Capillary electrophoretic determination of thiosulfate, sulfide and sulfite using in-capillary derivatization with iodine

A near-infrared ratiometric fluorescent probe for the sensing and imaging of sulfur dioxide derivatives in living systems

As a reactive sulfur species, sulfur dioxide (SO2) and its derivatives play crucial role in various physiological processes, which can maintain redox homeostasis at normal levels and lead to the occurrence of many diseases at abnormal levels. So, the development of a suitable fluorescent probe is a crucial step in advancing our understanding of the role of SO2 derivatives in living organisms. Herein, we developed a near-infrared fluorescent probe (SP) based on the ICT mechanism to monitor SO2 derivatives in living organisms in a ratiometric manner. The probe SP exhibited excellent selectivity, good sensitivity, fast response rate (within 50 s), and low detection limit (1.79 µM). In addition, the cell experiment results suggested that the SP has been successfully employed for the real-time monitoring of endogenous and exogenous SO2 derivatives with negligible cytotoxicity. Moreover, SP was effective in detecting SO2 derivatives in mice.

Dual-Response Functionalized Mitochondrial Fluorescent Probe for a Double Whammy Monitoring of Hypochlorite and Sulfur Dioxide in Heat Shock via Time Scales

Heat shock seriously affects the normal functioning of an organism and can lead to damage and even death in severe cases. To prevent or treat heat shock-related diseases, we require a better understanding of the mechanism of thermocytotoxicity. Here, we designed a functionalized dual-response fluorescent probe (HCy-SO2-HClO) that could individually or simultaneously detect hypochlorous acid (HClO) and sulfur dioxide (SO2) without interfering with each other and achieved the simultaneous tracing of both during the heat shock process for the first time. The introduction of the sulfonate group greatly increased the water solubility of the probe. Furthermore, the probe could effectively accumulate in the mitochondrial region. HCy-SO2-HClO could respond to HClO and SO2 within 10 s and 20 min, respectively, realizing a double whammy detection of both on the time scale. HCy-SO2-HClO exhibited high specificity and sensitivity for HClO and SO2. The highly biocompatible probe HCy-SO2-HClO successfully achieved the detection of endogenous and exogenous SO2 and HClO in living cells and in zebrafish. Moreover, the simultaneous detection of HClO and SO2 in heat shock cells and mouse intestines was realized for the first time. This probe has achieved the detection of dual markers, which enhanced the accuracy and precision of disease detection and could serve as an effective research tool to prevent heat stroke-related diseases.

Treatment of complex sulfur-containing solutions in ammonia desulfurization ammonium sulfate production by ultrasonic-assisted ozone technology

In this work, the cause of abnormal color in ammonium sulfate products formed by flue gas desulfurization is revealed by investigating the conversion relationship between different sulfur-containing ions and their behavior in a sulfuric acid medium. Both thiosulfate (S2O32-) and sulfite (SO32- ＆ HSO3-) impurities affect the quality of ammonium sulfate. The S2O32- is the main reason for the yellowing of the product due to the formation of sulfur impurities in concentrated sulfuric acid. To address the yellowing of ammonium sulfate products, a unified technology (US/O3), using ozone (O3) and ultrasonic waves (US) simultaneously, is exploited to remove both thiosulfate and sulfite impurities from the mother liquor. The effect of different reaction parameters on the degree of removal of thiosulfate and sulfite is investigated. The synergistic effect of ultrasound and ozone on ion oxidation is further explored and demonstrated by the comparative experiments with O3 and US/O3. Under the optimized conditions, the thiosulfate and sulfite concentration in the solution is 2.07 and 5.93 g/L, respectively, and the degree of removal is 91.39 and 90.83%, respectively. The product obtained after evaporation and crystallization is pure white and meets the national standard requirements for ammonium sulfate products. Under the same conditions, the US/O3 process has apparent advantages, such as saving reaction time compared with the O3 process alone. Introducing an ultrasonically intensified field improves the generation of oxidation radicals ·OH, 1O2, and ·O2- in the solution. Furthermore, the effectiveness of different oxidation components in the decolorization process is studied by adding other radical shielding agents using the US/O3 process supplemented with EPR analysis. The order of the different oxidation components is O3(86.04%) > 1O2(6.53%) > •OH(4.45%) > •O2-(2.97%) for the oxidation of thiosulfate, and it is O3(86.28%) > •OH(7.49%) > 1O2(4.99%) > •O2-(1.25%) for the oxidation of sulfite.

