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.