Pyridinic-N-rich carbon dots in IFE-based Turn-off Fluorometric detection of nerve agent Mimic- Diethyl chlorophosphate and multicolor cell imaging

Fluorometric sensors for the detection of nerve agent mimics have received a lot of interest nowadays due to their high sensitivity and selectivity, ease of operation, and real-time monitoring. Pyridinic-N-rich carbon dots (NCDs) prepared through microwave-assisted pyrolysis of l-Malic acid and urea have been explored first time in this work as a novel turn-off fluorescent probe for the sensitive and selective detection of diethyl chlorophosphate (DCP), a nerve agent mimic. The as-prepared carbon dots contained a large amount of pyridinic nitrogen on their surface, which can modulate the photoluminescence properties of the NCDs. The blue emissive NCDs possessed both excitation wavelength-dependent and independent emission behavior. The detection of DCP was premised on quenching of the fluorescence emission intensity of NCDs in the presence of similar chemical reagents (e.g., trimethyl phosphate, triethyl phosphate, triethyl phosphonoacetate, triphenyl phosphate, diphenyl phosphate, tributyl phosphate). Fluorescence quenching of the NCDs in the presence of DCP has been attributed to the inner filter effect (IFE). From the linear Stern-Volmer plot (R² = 0.9992), the limit of detection (LOD) was found to be 84 μM for sensing DCP for the concentration ranging between 3 and 15 mM. The biocompatibility of NCDs was assessed through cytotoxicity assay on MDA-MB-231 breast cancer cells. Fluorescence imaging demonstrated that NCDs have low cytotoxicity and can be employed successfully in cell imaging.

Dual-State Fluorescent Probe for Ultrafast and Sensitive Detection of Nerve Agent Simulants in Solution and Vapor

The development of fluorescent probes for detecting nerve agents has been the main concern focus of research because of their lethal toxicity for humans. Herein, a probe (PQSP) based on the quinoxalinone unit and the styrene pyridine group was synthesized and could visually detect a sarin simulant diethyl chlorophosphate (DCP) with excellent sensing properties in solution and solid states. Interestingly, PQSP showed an apparent intramolecular charge-transfer process by catalytic protonation after reacting with DCP in methanol, accompanied with the aggregation recombination effect. The sensing process was also verified by nuclear magnetic resonance spectra, scanning electron microscopy, and theoretical calculations. In addition, the papered test strips of loading probe PQSP exhibited an ultrafast response time within 3 s and high sensitivity with a limit of detection of 3 ppb for the detection of DCP vapor. Therefore, this research provides a designed strategy for developing the probes with dual-state emission fluorescence in solution and solid states for detecting DCP sensitively and rapidly, which can be fabricated as chemosensors to visually detect nerve agents in practice.

Uncovering the dependence of ESIPT behaviors and fluorescence properties of two new benzothiazole-based fluorophores on solvent polarity: A TD-DFT study

We have studied the spectral features and excited state intramolecular proton transfer (ESIPT) processes of 2-(2',4'-dihydroxyphenyl)benzothiazole (OHBT) and 2-(2'-hydroxy-5'-chlorophenyl)benzothiazole (CHBT) using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). To consider the impact of solvent polarity and intermolecular hydrogen bond (H-bond) on the ESIPT behavior and photophysical properties, four solvents including toluene (TL), tetrahydrofuran (THF), methanol (MeOH) and dimethylsulfoxide (DMSO) were used. The simulated absorption and fluorescence wavelengths of OHBT and CHBT are well consistent with the experimental values. According to the results of structures, electron density and infrared (IR) vibrational frequencies, we found that the intramolecular H-bonds in OHBT/CHBT and OHBT-MeOH/CHBT-MeOH are strengthened in the first singlet excited state (S₁), which will be benefical to the ESIPT process. The potential energy curves (PECs) verified that the ESIPT processes in OHBT/CHBT and OHBT-MeOH/CHBT-MeOH can take place much easier because of their lower energy barrier. The influences of solvent polarity on ESIPT behaviors and photophysical properties of OHBT and CHBT are summarized below. As the solvent polarity becomes stronger from TL to DMSO, the energy gaps enlarges a little, the maximum absorption and fluorescence peaks at normal form red-shift slightly, and the strengths of H-bond in S₁ state become weaker, which makes the ESIPT process occur much harder. The formation of intermolecular H-bond between OHBT/CHBT and MeOH is conducive to promote the ESIPT process of OHBT/CHBT.

