Gold-graphene quantum dot-N-doped porous carbon-based electrochemical aptasensor with DNA amplification for ultrasensitive detection of omethoate

The synthesis of highly catalytically active gold‑carbon composites remains a significant challenge. This study reports a novel approach for synthesizing a gold-histidine functionalized graphene quantum dots-N-doped porous carbon composite (Au-HFGQD-NPC). Gold ions (Au³⁺) were coordinated with HFGQD through AuN bonds to form Au-HFGQD complexes, which were then combined with polyacrylamide, freeze-dried, and thermally reduced under a N₂ atmosphere at 500 °C. The resulting Au-HFGQD-NPC features a three-dimensional porous architecture with uniformly dispersed, small Au nanoparticles within the carbon matrix, which enhances its catalytic performance. This composite was utilized as a sensing material to develop an electrochemical aptasensor for omethoate detection that incorporates a DNA recycling amplification strategy. The aptasensor employed a triple-helix aptamer probe (TAP) consisting of an aptamer loop, two segment stems, and a triplex oligonucleotide (probe). Omethoate binding to the aptamer induces the TAP conformational change, releasing the probe. The released probe hybridizes with hairpin DNA 1 (H1) immobilized on the electrode surface via AuS bonds. Subsequently, ferrocene-modified hairpin DNA 2 (H2-Fc) hybridizes with H1, releasing the probe and triggering the next cycle. This recycling mechanism results in the accumulation of multiple H2-Fc molecules on the electrode. The highly catalytically active Au-HFGQD-NPC then catalyzes the oxidation of Fc, leading to a significantly enhanced detection signal. The differential pulse voltammetry peak current exhibited a linear relationship with the logarithm of omethoate concentration over the range of 3 × 10⁻¹⁵ to 1 × 10⁻⁹ M, achieving a detection limit of 1.2 × 10⁻¹⁵ M. The proposed aptasensor demonstrates high sensitivity, selectivity, and stability, and has been successfully applied for determine omethoate in cabbage samples.