An animal cell culture monitoring system using a smartphone-mountable paper-based analytical device

[Display omitted] •A smartphone-based cell culture monitoring system was developed.•Paper-based analytical device was used for enzyme-mediated chromogenic assay.•Embedded flash light source and detector for smartphone were directly utilized.•Both glucose and lactate assays were accomplished simultaneously within a minute.•Real samples from animal cell culture were monitored easily and cost-effectively. We developed a simple and low-cost cell culture monitoring system utilizing a paper-based analytical device (PAD) and a smartphone. The PAD simultaneously analyses glucose and lactate concentrations in the cell culture medium. Focusing on the fact that animal cells consume glucose and produce lactate under anaerobic conditions, oxidase- and horseradish peroxidase (HRP) enzyme-mediated colorimetric assays were integrated into the PAD. The PAD was designed to have three laminated layers. By using a double-sided adhesive tape as the middle layer and wax coating, a bifurcated fluidic channel was prepared to manipulate sample flow. At the inlet and the outlets of the channel, a sample drop zone and two detection zones for glucose and lactate, respectively, were positioned. When sample solution is loaded onto the drop zone, it flows to the detection zone through the hydrophilic fluidic channel via capillary force. Upon reaching the detection zone, the sample reacts with glucose and lactate oxidases (GOx and LOx) and HRP, immobilized on the detection zone along with colorless chromophores. By the Trinder’s reaction, the colorless chromophore is converted to a blue-colored product, generating concentration-dependent signal. With a gadget designed to aid the image acquisition, the PAD was positioned to the smartphone-embedded camera. Images of the detection zones were acquired using a mobile application and the color intensities were quantified as sensor signals. For the glucose assay using GOx/HRP format, we obtained the limit of detection (LOD ∼0.3mM) and the limit of quantification (LOQ ∼0.9mM) values in the dynamic detection range from 0.3 to 8.0mM of glucose. For lactate assay using LOx/HRP, the LOD (0.02mM) and the LOQ (0.06mM) values were registered in the dynamic detection range from 0.02 to 0.50mM of lactate. With the device, simultaneous analyses of glucose and lactate in cell culture media were conducted, exhibiting highly accurate and reproducible results. Based on the results, we propose that the optical sensing system developed is feasible for practical