Zinc porphyrin/MXene hybrids with phosphate-induced stimuli-responsive behavior for dual-mode fluorescent/electrochemiluminescent ratiometric biosensing.

Highly sensitive ratiometric biosensors have attracted much attention in biomarker detection, but most rely on single-mode signals, which can affect accuracy. The development of new principles and methods for dual-mode ratiometric sensing can enhance detection accuracy. Herein, the zinc(II) meso-tetra(4-carboxyphenyl) porphyrin/MXene (ZnTCPP/TiCT) hybrids with phosphate-induced stimuli-responsive behavior are used to develop a novel dual-mode fluorescent/electrochemiluminescent (FL/ECL) ratiometric biosensor. The composites exhibit FL quenching and enhanced ECL behavior involving dissolved O. The FL quenching of ZnTCPP/TiCT is caused by energy transfer (EnT) and photo-induced electron transfer (PET) from ZnTCPP to TiCT. While the introduction of MXene compensates for the inadequate conductivity of ZnTCPP, facilitating electron transfer, which further makes the surface ZnTCPP more capable of activating O to produce singlet oxygen (O), thereby generating enhanced cathodic ECL. Furthermore, phosphate ions (PO) can interact with the Ti sites of ZnTCPP/TiCT, leading to competition for coordination with ZnTCPP, which in turn detaches ZnTCPP, resulting in enhanced FL and reduced ECL. On the basis of the phosphate-induced stimuli-responsive behavior, the dual-mode FL/ECL ratiometric biosensing of alkaline phosphatase (ALP) is achieved through ALP-catalyzed production of PO cascade effect with ZnTCPP/TiCT. The linear detection range for ALP is 0.1-50 mU/mL, with a detection limit as low as 0.0083 mU/mL. This proposed ZnTCPP/TiCT composites with stimuli-responsive behavior is expected to provide new ideas for the development of high-sensitivity dual-mode ratiometric biosensors with promising applications in the precise detection of important biomarkers.