Yusheng Yuan

Determination of sunset yellow in soft drinks based on fluorescence quenching of carbon dots

Fluorescent carbon dots was prepared by heating N-(2-hydroxyethyl)ethylene diaminetriacetic acid in air. The carbon dots were not only highly soluble in water but also uniform in size, and possessed strong blue fluorescence and excitation wavelength-dependent emission properties with the maximum excitation and emission wavelength at 366nm and 423nm, respectively. Food colorant sunset yellow whose excitation and emission wavelength at 303nm and 430nm could selectively quench the fluorescence of carbon dots, efficient fluorescent resonance energy transfer between the carbon dots and sunset yellow is achieved. This was exploited to design a method for the determination of sunset yellow in the concentration range from 0.3 to 8.0μmolL(-1), with a limit of detection (3σ/k) of 79.6nmolL(-1). Furthermore the fluorimetric detection method was established and validated for sunset yellow in soft drinks samples with satisfactory results.

Determination of hypochlorite by quenching the fluorescence of 1-pyrenylboronic acid in tap water

In neutral conditions, hypochlorite-assisted oxidative conversion of 1-pyrenylboronic acid into 1-hydroxypyrene, which leads to 1-pyrenylboronic acid fluorescence quenching, was used as the signaling tool. Compared with 1-pyrenylboronic acid, the maximum excitation (λex = 347 nm) and emission (λem = 392 nm) wavelength of 1-hydroxypyrene had no obvious change. The surfactant Triton X-100, as a micellar additive, was not only used to enhance the stability of the fluorescence probe, but also to improve its sensitivity. When using Triton X-100, the signaling of 1-pyrenylboronic acid was markedly enhanced. Herein, a spectrofluorimetric method for highly selective and sensitive hypochlorite determination has been performed. It can be noted that the fluorescence intensities positively correlated with the hypochlorite concentration over the range of 0.69–6.0 μmol L−1. The detection limit was 0.21 μmol L−1, which is lower than for most of the recently published methods. The experimental conditions were optimized and the effects of coexisting substances are evaluated. The results showed excellent priority because a certain amount of ions, including SO32−, NH4+, Cu2+ and other acid radicals, would not interfere with the measurement. The accuracy and reliability of the method was further ensured by recovery studies using the standard-addition method. In addition, the quenching mechanism, which was proven to be static quenching, has been investigated systematically by the linear plots at varying temperatures based on the Stern–Volmer equation, fluorescence lifetime, and UV-visible absorbance spectra. This method was finally used to detect hypochlorite in local water samples.

A portable synthesis of water-soluble carbon dots for highly sensitive and selective detection of chlorogenic acid based on inner filter effect

In this work, a simple and facile hydrothermal method for synthesis of water-soluble carbon dots (CDs) with malic acid and urea, and were then employed as a high-performance fluorescent probe for selective and sensitive determination of chlorogenic acid (CGA) based on inner filter effect. The as-synthesized CDs was systematically characterized by Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Energy disperse spectroscopy (EDS), UV-vis absorption spectroscopy, spectrofluorophotometry, and the results indicated that the sizes of CDs were mainly distributed in the range of 1.0nm-3.0nm with an average diameter of 2.1nm. More significantly, the as-prepared CDs possessed remarkable selectivity and sensitivity towards CGA with the linear range of 0.15μmolL-1-60μmolL-1 and the detection limit for CGA was 45nmolL-1 (3σ/k). The practical applications of CDs for detection of CGA have already been successfully demonstrated in Honeysuckle. This sensitive, selective method has a great application prospect in the pharmaceutical and biological analysis field owing to its simplicity and rapidity for the detection of CGA.

