Characteristic Fluorescence Peak Research Articles

Abatement of algal extracellular organic matter by vacuum ultraviolet: Effect of dissolved oxygen and role of in-situ formed reactive oxygen species

Algal extracellular organic matter (EOM) in water produced during the outbreak of algal blooms is difficult to be effectively removed by conventional water treatment processes. Compared with ultraviolet (UV), vacuum ultraviolet (VUV) can additionally radiate 185 nm photons, and VUV can split water to produce reactive oxygen species (ROS) in-situ. Herein, abatement and characteristic variation of EOM under VUV irradiation and the mechanism were investigated. Results indicated that EOM abatement by VUV irradiation were significantly higher than that by UV irradiation. The mineralization rate constant of EOM under VUV was 2.25 times of that under UV. Besides, under VUV irradiation, the abatement efficiency of EOM was promoted with the increased dissolved oxygen (DO), and EOM with a lower initial concentration had a higher abatement efficiency. Intensities of characteristic fluorescence peaks of EOM decreased obviously after VUV irradiation, and removal rates of specific fluorescent organic components were ≥ 74.4%. Under VUV irradiation, organic matter in EOM with higher molecular weight was transformed into that with lower molecular weight. Moreover, hydroxyl radical (•OH) generated in-situ by VUV dissociating water with different DO was directly identified by fluorescence molecular probe technology, and the higher DO caused the higher production of •OH. Furthermore, the mechanism of EOM abatement by VUV was proposed. DO and the produced ROS enhanced the abatement efficiency of EOM, and they played important roles in EOM abatement. This study disclosed abatement characteristics of EOM under VUV irradiation and provided great value for expanding the utilization of VUV in water treatment.

Ratiometric fluorescent and electrochemiluminescent dual modal assay for detection of 2,6-pyridinedicarboxylic acid as an anthrax biomarker

2,6-pyridinedicarboxylic acid (DPA) is an excellent biomarker of Bacillus anthracis (B. anthracis). The sensitive detection of DPA, especially through visual point-of-care testing, was significant for accurate and rapid diagnosis of anthrax to timely prevent anthrax disease or biological terrorist attack. Herein, a ratiometric fluorescent (R-FL) and electrochemiluminescent (ECL) dual-mode detection platform with a lanthanide ion-based metal-organic framework (Ln-MOF, i.e., M/Y-X: M = Eu, Y = Tb, and X = 4,4′,4″-s-triazine-1,3,5-triyltri-m-aminobenzoic acid) was developed. Eu/Tb-TATAB nanoparticles were constructed to identify DPA. The R-FL detection platform quantitatively detected DPA by monitoring the I545/I617 ratio of the characteristic fluorescence peak intensities of Tb3+ ions and Eu3+ ions. The ECL sensing platform successfully quantified DPA by exploiting the burst effect of DPA on the ECL signal. The above methods had highly sensitive and rapid detection of DPA in water and serum samples. The results showed that this dual-mode detection platform may be projected to be a powerful instrument for preventing related biological warfare and bio-terrorism.

In situ formation of fluorescence species for the detection of alkaline phosphatase and organophosphorus pesticide via the ascorbate oxidase mimetic activity of AgPd bimetallic nanoflowers

Sensitive detection strategies for enzymes and their inhibitors not only have critical significance in clinical diagnosis but can be extended to food and environment analysis. Here, bimetallic AgPd alloy nanoflowers were synthesized using carbon dots as the reductant via a two-step reduction method. The AgPd bimetallic nanoflowers exhibit ascorbate oxidase mimetic activity, which can rapidly catalyze the oxidization of ascorbic acid to dehydroascorbic acid (DHA). The DHA can then react with o-phenylenediamine (OPD) to produce 3-(1, 2-dihydroxyethyl)furo[3,4-b] quinoxalin-1(3H)-one (DFQ), accompanying with the characteristic fluorescence peak at 440 nm for DFQ. Alkaline phosphatase catalyzes l-ascorbyl-2-phosphate to generate AA, while organic phosphorus pesticides (OPPs) such as chlorpyrifos can inhibit the activity of alkaline phosphatase. By utilizing the enzyme-nanozyme tandem catalytic reaction, the fluorescence of the system varies in the presence of different concentrations of ALP or OPPs, which can be used to detect ALP in serum and OPPs in vegetables and fruits.

