1920
Anal. Chem. 1985, 57, 1920-1923
(7) Mlyhara, Y.; Matsu, F.; Morilzurni, T. Proc. Chem. Sensors 1983, 501-506. (8) Thomas, D.;Broun, G. Blochemle 1972, 54, 229-244. (9) Blaedel, W. J.; Klssei, T. R.; Boguslaskl, R. C. Anal. Chem. 1972 42, 2030-2037. (10) Brady, J.; Carr, P. Anal. Chem. 1980, 52, 977-980. (11) Hameka, H.; Rechnitz. G. A. J . Phys. Chem. 1983, 87, 1235-1241. (12) Jochum, P.: Kowalski, 8. Anal. Chlm. Acta 1982. 144. 25-38. (13) Gough, D.; Leypoldt, L. “Appl. Biochemlstry and Bloenglneerlng”; Aca-
demlc Press: New York, 1981; pp 175-207. (14) Morf, W. E. Mkrochim. Act8 1980, 2 , 317-332. (15) “man, J., Los Alarnos National Laboratory, Computer Library.
RECEIVED for review January 22,1985. Accepted April 5,1985. The support of this project from the NIGMS, Grant No. GM 22952-08, is greatly appreciated.
pH-Based Enzyme Potentiometric Sensors. Part 2. Glucose-Sensitive Field Effect Transistor Steve D. Caras,’ Danuta Petelenz, and Jii.! Janata* Department of Bioengineering, University of Utah, Salt Lake City, Utah 84112
A theoretlcal model for a pH-based enzymatic glucose probe has been developed and tested experimentally with a dualtransistor chlp. It has been shown that the response of thls probe Is governed mainly by the buffer capacity, transport properties, and the concentratlon of oxygen In the enzymecontalnlng layer. & new enzyme lmmoblilzatlon procedure has been used In which the enzymes are covalently bound to the uncharged gel matrlx.
Enzyme electrodes for glucose are the oldest and the most extensively studied sensors of this type. They are based either on amperometric principle, using the reduction of oxygen or hydrogen peroxide as the primary electrode reaction, or on the potentiometric principle using the hydrogen peroxide or hydrogen ion as potential determining species. The latter falls into the group of pH-based enzyme potentiometric sensors, properties of which are examined in this series. Response of pH-based glucose enzyme electrodes has been studied by Nilsson et al. (1)and by Gough et al. (2). So far only one enzyme transistor sensitive to glucose has been described (3). In neither of these papers have the effects of buffer, oxygen partial pressure, or time response been studied in detail. All the above glucose enzyme sensors are based on the following reaction &D-glucose + O2
glucose
gluconate
+ H+ + H20z
Scheme I ti* 4
G
The partial differential equations for the glucose ENFET are similar to those described in part 1 of this series. The major difference is the presence of the second substrate, oxygen, which results in the more complex system of rate equations
-a[GI - - DG,,@[GI z at .]-l
(1)
For the purpose of modeling, this reaction has to be expanded in order to take into the account the effect of pH (Scheme I). It is assumed that the catalase is always present in quantity sufficient to decompose the hydrogen peroxide instantly. This is the reason for the factor 0.5 in front of the second term in eq 2.9.
G1u
L
Present address: Naval Research Laboratory, 4555 Overlook Ave., SW, Washington, DC 20375.
0003-2700/85/0357-1Q20$01.50/00 1985 Amerlcan Chemical Society
(2.8)
ANALYTICAL CHEMISTRY, VOL. 57, NO. 9, AUGUST 1985 1921
S
REFERENCE ELECTRODE
P
J (2.10)
L
- -
The corresponding boundary conditions are
G,(O,t)
I
02,(0,t) = H,(O,t) = HA,(O,t) = A,(O,t) = 0
G(L,t) = GBYG O,G,t) = 0 2 B Y O
Figure 1. Schematicdiagram of the ENFET chip. D and S are transistor drain and source, respectively. V , is the applied gate voltage and I is the drain-to-source current.
H ( U ) = HBYH HA(L,t) = HABrA A(L,t) = AB Where 7's are the partitioning coefficients having values between 0.4 and 1,and subscript B denotes the bulk solution concentrations. The initial conditions are
G(x,O) = 0 for x 02(X,o)
520
-
543
..
S 60 .. 580
SURF ACE
6.00
.. ..
