Molecules that experience a change in their fluorescence emission due to the effect of fluorescence enhancement upon binding events, like chemical reactions or a change in their immediate environment, are regarded as fluorescent probes, because of their high selectivity and advantages in the fields of chemical, biological, and medical chemistry. Fluorescent probes have become a predominant aid for the detection of target materials like metal cations, anions, and neutral molecules in the bio-imaging field and also have great importance in the detection of reactive oxygen species (ROS) and reactive carbonyl species (RCS) in living cells, air, soil, and food. Pyrene and its derivatives are important polycyclic aromatic hydrocarbons that act as fluorophores and are widely used as a fluorescent probe on account of their strong emission of fluorescence in live cells, very low cytotoxicity, high fluorescence quantum yield, easy modification, and outstanding cell permeability. In this review, the methods of design and synthesis of versatile pyrene fluorophores for the selective and sensitive quantification of their activity will inspire further reaction development in this interesting area.

Pyrene based materials as fluorescent probes in chemical and biological fields

Peptide-based colorimetric and fluorescent dual-functional probe for sequential detection of copper(Ⅱ) and cyanide ions and its application in real water samples, test strips and living cells.

A highly selective and sensitive fluorescent ratiometric probe (1) based on pyrene-containing Schiff base for the dection of Cu2+ was synthesized. In acetonitrile–HEPES buffer solution (20.0 mM HEPES, 8:2, v/v, pH 7.4), only Cu2+, out of tested common cations, could induce the aggregation of probe 1. Fluorescence analysis showed that the excimer emission band of pyrene groups of probe 1 appeared and gradually increased with the addition of Cu2+. The fluorescent intensity ratio of excimer and monomer (I470/I409) of probe 1 increased 27.8-fold upon the addition of one equiv. of Cu2+ with a detection limit of 20.2 nM (1.28 ppb). The addition of Cu2+ also induced obvious color change and the characteristic peaks of pyrene excimer in UV–vis spectrometra of the relutant solution. Results from the Job plot, metal-binding fluorescent titration, mass spectra experiments and density functional theory calculations indicated a binding ratio of 2:1 (probe 1: Cu2+). In addition, probe 1 showed good potential as a fluorescent visualizing probe for the detection of Cu2+ in living GS cells of epinepheluscoioides.

A pyrene-containing Schiff base fluorescent ratiometric probe for the detection of Cu2+ in aqueous solutions and in cells

An efficient donor triphenylamine aldehyde Schiff-base with p-toluene sulfonyl hydrazine fluorescent probe (TPA-PTH) was synthesized and characterized by various spectroscopic techniques. The probe TPA-PTH displayed drastic color changes with Cu2+ ions over metal ions in aqueous environment with a fluorescence-off mechanism.The detection limit of Cu2+ was found to be 1.25 × 10-8 M by using the equation LOD = K × SD/S. The 2:1 binding stoichiometric mode of TPA-PTH with Cu2+ ion was further tested by HR mass and Job’s plot analyses. Furthermore, the proposed probe has been effectively applied to determine the trace amount of Cu2+ ions in different water samples with 96%∼98% recoveries. The sensing mechanism of TPA-PTH was further investigated by Density Functional Theory (DFT) calculations using a Gaussian 16 program. DFT calculations were theoretically supported the experimental findings. 

A simple triphenylamine based turn-off fluorescent sensor for copper (II) ion detection in semi-aqueous solutions

In recent years, heavy metal pollution has become increasingly serious. Heavy metals exist in an environment mainly in the form of ions (heavy metal ions, HMs). They can contaminate food, water, soil, and the atmosphere, leading to serious harm to plants and animals. With high bioavailability and nonbiodegradability, HMs can accumulate through biomagnification. Consequently, heavy metal pollution has become the cause of many fatal diseases threatening human health and ecological environment. Therefore, the accurate detection of HMs is vital and necessary. In this paper, the harm and limit standards of heavy metals were systematically summarized and the common analysis methods were overviewed and compared. Specifically, the latest research progress of ratiometric photoelectric sensor, including optical and electrical sensor, were mainly described. The research status and advantages and disadvantages of a photoelectric sensor were summarized. Furthermore, the future directions were proposed, which provided the reference for the further research and application of the ratiometric photoelectric sensor.

Ruihong Feng

Papers

A pyrene-containing Schiff base fluorescent ratiometric probe for the detection of Cu2+ in aqueous solutions and in cells

A sensitive pH fluorescent probe based on triethylenetetramine bearing double dansyl groups in aqueous solutions and its application in cells

An intermolecular pyrene excimer-based ratiometric fluorescent probes for extremely acidic pH and its applications