fig2

Figure 2. (A) Schematic of the aptamer-based MTC-displacement assay; (B) Principle of aptamer-based colorimetric cocaine tests. MTC: Methylene tripeptide complex; TMB: 3,3′,5,5′-Tetramethylbenzidine; G4: G-quadruplex; PPIX: protoporphyrin IX; oxTMB: oxidized 3,3′,5,5′-Tetramethylbenzidine.