C. Preininger et Os. Wolfbeis, DISPOSABLE CUVETTE TEST WITH INTEGRATED SENSOR LAYER FOR ENZYMATIC DETERMINATION OF HEAVY-METALS, Biosensors & bioelectronics, 11(10), 1996, pp. 981-990
We report on a quick and simple test for detection of heavy metals bas
ed on the inhibition of free urease contained in a disposable cuvette.
The wall of the cuvette has been covered with sensors for either ammo
nia or ammonium ion, and the kinetics of the enzymatic reaction has be
en monitored by monitoring the color of the sensing layer rather than
that of the whole solution. In order to perform the test, buffer, enzy
me and sample are placed in the cell. On addition of urea, enzymatic h
ydrolysis results in the formation of ammonia (and ammonium ion), and
this is detected by one of the sensors. Heavy metals are detected by t
heir inhibitory effect. This sensing scheme is new in that it enables
even strongly colored and highly turbid samples to be analyzed, becaus
e it is the optical properties of the 4 mu m sensing layer on the wall
that are monitored rather than the sample itself. Since sample cells
can be made at low cost, they may be disposed of after use. Heavy meta
l ions are found to inhibit urease in the following decreasing order:
Ag(I)>Hg(II)>Cu(II)much greater than Ni(II)>Co(II)>Cd(II)>Fe(III)>Zn(I
I)>Pb(II). The lowest limits of detection are found for Ag(I) (20 ppb)
, Hg(II) (70 ppb) and Cu(II) (250 ppb). A comparison of the ammonia ga
s-sensitive optode and the ammonium ion-sensitive optode showed the fo
rmer to be more precise and appropriate for determination of heavy met
als. The toxicity of the heavy metals correlates well with the stabili
ty constants of the corresponding metal sulfides. We also discuss the
inhibitory effect of metal combinations on the activity of the enzyme
and the effects of ionic strength and incubation time. (C) 1996 Elsevi
er Science Limited.