Experimental evidence of the chaotic regime in a salicylate biosensor

In a biosensor for salicylate, developed using a modified carbon paste electrode with silica gel coated with Meldolaʹs Blue and salicylate hydroxylase, the current time series presented a complex oscillatory pattern, for salicylate and NADH concentrations close to 2.0 × 10−5 and 3.6 × 10−5 mol 1−1, respectively. These experimental results suggest that the biosensor response presents chaotic characteristics. The complex temporal behavior of these series was diagnosed as deterministic chaos by measurement of the Grassberger-Procaccia dimension, and the calculation of the first Lyapunov exponent. The value determined for the correlational dimension is lower than 5. These results suggest a coupling of five or six differential equations to describe the redox reactions of the biosensor system.