Importance of BODIPY-based Chemosensors for Cations and Anions in Bio-imaging Applications

Background:

Chemosensor compounds are useful for sensitive selective detection of cations and anions with fluorophore groups in an attempt to develop the effective selectivity of the sensors. Although familiar fluorescent sensors utilizing inter-molecular interactions with the cations and anions, an extraordinary endeavor was executed the preparation of fluorescent-based sensor compounds. 4,4-difluoro-4- bora-3a,4a-diaza-s-indacene (Bodipy) and its derivatives were firstly used as an agent in the imaging of biomolecules due to their interesting structures, complexation, and fluorogenic properties. Among the fluorescent chemosensors used for cations and anions, Bodipy-based probes stand out owing to the excellent properties such as sharp emission profile, high stability, etc. In this review, we emphasize the Bodipy-based chemosensor compounds, which have been used to image cations and anions in living cells, because of as well as the biocompatibility and spectroscopic properties.

Methods:

Research and online content related to chemosensor online activity is reviewed. The advances, sensing mechanisms and design strategies of the fluorophore exploiting selective detection of some cation and anions with Bodipy-based chemosensors are explained. It could be claimed that the using of Bodipy-based chemosensors is very important for cations and anions in bio-imaging applications.

Results:

Molecular sensors or chemosensors are molecules that show a change can be detected when affected by the analyte. They are capable of producing a measurable signal when they are selective for a particular molecule. Molecular and ion recognition that it is important in biological systems such as enzymes, genes, environment, and chemical fields. Due to the toxic properties of many heavy metal ions, it is of great importance to identify these metals due to their harmful effects on living metabolism and the pollution they create in the environment. This process can be performed with analytical methods based on atomic absorption and emission. The fluorescence methods among chemosensor systems have many advantages such as sensitivity, selectivity, low price, simplicity of using the instrument and direct determination in solutions. The fluorescence studies can be applied at nanomolar concentrations.

Conclusion:

During a few decades, a lot of Bodipy-based chemosensors for the detection of cations & anions have been investigated in bio-imaging applications. For the Bodipy-based fluorescent chemosensors, the Bodipy derivatives were prepared by different ligand groups for the illumination of the photophysical and photochemical properties. The synthesized Bodipy-based chemosensors have remarkable photophysical properties, such as a high quantum yield, strong molar absorption coefficient etc. Moreover, these chemosensors were successfully implemented on living organisms for the detection of analytes.

An efficient down conversion luminescencent probe based on a NaGdF4:Eu3+/Ce3+ nanophosphor for chemical sensing of heavy metal ions (Cd2+, Pb2+ and Cr3+) in waste water

Eu³⁺ doped and Eu³⁺/Ce³⁺ co-doped NaGdF₄ nanophosphors are fabricated via a facile hydrothermal route. The codoped counterpart is demonstrated for efficient photoluminescence sensing of heavy metal ions (Cd²⁺, Pb²⁺ and Cr³⁺) present in industrial effluents.

A novel fluorescent-colorimetric probe for Al3+ and Zn2+ ion detection with different response and applications in F- detection and cell imaging

A novel Schiff base fluorescence probe (HL) was synthesized by the condensation of salicylaldehyde and an 8-aminoquinoline derivative. This probe acts as a "turn-on" dual selectivity fluorescence probe for Zn²⁺ and Al³⁺ ions, providing different colors and detection limits (DL) of 11.5 and 23.5 nM, respectively. Moreover, when Zn²⁺ and Al³⁺ co-exist, HL exhibits a preference for Al³⁺ by displacing Zn²⁺ from the HL-Zn²⁺ complex, realizing a dual-channel signal output for Al³⁺. The HL-Al³⁺ system could further discern F^- by a "turn-off" fluorescence response with a DL of 86.0 nM. Furthermore, the probe HL was capable of monitoring intracellular Al³⁺, Zn²⁺ and F^- in living PC12 cells in vitro through fluorescence imaging, which proved its value in potential in vivo applications.

A selective emissive chromogenic and fluorogenic seleno-coumarin probe for Cu2+ detection in aprotic media

A new selenium containing coumarin (compound 7) was designed and synthesized from the amide linkage between coumarin-519 (6) and 2-(butylselanyl)ethanamine (5). The molecular structure of 7 was accurately characterized, and its photophysical properties in acetonitrile, ethanol and chloroform solutions were studied by absorption, stationary and time-resolved fluorescence spectroscopies. Changes in the solvent polarity affected the Stokes shift, quantum yields and lifetime of the excited states. The spectroscopic behavior of compound 7 was evaluated in the presence of different monovalent, divalent and trivalent metallic cations (Na⁺, K⁺, Ca²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, Hg²⁺, Hg⁺, Ag⁺, Al³⁺, Fe³⁺, Ga³⁺ and Cr³⁺) in acetonitrile solution. Among the tested cations, 7 exhibited high selective interaction with Cu²⁺, which was evidenced by the not expected absorption hypsocromic shift (usually coumarin-519 gives red-shifted complexes) and intense chelation-enhanced fluorescence quenching (CHEQ). We performed spectrophotometric and spectrofluorimetric titrations of 7 upon addition of Cu²⁺. From these data, the minimal detectable and quantifiable amounts were calculated and found to be 0.2 and 0.4 μmol L^-1 by absorption and 0.6 and 1.0 μmol L^-1 by emission, respectively. The 7-Cu²⁺ compound presented the 1 : 1 stoichiometry and the stability constant values of absorption and emission were found to be log β = 5.78 and log β = 6.32 respectively. Taking into account the high selectivity of the 7-Cu²⁺ compound in organic solvent systems, and considering the role of copper in organic transformations, it can be regarded as a promising fluorescent sensor for studies concerning the determination of oxidation-dependent transient entities in organic reactions like those involving cuprates. Additionally, it can be used for the detection and quantification of this metal cation in vitro in aprotic biological systems.