Evaluation of a nitrogen-incorporated tetrahedral amorphous carbon thin film for the detection of tryptophan and tyrosine using flow injection analysis with amperometric detection

We report on the analytical performance of a tetrahedral amorphous carbon (ta-C:N) thin-film electrode in flow injection analysis with amperometric detection. Two model redox analytes were used to evaluate the electrode response because of their positive detection potentials and propensity (i.e., reaction products) to adsorb and foul sp(2) carbon electrodes: tyrosine and tryptophan. ta-C:N electrodes are attractive for electroanalytical applications because they possesses many of the excellent properties of boron-doped nanocrystalline diamond (BDD) and they can be deposited at or near room temperature. The results show that the ta-C:N electrode exhibits lower background current and noise than glassy carbon (GC). The electrode was stable microstructurally at the positive potentials used for detection, similar to 1.1 V, of these two amino acids and it exhibited superior analytical detection figures of merit as compared to GC and as good or superior to BDD. The linear dynamic range for both analytes at ta-C:N was from 0.1 to 100 mu mol L-1, the sensitivity was 8-12 mA L mol(-1), the short-term response variability was 1-2%, and the minimum detectable concentration was 89.7 +/- 0.9 nM (18.3 mu g L-1 or 0.46 ng) for tryptophan and 120 +/- 11 nM (21.7 mu g L-1 or 0.54 ng) for tyrosine. The analytical detection figures of merit for these amino acids at GC and BDD are also presented for comparison as is characterization data for the chemical composition and microstructure of the ta-C:N film.