Attractive benzothiazole-based fluorescence probe for the highly efficient detection of hydrogen peroxide

A near-infrared fluorescent probe with thiadiazole unit as key skeleton for ICT and ESIPT mechanism and effective detection of Cu2

Fluorescent probe L-I was synthesized to demonstrate that 1,3,4-thiadiazole is an attractive moiety and could be utilized as positive hydrogen bond acceptor for excited state intramolecular proton transfer (ESIPT) processes, guider of electrons movement for intramolecular charge transfer (ICT) process and identify group for mental ions. Furthermore, dicyanoisophorone framework was employed to improve the fluorescence characteristics and near-infrared (NIR) fluorescent emission at 695 nm accompanied by a Stoke's shift as large as 260 nm was obtained. L-I could selectively detect Cu2+ over other analytes taking advantages of high sensitivity, fast response within 30 s and low detection limit (0.026 μM). More important, L-I exhibited good performance for detection of Cu2+ in actual water samples, food products, traditional Chinese medicine and for cell imaging which demonstrates practical significance in the fields of environmental monitor, food safety and biotechnology.

A fluorescent probe for detecting H2O2 and delivering H2S in lysosomes and its application in maintaining the redox environments

Hydrogen peroxide (H2O2) is a reactive oxygen species (ROS) that can be used as a marker for the occurrence of oxidative stress in the organism. Lysosomes serve as intracellular digestive sites, and when the concentration of H2O2 in them is abnormal, lysosomal function is often impaired, leading to the development of diseases. Hydrogen sulfide (H2S) acts as a gaseous signaling molecule that scavenges H2O2 from cells and tissues, thereby maintaining the redox environment of the body. However, most of the reported hydrogen peroxide fluorescent probes so far can only detect H2O2, but cannot maintain the intracellular redox environment. In this paper, an H2O2 fluorescent probe LN-HOD with lysosomal targeting properties was designed and synthesized by combining the H2O2 recognition site with a naphthylamine fluorophore via a thiocarbamate moiety. The probe has the advantages of large Stokes shift (110 nm), high sensitivity and good H2S release capability. The probe LN-HOD can be used to detect H2O2 in cells, zebrafish and plant roots. In addition, LN-HOD detects changes in the concentration of H2O2 in plant roots when Arabidopsis is stressed by cadmium ion (Cd2+). And through its ability to release H2S, it can help to remove excess H2O2 and maintain the redox environment in cells, zebrafish and plant roots. The present work provides new ideas for the detection and assisted removal of H2O2, which contributes to the in-depth study of the cellular microenvironment in organisms.

A near-infrared fluorescent probe for tracking endogenous and exogenous H2O2 in cells and zebrafish

H2O2 is an important signaling molecule in the body, and its levels fluctuate in many pathological sites, therefore, it can be used as a biomarker for early diagnosis of disease. Since the environment in vivo is extremely complex, it is of great significance to develop a probe that can accurately monitor the fluctuation of H2O2 level without interference from other physiological processes. Based on this, we designed and synthesized two new near-infrared H2O2 fluorescent probes, LTA and LTQ, based on the ICT mechanism. Both of them have good responses to H2O2, but LTA has a faster response speed. In addition, the probe LTA has good biocompatibility, good water solubility, and a large Stokes shift (95 nm). The detection limit is 4.525 μM. The probe was successfully used to visually detect H2O2 in living cells and zebrafish and was successfully used to monitor the changes in H2O2 levels in zebrafish due to APAP-induced liver injury.

ESIPT-based probes for cations, anions and neutral species: recent progress, multidisciplinary applications and future perspectives

Fluorescent and colourimetric probes for small analytes (cations, anions and neutral molecules) have drawn significant attention in recent years. These probes interact with analytes and induce spectral change due to the variations in the photo-physical properties of the fluorophore/chromophore used. Among several photo-physical mechanisms, ESIPT (excited state intramolecular proton transfer) based probes are more advantageous due to their photo-physical properties viz. solvent polarity effect, large spectral shift with multi-channel fluorescence, high quantum yield etc. In recent years, ESIPT-based probes have shown several promising applications, especially monitoring small analytes in biological samples, smartphone app-assisted heavy metal detection in environmental samples, inkless writing, anti-counterfeiting applications etc. Therefore, this review is dedicated to recently reported ESIPT-based probes for small analytes. We have highlighted the organic units responsible for the ESIPT mechanism, their photo-physical parameters, selectivity and sensitivity properties and recent advances in their applications.

Multiple fluorescence and hydrogen peroxide-responsive properties of novel triphenylamine-benzothiazole derivatives

A novel fluorescent dye molecule - triphenylamine (TPA)-benzothiazole (BZT) - based on excited state intramolecular proton transfer (ESIPT) was prepared by the Suzuki coupling reaction. The photophysical property assay indicates that BZT-TPA appeared in distinguishable colors in mixed solvents with different water contents. Moreover, BZT-TPA exhibited observable AIE behavior. On this basis, a fluorescent probe BZT-TPA-BO was synthesized for detecting H2O2. This probe molecule was found to have excellent selectivity, rapid response, and good linear relationship (R2 = 0.989) for detecting H2O2 in aqueous medium. Through DFT calculation, fluorescence spectrum, nuclear magnetic titration and HR-MS, the mechanism of recognition of H2O2 by the probe BZT-TPA-BO is proposed. In addition, the probe BZT-TPA-BO to some extent exhibited better performance for detecting exogenous H2O2 in HeLa cells.

