Colorimetry/fluorescence dual-signal sensing system based on peptide nanotubes activating hemin and PPIX for...

Recently, it has become valuable to develop strategies based on multi-mode sensors to detect analytes related to human health, food safety and environmental pollution. In this study, KL@PPIX-hemin composite prepared by immobilizing hemin and protoporphyrin IX (PPIX) on self-assembled peptide nanotubes (PNTs) through multiple non-covalent interactions were used for colorimetric/fluorescent dual-mode sensing of tannic acid (TA). PNTs as a carrier can provide the hydrophobic microenvironment for hemin and PPIX to protect them from dimerization, thus activating their respective peroxidase-mimicking activity and fluorescence emission. Further experiments show that the composite could catalyze H₂O₂ to oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) to generate blue ox-TMB, which could exactly quench the emission of PPIX by inner filter effect. The added TA can reduce ox-TMB to TMB and further turn on the fluorescence of system. A colorimetric/fluorescent dual-mode sensing system for TA was thus constructed and a low limit of detection (13.2 nM) was obtained. In addition, the analytical strategy has been successfully applied to accurate TA determination in actual tea samples. The method was also combined with smartphone to achieve visual detection of TA, which provides a broad prospect for portable and rapid tannic acid analysis.