Monitoring Hg2+ ions in food and environmental matrices using a novel ratiometric NIR fluorescent sensor via carbonothioate-deprotection reaction.

Mercury toxicity and its environmental impact are significant concerns for public health and environmental protection. Therefore, the development of effective, rapid, and reliable detection methods for trace levels of Hg2+ is crucial. Herein, a cyanine dye bearing a carbonothioate group is reported as a potential NIR fluorescent probe for Hg2+ detection. The spectral properties of the free probe have been characterized by the presence and absence of a series of analytes. The addition of Hg2+ leads to significant changes in the fluorescence signal with distinct red coloration compared to other competing analytes, indicating that the probe is highly selective for Hg2+. The fluorescence quantum yield increases from 0.073 to 0.315. The detection limit is 0.10 µM, indicating the high sensitivity of the probe to low Hg2+ levels. The most prominent sensing features of the probe include NIR fluorescence, low cytotoxicity, ratiometric fluorescence response, and fast response compared to most of the currently available fluorescent probes. In addition, the probe can detect Hg2+ in actual samples such as foodstuff, soil, water, and live cells. Bioimaging studies have demonstrated that the present probe is highly efficient in targeting mitochondria and possesses good imaging abilities for detecting Hg2+ in cells. Therefore, these results suggest that it can be proposed as a powerful NIR fluorescent probe for the highly sensitive detection of Hg2+.

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.

Engineering a "turn-on" NIR fluorescent sensor-based hydroxyphenyl benzothiazole with a cinnamoyl unit for hydrazine and its environmental and in-vitro applications.

Hydrazine (N2H4), a chemical compound widely used in various industrial applications, causes significant environmental and biological hazards. Therefore, it is crucial to develop methodologies for the visualization and real time tracking of N2H4. In this regard, we have constructed a novel near-infrared fluorescent probe (HBT-Cy) that can effectively detect N2H4 in various samples. HBT-Cy contains 2-(2'-hydroxyphenyl)benzothiazole (HBT), cinnamoyl (Cy), and pyridinium (Py) moieties. Importantly, HBT-Cy exhibits a rapid, selective, and highly sensitive response to N2H4. This response results in the release of HBT-Py and the generation of considerable colorimetric changes along with a significant NIR (near infrared) fluorescence signal, peaking at 685 nm. Advantages of this system include turn on NIR fluorescence with large Stokes shift, (approximately 171 nm), low limit of detection (LOD = 0.11 µM) and quantum yield (0.211). The probe with low cytotoxic behavior demonstrates strong NIR fluorescence imaging capabilities to visualize endogenous and exogenous N2H4 in live cells. This mitochondria-targetable probe shows effective subcellular localization. These results suggest that HBT-Cy is a valuable probe for tracking and investigating the behavior of N2H4 in biological systems and environmental samples.

Cu2+-assisted sensing of fungicide Thiram in food, soil, and plant samples and the ratiometric detection of Hg2+ in living cells by a low cytotoxic and red emissive fluorescent sensor.

Metal ions and pesticides are extensively used in many industries and agriculture. However, they cause significant environmental pollution and various adverse health effects. Therefore, the development of sensitive and selective techniques to detect them is necessary for human health and the ecosystem. In this paper, we report a novel red-emitting fluorescence probe with a large Stokes shift (∼220 nm) based on rhodamine and isophorone units. The probe shows a ratiometric fluorescence response toward Hg2+ ions; however, Cu2+ ions quench the red fluorescence signal. The decomposition of the probe-Cu2+ complex allows detection of Thiram followed by recovery of the red fluorescence signal of the probe. In addition, the probe shows a good linear response to Hg2+, Cu2+, and Thiram, with detection limits of 122.0 nM, 29.0 nM, and 72.0 nM, respectively. The practical applicability of the probe has been successfully tested in real samples. Moreover, smartphone detection and light-responsive capsule fabrication have been established, for easy and quick detection. The probe possesses very low cytotoxicity and allows visualization of Hg2+ and Cu2+ ions in HeLa cells. Therefore, the present probe is expected to be an effective tool assisting in easy, quick, and reliable detection of Thiram, Hg2+, and Cu2+ ions.

Lighting up trace carbon monoxide and residual palladium species by a low cytotoxic mitochondria targetable red fluorescent probe: Its large scaled applications.

