A sensitive TICT Probe exhibiting ratiometric fluorescence repose to detect hydrazine in solution and gas phase

Advances in Optical Probes for the Detection of Hydrazine in Environmental and Biological Systems

Hydrazine, as a crucial raw material in the fine chemical industry, plays an indispensable role in fuel, catalyst, pesticide and drug synthesis. Due to its good water solubility and high toxicity, hydrazine can cause irreparable damage to water and soil in the environment, and it can also be released by taking certain drugs, which brings potential risks to human health. Therefore, it is vital to develop a method that can specifically detect hydrazine in the environment and in vivo. As an effective analysis and detection tool, fluorescence probe has attracted extensive attention in recent years. In this review, we summarized and classified hydrazine fluorescence probes based on various reaction mechanisms, and discussed their structures and applications in the past ten years. At least, we briefly outline the challenges and prospects in this field.

A fluorescent probe based on triphenylamine with AIE and ICT characteristics for hydrazine detection

A fluorescent probe MAM based on triphenylamine scaffold was synthesized. The electron donating group 4-methoxyphenyl and the electron acceptor dicyanoethylene were introduced on the triphenylamine scaffold to form a D-π-A fluorescent probe. The probe MAM exhibited the typical aggregation-induced emission (AIE) and intramolecular charge transfer (ICT) characteristics with the bright orange-red fluorescent emission in high water fraction (f_w ≥ 50%) and negligible emission in low water fraction. The probe MAM could detect hydrazine (N₂H₄) in DMSO-tris-HCl (10 mM, pH7.4, v/v, 3:1) with high selectivity and sensitivity. The specific reaction between MAM and hydrazine and the formation of the hydrazone blocked the ICT process, and the system emitted the cyan fluorescence which could be easily observed by naked eyes. The limit of detection (LOD) was 0.196 μM (6.25 ppb), which is lower than the US Environmental Protection Agency standard (10 ppb). The test strips prepared by the probe MAM could realize the convenient and rapid detection of N₂H₄ solution and vapor. The application of MAM in actual water samples and cells was investigated, and the results showed that MAM could sense N₂H₄ in environmental and biological aspects with potential application prospects.

A novel ESIPT-based fluorescent probe with dual recognition sites for the detection of hydrazine in the environmental water samples and in-vivo bioimaging

Hydrazine (N₂H₄), an important chemical intermediate, has been widely used in industrial production and agricultural life, but it has also caused environmental pollution. A novel ESIPT-based fluorescent probe with dual recognition sites, 2-(benzothiazole-2-yl)-1,4-imphenyl bis 4-bromobutyric acid (BRBA), was developed to selectively detect N₂H₄ under complex conditions. BRBA exhibits accurate detection for N₂H₄ with a good linear relationship ranging from 0 to 150 μM, and the LOD can reach 0.1 μM. Importantly, taking advantage of low cytotoxicity and a large Stokes shift, BRBA can be utilized to monitor environmental water samples and successfully applied to imaging HeLa cells and zebrafish.

A dual-ratiometric mitochondria-targeted fluorescent probe to detect hydrazine in soil samples and biological imaging

Hydrazine (N₂H₄) is carcinogenic, extremely toxic, and induces serious environmental contamination and physiological dysfunction; however, it is widely used as an industrial material. Hence, the development of a simple and effective analytical method to detect N₂H₄ detection in both environmental and biological sectors is warranted. In this work, an intramolecular charge transfer (ICT)-based fluorescent probe 1, namely (Z)- 1-(4-acetoxybenzyl)- 4-(1-cyano-2-(7-(diethylamino)- 2-oxo-2 H-chromen-3-yl)vinyl)pyridin-1-ium, was designed for dual-excitation (420 and 600 nm, excitation separations >160 nm), near infrared (NIR)-emissive, and ratiometric fluorescent detection of N₂H₄. The sensing behavior of probe 1 for N₂H₄ detection was shown to be available over a wide pH range, and detection limits of 68 nM and 569 nM were achieved at excitation wavelengths of 420 and 600 nm, respectively. In addition, probe 1 was successfully used to image mitochondrial N₂H₄ in living cells and zebrafish. Furthermore, the probe was also capable of determining hydrazine signals in test strips and environmental soil.

