On-site and low-cost detection of cyanide by simple colorimetric and fluorogenic sensors: Smartphone and test strip applications

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.

Selective and Effective Sensing of Cyanide Ion with no Interference in Water by Phenothiazine-indolium Fused Optical Sensor

The sensor with electron donor phenothiazine-2-carbaldehyde and electron acceptor indolium carboxylic acid, is developed with an intramolecular charge transfer transition between them. The synthesized molecule senses cyanide ion in water. The cyanide ion reacts with the molecule via nucleophilic addition in the indolium ring with a noticeable purple to colorless change in the solution observed. Also with the cyanide ion interaction, the sensor exhibits change in UV-visible absorption and fluorescence spectra. While the other ion does not show spectral and visual changes when interacts with the sensor molecule. Also the interference study reveals that the molecule is highly selective towards cyanide ion. Different source of water samples confirms the CN- ion sensing efficiency of the molecule. 1:1 interaction between the molecule PTI and cyanide ion is confirmed from the results of Jobs plot, 1H NMR and HRMS. Paper strips were prepared and this can act as a simple tool to sense cyanide ion in various water samples.

Small Molecule Optical Probes for Detection of H2S in Water Samples: A Review

Hydrogen sulfide (H2S) is closely linked to not only environmental hazards, but also it affects human health due to its toxic nature and the exposure risks associated with several occupational settings. Therefore, detection of this pollutant in water sources has garnered immense importance in the analytical research arena. Several research groups have devoted great efforts to explore the selective as well as sensitive methods to detect H2S concentrations in water. Recent studies describe different strategies for sensing this ubiquitous gas in real-life water samples. Though many of the designed and developed H2S detection approaches based on the use of organic small molecules facilitate qualitative/quantitative detection of the toxic contaminant in water, optical detection has been acknowledged as one of the best, attributed to the simple, highly sensitive, selective, and good repeatability features of the technique. Therefore, this review is an attempt to offer a general perspective of easy-to-use and fast response optical detection techniques for H2S, fluorimetry and colorimetry, over a wide variety of other instrumental platforms. The review affords a concise summary of the various design strategies adopted by various researchers in constructing small organic molecules as H2S sensors and offers insight into their mechanistic pathways. Moreover, it collates the salient aspects of optical detection techniques and highlights the future scope for prospective exploration in this field based on the limitations of the existing H2S probes.

Glucose Oxidase Activity Colorimetric Assay Using Redox-Sensitive Electrochromic Nanoparticle-Functionalized Paper Sensors

Glucose oxidase (GOx) activity assays are vital for various applications, including glucose metabolism estimation and fungal testing. However, conventional methods involve time-consuming and complex procedures. In this study, we present a colorimetric platform for in situ GOx activity measurement utilizing redox-sensitive electrochromic nanoparticles based on polyaniline (PAni). The glucose-adsorbed colorimetric paper sensor, herein termed Glu@CPS, is created by immobilizing ferrocene and glucose onto paper substrates that have been functionalized with PAni nanoparticles. Glu@CPS not only demonstrated rapid detection (within 5 min) but also exhibited remarkable selectivity for GOx and a limit of detection as low as 1.25 μM. Moreover, Glu@CPS demonstrated consistent accuracy in the measurement of GOx activity, exhibiting no deviations even after being stored at ambient temperature for a duration of one month. To further corroborate the effectiveness of this method, we applied Glu@CPS in the detection of GOx activity in a moldy red wine. The results highlight the promising potential of Glu@CPS as a convenient and precise platform for GOx activity measurement in diverse applications including food quality control, environmental monitoring, and early detection of fungal contamination.

