Resumo:
A new amperometric biosensor for the determining cholesterol based on
the immobilization of cholesterol oxidase (ChOx) in a crosslinked poly(vinyl alcohol)
(PVA) matrix and the charge transfer mediator copper phtahalocyanine (Ftc) is
described. The biosensor was obtained by the complexation-mediated solubilization
method, where Ftc was dispersed in high concentration in an organic aprotic solvent for
the formation of the electron donor-acceptor complex. The crosslinked PVA membranes
were characterized by differential scanning calorimetry (DSC), thermomechanical
analysis (TMA), electronic spectroscopy (UV/Vis) and vibrational (FTIR) spectroscopy.
The water transport through the biosensor membrane was studied by the equilibrium
degree of swelling. The results of DSC and TMA indicate that both, the glass transition
temperature (Tg) and Young modulus were increased systematically with crosslinking
density of the hydrogel. The water diffusion coefficient decreased with the increase in
the crosslinking degree indicating that the water molecules possess a lower degree of
translational mobility and are "tightly bound" in the PVA-borate complex structure.
Semiempirical calculations using PM3-d have been performed on the Ftc/PVA charge
transfer complex. The geometry parameters, heats of formation, ionization potential,
HOMO-LUMO energy differences are also reported and compared with the vibrational
(FTIR) spectra and conductivity experimental results. The developed biosensor has
been used for the determination of cholesterol with an acceptable accuracy. Under
optimal conditions, the biosensor shows a linear response to cholesterol in the range of
0.1 mM to 5.17 mM, with a fast response (12 s) and high sensitivity.
