The Enhanced Electrochemiluminescence of Luminol by Resonance Energy Transfer with Solid-phase CdTe Quantum Dots

Accepted Manuscript Title: The Enhanced Electrochemiluminescence of Luminol by Resonance Energy Transfer with Solid-phase CdTe Quantum Dots Author: Chen Yuanyuan Tu Yifeng PII: DOI: Reference:

S0013-4686(14)00957-8 http://dx.doi.org/doi:10.1016/j.electacta.2014.04.177 EA 22683

To appear in:

Electrochimica Acta

Received date: Revised date: Accepted date:

14-2-2014 20-4-2014 29-4-2014

Please cite this article as: C. Yuanyuan, T. Yifeng, The Enhanced Electrochemiluminescence of Luminol by Resonance Energy Transfer with Solid-phase CdTe Quantum Dots, Electrochimica Acta (2014), http://dx.doi.org/10.1016/j.electacta.2014.04.177 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

The Enhanced Electrochemiluminescence of Luminol by

Chen Yuanyuan and Tu Yifeng*

ip t

Resonance Energy Transfer with Solid-phase CdTe Quantum Dots

Institute of Analytical Chemistry, Soochow University,

cr

The Key Lab of Health Chemistry and Molecular Diagnosis of Suzhou,

us

Dushu Lake Higher Education Town, Industrial Park, 215123, Suzhou, P.R.China

an

*: corresponding author, Prof. Yifeng Tu, Tel: 86-13812768378; Fax: 86-512-65101162;

Ac ce p

te

d

M

Email: [email protected]

Page 1 of 18

Abstract Herein a new approach will be reported to enhance the electrochemiluminescence (ECL) of luminol by resonance energy transfer (ECRET) with solid-phase CdTe

ip t

quantum dots (QDs) which were immobilized on the surface of indium tin oxide coated glass. This progressive result suggests a solid-phase ECL substrate which

cr

commenced more sensitive response upon luminol needless any co-reactant. Also the

us

graphene oxide was applied to promote the performance of matrix. On this solid-phase ECL substrate, the detection limit of luminol decreased about one order of

an

magnitude, meanwhile the practicable pH range was enlarged. Also it provides an excellent platform for H2O2 or oxygen monitoring due to they further intensified the

M

ECL. The detection limit for H2O2 decreased two to three orders of magnitudes (to the

d

level of 10-11M).

te

Keywords: Electrochemiluminescence; luminol; CdTe quantum dots; graphene oxide;

Ac ce p

resonance energy transfer; solid-phase substrate

Page 2 of 18

1. Introduction Electrochemiluminescence (ECL) has advantages over chemiluminesence and electrochemistry mainly including better spatio-temporal controllability, higher

ip t

sensitivity and selectivity, universality for inorganic, organic or bio-compounds etc for analytical applications [1, 2]. As one of the most classical luminescent reagents,

cr

luminol has been extensively applied in ECL analysis, but its uses are generally limited

us

to strong alkaline condition and high electrolytic potential [3, 4]. Presently, growing attention has been paid to the ECL of quantum dots (QDs) owing to their unique

an

size-dependent optical, electronic, photophysical and electrochemical properties [5-8]. It originates the possibility to develop the solid-phase ECL substrate but there was the

M

requirement of necessary strong oxidative co-reactants to get recordable ECL emission. So, stronger ECL emission of QDs is aspired best required no co-reactants because

d

they would lead to severe side effects [9, 10]. And, aside the analytical application of

te

QDs’ ECL in solution [11, 12], only few researchers reported the solid-phase QDs for ECL application until today. Wan et al [13] and Tu et al [14] have reported the

Ac ce p

solid-phase TGA-capped CdTe QDs ECL sensor for flow injection analysis respectively, with durabolin or triethylamine (TEA) as co-reactant. Resonance energy transfer (RET), a nonradioactive energy transfer between

closely located donors and acceptors (in normally less than 10 nm) [15], has established a sensitizing platform for fluorescence (FRET) [16], chemiluminesence (CRET) [17] or bioluminescence (BRET) [18, 19]. Thus, the RET with ECL (ECRET) is in expectation to be a more effective technique to get more sensitive ECL performance, but was minimally reported [20, 21]. We have discovered the ECRET between CdTe QDs and luminol in aqueous solution in previous research [22], suggests the prospect to develop the solid-phase ECL substrate for high sensing ability.

