Kinetics Simulation of Luminol Chemiluminescence Based on

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Kinetics Simulation of Luminol Chemiluminescence based on Quantitative Analysis of Photons Generated in Electrochemical Oxidation. Yozo Koizumi, and Yoshio Nosaka J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/jp404891h • Publication Date (Web): 23 Jul 2013 Downloaded from http://pubs.acs.org on July 30, 2013

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The Journal of Physical Chemistry

Kinetics Simulation of Luminol Chemiluminescence based on Quantitative Analysis of Photons Generated in Electrochemical Oxidation

Yozo Koizumi and Yoshio Nosaka*

Department of Materials Science and Technology, Nagaoka University of Technology, Nagaoka, 940-2188 Japan

1 ACS Paragon Plus Environment


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ABSTRACT

Kinetics of electrogenerated chemiluminescence (ECL) of luminol at a gold electrode in alkaline solution was investigated by measuring absolute number of photons emitted in an integrating sphere. The ECL efficiency as the ratio of photon to electric charge was 0.0004 in cyclic voltammography and 0.0005 in chronoamperometry. By numerically solving the rate equations based on a diffusion layer model, the observed time profile of the luminescence intensity could be successfully simulated from the oxidation current of luminol in the chronoamperometry. In the simulation, the rate constant for the oxidation of luminol by superoxide radicals in alkaline solution was determined to be 6 x105 M-1s-1 . The present methodology and the achievement could be widely applicable to various analytical techniques using chemiluminescence.

Keywords: ECL, Integrating Sphere, Superoxide Radical, Cyclic Voltammograph, Gold Electrode, Visual Basic for Applications


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1. INTRODUCTION Electrogenerated chemiluminescence, or electrochemiluminescence (ECL), has been used in a variety of fields such as clinical diagnostics, immunological analysis and environmental monitoring due to its simplicity and high efficiency.1, 2 Luminol (5-amino-2,3-dihydro-1,4-phthalazinedione) is one of the most popular ECL reagents, and a large number of studies for analytical applications have been carried out by utilizing both anodic and cathodic polarized electrodes 3-16. Since luminescence is produced by the reaction of oxidized luminol with reactive oxygen species such as H2O2 and O2-, the mechanism of ECL of luminol involves many reaction processes. In spite of the complex reaction mechanism, cathodic ECL was employed with several kinds of electrodes, such as C-doped TiO2,3 niobate semiconductor,4 and indium tin oxide5 for sensing reactive oxygens in bioactive compound. Furthermore, under anodic polarization, Pt micro electrodes,6 Pt film electrodes,7 metaloporphyrinmodified carbon electrodes,8 and boron-doped diamond electrodes12 have also been applied to detect reactive oxygens. On the other hand, Au electrodes have been used to investigate details of the ECL reaction,17 because the electrode process of Au seems simple. In these cases, however, the intensity of chemiluminescence was measured to be a relative value. As far as we know, there are no reports in literature on studying the absolute number of photons generated by ECL in connection with the observed electrode current. The authors have been investigating a method for detecting the O2- ・ and H2O2 produced in TiO2 photocatalysis by using luminol chemiluminescence.18, 19 As for the luminol chemiluminescence reaction in homogeneous solution, Merenyi and coworkers extensively investigated the kinetic parameters based on the experiments of radiolysis and stopped flow spectroscopy.20-24 These reported kinetic data have been adopted to the analysis of luminol chemiluminescence caused in TiO2 photocatalytic systems.18 Since the CL reaction is used after photoirradiation in photocatalysis, the reported kinetic parameters were not enough for full analysis. Therefore, it would be desirable to analyze ECL reaction by measuring absolute number of photons produced by electrochemical reaction, in which the amount of active oxygens could be estimated from the current measured. Thus, we investigated the absolute number of photons in ECL of luminol and successfully analyzed the reaction processes by determining one of the reaction rate constants which has not been reported so far.



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Furthermore, this method of analysis opens the way to a quantitative technique for sensing the active oxygens.

