Detection of Tyrosinase in Real Food Samples and Living Cells by a Novel Near-Infrared Fluorescence Probe

MnO4--triggered wavelength-changeable and rapid-response fluorescence sensor for paper-based on-site sensing of tyrosinase activity in potato

Rapid-response in situ fluorogenic reactions in aqueous solution are important for designing sensitive and stable sensing platforms. Herein, a wavelength-changeable and rapid-response (within 5 s) fluorescence sensing platform for monitoring tyrosinase (TYR) activity is constructed. The developed assay is based on TYR catalyzing the hydroxylation of mono-phenol to o-diphenol and MnO4--triggered fluorogenic between dopamine (DA) and phenol derivatives in aqueous solution. The fluorescence wavelength can be changeable from 470 to 550 nm with strong fluorescence according to different phenol derivatives. Our proposed sensor not only exhibits a good recovery for TYR in high serum concentration (20 %), but also has been successfully applied to the screening of TYR inhibitors modeled on kojic acid. Furthermore, a paper-based wavelength-changeable fluorescence sensor was developed for on-site detection of TYR activity in potatoes with high recovery, which is consistent with our previously reported method. Consequently, the proposed sensing system has broad prospects in the practical application of TYR-associated food monitoring and clinical diagnosis.

A mitochondrial targeted dual ratiometric near-infrared fluorescent probe based on ICT effect for the detection of SO2 derivative and its bioimaging

SO2 derivatives play an important role in many metabolic processes, excessive ingestion of them can lead to serious complications of various diseases. In this work, a novel dual ratiometric NIR fluorescent probe XT-CHO based on ICT effect was synthesized for detecting SO2 derivative. In the design of the probe, the α, β-unsaturated bond formed between benzopyran and coumarin was used as the reaction site for SO2, meanwhile, the extended π-conjugate system promoted maximum emission wavelength of the probe up to 708 nm. Notably, the probe exhibited high selectivity and sensitivity for detecting SO2, the limit of detection reached 2.13 nM and 58.5 nM in fluorescence spectra and UV-Vis absorption spectra, respectively. The reaction mechanism of SO2 and XT-CHO had been verified by 1H NMR, ESI-MS spectra and DFT calculation. Moreover, the probe was successfully applied in detecting endogenous and exogenous SO2 in living cells and proved possessed the mitochondrial targeted ability.

A fluorescent nanoprobe and paper-based nanofiber platform for detection and imaging of Fe3+ in actual samples and living cells

In this study, a novel fluorescent nanoprobe (ZIF-90@FSS) was constructed using a zeolite imidazolium ester skeleton (ZIF-90) incorporating sodium fluorescein within its porous structure. Notably, this nanoprobe exhibited regular fluorescence "off" detection performance of Fe3+ in actual samples and living cells. The concentration range of 0-150 ng/mL exhibited a lowest detection limit of 0.26 ng/mL. A nanofiber paper-based platform (VL78/ZIF-90@FSS) was further developed by coupling the prepared nanoprobe to a multi-dimensional fiber paper via CN bonds, enabling rapid visual white light colorimetric and fluorescence imaging of Fe3+ within 2 min. The constructed nanoprobe and its paper-based detection platforms demonstrated a stable recovery range in tap water, beer, and soy sauce samples during spiking-recovery assessments. The recovery rates ranged from 98.46 % to 108.24 % for the nanoprobe and from 91.75 % to 108.71 % for the nanofiber paper-based platform. Therefore, the developed nano-fluorescent sensor and paper-based nanofiber sensing platform offer a promising strategy for the visual detection of Fe3+, while also presenting novel and valuable methods to investigate the regulatory mechanisms of Fe3+ in living cells.