Page 3 of 18

Herein, we will report a new progress on the immobilization of CdTe QDs on the surface of indium tin oxide (ITO) coated glass to successfully realize the ECRET with luminol. The ECRET greatly boosts the light emission needless any co-reactant, thus

ip t

promotes the response of luminol on electrode. On the other hand, graphene is a nano-sized 2D amphiphile with low interfacial energy [23]. It has been proved to be an

cr

effective matrix for promoting the performance of chemo-/bio-sensing [24] and

us

electrochemisty [25, 9]. It is introduced into the matrix for immobilization of QDs to enhance the performance. On those solid-phase ECL substrates, the ECRET enhanced

an

the luminescence of luminol, provides an excellent platform for H2O2 or oxygen

M

monitoring due to they further intensified the light emission.

2. Experiments

d

2.1. Reagents and apparatus

te

The luminol was purchased from Fluka (Buchs, Switzerland). 3-aminopropyltrimethoxysilane (APTMS) was purchased from Chengdu Aikeda Chemical Reagent

Ac ce p

Co. Ltd (Chengdu, China). Glutaric dialdehyde (GD) was purchased from Sinopharm Chemical Reagent Co. Ltd (Shanghai, China). Other reagents are all analytical grade and used without further purification. Thioglycolic acid capped CdTe QDs (CdTe/TGA) was synthesized according to

previous paper [26]. The graphene oxide (GO) was synthesized from graphite by a modified Hummers method referred to report [27]. The ECL experiments were carried out on a lab-built system as reported in our previous paper [28]. The electrochemical investigations are carried out with an RST 3000 Electrochemical Workstation (Risetest, Suzhou, P.R.China). Scanning electron microscopy (SEM) was taken with an S-4700 scanning electron microanalyzer (Hitachi,

Page 4 of 18

Japan). The 3D AFM micrographs were obtained with a Dimension Icon Atomic Force Microscope (Bruker AXS Inc., Madison, WI, USA). ITO glass was purchased from Suzhou Nippon Sheet Glass Electronics Co. Ltd. (Suzhou, China).

ip t

2.2. The immobilization of CdTe QDs on ITO The ITO glass was cleaned before use with acetone, ethanol and ethanol/1M

cr

NaOH (1:1, v/v) under sonication for 25 min respectively, flushed with water and dried

us

by N2 blowing. 20 μL of anhydrous ethanol solution of APTMS (0.1%, v/v) was then dropped onto the surface of ITO, and laid in air to allow the volatilization of ethanol.

an

After 20 μL of 0.1% (v/v) GD solution was dropped onto this surface and dried at room temperature, 20 μL of CdTe QDs dispersoid was then cast onto it and airing dried.

0.2 mg/mL.

d

2.3. The optimization of ECL research

M

With related to GO, it was mixed into the APTMS solution previously as the content of

te

The detection conditions such as upper limiting potential, lower limiting potential and the period of pulsed electrolytic potential including other important factors which

Ac ce p

would influence the ECL performance were optimized.

3. Results and discussion

3.1. The morphology and performance of immobilized CdTe QDs film By using cross-linked APTMS/GD as the matrix, the CdTe QDs can be attached

onto the surface of ITO. The SEM images in Figure 1 clearly display the morphology of those films; here the APTMS shows as a cloudy film (Fig. 1A) and the APTMS/GD is spread as a gauzy and serried film (Fig. 1B). When the CdTe QDs had been attached onto this matrix, they were dispersed uniformly and compactly on it (see Fig. 1D). The images C and E in Fig. 1 display the morphology of the film if there was GO mixed in.

Page 5 of 18

Clearly, the presence of GO resulted in a thicker film there the GO built a piled porous structure then the QDs dispersed on it evenly.

ip t

Fig. 1 should be placed here

cr

The AFM investigation revealed the difference of two films, remarkably the

us

insertion of GO resulted a thicker and rougher film (see Fig. 2A and B), just agreed with the SEM observation. The electrochemical impedance spectroscopy (EIS) also

an

evidences the surface alteration during the formation of immobilized QDs film on ITO. As showed in Fig. 2C, the electron transfer resistance (Ret) will obviously increase

M

along with the procedure (10.12, 21.22 and 60.5Ω respectively), meaning the deposition of materials. The function of GO can be found in EIS research, the Ret

d

decreased to 6.76, 17.99 and 38.41Ω respectively (see Fig. 2D) while the GO was

te

mixed in. All of the SEM, AFM and EIS tests indicate that the GO greatly promoted

Ac ce p

the loading quantity of QDs and improved the conductivity of solid substrate.