A new lysosome-targeted fluorescent probe for hydrogen peroxide based on a benzothiazole derivative

As an important member of reactive oxygen species, hydrogen peroxide (H2O2) plays a key role in oxidative stress and cell signaling. Abnormal levels of H2O2 in lysosomes can induce damage or even loss of lysosomal function, leading to certain diseases. Therefore, real-time monitoring of H2O2 in lysosomes is very important. In this work, we designed and synthesized a novel lysosome-targeted fluorescent probe for H2O2-specific detection based on a benzothiazole derivative. A morpholine group was used as a lysosome-targeted unit and a boric acid ester was chosen as the reaction site. In the absence of H2O2, the probe exhibited very weak fluorescence. In the presence of H2O2, the probe showed an increased fluorescence emission. The fluorescence intensity of the probe for H2O2 displayed a good linear relationship in the concentration range of H2O2 from 8.0 × 10-7 to 2.0 × 10-4 mol·L-1. The detection limit was estimated to be 4.6 × 10-7 mol·L-1 for H2O2. The probe possessed high selectivity, good sensitivity and short response time for the detection of H2O2. Moreover, the probe had almost no cytotoxicity and had been successfully applied to confocal imaging of H2O2 in lysosomes of A549 cells. These results illustrated that the developed fluorescent probe in this study could provide a good tool for the determination of H2O2 in lysosomes.

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.

An ESIPT-based ratiometric fluorescent probe for detecting H2O2 in water environment and biosystems

The outbreak of the COVID-19 has resulted in a great increase in the use of H₂O₂ disinfectant, which is listed as one of the commonly used disinfectants for COVID-19 by the U.S. Environmental Protection Agency. However, excessive use of H₂O₂ disinfectant can threaten human health and damage the water environment. Therefore, it's of great importance to detect H₂O₂ in aquatic environments and biological systems. Herein, we proposed a novel ESIPT ratio fluorescent probe (named probe 1) for detecting H₂O₂ in water environment and biosystems. Probe 1 emits blue fluorescence as the introduction of the phenylboronic acid disrupts the ESIPT process. After reacting with H₂O₂, the phenylboronic acid is oxidatively removed, and the ESIPT process is restored, which makes the fluorescence emission wavelength red-shifted. Probe 1 exhibited a short response time, high sensitivity, and a large Stokes shift to H₂O₂. Importantly, it has been successfully used to detect H₂O₂ not only in actual water samples, but also endogenous and exogenous H₂O₂ in living cells. The characteristics of probe 1 have a wide range of applications in environmental and biological systems.

A Cascade Enzyme System Integrating Peroxidase Mimic with Catalase for Linear Range Expansion of H2 O2 Assay: A Mechanism and Application Study

Peroxidase (POD) Nanozyme-based hydrogen peroxide (H₂ O₂ ) detection is popular, but hardly adapt to high concentration of H₂ O₂ owing to narrow linear range (LR) and low LR maximum. Here, a solution of combining POD and catalase (CAT) is raised to expand the LR of H₂ O₂ assay via decomposing part of H₂ O₂ . As a proof of concept, a cascade enzyme system (rGRC) is constructed by integrating ruthenium nanoparticles (RuNPs), CAT and graphene together. The rGRC-based sensor does perform an expanded LR and higher LR maximum for H₂ O₂ detection. Meanwhile, it is confirmed that LR expansion is closely associated with apparent K_m of rGRC, which is determined by the relative enzyme activity between CAT and POD both in theory and in experiment. At last, rGRC is successfully used to detect high concentration of H₂ O₂ (up to 10 mm) in contact lens care solution, which performs higher assay accuracy (close to 100% recovery at 10 mm of H₂ O₂ ) than traditional POD nanozymes. This study brings up a kind of POD/CAT cascade enzyme system and provides a new concept for accurate and facile H₂ O₂ detection. Additionally, it replenishes a new enzyme-substrate model of achieving the same pattern with competitive inhibition in enzyme reactions.

A red-emissive benzothiazole-based luminophore with ESIPT and AIE natures and its application for detecting and imaging hypochlorous acid

A new "ESIPT + AIE" based dye of benzothiazole with red emission and a large Stokes shift was constructed by combining 2-(2'-hydroxyphenyl)benzothiazole as the ESIPT unit and α-cyanostilbene as the AIE unit. The compound BACN was found to be a ideal HClO chemosensor, and presented palpable fluorescence and colorimetric responses toward HClO via the HClO-trigged oxidation cleavage of the ethylene bridge activated by the electron withdrawing cyano group. BACN was capable of recognizing HClO rapidly (12 s) and sensitively under physiological conditions, with good selectivity over other biologically pertinent substances. Thanks to strong red emission (λ_em = 606 nm) and large Stokes shift (213 nm) resulted from the combination of ESIPT and AIE effects, it was successfully utilized for the recognition of exogenous and endogenous HClO in living HeLa cells.