Nitrite Biosensing Using Cytochrome C Nitrite Reductase: Towards a Disposable Strip Electrode - Biomedical Engineering Systems and Technologies - page 26

solvent did not evaporate completely at 40 ° C, enhancing its detrimental effect on the

enzyme activity.
In accordance to the results obtained in this combined study, we have selected ace-
tone for ink solubilization and a curing temperature of 40

° C.

3.3 Analytical Parameters
The analytical performance of the bioelectrodes was further evaluated by chronoam-
perometry, poising the working electrodes at -0.5 or 0.7 V either (Fig. 6) or not (not
shown) with self-rotation. Results were compared with the ones obtained by cyclic
voltammetry (Table 1).

Fig. 6. Amperometric measurements of a ccNiR/carbon ink (acetone, 60°C)/PG electrode
poised at different working potentials: ( ⎯ ) -0.5 V; (⎯) -0.7 V ( vs Ag/AgCl), in the presence of
increasing concentrations of nitrite. ω = 1000 rpm

Table 1. Analytical parameters of optimal ccNiR/carbon paste/PG electrodes (3.3 μg enzyme in
an acetone:ink mix; curing temperature, 40°C), as obtained by chronoamperometry and cyclic
voltammetry assays

Potential
(V)

Electrode
Rotation

Sensitivity
(A.µM -1 .cm -2 )

Linear range
(µM)

Catalytic
efficiency

Technique r 2

-0.5 No 5x10 -7 ± 3x10 -7 0.995 0.666 - 132 27 ± 26

Chrono-
amperometry

-0.7 No 5x10 -7 ± 3x10 -7 0.995 0.167 - 132 48 ± 12

2.6x10 -6 ± 6x10 -7

-0.5 Yes 0.991 0.666 - 13.2 54 ± 24

2.0x10 -6 ± 3x10 -7 -0.7 Yes 0.996 0.666 - 264 56 ± 23

2.3x10 -7 ± 2x10 -8 6.64 - 1.97x10 3 CV -0.8 No 0.995 26 ± 11

The amperometric response upon nitrite addition was always prompt, indicative of
a fast heterogeneous electron transfer. Although not being a practical option in real
situations, the electrode rotation delivers a much better performance (Table 1). In fact,
because there are no mass transport limitations, both the sensitivity and catalytic effi-
ciency of the biosensor were higher in these conditions, no matter the operating vol-
tage. On the other hand, the linear range was much wider (almost three orders of
magnitude) if measurements were made through cyclic voltammetry. In these condi-
tions, the current response is diffusion controlled, which slows down the overall