Rational design of a FRET-based ratiometric fluorescent chemosensor for detecting ClO− with large Stokes based on rhodamine and naphthalimide fluorophores

Ratiometric fluorescent probe with AIE characteristics for hypochlorite detection and biological imaging

It is very important and highly valuable to detect ClO- in samples and living cells with accuracy and speed. In this work, a novel fluorescent probe NA was prepared from 4-bromo-1,8-naphthalic anhydride by acylation reaction and Suzuki coupling reaction and used for the detection of ClO-. Thiomethyl serves as the recognition group for probe NA, while naphthalimide serves as fluorescent chromophore. The probe exhibited an extremely pronounced blue shift from yellow to blue fluorescence within 1 min after the addition of hypochlorite (ClO-). The probe demonstrates high sensitivity to ClO- with a limit of detection (LOD) of 1.22 µM. Also, probe NA demonstrates excellent selectivity and immunity to interference. Additionally, simple fluorescent test strips containing probe NA were prepared in this study, enabling rapid detection of ClO- in water samples. And NA had been effectively used to image endogenous and exogenous ClO-fluorescence in living cells. The results suggest that probe NA has significant potential for portable detection and biological applications.

Progress and limitations in reactive oxygen species quantitation

Reactive oxygen species (ROS) are a set of oxygen- and nitrogen-containing radicals. They are produced from a wide range of sources. In biological contexts, cellular stress leads to an overproduction of ROS, which can lead to genetic damage and disease development. In industry, ROS are often productively used for water purification or for analyzing the possible toxicity of an industrial process. Because of their ubiquity, detection of ROS has been an analytical goal across a range of fields. To understand complicated systems and origins of ROS production, it is necessary to move from qualitative detection to quantitation. Analytical techniques that combine quantitation, high spatial and temporal resolution, and good specificity represent detection methods that can fill critical gaps in ROS research. Herein, we discuss the continued progress and limitations of fluorescence, electrochemical, and electron paramagnetic resonance detection of ROS over the last ten years, giving suggestions for the future of the field.

A Review on Recent Development of Phenothiazine-Based Chromogenic and Fluorogenic Sensors for the Detection of Cations, Anions, and Neutral Analytes

This review provides an in-depth examination of recent progress in the development of chemosensors, with a particular emphasis on colorimetric and fluorescent probes. It systematically explores various sensing mechanisms, including metal-to-ligand charge transfer (MLCT), ligand-to-metal charge transfer (LMCT), photoinduced electron transfer (PET), intramolecular charge transfer (ICT), and fluorescence resonance energy transfer (FRET), and elucidates the mechanism of action for cation and anion chemosensors. Special attention is given to phenothiazine-based fluorescence probes, highlighting their exceptional sensitivity and rapid detection abilities for a broad spectrum of analytes, including cations, anions, and small molecules. Phenothiazine chemosensors have emerged as versatile tools widely employed in a multitude of applications, spanning environmental and biomedical fields. Furthermore, it addresses existing challenges and offers insights into future research directions, aiming to facilitate the continued advancement of phenothiazine-based fluorescent probes.

A "Turn-on" Fluorescent Probe Based on Phenothiazine for Selectively Recognizing ClO- and its Practical Applications

Hypochlorous acid (HClO), a highly reactive oxygen species, has important effects on human health. High selectivity and sensitivity remain challenges of fluorescent probes for detection of ClO- with a large Stokes shift. This work designed and synthesized a novel phenothiazine-based fluorescent probe TF which can detect ClO- by colorimetric and fluorescent dual signals. TF displayed turn-on fluorescence effect toward ClO- with high selectivity (≥ 28-folds) and sensitivity (LOD = 0.472 μM), fast response time (< 1 min) and large Stokes shift (150 nm) in PBS (pH = 7.4, 40% DMSO). Meanwhile, TF can visualize ClO- on the mung bean sprouts model and apply as testing strips for portable and rapid detecting ClO- by the naked eyes. A phenothiazine-based fluorescent probe with large Stokes shift was synthesized and its responding rapidly ability to detect ClO- was studied.

