Responsive small-molecule luminescence probes for sulfite/bisulfite detection in food samples

A water-soluble red-emitting fluorescence probe for detecting hazardous hydrazine in environmental waters and biosystems

Hydrazine (N2H4), a crucial chemical raw material, enhances people's lives and fosters human progress. Hydrazine usage or leakage has caused environmental contamination, affecting water, soil, and living beings. Hydrazine simultaneously presents a possible risk to human health due to its carcinogenic properties. Thus, quick and precise detection of hydrazine is crucial in environmental studies and biological contexts. We prepared a red-emitting fluorescence turn-on probe (XT-HZ) to detect hydrazine specifically. The probe has a low detecting limit for hydrazine (63 nM) with excitation wavelength at 570 nm and emission wavelength at 625 nm. Besides, the probe XT-HZ had excellent water solubility, high selectivity, and good sensitivity for detecting hydrazine. Finally, probe XT-HZ was applied in the imaging of N2H4 in living cells, zebrafish and environmental water samples.

Fast detection of sodium dithionite in sugar using a xanthylium-based fluorescent probe

Dithionite remained in the foodstuff may pose a great threat to the health of consumers. Three xanthylium-based probes were synthesized and their responses to dithionite were explored. Probe SH-1 could respond to dithionite selectively in PBS buffer (15% DMSO, 10 mM, pH = 7.4). Upon the addition of dithionite, the fluorescent emission of SH-1 at 684 nm dropped quickly (within 10 s) and the fluorescence decline was proportional to the concentration of dithionite (0-7.0 μM). The limit of detection was determined to be 0.139 μM. Then, the sensing mechanism was tentatively presented and the structure of resulted adduct (SH-1-SO3-) which was the reaction product of SH-1 and dithionite via a Micheal addition reaction followed by an oxidation reaction was verified. Moreover, white granulated sugar was subjected to the standard spike experiments and the results demonstrated a great potential of SH-1 for the quantitative monitoring of dithionite in foodstuffs.

A triphenylamine-benzofuran-derived fluorescent probe for monitoring sulfite in Chinese medicinal materials and bioimaging

In this work, a triphenylamine-benzofuran-derived fluorescent probe TBSF was developed for monitoring the sulfite level in Chinese medicinal materials and imaging in living cells. In the testing system, under 445 nm excitation, TBSF responded to sulfite steadily with a 540 nm fluorescence reporting signal. The testing system showed advantages including high sensitivity, rapid response, and high selectivity. In particular, TBSF achieved the sulfite detection in the water decoction of Chinese medicinal materials from both addition and excessive fumigation. It also realized the intracellular imaging of both exogenous and endogenous sulfite in living HepG2 cells. The imaging in water decoction-treated cells inferred the potential for the interdisciplinary detection.

Rapid visual detection of sulfur dioxide residues in food using acid-sensitive CdTe quantum dots-loaded alginate hydrogel beads

Acid-sensitive CdTe quantum dots-loaded alginate hydrogel (CdTe QDs-AH) beads were designed for the visual detection of SO2 residues. As proof of concept, two types of CdTe QDs were selected as model probes and embedded in AH beads. The entire test was performed within 25 min in a modified double-layer test tube with one bead fixed above the sample solution. Adding citric acid and heating at 70 ℃ for 20 min transformed the sulfites in the solution into SO2 gas, which then quenched the fluorescence of the CdTe QDs-AH beads. Using this assay, qualitative, naked-eye detection of SO2 residues was achieved in the concentration range of 25-300 ppm, as well as precise quantification was possible based on the difference in the average fluorescence brightness of the beads before and after the reaction. Five food types were successfully analysed using this method, which is simpler and more economical than existing methods, and does not require complex pretreatment.

A practical chromogenic and fluorogenic dual-mode sensing platform for rapid quantification of sulfite in food

Sulfur dioxide (SO2) and its derivatives (HSO3- and SO32-) are widely used in food-processing. Whereas excessive consumption of sulfur dioxide and its derivatives (>0.70 mg·kg-1day-1) severely endangers human health. In this work, we rationally constructed a practical dual-mode probe (dicyanomethylene)-1-methyl-1,4-dihydroquinolin-2-yl)vinyl)-1-methylquinolinium (QMN), which underwent a specific 1, 4-Michael addition with sulfite to afford a noticeable color change from pale yellow to red along with a high-contrast fluorescence turn-on response at 598 nm. QMN has the advantages of rapid response, high signal-to-noise ratio, excellent selectivity, good water-solubility, large Stokes shift and low detection limit (LOD = 31.9 nM). QMN has been successfully used to on-site visually determine sulfite in a diversity of foods with satisfactory recoveries (91.33-111.33 %) and high accuracy (93.74-98.71 %). Furthermore, a portable smartphone-based fluorescence sensing platform was fabricated for on-site determination of sulfite in food with good performance.

