Broad Applications of Thiazole Orange in Fluorescent Sensing of Biomolecules and Ions

Abstract

Fluorescent sensing of biomolecules has served as a revolutionary tool for studying and better understanding various biological systems. Therefore, it has become increasingly important to identify fluorescent building blocks that can be easily converted into sensing probes, which can detect specific targets with increasing sensitivity and accuracy. Over the past 30 years, thiazole orange (TO) has garnered great attention due to its low fluorescence background signal and remarkable ‘turn-on’ fluorescence response, being controlled only by its intramolecular torsional movement. These features have led to the development of numerous molecular probes that apply TO in order to sense a variety of biomolecules and metal ions. Here, we highlight the tremendous progress made in the field of TO-based sensors and demonstrate the different strategies that have enabled TO to evolve into a versatile dye for monitoring a collection of biomolecules.

Fluorogenic U-rich internal loop (FLURIL) tagging with bPNA enables intracellular RNA and DNA tracking

“…9 An RNA hairpin construct with a fully base-paired duplex stem (RNAII) does not improve the brightness of the TO-bPNA derivatives (Figure 3C) while binding to URIL-containing RNAs enhanced thiazole orange emission by up to ~600X, with the greatest increase observed between the tripeptide bPNAs and 12-U 4 -12 (Figure 3D). While this degree of fluorescence turn-on upon RNA binding is expected for non-specific intercalation of thiazole orange dyes at higher concentrations, 63 the null response with the control RNA that lacks a URIL (RNAII) testifies to the essential role of bPNA triplex hybridization in guiding TO binding. All bPNAs gave a strong fluorogenic response to URIL RNAs, but there appeared to be a significant difference in efficacy between the α-linked tripeptides and the isodipeptide bPNA.…”

Targeting of Telomeric Repeat-Containing RNA G-Quadruplexes: From Screening to Biophysical and Biological Characterization of a New Hit Compound

“…To gain insight into the binding affinity of BPBA for the different RNA/DNA G4s, fluorescent intercalator displacement (FID) experiments were carried out. This assay is based on the competitive displacement of a light-up fluorescent probe, in this case, thiazole orange (TO), from the DNA upon addition of increasing amounts of a candidate ligand [ 73 , 74 , 75 ]. TO is almost nonfluorescent when free in solution, while it is strongly fluorescent when bound to DNA [ 75 ].…”

“…This assay is based on the competitive displacement of a light-up fluorescent probe, in this case, thiazole orange (TO), from the DNA upon addition of increasing amounts of a candidate ligand [ 73 , 74 , 75 ]. TO is almost nonfluorescent when free in solution, while it is strongly fluorescent when bound to DNA [ 75 ]. Ligand-induced TO displacement decreases fluorescence, thus allowing for the determination of their relative binding affinity for the structure under examination.…”

1-(Hex-5-en-1-yl)-4-{[3-methyl-2,3-dihydro-1,3-benzothiazol-2-ylidene]methyl}quinolin-1-ium iodide monohydrate

“…Intercalating dyes are a standard means to detect duplex DNA or RNA in vitro and in vivo. The cyanine dye thiazole orange has been used extensively as a on/off fluorescent probe in a host of biological applications (Suss et al, 2021). The bis-intercalating dye based on thiazole orange has been shown to have an increased affinity towards duplexed oligomers and retains its fluorogenic characteristic (Rye et al, 1992).…”