2. EXPERIMENTAL SECTION

Experimental set up for measuring absolute number of photons induced by electrochemical reaction is shown in Figure 1. Two glass bottles of 10 mL were placed at the middle of an integrating sphere (IS) of 13 cm diameter (Edmund Optics, #58-586 ). One of the bottles contains aqueous solution of 0.1 or 0.5 mM luminol, 0.01 M NaOH, and 0.1 M KCl. Then, an Au-mesh working electrode (WE) (BAS, 012017, surface area of 0.98 cm2) and an Ag/AgCl reference electrode (RE) (BAS, RE-1B, 3M NaCl, E0=0.199 V vs NHE ) were placed in it. The solution was saturated with O2 gas by bubbling for 10 min before the measurements unless stated otherwise. By using a salt bridge, this bottle was connected with another bottle containing 0.1 M KCl solution and a Pt coil counter electrode (CE). This bottle and the inside of the lid of the IS were covered with white filter paper to scatter the light. The potentiostat used was Hokuto Denko HSV-100. One optical port of the IS was connected to a detector with a light-guide. The light incident into the light-guide was path through a 450-nm interference filter and the intensity was measured with a photomultiplier (Hamamatsu, R928) mounted on a socket assembly (Hamamatsu, C1053-01) operated with a high tension at 1000 V. The sensitivity of the photomultiplier and the conversion factor of the assembly were 0.6 mA/W and 0.3V/µA as the catalog values, respectively. The signal was amplified by 100 times by a preamplifier (NF electronics, Model 5307) and recorded with a data logger. Another optical port of the IS was connected to a calibrated standard light source (Avantes, AvaLight-HAL-CAL) with a 200-µm glass fiber. Luminol, NaOH, and KCl (Nacalai Tesque, Ltd.) were used without further purification. The water used was distilled followed by purification with a Milli-Q system.

3. RESULTS AND DISCUSSION


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3.1 Cyclic voltammetry Figure 2(a) shows the cyclic voltammograph (CV) at different scan rates. The aqueous solution for the Au working electrode contains 0.1 mM luminol, 0.01 M NaOH, and 0.1 M KCl. In the CV, two anodic peaks (1 and 2) and three cathodic peaks (3, 4, and 5) are observed. Figure 2(b) shows the CL intensity measured simultaneously with the CV of Figure 2(a). The peak in the CL intensity corresponds to the current peak 1 and the intensity appears proportional to the amplitude of current at the peak. In the absence of the luminol, the peak 1 was not observed. (see Figure S1 in the Supporting Information). On the other hand, when the solution was saturated with N2 gas instead of O2 gas, peaks 4 and 5 and CL peak were not observed (Figure S2). These fact would lead to the conclusion that the peak 1 at +0.35 V (vs. Ag/AgCl) corresponds to the oxidation of luminol and peaks 4 and 5 to the reduction of O2. Since the peaks 2 and 3 was not disappeared even when luminol (Fig. S1) nor O2 (Figure S2) were absent, they are attributable to the oxidation of Au surface and the reduction of the oxidized Au as suggested in literature.17 Figure 3 shows the plot of current at each peak as the function of the square root of the scan rate. The linear relationship indicates that these electrode processes are determined by material diffusion and the amount of reactants could be calculated from the each current. In order to investigate the reaction of luminol CL, we changed the lower limit potential of the CV. Figure 4(a) and (b) show the CV and the CL intensity measured simultaneously, respectively. The CL intensity did not change much or altering the return potentials from -0.75 V (A) to -0.35 V (B). When the return potential was 0 V (C), the CL intensity became almost one half. From these behaviours of the CL intensity, the electrode reaction of luminol can be expressed by the following processes. When electrode potential in the CV was -

limited between 0.0 V and +0.75 V, at the peak 1 (+0.35 V), luminol (LH ) was -

-

oxidized to L ・ (Eq 1) in electrolysis. Then, in successive chemical reactions, L ・ -

-

-

reduces O2 to O2 ・ and then L ・is oxidized to L (Eq 2). The resultant O2 ・reacts -

-

with L ・to produce intermediate hydroperoxy, L O2H, (Eq 3), which becomes an excited state of 3-amino-phthalate ion, AP*, by releasing N2 (Eq 4). A certain fraction (φF) of AP* returns to the ground state by emitting fluorescence (Eq 5). The chemical -

-

-

structures of LH , L ・, L, L O2H , and AP were shown in Figure 5. 5 ACS Paragon Plus Environment


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-

-

LH → L ・+ H++ e-

(1)

-

L ・+ O2 → O2 ・+ L -

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(2)

-

-

L ・ + O2 ・+ H2O → L O2H + OH

-

-

(3)

L O2H → AP* + N2

(4)