Rapid determination of free sulfur dioxide in wine and cider by capillary electrophoresis

A novel method for the determination of "true" free sulfur dioxide (SO₂) in wine and cider was developed using capillary electrophoresis with direct ultraviolet-visible spectrophotometric detection (CE-UV/vis). Free SO₂ was measured in model solutions with different SO₂-binding agents present (α-ketoglutarate, pyruvate, acetaldehyde, glucose, fructose, and malvidin-3-glucoside) as well as a variety of white and red wines and ciders. The CE method was compared to three conventional methods for measuring free SO₂, the Ripper method, Aeration-Oxidation (AO), and pararosaniline by discrete analyzer (DA). While some statistically significant differences (p<0.05) were found between the four methods in unpigmented model solutions and samples, the values generally agreed. In the presence of anthocyanins in model solution and red wines, free SO₂ values found by CE were significantly lower than the other three methods (p<0.05). The difference in values found by Ripper and CE correlated strongly with anthocyanin content (R² = 0.8854) and even more strongly when accounting for polymeric pigments (R² = 0.9251). The results in red ciders differed from those in red wines, while the CE measured significantly lower free SO2 values than the other three methods, the difference in free SO₂ values measured by CE and Ripper correlated more closely with anthocyanin concentration (R² = 0.8802) than absorbance due to bleachable pigment (R² = 0.7770). The CE method was found to be rapid (4 min/injection), sensitive (LOD=0.5 mg/L, LOQ=1.6 mg/L free SO₂ in wine, 0.8 and 2.8 mg/L, respectively, in cider), robust, and repeatable (average RSD = 4.9%) and did not suffer from the issue of over-reporting free SO₂ in pigmented samples often observed with currently accepted methods.

Rapid detection of hydrogen sulfide in vegetables and monosodium glutamate based on perylene supramolecular aggregates using an indicator displacement assays strategy

Hydrogen sulfide (H₂S) has been clearly identified as a hazardous chemical pollutant that seriously affects food safety and human health. In order to develop a rapid, accurate and efficient H₂S tracking method, this work propose a strategy based on indicator displacement assays (IDA). A water-soluble histidine-modified perylene diimide fluorescent probe was synthesized by a one-step method, and the probe can form supramolecular aggregates in the presence of Cd²⁺. There will be a fluorescence transformation of probe, caused by the change of the state of aggregation and adjusted by various concentration of S^2-, which can achieve the fluorescence detection of S^2-. The limit of detection is as low as 0.41 µmol/L. Particularly worth mentioning is that the probe in this work can be recycled for at least 5 times, which is environmentally friendly and economical. Finally, this method was applied in three kinds of vegetables and monosodium glutamate samples.

A dual-positive charges strategy for sensitive and quantitative detection of mitochondrial SO2 in cancer cells and tumor tissue

Mitochondrial sulfur dioxide (SO₂) correlates with various activities of the development and progression of cancer. However, the specific biological function of mitochondrial SO₂ in cancerous cells remains amphibolous. Therefore, it is of great significance and urgency to develop a rapid and accurate method to monitor the dynamic fluctuations of mitochondrial SO₂ in cancer cells and tumor tissue. Herein, in this work, we introduce a "dual-positive charges" strategy for simultaneously enhancing the sensitivity and mitochondrial targeting ability of SO₂ detection in cancer cells for the first time. For proof of concept, the dual positive charged probe DCP was rationally designed and synthesized based on chromenoquinoline fluorophore. Correspondingly, we also synthesized single positive charged SO₂ probe MCP as controls. As expected, the detection limit of dual positive charged DCP for SO₂ detection was 0.06 μM, which was 7-fold lower than that of the single positive charged probe MCP. Besides, DCP showed a higher mitochondrial co-localization coefficient in cancer cells and it could distinguish cancer cells (HeLa) and normal cells (L929) in co-incubated system. In a word, the evidence suggested that the implementation of dual-positive charges strategy greatly improved the sensitivity to SO₂ response and the specificity of mitochondrial targeting in cancer cells. Finally, DCP was successfully applied to monitor SO₂ fluctuation in cancer cells, tumor tissue and living zebrafish. Thus, this work provides a powerful tool to investigate the role of mitochondrial SO₂ in cancer and other related diseases.

