A Modified Carbon Paste Electrode with Silica Gel Coated with Meldola's Blue and Salicylate Hydroxylase as a Biosensor for Salicylate

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Abstract
A biosensor for salicylate was developed using a modified carbon paste electrode with silica gel coated with Meldola's Blue and salicylate hydroxylase. This biosensor detects the catechol produced in the enzymatic reaction through its electroxidation on the mediator. The influence of NADH/substrate ratio was verified and the biosensor presented response when this ratio was higher than 1.8. The pH of the medium significantly influences the results, requiring control within a narrow range of pH. The effect of the applied potential in the biosensor response showed that 200 mV vs SCE is the best potential to use in the measurements. The biosensor has a good linear response range of 10 to 60 μmol L−1, adjusted by the equation I = 11.7 (×1.3) + 6.78 (×0.03)[salicylate], with high sensitivity. The relative standard deviation for 6 measurements was 3.7%. The biosensor showed good stability for 20 days when used daily or for one month when stored in a refrigerator.