Sensing of l-cysteine at glassy carbon electrode using Nile blue A as a mediator

The oxidation of l-cysteine has been studied at a glassy carbon electrode by electrocatalytic effects of Nile blue A (NBA) as a mediator using cyclic, linear sweep voltammetry and chronoamperometry as diagnostic techniques. The results showed that the catalytic current of NBA depended on the concentration of l-cysteine. Although l-cysteine itself showed a very poor electrochemical response at the glassy carbon electrode, the response could be greatly enhanced by using NBA as a mediator, which enabled a sensitive determination of l-cysteine. This sensor could be used for determination of l-cysteine in the range of 10.0 × 10−6 to 2.5 × 10−4 M with a limit of detection of 1.3 μM. The rate constant was estimated for catalytic reaction of NBA with l-cysteine using chronoamperometry. The influence of potential interfering substances on the peak current was studied and the results showed that the method was highly selective for l-cysteine determination. The proposed method was used for the determination of l-cysteine in synthetic and real samples.