Resonance Rayleigh Scattering Enhancement Research Articles

A resonance Rayleigh scattering method for sensitive detection of chitosan based on supramolecular complex and mechanism study

A convenient and sensitive resonance Rayleigh scattering (RRS) method for the detection of chitosan (CTS) has been developed via forming Cu-Zn supramolecular complex by complexation reaction, hydrophobic force and electrostatic attraction. The microstructure of the complex was characterized by FT-IR, zeta potential, scanning electron microscope (SEM), UV–vis and RRS. Furthermore, the interaction mechanism among Cu(II), Zn(II), CTS and sodium dodecyl benzene sulfonate (SDBS) was studied. The results revealed that CTS and Cu(II) or Zn(II) formed a supramolecular complex with RRS enhancement in weak acid condition. In the presence of SDBS, the RRS intensity of CTS-Cu(II)-SDBS or CTS-Zn(II)-SDBS was significantly higher than that of the binary system without SDBS at the same CTS concentration. The RRS intensity of CTS-Cu(II)-Zn(II)-SDBS was higher than that of CTS-Cu(II)-SDBS and CTS-Zn(II)-SDBS. The RRS intensity increased linearly with the increase of CTS concentration made it possible to determine CTS quantitatively. In the range extending from 0.10 to 5.00 μg/mL, the equation of linear regression was ΔI=1848.8c-138.3 with a correlation coefficient 0.9996, and the detection limit was estimated to be 37.96 ng/mL. The study was successfully applied for the determination of CTS in health food samples, suggesting its great potential toward CTS analysis.

A resonance Rayleigh scattering and colorimetric dual-channel sensor for sensitive detection of perfluorooctane sulfonate based on toluidine blue.

This work described the use of a basic phenothiazine dye (toluidine blue, TB) as a resonance Rayleigh scattering (RRS) and colorimetric probe for the detection of perfluorooctane sulfonate (PFOS). Owing to the electrostatic interactions between TB and PFOS, TB in the presence of PFOS caused great enhancement of RRS signal at dual-wavelength (I345nm and I506nm) and the ratio changes of absorbance (A502nm/A630nm). The RRS enhancement was attributed to the absorption-rescattering resonance effect, the increase of the molecular size, and the enhancement of hydrophobicity. The analytical procedure was implemented by physically mixing TB, Britton-Robinson buffer solution, and PFOS solution (or sample solution) all-in-one, avoiding the tedious pre-derivatization or the preparation of nanoparticles. The whole approach was less than 8min. Under the optimal conditions, the analytical performance was acquired. The linear ranges for RRS and colorimetry were 0.04-8.0 and 1.0-20μmol/L, with detection limits of 4.2nmol/L and 112nmol/L, respectively. The RRS method was applied to the determination of PFOS in environmental water with recoveries of 93.2-106%. The dual-channel sensor is convenient, rapidly responsive, sensitive, and cost-effective, integrating the advantages of RRS and colorimetry. Graphical abstract.

Redox-derivatization reaction-based rapid and sensitive determination of nitrite using resonance Rayleigh scattering method.

It remains a problem for direct detection of small inorganic nitrite ions using resonance Rayleigh scattering (RRS) method based on the direct dye-binding reaction. In the present study, a redox-derivatization reaction taking only 5min was introduced prior to nitrite detection. In the redox-derivatization reaction, nitrite ions were reduced by excess iodine ions to generate triiodide ions (I3-), which were further derivatized with a cationic dye (basic violet 1, BV1) to form the ion associates of I3--BV1. Therefore, the RRS signal was significantly enhanced, resulting from the increase of particle size and resonance-enhanced scattering effect. The analytical procedure was performed by just mixing nitrite, oxidant, acid, and dye all-in-one, avoiding the tediousness of a multi-step process or the preparation of nanoparticles. The whole detection process including the redox-derivatization reaction was less than 6min. The reaction conditions such as concentration of hydrochloric acid, potassium iodide, and BV1, reaction time, and temperature were investigated. Under optimum conditions, the concentration of nitrite was linear with an RRS signal of I3--BV1 ion associates at 320nm in the range of 0.015-1.2mg/L. The limit of detection (LOD) was calculated to be 3.0μg/L. The RRS method was applied to the determination of nitrite in real samples such as pork sausage, milk powder, and water with recovery of 95.2-112%. With advantages of rapidness, high sensitivity, and high selectivity, the method indicates potential applicability for detection of nitrite in complex samples. The method also provides an instructive protocol for detection of analytes that generate no/weak RRS enhancement after the direct dye-binding reaction. Graphical abstract.