AP* → AP + hν

(5)

When the lower limiting potential of CV was spanned down to -0.35 V, O2 -

was electronically reduced to HO2 (Eq 6) , which can react with L in Eq (2) to form the same hydroperoxy intermediate L-O2H (Eq 7) as produced by reaction (3). -

-

-

O2+ H2O + 2e → HO2 + OH -

-

L + HO2 → L O2H

(6) (7)

-

Since HO2 is stable enough to remain during CV, whole L produced in -

reaction (2) can react with HO2 and then this reaction contributes to the CL intensity. Therefore, the observation in Figure 4C, in which the CL intensity became half when the lower limitting potential was 0.0 V, can be explained by the luck of processes of (6) and (7) because O2 was not reduced at this potential. 3.2 Calibration of number of photons In Figures 2 and 4, the unit was mV for the CL intensity recorded after the amplification by 100 times. From the specifications of the photomultiplier and the socket assembly, power to voltage conversion is 180 V/W (=0.3 V/µA × 0.6 mA/W ). Therefore, 1 mV of the recorded voltage corresponds to 56 nW (=10-3/(100×180)) of the power emitted in the IS. To estimate the accurate conversion factors, calibrated standard light was put into the IS. The light power intensity spectrum of the standard light was shown in Figure 6(a) and the calculated power intensity spectrum after passing the 450-nm interference filter was shown in (b). From the power intensity spectrum, the number of photons per unit time at each wavelength was calculated from the Einstein equation 6 ACS Paragon Plus Environment

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( ch/λ ). Then, the integration over the wavelength gave 2.34×1010 photons/s or 10.3 nW as the average value at the wavelength of 450 nm. For this situation of the IS, the recorded voltage was 0.568 mV. Therefore, the conversion factor became 18.2 nW/mV. This value is comparable to the value of 56 nW/mV estimated above by, taking account of the deterioration of the photomultiplier and the difference in the setup arrangement of the two measurements. Since the CL emitted in the IS was measured through the 450-nm interference filter, the observed luminescence intensity was decreased by the filter. To calculate the factor of the decrease, fluorescence spectrum of AP was measured and shown in Figure 6(c). By multiplying the transmittance of the filter at each wavelength, the obtained emission spectrum (d) was obtained. Each intensity was integrated over the wavelength and found that 23 % of the CL intensity in the IS was detected by passing the interference filter. Therefore, the conversion factor for 1 mV of the output voltage was calculated to be 3.0×10-4 nmol/s ( = (1/0.23)×(18.2 nW / 96500 C mol-1)/(1240 V nm / 450 nm)). By using this relationship, the CL intensity observed in Figure 2 can be converted into the amount of photons (in the unit of nmol) after integrating it against the time. On the other hand, the number of electric charge used for the oxidation of luminol can be calculated by integrating the current for peak 1 in Figure 2. In Figure 7 plotted are the number of photons and the charges measured simultaneously in the CV reaction at the scan rates of 20, 40, and 100 mV/s. This figure shows that, at each scan rate, the efficiency of the CL to the oxidation of luminol was ca. 0.0004.

3.3

Chronoamperometry In order to analyze precisely the relationship

between oxidation current and the amount of photons, chronoamperometric measurements were performed using the same experimental setup, but the concentration of luminol was increased for more precise detection of the CL intensity. Figure 8(a) shows the current observed after applying +0.35V to the Au mesh electrode and Figure 8(b) is the CL intensity recorded simultaneously. The electric current (in the unit of mA) can be converted to the oxidation charge in the unit of nmol/s with Faraday constant, while the CL intensity ( in the unit of nW) can be converted to the production rate of photons in the unit of nmol/s. Therefore, the ECL yield was calculated as the ratio of photons to charge and plotted in Figure 8(c). Thus, 7 ACS Paragon Plus Environment


