A highly sensitive ratiometric fluorescence probe for sensing and imaging sulfite in food samples and living cells

In this work, a ratiometric and chromogenic fluorescent probe 1 was synthesized for the detection of SO32-. The probe 1 at PBS (10 mM, pH = 7.4) presented a marked emission band at 661 nm. Upon addition of SO32- ions, a highly emissive adduct with a marked fluorescence at 471 nm were obtained through a Michael addition. The probe 1 displayed a noticeable fluorescence ratiometric response with a large shift (190 nm) in emission wavelength. The probe can quantitatively detect SO32- with high specificity, fast response (within 130 s) as well as low detection limit (13 nM), and a large Stokes shift (139 nm). Fluorescence imaging of HeLa cells indicated that 1 could be used for monitoring the intrinsically generated intracellular SO32- in living cells by ratiometric fluorescence imaging. Furthermore, 1 could be application in real water and sugar samples with high sensitivity and good recoveries.

Dual-responsive fluorescence probe for measuring HSO3- and viscosity and its application in living cells and real foods

Microenvironmental indicators in organisms drive the operation of different physiological functions. In contrast, disruption of microenvironmental homeostasis is often closely associated with various pathological processes. A novel dual-response fluorescent probe based on hemicyanine dye (HT-Bzh) was designed and synthesized for the detection of HSO3- and viscosity changes. The probe not only provides high sensitivity (limit of detection = 0.2526 μM) for the detection of HSO3- using the Michael addition reaction, but also allows the observation of fluorescence emission at 528 nm and thus the monitoring of viscosity changes through hindering of the twisted intramolecular charge transfer (TICT) mechanism. Additionally, dual-response probe has been successfully used to image living cells and detect real food samples. As a new designed tool, HT-Bzh shows excellent anti-interference capability and biocompatibility, which makes it have application potential in other biological systems and in-vivo imaging.

Reversible colorimetric and NIR fluorescent probe for sensing SO2/H2O2 in living cells and food samples

Preservative sulfur dioxide (SO₂) and bleach hydrogen peroxide (H₂O₂) were widely used in the food industry, at the same time, they were also a redox pair in biological systems. Therefore, the reversible sensing SO₂/H₂O₂ was of great significance in food safety and biology. In this paper, a colorimetric and NIR fluorescent dual channels response probe (DCA-Bba) for SO₂/H₂O₂ based on chromene-barbiturate was developed. DCA-Bba exhibited a rapid and sensitive recognition of SO₂, and the adduct DCA-Bba-HSO₃^- could detect H₂O₂ in PBS (with 10 % DMSO, v/v, pH 7.4) solution. The reversible response of DCA-Bba was implemented by HSO₃^- involved 1,4-addition and H₂O₂ induced elimination reaction. DCA-Bba showed a strong red fluorescence based on the intramolecular charge transfer (ICT) process, after the recognition of SO₂, the fluorescence of the adduct was quenched based on the photoinduced electron transfer (PET) process. And importantly, DCA-Bba had been applied for imaging SO₂/H₂O₂ redox cycles in living cells, as well as could detect the levels of SO₂ in white sugar, biscuit, Chinese liquor and red wine samples.

A mitochondria-targetable fluorescent probe for sulfur dioxide detection and visualisation in living cells

Sulfur dioxide (SO₂) is a one of reactive sulfur species (RSS) that plays significant roles in many physiological processes. While abnormal levels of SO₂ in mitochondria have been related to various diseases. Hence, developing suitable fluorescent probe for monitoring SO₂ is significant in living organisms. In this research, we designed and synthesized a mitochondrial-target probe Mito-NPH featuring the graft of a strong electron-withdrawing 4-pyridiniumylacrylonitrile unit to an electron-donating naphthalenic unit that intramolecular charge transfer (ICT) process happened. The probe Mito-NPH underwent a nucleophilic addition of HSO₃^-/SO₃^2-to give fluorescent emission signal change from red to blue and exhibited specific response toward HSO₃^-/SO₃^2-over other analytes. Moreover, Mito-NPH showed ultrafast response rate (within 10 s) for HSO₃^-. Importantly, cell imaging results demonstrated that the probe can sense endogenous SO₂ in mitochondria.