Determination of adenine based on the fluorescence recovery of the L-Tryptophan–Cu2+ complex

A simple and sensitive method for determination of adenine was developed based on fluorescence quenching and recovery of L-Tryptophan (L-Trp). The fluorescence of L-Trp could efficiently quenched by copper ion compared with other common metal ions. Upon addition of adenine (Ade) in L-Trp-Cu(II) system, the fluorescence was reoccurred. Under the optimum conditions, the recovery fluorescence intensity was linearly correlated with the concentration of adenine in the range from 0.34 to 25.0μmolL(-1), with a correlation coefficient (R(2)) of 0.9994. The detection limit (3σ/k) was 0.046μmolL(-1), indicating that this method could applied to detect trace adenine. In this study, amino acids including L-Trp, D-Trp, L-Tyr, D-Tyr, L-Phe, D-Phe were investigated and only L-Trp could well chelated copper ion. Additionally, the mechanism of quench and recovery also were discussed and the method was successfully applied to detect the adenine in DNA with satisfactory results.

Fluorescence quenching and spectrophotometric methods for the determination of 6-mercaptopurine based on carbon dots

It is of great significance to develop an eco-friendly and sensitive platform for the detection of 6-mercaptopurine (6-MP) because of its side effects and variable activity. Herein, fluorescence quenching and spectrophotometric methods for the detection of 6-mercaptopurine (6-MP) using carbon dots (CDs) as a fluorescence probe are established. 6-MP not only serves to shelter the CDs effectively from being quenched, but also to reverse the quenching and restore the fluorescence due to its ability to remove Hg2+ from the surface of CDs. After the experimental conditions are optimized, the linear range for the detection of 6-MP is 0.04 to 12 μmol L−1, and the detection limit is 0.01 μmol L−1. When it refers to the spectrophotometric method, the linear range is 0.08 to 12 μmol L−1 and the detection limit is 0.02 μmol L−1. The CDs with 6-MP are systematically characterized with transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) absorption and so on. Furthermore, the proposed methods are not only expected to become a potential tool for the fast response of 6-MP but also possess the potential for practical application to be applied in the determination of 6-MP in human serum samples with satisfactory results.

Manganese(III)meso-tetrakis(4-N-methylpyridyl)-porphyrin and mediator thionine co-decorated DNA nanowires for sensitive electrochemical monitoring of mercury(II)

We developed a novel electrochemical DNA biosensor for mercury(II) ion (Hg2+) detection on the basis of manganese(III) meso-tetrakis(4-N-methylpyridyl)-porphyrin (MnTMPyP) and electron mediator thionine (Thi) co-decorated DNA nanowires for signal amplification. The T-rich capture DNA assembled on the electrode could successfully immobilize the primer DNA via specific base-pairing, which triggered the hybridization chain reaction (HCR) to form long DNA nanowires with the aim of loading abundant MnTMPyP and electron mediator Thi. In the electrolyte containing H2O2, the MnTMPyP loaded in the DNA nanowires showed superior peroxidase-like activity and electrocatalyzed the reduction of H2O2, promoting the redox reaction of Thi with a dramatically amplified electrochemical signal. However, in the presence of target Hg2+, Hg2+-mediated thymine base pairs (T–Hg2+–T) are formed between the two neighboring T-rich capture DNAs, which resulted in the release of the MnTMPyP and Thi co-decorated DNA nanowires from the electrode surface, providing a reduced readout signal for the quantitative electrochemical detection of Hg2+. The results showed that the proposed electrochemical DNA biosensor was highly sensitive to Hg2+ in the concentration of 1.0 ng L−1 to 107 ng L−1 with a detection limit of 0.5 ng L−1 (2.5 pM), and it also exhibited excellent selectivity against other interferential metal ions.