A ratiometric fluorescence probe for bisulfite detection in live cells and meat samples

The development of reliable probe technology for the detection of bisulfite (HSO3-) in situ in food and biological samples is contributing significantly to food quality and safety assurance as well as community health. In this work, a responsive probe, EHDI, is developed for ratiometric fluorescence detection of HSO3- in aqueous solution, meat samples, and living cells. The probe is designed based on the HSO3- triggered 1,4-addition of electron deficit C = C bond of EHDI. As a result of this specific 1,4-addition, the π-conjugation system was destructed, resulting in blue shifts of the emission from 687 to 440 nm and absorption from 577 to 355 nm. The probe has good water solubility, high sensitivity and selectivity, allowing it to be used for imaging of HSO3- internalization and production endogenously. The capability of probe EHDI for HSO3- was then validated by traditional HPLC technology, enabling accurately detect HSO3- in beef samples. The successful development of this probe thus offers a new tool for investigating HSO3- in situ in food and biological conditions.

Design and application of a novel "turn-on" fluorescent probe for imaging sulfite in living cells and inflammation models

Sulfite is one of the main existing forms of sulfur dioxide (SO2) in living system, which has been recognized as an endogenous mediator in inflammation. Evidence has accumulated to show that abnormal level of sulfite is associated with many inflammatory diseases, including neurological diseases and cancers. Herein, a novel fluorescent probe named QX-OA was designed and synthesized to detect sulfite. QX-OA was constructed by choosing quinolinium-xanthene as the fluorophore and levulinate as the specific and relatively steady recognition reaction. The probe showed remarkable green turn-on signal at 550 nm, together with high sensitivity (90-fold) and excellent selectivity to sulfite over other possible interfering species. In the meantime, QX-OA was successfully applied to visualize endogenous and exogenous sulfite in Hela cells. In the LPS-induced inflammation model, QX-OA could visualize the dose-dependent increase of sulfite level (0-2 mg/mL). Consequently, QX-OA was determined to be a potential method for detecting sulfite in pre-clinical diagnosis.

Rational design of a rapidly responsive and highly selective fluorescent probe for SO2 derivatives detection and imaging

Sulfur dioxide (SO2) is emerging as a double-edged molecule, while plays vital roles in food and biological system. However, the fast, highly sensitive, and versatile fluorescent probe still remains a tough challenge among current reports. Herein, we developed a novel aggregation-induced emission (AIE) fluorescent probe TPE-PN for specifically sensing SO2 derivatives with high sensitivity (150 nmol/L) and rapid response time (10 s) based on intramolecular charge transfer (ICT) mechanism. And the fluorescence at 575 nm decreased tremendously with 31-fold after the probe was treated with HSO3-. Employing the probe, the accurate analysis of HSO3- was successfully realized in food samples, cells, plant tissues, and zebrafishes. Furthermore, we successfully demonstrate the eruption of SO2 derivatives within plant during drought and salt stress processes. Therefore, probe TPE-PN illustrates significant potential for applications in food analysis and monitoring of SO2 derivatives levels in biological systems under stress conditions.

A colorimetric and NIR fluorescent probe for ultrafast detecting bisulfite and organic amines and its applications in food, imaging, and monitoring fish freshness

Herein, for the first time, we have successfully constructed a novel near-infrared (NIR) emission fluorescent probe Dpyt for ultrafast detecting (within 5 s) bisulfate and organic amines based on a 1,2-dihydrocyclopenta[b]chromene-barbiturate conjugation system. Upon addition of bisulfate or organic amines, Dpyt displayed a distinct color change from blue to colorless or from purple to blue, respectively, suggesting that the Dpyt can be used to detect two analytes by the naked eye. Based on quantum chemistry calculations, the fluorescence quenching of Dpyt after the addition of HSO3- is caused by the photoinduced electron transfer (PET) process of the adduct Dpyt-HSO3-. The fluorescence enhancement of Dpyt caused by most organic amines is due to the enhanced intramolecular charge transfer (ICT) process of deprotonated Dpyt. Notably, Dpyt can be applied for detecting HSO3- in actual food samples such as red wine and sugar, as well as for imaging of HSO3- and representative propylamine in living cells. And more importantly, indicator labels constructed by filter paper loaded with Dpyt can visually monitor the freshness of salmon in real-time by daylight and fluorescence dual-mode. The comparison with national standard method of China manifests that indicator labels are a valid tool to assess the freshness of seafood.

A ratiometric fluorescence platform for on-site screening meat freshness

Meat freshness is related to food safety and human health. Developing a simple and effective method for on-site detection of meat freshness is essential to ensure food safety. This study aimed to explore a ratiometric fluorescence platform for on-site screening of meat freshness. We synthesized a series of benzothiazole-based fluorescent compounds (BM, BHM and BTH), each with different recognition groups for detecting meat freshness biomarkers cadaverine (Cad) and putrescine (Pte). The optimized 2-(2'-hydroxyphenyl-3-aldehyde-5-1,3-indanedione) benzothiazole (BTH) demonstrated a noticeable color and fluorescence change, a fast response (<15 min), and high selectivity and sensitivity (LOD = 70 nM) to Cad. Portable test strips based on BTH were prepared for rapid visual detection of meat freshness, which exhibited visible color and fluorescen color changes to Cad and Pte. Furthermore, a portable smartphone-based fluorescence device integrated with a self-programmed Python program was fabricated and used on-site to monitor Cad and Pte within 5 min. The BTH-loaded portable test strips were successfully employed as low-cost, high-contrast, fast-response, and smartphone-adaptable fluorescent labels for detecting Cad and Pte in meat samples under different temperatures (25 °C, 4 °C, and -20 °C). This enabled consumers and food supply chain stakeholders to quickly and visually monitor the meat freshness in real beef, chicken, and pork products.