High levels of residual palladium can lead to serious negative health effects. Carbon monoxide (CO) is a significant gasotransmitter in transporting intermolecular and intramolecular signals to balance several physiological processes. Therefore, there is a need for rapid detection of CO and palladium residue. To address these issues, we have designed a novel light-up fluorescent probe for the detection of Pd and CO. It can not only detect Pd and CO selectively with a remarkable chromogenic and red fluorescent response over other metal ions allowing detection with naked eyes but also discriminate Pd0 and Pd2+/Pd4+ species. The detection reaction is confirmed by HPLC analysis. The probe demonstrates biocompatibility and mitochondrial target ability for potential biological applications. The practical applications based on drug residue and soil analysis, and smartphone have been successfully performed. Bioimaging of the concentration change of Pd and CO in HeLa cells using the probe is successfully applied. Therefore, the present approach can provide early diagnosis of Pd and CO with low detection limit, low cytotoxicity, high selectivity, and sensitivity.

Visual and quantitative monitoring of thiophenol by a novel deep-red emitting fluorescent probe in environmental and biological systems.

Detection of highly toxic thiophenols in biological or environmental systems is of great importance. Therefore, fast, reliable, and sensitive probes are needed to detect thiophenols. Herein, a novel triphenylamine conjugated dicyanoisophorone-based near infrared fluorescence probe is reported to determine trace thiophenol (PhSH) levels. The probe demonstrates a distinct "turn-on" fluorescence response to thiophenol among the tested analytes and its quantum yield (Φ) increases from 0.011 to 0.142. It has low cytotoxicity with cell viability of 90-100% up to 10.0 µM of the probe, a strong anti-interference capability, a large Stokes shift (150 nm), and a fast response time (<1 min). In addition, the probe exhibits a good linear response to PhSH over the range from 0 to 15.0 µM with a detection limit of 32.3 nM (R2 = 0.9978). The detection process is also confirmed through HPLC. The practical applicability of the probe is proved by a smartphone platform, TLC kit, plant tissue imaging, soil assay, tap, and lake water analysis with good recovery values (92.3-117%), and concentration-dependent live cell bioimaging PhSH from 5.0 to 15.0 µM. Therefore, the present probe is a robust candidate for monitoring PhSH levels in biological and environmental systems.

Discrimination of Pd-species by an ultra-fast, long wavelength and biocompatible fluorescent sensor: Its on-site kit assay, drug, and cancer/epithelial cell studies.

Extensive use of palladium in many catalysts and catalytic converters causes a high degree of pollution of water and soil resources. Therefore, there is an urgent need to develop rapid and sensitive palladium probes. Herein, a novel "turn-on" near-infrared (NIR) fluorescence and colorimetric probe for Pd has been designed on the basis of the deallylation of the probe, followed by the release of NIR emissive fluorophore through the Tsuji-Trost reaction. The probe can selectively discriminate between the oxidation states of Pd0 and Pd2+. Sensing results demonstrates that the probe has excellent selectivity, sensitivity, fast response time, NIR fluorescence, high biocompatibility, and low detection limit for the Pd detection over a series metal ion. The probe has been successfully applied in visualization of residual Pd content from water, soil, drug and living cell samples by fluorescence observation with the naked eye.

An effective benzothiazole-indandione D-π-A fluorescent sensor for "ratiometric" detection of hydrazine: Its solvatochromism properties and applications in environmental samples and living cells.

Hydrazine (N2H4) has high toxic impact and is widely used as raw material. As a result, it poses serious health risks and the following environmental pollution. Therefore, hydrazine's detecting techniques remains constantly under investigation. Herein, we report a ratiometric D-π-A fluorescent probe displaying NIR emission based on the ICT mechanism to detect N2H4. Other tested analytes have no observable interferences on the sensitivity and selectivity. The probe has sensitivity for N2H4 down to 1.29 µM with quick detection time (about 2.0 min). Moreover, the probe demonstrates solvatochromism with obvious emission varying from dull red to green, which implied high sensitivity to medium polarity. A portable smartphone platform for point-of-care detection of N2H4 in water samples is constructed. As a proof of real samples, the probe is successfully applied to sense N2H4 in water samples, to bioimage N2H4 in living cells and in plant cells with low cytotoxicity, suggesting significant potential application. This strategy opens up the preparation of new ratiometric fluorescence systems for bioimaging and environmental monitoring applications.

