Label-free G-Quadruplex aptamer and Thioflavin-T based turn-off fluorescent detection of ethanolamine

The benzothiazolium salt, Thioflavin T (ThT), has been widely adopted as the "gold-standard" fluorescent reporter of amyloid in vitro. Its properties as a molecular rotor result in a large-scale (∼1000-fold) fluorescence turn-on upon binding to β-sheets in amyloidogenic proteins. However, the complex photophysics of ThT combined with the intricate and varied nature of the amyloid binding motif means these interactions are poorly understood. To study this important class of fluorophores, we present a detailed photophysical characterization and comparison of a novel library of 12 ThT-inspired fluorescent probes for amyloid protein (PAPs), where both the charge and donor capacity of the heterocyclic and aminobenzene components have been interrogated, respectively. This enables direct photophysical juxtaposition of two structural groups: the neutral "PAP" (class 1) and the charged "mPAP" fluorophores (class 2). We quantify binding and optical properties at both the bulk and single-aggregate levels with some derivatives showing higher aggregate affinity and brightness than ThT. Finally, we demonstrate their abilities to perform super-resolution imaging of α-synuclein fibrils with localization precisions of ∼16 nm. The properties of the derivatives provide new insights into the relationship between chemical structure and function of benzothiazole probes.

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A Comparative Photophysical Study of Structural Modifications of Thioflavin T-Inspired Fluorophores

A study on computerized selection of fluorescent dyes for environmentally friendly textile applications

It was found that the spectral and fluorescent properties of BTA-1C cation in protic and aprotic solvents differ. It was shown that for solutions in long-chain alcohols viscosity is the main factor that determines the dynamics of intramolecular charge transfer in the excited state of the BTA-1C molecule. In the case of aprotic solvents a correlation was found between the rate constant of twisted intramolecular charge transfer (TICT) during rotation of fragments of the molecule in relation to each other in the excited state and the solvent relaxation rate: kTICT ~ 1/τ
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Effect of Viscosity and Polar Properties of Solvent on Dynamics of Photoinduced Charge Transfer in BTA-1 Cation — Derivative of Thioflavin T

New fluorescent molecular rotors (FMRs) were developed by modification of the Thioflavin T (ThT) structure via introduction of methyl and methoxy groups. Effects of the substituents on fluorescence...

Effect of Substituents on TICT Rate in Thioflavin T-Based Fluorescent Molecular Rotors

Fluorescent molecular rotors (FMR) have wide range of applications due to high sensitivity of their emission intensity to microenvironment viscosity. Thioflavin T (ThT), which exhibits FMR properties, is widely used as fluorescent probe for in vitro detection of amyloid fibrils (AF) due to its high affinity and “light-up” feature (fluorescence quantum yield of ThT changes by ∼3 orders of magnitude upon binding to AF). At physiological pH, ThT is positively charged and, therefore, it does not cross blood-brain barrier (BBB). It has been proposed that neutral derivatives of ThT are more likely to cross BBB, which should make them suitable for in vivo applications. However, for in vivo applications as fluorescent imaging agents, the neutral ThT derivatives must retain the FMR properties of ThT. In this paper, we examined whether neutral ThT derivatives exhibit FMR properties by studying the effect of solvent viscosity on their fluorescence intensity and decay lifetime. We observed that while the cationic ThT derivatives possess FMR properties, the neutral forms behave as regular highly-emitting fluorophores. Further, quantum chemical calculations in gas phase showed significant differences in the shape of excited state potential energy surfaces for the neutral and cationic derivatives of ThT. While, for charged ThT derivatives, the E(S1*) energy is minimal for the twisted conformation with dihedral angle φ = 90° between molecular fragments, the coplanar conformation with φ = 0° (or 180°) is more favorable for the neutral derivatives. From our experimental and theoretical studies we conclude that the neutral ThT derivatives lack FMR properties as their photoexcitation does not induce twisting motion coupled with internal charge transfer and, therefore, their specificity as fluorescent imaging agents for AF detection is lower than that of parent ThT.

Elena V. Kalganova

Papers

Neutral derivatives of Thioflavin T do not exhibit viscosity-dependent fluorescence