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the averaged value of the ECL yield by the chronoamperometry is determined to be 0.0005. This ECL yield is comparable to that observed in the case of cyclic voltammetry of 0.0004 (Figure 7). However, in the case of CV, since HO2- was formed during cathodic scan, the photoemission yield in the anodic reaction should be half of the value observed in Figure 7 as described above (Figure 2). Thus, ECL yield limited in the anodic reaction should be 0.0002. Namely, the photoemission yield for ECL observed by the chronoamperometry was 2.5 times larger than that of the CV experiment. This difference may be caused by a transient character of scanning voltammetry in the CV experiment. By the oxidation of luminol with K3Fe(CN)6 in aqueous solution saturated with air, the CL quantum yield was reported to be 0.0002.25 Therefore, by taking account that the O2 concentration was five times lager, the quantum yield obtained in the present study is consistent with the literature value. The chronoamperometric curve in Figure 8(a) can be analyzed by Cottrell equation as shown in Figure 9(a), where current density was plotted as the reciprocal function of square root of the time. From the slope and the concentration of 5 × 10-7 mol/cm3 (= 0.5 mM), the diffusion constant DR for luminol was calculated to be 1.35 ×10-5 cm2/s. By using this value the diffusion length at time t can be calculated by (πDRt)-1/2 Thus, the volume of the diffusion layer, Vd(t), was calculated as a function of time from the diffusion length by multiplying the electrode surface area and it was plotted in Figure 9(b).

3.4

Kinetics

simulation

For

the

reaction

processes

of

luminol

chemiluminescence, Merenyi and co-workers extensively studied the reaction mechanisms by using a radiation chemical method and a stopped flow technique, and reported kinetic parameters.20-24 According to the reaction mechanism, the reaction path originated from the oxidation of luminol to generate CL via the formation of -

hydroperoxy intermediate, L O2H, was shown in Figure 10. The broken arrows are -

classified to the minor reaction paths to the formation of L O2H under the present experimental condition and the heavy arrows indicate the major paths. On the assumption of a uniform distribution of reactant in the diffusion layer and using the -

kinetic parameters shown in Figure 10, the formation rate of L O2H can be calculated. On the other hand, the amount of excited state of 3-amino-phthalate, AP*, can be calculated from the experimentally obtained emission intensity and the reported 8 ACS Paragon Plus Environment

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-

fluorescence quantum yield, φF .25 Since the formation of AP* from L O2H (Eq 4) is a monomolecular reaction and no other reaction takes place in alkaline solution, the -

formation rate of L O2H should be the same as that of AP*. Therefore, the calculated -

amount of L O2H can be compared to that of AP* obtained by the experiment. In the chronoamperometric experiment at +0.35 V, since the reduction of O2 -

(Eq 6) cannot occur, O2 ･ is produced from O2 by Eq 2. Therefore, the intermediate -

-

HO2 can be formed by the reduction of O2 ･ by two processes; One rout is -

disproportionation (Eq 8) and another is the reduction with LH (Eq 9)

O2-･ + O2-･ + H+ → O2 + HO2-

-

-

O2 ･ + LH → L ・ + HO2

(8)

-

(9)

The rate constant for reaction (8), k8, was reported to be 6× 1012 [H+] M-1s-1.26 Therefore, in the present experiment where [H+] is 10-12 M, the reaction (8) is negligibly slow. On the other hand, the rate constant for Eq 9 was not reported in the -

literature. The intermediate O2 ･ does not react26 with Na+ and K+ and the reaction rate constant with Cl- was less than 0.014 M-1s-1 .27 Therefore, the reaction (9) may -

play an important role in the decay process of O2 ･. In our previous experiment for -

-

O2 ･ detection,18 the decay rate of CL was increased with LH concentration. From this experimental data, k9 could be estimated to be 104 M-1s-1 by assuming that [L-･] > -

[O2 ･].18 Since this assumption was not supported in the previous experiment, the -

-

decay rate of O2 ･ was affected by the formation of L-･ because O2 ･ was produced by reaction (2). Therefore, the actual value of k9 should be larger than this value. To determined the value, we employed k9 as an adjustment parameter in the present study. -

Since L O2H is produced by the reactions (3) and (7)

23

as shown in the

-

reaction scheme of Figure 10, the formation rate for L O2H is expressed by Eq 10,

-

-

-

= k3 [L ・][O2 ・] + k7 [L][HO2 ]

(10)



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where the concentrations of L-･, O2-･, L, and HO2- can be calculated by solving the following simultaneous rate equations (11)-(14).

