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Yeast fermentation products contain multiple ingredients such as succinate, pyruvate, and acetate; and high performance liquid chromatography (HPLC) is commonly applied to the monitoring of these compositions. However, applying lab-scale fermentation for optimizing the process or screening high-yield strains can be time consuming, labor intensive, and sample devouring. Microfluidic platforms are currently more favorable setups for early-stage screening and optimization. Nonetheless, the minute sample amount in microfluidic setup is challenging for HPLC analysis. Therefore, this study focuses on the development of micro-sensors for rapid and high dynamic range detections not only in performing the monitoring of the metabolic products (lactic acid, ethanol…etc.) and the substrate (glucose) but also the pH environment in the micro-scale fermentation. The micro-sensors utilized the NiONPs/GO/Nafion/Au electrode and NiONPs/GO/Nafion/SPEs for detecting metabolic products and substrates while the IrOx electrode for pH measurements. Two kinds of microelectrodes, gold and screen-printed carbon, were applied and their performance was compared. Both electrodes had a linear detection range of 1 – 50 mM for lactate detection but the sensitivity of screen-printed carbon electrode had a sensitivity of 11.74±1.05μA/mM, which was two folds higher than the gold electrode. The screen-printed electrode also had good performance in ethanol detection: the detection range was 1 – 50 mM and the sensitivity was 13.70±1.84μA/mM. However, the screen-printed carbon electrode was highly prone to poisoning in glucose detection. The gold electrode showed stable detection of ethanol and glucose in 17 days. The glucose detection had a detection range of 1 - 20mM and a sensitivity of 27.09±3.04μA/mM. Both gold and screen-printed electrodes had a linear detection range for pH value from pH 2 to pH 10 with a sensitivity of 54 mV/pH. All detections were highly linear with correlation coefficients higher than 0.99.
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