Scandium-mediated photosensitization oxidation: A new strategy for fast and neutral pH colorimetric detection of cocaine by coupling split aptamer

The sensors integrating the use of aptamer recognition and catalytic oxidation of substrate-based colorimetry have been developed for various analytes detection. However, the available sensors largely suffer from the contradiction of physiological conditions involved in aptamer recognition and acid condition employed in catalytic oxidation colorimetry and causing inferior performance. Herein, we reported a neutral photocatalytic oxidation strategy induced by scandium (Sc3+), which was further used to develop a novel photosensitization colorimetric assay based on G-quadruplex/PPIX for the visual detection of cocaine within 40 s. The assay was achieved by split aptamers containing G-quadruplex fragments, which would reassemble into an intact aptamer and induce the formation of G-quadruplex/PPIX complex in the presence of cocaine, allowing the activation of Sc3+-mediated photosensitization oxidation of TMB. This colorimetric assay exhibits high sensitivity for cocaine with detection of limits as low as 1 μM by naked eye observation and 0.38 μM by UV–vis spectrometer. The specificity of cocaine against other illicit drugs and the applicability of diluted saliva analysis were eventually investigated. Coupling of split aptamers, we believe that this rapid and neutral photosensitization oxidation strategy retains promising potential for the visual detection of other illicit drugs and medical biomarkers specific in the biological samples.