A fluorescent ESIPT-based benzimidazole platform for the ratiometric two-photon imaging of ONOO(–)in vitro and ex vivo

In this work, we have developed an ESIPT-based benzimidazole platform (MO-E1 and MO-E2) for the two-photon cell imaging of ONOO(–) and a potential ONOO(–)-activated theranostic scaffold (MO-E3). Each benzimidazole platform, MO-E1–3, were shown to rapidly detect ONOO(–) at micromolar concentrations (LoD = 0.28 μM, 6.53 μM and 0.81 μM respectively). The potential theranostic MO-E3 was shown to release the parent fluorophore and drug indomethacin in the presence of ONOO(–) but unfortunately did not perform well in vitro due to low solubility. Despite this, the parent scaffold MO-E2 demonstrated its effectiveness as a two-photon imaging tool for the ratiometric detection of endogenous ONOO(–) in RAW264.7 macrophages and rat hippocampus tissue. These results demonstrate the utility of this ESIPT benzimidazole-based platform for theranostic development and bioimaging applications.