Killing two birds with one stone: phosphorylation by a tabun mimic and subsequent capture of cyanide using a single fluorescent chemodosimeter

In the presence of the tabun mimic diethylcyanophosphonate (DECP), a fluorescent bifunctional coumarin–enamine chemodosimeter is first phosphorylated and subsequently attacked by the released cyanide ions.

A bisphenol based fluorescence chemosensor for the selective detection of Zn2+ and PPi ions and its bioluminescence imaging

A bisphenol based fluorescence "turn-on" chemosensor 4,4'-(propane-2,2-diyl)bis(2-((E)-(2-(benzo[d]thiazol-2-yl)hydrazineyldene)methyl)phenol) (BHMP) has been synthesized and its sensing behavior was tested towards various ionic species. The chemo-sensing behavior of BHMP has been established through absorption, fluorescence, NMR, and mass spectroscopic techniques. The probe BHMP selectively detects zinc ions over other metal ions and the resulting BHMP + Zn²⁺ ensemble serves as a secondary probe for the detection of pyrophosphate (PPi) anion specifically over other anions. The spectroscopic studies reveal the fluorescence enhancement of BHMP in association with Zn²⁺ ions was quenched in the presence of pyrophosphate (PPi) anions. A probable mechanism of this selective sensing behavior was described on the basis of "OFF-ON-OFF" strategy for detection of both cations and anions. Moreover, the biological applicability of the chemosensor BHMP was examined via cell imaging studies.

A novel near-infrared turn-on fluorescent probe for the detection of Fe3+ and Al3+ and its applications in living cells imaging

In this study, a new hemicyanidine-based colorimetric-fluorescent probe L has been synthesized and characterized by X-ray single crystal diffraction, NMR, HRMS and other technologies. The probe L serves as a "turn-on" probe for the detection of Fe³⁺ and Al³⁺ ions in DMF-HEPES system with a high sensitivity and an excellent selectivity. The probe L manifesting the color of the solution containing L turns red on the addition of Fe³⁺, and turns pink on the addition of Al³⁺. The fluorescence turn-on detection of Fe³⁺ and Al³⁺ ions is attributed to the photo-induced electron transfer (PET) process and the exertion of the chelation-enhanced fluorescence effect (CHEF) mechanism. The results of thin layer silica gel plate coloration experiments also present the same characteristics. Additionally, we further demonstrate that the probe L exhibit good cell permeability and could be employed to monitor Fe³⁺ and Al³⁺ ions in the living cells.

A naphthalimide-based fluorescent probe for the highly sensitive and selective detection of nerve agent mimic DCP in solution and vapor phase

The fluorescent probe for DCP displays excellent selectivity and sensitivity with a low detection limit of 5.5 nM in DMF.

A Selective Fluorescence Turn-On Probe for the Detection of DCNP (Nerve Agent Tabun Simulant)

Diethylcyanophosphonate (DCNP) is a simulant of Tabun (GA) which is an extremely toxic chemical substance and is used as a chemical warfare (CW) nerve agent. Due to its toxic properties, monitoring methods have been constantly come under the spotlight. What we are proposing within this report is a next-generation fluorescent probe, DMHN1, which allows DCNP to become fully traceable in a sensitive, selective, and responsive manner. This is the first fluorescent turn-on probe within the dipolar naphthalene platform induced by ESIPT (excited state intramolecular proton transfer) suppression that allows us to sense DCNP without any disturbance by other similar G-series chemical weapons. The successful demonstrations of practical applications, such as in vitro analysis, soil analysis, and the development of an on-site real-time prototype sensing kit, encourage further applications in a variety of fields.

