Dual mode quantitative imaging of microscopic viscosity using a conjugated porphyrin dimer

Abstract

Microviscosity is of paramount importance in materials and bio-sciences. Fluorescence imaging using molecular rotors has emerged as a versatile tool to measure microviscosity, either using a fluorescence lifetime or a ratiometric signal of the rotor; however, only a limited number of blue -to-green-emitting fluorophores with both the lifetime and the ratiometric signal sensitivity to viscosity have been reported to date. Here we report a deep red emitting dual viscosity sensor, which allows both the ratiometric and the lifetime imaging of viscosity. We study viscosity in a range of lipid-based systems and conclude that in complex dynamic systems dual detection is preferable in order to independently verify the results of the measurements as well as perform rapid detection of changing viscosity .

A Molecular Rotor that Measures Dynamic Changes of Lipid Bilayer Viscosity Caused by Oxidative Stress

“…PD alone absorbs at the excitation wavelength of BODIPY‐C 10 (480 nm). However, even though PD absorbs at 480 nm, its fluorescence is centered at 630–750 nm,39 which does not overlap with fluorescence of BODIPY‐C 10 (510–600 nm). Thus, we made sure that the time‐resolved fluorescence decays recorded belong to the molecular rotor and are not contaminated by the signal from the PDT photosensitizer used.…”

“…The first set of GUVs studied contained PD, a known singlet oxygen photosensitizer45, 46 that is bound to the lipid bilayer surface39 and BODIPY‐C 10 , which probes viscosity of the inner part of the lipid bilayer 40. Previously, we have utilized PD as both the photosensitizer and as a molecular rotor and recorded a large increase in the DOPC monolayer viscosity upon PDT 39.…”

“…Previously, we have utilized PD as both the photosensitizer and as a molecular rotor and recorded a large increase in the DOPC monolayer viscosity upon PDT 39. Here, we aimed to separate out the dual function of PD as a photosensitizer and a molecular rotor.…”

“…In this work, we utilized BODIPY‐C 10 17, 18 (Figure 1), a fluorophore that belongs to a group of dyes termed ‘molecular rotors’ that have viscosity‐dependent fluorescence quantum yields, lifetimes,19, 20 and depolarization 21, 22. When combined with fluorescence lifetime imaging microscopy (FLIM), molecular rotors can be used to obtain spatially resolved viscosity maps of microscopic objects,17, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40 as well as to observe dynamic change in viscosity during relevant processes of interest 37, 39, 41, 42. Thus, we aimed to use BODIPY‐C 10 , which is known to completely embed into the fluid‐phase lipid bilayers40 to directly examine how photooxidation during PDT affects viscoelastic properties of model lipid membranes, with spatial‐ and time‐resolution.…”

Tuning the Sensitivity of Fluorescent Porphyrin Dimers to Viscosity and Temperature

“…Such a dual sensing approach is beneficial, since it allows us to independently verify the viscosity read‐out using two independent measurements 18, 30. Here, we tested whether the dimers 1 , 3 and 4 also have viscosity‐sensitive fluorescence decays.…”