Fig. 7.

Schematic illustration of representative optical aptasensors. (a) Working principle of an ELONA aptasensor. Colorless substrate TMB is oxidized by enzymes like HRP to generate a blue color. (b) Working principle of a AuNPs-based colorimetric aptasensor. Released AuNPs aggregate in the presence salt accompanied by a color change from red to purple. (c) Working principle of a fluorescent aptasensor. The fluorescence of the fluorophore is recovered due to inhibition of FRET upon target binding. (d) Working principle of a SERS aptasensor. Raman intensity is amplified via the formation of a sandwich style complex. (e) Working principle of a SPR aptasensor. Aptamer-target binding leads to the variation of refractive index