Biomedical Engineering Reference
In-Depth Information
process, thereby decreasing the sensitivity and broadening the quantification range.
For this reason, subsequent analyses were preferably made by cyclic voltammetry.
Nevertheless, if very low detection limits are required (low nano range), chronoampe-
rometry measurements should be carried out at the lowest potential (-0.7 V vs
Ag/AgCl), using non-rotating electrodes.
3.4
Application of Carbon Paste Screen Printed Electrodes (CPSPEs)
Following the optimization of the ccNiR containing conductive paints, the en-
zyme/carbon inks were deposited on CPSPEs. The CVs displayed higher background
currents (Fig. 7A), which is most likely related to the roughness of the SPEs surfaces,
generating higher capacitive currents. Nonetheless, the analytical parameters (Fig. 7B)
were quite similar, with a sensitivity of 5.3x10 -7 A.
M -1 .cm -2 and a linear range of
μ
0.001 - 1.5 mM, while the K M app was even higher (2.2
±
0.4 mM).
7,0E-05
A
1,0E-05
B
6,0E-05
-1,0E-05
5,0E-05
4,0E-05
-3,0E-05
3,0E-05
-5,0E-05
2,0E-05
-7,0E-05
1,0E-05
-9,0E-05
0,0E+00
-1
-0,8
-0,6
-0,4
-0,2
0
0
500
1000
1500
Fig. 7. (A) CVs of a CPSPE coated with a ccNiR/carbon ink/acetone composite, in the presence
of increasing nitrite concentrations (0 - 6 mM) and (B) corresponding calibration curve. Elec-
trolyte: 0.1 M KCl in 0.05 M Tris-HCl buffer, pH 7.5; scan rate, 20 mV/s.
μ
Potential vs pseudo-Ag/AgCl (V)
[Nitrite] (
M)
However, despite the successful incorporation of ccNiR within the thermally
cured conductive ink and the good sensitivity of detection displayed by the enzyme
coated CPSPEs, the low limit of the linear range is higher than the ones provided by
the previous biosensor configurations [10-15] and should be further improved if the
main target is plasma and blood analysis.
3.5
Interferences
The chemistries of nitrate and nitrite, which are present in mammalian physiological
systems either from dietary provision or endogenous formation, are nearly
indissociable [2,3]. Aiming at evaluating the potential interfering effect of nitrate on
the analytical assay, the biosensor response to nitrite (666
M) 1 was compared with
the one recorded in the presence of an equal amount of nitrate; though, the
μ
1 This concentration fits in the first half of the calibration curve.
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