Label‐Free Fluorescent Probing of G‐Quadruplex Formation and Real‐Time Monitoring of DNA Folding by a Quaternized Tetraphenylethene Salt with Aggregation‐Induced Emission Characteristics

Abstract

Biosensing processes such as molecular beacons require non-trivial effort to covalently label or mark biomolecules. We report here a label-free DNA assay system with a simple dye with aggregation-induced emission (AIE) characteristics as the fluorescent bioprobe. 1,1,2,2-Tetrakis[4-(2-bromoethoxy)phenyl]ethene is nonemissive in solution but becomes highly emissive when aggregated. This AIE effect is caused by restriction of intramolecular rotation, as verified by a large increase in the emission intensity by increasing viscosity and decreasing temperature of the aqueous buffer solution of 1,1,2,2-tetrakis[4-(2-triethylammonioethoxy)phenyl]ethene tetrabromide (TTAPE). When TTAPE is bound to a guanine-rich DNA strand (G1) via electrostatic attraction, its intramolecular rotation is restricted and its emission is turned on. When a competitive cation is added to the G1 solution, TTAPE is detached and its emission is turned off. TTAPE works as a sensitive poststaining agent for poly(acrylamide) gel electrophoresis (PAGE) visualization of G1. The dye is highly affinitive to a secondary structure of G1 called the G-quadruplex. The bathochromic shift involved in the G1 folding process allows spectral discrimination of the G-quadruplex from other DNA structures. The strong affinity of TTAPE dye to the G-quadruplex structure is associated with a geometric fit aided by the electrostatic attraction. The distinct AIE feature of TTAPE enables real-time monitoring of folding process of G1 in the absence of any pre-attached fluorogenic labels on the DNA strand. TTAPE can be used as a K+ ion biosensor because of its specificity to K+-induced and -stabilized quadruplex structure.

Synthesis of an AIE-active fluorogen and its application in cell imaging

“…When dispersed in aqueous media, the molecules form highly emissive nanoaggregates, thanks to their AIE attributes. These intriguing properties of the AIE fluorogens have prompted us to explore the possibility of utilizing them as fluorescence biosensors [16,17] . It is envisioned that the AIE nanoparticles can be as emissive as, but much less cytotoxic than, their inorganic QD counterparts.…”

New Chemo-/Biosensors with Silole and Tetraphenylethene Molecules Based on the Aggregation and Deaggregation Mechanism

“…They attributed this to the electrostatic binding of negatively charged DNA with 12 with a positively charged moiety, and as a result molecules of 12 were docked on the surface of DNA and aggregation of TPE fluorophores occurred. They further reported compound 13 with four positively charged moieties, which was able to discriminate the folded DNA G-quadruplex from its random-coil structure [18]. This is based on the observation that the fluorescence of 13 is weaker after mixing with the G-quadruplex than that in the presence of the respective ssDNA; moreover, the fluorescence spectrum of 13 is more red shifted after the addition of the G-quadruplex.…”

Synthesis and Functionality of Substituted Polyacetylenes

“…Retrostructural analysis of another AIE-active 1,1,2,2-tetraphenylethene (TPE) developed by us reveals that there is one common structural feature between TPE, and disubstituted poly(1-phenyl-1-octyne) 66 and poly(diphenylacetylene) 67: one or more aromatic peripheries are connected to an olefinic core [49][50][51][52][53]. In a dilute solution of TPE, intramolecular rotations of the aromatic rings against the olefinic core effectively and nonradiatively deactivate the excited states, thus making the molecules nonemissive (''off'').…”