・

=

･

-

-

+ k9 [LH ][ O2 ・]

– kd [L-･][ L-･] – k2[L-･][ O2] – k3 [L-･][ O2-･]

・

-

(11)

-

= k2 [L-･][O2] – k3 [L ・][O2 ・]

-

-

-

-

– k8 [O2 ・][ O2 ・] – k9 [LH ][ O2 ・]

(12)

= kd [L-･][ L-･] + k2 [L-･][O2] -

-

-

– ka [L] – kb [L][OH ] – kc [L][LH ] – k7[L][HO2 ]

-

-

-

-

-

= k8 [O2 ・][ O2 ・] + k9 [LH ][ O2 ・] – k7[L][HO2 ]

(13)

(14)

Where, i(t) is the observed oxidation current (in the unit of mA), F represents Faraday constant, and Vd(t) is the volume of diffusion layer (in the unit of cm3). The rate constants used

23

are shown in Figure 10. The protonated form of L-･, i.e., LH･ in

Figure 10, was ignored in the simulation because the pH of the solution (pH 12) was extremely higher than pKa of 7.7. Therefore, the oxidation current for LH- observed at each time was regarded as the formation rate of L-･in Eq 11. By numerical solving of the simultaneous equations using Runge-Kutta-Gill method, the concentrations of L-･, O2-･, L, and HO2- at each time after starting the constant potential electrolysis have been obtained. The program for the calculation was coded in a VBA (Visual Basic for Applications) macro of Microsoft Excel 2010 and shown in the Supporting Information. The unit of time in the calculation was 5x10-5s. In the calculation, the concentration of O2 was fixed to 1.28 mM, which is calculated from the solubility at the temperature of 293 K and the Cl-concentration of 0.1 M. Since NaOH of 0.01M is contained in the solution, the value of pH was set to 12 in the simulation.


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By using the simulated concentration of the reactants, L-･, O2-･, L, and HO2- , -

the rate of L O2H formation was calculated from Eq 10 with the volume Vd(t) at each -

time. In Figure 11 plotted is the time profile of the formation rate of L O2H for different values of k9. The rate of AP* formation calculated from the number of photons observed at each time was also plotted in this figure. Figure 11 shows that the experimental data fit well at k9 = 6×105 M-1s-1. The discrepancy of the simulated result up to 2s is possibly due to the simplicity of the model. The obtained rate constant for the oxidation of luminol by O2- ･ is comparable to that reported for ascorbic acid with 2.7×105 M-1s-1 and that for cytochrome C (ferro) with 5×105 to 6 ×106 M-1s-1.26 The amounts of L- ･ , O2- ･ , L, and HO2- can be also calculated from the simulated concentrations by multiplying volume Vd(t) at each time. On employing k9 = 6×105 M-1s-1, the amount of the intermediates were shown in Figure 12 as a function of time. Since the value of HO2- was oscillated in the simulation, averaged values are plotted as curve (d). As shown in Figure 12, the amount of L-･ (curve (a)) reached a steady value in an early stage of the reaction. However, the concentration of L-･was decreased with time, because the volume of diffusion layer Vd(t) in which the reactants locate was increased as shown in Figure 9(b). In contrast to the steady amount of L-･, the amount of O2-･ was increased gradually as shown in Figure 12(b), where the intermediate O2- ･ is produced by the reaction of L- ･ with O2, whose concentration is constant to time. Therefore, the intermediate O2-･ was increasingly accumulated with time. As for the intermediate HO2-, the formation process is restricted to the disproportionation of O2-･ (Eq 8) and the reduction by LH- (Eq 9) as described above. Although HO2- is a stable intermediate, the concentration was very low under the anodic reaction condition. Therefore, it was revealed by the simulation that the second -

term in the Eq 10, that is the reaction of L with HO2- to form L O2H, is almost negligible. Therefore, this indicates that the factors which affect the amount of L, such -

as pH ([OH ] with reaction rate constant kb in Eq 13), does not vary the total amount -

of L O2H, or ECL intensity. At pH lower than 10.4, the formation of LHO2H may



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become compete with the formation process of AP* as indicated in Figure 10. But the fraction of the suppression can be calculated from the kinetic data.

4. CONCLUSIONS In the present study an electrogenerated chemiluminescence (ECL) of luminol at an Au electrode was performed in an integrating sphere, and the absolute number of photons was measured along with electrode current. The ECL efficiency as the ratio of photon to electric charge was 0.0004 in cyclic voltammetry and 0.0005 in chronoamperometry. The number of photons emitted by chemiluminescence (CL) in chronoamperometry was successfully estimated from the measured current for luminol oxidation by solving kinetic equations based on a diffusion layer model. For the simulation on the CL reaction, a rate constant for the oxidation of luminol by O2-･ , which is an important parameter for the CL photometry of O2-･, was obtained to be 6 ×105 M-1s-1 for the first time. The present procedure of the investigation could be used widely for the analysis of chemiluminescence and then the method employed for the analysis will open the way to develop quantitative detection methods for sensors.

