Highly selective, colorimetric probes for cyanide ion based on β-formylBODIPY dyes by an unprecedented nucleophilic addition reaction

A reaction based carbazole-indolium conjugate probe for the selective detection of environmentally toxic ions

A nucleophilic addition based chemodosimeter was designed and synthesized with a carbazole donor and an indole acceptor. The addition of a cyanide ion to an electron-deficient indole moiety disrupts the acceptor-donor relationship, resulting in noticeable color shifts and spectrum differences in both the absorption and emission profiles. The design has a D-π-A molecular arrangement. Selectivity was investigated in 90% aqueous DMSO solution of probe CI with various anions such as SCN-, PF6-, NO3-, N3-, I-, HSO4-, CN-, H2PO4-, F-, HS-, ClO4-, Cl-, Br-, and AcO-. An intermolecular charge transfer (ICT) band at 506 nm in the UV-visible spectra vanished and the intensity of emission was quenched at 624 nm upon the addition of CN- ions. These outcomes demonstrate the effective nucleophilic addition of cyanide ions to the electron-deficient indole moiety of the probe, resulting in the formation of a new adduct in which the ICT transition is interrupted when π conjugation is blocked. The Job plot, 1H NMR spectroscopy, and HRMS analysis confirmed the formation of a new product. An outstanding response was shown by paper test strips made using probe molecules for the easy detection of cyanide ions in aqueous solutions. Besides, the probe selectively senses cyanide ions in different water samples.

Fluorescence-based ratiometric sensors as emerging tools for CN- detection: Chemical structures, sensing mechanisms and applications

Hazardous cyanide anions (CN-) are increasingly threatening the environment and human health due to their widespread use in industry and many other fields. Over the past three decades, a large number of probes have been reported to sensitively and selectively detect this toxic anion, while a rather limited number of ratiometric fluorescent probes have been developed. The ratiometric probes have significant potential in bio-imaging and biomedical applications because of the ability to detect CN- in a quick, convenient and affordable way. In this review, we introduce 42 ratiometric fluorescent probes reported in the past 6 years (2018-2023) for CN- detection. Our description includes the chemical structures, photo-physical properties, CN- sensing mechanisms, solution color changes, limits of detection (LODs) and/or various applications of these chemical probes. This review provides guidelines for design and development of a new ratiometric probe for effective CN- detection.

An innovative fluorescent probe for the detection of cyanide - enhanced sensitivity by controlling its electrostatic potential and suitable for applications such as cell imaging and food analysis

As cyanide is a huge hazard to the environment and human health, the study of the method of detecting low concentrations of cyanide is of great significance. In general, materials with strong positive electrostatic properties can use electrostatic attraction to enrich anions in the water near the materials, then realize rapid detection of low concentration anions by fluorescent probes. In this paper, fluorescent probes PI-S, PI-I and PI-N with cyanide-specific recognition and different charges were synthesized to study the relationship between the charge effect of probes and the sensing sensitivity. Through the zeta potential test and the calculation of the surface electrostatic potential, the positive electricity of PI-S, PI-I and PI-N gradually increased, the ΔG < 0 of the adsorption process gradually decreased, CN- could be aggregated to the vicinity of probes. As a result, the detection limit of the probe was gradually reduced from 1.07 × 10-6 to 5.03 × 10-8 M, the sensitivity was significantly enhanced. Therefore, this is expected to be a new strategy to improve the sensitivity of anion probes by increasing the positive electricity of molecules. In addition, PI-N has good anti-interference ability, short response time and certain application value in cell imaging and identification of endogenous cyanide in food.

Bioimaging and detecting endogenous and exogenous cyanide in foods, living cells and mice based on a turn-on mitochondria-targeted fluorescent probe

A novel fluorescent probe, with advanced features including "turn-on" fluorescence response, high sensitivity, good compatibility, and mitochondria-targeting function, has been synthesized based on structural design for detecting and visualizing cyanide in foods and biological systems. An electron-donating triphenylamine group (TPA) was employed as the fluorescent and an electron-accepting 4-methyl-N-methyl-pyridinium iodide (Py) moiety was used as a mitochondria-targeted localization unit, which formed intramolecular charge transfer (ICT) system. The "turn-on" fluorescence response of the probe (TPA-BTD-Py, TBP) toward cyanide is attributed two reasons, one is the insertion of an electron-deficient benzothiadiazole (BTD) group into the conjugated system between TPA and Py, and the other is the inhibition of ICT induced by the nucleophilic addition of CN^-. Two active sites for reacting with CN^- were involved in TBP molecule and high response sensitivity were observed in tetrahydrofuran solvent containing 3 % H₂O. The response time could be reduced to 150 s, the linear range was 0.25-50 μM, and the limit of detection was 0.046 μM for CN^- analysis. The TBP probe was successfully applied to the detection of cyanide in food samples prepared in aqueous solution, including the sprouting potato, bitter almond, cassava, and apple seeds. Furthermore, TBP exhibited low cytotoxicity, clear mitochondria-localizing capability in HeLa cells and excellent fluorescence imaging of exogenous and endogenous CN^- in living PC12 cells. Moreover, exogenous CN^- with intraperitoneal injection in nude mice could be well monitored visually by the "turn-on" fluorescence. Therefore, the strategy based on structural design provided good prospects for optimizing fluorescent probes.

