Probing trace phenols based on mediator-free alumina sol-gel derived tyrosinase biosensor

A novel tyrosinase biosensor has been developed for the subnanomolar detect ion of phenols, based on the immobilization of tyrosinase in a positively c harged Al2O3 sol-gel membrane on a glassy carbon electrode. It has been fou nd that Al2O3 sol-gel is perfectly beneficial to the immobilization of tyro sinase, because it not only possesses the general advantages of sol-gel but it also is an effective promoter of the biosensor. The large microscopic s urface area, porous morphology, and hydrophilic property of the sol-gel mat rix result in high enzyme loading, and the enzyme entrapped in this matrix retains its activity to a large extent. The Al2O3 sol-gel-containing surfac e also displays an intrinsic electrocatlytic o-quinone response and, hence, offers a high-sensitivity (127 mu A.mM(-1)) monitoring of phenols. The det ection limit is 0.2 nM at a signal-to-noise ratio of 3, the response time i s less than 4 s reaching 95% of the steady-state value, and 70% of the acti vity is retained after 3 months.