Over the last few years, the development of fluorescent probes has received considerable attention. Fluorescence signaling allows noninvasive and harmless real-time imaging with great spectral resolution in living objects, which is extremely useful for modern biomedical applications. This review presents the basic photophysical principles and strategies for the rational design of fluorescent probes as visualization agents in medical diagnosis and drug delivery systems. Common photophysical phenomena, such as Intramolecular Charge Transfer (ICT), Twisted Intramolecular Charge Transfer (TICT), Photoinduced Electron Transfer (PET), Excited-State Intramolecular Proton Transfer (ESIPT), Fluorescent Resonance Energy Transfer (FRET), and Aggregation-Induced Emission (AIE), are described as platforms for fluorescence sensing and imaging in vivo and in vitro. The presented examples are focused on the visualization of pH, biologically important cations and anions, reactive oxygen species (ROS), viscosity, biomolecules, and enzymes that find application for diagnostic purposes. The general strategies regarding fluorescence probes as molecular logic devices and fluorescence–drug conjugates for theranostic and drug delivery systems are discussed. This work could be of help for researchers working in the field of fluorescence sensing compounds, molecular logic gates, and drug delivery.
A new highly water-soluble 1,8-naphthalimide fluorophore designed on the “fluorophore-spacer-receptor1-receptor2” model has been synthesized. Due to the unusually high solubility in water, the novel compound proved to be a selective PET-based probe for the determination of pHs in aqueous solutions and rapid detection of water content in organic solvents. Based on the pH dependence of the probe and its high water solubility, the INH logic gate was achieved using NaOH and water as chemical inputs, where NaOH is the disabler and the water is an enabler. In addition, the probe showed effective fluorescence “off-on” reversibility on glass support after exposure to acid and base vapors, which defines it as a promising platform for rapid detection of acid/base vapors in the solid-state, thus extending the molecular sensing concept from solution to the solid support.
In this work we focused on the design and synthesis of a fluorescence sensing 4-chloro-1,8-naptalimide derivative operating simultaneously by photoinduced electron transfer (PET) and aggregation induced emission (AIE) mechanisms. Absorption and fluorescence properties of the probe were studied as a function of pH in solution and in solid state as compared to the properties of similar 1,8-naphthalimide derivatives without a substituent at the 1,8-naphthalimide C-4 position. The photoinduced fluorescence enhancement of the probe was FE = 22 after protonation in solution (λ F = 405 nm, pK a = 8.50 � 0.08) and FE = 44 (λ F = 472 nm) in solid state after reversible exposure on HCl and ammonia vapours due to the amalgamation of monomer emission and AIE. In solid state on paper support the PET process in the probe was switched "off" in a pH window 2.5-1.5. Due to the remarkable changes in the fluorescence emission the synthesized compound was successfully applied as a solid-state chemosensing material for rapid detection of acid-base vapours and pH in aqueous solutions. The concept proposed herein could drive the classic AIE and PET molecular sensors towards new directions and practical applications.In the last three decades the development of new materials with chemosensing properties became a major task in scientific community. [1] Particularly chemosensing materials allowing a fluorescent signalling output have received great attention. [2] Their attractiveness is due to the fluorescence-based techniques, which have several advantages, such as rapid response with high sensitivity, cheap and portable equipment suitable for real-time monitoring. [3] Several photophysical phenomena including photoinduced electron transfer (PET), [4] intramolecular charge transfer (ICT), [5] twisted intramolecular charge transfer (TICT), [6] fluorescence resonance energy transfer (FRET) [7] and excited-state intramolecular proton transfer (ESIPT) [8] have been successfully employed in construction of chemosensing materials. Among them, the PET based "fluorophore-spacer-receptor" format developed by de Silva is the most popular approach used in the design of fluorescent chemosensors. In this respect, a number of architectures for detection of different chemical species have been synthesised and PET was well studied in the most popular fluorophores. [9] Nevertheless, the synthesis of new PET based chemical sensors with improved characteristics is still a great challenge. Usually, the traditional organic fluorophores possess provide high quantum yields only in dilute solutions while their fluorescence capability is largely weakened in high concentrations due to the aggregationcaused quenching (ACQ) phenomenon resulting in a nonradiative decay. [10] This significantly restricts their practical applications as chemosensing materials. Thus, extension of the principles of molecular sensors from liquid solution to solid support currently is a major goal which opens up new perspectives for their practical applications. [11] A step in this di...
pH-sensitive polymers can be defined as polyelectrolytes that include in their structure weak acidic or basic groups that either accept or release protons in response to a change in the environmental pH. This work summarizes the design, synthesis, and potential applications of pH-responsive fluorescent copolymers in the biomedical field.This was achieved using atom transfer radical polymerization (ATRP) of tert-butyl acrylate using a CuBr/N,N,N 0 ,N 00 N 00 -pentamethyldiethylenetriamine catalyst system in conjunction with an alkyl bromide as the initiator. Well-defined macroinitiators based on poly(tert-butyl acrylate) with narrow molecular weight distributions were obtained by the addition of an appropriate solvent system in order to create a homogeneous catalytic system. The addition of n-butyl acrylate as a second building block in order to create well-defined poly(tert-butyl acrylate)-b-poly(n-butyl acrylate) block copolymers (PtBA-b-PnBA) followed by chemical modification of the block copolymers and functionalization with an appropriate fluorescent compound are the basis for the preparation of well-defined fluorescent pH-sensitive micelles. Thus, prepared water soluble nanosized pH-sensitive micelles consisting of hydrophobic poly(n-butyl acrylate) core and hydrophilic polyacrylic acid shell decorated with an appropriate fluorescent compound determined their potential applications of these systems in the field of biomedicine as biosensors, controlled drug delivery systems, and so on. In this respect, the cell viability and internalization of the polymer micelles were studied. K E Y W O R D S bioimaging, fluorescent nanosized micelles, personalized theranostic systems, pH-sensitive block copolymers 1 | INTRODUCTION These days, a wide range of compounds being developed are polymers, because of the variety of their chemical and physical properties and the possibility to be tailored towards many applications. In the last two decades, tremendous interest has been shown in polymeric materials that could reversibly or irreversibly change their physical and chemical properties under the influence of external stimuli, eg, pH, temperature, presence of specific ions, light radiation, mechanical forces, magnetic fields, electric fields, and bioactive molecules. 1 Among them, special attention is paid to the well-defined pH block copolymers, which at physiological pH (7.1-7.3) self-assemble into micellar structures and the acidification of the media lead to controlled micelle dissociation and triggered drug release. Several modern techniques can be applied for their synthesis as atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT), and stable free radical polymerization (SFRP). 2 These techniques are based on a reversible activation/deactivation cycle of
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