ACKNOWLEDGMENT We thank Dr. Tsutomu Hirakawa and Dr. Atsuko Y. Nosaka for their fruitful discussion to this work.

ASSOCIATED CONTENT Supporting Information. The experimental data for ECL with CV measured without luminol (Figure S1) and under deaerated condition (Figure S2). The VBA program used in the present study. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION 12 ACS Paragon Plus Environment

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Corresponding Author * E-mail: [email protected], Tel/Fax: +81-258-47-9315

ABBREVIATIONS CL; chemiluminescence, ECL; Electrochemiluminescence, CV; cyclic voltammogram, IS; integrating sphere, AP; amino phthalate.

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Chen, J. Electrogenerated

Chemiluminescence of Luminol at A Polyaniline/Graphene Modified Electrode in Neutral Solution. Electrochim. Acta, 2013, 91, 240-245. (10) Cheng, Y.; Yuan, R.; Chai, Y.; Niu, H.; Cao, Y.; Liu, H.; Bai, L.; Yuan, Y. Highly Sensitive Luminol Electrochemiluminescence Immunosensor Based on ZnO Nanoparticles and Glucose Oxidase Decorated Graphene for Cancer Biomarker Detection. Anal. Chim. Acta, 2012, 745, 137-142. (11) Wang, S.; Ge, L.; Yan, M.; Yu, J.; Song, X. ; Ge, S.; Huang, J. 3D Microfluidic Origami Electrochemiluminescence Immunodevice for Sensitive PointOf-Care Testing of Carcinoma Antigen 125. Sensor. Actuator. B, 2013, 176, 1-8. (12) Garcia-Segura, S.; Centellas, F.; Brillas, E. Unprecedented Electrochemiluminescence of Luminol on a Boron-Doped Diamond Thin-Film Anode. Enhancement by Electrogenerated Superoxide Radical Anion. J. Phys. Chem. C 2012, 116, 15500−15504. (13) Haghighi, B.; Bozorgzadeh, S. Enhanced Electrochemiluminescence from Luminol at Multi-Walled Carbon Nanotubes Decorated with Palladium Nanoparticles: A Novel Route for the Fabrication of an Oxygen Sensor and a Glucose Biosensor. Anal. Chim. Acta, 2011,697, 90–97. (14) Cui, H.; Wang, W.; Duan, C.-F.; Dong, Y.-P.; Guo, J.-Z. Synthesis, Characterization,

and

Electrochemiluminescence

of

Luminol-Reduced

Gold

Nanoparticles and Their Application in a Hydrogen Peroxide Sensor. Chem. Eur. J. 2007, 13, 6975 –6984. (15) Han, J. H.; Jang, J.; Kim, B. K.; Choi, H. N.; Lee, W.-Y. Detection of Hydrogen

Peroxide

with

Luminol

Electrogenerated

Chemiluminescence

at

Mesoporous Platinum Electrode in Neutral Aqueous Solution. J. Electroanal. Chem. 2011, 660, 101–107. (16) Ballesta-Claver, J.; Valencia-Mirón, M. C.; Capitán-Vallvey, L. F. Copolymerization

of

Luminol

on

Screen-Printed

Cells

for

Single-Use

Electrochemiluminescent Sensors. Anal. Bioanal. Chem. 2011, 400, 3041–3051. (17) Cui, H.; Zhang, Z.-F.; Zou, G.-Z.; Lin, X.-Q.