Neo-construction of a SO2-tunable near-infrared ratiometric fluorescent probe for high-fidelity diagnosis and evaluation hazards of Cd2+-induced liver injury

Cadmium-contaminated water and food are seriously hazardous to the human health, especially liver injury. To understand the entanglement relationship between cadmium ion (Cd2+)-induced liver injury and the biomarker sulfur dioxide (SO2), a reliable bioanalytical tool is urgently needed, detecting SO2 to diagnose and evaluate the extent of liver injury in vivo. Herein, based on the Förster resonance energy transfer (FRET) mechanism, a novel SO2-tunable NIR ratiometric fluorescent probe (SMP) was developed, it was used to diagnose and treat liver injury induced by Cd2+ in biosystems. Specifically, it was constructed by conjugating a NIR dicyanoisophorone with a NIR benzopyranate as the donor and acceptor, respectively, and the ratiometric response of SO2- regulated by the Michael addition reaction. In addition, SMP exhibits rapid reaction time (<15 s), two well-resolved emission peaks (68 nm) with less cross-talk between channels for high imaging resolution, superior selectivity, and low limit of detection (LOD=80.3 nM) for SO2 detection. Impressively, SMP has been successfully used for intracellular ratiometric imaging of Cd2+-induced SO2 and diagnostic and therapeutic evaluation in liver injury mice models with satisfactory results. Therefore, SMP may provide a powerful molecular tool for revealing the occurrence and development relationship between SO2 and Cd2+-induced liver injury. ENVIRONMENTAL IMPLICATION: Cadmium ions are one of the well-known toxic environmental pollutants, which are enriched in the human body through inhalation of cadmium-contaminated air or from the food chain, leading to damage in various organs, especially liver injury. Therefore, we developed a novel fluorescent probe that can specifically detect SO2 in Cd2+-induced liver injury, which is critically important for the diagnosis and evaluation of Cd2+-induced liver injury diseases. The specific detection of SO2 of this probe has been successfully demonstrated in live HepG2 cells and Cd2+-induced liver injury mice.

A near-infrared fluorescent probe for rapid and on-site detection of sulfur dioxide derivative in biological, food and environmental systems

Emission of toxic gaseous sulfur dioxide (SO2) and its derivative bisulfite (HSO3-) from various industrial applications, like food processing, transportation, and the coking process, has raised substantial concerns regarding environmental quality and public health. The probes for specific and sensitive detection of SO2 derivatives plays an essential role in their regulation, and ultimately mitigating their environmental and health implications, but the one that can detect SO2 derivatives onsite by end users remains limited. Herein, we report a new near-infrared fluorescence probe (SL) for rapid and onsite detection of SO2 derivative, HSO3- in industrial wastewater, food samples and for sensing its interaction with biological organisms. The SL is developed through coupling of quinolinium and coumarin moiety through an electron deficit CC bond that can specifically react with HSO3- via a Michael addition. By recording the blue shift of absorption and emission spectra, SL can sensitively detect HSO3- (limit of detection, 38 nM) in aqueous solution within 40 s SL is biocompatible, can be used for evaluating toxicity of SO2 derivatives in living organisms. The preparation of SL-stained test paper allows the colorimetric/fluorometric analysis for quantification of HSO3- onsite in food, river and coking wastewater samples using a smartphone. The successful development of SL not only provides a new tool to investigate HSO3- in biological, food and environmental systems, but also potentially promotes the application of fluorescence technique for rapid and onsite analysis of real-world samples by end users.

A multi-signal mitochondria-targeted fluorescent probe for simultaneously distinguishing biothiols and realtime visualizing its metabolism in cancer cells and tumor models

Biothiols and its metabolite SO2 derivatives play vital roles in various physiological processes. Although a few probes have been designed for monitoring the metabolism of biothiols, developing multi-signal fluorescent probes with practicability for simultaneously distinguishing biothiols (GSH, Cys and Hcy) and real-time visualizing SO2 derivatives is an enormous challenge. To better visualize biothiols metabolism in vitro and vivo, we developed a novel multi-signal NIR fluorescent probe (probe 2) with mitochondria-targeted for distinguishing biothiols and its metabolism, based on an ICT-PET synergetic mechanism. Probe 2 with dual recognition sites distinguishing detected Cys/Hcy (Red-Green), GSH (Green) and SO32- (Blue) via three channels. First probe 2 distinguished Cys and GSH to estimate main biothiols in living cells through the ratio changes of two well-defined emission bands (Red-Green), and then imaged its metabolite SO2 with ratiometric fluorescence (Red-Blue), eliminating the interference by different biothiols. Notably, probe 2 exhibits satisfactory sensitivity (detection limit: 0.21, 0.13, 0.14 and 3.06 μM for Cys, Hcy, GSH and SO32-, respectively), high selectivity, reliability at physiological pH, and rapid fluorescence response (within 10 min). Given these advantages, probe 2 has been successfully applied to the real-time monitor GSH metabolic process in MCF-7 cells and biothiols metabolism in breast cancer, suggesting biothiols metabolic changes might be a diagnostic indicator during cancer treatment. So probe 2 is a convenient and efficient tool for understanding the physiological functions of biothiols and its metabolism.