Fluorescent probes for the detection of chemical warfare agents

Chemical warfare agents (CWAs) are toxic chemicals that have been intentionally developed for targeted and deadly use on humans. Although intended for military targets, the use of CWAs more often than not results in mass civilian casualties. To prevent further atrocities from occurring during conflicts, a global ban was implemented through the chemical weapons convention, with the aim of eliminating the development, stockpiling, and use of CWAs. Unfortunately, because of their relatively low cost, ease of manufacture and effectiveness on mass populations, CWAs still exist in today's world. CWAs have been used in several recent terrorist-related incidents and conflicts (e.g., Syria). Therefore, they continue to remain serious threats to public health and safety and to global peace and stability. Analytical methods that can accurately detect CWAs are essential to global security measures and for forensic analysis. Small molecule fluorescent probes have emerged as attractive chemical tools for CWA detection, due to their simplicity, ease of use, excellent selectivity and high sensitivity, as well as their ability to be translated into handheld devices. This includes the ability to non-invasively image CWA distribution within living systems (in vitro and in vivo) to permit in-depth evaluation of their biological interactions and allow potential identification of therapeutic countermeasures. In this review, we provide an overview of the various reported fluorescent probes that have been designed for the detection of CWAs. The mechanism for CWA detection, change in optical output and application for each fluorescent probe are described in detail. The limitations and challenges of currently developed fluorescent probes are discussed providing insight into the future development of this research area. We hope the information provided in this review will give readers a clear understanding of how to design a fluorescent probe for the detection of a specific CWA. We anticipate that this will advance our security systems and provide new tools for environmental and toxicology monitoring.

Nucleophilic Approach to Cyanide Sensing by Chemosensors

Cyanide anion has wide use in industrial areas; however, it has a high toxic effect on the environment as waste. Moreover, plant seeds contain cyanide that is often consumed by human beings. Therefore, many studies are carried out to determine cyanide. Especially, optical sensors showing colorimetric and fluorimetric changes have been of considerable interest due to their easy, cheap, and fast responses. This review discusses recent developments in the colorimetric and fluorimetric detection of cyanide by nucleophilic addition to different types of receptors via the chemodosimeter approach. The sensitivity and selectivity of the sensors have been reviewed for changes in absorption and fluorescence, naked-eye detection, real sample application, and detection limits when interacting with cyanide.

Extending the Chemistry of Reaction between BODIPY and Cyanide Ions: An Application in Selective Sensing of Fluoride and Cyanide Ions

A novel colorimetric BODIPY-based probe for selective detection of fluoride and cyanide has been developed. The color of the solution significantly changes upon addition of fluoride and cyanide ions with detection limits of 2.2 × 10^-7 and 1.8 × 10^-7 M calculated by UV-vis absorption method for F^- and CN^- respectively. An unprecedented phenomenon about the interaction of cyanide ions with the probe was discovered which has not been reported yet. The green color of the paper strip in the presence of cyanide ions changes with time. This observation indicates that unlike fluoride, the cyanide ion interaction with the probe is beyond mere deprotonation of the phenolic group rather envisaged as nucleophilic addition reaction. The phenomenon was also observed in the solution phase and subsequently the reaction order and rate constant of the reaction were determined from absorption versus time graph which were found to be first order and 0.3465 s^-1 respectively. The emission spectra also showed different behavior of interaction with time for the two ions. The rate of the reaction was found to be independent of the solvent polarity. The plausible mechanism of the reaction between cyanide and fluoride ions with the probe was proposed based on ¹H NMR titration experiments and mass spectrometry.