Fluorogenic Detection of Sulfite in Water by Using Copper(II) Azacyclam Complexes

Copper(II) azacyclam complexes (azacyclam = 1,3,5,8,12-pentaazacyclotetradecane) containing naphthyl or dansyl subunits can be prepared by template synthesis involving proper sulfonamide derivatives as locking fragments. The macrocyclic complexes are very poorly emissive due to the fluorescence-quenching behavior displayed by Cu²⁺ ions. However, the fluorescence can be recovered as a result of the decomposition of the complexes, which induces the release of free light-emitting subunits to the solution. This reaction takes place very slowly in neutral water but its rate is increased by the presence of sulfite. Therefore, [Cu(azacyclam)]²⁺ derivatives have been investigated as simple chemical probes for the fluorogenic detection of sulfite both on laboratory and real samples. Preliminary tests performed on samples of white wine provided sulfite concentration values that are in agreement with those obtained by a standard analytical method.

A ratiometric water-soluble fluorescent probe for the detection of sulfur dioxide derivative in sinusitis mice model

Sulfur dioxide (SO₂) plays an extremely important role in the basic processes of physiology and pathology. As an antioxidant, SO₂ can maintain the redox homeostasis in the cell. Excessive inhalation of SO₂ would lead to irreparable respiratory damage, resulting in respiratory diseases, neurological disorders, and even cardiovascular disease. Thus, it is urgent to exploit an excellent way to monitor SO₂ derivatives in biological system. Herein, we design a water-soluble ratiometric fluorescent probe to fast detect the level of SO₂ derivatives in living cells in vivo. The probe displays obvious fluorescence signal at long wavelength, which is helpful for imaging of biological system. After respond to SO₂ derivatives, the fluorescence signal at 465 nm increases rapidly due to the Michael addition reaction is triggered, further causing the disruption of large conjugated system. The probe exhibits high selectivity and fast respond to SO₂ derivatives, which can be able to sensitive and real-time monitoring of SO₂ derivatives level in living cells. Moreover, the probe reveals a low detection limit and a great linear relationship to SO₂ derivatives. Based on the negligible cytotoxicity and good biocompatibility of the probe, which is employed to detect exogenous and endogenous SO₂ derivatives in living cells. In addition, it is also served as a potential chemical tool to detect SO₂ derivatives in mice model of sinusitis.

Novel styrylbenzimidazolium-based fluorescent probe for reactive sulfur species: Selectively distinguishing between bisulfite and thiol amino acids

In this study, a new fluorescent probe containing dicyanovinyl moiety has been designed and synthesized. Fluorescent probe based on styrylbenzimidazolium derivative was reported for the effective detection of bisulfite and distinguish it from biothiols by exploiting dicyanovinyl group as the recognition site. The photophysical properties of the novel styrylbenzimidazolium derivative were assessed by determination of absorption and fluorescence spectra, fluorescence quantum yield, and fluorescence lifetime. Its spectroscopic behavior towards various analytes has been evaluated in aqueous media at a pH of 7.4. The highest increase in fluorescence intensity of compound 5 in the presence of different analytes was observed for sodium bisulfite and the limit of detection was estimated to be 0.25 μM. The styrylbenzimidazolium dye was applied to detect bisulfite in various wine sample using fluorimetry. Finally, the ability of this novel probe to detect HSO₃^- in red wine samples was evaluated.