Ratiometric fluorescence chemodosimeter for hydrazine in aqueous solution and gas phase based on Quinoline-Malononitrile

The widespread use of Hydrazine (N₂H₄) in many areas of the chemical industry, brings potential risks to human health and environmental pollution. To detect N₂H₄ effectively, a simple ratio fluorescence probe (QMM), designed and synthesized through Vilsmeier reaction and Knoevenagel reaction, was prepared for the specific response of N₂H₄ based on the irreversible chemical reaction. The ratiometric fluorescence chemodosimeter displayed a response for hydrazine with high selectivity, sensitivity and anti-interference ability. The measured detection limit is 38.30 nm (0.122 ppb), which is far lower than the maximum allowable level of the U.S. Environmental Protection Agency (10 ppb). Moreover, test paper and TLC plates loading QMM had been made, which could be utilized to detect hydrazine both in aqueous solution samples and in gas phase samples. Thus QMM could serve as an easily manufactured, low-cost, efficient and portable solid-state optical probe to detect hydrazine in field measurements.

Design, synthesis and mechanistic studies of a TICT based fluorogenic probe for lighting up protein HSA

Human serum albumin (HSA) in blood serves as an important biomarker for clinical diagnosis, and fluorescence sensing method has attracted extensive attention. In this work, a small organic molecule probe, YS8, involving twisted intramolecular charge transfer (TICT) characteristic, was designed and investigated to detect HSA. YS8 kept silent state in fluorescence under physiological conditions, but the encapsulation of YS8 in the hydrophobic subdomain IB region of HSA inhibited the TICT state and produced a clear light-up fluorescent signal. Especially, YS8 was demonstrated to be an efficient fluorogenic probe to discriminate HSA from other proteins including the bovine serum albumin (BSA). Moreover, YS8/HSA complex could be applied in fluorescence imaging in living cells and is also useful in the study of artificial fluorescent protein (AFP).

Coumarin 1,4-enedione for selective detection of hydrazine in aqueous solution and fluorescence imaging in living cells

Hydrazine is a widely used but highly toxic chemical reagent, and the development of a fluorescent probe for hydrazine detection is very meaningful. In this study, a novel coumarin-derived fluorescent probe containing a 1,4-enedione moiety for hydrazine detection was developed. The recognition of hydrazine with the probe brings about obvious fluorescence enhancement over other environmentally relevant ions and amine-containing species. The limit of detection for hydrazine is 2.7×10^-8 M in aqueous solution. The fluorescence enhancement was ascribed to the cyclization reaction of the 1,4-enedione moiety of the probe and hydrazine which form a six-membered pyridazine ring and intramolecular charge transfer (ICT) mechanism. The mass spectrometry (MS), nuclear magnetic resonance (NMR) analysis and theoretical calculations confirmed the recognition produced. The probe can be used to determine trace hydrazine in real water samples. More importantly, the probe also showed good potential in detecting hydrazine by imaging of living HeLa cells.

A time-dependent density functional theory study of a fluorescent probe to detect hydroxyl radicals: Inhibiting the twisted intramolecular charge-transfer process