Highly selective detection of epidermal growth factor receptor by multifunctional gold-nanoparticle-based resonance Rayleigh scattering method

Gold nanoparticles (AuNPs) were modified by anti-epidermal growth factor receptor (EGFR) antibody (Ab) and EGFR aptamer (Apt) to obtain multifunctional Apt-AuNP-Ab nanoconjugate immunoprobe. The probe is specifically combined with EGFR to form large volume binding products that exhibited a remarkable enhancement of the resonance Rayleigh scattering (RRS) intensity, and to appear characteristic RRS peak at 312 nm. The scattering enhancement (ΔI) is linear to the EGFR concentration in the range of 20∼100 ng mL−1 with limit of detection of 0.1 ng mL−1. The immunoassay was successfully tested and validated by using esophageal squamous cell carcinoma (ESCC) cell Eca109 cell lysates, as well as human serum samples. The mechanism of selectivity and the reasons for RRS enhancement have been discussed. The experimental results reported in this article opened a new possibility of simple, rapid, selective and reliable determination of EGFR by measuring RRS intensity from multifuncition gold nanosystems.

Resonance Light-Scattering Enhancement Effect of the Y(III)–PUFX–Eosin System and its Fluorescence Study

Highly sensitive and rapid method for the determination of prulifloxacin (PUFX) has been developed on the basis of ion association reaction of PUFX, Y(III) and eosin Y (EY). In pH 6.5 BR buffer medium, PUFX reacts with Y(III) to form a 2:1 cationic chelate which further reacts with EY to form 2:1 ion-association complex. As a result, not only the spectra of absorption are changed, but quenching of fluorescence and significant enhancement of resonance Rayleigh scattering (RRS) is observed. Furthermore, a new RRS spectrum would appear, and the maximum RRS wavelength was located at about 375 nm. The fluorescence quenching (FQ) and enhanced RRS intensity were directly proportional to the PUFX concentration in the ranges of 1.5 – 7.6 μg mL–1 and 0.004 – 3.0 μg mL–1 with detection limits 8.5 ng mL–1 and 1.1 ng mL–1, respectively. The optimum conditions of RRS method and the effects of coexisting substances on the reaction were investigated. In addition the composition of ion-association complexes, the reaction mechanism, the energy transfer between absorption, fluorescence and RRS and reasons for RRS enhancement were discussed. The methods were applied to the determination of PUFX in pharmaceutical samples with satisfactory results.

A convenient method for determination of malathion based on the resonance Rayleigh scattering enhancement

A convenient method for determination of malathion (Mala) based on resonance Rayleigh scattering (RRS) enhancement of L-Tryptophan (L-Try)-Pd(II)-Mala system was proposed in this paper. The interaction between L-Try, Pd(II) and malathion in the system was investigated by fluorescence, RRS and UV–Vis absorption spectroscopy. In the optimum conditions, the RRS intensity of L-Try-Pd(II)-Mala system had a remarkable enhancement because the hydrolysis products of malathion would interact with Pd(II) and L-Try each other formed new complexes, which enhanced intensity was directly proportional to the malathion concentration within a certain range. Based on the RRS enhancement of L-Try-Pd(II) system by Mala, a novel, convenient and specific method for Mala determination was developed. To our knowledge, the method is the first RRS method for determination of Mala was reported. The detection limit for Mala was 6.7 ng/mL and the quantitative determination range was 0.06–0.6 μg/mL. The influence of coexisting substances on RRS was also investigated, and the RRS method exhibited good anti-interference ability. The new analytical method has been applied to determine of malathion in real samples with satisfactory results.

Resonance Rayleigh scattering technique as a detection method for the RP-HPLC determination of local anaesthetics in human urine.

