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Urease Activity Assay.

A colorimetric assay based on the
hydrolysis of urea was used for the activity control of free and
immobilized urease, as monitored by the pH-sensitive dye
bromcresol purple. The enzymatic reaction was monitored by
following the dye absorption at 588 nm.18,19 A control solution
containing 25 mM urea, 0.015 mM bromcresol purple, and 0.2
mM EDTA was adjusted to pH 5.8. This solution was placed in a
3-mL UV cell and magnetically stirred. A known amount of the
urease multilayer-coated PS spheres (or free urease for the
calibration) was then added, and the kinetics were monitored by
following the absorption at 588 nm. The solution changed from
yellow to dark purple during the reaction, corresponding to a
change in solution pH from 5.8 to 7.5. The increment of the
absorbance with time was used to characterize the urease activity
in the sample


Biocolloids with Ordered Urease Multilayer Shells
as Enzymatic Reactors
Yuri Lvov† and Frank Caruso*,‡
Institute for Micromanufacturing, Louisiana Tech University, Ruston, Louisiana 71272, and Max Planck Institute of Colloids
and Interfaces, D-14424 Potsdam, Germany

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