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Updated: Aug 3, 2026

Development of Whispering Gallery Mode Polymeric Micro-optical Electric Field Sensors
Published on: January 29, 2013
Direct response of liquid crystal to pH changes for wide range pH sensing via the whispering gallery mode
Abstract:
pH sensing is essential in various fields including healthcare, environmental monitoring, food safety, and agriculture. In this Letter, we propose a method for a wide-range pH measurement based on the direct response of liquid crystal (LC) to pH variations via the whispering gallery mode (WGM). The liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) is selected for its excellent optoelectronic properties and the birefringence of 5CB microdroplets serving as spherical resonators. This sensor achieves wide-range pH sensing without any intermediaries. Polarized optical microscopy (POM) and WGM provide a qualitative morphological analysis and accurate quantitative spectral measurements. Under alkaline conditions (pH 7.6 to 13.3), POM images of 5CB microdroplets show a complete transition from bipolar to radial structures, with an average sensitivity of 1.78 nm/pH of redshift in WGM spectra. In acidic conditions (pH 6.65 to 1.5), structural changes observed by POM are minor, with a sensitivity of 1.06 nm/pH of blueshift in WGM spectra. This difference is attributed to the varying refractive indices of HCl and NaOH solutions. This method offers a reference for theoretical studies on pH and LC interactions and holds promise for the development of LC-based pH sensors.
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