Phenothiazine-coumarin-pyridine hybrid as an efficient fluorescent probe for ratiometric sensing hypochlorous acid

Design, synthesis and application of dual-channel fluorescent probes for ratiometric detection of HClO and H2S based on phenothiazine coumarins

The ubiquity of diverse material entities in environmental matrices renders the deployment of unifunctional fluorescent indicators inadequate. Consequently, this study introduces a ratiometric dual-emission fluorescent sensor (Probe CP), synthesized by conjugating phenothiazine coumarin to hydroxycoumarin through a piperazine linker for concurrent detection of HClO and H2S. Upon interaction with HClO, the phenothiazine unit's sulfur atom undergoes oxidation to sulfoxide, facilitating a shift from red to green fluorescence in a ratiometric manner. Concurrently, at the opposite terminus of Probe CP, 2,4-dinitroanisole serves as the reactive moiety for H2S recognition; it restores the blue emission characteristic of 7-hydroxycoumarin while maintaining the red fluorescence emanating from phenothiazine coumarin as an internal standard for ratio-based assessment. Exhibiting elevated specificity and sensitivity coupled with minimal detection thresholds (0.0506 μM for HClO and 1.7292 μM for H2S) alongside rapid equilibration periods (3 min for HClO and half an hour for H2S), this sensor was efficaciously employed in cellular environments and within zebrafish models as well as imaging applications pertaining to alcohol-induced hepatic injury in murine subjects.

Recent Advances in Photoswitchable Fluorescent and Colorimetric Probes

In recent years, significant advancements have been made in the research of photoswitchable probes. These probes undergo reversible structural and electronic changes upon light exposure, thus exhibiting vast potential in molecular detection, biological imaging, material science, and information storage. Through precisely engineered molecular structures, the photoswitchable probes can toggle between "on" and "off" states at specific wavelengths, enabling highly sensitive and selective detection of targeted analytes. This review systematically presents photoswitchable fluorescent and colorimetric probes built on various molecular photoswitches, primarily focusing on the types involving photoswitching in their detection and/or signal response processes. It begins with an analysis of various molecular photoswitches, including their photophysical properties, photoisomerization and photochromic mechanisms, and fundamental design concepts for constructing photoswitchable probes. The article then elaborates on the applications of these probes in detecting diverse targets, including cations, anions, small molecules, and biomacromolecules. Finally, it offers perspectives on the current state and future development of photoswitchable probes. This review aims to provide a clear introduction for researchers in the field and guidance for the design and application of new, efficient fluorescent and colorimetric probes.

A ternary nucleotide-lanthanide coordination nanoprobe for ratiometric fluorescence detection of ciprofloxacin

Ciprofloxacin (CIP) is a widely used broad-spectrum antibiotic and has been associated with various side effects, making its accurate detection crucial for patient safety, drug quality compliance, and environmental and food safety. This study presents the development of a ternary nucleotide-lanthanide coordination nanoprobe, GMP-Tb-BDC (GMP: guanosine 5'-monophosphate, BDC: 2-amino-1,4-benzenedicarboxylic acid), for the sensitive and ratiometric detection of CIP. The GMP-Tb-BDC nanoprobe was constructed by incorporating the blue-emissive ligand BDC into the Tb/GMP coordination polymers. Upon the addition of CIP, the fluorescence of terbium ion (Tb3+ ) was significantly enhanced due to the coordination and fluorescence sensitization properties of CIP, while the emission of the BDC ligand remained unchanged. The nanoprobe demonstrated good linearity in the concentration range of 0-10 μM CIP. By leveraging mobile phone software to analyze the color signals, rapid on-site analysis of CIP was achieved. Furthermore, the nanoprobe exhibited accurate analysis of CIP in actual drug and milk samples. This study showcases the potential of the GMP-Tb-BDC nanoprobe for practical applications in CIP detection.

A Photoelectrochemical Sensor for the Detection of Hypochlorous Acid with a Phenothiazine-Based Photosensitizer

This paper presents the development of a photoelectrochemical sensor for hypochlorous acid (HOCl) detection, employing a phenothiazine-based organic photosensitizer (Dye-PZ). The designed probe, Dye-PZ, follows a D-π-A structure with phenothiazine as the electron-donating group and a cyano-substituted pyridine unit as the electron-accepting group. A specific reaction of the phenothiazine sulfur atom with HOCl enables selective recognition. The covalent immobilization of Dye-PZ onto a titanium dioxide nanorod-coated fluorine-doped tin oxide electrode (FTO/TiO2) using bromo-silane coupling agent (BrPTMS) resulted in the fabrication of the photoanode FTO/TiO2/BrPTMS/Dye-PZ. The photoanode exhibited a significant photoresponse under visible-light irradiation, with a subsequent reduction in photocurrent upon reaction with HOCl. The oxidation of the phenothiazine sulfur atom to a sulfoxide diminished the internal charge transfer (ICT) effect. Leveraging this principle, the successful photoelectrochemical sensing of HOCl was achieved. The sensor showed high stability, excellent reproducibility, and selective sensitivity for HOCl detection. Our study provides a novel approach for the development of efficient photoelectrochemical sensors based on organic photosensitizers, with promising applications in water quality monitoring and biosensing.