A novel heptamethine cyanine photosensitizer for FRET-amplified photodynamic therapy and two-photon imaging in A-549 cells

In this study, a new cyanine-based photosensitizer Cy-N-Rh was developed for photodynamic therapy. Based on fluorescence resonance energy transfer (FRET) mechanism, utilizing the absorption of the donor rhodamine (Rh), the acceptor heptamethine cyanine unit (Cy) was indirectly excited to produce singlet oxygen (¹O₂). The efficiency of energy transfer from the donor Rh to the acceptor Cy was 78.5%. Meanwhile, the singlet oxygen yield of Cy-N-Rh (Φ_Δ = 12.00%) was much higher than that of the acceptor Cy (Φ_Δ = 4.35%) without FRET. Moreover, the dual cation gave Cy-N-Rh with excellent mitochondria-targeting ability with Pearson's correlation coefficients of 0.90 and 0.91, respectively. In the MTT test, Cy-N-Rh had low dark cytotoxicity with cell survival rate above 90% and high photo cytotoxicity with cell survival rate below 40%. The cell apoptosis assay also demonstrated the role of the photosensitizer Cy-N-R visually. More importantly, Cy-N-Rh fulfilled two-photon excitation fluorescence imaging under the 800 nm femtosecond laser. All results indicate that this design strategy provides a new method for the development of higher-level cyanine photosensitizers.

A near-infrared emitted fluorescence probe for the detection of biosulfite in live zebrafish, mouse and real food samples

Bisulfite (HSO₃^-) has been widely used as an important food additive in daily life. Furthermore, a normal amount of HSO₃^- plays a significant role in biological systems. However, excessive intake of HSO₃^- will lead to a variety of diseases. Therefore, it is of great significance to develop an efficient fluorescent probe that can be used for detection of HSO₃^- in biological systems and food samples. In this work, a near-infrared (NIR) emitted fluorescent probe (SZY) based on hemicyanine dye was successfully synthesized and applied to detect HSO₃^- in several food samples and live animals. The proposed nucleophilic addition sensing mechanism of SZY towards HSO₃^- has been confirmed by ¹H NMR titration, high resolution mass spectrometry (HR-MS) and density functional theory (DFT) theoretical computation. The HSO₃^--induced nucleophilic reaction with α,β-unsaturated C=C binding of SZY results in the dramatic decline of the UV-vis absorption and remarkable quenching of the fluorescence emission. SZY features the advantages of near infrared emission (centered at 720 nm), high water solubility (in 98% aqueous solution), fast response time (50 s), large Stokes shift (244 nm) and low cytotoxicity. The probe SZY was successfully applied to image of HSO₃^- in live nude mouse and adult zebrafish. Semi-quantitatively analyzing the HSO₃^- level by "naked eye" in several food samples including canned fruit, white wine, white sugar and jasmine tea drinks has been realized by the colorimetric method.

Insight into sulfur dioxide and its derivatives metabolism in living system with visualized evidences via ultra-sensitive fluorescent probe

Sulfur dioxide (SO₂) and its derivatives have long been considered as hazardous environmental pollutants but commonly used as food additives in safe dose range. They also could be produced from biological metabolism process of sulfur-containing amino acids. However, their physiological roles remain extremely obscure mainly due to lack of efficient tools for monitoring and imaging strategy establishment. Furthermore, most of current studies of this aspect focus on novel probe design or just imaging them rather than on the ins and outs. Therefore, there is a high significance of establishing highly sensitive detection strategy for monitoring SO₂ derivatives in living systems, food and environment. Herein, we design a fluorescent probe MS-Bindol for sensitively detecting SO₂ derivatives with a low detection limit (0.2 nM). We have established an imaging strategy for investigation of SO₂ derivatives metabolism in living cells and zebrafish, providing visualize evidences and verified that SO₂ derivatives could be synthetized from thiosulfate and glutathione(GSH) and be hardly consumed by using sulfite oxidase inhibitors (ferricyanide or arsenite). Moreover, the probe also exhibits excellent practicability in food as well as environmental samples. Our studies may help biologist for better understanding SO₂ derivatives metabolism and deeply explore their physiological roles in biological systems.

Optimizing the framework of indolium hemicyanine to detect sulfur dioxide targeting mitochondria

Endogenous sulfur dioxide (SO₂) is mainly produced by the enzymatic reaction of sulfur-containing amino acids in mitochondria, which has unique biological activity in inflammatory reaction, regulating blood pressure and maintaining the homeostasis of biological sulfur. It is more and more common to detect monitor SO₂ levels by fluorescence probe. In recent years, the indolium hemicyanine skeleton based on the D-π-A structure has been widely used in the development of fluorescent sensors for the detection of SO_2. However, subtle changes in the chemical structure of indolium may cause significant differences in SO₂ sensing behavior. In this article, we designed and synthesized two probes with different lipophilicities to further study the relationship between the structure and optical properties of hemicyanine dyes. On the basis of previous studies, the structure of indolium hemicyanine skeleton was optimized by introducing -OH group, so that MC-1 and MC-2 had the best response to SO₃^2- in pure PBS system. In addition, the lipophilicity of MC-2 was better than that of MC-1, which enabled it to respond quickly to SO₃^2- and better target mitochondria for SO₂ detection. Most importantly, the low detection limits of MC-1 and MC-2 conducive to the detection of endogenous SO₂. This work provided an idea for developing SO₂ fluorescent sensors with excellent water solubility and low detection limit.