Illuminating the path: aggregation-induced emission for food contaminants detection

Food safety is a global concern that deeply affects human health. To ensure the profitability of the food industry and consumer safety, there is an urgent need to develop rapid, sensitive, accurate, and cost-effective detection methods for food contaminants. Recently, the Aggregation-Induced Emission (AIE) has been successfully used to detect food contaminants. AIEgens, fluorescent dyes that cause AIE, have several valuable properties including high quantum yields, photostability, and large Stokes shifts. This review provides a detailed introduction to the principles and advantages of AIE-triggered detection, followed by a focus on the past five years' applications of AIE in detecting various food contaminants including pesticides, veterinary drugs, mycotoxins, food additives, ions, pathogens, and biogenic amines. Each detection principle and component is comprehensively covered and explained. Moreover, the similarities and differences among different types of food contaminants are summarized, aiming to inspire future researchers. Finally, this review concludes with a discussion of the prospects for incorporating AIEgens more effectively into the detection of food contaminants.

A wide-range ratiometric sensor mediating fluorescence and scattering based on carbon dots/metal-organic framework composites for the detection of bisulfite/sulfite in sugar

Bisulfite (HSO₃^-) and sulfite (SO₃^2-) are commonly employed in food preservatives and are also significant environmental pollutants. Thus, developing an effective method for detecting HSO₃^-/SO₃^2- is crucial for food safety and environment monitoring. In this work, based on carbon dots (CDs) and zeolitic imidazolate framework-90 (ZIF-90), a composite probe (named CDs@ZIF-90) is constructed. The fluorescence signal and the second-order scattering signal of CDs@ZIF-90 are employed to ratiometricly detect HSO₃^-/SO₃^2-. This proposed strategy exhibits a broad linear range for HSO₃^-/SO₃^2- determination (10 µM to 8.5 mM) with a limit of detection of 2.74 μM. This strategy is successfully applied for evaluating HSO₃^-/SO₃^2- in sugar with satisfactory recoveries. Therefore, this work has uniquely combined the fluorescence and second-order scattering signals to establish a novel sensing system with a wide linear range, which is applicable for ratiometric sensing of HSO₃^-/SO₃^2- in actual samples.

Bioimaging and detecting endogenous and exogenous cyanide in foods, living cells and mice based on a turn-on mitochondria-targeted fluorescent probe

A novel fluorescent probe, with advanced features including "turn-on" fluorescence response, high sensitivity, good compatibility, and mitochondria-targeting function, has been synthesized based on structural design for detecting and visualizing cyanide in foods and biological systems. An electron-donating triphenylamine group (TPA) was employed as the fluorescent and an electron-accepting 4-methyl-N-methyl-pyridinium iodide (Py) moiety was used as a mitochondria-targeted localization unit, which formed intramolecular charge transfer (ICT) system. The "turn-on" fluorescence response of the probe (TPA-BTD-Py, TBP) toward cyanide is attributed two reasons, one is the insertion of an electron-deficient benzothiadiazole (BTD) group into the conjugated system between TPA and Py, and the other is the inhibition of ICT induced by the nucleophilic addition of CN^-. Two active sites for reacting with CN^- were involved in TBP molecule and high response sensitivity were observed in tetrahydrofuran solvent containing 3 % H₂O. The response time could be reduced to 150 s, the linear range was 0.25-50 μM, and the limit of detection was 0.046 μM for CN^- analysis. The TBP probe was successfully applied to the detection of cyanide in food samples prepared in aqueous solution, including the sprouting potato, bitter almond, cassava, and apple seeds. Furthermore, TBP exhibited low cytotoxicity, clear mitochondria-localizing capability in HeLa cells and excellent fluorescence imaging of exogenous and endogenous CN^- in living PC12 cells. Moreover, exogenous CN^- with intraperitoneal injection in nude mice could be well monitored visually by the "turn-on" fluorescence. Therefore, the strategy based on structural design provided good prospects for optimizing fluorescent probes.

Visual inspection of acidic pH and bisulfite in white wine using a colorimetric and fluorescent probe

The acidic pH and total amount of SO₂ are both important quality control indexes of wine, but conventional detection techniques depend heavily on specialized instrument and professional staff, thus are not available to general customers. In this paper, a hemicyanine-based colorimetric and fluorescent probe Hcy-Py was designed and synthesized. It responded to bisulfite selectively with a LOD of 0.68 μM and responded to proton with a pKa of 3.78. Upon the treatment of solutions with different pH values and concentrations of bisulfite, the probe-loaded paper strips displayed distinct color changes under both natural light and UV lamp. When a real white wine sample was subjected to the paper strip experiment, pH as well as bisulfite concentration could be determined by naked-eye quickly and conveniently, thus a visual detection of acidic pH and bisulfite in white wine without involving any sophisticated instrument or professional skill was successfully demonstrated.