Synthesis, fluorescence properties and structural characterization of two heteronuclear Zn(II)-Pr(III) clusters with a chain-shaped ether Schiff base ligand

Two new Zn(II)-Pr(III) heteronuclear clusters were synthesized by interfacial diffusion, [ZnPr(L)(NO3)2(OAc)(CH3OH)]·CH3CN (1) and [Zn4Pr2L4(terephthalate)2]·(NO3)2 (2) (H2L = bis(3-methoxysalicylaldehyde-3-oxopene-1,5-diamine). They have been characterized by elemental analysis, UV-Vis and IR spectroscopy, and single-crystal X-ray diffraction. Structural analysis revealed that 1 has a heterodinuclear structure, with Zn(II) in the inner cavity generated by deprotonated ligands L2- and Pr(III) in the larger outer cavity. Cluster 2 is a heterohexanuclear structure, in which the Pr(III) bridges two [ZnL] to form a heterotrinuclear secondary unit [Zn2PrL2], and then two terephthalates connect two secondary units to form a heterohexanuclear cluster structure. The solid-state fluorescence properties of clusters and ligand show that there are not only slightly blue-shifted fluorescence peak of ligand, but also characteristic fluorescence peaks of Pr(III) ions in the two clusters: 615 nm (3P0→3H6) for 1, 609 nm (1D2→3H4) and 646 nm (3P0→3F2) for 2, respectively. In the two clusters, the difference of ion fluorescence peaks is attributed to the symmetry difference of coordination geometric environment of Pr(III).

A Ratiometric Fluorescence Amplification Using Copper Nanoclusters with o-Phenylenediamine Sensor for Determination of Mercury (II) in Natural Water

A simple and rapid method for determining mercury (II) has been developed using L-cysteine-capped copper nanocluster (CuNCs) with o-phenylenediamine (OPD) as the sensor. The characteristic fluorescence peak of the synthesized CuNCs was observed at 460 nm. The fluorescence properties of CuNCs were strongly influenced by the addition of mercury (II). Upon addition, CuNCs were oxidized to form Cu2+. Then, the OPD were rapidly oxidized by Cu2+ to form o-phenylenediamine oxide (oxOPD), as evidenced by the strong fluorescence peak at 547 nm, resulting in a decrease in the fluorescence intensity at 460 nm and an increase in the fluorescence intensity at 547 nm. Under optimal conditions, a calibration curve between the fluorescence ratio (I547/I460) and mercury (II) concentration was constructed with a linearity of 0–1000 µg L−1. The limit of detection (LOD) and limit of quantification (LOQ) were found at 18.0 µg L−1 and 62.0 µg L−1, respectively. The recovery percentage was in the range of 96.8–106.4%. The developed method was also compared with the standard ICP-OES method. The results were found to be not significantly different at a 95% confidence level (tstat = 0.365 < tcrit = 2.262). This demonstrated that the developed method could be applied for detecting mercury (II) in natural water samples.

Fluorescence Nanoparticle Sensor Array Combined with Multidimensional Data Processing for the Determination of Small Organics and the Identification of Baijiu

The discrimination and determination of small organics may be employed for baijiu identification. A single nanoparticle was designed as a fluorescence sensor to address this issue. Via specific host-guest interactions, small organics may significantly disrupt the energy transmission of nanoparticles, resulting in sharp changes in characteristic fluorescence peaks, thus allowing the discrimination of single substances or mixtures by principal component analysis (PCA), hierarchical clustering analysis (HCA), and linear discriminant analysis (LDA). The system was characterized by transmission electron microscopy with energy dispersive spectrometry and fluorescence spectroscopy. 15 small flavor organics in baijiu were successfully discriminated. Moreover, the linear relationship between the concentrations of tryptophan and ethyl butyrate with the corresponding responsiveness demonstrated the capabilities of the sensor. The reported device was successfully applied to distinguish 16 baijiu brands. This simple and rapid method has outstanding potential for the characterization of alcoholic beverages.

