Metal cations and anions are essential for versatile physiological processes. Dysregulation of specific ion levels in living organisms is known to have an adverse effect on normal biological events. Owing to the pathophysiological significance of ions, sensitive and selective methods to detect these species in biological systems are in high demand. Because they can be used in methods for precise and quantitative analysis of ions, organic dye-based ratiometric fluorescent probes have been extensively explored in recent years. In this review, recent advances (2015-2019) made in the development and biological applications of synthetic ratiometric fluorescent probes are described. Particular emphasis is given to organic dye-based ratiometric fluorescent probes that are designed to detect biologically important and relevant ions in cells and living organisms. Also, the fundamental principles associated with the design of ratiometric fluorescent probes and perspectives about how to expand their biological applications are discussed.

Synthetic ratiometric fluorescent probes for detection of ions

Congratulations to Dr. Baselt for the publication of his 10th edition and the expansion of his classic toxicology text to cover over 1,500 medications and chemicals. This enduring work provides a c...

Disposition of Toxic Drugs and Chemicals in Man

Following a brief introduction to the principle of fluorescent PET (photoinduced electron transfer) sensors and switches, the outputs of laboratories in various countries from the past year or two are categorized and critically discussed. Emphasis is placed on the molecular design and the experimental outcomes in terms of target-induced fluorescence enhancements and input/output wavelengths. The handling of single targets takes up a major fraction of the review, but the extension to multiple targets is also illustrated. Conceptually new channels of investigation are opened up by the latter approach, e.g.'lab-on-a-molecule' systems and molecular keypad locks. The growing trends of theoretically-fortified design and intracellular application are pointed out.

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Current developments in fluorescent PET (photoinduced electron transfer) sensors and switches.

Transition metals (d-blocks) are recognized as playing critical roles in biology, and they most often act as cofactors in diverse enzymes; however, improper regulation of transition metal stores is also connected to serious disorders. Therefore, the monitoring and imaging of transition metals are significant for biological research as well as clinical diagnosis. In this article, efforts have been made to review the chemical sensors that have been developed for the detection of the first-row d-block metals (except Cu and Zn): Cr, Mn, Fe, Co, and Ni. We focus on the development of fluorescent sensors (fall into three classes: “turn-off”, “turn-on”, and ratiometric), colorimetric sensors, and responsive MRI contrast agents for these transition metals (242 references). Future work will be likely to fill in the blanks: (1) sensors for Sc, Ti, and V; (2) MRI sensors for Cr, Mn, Co, Ni; (3) ratiometric fluorescent sensors for Cr6+, Mn2+, and Ni2+, explore new ways of sensing Fe3+ or Cr3+ without the proton interference, as well as extend applications of MRI sensors to living systems.

Fluorescent, MRI, and colorimetric chemical sensors for the first-row d-block metal ions

Colorimetric metal ion sensors – A comprehensive review of the years 2011–2016

A simple and low cost chemosensor is described. This sensor could simultaneously detect three biologically important metal ions through fluorogenic (Zn2+) and chromogenic (Fe2+, Cu2+, and Zn2+) methods in aqueous solution. The sensor could function as a “turn-on” fluorescence receptor only to Zn2+ ions. In addition, the sensor could be successfully applied to the detection of intracellular Zn2+. Meanwhile, the sensor displayed an obvious red color upon selective binding with Fe2+. Therefore, the sensor could serve as a useful tool for the discrimination of Fe2+ from Fe3+ in aqueous media. Moreover, the sensor also showed color changes from yellow to colorless upon selective binding with Zn2+ and Cu2+, respectively. The detection limit of the sensor for Cu2+ (1.5 μM) is far below the guidelines of the World Health Organization (30 μM) as the maximum allowable copper concentration in drinking water, and therefore it is capable of being a practical system for the monitoring of Cu2+ concentrations in aqueous samples. These results provide a new approach for selectively recognizing the most important three trace elements in the human body simultaneously, for Zn2+ by emission spectra and Fe2+, Cu2+, and Zn2+ by the naked eye.

A cap-type Schiff base acting as a fluorescence sensor for zinc(II) and a colorimetric sensor for iron(II), copper(II), and zinc(II) in aqueous media

A colorimetric and fluorescent sensor for sequential detection of copper ion and cyanide

A new metal ion sensor that contains quinoline and pyridylaminophenol has been synthesized In acetonitrile and in the presence of Zn2+, the sensor fluoresces In contrast, in aqueous solutions the sensor fluoresces in the presence of Cd2+ The fluorescence of the molecule is selective for Zn2+ or Cd2+ and shows no fluorescence with other metal ions The crystal structure of the Cd2+ complex shows coordination through the amide and phenol oxygens, as well as the amine nitrogen of the sensor The sensor also acts as a colorimetric sensor for Co2+ by changing color from colorless to yellow The color change is selective for Co2+ and is not observed with other metal ions The unique combination of pyridine and phenol groups with quinoline results in the properties of this sensor

A single molecule that acts as a fluorescence sensor for zinc and cadmium and a colorimetric sensor for cobalt.

Fluorescent dye containing phenol-pyridyl for selective detection of aluminum ions

A structurally simple 2-((1-hydroxynaphthalene-2-yl)methyleneamino)acetic acid ( 1 ) was used as a turn-on fluorescent sensor for both Zn 2+ and F − . This receptor 1 showed a significant fluorescence enhancement in the presence of zinc ion over most other competitive metal ions in 100% aqueous solution. In particular, this chemosensor could clearly distinguish Zn 2+ from Cd 2+ . The spectroscopic studies suggested that the selective response to zinc ion involved the disruption of the internal charge transfer (ICT), and the inhibition of the C N isomerization and the excited-state proton transfer (ESIPT). In vitro studies with fibroblasts showed fluorescence when sensor 1 and Zn 2+ were present. The receptor 1 could also sense F − selectively in DMSO. The fluorescence, UV–vis titration and 1 H NMR titration indicated that F − ion enhanced the fluorescence of 1 through deprotonation.

Eun Joo Song

Papers

A cap-type Schiff base acting as a fluorescence sensor for zinc(II) and a colorimetric sensor for iron(II), copper(II), and zinc(II) in aqueous media

A colorimetric and fluorescent sensor for sequential detection of copper ion and cyanide

A single molecule that acts as a fluorescence sensor for zinc and cadmium and a colorimetric sensor for cobalt.

Fluorescent dye containing phenol-pyridyl for selective detection of aluminum ions

A single fluorescent chemosensor for multiple target ions: Recognition of Zn2+ in 100% aqueous solution and F− in organic solvent