Ruilin Duan

A novel method for detecting allura red based on triple-wavelength overlapping resonance Rayleigh scattering

A method is presented for the sensitive and selective determination of trace allura red (AR) with ethyl violet (EV) in drink samples, based on triple-wavelength overlapping resonance Rayleigh scattering (TWO-RRS). At pH 10.0 in a Britton–Robinson (BR) buffer medium, AR combined with EV to form an ion-association complex, which resulted in the RRS intensity getting enhanced significantly with new RRS peaks appearing at 341, 508 and 666 nm. The scattering intensities of the three peaks were proportional to the concentration of AR in the range of 0.057–5.0 μmol L−1 (0.028–2.48 μg mL−1). The detection limits for the three single peaks were 0.048 μmol L−1 (0.024 μg mL−1), 0.050 μmol L−1 (0.025 μg mL−1), and 0.057 μmol L−1 (0.028 μg mL−1), while that of the TWO-RRS method was 0.017 μmol L−1 (0.008 μg mL−1), indicating that the TWO-RRS method could detect trace AR with high sensitivity. In addition, the optimum reaction conditions and the effects of foreign substances were studied. The composition of the ion-association complex, and the reasons for the enhancement of RRS were also investigated. The proposed method was successfully applied in a real sample analysis 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.

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.

Spectrofluorometric determination of ascorbic acid using thiamine and potassium ferricyanide

ABSTRACT A simple and sensitive spectrofluorometry method for the determination of ascorbic acid was reported. In alkaline solution, the nonfluorescent thiamine was oxidized by potassium ferricyanide and formed the fluorescent thiochrome with an excitation maximum at 367 nm and an emission peak at 441 nm. However, the fluorescence intensity gradually decreased in the presence of ascorbic acid. The decreased fluorescence was linearly dependent under the optimum conditions with the concentration of ascorbic acid from 0.086–1.5 µmol L−1 with a correlation coefficient of 0.9996. The detection limit of 0.026 µmol L−1 was lower than many other methods. Additionally, the mechanism underlying the enhancement and quenching of this method was discussed. The protocol was used to determine ascorbic acid in tablets and juice 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.

Study on erythrosine-phen-Cd(II) systems by resonance Rayleigh scattering, absorption spectra and their analytical applications.

In pH 7.0-8.0 KH2PO4-Na2HPO4 buffer solution, Cd(II) reacted with 1,10-phenanthroline to form chelate cation [Cd(phen)3]2+, which further reacted with anion of erythrosine to form ternary ion-association complex through electrostatic attraction and hydrophobic effect. This process could result in remarkable absorption spectra change and produce obvious fading reaction at 528 nm. Absorbance change (ΔA) of system was directly proportional to the concentration of Cd(II). Hereby, a highly sensitive spectrophotometric method for the determination of Cd(II) was established. The molar absorption coefficient was 2.29×10(5) L mol(-1) cm(-1) and the detection limit of Cd(II) was 26.5 ng mL(-1). Furthermore, the resonance Rayleigh scattering (RRS) of this system with two peaks located at 371 and 590 nm enhanced significantly, and second-order scattering (SOS) and frequence doubling scattering (FDS) of this system changed notably at 640 and 350 nm, respectively. Under the optimum conditions, the scattering intensities (ΔIRRS, ΔIDWO-RRS, ΔISOS and ΔIFDS) had good linear relationship with the concentration of Cd(II) in certain ranges. The detection limits of Cd(II) were 1.27 ng mL(-1), 1.39 ng mL(-1), 4.03 ng mL(-1), 5.92 ng mL(-1) and 14.7 ng mL(-1) for dual-wavelength overlapping resonance Rayleigh scattering (DWO-RRS), RRS (371 nm), RRS (590 nm), SOS and FDS, respectively. In addition, the suitable reaction conditions and effects of coexisting substances were investigated. The methods had been successfully applied to the determination of Cd(II) in environmental water samples. The recovery range was between 93.0% and 103.0% and the relative standard deviation (RSD) was between 2.5% and 4.3%. The results were in agreement with those obtained from atomic absorption spectroscopy.

Resonance Rayleigh scattering technique for simple and sensitive analysis of tannic acid with carbon dots

Carbon dots (CDs) are raising a substantial amount of attention owing to their many unique and novel physicochemical properties. Herein one-pot synthesized CDs, to the best of our knowledge, were first served as the robust nanoprobe for detection tannic acid (TA) based on resonance Rayleigh scattering technique. The as-prepared CDs can combine with TA via hydrogen bond, resulting in remarkable enhancement of scattering signal with no changes in the fluorescence of CDs. Therefore, a novel protocol for TA determination was established and this strategy allowed quantitative detection of TA in the linear range of 0.2-10.0μmolL-1 with an excellent detection limit of 9.0nmolL-1. Moreover, the CDs based nanoprobe can be applied to the determination of TA in water sample with satisfactory results. Our study can potentially influence our current views on CDs and particularly impressive and offers new insights into application of CDs beyond the traditional understanding of CDs.

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 norfloxacin in food by an enhanced spectrofluorimetric method

BACKGROUND Using a norfloxacin (NFLX)-Nd3+ -cetyltrimethylammonium bromide (CTAB) system for the detection of NFLX, a simple and sensitive method based on fluorescence enhancement was developed. RESULTS In pH 7.0 buffer solution, NFLX reacted with Nd3+ to form a complex, which resulted in fluorescence enhancement of NFLX, and the maximum emission peak shifted from 415 nm for NFLX to 450 nm for NFLX-Nd3+ . Moreover, the fluorescence intensity increased further when the surfactant CTAB was added to NFLX-Nd3+ . Under the optimum conditions, the fluorescence intensity of the NFLX-Nd3+ -CTAB system was linearly correlated with the NFLX concentration in the range 0.038-10 µmol L-1 , with a correlation coefficient (R2 ) of 0.9997. The detection limit (3σ/k) was 0.021 µmol L-1 , indicating that this method can be applied to detect trace NFLX levels. The mechanism of fluorescence enhancement is discussed. The method was used to detect NFLX in fish and chicken samples with satisfactory results. CONCLUSION The present results indicate that this method has the potential for fast and real-time determination of NFLX in food samples