Articles | Volume 6, issue 2
https://doi.org/10.5194/jsss-6-351-2017
https://doi.org/10.5194/jsss-6-351-2017
Regular research article
 | 
16 Oct 2017
Regular research article |  | 16 Oct 2017

Transmitted light pH optode for small sample volumes

Christian Rogge, Steffen Zinn, Paolo Prosposito, Roberto Francini, and Andreas H. Foitzik

Abstract. An innovative concept of a low-cost pH optode with working volumes of less than 150 µL is presented. The pH monitoring is based on the color changing effect of pH indicators. The optode includes an RGB color sensor patch TCS34725 from Adafruit, a controllable LED and reactor slides and is addressed by a self-written LabVIEW© software. Utilizing the hue value of the HSV color model, it is possible to analyze the color change of the indicator and estimate the pH value of the analyzed samples by exploiting sigmoidal fit models. Measurements carried out with phenol red and DMEM (Dulbecco's Modified Eagle's Medium) reported a standard error of calibration in the physiologic pH range (6.5–7.5) of ±0.04 pH units.

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Short summary
This work presents a cost-effective optical-based sensor for pH monitoring of sample volumes less than 150 µL. As part of a bigger project to develop a stand-alone micro bioreactor system, measurements carried out with phenol red and DMEM reported a standard error of calibration in the physiologic pH range (6.5–7.5) of pH ±0.04. Compared to other accessible optical-based sensors this reported system is a good alternative regarding the overall costs of less than EUR 50.