Fluid Embeddable Coupled Coil Sensor for Wireless pH Monitoring in a Bioreactor

SKU: 010615


A passive embeddable coupled coil sensor for remote bioprocess pH monitoring is described. The sensor is sterilizable, able to operate in a fluid medium, and small enough to fit inside a small bioreactor or test tube. It consists of a planar spiral inductor connected parallel to a varactor forming an LC resonant circuit. A pH combination electrode made of an iridium/iridium oxide sensing electrode and a silver/silver chloride reference electrode is connected parallel to the varactor. A potential difference change across the electrodes due to pH variation of the medium changes the voltage-dependent capacitance and shifts the resonant frequency of the sensor. An interrogator coil is i nductively coupled to the sensor coil and remotely tracks the resonant frequency of the sensor. For in-fluid monitoring, the sensor is encapsulated in a manner that reduces the influence of the permittivity and conductivity of the medium. The sensor, calibrated over 2–12 pH range, exhibits a rapid response with 2.477-MHz/pH sensitivity. The sensor was used for remote pH monitoring of Yarrowia lipolytica and Saccharomyces cerevisiae fermentation in a shake flask over 63 and 25 h, respectively. The experiments demonstrate that the medium pH can be monitored repeatedly with an accuracy of 0.08 pH
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