A photo-controlled fluorescent switching based on carbon dots and photochromic diarylethene for bioimaging

Carbon dots (CDs) as luminescent zero-dimensional carbon nanomaterials have good aqueous dissolution, photostability, high quantum yield, and tunability of emission color. It has great application potential in many fields, including bioimaging, labeling of biological species, drug delivery, and sensing in biomedical. However, controlling the fluorescence emission of carbon dots remains a formidable challenge. Herein, we designed and exploited a photo-controlled fluorescent switching based on photochromic diarylethene (DT) and CDs for bioimaging. It could be modulated reversibly between "ON" and "OFF" under UV/vis light exposure. The fluorescent modulation efficiency was as high as 95.3%. The fluorescent switching could be used to the bioimaging in HeLa cells with low cell toxicity. Therefore, this fluorescent switching could be a promising candidate in many potential application areas, especially in bioimaging.

A novel lipid droplets/lysosomes-targeting colorimetric and ratiometric fluorescent probe for Cu2+ and its application

A novel multifunctional fluorescent probe LL2 was prepared via a one-step condensation reaction between 3-formyl-N-butylcarbazole and 2-Hydroxy-1-naphthylhydrazone. LL2 can work as a colorimetric probe for Cu²⁺, and can also selectively recognize Cu²⁺ via ratiometric fluorescence signal. After the addition of Cu²⁺, the probe LL2 responded rapidly within 5 s and reached stability within 30 s. In natural light, when Cu²⁺ were added to the solution, the color of probe LL2 changed from yellowish to colorless, while there was a discernible fluorescence changed from green to blue under a 365 nm UV lamp. The ratiometric fluorescence intensity (F₄₄₉/F₅₁₀) showed a good linear relationship (R² = 0.9902) with Cu²⁺ concentration in the concentration range of 0-5 μmol/L, and the minimum detection limit was 1.96 μM. Cell imaging experiments showed that LL2 could capture fluorescence signals in the green and blue channels of HepG2 cells through fluorescence confocal microscope, and successfully recognize exogenous Cu²⁺ in HepG2 cells. In addition, fluorescence co-localization experiments showed that LL2 could target both lipid droplets and lysosomes. Meanwhile, LL2 could be applied to filter paper strip assay and detection of Cu²⁺ in actual water samples. These results indicated that probe LL2 has a good capability for monitoring Cu²⁺ in environment and living cells.

Research Progress of Small Molecule Fluorescent Probes for Detecting Hypochlorite

Hypochlorous acid (HOCl) generates from the reaction between hydrogen peroxide and chloride ions via myeloperoxidase (MPO)-mediated in vivo. As very important reactive oxygen species (ROS), hypochlorous acid (HOCl)/hypochlorite (OCl⁻) play a crucial role in a variety of physiological and pathological processes. However, excessive or misplaced production of HOCl/OCl⁻ can cause variety of tissue damage and human diseases. Therefore, rapid, sensitive, and selective detection of OCl⁻ is very important. In recent years, the fluorescent probe method for detecting hypochlorous acid has been developed rapidly due to its simple operation, low toxicity, high sensitivity, and high selectivity. In this review, the progress of recently discovered fluorescent probes for the detection of hypochlorous acid was summarized with the aim to provide useful information for further design of better fluorescent probes.

A solvent-assisted ESIPT fluorescent dye for F-/Ag+ sensing and high-resolution imaging of the cilia in live cells

A solvent-assisted ESIPT fluorescent dye was synthesized and used as a probe (2-PPN) for the detection of F^-/Ag⁺ and high-resolution imaging of the cilia in live cells. The developed ESIPT fluorophore exhibited strong tautomeric fluorescence in protic solvents and normal emission in aprotic solvents, which is a significant departure from that of conventional intramolecular ESIPT compounds. The H-binding interaction of F^- and the chelation of Ag⁺ with the ESIPT module of 2-PPN resulted in significant tautomeric emission quenching. From this basis, the 2-PPN-based assays for the detection of F^- and Ag⁺ were established. The detection limit for F^- and Ag⁺ sensing is 2.4 nM and 1.5 nM, respectively. The selective experimental results showed that no tautomeric fluorescence change of 2-PPN could be observed in the presence of the other inorganic ions in the same medium, revealing high selectivity of 2-PPN to F^- and Ag⁺. Furthermore, MTT assay experiments proved that the probe 2-PPN exhibited low cytotoxicity and good cell membrane permeability. The probe was also further successfully utilized to image the cilia in vitro MCF7 cells, displaying its high-resolution imaging performance.Graphical abstract.