. High-quality whispering-gallery-mode (WGM) microresonators have been utilized for surface sensing and are mainly based on the tracking of refractive index changes occurring within a wavelength range from their wall surface. This high sensitivity, reaching up to 10-5 RIU (∼2.5 nm/RIU and measured at a femtometer resolution) leads to a broad range of applications, especially for biosensing purposes through the monitoring of molecular binding events. Here, we study the deposition of thin layers of poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) hydrogels inside a whispering gallery mode (WGM) microbubble resonator (MBR), fabricated inline with a silica capillary. The generation of such layers is achieved by withdrawing a liquid solution of 25% PVA/PAA in pure water into the MBR and locally heating the microbubble region, resulting in hydrogel formation only in the cavity. The capillary is then rinsed and tested with varying pH solutions. The swelling ability of these gels is directly proportional to the pH of samples brought into contact with the cavity, leading to physical modifications of the WGM coupling properties. We show the preliminary results obtained for the polymerization and characterization of these gels in microbubbles and present the related signal shifts observed for several pH values. We also discuss the gel kinetics over time and investigate practical uses such as reversible and tunable detection of small pH changes.

Original languageEnglish
Title of host publicationOptics and Biophotonics in Low-Resource Settings IX
EditorsDavid Levitz, Aydogan Ozcan
ISBN (Electronic)9781510658431
StatePublished - 2023
EventOptics and Biophotonics in Low-Resource Settings IX 2023 - San Francisco, United States
Duration: Jan 28 2023Jan 29 2023

Publication series

NameProgress in Biomedical Optics and Imaging - Proceedings of SPIE
ISSN (Print)1605-7422


ConferenceOptics and Biophotonics in Low-Resource Settings IX 2023
Country/TerritoryUnited States
CitySan Francisco


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