Ultrasensitive Visual Tracking of Toxic Cyanide Ions in Biological Samples Using Biocompatible Metal-Organic Frameworks Architectures

The extraordinary accumulation of cyanide ions within biological cells is a severe health risk. Detecting and tracking toxic cyanide ions within these cells by simple and ultrasensitive methodologies are of immense curiosity. Here, continuous tracking of ultimate levels of CN--ions in HeLa cells was reported employing biocompatible branching molecular architectures (BMAs). These BMAs were engineered by decorating colorant-laden dendritic branch within and around the molecular building hollows of the geode-shelled nanorods of organic-inorganic Al-frameworks. Batch-contact methods were utilized to assess the potential of hollow-nest architecture for inhibition/evaluation of toxicant CN--ions within HeLa cells. The nanorod BMAs revealed significant potential capabilities in monitoring and tracking of CN- ions (88 parts per trillion) in biological trials within seconds. These results demonstrated sufficient evidence for the compatibility of BMAs during HeLa cell exposure. Under specific conditions, the BMAs were utilized for in-vitro fluorescence tracking/sensing of CN- in HeLa cells. The cliff swallow nest with massive mouths may have the potential to reduce the health hazards associated with toxicant exposure in biological cells.

Two red/blue-emitting fluorescent probes for quick, portable, and selective detection of thiophenol in food, soil and plant samples, and their applications in bioimaging

Thiophenol (PhSH), which is widely used in many industries, poses significant health risks owing to its acute toxicity and irritating effects. Thus, the detection of PhSH is crucial for ensuring environmental and food safety. There is significant room for improvement in the sensing properties of the reported analytical methods, such as response time, detection limit, selectivity, and portable detection. Herein, we present two new red/blue fluorescence-emissive sensors (NS1 and NS2) for PhSH detection. After reacting with PhSH, NS1 exhibited a low detection limit (66.7 nM), red emission, fast response time of just 10 s, and large Stokes shift (240 nm). NS2 could detect PhSH with a low detection limit (75.8 nM), fast response time of 20 s, and blue emission. The noticeable color response and portability of the two probes made them suitable for on-site detection of PhSH in various samples, such as water, soil, plant, food samples, and living cells. Moreover, it has been shown that these probes could be used to determine PhSH content in smartphone applications, thin layer chromatography kits, and polysulfone capsule kits. Prepared probes have low cytotoxicity and show good permeability in tested living cells, which is important for early diagnosis, disease research, and emergency analysis. Compared with other studies, the proposed approach has remarkable advantages in terms of detection limit, portability, response time, and low cytotoxicity. Thus, it meets the crucial demand for ensuring health, environmental and food safety, and adherence to regulatory standards.

Spectroscopic and TD-DFT studies on the chromo-fluorogenic detection of cyanide ions in organic and aquo-organic media

A new naked-eye chromogenic and fluorogenic probe KS5 has been developed for the detection of CN- ions in neat DMSO and H2O:DMSO (1:1 v/v) media. The probe KS5 exhibited selectivity towards CN- and F- ions in organic and high selectivity towards CN- ions in aquo-organic media resulting in a colour change from brown to colourless and a turn-on fluorescence response. The probe could able to detect CN- ions via a deprotonation process, which was conceived by consecutive addition of hydroxide and hydrogen ions and confirmed using 1H NMR studies. The limit of detection (LOD) of KS5 towards CN- ions were in the range of 0.07-0.62 µM in both these solvent systems. Suppression of intra-molecular charge transfer (ICT) transition and photoinduced electron transfer (PET) process of KS5 by the added CN- ions are responsible for the chromogenic and fluorogenic changes observed, respectively. Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) calculations strongly supported the proposed mechanism along with the optical properties of the probe before and after the addition of CN- ions. To prove the practical applicability, KS5 was successfully utilized to detect CN- ions in cassava powder and bitter almonds as well as to determine CN- ions in various real water samples.