Potential-Dependent

Electrochemiluminescence of Luminol in Alkaline Solution at A Gold Electrode. J. Electroanal. Chem. 2004, 566, 305-313. (18) Nosaka, Y.; Yamashita, Y.; Fukuyama, H. Application of Chemiluminescent 14 ACS Paragon Plus Environment

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Probe to Monitoring Superoxide Radicals and Hydrogen Peroxide in TiO2 Photocatalysis. J. Phys. Chem. B, 1997, 101, 5822-5827. (19) Hirakawa, T.; Nosaka, Y. Properties of O2●- and OH● Formed in TiO2 Aqueous Suspensions by Photocatalytic Reaction and the Influence of H2O2 and Some Ions. Langmuir, 2002, 18, 3247-3254. (20) Merenyi, G.; Lind, J.; Eriksen, T. E. The Equilibrium Reaction of the Luminol Radical

with

Oxygen

and

the

One-Electron-Reduction

Potential

of

5-

Aminophthalazine-1,4-dione. J. Phys. Chem. 1984, 88, 2320-2323. (21) Merenyi, G.; Lind, J.; Eriksen, T. E. The Reactivity of Superoxide (O2●-) and Its Ability to Induce Chemiluminescence with Luminol. Photochem. Photobiol., 1985, 41, 203-208. (22) Merenyi, G.; Lind, J.; X. Shen,; Eriksen, T. E. Oxidation Potential of Luminol. Is the Autoxidation of Singlet Organic Molecules an Outer-Sphere Electron Transfer? J. Phys. Chem., 1990, 94, 748-752. (23) Merenyi, G.; Lind, J.; Eriksen, T. E. Luminol Chemiluminescence: Chemistry,Excitation, Emitter. J. Biolumin. Chemilumin. 1990, 5, 53-56. (24) Merenyi, G.; Lind, J.; Eriksen, T. E. Nucleophilic Addition to Diazaquinones. Formation and Breakdown of Tetrahedral Intermediates in Relation to Luminol Chemiluminescence. J. Am. Chem. Soc, 1986, 108, 7716-7726. (25) Lee, J.; Seliger, H. H. Quantum Yields of The Luminol Chemiluminescence Reaction Aqueous and Aprotic Solvents. Photochem. Photobiol. 1972, 15, 227-237. (26) Bielski, B. H. J.; Cabelli; D. E.; Arudi, R. L.; Ross, A. B. Reactivity of HO2/O2- Radicals in Aqueous Solution. J. Phys. Chem. Ref. Data, 1985, 14, 10411100. (27) Long, C. A.; Bielski, B. H. J. Rate of Reaction of Superoxide Radical with Chloride-Containing Species. J. Phys. Chem. 1980, 84, 555-557.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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TOC image


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


potentiostat A V

recorder salt bridge

Ag/AgCl (RE)

Pt (CE)

amplifier

luminol solution

Au mesh (WE)

white cover

photo multiplier

KClaq

standard light

integrating sphere（IS）

interference filter(450 nm)

Fig. 1 Experimental setup for measuring absolute number of photons of chemiluminescence derived from electrolysis.



1.0

current /mA

(a) 0.5

1

2

0.0 3

-0.5 -1.04

CLintensity intensity/(au) CL mV

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 28

5

-1

-0.5

(b)

3

4

0 potential/V

0.5

1

2 1 0 -1

-0.5 0 0.5 potential /V (vs. Ag/AgCl)

1

Fig. 2 (a) Cyclic voltammogram and (b) chemiluminescence(CL) intensity for 0.1 mM luminol in 0.1 M NaCl aqueous solution at different scan rates; 20, 40, and 100 mV/s.


Page 19 of 28

1 0.9 0.8 peak 1 2 3 4 5

0.7

peak current / mA

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.6 0.5 0.4 0.3 0.2 0.1 0

4

6

8

10

12

1/2 1/2 //(mV/s) Vv1/2 (mV/s)-1/2

Fig. 3 Plot of peak current as a function of square root of the sweep rate. Numbers correspond to the peaks in Fig. 2.



current / mA

0.5

(a)

0.0

-0.5

A

B

-1.0

-1

-0.5

C

0

0.5

1

Potential /V

CL mV CL intensity Intensity /(au.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 28

6 5

(b)

B A

4 3

C

2 1 0 -1

-0.5

0

0.5

1

Potential /V

Fig. 4. Dependence of CL intensities on the return potential in the single sweep of cyclic voltammogram; (A) -0.75 V, (B) -0.35 V, and (C) 0.0 V.


