Self-Assembly of a Monochromophore-Based Polymer Enables Unprecedented Ratiometric Tracing of Hypoxia

Abstract

The accuracy of traditional bischromophore-based ratiometric probes is always compromised by undesirable energy/charge transferring interactions between the internal reference moiety and the sensing chromophore. In this regard, ratiometric sensing with a monochromophore system is highly desirable. Herein, an unprecedented monochromophore-based ratiometric probe, which consists of a hydrophilic backbone poly(N-vinylpyrrolidone) (PVP) and single chromophore of platinum(II) tetraphenylporphyrin (Pt-TPP) is reported. Combination of the specific assembled clustering-triggered fluorescent emission (oxygen-insensitive) with the original Pt-TPP phosphorescence (oxygen-sensitive) enables successful construction of a monochromophore-based ratiometric nanosensor for directly tracing hypoxia in vivo, along with the preferable facilitation of enhanced permeation and retention effect and long excitation wavelength. The unique ratiometric signals enable the direct observation from normoxic to hypoxic environment in both living A549 cells and a tumor-bearing mice model, providing a significant paradigm of a monochromophore-based dual-emissive system with the specific assembled cluster emission. The work satisfactorily demonstrates a valuable strategy for designing monochromophore-based dual-emissive materials, and validates its utility for in vivo ratiometric biological sensing without the common energy/charge interference in bischromophore-based system.

Keywords: NIR ratiometric mode; clustering-triggered emission; hypoxia sensing; monochromophore-based polymers; self-assembly.