Fluorescence switchable sensor enabled by a calix[4]arene-Cu(II) complex system for selective determination of itraconazole in human serum and aqueous solution.

A switchable fluorescence sensor based on a calix (Monapathi et al., 2021) [4]arene:Cu2+ complex (FLCX/Cu) has been developed for the detection of itraconazole (ITZ) with high sensitivity and specificity. For the development of the sensor, the selective complexation of a fluorescent calix (Monapathi et al., 2021) [4]arene derivative (FL-CX) with the Cu2+ ion causing fluorescence quenching was utilized. In addition, the sensor properties of the FLCX/Cu prepared were investigated. For this purpose, various substances (selected anions, cations, and drugs) with which ITZ can be found together were studied in an aqueous solution. Limit of detection (LOD) and limit of quantification (LOQ) values were determined in the range of 1.00-60.0 µg/L as 3.34 µg/L and 11.1 µg/L for ITZ, respectively. Moreover, the real sample analyses were performed in human serum and tablet form. Furthermore, the effect of some possible serum contents on sensor performance was also studied. All these studies confirmed the development of a simple, precise, accurate, reproducible, highly sensitive, and very stable fluorescence sensor.

A NIR fluorescent sensor based on thiazoline-isophorone with low cytotoxicity in living cells for Hg2+ detection through ICT associated hydrogen bonding effect.

Mercury (Hg) is a toxic pollutant and may cause serious health and environmental threats even at low concentrations. Thus, sensitive, efficient, and accurate techniques for the detection of Hg2+ ions in biological systems are in particular demand. In the current paper, a new, red emitting fluorescence probe (THI) based on electron deficient dicyanovinyl, electron-rich diethylamino, and receptor thiazoline toward Hg2+ has been developed. It has been determined that the recognition behavior of the probe toward Hg2+ is reversible with S2-. The probe not only shows perfect selectivity toward Hg2+ with a low detection limit over a series of metal ions, but it also displays positive solvato-chromism among the tested solvents via modulation of intramolecular energy transfer from the diethylamino to a dicyanovinyl moiety. Furthermore, it has been shown that the probe can be applied as a fluorescent probe for visualizing Hg2+ in living HeLa cells through a confocal laser scanning microscope. Also, the probe THI has not shown any toxic effect in cervical cancer and epithelial cells. Thus, the probe demonstrates high promise for Hg2+ detection in biomarker screening, disease diagnosis, and clinical medicine with low cytotoxicity.

Cyanobiphenyl-spiropyrane and -hemicyanine conjugates for cyanide detection in organic/aqueous media through reverse ICT direction: Their practical applications.

Cyanide is one of the most known toxic substances. It is used in many industries and threats human health and environment through releasing with wastewater. Therefore, it is very important to detect its accurate amount, rapidly. Herein, turn-on and turn-off fluorescence sensors of hybrid cyanobiphenyl-spiropyrane and -hemicyanine were developed for the detection of CN- ions on the basis of nuchleophilic addition to indolium moiety. Detection behavior of the both probes toward a series of anions was investigated by means of fluorescence, UV-vis, NMR and TOF-MS techniques. The results obviously indicate that both probes show remarkable spectral changes and high selectivity toward CN- with respect to other tested anions. Cyanide levels in water samples up to 0.208 µM could be quantitatively detected as practical application. A smartphone imaging application was successfully constructed for CN- detection. Noticeably, production of cotton kids and PSF capsules revealed that the probe could be conveniently used for on-site measurement of cyanide without complicated instruments.

Nano-scale selective and sensitive optical sensor for metronidazole based on fluorescence quenching: 1H-Phenanthro[9,10-d]imidazolyl-calix[4]arene fluorescent probe.