Fig. 2 should be placed here

3.2. The optimization of detection conditions Fig. 3 shows the influence of the parameters of applied pulsed potential (including

lower, upper limiting potentials and period) on the ECL emission of luminol. It is clear that the greater intensity appeared at -0.5 to -0.6 V of lower limiting potential and above 0.9V of upper limiting potential (see Fig. 3A). As a general knowledge, the luminol will emit the ECL by the ring-opening oxidation under the potential for at least 1.2V; it will lead to the consumption of luminol reagent. In this study, it is clear that

Page 6 of 18

the luminol would emit the ECL under lower potential, meaning the presence of excitons at its first step oxidation [29] by the resonance energy transfer with those reactive oxygen species (ROSs) [30]. This is a meaningful phenomenon which would

ip t

bring in the possibility of non-consumption ECL analysis. On another hand, lower potential is benefit to avoid the possible interfering reactions everyway. So, for

cr

considering to maximizing the efficiency meanwhile to reduce the applied potential,

us

about 0.9 V of upper limiting potential is selectable. The period of pulse is another important factor that influenced the ECL performance. Fig. 3(B) shows an optimal 3s

an

of period. Under these optimal conditions, Fig. 3C shows the ECL signal of luminol on

Fig. 3 should be placed here

d

M

each electrode.

te

3.3. The function of CdTe QDs solid-phase ECL substrate The experimental results indicated that the ECL intensity of luminol on both two

Ac ce p

modified electrodes was heavily pH dependent just as on bare electrode but the optimal pH decreased to 11.0 (see Fig. 4A) from originally about 13.0. It provides wider applicable pH range for more analytical purpose.

Fig. 4 should be placed here

Within those optimized conditions and suitable pH range, the ECL of luminol on both two solid-phase QDs substrates is significantly higher than on bare ITO electrode. The enhanced multiple is 8 or 16 respectively in buffer solution of pH 11.0 (see Fig. 4B). The SFig. 1 displays the linear response of luminol on bare ITO and modified

Page 7 of 18

electrodes. The detection limit is 9.97×10-10M and 9.03×10-10M respectively (see Table 1); lower about one order of magnitude than on bare ITO. Also the modified electrodes have excellent stability. The ECL intensity of luminol on two electrodes decreased only

ip t

4.3% or 2.0% over 18 days, with the RSD of 2.0% and 1.5%, respectively. The RSD for nine repetitive detections with single electrode and seven detections on different

cr

electrodes are 4.2% / 5.6% for APTMS/GD/CdTe/ITO and 3.7% / 7.9% for

us

APTMS/GO/GD/CdTe/ITO, respectively, demonstrates quite acceptable repeatability and reproducibility. It demonstrates the function of immobilized CdTe QDs for

Table.1 should be placed here

d

M

sensitive ECL substrates for application.

an

intensification of ECL of luminol, and suggests a new approach to develop more

te

Also it can be found that the ECL of luminol on both two modified electrodes was related to the intensification from oxygen or H2O2 (see Fig. 4C, D). The SFig. 2 shows

Ac ce p

the linear response of H2O2 on those electrode in different pH conditions and the detection limit of H2O2 declined for two to three orders of magnitude (for 1.13×10-11M and 2.45×10-10M respectively, listed in Table 1). 3.4. The origination of enhanced ECL of luminol on QDs solid-phase ECL substrate It is very important to understand the origination of this enhanced ECL of luminol

by immobilized QDs. Just as discussed in our previous paper, there is a resonance energy transfer between oxidation intermediate of luminol, CdTe QDs and ROSs which strongly enhanced the ECL emission in solution [22]. It offers an opportunity to develop the solid-phase ECL substrate for analytical application. This research has progressed to immobilize the QDs on ITO surface which implied the first evolvement

Page 8 of 18

on the goal. From the results, it is clear there were still the presence of RET to greatly enhance the ECL of luminol. Here also clearly the ROSs acted as an important role in intensification of ECL, proves the similar mechanism of ECRET as in solution. We can

ip t

inference that the RET from QDs to luminol was the main principle of ECL enhancement and the ROSs promoted the process as a moderate oxidant. Ought to be

cr

noted, aside the great enhancement of ECL intensity, the optimal pH condition had

us

decreased, truly benefits the application of ECL. But it is wondering about what actually happened during the process. Refer to the literature [31], we get the

an

knowledge that QDs was very sensitive to the surface status and local environment, especially when they were immobilized on electrode surface. As we known, there were

M

some surface defects on CdTe QDs which had been modified during the refluxing together with TGA in the process of its synthesis. But the Cd2+ ions in those sites will

d

trend to outflow under high pH, may lead to the structural changes or passivation. Thus

te

those QDs will partly disabled under high pH condition. The contribution of GO for the ECL enhancement can be ascribed to the reduced barrier for electron injection

Ac ce p

which will result in a lower onset potential and the enlarged real area of electrode. The following scheme clearly illustrates the mechanism of this enhanced ECL.