Enzyme-catalyzed Michael addition for the synthesis of warfarin and its determination via fluorescence quenching of l-tryptophan

A sensitive fluorescence sensor for warfarin was proposed via quenching the fluorescence of l-tryptophan due to the interaction between warfarin and l-tryptophan. Warfarin, as one of the most effective anticoagulants, was designed and synthesized via lipase from porcine pancreas (PPL) as a biocatalyst to catalyze the Michael addition of 4-hydroxycoumarin to α, β-unsaturated enones in organic medium in the presence of water. Furthermore, the spectrofluorometry was used to detect the concentration of warfarin with a linear range and detection limit (3σ/k) of 0.04-12.0μmolL-1 (R2=0.994) and 0.01μmolL-1, respectively. Herein, this was the first application of bio-catalytic synthesis and fluorescence for the determination of warfarin. The proposed method was applied to determine warfarin of the drug in tablets with satisfactory results.

A Simple and Sensitive Method for Auramine O Detection Based on the Binding Interaction with Bovin Serum Albumin.

A simple, rapid and effective method for auramine O (AO) detection was proposed by fluorescence and UV-Vis absorption spectroscopy. In the BR buffer system (pH 7.0), AO had a strong quenching ability to the fluorescence of bovin serum albumin (BSA) by dynamic quenching. In terms of the thermodynamic parameters calculated as ΔH > 0 and ΔS > 0, the resulting binding of BSA and AO was mainly attributed to the hydrophobic interaction forces. The linearity of this method was in the concentration range from 0.16 to 50 μmol L(-1) with a detection limit of 0.05 μmol L(-1). Based on fluorescence resonance energy transfer (FRET), the distance r (1.36 nm) between donor (BSA) and acceptor (AO) was obtained. Furthermore, the effects of foreign substances and ionic strength were evaluated under the optimum reaction conditions. BSA as a selective probe could be applied to the analysis of AO in medicines with satisfactory results.

Determination of hydroquinone based on the formation of Turnbull's blue nanoparticles using resonance Rayleigh scattering

A novel simple sensitive and inexpensive method based on the formation of Turnbulls blue nanoparticles using resonance Rayleigh scattering has been developed for the determination of hydroquinone (HQ). The results show that Fe3+ is deoxidized to Fe2+ by hydroquinone in pH 2.7 HCl (0.002 mol L−1) solution, then Fe2+ reacts with potassium ferricyanide to form a soluble Turnbulls blue (KFe[Fe(CN)6]), and further aggregates to form {KFe[Fe(CN)6]}n nanoparticles. These results induce a significant enhancement of resonance Rayleigh scattering (RRS). The maximum scattering wavelength of the ion-association complex is located at about 310 nm. The increment of scattering intensity (IRRS) is directly proportional to the concentration of HQ in the range of 0.46–50.0 μmol L−1. This method has high sensitivity and the detection limit (3σ/k) for HQ is 0.14 μmol L−1. In this work, the characteristics of absorption and RRS spectra of this reaction have been studied. The optimum reaction conditions and influencing factors have been investigated. Furthermore, the reaction mechanism and the reasons for the RRS enhancement have been explored. Additionally, the method is applied to the determination of HQ in local river water samples with satisfactory results.

Determination of Sunset Yellow Based on Its Quenching Effect on the Fluorescence of Acridine Orange

Acridine orange (AO) is widely applied as an organic fluorescent probe. In this work, AO was reacted with sunset yellow (SY) to form an ion-association complex in pH 3.4 Britton-Robinson (BR) buffer solution medium. This resulted in the fluorescence quenching of the former and helped to detect the latter with the maximum excitation wavelengths (λex) and emission wavelengths (λem) near 490 and 530 nm, respectively. The assay exhibits high sensitivity and selectivity with a detection limit of 0.002 μmol L-1 and the remarkable quenching of fluorescence was proportional to the concentration of SY in the range of 0.008 - 9.0 μmol L-1. Herein, this finding was utilized to develop a new strategy for simple, rapid, sensitive and selective detection of SY by combining AO based on fluorescence quenching. In addition, the optimum reaction conditions and the effect of foreign substances were studied. The reasons for fluorescence quenching were also investigated, which showed the quenching of fluorescence of AO with SY was a static quenching process. Furthermore, the proposed method was applied in a real sample analysis with satisfactory results.