Fluorometric Assay of Tyrosinase and Atrazine Based on the Use of Carbon Dots and the Inhibition of Tyrosinase Activity

Sensitive and convenient strategy of tyrosinase (TYR) and its inhibitor atrazine is in pressing demand for essential research as well as pragmatic application. In this work, an exquisite label-free fluorometric assay with high sensitivity, convenience and efficiency was described for detecting TYR and the herbicide atrazine on the basis of fluorescent nitrogen-doped carbon dots (CDs). The CDs were prepared via one-pot hydrothermal reaction starting from citric acid and diethylenetriamine. TYR catalyzed the oxidation of dopamine to dopaquinone derivative which could quench the fluorescence of CDs through a fluorescence resonance energy transfer (FRET) process. Thus, a sensitive and selective quantitative evaluation of TYR can be constructed on the basis of the relationship between the fluorescence of CDs and TYR activity. Atrazine, a typical inhibitor of TYR, inhibited the catalytic activity of TYR, leading to the reduced dopaquinone and the fluorescence was retained. The strategy covered a broad linear range of 0.1-150 U/mL and 4.0-80.0 nM for TYR and atrazine respectively with a low detection limit of 0.02 U/mL and 2.4 nM/mL. It is also demonstrated that the assay can be applied to detect TYR and atrazine in spiked complex real samples, which provides infinite potential in application of disease monitoring along with environmental analysis.

Biomass-based indole derived fluorescence sensor composited with cellulose paper: Detection of picric acid in food and environment samples

Picric acid (PA) is highly water-soluble, the fact makes it stand out as the most hazardous environment pollutant. Therefore, accurate determination of PA is of great significance for human health and environmental protection. Herein, a novel indole-based fluorescent sensor (H1) with good water solubility and fluorescence stability was reported. H1 exhibited 'turn-off' fluorescence response for PA with fast reaction rate (<30 s), unique specificity and excellent selectivity and high sensitivity (limit of detection = 34 nM). Further, H1 was successfully applied to detect PA in real samples (tap water, Yangtze River, Xuanwu Lake, soil, food, fish and shrimp) with satisfactory recoveries at three spiking levels ranging from 98.0 to 112.0 %. In addition, H1 displayed high biocompatibility in mung beans and fresh blood. Moreover, aiming to attain portable analysis, H1 was composited with biomass cellulose paper (H1-FP) and integrated with smartphone for construction as a solid-state fluorescence platform to achieve fast and visual detection of PA in suit with significant stability, high sensitively and selectivity. The establishment of this sensing approach is expected to offer new insight into rapid, selective, and sensitive detection of major pollutants for food and environmental safety.

Novel Green Fluorescent Probe Stem From Carbon Quantum Dots for Specific Recognition of Tyrosinase in Serum and Living Cells

Tyrosinase (TYR), an important biomarker for melanoma, offered significant information early detection of melanoma and may decrease the likelihood of mortality. Therefore, this article constructed a highly sensitive and selective green fluorescent functionalized carbon quantum dots (TYR-CQDs) for tyrosinase (TYR) activity detection by one-step hydrothermal protocol utilizing catechol, citric acid and urea as precursors. The prepared TYR-CQDs illustrated excellent linear relationship and broad linear range with a low detection limit, which exhibited high accuracy and recovery in quantitative determination of TYR in human serum samples. Furthermore, the TYR-CQDs had successfully realized intracellular TYR detection owing to excellent biocompatibility, high anti-interference ability and good cellular imaging capability, suggesting the potential biomedical applications in early diagnosis of melanoma and other tyrosinase-related diseases.

Fluorescent molecular probes for imaging and detection of oxidases and peroxidases in biological samples

Oxidases and peroxidases are two subclasses of oxidoreductases. The abnormal expression of oxidases (such as tyrosinase, cytochrome P450 oxidases, and monoamine oxidases) and peroxidases (such as glutathione peroxidase, myeloperoxidase, and eosinophil peroxidase) is relative with some diseases. Therefore, the analysis of oxidases and peroxidases is great important for disease diagnosis and treatment. Fluorescent probes present simple protocol, high sensitivity and good stability in sensing field. Molecule fluorescent probes are constructed with chemical groups that tunes their fluorescence emission in response to binding events, chemical reactions, and the surrounding environment. A fluorescent probe is an efficient tool for visualizing the activity of enzymes in living organisms on the basis of its high specificity, sensitivity, and noninvasiveness characteristics. In this review, we focus on the sensing of oxidases and peroxidases by molecule fluorescent probes, and hope to bring new insight to wide researchers about oxidases and peroxidases in biological samples.