Selective visualization of cyanide in food, living cells and zebrafish by a mitochondria targeted NIR-emitting fluorescent probe

Cyanide is a highly toxic substance, and the detection of cyanide in the environment and food samples is critical to public health care. Herein, we rationally designed a mitochondria-targeted near-infrared fluorescent probe BTC for ratiometric monitoring of CN^- in water, food, living cells, and zebrafish. BTC exhibits a remarkable colorimetric ratiometric fluorescence response to CN^- with high selectivity, low detection limit (54.3 nM), and large Stokes shift. The cyanide sensing mechanism was demonstrated by NMR and ESI-MS analysis and density functional theory (DFT). More importantly, BTC was used for efficient naked-eye colorimetric detection of CN^- in sprouting potatoes, almonds, and ginkgo fruit samples. Further, the BTC is capable of situ tracking and imaging cyanide in mitochondria of SMMC-7721 cells and in zebrafish via dual emission channels, and was prepared into a kit for convenient and visual on-site sensing of cyanide in food samples.

A Colormetric and Fluorescence Probe for Highly Specific Cu2+ and its Application in Live Cell Imaging

Fluorescent probes are intriguing material for ion detection. In this study, 4,4-difluoro-4-bora3a,4a-diaza-s-indacene (BODIPY) containing a dipicolylethylenediamine unit was developed as a colorimetric and fluorescence "turn-off" probe for Cu²⁺. The probe exhibited higher selectivity for Cu²⁺ than other common metal ions with a detection limit of 8.49 μM. With increasing Cu²⁺ concentration, the probe showed a red-shift in the absorption spectrum as well as fluorescence quenching, possibly due to the intramolecular charge transfer effect of the probe-Cu(II) complex. Furthermore, the probe was used for imaging Cu²⁺ in living cells based on confocal fluorescence imaging. The results show that the probe is an effective tool for detection copper ions.

A benzothiazole-based new fluorogenic chemosensor for the detection of CN− and its real-time application in environmental water samples and living cells

Since the cyanide ion is used in a wide range of industries and is harmful to both human health and the environment, a number of research efforts are dedicated to creating fluorescence sensors for the detection of cyanide (CN⁻). Herein, for the fluorescence detection of CN⁻, a new highly selective and sensitive sensor 2-(3-(benzo[d]thiazol-2-yl)-4-hydroxybenzylidene)-1H-indene-1,3(2H)-dione (BID) was created by conjugating a benzothiazole moiety with 1H-indene-1,3(2H)-dione. The donor and acceptor components of this hybrid receptor were covalently connected through a double bond. The nucleophilic addition of a cyanide anion to the BID inhibits the intramolecular charge transfer (ICT) transition, resulting in spectral and colour alterations in the receptor. When the solvent polarity was increased from n-hexane to methanol, this molecule exhibited a bathochromic shift in the emission wavelength (610 to 632 nm), suggesting the presence of a solvatochromic action. The sensor BID has shown strong specificity towards CN⁻ by interrupting its internal charge transfer (ICT), resulting in a significant change in the UV-vis spectrum and a notable blue shift in the fluorescence emission spectrum. The cyanide anion (CN⁻) is responsible for the optical alterations observed by BID, as opposed to the other anions examined. The detection limit was 5.97 nM, significantly less than the WHO's permitted amount of CN⁻ in drinking water. The experimental findings indicate that BID's fluorescence response to CN⁻ is pH insensitive throughout a wide pH range of 6.0 to 12.0. The interaction mechanism between the BID and CN⁻ ions has been studied by HRMS, ¹H-NMR titration experiments, FT-IR, and DFT, which confirmed the nucleophilic addition of CN⁻ on vinylidene and subsequent disturbance of ICT. Additionally, we demonstrated the real-time detection application of CN⁻ in environmental water samples and live-cell imaging.

Since the cyanide ion is used in a wide range of industries and is harmful to both human health and the environment, a number of research efforts are dedicated to creating fluorescence sensors for the detection of cyanide (CN⁻).

Magnetic mesoporous nanomaterials with AIE properties for selective detection and removal of CN- from water under magnetic conditions

We have prepared a type of magnetic mesoporous nanomaterial with aggregation-induced emission properties (Fe₃O₄@mSiO₂@TPA@BA, hence abbr. FSTB) to detect and remove cyanide ions (CN^-) under magnetic conditions. FSTB has a large specific surface area and improved fluorescence performance to identify CN^-, and its superparamagnetic behavior plays an important role in removing CN^-. The magnetic sensor FSTB shows excellent selectivity and anti-interference for the detection of CN^- in aqueous solutions. It is obvious from the equation LOD = 3δ/S that the limit of detection (LOD) of FSTB for CN^- is significantly lower than the permissible level of CN^- in drinkable water recommended by the World Health Organization. Therefore, the magnetic sensor FSTB has a wide range of applications for detecting and removing harmful CN^-.