1924
Anal. Chem. 1985, 57, 1924-1925
pH-Based Enzyme Potentiometric Sensors. Part 3. Penicillin-Sensitive Field Effect Transistor Steve D.Caras' and JiEI Janata* Department of Bioengineering, University of Utah, Salt Lake City, Utah 84112
A dlffuslon-klnetlc model for penlclllln enzyme fleld effect translstor has been developed and solved numerically. It Is shown that the external buffer plays a crltlcal role In the response of thls device. It Is also shown that the second, weakly acidic group In the penlclllolc acld affects the response characterlstlcs, namely, at the high substrate concentrations.
concentration, D, is the diffusion coefficient within the gel layer, HA is the associated buffer, and P H is the associated product. The total concentration of hydrogen ions generated by the enzymatic reaction is [HIT= [HA] + [H+] + [PHI. Similarly, total product is [PIT = [PHI + [PA-]
-a[plT at
An enzyme sensor for penicillin is based on the hydrolysis of the P-lactam ring of penicillins which is catalyzed by the penicillinase. If the substrate is benzylpenicillin, the Michaelis-Menten constant is independent of pH in the range of 4 to 8 ( I ) . The first penicillin enzyme electrode was described by Papariello et al. (2). In that work the enzyme was entrapped in a polyacrylamide gel over a pH glass electrode. In a similar work Nillson and co-workers ( 3 , 4 )studied experimentally the effect of buffer capacity on the response of their penicillin sensor. They have observed that at low buffer concentration (