Efficient cyanide sensing using plasmonic Ag/Fe3O4 nanoparticles

In the line of our previous studies, we have reported a developed sensitive and selective probe for cyanide detection based on Ag/Fe3O4 nanoparticles (NPs) with an extremely low limit of detection at the level of ng per milliliter. Herein, we report the improvement of the easy-to-make magnetic silver nanoparticle-based sensor system for cyanide determination in an extended calibration range with higher selectivity and precision. As far as our knowledge is concerned, the detectable linear range from 1.0 nM to 160 μM (0.026 ng mL-1 to 4.16 μg mL-1) of the improved simple highly precise technique represents the widest assay that has been reported so far. The method is based on strong enhancement of scattered light of the plasmonic nanoparticles and simultaneously cyanide fluorescence quenching. Although the fluorescence of cyanide is highly selective and precise, its intensity is poor. On the other hand, the strongly enhanced Rayleigh signal has a low repeatability. We proposed a method to remove the interference and obtained an effective factor that is directly proportional to cyanide concentration utilizing both above signals simultaneously. In this work, Ag/Fe3O4 NPs have been synthesized easily using a green preparation method and the NPs were consequently characterized using powder XRD, UV-Vis absorption spectroscopy, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). A combination of absorption, Rayleigh and fluorescence characteristics were used for detection of cyanide in real samples and an overview of recently reported sensors for cyanide was also provided.

Ultrasensitive Monitoring of Cyanide Concentrations in Water Using a Aucore-Agshell Hybrid-Coating-Based Fiber Optical Sensor

Cyanides, which are extremely toxic chemicals that are rapidly absorbed into the human body and interact with cytochrome oxidase, strongly inhibit cellular respiration to body death with convulsions. Cyanide ions that exist in many forms in nature such as those found in apricot kernels, cassava roots, and bamboo shoots as cyanogenic glycosides are inevitably used in various industries, including gold and silver mining as well as in dyes and plastic industries. In this study, for the sake of developing ultrahigh-sensitive sensors for cyanide monitoring in a simple manner, we chemically synthesize Aucore-Agshell hybrid nanomaterials of different core/shell thicknesses for colorimetric sensors and fiber optical sensors. Their sensing principle relies on the formation of the Ag/Au cyanocomplex upon cyanide injection. The generated metal cyanocomplex induced changes in refractive indices, causing changes in properties of localized surface plasmon resonance (LSPR), i.e., optical absorbance change for the colorimetric sensors. For fiber optical sensors, the hybrid metal nanoparticles were immobilized on the fiber core surface and the metal cyanocomplex formation induced changes in the fiber cladding refractive index, enabling quantitative cyanide detection with ultrahigh sensitivity. The LSPR-based colorimetric sensor provided the lowest detectable cyanide concentration of 5 × 10-6 M, whereas the value for the fiber-based sensor was 8 × 10-11 M.

A colorimetric and turn-on fluorescent sensor for cyanide and acetate-based Schiff base compound of 2,2'-((1E,11E)-5,8-dioxa-2,11-diazadodeca-1,11-diene-1,12-diyl)bis(4-((E)-phenyldiazenyl)phenol)

A novel Schiff base-based sensor (L) has been designed, synthesized, and developed as a fluorescent and colorimetric sensor for cyanide and acetate. This L exhibited a quick response with rapid sensitivity to CN^- and AcO^- through a remarkable color change from yellow to red which was detectable by the naked eyes. It also sensed CN^- and AcO^- in a fluorescent way via an enhancement in fluorescence intensity. The interaction between L and anions (CN^- and AcO^-) was investigated by using UV-Vis studies, and ¹H NMR titration. The theoretical DFT calculations were also employed to support the results, which displayed good agreement with the experimental value acquisition. As the detection limit for cyanide and acetate were 2.1 × 10^-9 M and 1.7 × 10^-9 M; respectively, low concentrations of these anions could be detectable in the proposed L sensor. In addition, L showed significant reversibility of CN^- detection by using Cu²⁺ as a proper reagent with two different sensing methods including color change and UV-Vis. Last but not least, L could be applied to rapidly detect CN^- in a wide range of pH. As a result, the proposed sensor is promising to identify cyanide and acetate in practical applications in medical, biological, and chemical fields.

