Abstract
The electrochemical detection of oxytocin using boron-doped diamond (BDD) electrodes was studied. Cyclic voltammetry of oxytocin in a phosphate buffer solution exhibits an oxidation peak at +0.7 V (vs. Ag/AgCl), which is attributable to oxidation of the phenolic group in the tyrosyl moiety. Furthermore, the linearity of the current peaks obtained in flow injection analysis (FIA) using BDD microelectrodes over the oxytocin concentration range from 0.1 to 10.0 μM with a detection limit of 50 nM (S/N = 3) was high (R2 = 0.995). Although the voltammograms of oxytocin and vasopressin observed with an as-deposited BDD electrode, as well as with a cathodically-reduced BDD electrode, were similar, a clear distinction was observed with anodically-oxidized BDD electrodes due to the attractive interaction between vasopressin and the oxidized BDD surface. By means of this distinction, selective measurements using chronoamperometry combined with flow injection analysis at an optimized potential were demonstrated, indicating the possibility of making selective in situ or in vivo measurements of oxytocin.
Highlights
Oxytocin: Cys-Tyr-IIe-Gln-Asn-Cys-Pro-Leu-Gly-NH2 Vasopressin: Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly-NH2 The difference between these two peptides is only in two amino acids
Due to the similarity of the structures, both peptides compete for antibodies that may have some degree of affinity for peptides with similar amino acid sequences leading to low specificity in the main available method for oxytocin detection, i.e. radio immunoassay (RIA)[7,8,9]
Only a few reports have been published in regard to the direct electrochemical detection of peptides or proteins[10,11,14,15], which might be due to the lower sensitivity of electrochemical methods compared to those of immunoassay or mass spectrometry
Summary
Oxytocin: Cys-Tyr-IIe-Gln-Asn-Cys-Pro-Leu-Gly-NH2 Vasopressin: Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly-NH2 The difference between these two peptides is only in two amino acids (highlighted in bold). First, electrochemical detection of oxytocin and vasopressin was studied using BDD electrodes. The oxidation peaks of oxytocin and vasopressin could clearly be distinguished due to the difference in electrostatic interactions between the peptides and BDD surface.
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