Chemical polymerization/oligomerization opens numerous opportunities, from fundamental materials research to practical applications in catalysis, energy, sensing, and medicine. The electrochemical detection of vitamins B9 (folic acid) and C (ascorbic acid) requires new approaches because of low selectivity, electrode fouling, and interference from other chemicals. As an excellent material for long-term vitamin detection, oligo 3,5-diamino-1,2,4-triazole (oligo DAT) enhances the sensitivity, selectivity, and stability of sensors by creating a stable, conductive layer that facilitates electron transfer and reduces interference from common substances like glucose or uric acid. This work investigates the electrochemical sensing properties of oligo DAT, utilizing hydrogen tetrachloroaurate (III) (HAuCl4) as an oxidizing agent at ambient temperature for the concurrent and sensitive detection of vitamins B9 and C. The oligo DAT was carefully characterized by spectroscopic and microscopic techniques to confirm its structure and properties. The GC electrode was subsequently connected to the oligo DAT by a potentiodynamic technique. The oligo DAT-modified electrode exhibited higher catalytic activity than the unmodified GC electrode for the oxidation of vitamins B9 and C. This led to the determination of the sensitivity levels for both vitamins; the lowest measured concentration for vitamin C was 1 x 10-11 M with a theoretical limit of detection (LOD) of 1.9 x 10-11 M, and for vitamin B9, the lowest measured concentration was 1 x 10-11 M with a theoretical LOD of 3.5 x 10-11 M. The practical efficacy of this straightforward method was proven by the quantification of vitamins B9 and C in human plasma samples.