Colorimetric and fluorescent dual-signals probes for naked-eye detection of hydrogen peroxide and applications in milk samples and in vivo

Excessive residual hydrogen peroxide (H₂O₂) disinfectant in food is harmful to human health. Therefore, it is necessary to develop efficient detection methods for H₂O₂ detection. In this work, we designed and synthesized five D-A molecules 3a-3e by introducing electron-donor substituents (-OCH₃ and -CH₃) to the electron-acceptor dicyanoisophorone skeleton in order to find out the suitable probes for H₂O₂ detection. Among them, two promising probes, 3a and 3c, are screened out according to structure-property relationships. Based on the principle of intramolecular charge transfer (ICT), 3a and 3c express colorimetric and fluorescent dual-signals towards H₂O₂ with low detection limits (0.20 μM and 0.14 μM) and rapid response (within 20 mins). The reaction mechanism between probes and H₂O₂ is determined by ¹H NMR and HRMS. Density functional theory (DFT) calculations are measured to study the regulation mechanism of structure adjustment on probs performance. Furthermore, a smartphone RGB analysis is utilized as a portable platform for the quantitative detection of H₂O₂ without complicated instruments, indicating a high efficiency and on-site detection method for H₂O₂. In addition, probes are applied to detect H₂O₂ in milk samples, HepG-2 cells and zebrafish, suggesting the promising applications in food samples and physiological systems.

Paper-based analytical devices for point-of-need applications

Paper-based analytical devices (PADs) are powerful platforms for point-of-need testing since they are inexpensive devices fabricated in different shapes and miniaturized sizes, ensuring better portability. Additionally, the readout and detection systems can be accomplished with portable devices, allying with the features of both systems. These devices have been introduced as promising analytical platforms to meet critical demands involving rapid, reliable, and simple testing. They have been applied to monitor species related to environmental, health, and food issues. Herein, an outline of chronological events involving PADs is first reported. This work also introduces insights into fundamental parameters to engineer new analytical platforms, including the paper type and device operation. The discussions involve the main analytical techniques used as detection systems, such as colorimetry, fluorescence, and electrochemistry. It also showed recent advances involving PADs, especially combining optical and electrochemical detection into a single device. Dual/combined detection systems can overcome individual barriers of the analytical techniques, making possible simultaneous determinations, or enhancing the devices' sensitivity and/or selectivity. In addition, this review reports on distance-based detection, which is also considered a trend in analytical chemistry. Distance-based detection offers instrument-free analyses and avoids user interpretation errors, which are outstanding features for analyses at the point of need, especially for resource-limited regions. Finally, this review provides a critical overview of the practical specifications of the recent analytical platforms involving PADs, demonstrating their challenges. Therefore, this work can be a highly useful reference for new research and innovation.

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.

Aryl-Phenanthro[9,10-d]imidazole: A Versatile Scaffold for the Design of Optical-Based Sensors

Fluorescent and colorimetric sensors are important tools for investigating the chemical compositions of different matrices, including foods, environmental samples, and water. The high sensitivity, low interference, and low detection limits of these sensors have inspired scientists to investigate this class of sensing molecules for ion and molecule detection. Several examples of fluorescent and colorimetric sensors have been described in the literature; this Review focuses particularly on phenanthro[9,10-d]imidazoles. Different strategies have been developed for obtaining phenanthro[9,10-d]imidazoles, which enable modification of their optical properties upon interaction with specific analytes. These sensing responses usually involve changes in the fluorescence intensity and/or color arising from processes like photoinduced electron transfer, intramolecular charge transfer, intramolecular proton transfer in the excited state, and Förster resonance energy transfer. In this Review, we categorized these sensors into two different groups: those bearing formyl groups and their derivatives and those based on other molecular groups. The different optical responses of phenanthro[9,10-d]imidazole-based sensors upon interaction with specific analytes are discussed.

