Fullerene-cryptand coated piezoelectric crystal urea sensor based on urease Original Research Article

A Fullerene C60-cryptand22 coated piezoelectric quartz crystal urea sensor based on either solvated or immobilized urease was developed and applied to detect urea in aqueous solutions. The C60-cryptand22 coated quartz crystal membrane showed the ability to adsorb ammonium ion which is the reaction product of the catalytic hydrolysis of urea by urease. The piezoelectric crystal urea sensor based on solvated urease gave a linear frequency response to the log concentration of urea with a slope of 80 Hz per decade (Δ (Hz)/Δ (log M)) within the concentration range 10−1 to 10−4 M and a detection limit of ≤10−4 M for urea in aqueous solutions. The piezoelectric sensor also exhibited comparatively good selectivity for urea with respect to other biological species, e.g. proteins, enzymes, ascorbic acid, glucose, serum and metal ions. Effects of pH, solvent, urea concentration, urease activity and coating load on the frequency response of the C60-cryptand22 coated quartz crystal based on solvated urease were investigated. An immobilized urease piezoelectric crystal sensor with C60-cryptand22 coating was also prepared and characterized.