An indirect electrochemical method for aqueous sulfide determination in freshwaters using a palladium chelate as a selective sensor

Sulfide anion is a highly toxic and corrosive compound and its presence above the threshold concentrations (i.e. μmol L^-1) in freshwaters may indicate environmental pollution. Besides, the increase in sulfide concentration results in modifications of the organoleptic proprieties of water and air. Many analytical methodologies have been designed for aqueous sulfide quantification, however, due to the high reactivity and instability of sulfide, the pursue of a simple, sensitive, selective, and portable analytical method is still a current demand. In this study, an indirect electrochemical method for the determination of sulfide based on its interaction with a palladium complex - bis(2-aminobenzoate) palladium(II) - acting as a selective chemosensor is described. The reaction leads to the demasking of the electroactive ligand 2-aminobenzoic acid (i.e. anthranilic acid) and square wave voltammetry is employed to monitor its concentration using a glassy carbon electrode (GCE). Experimental conditions were optimized and the reaction was performed in Britton-Robinson (BR) buffer at pH 5 for 4 min, providing the higher magnitude of the analytical signal. A linear relation (r² > 0.99) from 3 to 30 μmol L^-1 of sulfide was obtained with a limit of detection of 0.10 μmol L^-1. Recovery experiments using freshwater samples spiked with sulfide revealed overall satisfactory results for the limit concentration levels permitted by regulatory agencies. Therefore, the proposed methodology shows advantages in terms of portability, selectivity, sensitivity, low-cost, and easiness-to-use enabling monitoring of sulfide in a variety of waters.

A ratiometric fluorescent probe for the rapid and specific detection of HSO3 - in water samples

Hydrosulphite (HSO₃ ^- ), as a common and important chemical reagent, is widely used in everyday life, however excessive use and abuse of HSO₃ ^- can cause potential harmful effects on the environment and in biological health. In this paper, we describe the design and preparation of a colorimetric and ratiometric fluorescence probe for the visual detection of HSO₃ ^- (excitation wavelengths were, respectively, 336 nm and 520 nm). This method showed some advantages including simple preparation, high selectivity, fast response, and significant colour and fluorescence ratio (F₄₅₀ /F₅₉₄ ) changes in the presence of HSO₃ ^- . In addition, this probe was used successfully for the detection of HSO₃ ^- in real water samples and showed a good recovery rate range.

The development of a biotin-guided and mitochondria-targeting fluorescent probe for detecting SO2 precisely in cancer cells

Mitochondrial sulfur dioxide (SO₂) is very closely associated with various activities of cancer cell. However, the specific physiological and pathological roles of mitochondrial SO₂ in cancer cells are still not well defined. Lacking a powerful molecular tool for detecting mitochondrial SO₂ in cancer cells precisely is an essential factor. So it is urgent to develop a specific method for monitoring mitochondrial SO₂ in cancer cells. Herein, we described a distinct cancer cell-specific fluorescent probe NS for detecting mitochondrial SO₂ accurately in cancer cells. Biotin, possessing of high affinity for cancer cells, was decorated into probe to provide its cancer cell-targeting property. Moreover, the positive charge hemicyanine group was used to anchor mitochondria selectively. A series of spectral results from concentration titration, dynamics and selectivity experiments showed that NS had high sensitivity, fast response and high selectivity to SO₂. These properties render NS ability for detecting SO₂ in living cells. In biological imaging, the achievements in detecting exogenous and endogenous SO₂ displayed the probe had favorable response to SO₂ in living cells with well biocompatibility. Significantly, assisted by competitive experiments with excess biotin, NS demonstrated distinct cancer cell-targeting for detecting mitochondrial SO₂. Furthermore, NS could locate mitochondria specially and detect mitochondrial SO₂ in cancer cells by co-localization. Moreover, NS can trace SO₂ in zebrafish with long wavelength emission. Therefore, NS can achieve in tracing mitochondrial SO₂ selectively in cancer cells. It would be a powerful tool for well defining the physiological and pathological roles of mitochondrial SO₂ in cancer cells.