It is crucial to determine and control the metronidazole (MET) ingredient in food and pharmaceuticals for human health and food safety. Even though many sensors have been previously reported to detect MET, there is still a need for a highly selective and sensitive, easy, fast, cost-effective sensor in this area. Herein, we report a fluorescent calix[4]arene derivative (PIMC) for highly selective and sensitive and facile and rapid MET detection based on fluorescence (FL) quenching. The highest FL quenching occurs when PIMC is exposed to MET solution at 400 nm (λex = 340). Owing to the quenching efficacy of MET linearly up to 5.5 × 104 nM was obtained a detection limit of 2.44 nM. Besides, interferences of other pharmaceuticals and ions on probe performance were investigated. The FL probe was successful in MET detection without the assistance of any separation techniques in a pharmaceutical sample (tablet) with an acceptable recovery of 101.3%. The applicability of the current probe as a paper-based sensor to MET detection has been successfully tested. As a result, the proposed probe presents a fast and suitable strategy to sensitive and selective detect MET and proves a good potential for practical applications, especially pharmaceutical preparations.

A switch-on xanthene-triphenylamine based fluorescent and colorimetric sensor for the detection of ultra-trace Hg2+ in food samples and living cells.

A novel colorimetric and fluorescent "switch-on" probe based on xanthene-triphenylamine was developed for detection of Hg2+, which threatens public health, food safety and the environment. The probe displayed superior colorimetric and fluorescent selectivity/sensitivity toward Hg2+ over a series of metal ions via Hg2+-triggered deprotection reaction. Hg2+ induced a ∼18-fold enhancement in emission intensity of probe TXS with yellow fluorescence (λem = 558 nm) and led to distinct color transition from light yellow to blue or yellow under daylight depending on solvent mixture. Detection parameters were optimized and examined for the influence that they exerted on the detection which involved the usage of the Box-Behnken design methodology. The sensing pathway was also examined theoretically by DFT and TD-DFT calculations. The probe was successfully utilized for the detection of Hg2+ in several food and water samples with good recoveries. Cell imaging studies demonstrated that the probe was suitable for Hg2+ detection in live cells.

Visual and quantitative detection of CN- ion in aqueous media by an HBT-Br and thiazolium conjugated fluorometric and colorimetric probe: Real samples and useful applications.

Cyanide released from mostly industrial production is a highly toxic chemical. Its heavy industrial use and transportation increase the danger of human exposure. Since it can often lead to rapid death, selective, sensitive and on-site and rapid monitoring techniques for the detection of cyanide are essential. Therefore, we report an efficient cyanide probe based on thiazolium conjugated HBT-Br derivative. It has striking color change toward cyanide blue to yellow under daylight or colorless to cyan under UV-light. Interaction modes of the probe are based on ESIPT and ICT processes. It is selectively able to react free aqueous cyanide with detection limit of 1.79 µM, lower than physiologically lethal blood levels, >20 µM. Smartphone assisted and test kit applications are able to detect cyanide, qualitatively. Moreover, real samples such as tap or lake water and apricot seeds including cyanide are successfully determined through the present probe. Therefore, the designed probe displays excellent practical potential toward cyanide.

Synthesis and cell imaging studies of an unusual "OFF-ON" fluorescent sensor containing a triazole unit for Al3+ detection via selective imine hydrolysis.

Monitoring excess Al3+ in biological and environmental samples is a major goal for scientists due to its harmful effects. Thus, the development of selective and convenient techniques for Al3+ recognition is essential. Herein, we present the design of a new fluorescent molecule, A1, for the recognition of Al3+. The results indicated that the recognition mechanism of the imine hydrolysis of A1 for Al3+ was completely different from those of other Al3+ probes that function based on chelation-enhanced fluorescence. A1 demonstrated a highly selective fluorescence response in the "OFF-ON" mode toward the presence of Al3+ among a pool of analytes including 18 cations with striking blue emission. Moreover, it has a prominent LOD value (0.117 µM), fast response time (10 s) and increasing linear emission relationship with Al3+ concentration (0-20.0 µM). Bioimaging studies in human colorectal carcinoma cells (DLD-1) and healthy epithelial cells (CCD-18Co) demonstrated excellent results. The performance of A1 toward Al3+ proved that it can be exploited as a signal tool for environmental and biological samples.

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

Cyanide is potentially hazardous and quickly acting chemical used in many fields of industry. Therefore, detection of cyanide is of main health concern due to its serious impacts on living organisms. In this context, we have developed rapid, low-cost and on-site sensory two molecules for the colorimetric and fluorogenic sensing of cyanide ion in aqueous samples and food samples. The prepared probes undergo distinct visual color change and exhibits selective fluorogenic turn-on or turn-off response towards cyanide. Competing anions have little or negligible effect on the detection of cyanide. The limit of detection for cyanide ion was calculated as low as 0.45 µM. Free receptors could be successfully regenerated by treating them with Ag+ ion. Moreover, a new visual colorimetric strip based on paper was fabricated with the pale yellow-to-pink color change signal. The fabricated test strips also demonstrated excellent selectivity towards cyanide ion without interfering possible fluoride and acetate ions. The smartphone-based technique which could directly read out the color value using a smartphone revealed an excellent potential for the cyanide detection without additional device.

