Figure 8. Biosensor integration with LOC. (A) Schematic diagram describing how to measure glucose in DMEM (B) The three-electrode system (working, reference, and counter electrodes) integrated with the LOC is connected to the potentiostat for performing cyclic voltammetry measurements. (C) & (D) Glucose measurement after drug tests (C: Nafion/GOx, D: Nafion/MWCNT/GOx).
To verify the sensitivity of the developed biosensor, a chronoamperometry analysis of the biosensor-integrated LOC was performed by subjecting it to treatment with two concentrations of DF (500 and 100 µM). The graphical data of current versus time are shown in Figure 8C and D. The Nafion/MWCNT/GOx-coated electrodes exhibited higher sensitivity compared to Nafion/GOx-coated electrodes, except for MWCNT, and a higher current was detected in the DF-treated LOC compared with the untreated LOC. As observed in the previous section (Figure 5), cells consume the glucose contained in the medium; thus, if cells are killed by drugs, glucose concentration should be reduced accordingly. However, as can be seen in Figure 8C, without MWCNT, all three graphs were similar, indicating the formation of non-specific graphs. In contrast, the higher current flow in Figure 8D directly indicated the presence of a high level of glucose in the medium due to cell death caused by the drug, resulting in a lesser amount of glucose being utilized by the resident cells. Among the drug-treated LOCs, a higher current flow was observed in the case of 500 µM DF treatment, which indicates a higher degree of cell death in this drug concentration range. Therefore, it can be concluded that the developed Nafion/MWCNT-based glucose biosensor is sensitive enough to detect minor changes in glucose concentration and has potential applications as an easily integratable OOC system.