Colorimetric and fluorescent dual-mode strategy for sensitive detection of sulfide: Target-induced horseradish peroxidase deactivation

Environmental pollution caused by sulfide compounds has become a major problem for public health. Hence, accurate detection of sulfide anions (S^2-) level is valuable and vital for environmental monitoring and protection. Here, we report a new colorimetric/fluorescent dual-mode sensor for the determination of S^2- based on the inhibition of enzyme activity and the unique optical properties of produced 2,3-diaminophenazine (DAP), thus making the analytical results more convincing. In this strategy, horseradish peroxidase (HRP) enzyme is used for catalyzing the H₂O₂-mediated oxidation of o-phenylenediamine (OPD) to produce DAP, and the color changed to bright yellow and produced orange yellow fluorescence. But the presence of S^2- could cause the deactivation of HRP, which decreased the amount of DAP and consequently resulted in a substantial SPR band fading and an evident fluorescence quenching simultaneously. The mechanism of S^2- sensor was examined by combining the UV-vis absorption spectra, fluorescence spectra and electrospray ionization mass spectrometry analysis. Under optimal conditions, the colorimetric and fluorescent linear responses of the proposed method exhibited a wide linear range from 2.5 nM-7.5 μM with ultralow detection limits of 1.2 nM and 0.9 nM, respectively. Some potential interferents (such as F^-, Cl^-, Br^-, I^-, SO₄^2-, SO₃^2-, SCN^-, H₂PO₄^-, HPO₄^2-, Ac^-, NO₃^-, CO₃^2-) in real samples showed no interference. Moreover, the proposed method offered advantages of simple, low-cost instruments and rapid assay without the utilization of nanomaterials and has been successfully applied to determine S^2- content in lake water samples with satisfying recoveries over 97.6%. More importantly, the present S^2- sensor not only afforded a new optical sensing pattern for bioanalysis and environment monitoring, but also extends the application field of HRP-catalyzed OPD-H₂O₂ system.

Hemicyanine based naked-eye ratiometric fluorescent probe for monitoring lysosomal pH and its application

Lysosome as the typical acidic organelle involved in many biological processes, the dysfunction of its pH would alter many diseases. Small-molecule fluorescent probe has been considered as vital tool for monitoring pH fluctuation in living cells. Herein, a hemicyanine based ratiometric fluorescent probe was synthesized, namely, 2,3-trimethy-3-[2-(dimethyl-amino-4-yl) vinyl]-3H-benzo[e]indole (BiDL), for rapidly detection pH under acidic conditions. BiDL exhibited ratio fluorescence emission (F_534nm/F_622nm) characteristic with pK_a 4.25. BiDL showed good linearly response in pH 3.4-4.82, indicating that the probe can be used for quantitative detection pH. The probe also displayed large Stokes shift (112 nm/201 nm) under neutral and acidic conditions, respectively, which could effectively reduce the excitation interference. BiDL had excellent cell membrane permeability, good photo-stability and low toxicity in living cells. The dual-channel confocal fluorescent microscopic ratiometric imaging application of pH in HeLa cells and lysosome were achieved successfully, indicating that BiDL has good potential for investigating lysosome-relevant pathological and physiological processes.

Imidazo[1,5-α]pyridine-based fluorescent probe with a large Stokes shift for specific recognition of sulfite

By taking advantage of the intramolecular charge transfer (ICT) process, we presented a novel fluorescent probe IPY-SO₂ based on imidazo[1,5-α]pyridine derivative for detecting SO₃^2- with a low detection limit (70 nM). Combining its favorable turn-on fluorescence feature (75-fold), rapid response (5 min), high selectivity, large Stokes shift (174 nm) and low cytotoxicity, IPY-SO₂ was successfully applied to imaging SO₃² in living MCF-7 cells and zebrafish.

A mitochondria-targeting ratiometric fluorescent probe for the detection of sulfur dioxide in living cells

A mitochondria-targeting ratiometric fluorescent probe was developed for the detection of sulfur dioxide in living cells.