B-doped graphene quantum dots array as fluorescent sensor platforms for plasticizers detection

Human health and environmental safety are imperceptibly disturbed by illegally used plasticizers. A fluorescence sensor array based on B-doped graphene quantum dots was designed to detect six plasticizers. Specifically, the dexterous design is the first to disperse B-doped graphene quantum dots in two solvents of different polarities (N,N-Dimethylformamide and Cyclohexane), select three characteristic fluorescence peaks of B-doped graphene quantum dots in the above two solvents, and construct a 3 × 2 array, with a total of 6 array points. The basis of the detection is that the plasticizers affect the dispersion of B-doped graphene quantum dots in different solutions, which are accompanied by the change of its fluorescence signals. Or the plasticizers affect the electron transfer process of B-doped graphene quantum dots in different solvents, resulting in fluorescence quenching. Fluorescence information output by the sensor array showed a good linear relationship with the concentrations of the six plasticizers. The quantitative detection capability can be specified as: the detection range is 100 ng/mL-195 mg/mL, and the detection limit is 1.05–11.58 ng/mL. The fluorescence sensor array also showed good analytical performance in real samples, with recoveries ranging from 95% to 106%. This method has satisfactory specificity, reproducibility, stability and practicality, making it potential for application.

A Reversible Optical Sensor Film for Mercury Ions Discrimination Based on Isoxazolidine Derivative and Exhibiting pH Sensing.

We developed a new optical sensor for tracing Hg(II) ions. The detection affinity examines within a concentration range of 0-4.0 µM Hg(II). The sensor film is based on Methyl 2-hydroxy-3-(((2S,2'R,3a'S,5R)-2-isopropyl-5,5'-dimethyl-4'-oxotetrahydro-2'H-spiro[cy-clohexane-1,6'-im-idazo[1,5-b]isoxazol]-2'-yl)methyl)-5-methylbenzoate (IXZD). The novel synthesized compound could be utilized as an optical turn-on chemosensor for pH. The emission intensity is highly enhanced for the deprotonated form concerning the protonated form. IXZD probe has a characteristic fluorescence peak at 481 nm under excitation of 351 nm with large Stocks shift of approximately 130 nm. In addition, the binding process of IXZD:Hg(II) presents a 1:1 molar ratio which is proved by the large quench of the 481 nm emission peak of IXZD and the growth of a new emission peak at 399 nm (blue shift). The binding configurations with one Hg(II) cation and its electronic characteristics were investigated by applying the Density Functional Theory (DFT) and the time-dependent DFT (TDDFT) calculations. Density functional theory (DFT) and the time-dependent DFT (TDDFT) theoretical results were provided to examine Hg(II)-IXZD structures and their electronic properties in solution. The developed chemical sensor was offered based on the intramolecular charge transfer (ICT) mechanism. The sensor film has a significantly low limit of detection (LOD) for Hg(II) of 0.025 μM in pH 7.4, with a relative standard deviation RSDr (1%, n = 3). Lastly, the IXZD shows effective binding affinity to mercury ions, and the binding constant Kb was estimated to be 5.80 × 105 M-1. Hence, this developed optical sensor film has a significant efficiency for tracing mercury ions based on IXZD molecule-doped sensor film.

Accumulation of Uroporphyrin I in Necrotic Tissues of Squamous Cell Carcinoma after Administration of 5-Aminolevulinic Acid.