A tyrosinase fluorescent probe with large Stokes shift and high fluorescence enhancement for effective identification of liver cancer cells

Tyrosinase is widely regarded as an important biomarker for melanocytic and liver cancer. However, most currently reported tyrosinase probes have been focused on malignant melanoma study, and few tyrosinase probe have been applied for liver cancer investigation. Herein, we developed a novel probe HFC-TYR for sensitive and selective tracking of tyrosinase activity at enzyme and cellular level, and investigated its application for liver cancer diagnosis. As expected, HFC-TYR has excellent response ability for tyrosinase sensing at enzyme level, such as large Stokes shift (170 nm), high fluorescence enhancement (178-fold), low detection limit (0.12 U/mL), which indicates its potential for efficient identification of endogenous tyrosinase activity at cellular levels. Unsurprisingly, HFC-TYR is proved to be able detect endogenous tyrosinase levels in various living cells. More importantly, HFC-TYR is successfully used to distinguish HepG2 cells from other cells (SKOV3, HeLa and 293T), indicating that tyrosinase is overexpressed in HepG2 cells and HFC-TYR can specifically identify HepG2 cells at cellular level. Meanwhile, HFC-TYR is able to further monitor the endogenous tyrosinase activity in zebrafish models. Therefore, all the findings confirm that HFC-TYR has the application potential of liver cancer diagnosis.

Near-Infrared Fluorescence Probe with a New Recognition Moiety for Specific Detection and Imaging of Aldehyde Dehydrogenase Expecting the Identification and Isolation of Cancer Stem Cells

Aldehyde dehydrogenase (ALDH) is a vital enzyme that converts aldehyde to acetic acid during alcohol metabolism. ALDH is also a cellular marker of cancer stem cells (CSCs), which plays an important role in cancer diagnosis and prognosis assessment. Therefore, there is a need to explore convenient, selective, and sensitive methods for the detection and imaging of ALDH. Because of the low background fluorescence and high penetration, near-infrared (NIR) fluorescent probes are powerful tools for the detection of ALDH. Until now, only one NIR fluorescent probe has been reported for detecting ALDH. Hence, we synthesized a novel NIR fluorescent probe, Probe-ALDH, by linking the new specific recognition moiety 4-hydroxymethyl benzaldehyde with NIR fluorophore AXPI. Compared with the existing ALDH fluorescent probes, Probe-ALDH has excellent properties, such as a new specific recognition moiety without the substitution of benzaldehyde, a simple synthesis method, emission wavelength in the NIR region, reaction time of only 30 min, and a detection limit as low as 0.03 U·mL^-1, which is better than those of the previously reported probes. The probe effectively eliminates the interference from reactive oxygen species (ROS), amino acids, and amines. More importantly, the flow cytometry results showed that Probe-ALDH has great potential applications in the identification and isolation of CSCs. Ultimately, it was successfully applied to the imaging analysis of endogenous ALDH in HepG2 cells by the addition of inhibitor disulfiram. The excellent performance of Probe-ALDH makes it a promising candidate for drug discovery, cancer diagnosis, and so forth.

Design of a New Hydrazine Moiety-Based Near-Infrared Fluorescence Probe for Detection and Imaging of Endogenous Formaldehyde In Vivo