Recent progress in the small-molecule fluorescent probes for the detection of sulfur dioxide derivatives (HSO3-/SO32-)

Sulfur dioxide (SO₂) had been recognized as an environmental pollutant produced from industrial processes. SO₂ is water soluble and forms hydrated SO₂ (SO₂·H₂O), bisulfite ion (HSO₃^-), and sulfite ion (SO₃^2-) upon dissolution in water. SO₂ could be also produced endogenously from sulfur-containing amino acids l-cysteine in mammals. Endogenous SO₂ can maintain the balance of biological sulfur and redox equilibrium in vivo, regulate blood insulin levels and reduce blood pressure. Excess intake of exogenous SO₂ can result in respiratory diseases, cardiovascular diseases and neurological disorders. As a result, fluorescent probes to detect HSO₃^-/SO₃^2- have attracted great attention in recent years. Herein, a general overview was provided with the aim to highlight the typical examples of the HSO₃^-/SO₃^2- fluorescent probes reported since 2010, especially those in the past five years. We have classified HSO₃^-/SO₃^2- fluorescent probes through different chemical reaction mechanisms and wish this review will give some help to the researchers in this field.

A fluorescent probe for colorimetric detection of bisulfite and application in sugar and red wine

A new fluorescent probe made from (E)-2-(benzo[d]thiazol-2-yl)-3-(6-hydroxynaphthalen-2-yl) acrylonitrile (Probe 1) was synthesized for the determination of bisulfite concentrations in real food samples (red wine and sugar). Adding bisulfite to a Probe 1 solution caused a marked decrease in fluorescence intensity and a visual color change from yellow to light yellow. This distinct color response indicates that Probe 1 could be used as a visual sensor for bisulfite. Probe 1 can detect bisulfite quantitatively in the range 0-400 μM with a detection limit of 0.10 μM. This makes Probe 1 a convenient signaling instrument for determining bisulfite levels in sugar and red wine samples.

Colorimetric Detection of Sulfide Anions via Redox-Modulated Surface Chemistry and Morphology of Au-Hg Nanorods

A new colorimetric assay for the detection of sulfide anions with high sensitivity and selectivity is reported, utilizing Au-Hg alloy nanorods (Au-HgNRs) as probe. Au-HgNRs were prepared by modifying gold nanorods (AuNRs) with reducing agent and mercury ions. In an aqueous solution with sulfide anions, the formation of mercuric sulfide due to redox reaction between the amalgams and sulfide anions greatly changed the surface chemistry and morphology of the Au-HgNRs, leading to a red shift of the localized surface plasmon resonance (LSPR) absorption peak, accompanied by a change in colorimetric response. A good linear relationship was obtained between the LSPR peak wavelength shift and concentration of sulfide anion in the range of 1 × 10⁻⁵−1 × 10⁻⁴mol/L. The selectivity of this method has been investigated by other anions. The colorimetric sensing system successfully detected sulfide in wastewater from leather industry.

Highly sensitive and selective sulfite sensors based on solution-gated graphene transistors with multi-walled carbon nanotube functionalized gate electrodes

Due to the potential toxicity of sulfite as widely used food additive, there is urgent need for the development of low-cost, rapid and convenient sensors for sulfite detection. Toward this end, highly sensitive and selective sulfite sensors based on solution gated graphene transistors (SGGTs) was innovatively developed. The performance of the device was significantly improved through the functionalization of the gate electrode with multi-walled carbon nanotubes (MWCNTs). We found that the MWCNT modified SGGT sensor showed an ultra-low detection limit of 30 nM toward sulfite. In addition, we also demonstrated that the SGGT-based sulfite sensor was capable of detecting sulfite content in practical liquor samples with high recovery rate. Considering its low-cost and easy-fabricating features, we believe that the SGGT-based sensor with appropriate functionalization may be applied as a highly potential platform for ultra-sensitive detection of a broad range of important analytes in practical samples for food safety purpose.

A real-time ratiometric fluorescent probe for imaging of SO2 derivatives in mitochondria of living cells

A real-time ratiometric fluorescent probe (IN-CZ) for highly selective detection of sulfite was designed and synthesized, which is based on modulating the intramolecular charge transfer (ICT) of the hemicyanine dye platform. The mechanism of using the probe is mainly through the Michael addition that occurs between IN-CZ and sulfite with a detection limit of 2.99 × 10⁻⁵ M. IN-CZ displays a fast response (within 1 minute) and is highly selective for SO₃²⁻/HSO₃⁻ over ROS, biologically relevant ions, biological mercaptans and other reactive species. More importantly, IN-CZ was suitable for ratiometric fluorescence imaging in living cells, by real-time monitoring of SO₃²⁻/HSO₃⁻ changes in mitochondria targeted in living cells.