5-aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PpIX) fluorescence is widely used for the intraoperative detection of malignant tumors. However, the fluorescence emission profiles of the accompanying necrotic regions of these tumors have yet to be determined. To address this, we performed fluorescence and high-performance liquid chromatography (HPLC) analyses of necrotic tissues of squamous cancer after 5-ALA administration. In resected human lymph nodes of metastatic squamous cell carcinoma, we found a fluorescence peak at approximately 620 nm in necrotic lesions, which was distinct from the PpIX fluorescence peak at 635 nm for viable cancer lesions. Necrotic lesions obtained from a subcutaneous xenograft model of human B88 oral squamous cancer also emitted the characteristic fluorescence peak at 620 nm after light irradiation: the fluorescence intensity ratio (620 nm/635 nm) increased with the energy of the irradiation light. HPLC analysis revealed a high content ratio of uroporphyrin I (UPI)/total porphyrins in the necrotic cores of murine tumors, indicating that UPI is responsible for the 620 nm peak. UPI accumulation in necrotic tissues after 5-ALA administration was possibly due to the failure of the heme biosynthetic pathway. Taken together, fluorescence imaging of UPI after 5-ALA administration may be applicable for the evaluation of tumor necrosis.

Cloning and expression of Allophycocyanin gene from Gracilariopsis lemaneiformis and studying the binding sites of phycocyanobilin on its α and β subunits

Allophycocyanin (APC) is a pigment-protein with optical activity in the core of phycobilisomes of cyanobacteria and red algae. Its wide application prospects make it necessary to carry out the recombinant expression of allophycocyanin with optical activity. In this study, apcA and apcB genes encoding two subunits of allophycocyanin were cloned from Gracilariopsis lemaneiformis. Then apcA and apcB genes expressed in Escherichia coli to obtain allophycocyanin. In order to investigate the active sites of allophycocyanin to bind with phycocyanobilin, the Cys-81 and Cys-138 of α subunit and Cys-81 and Cys-157 of β subunit were mutated. SDS-PAGE and Western blotting results verified the expression of allophycocyanin. The fluorescence emission spectra showed the characteristic fluorescence peak of allophycocyanin, which indicated that the recombinant allophycocyanin had optical activity. The recombinant strains with chromophore lyases—CpcU and CpcS—had the higher fluorescence emission peak, indicating that chromophore lyases would catalyze the combination of phycocyanobilin and apo-allophycocyanin more effectively. The binding sites were Cys-81 and Cys138 of allophycocyanin α subunit, and Cys-81 and Cys-157 of allophycocyanin β subunit. The catalytic effect of CpeT was not obvious. This research provides an experimental foundation for understanding the synthesis mechanism of optically active allophycocyanin in G. lemaneiformis.

Enhancing the fluorescence spectrum of frying oil using a nanoscale probe.

This study attempted to develop a probe-based fluorescence technology as a rapid method to discriminate the oxidation degree of oil. The fluorescence probe was made by dissolving the selected probe in a chloroform solvent. A fluorescence landscape profile for each oil sample was obtained to discriminate fluorescence changes during the oxidation process. Parallel factor analysis (PARAFAC) was performed to extract characteristic fluorescence peaks. Then, these characteristic fluorescence peaks and chemical indicators were used to build regression models based on support vector regression (SVR). The correlation coefficients (R) and mean squared error (MSE) in the prediction sets were applied as the assessment parameters for the SVR models as follows: R = 0.9724, MSE = 0.0088 for an acid value. This research suggests that probe-based fluorescence spectroscopy is useful for oxidation evaluation of oil and perhaps other food containing high amounts of oil.

Study on the Fluorescence Spectra Characteristics of Vinegar-Water Solutions

Fluorescence spectra and polarization spectra of vinegar-water solutions with different concentration of CH3COOH have been studied. The characteristics and mechanism of fluorescence spectra are discussed, and polarization degree is calculated. Vinegar-water solutions are excited by ultraviolet (UV) light at 380 nm. The characteristic fluorescence peaks of the solution were identified at 445 nm and 470 nm. The type of emission fluorescence isπ⁎→n. With the increasing concentration of CH3COOH/pH value, the peak intensity is enhanced first, and then fluorescence quenching occurs. The polarization degree confirms the molecular orientation of different sample solutions. This research provides theoretical and experimental basis for the physical/chemical properties and quality of vinegar detection by florescence spectroscopy.

