Self-quenching Mechanism: the Influence of Quencher and Spacer on Quencher-fluorescein Probes

Abstract

Fluorescent chemosensors provide an extremely sensitive optical method for the real-time monitoring of molecular recognition events. An understanding of the fluorescent on/ off mechanism is essential for the rational design of fluorescent chemosensors. The majority of fluorescent chemosensors working in aqueous media operate by one of three mechanisms: (1) the suppression of photoinduced electron transfer (PET); (2) alteration of the microenvironment of a solvatochromic fluorophore; and (3) modulation of the fluorescence resonance energy transfer (FRET) between two fluorophores.1 The first two mechanisms are suitable for small molecule sensing (e.g., cations, small organic compounds, etc.), but FRET is very useful in the biopolymer state, for its distance information can be obtained in the 10 to 100 Å region.2 In spite of the excellent applications of FRET for biomolecule sensing (c-AMP, insulin, etc.), the operations depend on a complicated biological pathway. 3Peptides with an FRET pair have been used as monitoring probes for a given enzyme activity. However, in various fluorophore pairs that have been examined, FRET peptide probes did not operate properly i.e., they were self-quenched. 4 This self-quenching can be explained in terms of an intramolecular ground-state dimer complex between the FRET fluorophore pair in an aqueous solution. 5 The strength of the aggregation between the two dye molecules depends on the molecular structure, solvent, temperature, and the presence or absence of electrolytes. 6Our aim is to systematically study the self-quenching mechanism for covalently linked fluorophore pairs. For simplicity, the factors influencing the efficiency of selfquenching are disassembled into four components ( Figure 1). A FRET pair was replaced by a quencher-fluorophore pair as the reporting group. This overcomes the restriction for the FRET donor-acceptor resonance condition.7 From a practical viewpoint, water and fluorescein were chosen as the solvent and fluorophore, respectively; water is a crucial solvent for physiological systems; furthermore, fluorescein has a high fluorescence quantum yield in aqueous solution and its synthetic handling has been well established.As the quencher part, carbazole, methyl red and 1,8-naphthalimide were selected. The effect of the spacer can be controlled by varying the alkyl chain length (-(CH 2 ) n -, n = 5, 11, 15) and a flexible tetraethylene glycol unit (Figure 2). At pH 7.5 (50 mM HEPES buffer, I = 0.1 (NaNO 3 )), the fluorescence emission of C-n (n = 5, 11, 15) and C-TE ([probes] = 1 μM) was measured (Figure 3). 8 It has been reported that there are two opposing factors determining the stability of aggregates of the derivatives containing two Rose Bengal moieties: the longer the chain, the easier it is to

Importance of Spectral Correction in Fluorescence Spectroscopic Studies of Crude Oils and Asphaltenes

“…There are also examples of intramolecular FRET when the donor and acceptor are part of the same molecules but independent in terms of fluorescence. 36 This could for asphaltenes be a naphthalene ring system covalently bonded but not conjugated with a larger ring system as sometimes depicted in the literature. 14 The distance requirement between independent molecules for FRET to efficiently affect spectra is below approximately 10 nm.…”

“…Self-quenching has been reported for many simple systems, where changes are observed in spectra as a function of the solute concentration with no added quencher. 3,10,36,37 Selfquenching may be attributed to the above mechanisms, the interaction of ground state and excited state molecules, or internal FRET, leading to a decrease in intensity with the concentration after all appropriate corrections. 36 In petroleum analysis, "self-quenching" appears either through encounters of like molecules (e.g., asphaltene− asphaltene) or with "other molecules" (e.g., in crude oil, resin−asphaltene).…”

“…3,10,36,37 Selfquenching may be attributed to the above mechanisms, the interaction of ground state and excited state molecules, or internal FRET, leading to a decrease in intensity with the concentration after all appropriate corrections. 36 In petroleum analysis, "self-quenching" appears either through encounters of like molecules (e.g., asphaltene− asphaltene) or with "other molecules" (e.g., in crude oil, resin−asphaltene). There is almost a continuous overlap of individual emission spectra of one type and excitation spectra of other types, leading to perfect conditions of energy transfer not necessarily reflecting aggregation or associative behavior.…”

Amphiphilic “Like-A-Brush” Oligonucleotide Conjugates with Three Dodecyl Chains: Self-Assembly Features of Novel Scaffold Compounds for Nucleic Acids Delivery

“…We attribute this difference to the existence of multiple mechanisms of molecular interactions involved in fluorescence quenching. Fluorescence of fluorescein and its derivatives are extremely sensitive for the quenching, even to the type of the binding linker [48]. An earlier finding of fluorescence quenching of 6-carboxyfluorescein in liposomes was reported decades ago [49].…”

Dual-Emitting EY@Zr-MOF Composite as Self-Calibrating Luminescent Sensor for Selective Detection of Inorganic Ions and Nitroaromatics

“…However, molecular dyes easily pollute the liquid detection system and are difficult to separate from the system. In addition, the aggregation state of dyes will strongly diminish their luminescence via quenching effect. , These characteristics of molecular dyes limited their further utilization in luminescence-related applications. Hence, it is necessary to develop molecular dyes that combine supporting materials to overcome the above challenges.…”