Colorimetric detection of total antioxidants in green tea with oxidase-mimetic CoOOH nanorings

Green tea is a popular beverage and is widely consumed due to its taste and antioxidative polyphenols. Herein, a smartphone-based colorimetric reader using cobalt oxyhydroxide (CoOOH) nanorings has been successfully applied to detect antioxidants in green tea with high reliability and robustness. By exploiting the oxidase-mimicking activity, the as-synthesized CoOOH nanorings replaces natural enzymes to directly catalyze oxidate colorless 3,3 ´ ,5,5 ´ -tetramethylbenzidine (TMB), while antioxidants can disintegrate CoOOH, leading to an antioxidant concentration-dependent color change. Benefiting from the CoOOH nanorings-based colorimetric strategy, a smartphone-assistant nanosensor was devised for portable and visual detection of antioxidants in green tea. The proposed method can be extended to visual detection of a diverse range of diseases by responding to their specific antioxidant, and thus provide a pivotal disease toolbox that is compatible for development at the point-of-care.

Cyanide Anion Determination Based on Nucleophilic Addition to 6-[(E)-(4-Nitrophenyl)diazenyl]-1′,3,3′,4-tetrahydrospiro[chromene-2,2′-indole] Derivatives

This work provides a novel approach for the instant detection of CN− anions based on chromogenic 6-[(E)-(4-nitrophenyl)diazenyl]-1′,3,3′,4-tetrahydrospiro[chromene-2,2′-indole] derivatives. New colorimetric detectors were synthesized and characterized. These compounds exhibited a substantial color change from orange to magenta and blue when treated with cyanide ions in a CH3CN solution buffered with sodium phosphate and demonstrated high selectivity to CN− anions. Common anions were tested, and they did not interfere with cyanide detection, except for carbonates and hydrosulfites. The simple preparation of a molecular sensor and the easily noticeable color change makes this a practical system for the monitoring of CN− ions. This color change is explained by nucleophilic substitution of the pyrane ring oxygen atom at the indoline C-2 atom by the cyanide anion. This generates the appearance of intensively colored 4-(4-nitrophenylazo)phenolate chromophore and allows for determining very low levels of CN− anion.

Pyrene functionalized oxacalix[4]arene architecture as dual readout sensor for expeditious recognition of cyanide anion

A pyrene functionalized oxacalix[4]arene architecture (DPOC) was utilized as a fluorescence probe for selective recognition of cyanide ions. The receptor DPOC shows excellent selectivity towards cyanide ion with a red shift of 108 nm in absorption band along with a significant change in colour from light yellow to pink. The fluorescence titration experiments further confirm the lower limit of detection as 1.7µM with no significant influences of competing anions. ¹ H-NMR titration experiments support the deprotonation phenomena, as the -NH proton disappears upon successive addition of cyanide ions. The DFT calculation also indicates a certain increment of -NH bond length upon interaction with cyanide ions. The spectral properties as well as colour of DPOC-CN^- system may be reversed upon the addition of Ag⁺/ Cu²⁺ ions up to 5 consecutive cycles. Moreover, DPOC coated "test strips" were prepared for visual detection of cyanide ions.

Quinoline based thiosemicarbazones as colorimetric chemosensors for fluoride and cyanide ions and DFT studies

High toxicity and extensive accessibility of fluoride and cyanide ions in diverse environmental media encouraged attention for scheming well-organized probes for their detection. Keeping in mind we have designed and synthesized thiosemicarbazone-based chemosensors RB-1, RB-2 and RB-3 for the detection of fluoride and cyanide ions. The structural elucidation of the synthesized chemosensors is done by employing different analytical techniques including nuclear magnetic resonance and electronic absorption specrtoscopies. Admirable detection limit, binding constant and fast response time (2 s) to F⁻ and CN⁻ ions enlarged the applications of these chemosensors. Additional confirmation of the sensing ability of these chemosensors is derived from DFT and TDDFT calculations with M06/6-311G(d,p) method by performing FMO, UV–Vis, QTAIM and global reactivity parameters elucidation. Overall results point out that investigated chemosensors are suitable candidates for sensing the F⁻ ions. These chemosensors were successfully applied to detect F⁻ ions in a commercial toothpaste sample.