A real-time ratiometric fluorescent probe (IN-CZ) for highly selective detection of sulfite was designed and synthesized, which is based on modulating the intramolecular charge transfer of the hemicyanine dye platform.

Regulating peroxidase-like activity of Pd nanocubes through surface inactivation and its application for sulfide detection

The peroxidase-like activity of Pd nanocubes is regulated by the formation of surface PdS layers, which has been applied for sulfide assay in environmental water samples.

A rapid cell-permeating turn-on probe for sensitive and selective detection of sulfite in living cells

A rapid cell-permeating probeNJUXJ-1was introduced for sensitive and selective detection of sulfite in living cells.

Rapidly Responsive and Highly Selective Fluorescent Probe for Bisulfite Detection in Food

The new fluorescent probe 4-hydroxy-3-((2E,4E)-5-phenylpenta-2,4-dienoyl)-2H-chromen-2-one (probe 1) was designed and synthesized for selective detection of sulfite. The fluorescence intensity of the probe was decreased only in the presence of HSO₃^-; all other anions assessed resulted in an increased fluorescence response. Hence, probe 1 acts as a highly selective sensor for HSO₃^-. This sulfite sensitivity can also be readily monitored visually, as once treated with sulfite the solution shows a marked color change from yellow to colorless. Moreover, probe 1 can be conveniently used as a signal tool to determine the HSO₃^- levels in various sugar samples.

A ratiometric fluorescence probe for selective detection of sulfite and its application in realistic samples

A new fluorescent probe 7-(diethylamino)-3-((1e,3e)-5-oxo-5-phenylpenta-1,3-dien-1-yl)-2H-chromen-2-one (SPH), based on Michael addition mechanism, was designed and synthesized for selective detection of sulfite. The probe was constructed by incorporating an α,β-unsaturated ketone conjugated with a C˭C bond into the coumarin fluorophore as a specifical reaction site for sulfite utilizing its nucleophilic property. The extra conjugated C˭C bond induced obvious red-shifts in both absorption and emission maxima, and remarkably promoted the nucleophilic addition rate. Once treated with sulfite, the solution's color changed from orange to yellow companied with a strong blue-green fluorescence. The ratio of fluorescence intensity at 488nm and 630nm (I₄₈₈/I₆₃₀) was linear with sulfite concentration over the range of 0-80μM with a detection limit of 0.23μM. High selectivity and good competition of the probe toward sulfite over other anions and thiols enable us to monitor sulfite levels in realistic samples as well as in living HeLa cells.

A fluorescent probe for bisulfite ions: its application to two-photon tissue imaging

Two-photon imaging of endogenous bisulphite ions of the hippocampus region of mouse brain.

Selective and sensitive chromofluorogenic detection of the sulfite anion in water using hydrophobic hybrid organic-inorganic silica nanoparticles

In water and wine: Chromofluorogenic detection of the sulfite anion in pure water was accomplished by using a new hybrid organic-inorganic material that contained a probe entrapped in hydrophobic biomimetic cavities. This material was used for the detection of sulfite in red wine.

Determination of sulfite with emphasis on biosensing methods: a review

Sulfite is used as a preservative in a variety of food and pharmaceutical industries to inhibit enzymatic and nonenzymatic browning and in brewing industries as an antibacterial and antioxidizing agent. Convenient and reproducible analytical methods employing sulfite oxidase are an attractive alternative to conventional detection methods. Sulfite biosensors are based on measurement of either O2 or electrons generated from splitting of H2O2 or heat released during oxidation of sulfite by immobilized sulfite oxidase. Sulfite biosensors can be grouped into 12 classes. They work optimally within 2 to 900 s, between pH 6.5 and 9.0, 25 and 40 °C, and in the range from 0 to 50,000 μM, with detection limit between 0.2 and 200 μM. Sulfite biosensors measure sulfite in food, beverages, and water and can be reused 100-300 times over a period of 1-240 days. The review presents the principles, merits, and demerits of various analytical methods for determination of sulfite, with special emphasis on sulfite biosensors.