The dynamic chemical diversity of elements, ions and molecules that form the basis of life offers both a challenge and an opportunity for study. Small-molecule fluorescent probes can make use of selective, bioorthogonal chemistries to report on specific analytes in cells and in more complex biological specimens. These probes offer powerful reagents to interrogate the physiology and pathology of reactive chemical species in their native environments with minimal perturbation to living systems. This Review presents a survey of tools and tactics for using such probes to detect biologically important chemical analytes. We highlight design criteria for effective chemical tools for use in biological applications as well as gaps for future exploration.

Reaction-based small-molecule fluorescent probes for chemoselective bioimaging

This critical review focuses on the development of anion sensors, being either fluorescent and/or colorimetric, based on the use of the 1,8-naphthalimide structure; a highly versatile building unit that absorbs and emits at long wavelengths. The review commences with a short description of the most commonly used design principles employed in chemosensors, followed by a discussion on the photophysical properties of the 4-amino-1,8-naphthalimide structure which has been most commonly employed in both cation and anion sensing to date. This is followed by a review of the current state of the art in naphthalimide-based anion sensing, where systems using ureas, thioureas and amides as hydrogen-bonding receptors, as well as charged receptors have been used for anion sensing in both organic and aqueous solutions, or within various polymeric networks, such as hydrogels. The review concludes with some current and future perspectives including the use of the naphthalimides for sensing small biomolecules, such as amino acids, as well as probes for incorporation and binding to proteins; and for the recognition/sensing of polyanions such as DNA, and their potential use as novel therapeutic and diagnostic agents (95 references).

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Colorimetric and fluorescent anion sensors: an overview of recent developments in the use of 1,8-naphthalimide-based chemosensors

Luminescent sensors and switches in the early 21st century

A long-term goal of cancer diagnosis is to develop tumor-imaging techniques that have sufficient specificity and sensitivity. To achieve this goal, minimizing the background signal originating from nontarget tissues is crucial. Here we achieve highly specific in vivo cancer visualization by using a newly designed targeted 'activatable' fluorescent imaging probe. This agent is activated after cellular internalization by sensing the pH change in the lysosome. Novel acidic pH-activatable probes based on the boron-dipyrromethene fluorophore were synthesized and then conjugated to a cancer-targeting monoclonal antibody. As proof of concept, ex vivo and in vivo imaging of human epidermal growth factor receptor type 2-positive lung cancer cells in mice was performed. The probe was highly specific for tumors with minimal background signal. Furthermore, because the acidic pH in lysosomes is maintained by the energy-consuming proton pump, only viable cancer cells were successfully visualized. The design concept can be widely adapted to cancer-specific, cell surface-targeting molecules that result in cellular internalization.

Selective molecular imaging of viable cancer cells with pH-activatable fluorescence probes.

The metalloneurochemistry of Zn(II) is of substantial current interest. Zinc is the second most abundant d-block metal ion in the human brain, and its distribution varies with relatively high concentrations found in the hippocampus. Brain zinc is generally divided into two types, protein-bound and loosely bound, the latter also being termed histochemically observable, chelatable, labile, or mobile zinc. The neurophysiological and neuropathological significance of mobile Zn(II) remains enigmatic. Studies of Zn(II) distribution, translocation, and function in vivo require tools for its detection. Because Zn(II) has a closed-shell d10 configuration and no convenient spectroscopic signature, fluorescence is a well-suited method for monitoring Zn(II) in biological contexts. This Account summarizes work by our laboratory addressing the design, preparation, characterization, and use of small-molecule fluorescent sensors for imaging Zn(II) in living cells and samples of brain tissue. These sensors provide “turn-o...

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Small-molecule fluorescent sensors for investigating zinc metalloneurochemistry.

Signaling Recognition Events with Fluorescent Sensors and Switches

Molecular Photoionic Switches with an Internal Reference Channel for Fluorescent pH Sensing Applications.

Luminescence and Charge Transfer. Part 3. The Use of Chromophores with ICT (Internal Charge Transfer) Excited States in the Construction of Fluorescent PET (Photoinduced Electron Transfer) pH Sensors and Related Absorption pH Sensors with Aminoalkyl Side Chains.

H. Q. N. Gunaratne

Papers

Signaling Recognition Events with Fluorescent Sensors and Switches

Molecular Photoionic Switches with an Internal Reference Channel for Fluorescent pH Sensing Applications.

Luminescence and Charge Transfer. Part 3. The Use of Chromophores with ICT (Internal Charge Transfer) Excited States in the Construction of Fluorescent PET (Photoinduced Electron Transfer) pH Sensors and Related Absorption pH Sensors with Aminoalkyl Side Chains.

Oxidations Catalyzed by Rhenium(V) Oxo Species. Part 1. Conversion of Furans to Enediones Using Methyltrioxorhenium and Urea Hydrogen Peroxide.

Fluorescent PET (Photoinduced Electron Transfer) Sensors