Kinetics of urease inhibition-based amperometric biosensors for mercury and lead ions detection

• Kinetics of amperomeric mercury and lead ions biosensors based on Nafion®(urease)/nano-structured polyaniline-Nafion®/Au/Al2O3 is investigated.
• The values of dissociation constant of adsorbed type urease-metal ions (Kd) and irreversible rate constant (kirr) are evaluated.
• The sensitivity of heavy metal ion biosensor is proportional to the inhibition efficiency (kirr/Kd).
• The inhibition efficiency and sensitivity of mercury ion biosensor is higher than that of lead ion biosensor.

The sensing element of biosensor is prepared by the immobilization of urease onto nano-structured polyaniline (PANi)-Nafion® (NSPN)/Au/Al2O3 synthesized by the chronopotentiometric technique. The sensitivity of lead ion at an amperometric urease based biosensor is obtained to be 743.5 µA ppm−1 for the linear dynamic range of 0.1–1.0 ppm Pb2+. The irreversible inhibiting kinetic models of the mercury and lead ions at the amperometric biosensors are proposed. The values of Kd (dissociation equilibrium constant of adsorbed type of enzyme and heavy metal ion) and kirr (irreversible inhibition reaction rate constant) for mercury and lead ions are obtained to be 0.45 ppm, 1.66 × 10−3 s−1, 8.67 ppm and 3.16 × 10−3 s−1, respectively. Compared with lead ion detection, the higher sensitivity to mercury ion of the biosensor is mainly caused by a higher inhibition efficiency (kirr/Kd).

The sensing ion (NH4+) (P) was obtained by the enzymatic reaction of urea (S). A part of enzyme (urease) (E) would be inhibited with heavy metal ions (Pb2+, Hg2+) (M) in phosphate buffer solution (PBS), and then the enzymatic activity and the concentration of sensing ion (NH4+) were decreased. Hence the level of Pb2+ and Hg2+ in the solution could be detected, and the irreversible inhibiting kinetic models of the Pb2+ and Hg2+ of the amperometric biosensors were proposed and investigated.Figure optionsDownload as PowerPoint slide