Development of a responsive probe for colorimetric and fluorescent detection of bisulfite in food and animal serum samples in 100% aqueous solution

Bisulfite (HSO₃^-) has the functions of bleaching, antiseptic, antioxidant, inhibiting bacterial growth, and controlling enzymatic reactions in food. However, long-term consumption of foods containing excessive amounts of bisulfite can be harmful to health. In addition, large doses of sulfur dioxide (SO₂) can cause diarrhea, hypotension, allergic and asthmatic reactions in susceptible individuals. Therefore, it is urgent and essential to explore some rapid, reliable, and convenient tools to detect HSO₃^- in food and SO₂ gas. Herein, we exploited a fluorescent probe, NPO, to detect HSO₃^- in 100 % aqueous solution. The probe has the advantages of easy synthesis, excellent water solubility, significant colorimetric change, good selectivity, high sensitivity, and fast response (within 1 min). Probe NPO was successfully applied for testing strips to visualize the behavior of HSO₃^- and SO₂ gas. Moreover, the probe has been used to monitor the behavior of HSO₃^- in real food samples and animal serum samples.

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 unique ratiometric fluorescent probe for detection of SO2 derivatives in living cells and real food samples

Abnormal levels of SO₂ in organisms can cause cardiovascular disease and respiratory allergies. In addition, the amount of SO₂ derivatives used as food preservatives is strictly controlled, and excessive addition can also be harmful to health. Therefore, it is essential to develop a highly sensitive method for the detection of SO₂ and its derivatives in biological systems and real food samples. In this work, a new fluorescent probe (TCMs) with high selectivity and sensitivity for the detection of SO₂ derivatives was reported. The TCMs could quickly identify SO₂ derivatives. It has been successfully used to detect exogenous and endogenous SO₂ derivatives. Furthermore, the TCMs has high sensitivity to SO₂ derivatives in food samples. Moreover, the prepared test strips could be evaluated for the content of SO₂ derivatives in aqueous solutions. This work provides a potential chemical tool to detect SO₂ derivatives in living cells and real food samples.

Carbon dot and silver nanoparticle-based fluorescent probe for the determination of sulfite and bisulfite via inner-filter effect and competitive redox reactions

A new sensitive fluorescent probe (CDs-AgNP/H₂O₂) for detecting sulfite and bisulfite (SO₃^2- and HSO₃^-) based on the inner-filter effect (IFE) between silver nanoparticles (AgNPs) and carbon dots (CDs) was developed. Because of the spectral overlap between the absorption of AgNPs and the excitation of CDs, the fluorescence of CDs can be quenched by AgNPs owing to the IFE. H₂O₂ weakens the IFE and restores the fluorescence due to the oxidation of AgNPs by H₂O₂. However, the existence of SO₃^2-/HSO₃^- can quench the fluorescence again as a result of redox reaction between SO₃^2-/HSO₃^- and H₂O₂. The results showed a broad linear range of 20-200 μM with a low limit of detection (3.02 μM) toward SO₃^2-/HSO₃^-. The combination of IFE and redox reaction led to improvement of the sensitivity and selectivity. The probe was implemented to measure SO₃^2-/HSO₃^- in various agricultural products and foods with acceptable results (80.6 to 118.9% recovery).

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.

An AIE mechanism-based fluorescent probe for relay recognition of HSO3-/H2O2 and its application in food detection and bioimaging

In view of the important physiological role of HSO₃^- and H₂O₂, it is of great significance to develop fluorescent probes to detect HSO₃^- and H₂O₂ in aqueous medium. We herein report a new fluorescent probe (E)-3-(2-(4-(1,2,2-triphenylvinyl)styryl)benzo [d]thiazol-3-ium-3-yl)propane-1-sulfonate (TPE-y) possessing benzothiazolium salt based on tetraphenylethene (TPE) moiety with aggregation-induced emission (AIE) characteristics. TPE-y can sequentially recognize HSO₃^- and H₂O₂ through colorimetric and fluorescence dual-channel response in HEPES (pH = 7.4, 1% DMSO) buffer solution, and exhibits high sensitivity and selectivity, a large Stokes shift (189 nm), as well as a wide applicable pH range. The detection limits of TPE-y and TPE-y-HSO₃ for HSO₃^- and H₂O₂ are 3.52 μM and 0.15 μM, respectively. The recognition mechanism is verified by ¹H NMR and HRMS methods. Furthermore, TPE-y can detect HSO₃^- in sugar samples, and can image exogenous HSO₃^- and H₂O₂ in living MCF-7 cells. TPE-y can relay detect HSO₃^- and H₂O₂, which is of great significance to maintain the redox balance in organisms.