A highly selective and sensitive method of reversed phase high-performance liquid chromatography (RP-HPLC) coupled with resonance Rayleigh scattering (RRS) was developed for the determination of procaine, bupivacaine and tetracaine. Separation of three local anaesthetics was achieved at 35 °C on a C18 column. The mobile phase was 30: 70 (v/v) acetonitrile/triethylamine-phosphoric acid buffer (pH 2.9) at flow rate of 0.3 mL/min. The RRS detection was conducted by taking advantage of the strong RRS enhancement of the local anaesthetics with erythrosine reaction in an acidic medium. Under optimum conditions, the limit of detection (S/N = 3) values were in the range of 2.4-11.2 ng/mL. Recoveries from spiked human urine samples were 95.8%-104.5%. The proposed method applied to the determination of local anaesthetics in human urine achieved satisfactory results. In addition, the mechanism of the reaction is fully discussed. Copyright © 2016 John Wiley & Sons, Ltd.

Resonance Rayleigh Scattering Spectra of an Ion-Association Complex of Naphthol Green B-Chitosan System and Its Application in the Highly Sensitive Determination of Chitosan.

This work describes a highly-sensitive and accurate approach for the determination of chitosan (CTS) using Naphthol Green B (NGB) as a probe in the Resonance Rayleigh scattering (RRS) method. The interaction between CTS and NGB leads to notable enhancement of RRS, and the enhancement is proportional to the concentration of CTS over a certain range. Under optimum conditions, the calibration curve of ΔI against CTS concentration was ΔI = 1860.5c + 86.125 (c, µg/mL), R2 = 0.9999, and the linear range and detection limit (DL) were 0.01–5.5 µg/mL and 8.87 ng/mL. Moreover, the effect of the molecular weight of CTS on the accurate quantification of CTS was studied. The experimental data were analyzed through linear regression analysis using SPSS20.0, and the molecular weight was found to have no statistical significance. This method has been applied to assay two CTS samples and obtained good recovery and reproducibility.

Glutathione-capped CdTe nanocrystals as probe for the determination of fenbendazole

Water-soluble glutathione (GSH)-capped CdTe quantum dots (QDs) were synthesized. In pH 7.1 PBS buffer solution, the interaction between GSH-capped CdTe QDs and fenbendazole (FBZ) was investigated by spectroscopic methods, including fluorescence spectroscopy, ultraviolet–visible absorption spectroscopy, and resonance Rayleigh scattering (RRS) spectroscopy. In GSH-capped CdTe QDs solution, the addition of FBZ results in the fluorescence quenching and RRS enhancement of GSH-capped CdTe QDs. And the quenching intensity (enhanced RRS intensity) was proportional to the concentration of FBZ in a certain range. Investigation of the interaction mechanism, proved that the fluorescence quenching and RRS enhancement of GSH-capped CdTe QDs by FBZ is the result of electrostatic attraction. Based on the quenching of fluorescence (enhancement of RRS) of GSH-capped CdTe QDs by FBZ, a novel, simple, rapid and specific method for FBZ determination was proposed. The detection limit for FBZ was 42ngmL−1 (3.4ngmL−1) and the quantitative determination range was 0–2.8μgmL−1 with a correlation of 0.9985 (0.9979). The method has been applied to detect FBZ in real simples and with satisfactory results.

Resonance Rayleigh scattering method for direct determination of polyacrylamide in water samples using basic phenothiazine dyes

Binding polyacrylamide (PAM) with some basic phenothiazine dyes such as methylene blue (MB), toluidine blue (TB) or Azure B (AB) etc. can result in a significant enhancement of resonance Rayleigh scattering (RRS). The maximum RRS wavelengths (λmax) appear at 348, 340 and 342 nm for MB, TB, and AB systems, respectively. Accordingly, a new RRS method for the direct determination of PAM at nanogram levels has been established. The optimum conditions of these reactions, the influencing factors have been investigated. The RRS intensity is directly proportional to the concentration of PAM in the range of 0.040–5.0 μg/mL for three systems. The methods exhibit high sensitivities, and the detection limits are 15.9 ng/mL for MB system, 44.0 ng/mL for TB system, and 59.8 ng/mL for AB system. The selectivity of the method is investigated by using MB system owing to the highest sensitivity. Concentrations of PAM in tap water, synthetic water and practical waste water samples are determined satisfactorily. The reaction mechanism and RRS enhancement reasons are discussed.