Formaldehyde (FA), the smallest molecular aldehyde with strong reducing properties, could regulate body homeostasis endogenously during physiological and pathological processes. The effective near-infrared (NIR) fluorescent probe is needed as a visualizer of FA in biologic organisms. In this work, a novel NIR fluorescent Probe-NHNH₂ was designed on the basis of Probe-NH₂ via introducing a strong nucleophilic hydrazine group, which can be used as a quenching and recognizing moiety for the detection of FA. With the treatment of FA, the hydrazine group of Probe-NHNH₂ undergoes condensation and achieves a turn-on NIR fluorescence signal at a wavelength of 706 nm. The spectroscopic performance of Probe-NHNH₂ for FA was evaluated, and it exhibited high sensitivity and selectivity for the detection of FA in solution. Moreover, compared to the amine moiety-based Probe-NH_2, which our group reported, we found that hydrazine moiety-based Probe-NHNH₂, exhibited a better reaction time of within 10 min and a lower detection limit of 0.68 μM, reflecting that the reaction of FA with hydrazine moiety is faster and more sensitive than that of FA with the amino group. More importantly, Probe-NHNH₂ was successfully applied to real-time imaging of endogenous FA by reacting with effective stimulant tetrahydrofolate and scavenger sodium bisulfite in zebrafish and mice. It is expected that we can provide a new rapid, sensitive NIR fluorescence theoretical basis for FA detection and in vivo imaging applications.

A new amine moiety-based near-infrared fluorescence probe for detection of formaldehyde in real food samples and mice

A new amine moiety-based near-infrared fluorescent probe (Probe-NH₂) is developed for detection of formaldehyde in food samples and mice. Probe-NH₂ is constructed and synthesized from the IR-780 via two-step reactions as a hemicyanine skeleton bearing an amino moiety. The response mechanism is based on Schiff base reaction that formaldehyde reacts with amine group to form the corresponding imines. Probe-NH₂ for detection of formaldehyde exhibits excellent analytical performance, including near-infrared fluorescence emission at 708 nm, high selectivity and sensitivity, also provides a response time as low as 30 min with a detection limit of 1.87 μmolL^-1. Notably, we constructed a simple, rapid and visual formaldehyde detection platform based on paper chips in the near-infrared region for the first time. The accurate detection of formaldehyde in real food samples is of great significance, Probe-NH₂ was detected in dried beancurd sticks, endive sprout, frozen shrimp and squid, with good recoveries of 99.60%-112.72%, indicating the reliability of Probe-NH₂ for spiked determination of formaldehyde in contaminated foods. More importantly, Probe-NH₂ has been successfully applied to the detection of endogenous formaldehyde in mice.

Fast visual monitoring of the freshness of beef using a smart fluorescent sensor

Spoiled meat contains many pathogenic bacteria; hence, the intake of spoiled food can lead to various illnesses. To screen the freshness of food, in this study, we devised a ratiometric fluorescence sensor dicyanovinyl coumarin (CMDC) for the determination of cadaverine, an important biomarker for the spoilage of meat. CMDC underwent aza-Michael addition with cadaverine, exhibiting high sensitivity, fast response (50 s), and distinct fluorescence color transition. Test strips fabricated using CMDC showed a noticeable color change from red to green when exposed to cadaverine vapor. The test strips were successfully used to visually monitor the spoilage of beef based on the fluorescence color change. Furthermore, the as-developed test strip coupled with a smartphone provides a simple tool for consumers and suppliers to obtain information about meat quality.

A novel fluorescent off–on probe based on 4-methylumbelliferone for highly sensitive determination of tyrosinase

A novel fluorescent probe for high-sensitivity determination of tyrosinase, with 4-methylumbelliferone as the fluorophore and 3-hydroxybenzyl as the recognition group.

Preparation of Large Conjugated Polybenzimidazole Fluorescent Materials and Their Application in Metal Ion Detection

A new type of conjugated polybenzimidazole (CPBI) was synthesized through a simple polycondensation reaction without metal catalysis, and N-alkylation modification was carried out to solve the problems of solubility and fluorescence properties. A series of nano-microsphere polymers CPBI_n with large conjugation, good solubility, and strong fluorescence has been successfully used as “turn-off” fluorescent probes for the first time. The results show that, under suitable N-alkylation conditions, the obtained CPBI_n can be used as a highly sensitive and selective fluorescent probe for the detection of Cu²⁺ and Zn²⁺ at the same time, and their detection limits are both nM levels. In addition, CPBI₂ can be designed as an ultra-sensitive IMPLICATION logic gate at the molecular level, cyclically detecting Cu²⁺. With the test paper containing CPBI₂, easy and quick on-site detection can be achieved. This research provides a new idea for the brief synthesis of multifunctional materials.