Fluorescein derived Schiff base as fluorimetric zinc (II) sensor via 'turn on' response and its application in live cell imaging

A novel Schiff base L composed of fluorescein hydrazine and a phenol functionalized moiety has been designed and prepared via cost-effective condensation reaction. The L is utilized for selective sensing of Zn²⁺ over other environmental and biological relevant metal ions in aqueous alcoholic solution under physiological pH range. The binding of Zn²⁺ to the receptor L is found to causes ~23 fold fluorescence enhancement of L. The 1:1 binding mode of the metal complex is established by combined UV-Vis, fluorescence, and HRMS (high-resolution mass spectroscopy) spectroscopic methods. The binding constant (K_a) for complexation and the limit of detection (LOD) of Zn²⁺ is calculated to be 2.86 × 10⁴ M^-1 and 1.59 μM, respectively. Further photophysical investigations including steady-state, time-resolved fluorescence analysis and spectral investigations including NMR (nuclear magnetic resonance), IR (infrared spectroscopy) suggest introduction of CHEF (chelation enhance fluorescence) with the suppression of CN isomerization and PET (photo-induced electron transfer) mechanism for the strong fluorescent response towards Zn²⁺. Finally, the sensor L is successfully employed to monitor a real-time detection of Zn²⁺ by means of TLC (thin layer chromatography) based paper strip. The L is used in the cell imaging study using African green monkey kidney cells (Vero cells) for the determination of exogenous Zn²⁺ by Immunofluorescence Assay (IFA) process.

The salen based chemosensors for highly selective recognition of Zn2+ ion

Two novel salen based chemosensors have been successfully synthesized. UV-vis absorption, fluorescence emission spectroscopy and cyclic voltammetry (CV) were exploited to investigate their recognition toward various metal ions, including Na⁺, K⁺, Mg²⁺, Al³⁺, Zn²⁺, Ag⁺, Pb²⁺, Co²⁺, Li⁺, Ba²⁺, Ca²⁺, Cd²⁺, La³⁺, Cu²⁺ and Mn²⁺ ions. The results indicated that the sensor L1 and L2 exhibited highly selective and sensitive recognition for Zn²⁺ ions. The binding stoichiometry ratio of L1-Zn²⁺/L2-Zn²⁺ were recognized as 4:1 by the method of Job's plot. Meanwhile, this investigation is confirmed by ¹H NMR. These results indicated that L1 and L2 can be applied as chemosensor for the detection of Zn²⁺ ion.

Fast and Ultrasensitive Detection of a Nerve Agent Simulant Using Carbazole-Based Nanofibers with Amplified Ratiometric Fluorescence Responses

In this work, we report the fast and ultrasensitive detection of a nerve agent simulant in the gas phase, diethyl chlorophosphate (DCP), by using carbazole-based nanofibers from 1. When exposed to trace DCP, the formed pyridine-phosphorylated product in 1 nanofibers can cause amplified ratiometric fluorescence responses, i.e., amplified fluorescence quenching via quenching excitons within the diffusion length of 1 nanofibers and simultaneously amplified turn-on fluorescence responses via harvesting excitons within the diffusion length to give the intramolecular charge transfer (ICT) emission at a longer wavelength. On the basis of these amplified ratiometric fluorescence responses, detection of DCP with fast response (ca. 3 s), ultrasensitivity (4 ppb), and improved selectivity is achieved.

An ESIPT based naphthalimide chemosensor for visualizing endogenous ONOO− in living cells

An ESIPT based naphthalimide chemosensor with high sensitivity and selectivity for visualizing endogenous ONOO⁻ in living cells was developed.

A hexa-quinoline basedC3-symmetric chemosensor for dual sensing of zinc(ii) and PPi in an aqueous mediumviachelation induced “OFF–ON–OFF” emission

“OFF–ON–OFF” luminescence switching behavior of a hexa-quinoline based sensor towards Zn²⁺and PPi in an aqueous buffer medium is demonstrated.

Fluorescent carbon quantum dots chemosensor for selective turn-on sensing of Zn2+ and turn-off sensing of Pb2+ in aqueous medium and zebrafish eggs

Synthesized fluorescent carbon quantum dots exhibited selective turn-on sensing of Zn²⁺ and turn-off sensing of Pb²⁺ ions in aqueous media and zebrafish eggs.