Interaction of proteins with aluminum(III)–chlorophosphonazo III by resonance Rayleigh scattering method

In weak acid medium, aluminum(III) can react with chlorophosphonazo III [CPA(III), H(8)L] to form a 1:1 coordination anion [Al(OH)(H(4)L)](2-). At the same time, proteins such as bovine serum albumin (BSA), lysozyme (Lyso) and human serum albumin (HSA) existed as large cations with positive charges, which further combined with [Al(OH)(H(4)L)](2-) to form a 1:4 chelate. This resulted in significant enhancement of resonance Rayleigh scattering (RRS), second-order scattering (SOS) and frequency doubling scattering (FDS). In this study, we investigated the interaction between [Al(OH)(H(4)L)](2-) and proteins, optimization of the reaction conditions and the spectral characteristics of RRS, SOS and FDS. The maximum RRS wavelengths of different protein systems were located at 357-370 nm. The maximum SOS and FDS wavelengths were located at 546 and 389 nm, respectively. The scattering intensities (ΔI) of the three methods were proportional to the concentration of the proteins, within certain ranges, and the detection limits of the most sensitive RRS method were 2.6-9.3 ng/mL. Moreover, the chelate reaction mechanism or the reasons for the enhancement of RRS were discussed through absorption spectra, fluorescence spectra and circular dichroism (CD) spectra.

Resonance Rayleigh Scattering and Resonance nonlinear Scattering Spectra of Hg(Ⅱ)-phen-CR Systems and Their Analytical Application

In alkaline medium of pH=9.0,Hg2+ reacts with phenanthroline(phen) to form a colorless chelate [Hg(phen)3]2+,which further reacts with Congo red(CR) to form 1∶ 1 ion-association complex.As a result,new peaks appear in the spectra of resonance Rayleigh scattering(RRS),second order scattering(SOS) and frequency doubling scattering(FDS),and their intensities are enhanced greatly.The maximum peaks of RRS,SOS and FDS are located at 378 nm,612 nm and 352 nm,respectively.The enhanced RRS,SOS and FDS intensities are directly proportional to the concentrations of Hg2+.These methods have very high sensitivities and good selectivities,and the detection limits are 2.32 μg/L for RRS,3.20 μg/L for SOS,1.56 μg/L for FDS,respectively.In addition,the influencing factors and the effects of coexisting substances of the reaction were examined by RRS under optimum conditions.The results show that this method has a good selectivity.Therefore,a new method has been developed to determine trace amounts of Hg2+.The reasons for RRS enhancement of the system and reaction mechanism have been investigated.

Spectroscopic study on interaction between bovine hemoglobin and salmon DNA and the analytical applications

In weak acidic medium, bovine hemoglobin would bind with salmon DNA (sDNA) to form a complex. This resulted in changes of absorption and circular dichroism spectra, fluorescence quenching of hemoglobin and remarkable enhancement of resonance Rayleigh scattering (RRS), as well as the appearance of a new RRS spectrum. The spectral characteristics of these spectra were investigated. The type of fluorescence quenching was discussed via the fluorescence lifetime of hemoglobin before and after the reaction as well as effects of temperature on fluorescence intensity. The conformational change of bovine hemoglobin was explored through circular dichroism spectra. The reasons of RRS enhancement were also discussed. In addition, it was found that the fluorescence quenching and RRS methods using bovine hemoglobin as a probe could be used to the determination of DNA. The detection limits (3σ) for sDNA were 5.5ngmL−1 (RRS method) and 202.3ngmL−1 (fluorescence quenching method). The optimum reaction conditions of the two methods were tested. The selectivity of RRS method was examined owing to its higher sensitivity. The RRS method was used for the determination of DNA in synthetic samples with satisfactory results.

Incorporation of high performance liquid chromatography with resonance Rayleigh scattering detection for determination of procaine and lidocaine in human plasma

A reliable and novel high performance liquid chromatography (HPLC) incorporating resonance Rayleigh scattering (RRS) detection was developed for the determination of procaine (Pro) and lidocaine (Lid). This method was based on the weak intensity of RRS of procaine and lidocaine, which can be enhanced by the addition of Erythrosin Yellowish (E-Y) in pH 4.4 acidic medium. The RRS signal was detected at λex = λem = 370 nm. The conditions of separation and detection were optimized (pH, proportion of organic phase, flow rate, reaction temperature, concentration of E-Y and the length of reaction tube). The shape of ion-association complexes was observed by scanning electron microscopy. The reasons for RRS enhancement and the nature of the ion-association complexes were discussed by quantum chemistry calculation, scanning electron microscopy and absorption spectroscopy. The calibration curves of procaine and lidocaine were linear in the range from 0.005 to 15.375 μg mL−1 and the limit of detection (S/N = 3) was 2.3 ng mL−1 for procaine and 15 ng mL−1 for lidocaine. The developed method was validated for the assay of procaine and lidocaine in human plasma samples. The recoveries were between 97.8% and 105.9% which is within acceptable limits.