Due to the relevance to excited-state processes, sensing mechanisms of fluorescent probes were difficult to study directly by experimental methods. This work investigated theoretically the sensing mechanism of a reported bifunctional fluorescent probe to detect intracellular hydroxyl radicals and their environmental viscosity (J. Am. Chem. Soc. 2019, 141, 18301). Calculations were performed at the B3P86/TZVP/SMD level using density functional theory and time-dependent density functional theory. The transition from the ground-state (S₀) to the first singlet excited state (S₁) was calculated to have the largest oscillation strength for the probe. The wavelength that corresponded to the S₀-S₁ vertical excitation energy (427 nm) agreed well with the maximum absorption band at 400 nm in the ultraviolet-visible spectra. Theoretical results showed that the probe had two distinct geometries in the S₀ and S₁ states, respectively. This difference was caused by the different distributions of frontier molecular orbitals that were involved in the S₀-S₁ transition and corresponds to a twisted intramolecular charge transfer. The S₁-state potential energy curve of the probe molecule confirmed that the twisted intramolecular charge transfer could proceed spontaneously with a potential barrier of only 12.20 kJ/mol. This result provided an irradiative approach for the probe molecule to dissipate the S₁-state energy, which explained its fluorescence quenching. In contrast, the hydroxyl oxidation reaction changed frontier molecular orbitals of the probe molecule, which made its S₁ state a local S₁ state with a strong fluorescence emission. Precisely due to the mechanism, the hydroxyl radicals could be detected by changes in the fluorescence signal of the probe molecule.

A TICT + AIE based fluorescent probe for ultrafast response of hypochlorite in living cells and mouse

Hypochlorite (HClO/ClO^-), an important reactive oxygen species (ROS), plays a significant role in the human immune system. Thus, developing a fast and efficient method for detecting ClO^- is quite necessary. Herein, we designed and synthesized a fluorescent probe TPB-CN based on twisted intramolecular charge transfer (TICT) and aggregation-induced emission (AIE) characteristics. The probe could respond to ClO^- with an ultrafast response velocity (<2 s). The detection limit was calculated to be 6.198 nM. In addition, probe TPB-CN was successfully applied for detecting ClO^- in living cells and mouse.

TICT fluorescent probe for Al3+: Sequential detection of PPi, ATP and ADP in semi-aqueous medium and real-life applications

A ditopic Schiff base ligand, H₂L has been synthesized and characterized by all spectroscopic techniques. It is highly selective and specific towards Al³⁺ in semi aqueous medium (DMF/H₂O mixture) by exhibiting a drastic increase in the fluorescence intensity. The emission studies, spectroscopic data, life time and quantum yield results have been used to understand its binding mode, explore its specificity and establish its efficacy. The intensity difference is remarkable in physiological pH range. Due to its reversible behavior this ditopic fluorescent chemosensor can be used multiple times to make it cost effective. Detection limit for this chemosensor was found to be 0.65 μM. Experiments with TLC plates show that it can be used as a practical and portable sensor for studying environmental samples in real life. The L-Al³⁺ complex generated in the solution acts as a sensor to sequentially detect pyrophosphate groups present in inorganic pyrophosphates, ATP and ADP among other anions by turning off the fluorescence. Inhibit logic gate and its corresponding truth table has been developed to aid in further exploiting its multidimensional applications.

A practical pH-compatible fluorescent sensor for hydrazine in soil, water and living cells

The excellent water solubility of hydrazine (N₂H₄) allows it to easily invade the human body through the skin and respiratory tract, thereby damaging human organs and the central nervous system. To realize the monitoring of N₂H₄ effectively, first, coumarin was used to construct an inner alicyclic ring as the reaction site, extending the conjugation and strengthening the rigidity of the probe Co-Hy to improve its luminescence performance and enhance its ability to resist acids and alkalis. Second, we introduced a carboxyl group at the ortho position of the inner alicyclic ring to improve the water solubility of Co-Hy, and its strong electron pulling effect increased the activity of the reaction site. Spectroscopy experiments showed that Co-Hy featured excellent water solubility, high pH resistance (pH 4-11), excellent selectivity, fast analysis speed (within 5 minutes), and a low detection limit toward N₂H₄ (69 nM, 2.2 ppb). In addition, test-strip, spray, and cell-imaging experiments confirmed the outstanding application potential of Co-Hy for convenient N₂H₄ analysis in a variety of environments.