G-quadruplex fluorescent and lateral flow colorimetric aptasensor for the detection of capsaicin in illicit cooking oil

The safety of cooking oil is a major global concern and capsaicin (CAP) serves as a crucial marker for assessing its quality. To address this issue, we have devised an innovative biosensor using a truncated aptamer, Cap-1–2, as the foundation for a dual-mode aptasensor. The aptasensor employs a combination of Mg²⁺-dependent DNAzyme (MNAzyme) cleavage and hybridization chain reaction (HCR) to achieve highly sensitive CAP detection. Notably, the fluorescence signal originates from the inherent fluorescence of thioflavin T (ThT) embedded in a G-quadruplex (G4) structure, enabling the detection of CAP in high-throughput oil samples. Additionally, the biosensor employed the MNAzyme to cleave biotinylated DNA (S1-Biotin), which is subsequently ligated to functionalized gold nanoparticles (AuNPs-Poly A-cDNA), generating outstanding colorimetric signals on lateral flow test strips for immediate point-of-care testing (POCT). The linear detection ranges of the established fluorescence and colorimetric aptasensor were 0.15–80 ng mL⁻¹ and 0.2–100 ng mL⁻¹, respectively, and the limits of detection (LOD) were 0.054 ng mL⁻¹ and 0.137 ng mL⁻¹, respectively. These results demonstrate the practicality of the aptasensor for detecting CAP in real-world samples. Moreover, the aptasensor surpasses traditional biosensors in terms of high-throughput, portability, and sensitivity, making it highly promising for rapid detection in the food industry.