Direct determination of polyacrylamide in water samples by its enhancement effect on the resonance Rayleigh scattering of some basic diphenyl naphthylmethane dyes

Interaction of partially hydrolyzed polyacrylamide (HPAM) with basic diphenyl naphthylmethane dyes including victoria blue 4R (VB4R), victoria blue B (VBB) and night blue (NB), was characterized by resonance Rayleigh scattering (RRS) spectra. Accordingly a RRS method for the direct determination of HPAM at nanogram levels has been developed. The maximum RRS wavelengths (λmax) appear at 276 nm, 284 nm, and 374 nm for VB4R, VBB, and NB systems, respectively. The RRS spectral characteristics, the influencing factors, and the optimum conditions have been investigated. The RRS intensity was directly proportional to the concentration of HPAM in the range of 0.054∼3.5 µg mL−1 for VB4R system, 0.10∼5.0 µg mL−1for VBB system, and 0.10∼1.5 µg mL−1 for NB system. The methods exhibited high sensitivities. The detection limits were 16.5 ng mL−1 (VB4R system), and 31.0 ng mL−1 (VBB and NB systems). The selectivity of the method was investigated by using VB4R system owing to the highest sensitivity. Concentrations of HPAM in tap water, synthetic water and practical waste water samples were analyzed satisfactorily. The reaction mechanism and RRS enhancement reasons were discussed.

Highly sensitive detection of melamine based on gemini surfactant using enhanced resonance Rayleigh scattering signals

We present here a resonance Rayleigh scattering (RRS) spectrum method for the determination of melamine at the nanogram level using a gemini surfactant (disodium 4-dodecyl-2,4′-oxydibenzenesulfonate, DDOF). It was found that DDOF could react with cationic melamine to form an ion-association complex, which induced the enhancement of RRS intensity and the appearance of a new RRS spectrum in acetate buffer (pH 3.6). The RRS spectral characteristics of the melamine-DDOF system, the optimum conditions of the reaction, and the influencing factors have been investigated. Under optimum conditions, the enhanced RRS intensity was proportional to the concentration of melamine in the range of 0.38–6.30μg/mL. The method has high sensitivity, and the detection limit for melamine is 8.48ng/mL. Furthermore, the reaction mechanism and the reasons of RRS enhancement were evaluated.

Effects of the interaction between Na2Wo4‐6‐benzylaminopurine anionic chelate and rhodamine 6G on the resonance Rayleigh scattering and fluorescence spectra and their analytical applications

In pH 4.99-6.06 Britton-Robinson (BR) buffer medium, 6-benzylaminopurine (6-BA) reacted with Na2WO4 to form 1:1 anionic chelate (6-BA·WO4)(2-), which further reacted with rhodamine 6G to form ternary ion complexes at room temperature. This resulted in a significant enhancement of resonance Rayleigh scattering (RRS) with a maximum RRS wavelength of 316 nm. Meanwhile, the fluorescence of the solution was quenched and excitation (λ ex) and emission (λ em) wavelengths of the fluorescence were 290 and 559 nm, respectively. Intensities of RRS enhancing (ΔIRRS ) and fluorescence quenching (ΔIF) were directly proportional to concentrations of 6-BA. As a result, RRS and fluorescence quenching for determination of trace amounts of 6-BA were developed. Under optimal conditions, linear ranges and detection limits of the two methods were 0.05-15.00 µg/mL and 8.2 ng/mL (RRS), 0.50-15.00 µg/mL and 17.0 ng/mL, respectively. It was found that the RRS method was superior to fluorescence quenching. The influence of these methods were investigated and results showed that RRS had good selectivity. RRS was applied to determine 6-BA in vegetable samples with satisfactory results. Furthermore, the reaction mechanisms of the ternary ion-association system are discussed. In addition, the polarization experiment revealed that the resonance light scattering (RLS) peak of Na2WO4-6-BA-R6G consisted mainly of depolarized resonance fluorescence and resonance scattering. It was speculated that light emission fluorescence energy (EL) transformed into resonance light scattering energy (ERLS), which was a key reason for enhancement of RRS.