Naphthalene-based fluorescent probe for on-site detection of hydrazine in the environment

The widespread occurrence of hydrazine residues in the environment, including in water, soil, and organisms, is a potential health threat to humans. Therefore, the development of an efficient method for the detection of hydrazine in environmental samples is highly desirable although it poses a significant challenge. In this study, we designed and synthesized a series of naphthalene-based fluorescent dyes through structural engineering and developed a novel probe for hydrazine detection. The probe could provide a distinct fluorescence response toward hydrazine in aqueous solution with high sensitivity and selectivity. Moreover, paper-based test strips can be easily fabricated using this probe, enabling the portable on-site detection of hydrazine with the aid of a smartphone. Furthermore, we demonstrated that this probe is capable of recognizing hydrazine in various environmental samples, including water, soil, plants, and zebrafish embryos. This research provides a promising tool for the detection of hydrazine in the environment.

The first fluorescent sensor for the detection of closantel in meat

Closantel is widely used in the management of parasitic infestation in livestock, but is contraindicated in humans due to its high toxic to human retina. Thus, development of a fast and selective method for the detection of closantel residues in animal products is highly needed yet still challenging. In the present study, we report a supramolecular fluorescent sensor for closantel detection through a two-step screening process. The fluorescent sensor can detect closantel with a fast response (<10 s), high sensitivity, and high selectivity. The limit of detection is 0.29 ppm, which is much lower than the maximum residue level set by government. Moreover, the applicability of this sensor has been demonstrated in commercial drugs tablets, injection fluids, and real edible animal products (muscle, kidney, and liver). This work provides the first fluorescence analytical tool for accurate and selective determination of closantel, and may inspire more sensor design for food analysis.

A bis-chalcone based colorimetric probe for the selective detection of bisulfite/sulfite anions: exploring surfactant promoted Michael addition of anions to α, β-unsaturated ketones

A probe, (1E,4E)-1,5-di(thiophen-2-yl)penta-1,4-dien-3-one, was developed for rapid, colorimetric, and selective detection of bisulfite/sulfite anions in aqueous solutions. This probe is based on the Michael addition reaction which is favoured in the presence of cationic micellar medium CTAB. CTAB promoted Michael addition is an effective tool to determine SO₂ toxicity, which is mainly expressed in terms of collective concentration of bisulfite and sulfite anions. The probe showed high selectivity and sensitivity toward bisulfite and sulfite over other interfering anions, with a detection limit of 0.43 μM and 0.23 μM, respectively. The possible recognition mechanism of the probe and the analyte was illustrated by NMR, HR-MS, IR, and computational analysis. Moreover, this probe showed great potential for the detection of bisulfite/sulfite in real samples, such as crystal sugar and brown sugar.

Accurate quantification, naked eyes detection and bioimaging of nitrite using a colorimetric and near-infrared fluorescent probe in food samples and Escherichia coli

Nitrite (NO₂^-) is an inorganic contaminant that exists widely in the environment including water and food products, excessive amounts of NO₂^- would threaten humans and aquatic life. Developing a rapid and convenient sensing method for NO₂^- remains a great challenge. Herein, a colorimetric and near-infrared fluorescent probe (TBM) was synthesized and applied for sensitively and selectively detecting NO₂^- in water, food samples and Escherichia coli (E. coli). With the addition of NO₂^-, the probe TBM solution has a distinct visual color changed from red to colorless and fluorescence intensity at 620 nm quickly decreased. The probe TBM could detect NO₂^- quantitatively with a detection limit of 85 nM based on a 3σ/slope. Under optimum conditions, TBM has been successfully used to detect NO₂^- in real-world environmental and dietary samples, with positive results. Besides, paper strips loaded with TBM have been used to visually determine NO₂^- levels. Most importantly, TBM has also been proven to be able to discriminate from different concentrations of NO₂^- in E. coli by fluorescence imaging. In summary, the probe TBM was successfully developed for the accurate quantification, naked eyes detection and bioimaging of NO₂^- in water, food samples and E. coli, which provides a useful tool to better guarantee the quality and safety of daily life and food industry.

Photoacoustic Imaging Probes for Theranostic Applications

Photoacoustic imaging (PAI), an emerging biomedical imaging technology, capitalizes on a wide range of endogenous chromophores and exogenous contrast agents to offer detailed information related to the functional and molecular content of diseased biological tissues. Compared with traditional imaging technologies, PAI offers outstanding advantages, such as a higher spatial resolution, deeper penetrability in biological tissues, and improved imaging contrast. Based on nanomaterials and small molecular organic dyes, a huge number of contrast agents have recently been developed as PAI probes for disease diagnosis and treatment. Herein, we report the recent advances in the development of nanomaterials and organic dye-based PAI probes. The current challenges in the field and future research directions for the designing and fabrication of PAI probes are proposed.