Development of a ratiometric nitric oxide probe with baseline resolved emissions by an ESIPT and rhodol ring opened-closed integrated two-photon platform

In recent years, reflecting the degree of cellular inflammation through in situ monitoring of nitric oxide using fluorescence sensing has received much attention due to many merits such as non-invasiveness and easy operation. In particular, two-photon excitation microscopy can significantly improve the imaging resolution and visualization time. In the meantime, a ratiometric-based nitric oxide fluorescent sensor can avoid the interference of many factors, including light source intensity, solvent scattering degree, solvent color, solvent viscosity, probe distribution, and instrument performance, and improve the accuracy of the result. However, the mutual interference of two emission peaks is still an issue restricting the development of this field. In this work, the Rh-NO-F dye obtained by modifying the rhodol dye with benzothiazole exhibited excited state intramolecular proton transfer (ESIPT) in the closed ring state. In the open ring state, however, the emission wavelength can be significantly red-shifted by increasing the degree of dye conjugation. By introducing o-phenylenediamine, the recognition domain of NO, we successfully designed and synthesized a ratiometric two-photon NO fluorescent probe, Rh-NO-P, which showed a 154 nm increase in the maximum emission wavelength before and after the response and almost no interference between the two emission peaks. Confocal imaging showed that the probe could achieve in situ detection of exogenous NO fluctuations in cells. The probe was also successfully applied to detect the changes in NO content during wound healing in mice.

Water-soluble AIE-active fluorescent organic nanoparticles for ratiometric detection of SO2 in mitochondria of living cells

We report a water-soluble AIEgen (TYDL) to be self-assembled into fluorescent organic nanoparticles (TYDLs) for specific sensing of SO2 in living hepatoma cells. It is demonstrated that TYDLs were suitable...

An isocamphanyl-based fluorescent "turn-on" probe for highly sensitive and selective detection of Ga3+ and application in vivo and in vitro

A novel fluorescent probe 2-(4-(diethylamino)-2-hydroxybenzylidene)-N-(2,3,3-trimethylbicyclo[2.2.1]heptan-2-yl)hydrazinecarbothioamide (HT) was prepared in this study by a condensation reaction. HT has been confirmed to possess high specificity toward Ga³⁺ over other metal ions (including Al³⁺ and In³⁺) via a distinct fluorescence light-up response. Moreover, HT exhibited good detection performances for Ga³⁺ including high selectivity, excellent anti-interference ability, a wide working pH range, and good reversibility. The association constant and limit of detection (LOD) were calculated to be 5.34 × 10³ M^-1 and 1.18 × 10^-6 M, respectively. The detection mechanism of HT toward Ga³⁺ was proposed and confirmed by ¹H NMR analysis, HRMS analysis, and DFT calculations. A simple test strip-based portable detecting device and a molecular INHIBIT logic circuit were established for improving its practical applicability. Furthermore, the desirable sensing performance of HT for Ga³⁺ was successfully reconfirmed in MCF-7 cells and zebrafish.

A near-infrared fluorescent probe targeting mitochondria for sulfite detection and its application in food and biology

Sulfur dioxide (SO2) is the main air pollutant in the environment, causing great harm to human health. Abnormal SO2 levels are usually associated with some respiratory diseases, cardiovascular diseases, and neurological disorders (even brain cancer). Therefore, monitoring SO2 levels is helpful to better understand its special physiological and pathological role. Although many fluorescent probes for SO2 have been reported, many of them were not ideal for in vivo imaging due to the short emission wavelength. In this work, a near-infrared fluorescent probe NIR-BN with emission wavelength of 680 nm was constructed by conjugating the benzopyrylium moiety and 6-hydroxy-2-naphthaldehyde. NIR-BN had high selectivity and rapidity for SO2 detection. In addition, the detection limit of NIR-BN was relatively low, which can be used for the determination of sulfite in different sugar samples with high accuracy. Of course, due to the excellent spectral and structural properties of NIR-BN, we have applied NIR-BN to the detection of SO2 in biological systems.