Page 21 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 5. Chemical structure of substances related to the luminol chemiluminescence reaction in alkaline solution. LH －; luminol in alkaline solution, L－・; one electron oxidized state of luminol, L; two electron oxidized state of luminol. L－O2H; hydroperoxy luminol, AP; 3-amino-phthalate ion


Page 22 of 28

5 4

(a)

3 2

(b)

1 0 400 1.2 12

Emission intensity ( a.u.)

emission intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

-1 1 power / nW power intensity intensity / nW nm-nm


420

440

460

480

500

480

500

wavelength / nm

1.0

(c)

0.8 8 0.6

(d)

0.4 4 0.2 0.0 0

400

420

440

460

wavelength / nm

Fig. 6. (a) Irradiance spectrum of the standard light and (b) the calculated spectrum of the standard light in the integration sphere through the 450-nm interference filter. (c) Emission spectrum of 3-aminophthalate (AP) measured by the fluorescence spectrophotometer and (d) the calculated spectrum after transmitting the 450-nm interference filter.


Page 23 of 28

0.006 1.2E-08 0.006

12

1E-08

0.004 8E-09 0.004

8

6E-09

charge / nmol

photons / nmol

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Q/mol

0.002 0.002 4E-09

4

photon/nmol Q/mol

2E-09

0

0.000 0.0000 0

0

2

2

4

4

6

6

8

8

10

10

12

12

V1/2 / (mV/s)1/2

Fig . 7 The amount of photons calculated from the CL intensities and oxidation charges observed in Fig. 4 are plotted as a function of square root of scan rates of the CV experiments.



0.40.4

current / mA

(a) 0.30.3

0.20.2

電流値 0

0.10.1

CL intensity / nW

0.0 0 80 0

2

0

2

4

6

8

4 6 time / s

8

60

(b)

10

40

20

0

photons / charge

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 28

0.001

0.00075

10

(c) (c)

0.0008

0.0006

0.00050 0.0004

0.00025

系列1 0.0002

線形 (系列1)

0.00000

00

22

44

66

time / s

88

10 10

0

Fig. 8 (a) Chronoamperometric curve at the potential of +0.35 V (vs. Ag/AgCl) for 0.5 mM luminol solution containing 0.01 M NaOH and 0.1 M KCl. (b) CL intensity emitted in the integrating sphere. (c) ECL yield calculated from the oxidation current in (a) and the CL intensity in (b).


Page 25 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 9 (a) Cottrell plot of the chronoamperometric curve in Fig. 8(a). (b) Volume of the diffusion layer calculated from the slope of the plot in (a).



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

LH-

-

-e

-・ +O2 (k9)

+LH・ (9e8)

L +H2O +OH[0.45] (4e6)

products

pKa=7.7

LH・

L-・

+L-・(2.5e8) +O2(5.5e2)

-

+HO2 (5e7) +LH(1.3e4)

products

Page 26 of 28

+O2-・ (2.3e8)

L-O2H

pKa=10.4

LHO2H

-N2[2.5e5]

AP＊

emission φF= 0.30

-N2[1.5e3]

AP

Fig. 10 Reaction paths for electrochemical emission of luminol and kinetic parameters.17 Solid arrows are reactions involved in the calculation and dashed arrows are processes out of the simulation. Numbers in round brackets and square brackets indicate second order and first order rate constants in the units of M-1s-1 and s-1, respectively. en indicates multiplying by n-th powder of 10.


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Formation rates / 10-12 mol s-1

Page 27 of 28

0.003 3

0.003

[O2]=1.28 mM

k6=4e5 0.0025 AP2-*

0.002 2

k6=6e5 0.002

線形 (AP2-*)

k6=8e5 0.0015

0.001 1

0.001 0.0005

00

0

0 00

2

22

4

44

6

66

8

88

10

10 10

time / s

Fig. 11 Comparison between the formation rate of measured AP* (◆) and those of L-O2H simulated with the rate constants of k9 = 4, 6, and 8×105 M-1s-1.



1.2E-13

amounts of intermediates

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 28

(b)

1.E-11 1.0E-13 1.0E-14 1.0

X(L)/mol

(d)

8.0E-14

(a)

6.0E-14

0.5

X(O2-) 5.E-12

(c)

4.0E-14

X(L-・・）

2.0E-14

0.E+00 0.0E+00 0.0E+00 0.0E+00 0.0

0

0000

1

111

2

3

2222 333 time / s

4

4444

5

555

Fig. 12 The amount of reaction intermediates calculated from the oxidation current in chronoamperometry of LH- with k9 = 6 x 105 M-1s-1. (a) L-・, (b) O2-・, (c) L , and (d) HO2-, in the units of 10-11,10-14 , 10-13 , and 10-13 mol, respectively.


Kinetics Simulation of Luminol Chemiluminescence Based on

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