Azo‐Based Fluorogenic Probes for Biosensing and Bioimaging: Recent Advances and Upcoming Challenges

Abstract

The use of nonfluorescent azo dyes as dark quenchers in activatable optical bioprobes based on the Förster resonance energy transfer (FRET) mechanism and designed to target a wide range of enzymes has been established for over two decades. The key value of the azo moiety (-N=N-) to act as an efficient "ON-OFF" switch of fluorescence once introduced within the core structure of conventional organic-based fluorophores (mainly fluorescent aniline derivatives) has recently been exploited in the development of alternative reaction-based small-molecule probes based on the "profluorescence" concept. These unprecedented "azobenzene-caged" fluorophores are valuable tools for the detection of a wide range of reactive (bio)analytes. This review highlights the most recent and relevant advances made in the design and biosensing/bioimaging applications of azo-based fluorogenic probes. Emphasis is also placed on relevant achievements in the synthesis of bioconjugatable/biocompatible azo dyes used as starting building blocks in the rational and rapid construction of these fluorescent chemodosimeters. Finally, a brief glimpse of possible future biomedical applications (theranostics) of these "smart" azobenzene-based molecular systems is presented.

Synthesis and Photodynamics of Stilbenyl‐Azopyrroles: Two‐Photon Controllable Photoswitching Systems

“…In fact, as discussed later, transient absorbance measurements produced evidence for a low‐yield formation of a long‐lived species which was assigned to triplet states (see below). Given that the three stilbenyl‐azopyrroles have shifted absorption spectra, and extremely low fluorescence yields, they are clear candidates to be used as dark quenchers in azo‐based fluorogenic probes for biosensing and bioimaging …”

Experimental and Theoretical Studies of Novel Azo Benzene Functionalized Conjugated Polymers: In-vitro Antileishmanial Activity and Bioimaging

“…Studies on antileishmanial activity. Leishmania evades immune host immune system by dampening critical signalling pathways which are required for parasite clearance 5,6 . In this regard, the development of less toxic nanoparticles could also be helpful in providing therapeutic benefits 7 .…”

Development of a near infrared novel bioimaging agent via co-oligomerization of Congo red with aniline and o-phenylenediamine: experimental and theoretical studies

“…26 Azo dyes have specic physico-chemical and biological properties which are widely utilized in cellullar staining to visualize cellular components and metabolic processes. [27][28][29][30] With the aim to study the inuence of the multifunctional dye moiety on the structural properties of conventional conjugated polymers, the present work reports the chemical oxidative cooligomerization of Congo red with aniline and o-phenylenediamine. The main aim of this investigation was to prepare a water soluble non-cytotoxic NIR emitting polymer which could be utilized as a bioimaging agent.…”