Crystal structure and novel solid-state fluorescence behavior of the model benzoxazine monomer: 3,4-Dihydro-3,6-dimethyl-1,3,2H-benzoxazine

Solid-state fluorescent behavior of the model benzoxazine monomer, 3,4-dihydro-3,6-dimethyl-1,3,2H-benzoxazine denoted as MM, was firstly reported. Three characteristic fluorescence peaks were observed, i.e., (1) the ultraviolet peak at 317nm with the excitation wavelength of 258nm, (2) the blue emission peak at 450nm with the excitation wavelength of 324nm and (3) the other blue fluorescent peak at 454nm with the excitation wavelength of 360nm. It was proved that the benzoxazine core was responsible for the fluorescence of blue light due to the absence of the emission peak in the ring-opening benzoxazine dimer with the same moieties as the benzoxazine monomer MM. The single crystal X-ray structure of the compound MM recorded at 100K showed that the irregular chair conformation of the ring-closure benzoxazine MM gave rise to the fluorescent property since all the members of the oxazine ring other than nitrogen atom arranged themselves at the plane of the benzene ring.

纳米银粒子增强铕(Ⅲ)配合物荧光对鸭蛋蛋清中强力霉素残留量的检测

强力霉素能与铕(Ⅲ)相互作用生成EuDC配合物并发射出铕(Ⅲ)的荧光特征峰, 且该荧光峰能够通过纳米银粒子的金属增强荧光效应得到进一步增强。本文将这一方法应用于鸭蛋蛋清中强力霉素残留量的检测。首先, 利用三维荧光光谱法确定了检测鸭蛋蛋清中强力霉素残留量的最佳激发波长和最佳发射波长分别为390 nm和617 nm。然后, 在最佳激发波长下, 通过单因素实验确定了实验的最佳条件。最后, 通过对浓度范围为0.5~30 mg/L的样本进行分析, 发现鸭蛋蛋清中强力霉素的浓度与荧光强度呈现良好的线性关系, 并得到检测限为0.5 mg/L。研究结果表明, 通过纳米银粒子增强铕(Ⅲ)的荧光可以实现鸭蛋蛋清中强力霉素的快速检测。

Spectral properties of hydrogen-containing organic solution of neodymium chelate

Tris-thenoyltrifluroacetonate of Nd3+ has been prepared and dissolved in DMF solation with very high concentration, and the contained hydrogen has not been substituted by deuterium. The absorption spectrum, emission spectrum, and fluorescence lifetime of the solution were measured. Very obvious characteristic fluorescence peaks were observed at 898 and 1058 nm. Based on Judd-Ofelt theory, three intensity parameters were obtained: Ω2=4.9×10-20 cm2, Ω4=5.1×10-20 cm2 and Ω6=2.5×10-20 cm2. Line strengths Scal, oscillator strengths fcal, radiative transition probabilities Aed, radiative lifetimes τr and branch ratios β were calculated too. The measured lifetime τ of 1058 nm peak is 460 μs, and that of 898 nm 505 μs. Comparison between theoretically computed radiative lifetime τr (682 μs) and the measured lifetime indicates that the non-radiative transition probability of the solution is very low and the fluorescence quantum efficiency very high. High values of three intensity parameters prove the high asymmetric surroundings of Nd3+, which is important for Nd3+ to absorb the excitation energy. Spectropic quality factor Ω4/Ω6>1 makes radiation at 898 nm stronger than at 1058 nm.

2,3,6,7-Tetrasubstituted Decalins: Biconformational Transducers for Molecular Signal Transduction

2,3,6,7-Tetrasubstituted decalins of relative configuration (2β,3α,4aα,6α,7β,8aα) have been synthesized. If substituents as in 6 are chosen, the equilibrium of the biconformational system 2/3 is shifted towards conformer 2. Conversion into the bis(acetal) 16 resulted in a covalently induced double ring flip 17 → 18. A chelation-induced double ring flip (21 → 22) was achieved when 2,2′-bipyridyl substituents were attached by ether linkages at the receptor positions 6 and 7 of the decalin system. Effector groups were introduced by adding pyrene groups, through an (E)-olefin linker, in positions 2 and 3. The resulting compound 25 proved to be an effective device for molecular signal transduction over a signal distance of 1.5 nm. A zinc signal caused a conformational axial-to-equatorial change at the receptor site, which was transduced by a double ring flip of the decalin moiety (28 → 29) to the pyrene effector site, where the induced equatorial-to-axial flip induced a characteristic fluorescence peak.

