Analytical Sciences

A Wireless pH Sensor Using Magnetoelasticity for Measurement of Body Fluid Acidity

Pengfei PANG, Xianjuan GAO, Xilin XIAO, Wenyue YANG, Qingyun CAI, and Shouzhuo YAO

State Key Laboratory of Chemo/Biosensing and Chemometrics, and College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, P. R. China

The determination of body fluid acidity using a wireless magnetoelastic pH-sensitive sensor is described. The sensor was fabricated by casting a layer of pH-sensitive polymer on a magnetoelastic ribbon. In response to an externally applied time-varying magnetic field, the magnetoelastic sensor mechanically vibrates at a characteristic frequency that is inversely dependent upon the mass of the pH polymer film, which varies as the film swells and shrinks in response to pH. As the magnetoelastic sensor is magnetostrictive, the mechanical vibrations of the sensor launch magnetic flux that can be detected remotely using a pickup coil. The sensor can be used for direct measurements of body fluid acidity without a pretreatment of the sample by using a filtration membrane. A reversible and linear response was obtained between pH 5.0 and 8.0 with a measurement resolution of pH 0.1 and a slope of 0.2 kHz pH^-1. Since there are no physical connections between the sensor and the instrument, the sensor can be applied to in vivo and in situ monitoring of the physiological pH and its fluctuations.

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