Novel Colorimetric and NIR Fluorescent Probe for Bisulfite/Sulfite Detection in Food and Water Samples and Living Cells Based on the PET Mechanism

Despite their status of being widely used as food additives, bisulfite (HSO₃^-)/sulfite (SO₃^2-) can pose serious health risks when they are excessively added. Therefore, it is vital to develop a new method for detecting HSO₃^-/SO₃^2- in foodstuff. In this paper, a benzopyran-benzothiazole derivative (probe DCA-Btl) with near-infrared emission was designed and synthesized by constructing a "push-pull" electronic system. DCA-Btl can selectively recognize HSO₃^-/SO₃^2- via a colorimetric and fluorescence dual channel in DMF/PBS (1:1, v/v, pH = 8.4), and the emission wavelength of DCA-Btl can reach 710 nm. The fluorescence quenching of DCA-Btl after recognition of HSO₃^- is attributed to the photoinduced electron transfer (PET) process of the adduct DCA-Btl-HSO₃^- as evaluated by the DFT/TD-DFT method. In addition, DCA-Btl has many advantages, including a large Stokes shift (95 nm), good anti-interference ability, and little cytotoxicity. What's more, DCA-Btl has been successfully applied for the detection of HSO₃^-/SO₃^2- in actual water samples and food samples such as sugar, red wine, and biscuits with satisfying results, as well as for fluorescent imaging of HSO₃^- in living MCF-7 cells.

Molecular engineering-based a dual-responsive fluorescent sensor for sulfur dioxide and nitric oxide detecting in acid rain and its imaging studies in biosystems

Sulfur dioxide (SO₂) and nitric oxide (NO), known as sulfur oxides and nitrogen oxides, are toxic air pollutants and seriously threaten human health. Herein, for the first time, a robust dual-response fluorescent sensor CGT with two different emission fluorophores and dual well-known response-group for visual bisulphites (HSO₃^-) and nitrites (NO₂^-) detection was reported. Specifically, once CGT was incubated with HSO₃^- firstly, the color of the test solution changed to dark yellow with no-fluorescence emission, following added NO₂^-, the color of the test solution changed to yellow with a bright cyan emission. However, NO₂^- was added firstly, the color of the test solution changed to dark purple with a white emission, and then added HSO₃^-, the color of the test solution changed to yellow with a bright cyan emission. Furthermore, CGT showed high sensitivity and selectivity toward HSO₃^- and NO₂^- detecting with good detection limits as low as 20.17 nM and 4.14 nM, respectively. Impressively, CGT showed good detection capability in complex aqueous samples and was successfully used for the detection of HSO₃^- and NO₂^- in biosystems. Thus, the experimental results indicated CGT as a powerful novel visual detecting tool for HSO₃^- and NO₂^- detecting in complex acid rain and biosystems.

Designing of a high-performance fluorescent small molecule enables dual-mode and ultra-sensitive fluorescence visualizing of HSO3- and HClO in dried fruit, beverage, and water samples

Herein, a novel hemicyanine derivative (E)-3-(1,1-dimethyl-2-(4-(methylthio)styryl)-1H-benzo[e]indol-3-ium-3-yl)propane-1-sulfonate (BIS) has been reasonably designed. Compound BIS is long-wavelength emissive and water-soluble with a large Stokes shift. Intriguingly, probe BIS provides a dual-mode fluorescence response pattern for the sensing of bisulfite (HSO₃^-) and hypochlorous acid (HClO) with great limit of detections (3.6 and 57.4 nM). First, the 1,4-Michael addition of HSO₃^- on the conjugated double bond triggers a ratiometric response (I₄₆₅/I₅₇₅). Second, the rapid oxidation of HClO on the thioether moiety provides a turn-on response (I₅₇₅). Evaluation of HSO₃^- and HClO levels in dried fruit, beverage, and water samples has been carried out with satisfactory results. Moreover, motivated by an impressive chromatic variation (red to blue), smartphone-assisted signal readout system and thin-film sensing platform are facilely constructed for real-time and on-site measurement of HSO₃^- levels. Furthermore, probe BIS is used for the in vivo imaging of HSO₃^- in edible fish models.

Research Progress on Multifunctional Fluorescent Probes for Biological Imaging, Food and Environmental Detection

There has been rapid progress in the development of fast, sensitive, cheap and low-cytotoxicity micro-molecule fluorescent probes for application in various fields, including disease diagnosis, food safety and environmental safety. As an analytical tool, dual-function fluorescent probes with dual-emission responses have attracted considerable attention due to their cost-effectiveness and efficiency over single-function sensors. This review primarily describes research progress on multifunctional probes in terms of the reaction type and coordination type, as well as the general design principles of probes. The analytes include reactive oxygen species (ROS), reactive sulfur species (RSS), harmful cations and anions, etc. Multifunctional probes for food, medical and environmental applications are listed for future research. To improve the development of rapid detection methods, trends and strategies in the development of multifunctional fluorescent probes are also discussed.

Selective detection of HSO3- in living cells using a pyrroloquinoline structure containing turn-on fluorescent probe

A turn-on fluorescence probe PQP-1 with a pyrroloquinoline skeleton has been designed and synthesized. Probe PQP-1 showed high sensitivity to HSO₃^-, low detection limit (16.83 nM), and a wide linear range (50-3000 μM). More importantly, probe PQP-1 could distinguish between HSO₃^- and SO₃^2-. Furthermore, cell imaging experiments of HSO₃^- in HeLa cells revealed that probe PQP-1 had potential application value in biological systems.

