The efficiency of cellular production processes is directly related
to the cell growth conditions. Therefore, developing methods and
systems for the precise evaluation of growth conditions is becoming
increasingly crucial to bioprocess engineering [1,2]. During
growth, cells located furthest from the medium-air interface are
often exposed to hypoxic conditions. This is because the rate of
cells digesting oxygen is faster than that of oxygen dissolving
and diffusing into the medium to reach the cells [3,4]. Oxygendeficient
conditions significantly inhibit cell growth resulting in
∗ Corresponding author.
E-mail address: hcyoon@ajou.ac.kr (H.C. Yoon).
either reduced productivity or apoptotic death. In general, a wellevaluated
approach to analyzing cell growth conditions involves
measuring the pH, CO2 and dissolved oxygen concentrations, and
cell size, utilizing techniques such as flow-injection, near infrared
(NIR) spectroscopy, and high-performance liquid chromatography
(HPLC) [5–7]. Although these approaches offer high sensitivity and
accuracy,they are less user-friendly owing to their expensive apparatus
as well as complexity of their operations. To overcome these
limitations, paper-based analytical devices (PAD) using biomarkers
such as glucose and lactate have been developed, with focus
on real-time analysis of the changes in biomarker concentrations
during cell culture [8,9]. Glucose is the most frequently used energy
source for cell growth in culture; cells produce lactate under anaerobic
conditions [10–12]. Therefore, we focused on the evaluation
of glucose and lactate concentrations in cell culture media.