Diagnosis of head and neck precancerous lesions in an animal model using fluorescence spectroscopy.

Laser-induced fluorescence (LIF) of tissues depends on their biochemical and histomorphologic characteristics. LIF spectroscopic properties of 9,10-dimethyl-1,2-benzanthracene (DMBA)-induced precancerous and early cancerous lesions in a hamster buccal pouch mucosa model were studied. Fluorescence spectra from neoplastic lesions showed a characteristic fluorescence peak in the red region of the visible spectrum centered between 630 and 640 nm when excited with 410-nm light. Using this as a diagnostic criterion, 45 of 49 lesions studied were correctly diagnosed, including early dysplastic lesions. Follow-up study of four dysplastic lesions over 2 weeks revealed an increase in red fluorescence intensity. The findings of these experiments suggest that LIF spectroscopy may be a valuable noninvasive technique not only for early diagnosis of head and neck cancer, but also to probe a possible biochemical surrogate biomarker in the follow-up of suspected lesions.

XeCl excimer laser-induced fluorescence for selective ablation of atheromatous tissue.

In order to develop a reliable laser-induced fluorescence (LIF) guided laser angioplasty system, real time, pulse-by-pulse fluorescence spectra were recorded and the same fiberoptic was used for both detection of the fluorescence and for atheromatous tissue ablation. A 308 nm XeCl excimer laser served as the laser source for both the induction of fluorescence and the ablation. The fluorescence signal was induced at high laser energies during ablation without any serious change in the fluorescence pattern. A new characteristic fluorescence peak at 540 nm for atheromatous tissue was observed after treatment with chlortetracycline hydrochloride (CTC). This allowed the development of an algorithm and a subsequent index to discriminate the atheromatous tissue from the normal tissue. During atheromatous tissue ablation, this index changed as normal tissue was approached, thereby avoiding vessel perforation. Our results suggest that monitoring of this index through the catheter delivering the laser energy enhances selective ablation while simultaneously reducing the risk of vessel perforation.

Molecular film technology for biosensors

Two different molecular film technologies have been developed for fabricating biosensors. Firstly, bovine serum albumin spread on the air-water interface was cross-linked and transferred onto the glass surface, on which various molecular assemblies were formed by the bioaffinity technique. Secondly, a protein monolayer was adsorbed from an aqueous phase on the potential-controlled electrode surface, which was followed by electrochemical polymerization and deposition of pyrrole between the protein molecules to make the adsorbed protein film conductive. A unique optical biosensor for taste has been fabricated by depositing fluorophore-containing Langmuir-Blodgett (LB) films on the glass surface. Each layer of the LB films exhibits its characteristic fluorescence peak which is quenched or enhanced in contact with taste substances. The sensor consisted of three different LB films containing pyrene and anthracene and deposited on a glass plate. Novel performance was demonstrated with the response of the sensor to glutamate and nucleotide umami substances.

Anthocyanin Pigments in Bing Cherriesa

SUMMARYThe anthocyanin pigments of Bing cherries (Prunus avium L. var. Bing) were extracted with 1% methanolic HCl, partially purified by extraction from an n‐butanol‐ether mixture with water, and then separated by paper chromatography with various solvents. The anthocyanins were identified by, Rf values, sugar moiety, alkaline degradation products of the aglycone, partial acid hydrolysis, and absorption spectra. The major pigments were shown to be cyanidin 3‐rutinoside and cyanidin 3‐glucoside. Also present were small amounts of cyanidin, peonidin, peonidin 3‐gucoside, and peonidin 3‐rutinoside. The fluorescence spectra of the anthocyanin pigments, when excited with an incident light at 300 mμ, can be used to differentiate the anthocyanins. The cyanidin‐containing pigments have a characteristic fluorescence peak at 520 mμ, whereas the peonidin ones exhibited a peak at 610 mμ.