Plasmonic colorimetry and G-quadruplex fluorescence-based aptasensor: A dual-mode, protein-free and label-free detection for OTA.

G-quadruplexes (G4) have received significant attention in the field of aptasensors owing to their unique physicochemical characteristics. A dual-mode, protein-free and label-free aptamer sensor based on plasmonic colorimetry and G4 fluorescence (PC@GF-aptasensor) was proposed for ochratoxin A (OTA). Colorimetry mode was achieved through the surface plasmon resonance (SPR) effect, which related to the OTA-Apt-based G4-OTA. The fluorescence mode was reflected by the insertion of thioflavin T (ThT) into G4-OTA. The OTA could be interpreted via three readouts: (1) naked eye (LOD of 2.0 ng mL), (2) smartphone (LOD of 1.65 ng mL), and (3) spectrofluorometer (LOD of 0.93 ng mL). The PC@GF-aptasensor exhibited several advantages, such as a standardised recognition group, simplified operation, low background signal, and practicality. The proposed PC@GF-aptasensor integrated SPR-based multicolour interpretation and ThT-inserted fluorescence reflection to obtain a dual-mode optical biosensor, which may provide valuable insights for the development of other targets with G4-based aptamers.