Urea biosensor based on Zn3Al–Urease layered double hydroxides nanohybrid coated on insulated silicon structures

Urea biosensors for medical diagnostic monitoring were developed based on the immobilization of urease within layered double hydroxides (LDH). The urease–LDH material was obtained by a stepwise exchange reaction by urease of a Zn₃Al–dodecyl sulphate (ZnAl–DS) colloidal suspension. XR diffraction and FTIR analysis show that this method gives rise to a Zn₃Al–Urease LDH nanohybrid material with urease dispersion and textural properties. An aqueous suspension of this urease–LDH nanohybrid material was deposited on an insulated semiconductor (IS) structure. Biosensor responses to urea additions were obtained using capacitance (C vs. V) and impedance (Z vs. ω) measurements. An enhanced maximum limit of the dynamic range was observed in the case of the impedance measurements (110 mM) compared to (5.6 mM) the capacitive urea biosensor. The Michaelis–Menten constant was also calculated according to the Lineweaver–Burk plot. It was found that the K_m value with immobilized enzymes was lower (K_m = 0.67 mM) in comparison with free enzymes. This K_m value obtained from the capacitance measurements indicates that the urea degradation is performed within any inhibition action on the IS/Zn₃Al–Urease LDH electrode. A comparative study was carried out between these results and those obtained previously, using urease/ZnAl–Cl layered double hydroxides mixture coated on the pH-ISFET transducer.