Determination and Imaging of Small Biomolecules and Ions Using Ruthenium(II) Complex-Based Chemosensors

Luminescence chemosensors are one of the most useful tools for the determination and imaging of small biomolecules and ions in situ in real time. Based on the unique photo-physical/-chemical properties of ruthenium(II) (Ru(II)) complexes, the development of Ru(II) complex-based chemosensors has attracted increasing attention in recent years, and thus many Ru(II) complexes have been designed and synthesized for the detection of ions and small biomolecules in biological and environmental samples. In this work, we summarize the research advances in the development of Ru(II) complex-based chemosensors for the determination of ions and small biomolecules, including anions, metal ions, reactive biomolecules and amino acids, with a particular focus on binding/reaction-based chemosensors for the investigation of intracellular analytes’ evolution through luminescence analysis and imaging. The advances, challenges and future research directions in the development of Ru(II) complex-based chemosensors are also discussed.

Polyoxometalate-based materials in extraction, and electrochemical and optical detection methods: A review

Polyoxometalates (POMs) as metal-oxide anions have exceptional properties like high negative charges, remarkable redox abilities, unique ligand properties and availability of organic grafting. Moreover, the amenability of POMs to modification with different materials makes them suitable as precursors to further obtain new composites. Due to their unique attributes, POMs and their composites have been utilized as adsorbents, electrodes and catalysts in extraction, and electrochemical and optical detection methods, respectively. A survey of the recent progress and developments of POM-based materials in these methods is therefore desirable, and should be of great interest. In this review article, POM-based materials, their properties as well as their identification methods, and analytical applications as adsorbents, electrodes and catalysts, and corresponding mechanisms of action, where relevant, are reviewed. Some current issues of the utilization of these materials and their future prospects in analytical chemistry are discussed.

Mitochondria-Targeted Fluorescent Turn-On Probe for Rapid Detection of Bisulfite/Sulfite in Water and Food Samples

Bisulfite (HSO₃^-)/Sulfite (SO₃^2-) is widely used as a food additive, but excessive use often leads to serious consequences, so the detection of HSO₃^-/SO₃^2- is of great importance. In this paper, a novel 1,4-diethylpiperazine-modified coumarin-benzopyran derivative (probe QLP) has been synthesized and characterized. In PBS (10 mM, pH = 7.4), QLP displays good selectivity and is sensitive for HSO₃^-/SO₃^2- over various analytes with fluorescent "OFF-ON" rapid responding (2 min), long-wavelength emission (600 nm), and a detection limit of 177 nM. With the treatment of HSO₃^-/SO₃^2-, the color of the QLP solution obviously changes from blue-green to yellow, and the fluorescent color of QLP changes from colorless to amaranth. The fluorescence-enhanced mechanism is qualitatively evaluated by density functional theory calculations using the CAM-B3LYP/6-31G (d) method, which reveals that the photoinduced electron transfer leads to the fluorescence emission of the QLP-SO₃H adduct. Importantly, nontoxic QLP can be used to detect HSO₃^-/SO₃^2- in sugar, natural water samples, and living cells and localized to the mitochondria and monitor the mitochondrial HSO₃^-/SO₃^2- level.

A turn-on fluorescent probe based on indolizine for the detection of sulfite

Numerous SO32−/HSO3− fluorescent probes have been reported based on various mechanisms.

Detection and discrimination of sulfur dioxide using a colorimetric sensor array

Discrimination and detection of sulfur dioxide residues in foods using a simple colorimetric array have been achieved. The difference maps before and after the reaction showed that the specific color fingerprint was related to the amount of sulfur dioxide. The results of principal component analysis (PCA), hierarchical clustering analysis (HCA) and linear discriminant analysis (LDA) demonstrated that the as-fabricated colorimetric sensor array have good performance for the discrimination of sulfur dioxide and other interferents, as well as different concentrations of sulfur dioxide. Moreover, the array has been successfully applied to determine the concentration of sulfur dioxide residues in real samples and revealed good accuracy, precision and repeatability.

In this work, a colorimetric sensor array based on six specific color reactions was developed and used for the determination of sulfur dioxide content. The qualitative and quantitative analysis of sulfur dioxide residues in real samples was achieved.

A dual responsive fluorescent probe for selective detection of cysteine and bisulfite and its application in bioimaging

A coumarin-based dual responsive fluorescent probe with a simple structure was developed for the detection of Cys and HSO₃ ^-. Under simulated physiological conditions, Cou-F displayed an on-off fluorescence response to Cys at 521 nm and an off-on fluorescence response to HSO₃ ^- at 500 nm. Furthermore, Cou-F had the advantages of high sensitivity, strong specificity and rapid response. The detection limits of Cou-F toward Cys and HSO₃ ^- were 0.54 μM and 0.65 μM, respectively. Cou-F enabled high selective responses to Cys and HSO₃ ^- over other biologically related species. The response times of Cou-F toward Cys and HSO₃ ^- were 80 s and 100 s. The fluorescence imaging of Cys and HSO₃ ^- was achieved in living RAW246.7 cells.