Resonance Rayleigh scattering spectral method for determination of urinary 8-hydroxy-2′-deoxyguanosine using gold nanoparticles as probe

A simple, novel and sensitive method was developed to determine 8-hydroxy-2′-deoxyguanosine (8-OHdG), a biomarker of DNA oxidation damage in human urine. This method was based on that 8-OHdG can combined with gold nanoparticles (AuNPs) and enhance the resonance Rayleigh scattering (RRS) intensity of them, and the enhanced RRS intensity is linearly correlated with the concentration of 8-OHdG added over the range of 1.0 × 10−11–2.0 × 10−9 mol L−1. The absorption spectrum and RRS spectrum of the AuNPs–8-OHdG system were analyzed. Parameters that affect the RRS intensities such as pH value, concentration of AuNPs, mixing sequence of the reagents, and coexisting substances were systematically investigated and optimized. The limit of detection (LOD) was 3.0 × 10−12 mol L−1. Interference tests showed that the method developed had very good selectivity and could be used conveniently to determine urinary 8-OHdG without any complicated or time-consuming sample pretreatment processes. Possible mechanisms for the RRS enhancement of AuNPs–8-OHdG system were discussed, and it thought that the volume increase of AuNPs which caused by various reactions between in AuNPs and 8-OHdG were the fundamental factors.

Absorption and Resonance Rayleigh ScatteringSpectra of 6-Benzylaminopurine-Cu(Ⅱ)-Triphenylmthane Dyes Systems and Their Analytical Applications

In HAc-NaAc buffer medium with pH=5.37~5.58,6-benzylaminopurine(6-BA) reacted with Cu(Ⅱ) to form a chelate [6-BA·Cu]2+,which further reacted with triphenylmethane dyes to form 2∶1(Lissamine green system),3∶1(fast green system) and 2.5∶1(water-soluble aniline blue system) ternary ion-associations,respectively.It resulted in the change of the absorption spectra,the great enhancement of resonance Rayleigh scattering(RRS) spectra and frequency doubling scattering(FDS) intensities.The maximum RRS wavelengths were all located at 372 nm.And the increased amount of absorption,the enhancement degree of RRS(ΔIRRS),FDS(ΔIFDS) were all proportional to the concentration of 6-BA during a certain range.The detection limits of methods for Lissamine green system were 5.48 μg/L,119.70 μg/L and 64.20 μg/L,respectively.Therefore,a sensitive method for determination of trace 6-BA with RRS spectrum in 6-BA-Cu(Ⅱ)-LG system has been developed.The method could be applied to the determination of 6-BA in bean sprouts with satisfactory results.In this paper,we used Gaussview 3.07 and Gaussian 03W softwares at a B3LYP/6-31G(base group) level based on the density functional theory(DFT) to calculate the charge distribution of 6-BA.Furthermore,the reaction mechanism and the main reasons for the enhancement of RRS of the Lissamine green system were preliminarily discussed.

Determination of dopamine at the nanogram level based on the formation of Prussian blue nanoparticles by resonance Rayleigh scattering technique

In pH 2.6 HCl solution, dopamine (DA) could reduce Fe(III) to Fe(II), which further reacted with [Fe(CN) 6] 3− to form a Fe 3[Fe(CN) 6] 2 complex. By virtue of hydrophobic force and Van der Waals force, the complex aggregated to form Fe 3[Fe(CN) 6] 2 nanoparticles with the average diameter of about 20 nm. This resulted in a significant enhancement of resonance Rayleigh scattering (RRS). The maximum wavelength of the ion-association complex was located at about 350 nm. The increment of scattering intensity (Δ I RRS) was directly proportional to the concentration of DA in the range of 0.06–1.0 μg/mL. This method has high sensitivity and the detection limit (3 σ) for DA was 3.43 ng/mL. In this work, the characteristics of absorption and RRS spectra of this reaction have been studied. The optimum reaction condition and influencing factors have been investigated. The method was applied to the determination of DA in pharmaceutical samples with satisfactory results. Furthermore, the reaction mechanism and the reasons of RRS enhancement have been explored.