Development of a Screening Method for Sulfamethoxazole in Environmental Water by Digital Colorimetry Using a Mobile Device

Antibiotic resistance is a major health concern of the 21st century. The misuse of antibiotics over the years has led to their increasing presence in the environment, particularly in water resources, which can exacerbate the transmission of resistance genes and facilitate the emergence of resistant microorganisms. The objective of the present work is to develop a chemosensor for screening of sulfonamides in environmental waters, targeting sulfamethoxazole as the model analyte. The methodology was based on the retention of sulfamethoxazole in disks containing polystyrene divinylbenzene sulfonated sorbent particles and reaction with p-dimethylaminocinnamaldehyde, followed by colorimetric detection using a computer-vision algorithm. Several color spaces (RGB, HSV and CIELAB) were evaluated, with the coordinate a_star, from the CIELAB color space, providing the highest sensitivity. Moreover, in order to avoid possible errors due to variations in illumination, a color palette is included in the picture of the analytical disk, and a correction using the a_star value from one of the color patches is proposed. The methodology presented recoveries of 82–101% at 0.1 µg and 0.5 µg of sulfamethoxazole (25 mL), providing a detection limit of 0.08 µg and a quantification limit of 0.26 µg. As a proof of concept, application to in-field analysis was successfully implemented.

A water-soluble azobenzene-dicyano pendant polymeric chemosensor for the colorimetric detection of cyanide in 100% aqueous media and food samples

A polymeric chemosensor (P1) was developed for the colorimetric detection of cyanide in aqueous media and cyanogenic food samples.

A smartphone-based device for simultaneous measurement of ratiometric fluorescence and absorbance demonstrated by the determination of hypochlorous acid

Ratiometric fluorescence and absorbance are measured simultaneously by a smartphone-based device according to the corrected brightness ratio in a picture.

Rhodanine-based fluorometric sequential monitoring of silver (I) and iodide ions: Experiment, DFT calculation and multifarious applications

A simple rhodanine derived fluorophoric unit has been designed for selective detection of Ag⁺ and I^- ions in DMSO-H₂O medium. The sensor R1 showed an obvious "turn-on" fluorescence response toward Ag⁺ due to the inhibition of both C-N single bond free rotation, internal charge transfer (ICT) and the formation of chelation enhanced fluorescence (CHEF) effects. The fluorescence quantum yield (Φ) was increased from 0.0013 to 0.032 for receptor R1 upon the Ag⁺-complexation. In addition, the 1:1 complexing stoichiometry was employed based on Job's plot analysis with detection limit of 24.23 × 10^-7 M. Conversely, receptor R1+Ag⁺ particularly detects I^- ion over other co-existing anions by the "turn-off" fluorescence response due to the formation of AgI, displacing the receptor R1 with the quantum yield of 0.0014. The detection limit was calculated to be 22.83 × 10^-7 M. The sensing behaviour of receptor R1 toward Ag⁺ was also supported by density functional theory (DFT) calculations. Moreover, the sensing ability of reported receptor R1 could be exercised in multifarious applications like paper strip, silica-supported analysis, staining test for latent finger print, logical behaviour, smartphone-assisted quantitative detection and real water samples studies.

