Lab-scale fermentation tests of microchip with integrated electrochemical sensors for pH, temperature, dissolved oxygen and viable biomass concentration. 
This article shows the development and testing of a microchip with integrated electrochemical sensors for measurement of pH, temperature, dissolved oxygen and viable biomass concentration under yeast cultivation conditions.  Measurements were done both under dynamic batch conditions as well as under prolonged continuous cultivation conditions.  The response of the sensors compared well with conventional measurement techniques.  The biomass sensor was based on impedance spectroscopy.  The results of the biomass sensor matched very well with dry weight measurements and showed a limit of detection of approximately 1 g/L. The dissolved oxygen concentration was monitored amperometrically using an ultra-microelectrode array, which showed an accuracy of approximately 0.2 mg/L and negligible drift.  pH was monitored using an ISFET with an accuracy well below 0.1 pH unit.  The platinum thin-film temperature resistor followed temperature changes with approximately 0.1 degrees C accuracy.  The dimensions of the multi sensor chip are chosen as such that it is compatible with the 96-well plate format.