A New Phenothiazine-Based Fluorescent Sensor for Detection of Cyanide

A new fluorescent sensor for the detection of CN- was developed based on the conjugation of phenothiazine fluorophore and benzofuran unit. By the nucleophilic attacking of CN- to the fluoroacetylamino group in the sensor, the additional reaction of CN- and carbonyl group induced the ICT (intramolecular charge transfer) effect in the molecule and caused the fluorescence quenching sensor. The titration experiments show that the sensor has good sensitivity, selectivity and quick response for CN-. In addition, the fluorescent detection of CN- in the living cell and zebrafish experiments demonstrated the value of the sensor in tracing the CN- in biological systems.

A Commercially Available 2-aminoanthracene Fluorescent Probe for Rapid and Sensitive Detection of Hypochlorite in 100% Buffer Solution and its Application in Complex Water Samples

Hypochlorite (ClO-), a crucial chemical in the living organism, engages in various physiological activities. However, high amounts of ClO- result in oxidative damage. In this work, a commercially available 2-aminoanthracene (AA) was used to detect ClO-. AA demonstrated distinct properties such as superior selectivity and rapid response (< 30 s) with a low detection limit (140 nM) towards ClO- in 100% buffer solution. Furthermore, the probe exhibited a notable achievement by effectively identifying the presence of ClO- in complicated water samples. In conclusion, AA offers an easy-to-use and accurate method for quantifying ClO- in complex water samples.

A near-infrared ratiometric fluorescent probe for hydrazine and its application for gaseous sensing and cell imaging

Hydrazine (N₂H₄) is a widely used raw material in the chemical industry, but at the same time hydrazine has extremely high toxicity. Therefore, the development of efficient detection methods is crucial for monitoring hydrazine in the environment and evaluating the biological toxicity of hydrazine. This study reports a near-infrared ratiometric fluorescent probe (DCPBCl₂-Hz) for the detection of hydrazine by coupling a chlorine-substituted D-π-A fluorophore (DCPBCl₂) to the recognition group acetyl. Due to the halogen effect of chlorine substitution, the fluorophore has an elevated fluorescence efficiency and a lowered pKa value and is suitable for physiological pH conditions. Hydrazine can specifically react with the acetyl group of the fluorescent probe to release the fluorophore DCPBCl₂, so the fluorescence emission of the probe system significantly shifted from 490 nm to 660 nm. The fluorescent probe has many advantages, such as good selectivity, high sensitivity, large Stokes shift, and wide applicable pH range. The probe-loaded silica plates can realize convenient sensing gaseous hydrazine with content down to 1 ppm (mg/m³). Subsequently, DCPBCl₂-Hz was successfully applied to detect hydrazine in soils. In addition, the probe can also penetrate living cells and allow the visualization of intracellular hydrazine. It can be anticipated that probe DCPBCl₂-Hz will be a useful tool for sensing hydrazine in biological and environmental applications.

Screening of aggregation-induced emission and multi-response acrylonitrile-bridging fluorescent molecules tailored for rapid turn-on detection of HClO as well as ratiometric visualizing of extreme basicity

Realizing the rapid and sensitive tracing of multiple analysis indicators using single molecular probe through structural designing is urgently desired for exploring novel multi-response chemosensors. Herein, a series of acrylonitrile-bridging organic small molecules have been rationally designed. Among these donor-π-acceptor (D-π-A) compounds with efficient aggregation-induced emission (AIE) characteristics, a unique derivative, 2-(1H-benzo[d]imidazole-2-yl)-3-(4-(methylthio)phenyl) acrylonitrile, named MZS, has been screened out for multifunctional utilizing. First, probe MZS can respond to hypochlorous acid (HClO) through specific oxidation reaction, showing a marked fluorescence turn-on signal (I₄₉₅). This special sensing reaction is ultra-fast with a rather low detection limit (LOD = 13.6 nM). Next, versatile MZS is also sensitive to the extreme pH fluctuation, displaying an intriguing ratiometric signal variation (I₅₄₀/I₄₅₀), facilitating the real-time and naked-eye visualizing, which is even stable and reversible. Furthermore, probe MZS has been used for the monitoring of HClO in real water and commercially available disinfectant spray samples with satisfactory results. We envision that probe MZS would be a flexible and powerful tool for monitoring of environmental toxicity and industrial operations under realistic scenarios.

A novel near-infrared fluorescent probe for rapid sensing of HClO in living cells and zebrafish

Reactive oxygen species (ROS) are significant active species in living organisms, and their coordination maintains the function of organelles to resist the invasion of foreign substances. Hypochlorous acid (HClO) is not only an eventful signaling species but also a kind of ROS, which plays an irreplaceable role in the immune system. However, its abnormal levels can cause cell damage or even apoptosis, which in turn leads to the onset of a series of diseases such as inflammation, neurological diseases, and even cancer. Based on this, we designed a near-infrared fluorescent probe with a large Stokes shift for ultrafast response to HClO. Furthermore, the probe exhibits excellent sensitivity and selectivity toward HClO over other species. The probe was successfully applied to visualize endogenous and exogenous HClO in living cells and in zebrafish. This unique study is the key to providing a trustworthy tool for imaging based on the in vitro and in vivo imaging of endogenous HClO, which possesses great potential for the use in future studies of HClO-related biology and pathology.