The response of the AG/PyOx/CHIT biosensor exhibits a linear
dependence of the current density for the maltose concentration
between 0.25 and 2.0 mM. The linearity was defined by the equation
of y=0.844x+0.029 where x and y show concentration in mM and
current density as μA/cm2, respectively and R2 was calculated as
0.999. In the case of AG/PyOx/CHIT–CNT biosensor, the concentration
range was linear in the same concentration interval and this linearity
was defined by the equation of y=0.882x+0.0625, (x and y show
concentration in mM and current density as μA/cm2, respectively)
while R2=0.996. When higher maltose concentrations than 2.0 mM
were applied, current density stayed constant because of reaching to
saturated substrate amount. Obvious difference cannot be found
between responses of AG/PyOx/CHIT and AG/PyOx/CHIT–CNT. It is
clear that the presence of CNT didn't affect the response characteristics
at the defined conditions. Similar observations were also
obtained in our previous works in which CNT modification only
provided more stable immobilization platform with higher surface
area as other nanostructured materials [45,46]. It is also well known
that charged polymers are more efficient dispersing agents allowing
quicker dispersion of nanotubes compared to solvents and offer
higher stability of dispersion. On the other hand, other maltose
biosensors including amyloglucosidase/glucose oxidase enzymes
were described by Feng Ge et al. The linearity was detected in the
potassium ferricyanide mediated and non-mediated conditions in the
range of 5–20 mM [1] and 10–35 mM [47]. In compare to these
systems, the sensitivity of our system is higher than other maltose