Rapid and real-time detection of arginine enantiomers by QCM sensor having a Calix[4]arene receptor bearing asymmetric centers.

This paper describes the sensing studies of a chiral calix[4]arene receptor (5) having (R)-2-phenylglycinol moiety for arginine enantiomers (D-/L-arginine) by using Quartz Crystal Microbalance (QCM) technique. The initial experiments have revealed that the chiral calix[4]arene 5 coated QCM (CCC-QCM) sensor showed good sensing for arginine enantiomers, such that it has exhibited higher sensing towards D-arginine than that of L-arginine. It has been determined that the sensitivity, limit of detection values of CCC-QCM sensor for the D-/L-arginine solutions as 0.024/0.023 Hz/µM and 0.38/1.29 µM, respectively. On the other hand, the racemic mixture studies were optimized using the response surface methodology with central composite design. Consequently, it has been demonstrated that the QCM sensor modification with a calix[4]arene receptor bearing asymmetric centers provided rapid, real-time, sensitive and effective sensing of arginine enantiomers.

Fast and Reversible "Turn on" Fluorescent Sensors Based on Bisphenol-a for Zn2+ in Aqueous Solution.

Two novel bisphenol-A derivatives (R1 and R2) linked pyrene and napthylthiazole moieties were synthesized via condensation reaction, and positively applied for the selective recognition of Zn2+ ion in EtOH/H2O. Their optical properties were observed by using UV-vis and fluorescence measurements. R1 and R2 exhibited high selectivity and sensitivity towards Zn2+ over other metal ions. This fluorescence selectivity may be owing to inhibited excited-state intramolecular proton transfer (ESIPT) and photoinduced electron transfer (PET). The fluorescence titration analysis indicated detection limits of R1 and R2 for Zn2+ at 17.5 nM and 0.94 µM, respectively. Moreover, R1 and R2 were successfully applied to the detection of Zn2+ with different concentrations in water samples.

Selective chiral recognition of alanine enantiomers by chiral calix[4]arene coated quartz crystal microbalance sensors.

We describe the synthesis of new chiral calix[4]arene derivatives having (R)-1-phenylethylamine, (S)-1-phenylethylamine, (R)-2-phenylglycinol, and (S)-2-phenylglycinol moieties, and chiral recognition studies for enantiomers of some selected α-amino acid derivatives such as alanine, phenylalanine, serine, and tryptophan using a quartz crystal microbalance (QCM). Initial experiments indicated that the highest selective chiral recognition factor was 1.42 for alanine enantiomers. The sensitivity, limit of detection, and time constant for L-alanine were calculated as 0.028 Hz/µM, 60.9 µM, and 36.2 s, respectively. The results indicated that real-time, sensitive, selective, and effective chiral recognition of alanine enantiomers was achieved with a QCM sensor coated with a chiral calix[4]arene derivative having (R)-2-phenylglycinol moieties.

A reversible calix[4]arene armed phenolphthalein based fluorescent probe for the detection of Zn2+ and an application in living cells.

A reversible and easy assembled fluorescent sensor based on calix[4]arene and phenolphthalein (C4P) was developed for selective zinc ion (Zn2+ ) sensing in aqueous samples. The probe C4P demonstrated high selective and sensitive detection towards Zn2+ over other competitive metal ions. Interaction of Zn2+ with a solution of C4P resulted in a considerable increment in emission intensity at 440 nm (λex  = 365 nm) due to the suppression of photoinduced electron transfer (PET) process and the restriction of C=N isomerization. The binding constant (Ka ) of C4P with Zn2+ was calculated to be 4.50 × 1011  M-2 and also the limit of detection of C4P for Zn2+ was as low as 0.108 µM (at 10-7  M level). Moreover, the fluorescence imaging in the human colon cancer cells suggested that C4P had great potential to be used to examine Zn2+ in vivo.