Bisphenol-based cyanide sensing: Selectivity, reversibility, facile synthesis, bilateral "OFF-ON" fluorescence, C2ν structural and conformational analysis

A structurally characterized novel dual-pocketed tetra-conjugated bisphenol-based chromophore (fluorescence = 652 nm) was synthesized in gram scale in ~90% yield from its tetraaldehyde. Highly selective, naked-eye detection of CN^- (DMSO/H₂O) was confirmed by interferent testing. A detection limit of 0.38 µM, within the permissible limit of CN^- concentration in drinking water was achieved as mandated by WHO. The "reversibility" study shows potential applicability and reusability of Sen. Moreover, cost-effective and on-site interfaces, application tools such as fabricated cotton swabs, plastic Petri dishes, and filter papers further demonstrated the specific selectivity of Sen for the toxic CN^-. In addition, an easily available and handy smartphone-assisted "Color Picker" app was utilized to help estimate the concentration of CN^- ion present. A dual phenol deprotonation mechanism is active and supported by ¹H NMR spectroscopic data and DFT calculation results.

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^-.

Two cyanoethylene-based fluorescence probes for highly efficient cyanide detection and practical applications in drinking water and living cells

Cyanide detection methods are urgently needed due to the highly lethal to human beings. Herein, we report two fluorescence probes (Probe 1 and Probe 2) based on cyanoethylene group for cyanide anion (CN^-) detection. The selective recognition for CN^- was confirmed by the completely opposite green fluorescence of Probe 1 and red fluorescence of Probe 2 observed by fluorescence spectra and naked eyes. The probes take advantages of the large Stokes shift (~160 nm), rapid response (30 s), anti-interference performance and low detection limit (Probe 1: 12.4 nM, Probe 2: 101 nM). The sensing mechanism is certificated to the nucleophilic attack of CN^- to electron-deficient cyanoethylene group of probes, which was demonstrated by ¹H NMR titration, HR-MS, Job's plot and IR spectroscopy. Density functional theory (DFT) calculations were carried out to analyze the mechanism in theory. Further, practical applications were studied. Easy-to-use test strips treated with Probe 1 or Probe 2 are capable of CN^- detection in pure drinking water. The good biocompatibility and membrane penetrability have achieved the bioimaging capability of Probe 1 and Probe 2 in living HepG-2 cells, making the probes promising for use in real lives.

Controllable and reversible sensing cyanide ion using dual-functional Cu(II)-based ensemble

In this work, a dual-functional Cu²⁺-based ensemble (2S·Cu²⁺) was well designed and characterized. Then, the successional and discriminating sensing for CN^- over other competitive species (H₂PO₄^- and biothiols) was achieved based on the disaggregation of 2S·Cu²⁺ ensemble and the deprotonation of imidazole NH of regenerated sensor S in aqueous solution, respectively. The visual sensing mechanism could be clearly demonstrated by ¹H NMR, HRMS and energy changes between the HOMO-LUMO band gaps. Furthermore, the reversibility and reusability of S and 2S·Cu²⁺ upon alternating addition of CN^-/H⁺ and CN^-/Cu²⁺ were studied. Interestingly, the sequential sensing for biothiols (cysteine, glutathione and homocysteine) and CN^- was also realized through spectroscopic methodology and test paper strips. This work may provide a feasible strategy to discriminate CN^- over H₂PO₄^- and biothiols with high selectivity and sensitivity through Cu²⁺-based ensembles.

A multifunctional fluorescent probe for visualizing H2S in wastewater with portable smartphone via fluorescent paper strip and sensing GSH in vivo

In this paper, a bifunctional tri-site fluorescent probe was designed for the first time not only for visualization and quantitative analysis of sensing H₂S in wastewater by coupling paper strip and smartphone (Color recognizer, Xiyi Technology) but also for sensitively monitoring GSH in living cells, which relied on different emission channels and the pH of solutions. The recognition properties of GH towards H₂S/GSH were satisfactorily demonstrated through fluorescence, UV-vis, ¹H NMR and DFT calculations. More importantly, integrated with the paper strip, portable smartphone-sensing platform with a color recognizer app would accomplish cost-effective and rapid assays for colorimetric water quality testing, which displayed huge application potential in fields of environmental monitoring.