Figure 6.

(A) DPAdSV curves registered at the Nafion/GCE in 0.1 M H₂SO₄ solution containing increasing concentrations of Kyn: (a) 0 nM, (b) 2 nM, (c) 5 nM, (d) 10 nM, (e) 20 nM, (f) 50 nM; accumulation time 600 seconds. (B) and (C) Representative DPAdSV results obtained during Kyn quantification in samples obtained from SK-OV-3 cells (accumulation time 60 seconds). (B) Voltammograms for samples containing cellular lysates for IDO activity estimation (a) background (0.1 M H₂SO₄), (b) sample in 0.1 M H₂SO₄ (60 μL), (c) as in (b) +0.08 μM Kyn, (d) as in (b) +0.12 μM Kyn, (e) as in (b) +0.24 μM Kyn. (C) DPAdSV curves for samples of culturing medium from cancer cells: (a) background (0.1 M H₂SO₄), (b) sample in 0.1 M H₂SO₄ (15 μL), (c) as in (b) +0.2 μM Kyn, (d) as in (b) +0.4 μM Kyn, (e) as in (b) +0.6 μM Kyn.