Scheme 1. The mechanism of RET process to enhance the ECL of luminol

Page 9 of 18

4. Conclusion In conclusion, CdTe QDs was immobilized onto ITO by using GD crosslinked APTMS as matrix to construct the solid-phase ECL substrate. The GO is benefit to

ip t

build a thicker and porous film which provided greater loading amount of QDs and the better conductivity. These solid-phase QDs substrates provide effective interface to

cr

provide a pathway for resonance energy transfer from excited oxygen and QDs to

us

oxidative intermediate of luminol to intensify its excitation. It not only enhanced the ECL emission of luminol greatly than on bare ITO, but also reduced the required

an

potential for exciting the luminol. This is very significant for further research to explore the all-solid-state ECL electrode by immobilization of luminol onto this

M

substrate; it will lead to the non-consumption detection of luminescent reagent.

d

Acknowledgements

te

This work is supported by the National Natural Science Foundation of China (21175096, 21375091); The Project of Scientific and Technologic Infrastructure of

Ac ce p

Suzhou (SZS201207).

References

[1] M. M. Richter, Chemical Reviews, 104 (2004) 3003. [2] W. Miao, Chemical Reviews, 108 (2008) 2506. [3] C. A. Marquette, L. J. Blum, Analytical and Bioanalytical Chemistry, 385 (2006) 546. [4] J. Suomi, M. Håkansson, Q. Jiang, M. Kotiranta, M. Helin, A.J. Niskanen, S. Kulmala, Analytica Chimica Acta, 541 (2005) 165. [5] C. Burda, X. Chen, R. Narayanan, M.A. El-Sayed, Chemical Reviews, 105 (2005)

Page 10 of 18

1025. [6] S. N. Ding, J. J. Xu, H. Y. Chen, Chemical Communications, (2006) 3631. [7] G. Jie, P. Liu, L. Wang, S. Zhang, Electrochemistry Communications, 12 (2010)

ip t

22. [8] X. Liu, Y. Zhang, J. Lei, Y. Xue, L. Cheng, H. Ju, Analytical Chemistry, 82 (2010)

cr

7351.

us

[9] Y. Wang, J. Lu, L. Tang, H. Chang, J. Li, Analytical Chemistry, 81 (2009) 9710. [10] H. Jiang, H. Ju, Analytical Chemistry, 79 (2007) 6690.

an

[11] J. Lei, H. Ju, TrAC Trends in Analytical Chemistry, 30 (2011) 1351. [12] H. Huang, J. Li, J. J. Zhu, Analytical Methods, 3 (2011) 33.

M

[13] F. Wan, J. Yu, P. Yang, S. Ge, M. Yan, Analytical and Bioanalytical Chemistry, 400 (2011) 807.

d

[14] J. Zhao, M. Chen, C. Yu, Y. Tu, Analyst, 136 (2011) 4070.

te

[15] P. Wu, L. Brand, Anal. Biochem., 218 (1994) 1. [16] K.E. Sapsford, L. Berti, I.L. Medintz, Angewandte Chemie International Edition,

Ac ce p

45 (2006) 4562.

[17] X. Huang, L. Li, H. Qian, C. Dong, J. Ren, Angewandte Chemie, 118 (2006) 5264.

[18] H. Yao, Y. Zhang, F. Xiao, Z. Xia, J. Rao, Angewandte Chemie, 46 (2007) 4346. [19] K.D. Pfleger, K.A. Eidne, Nature Methods, 3 (2006) 165. [20] R. Wilson, M. Katherine Johansson, Chemical Communications, (2003) 2710. [21] M.S. Wu, H.W. Shi, J.J. Xu, H.Y. Chen, Chemical Communications, 47 (2011) 7752. [22] L. Sun, H. Chu, J. Yan, Y. Tu, Electrochemistry Communications, 17 (2012) 88. [23] J. Kim, L.J. Cote, F. Kim, W. Yuan, K.R. Shull, J. Huang, Journal of the

Page 11 of 18

American Chemical Society, 132 (2010) 8180. [24] M. Zhou, Y. Zhai, S. Dong, Analytical Chemistry, 81 (2009) 5603. [25] H. Zhang, X. Lv, Y. Li, Y. Wang, J. Li, ACS Nano, 4 (2009) 380.

ip t

[26] C. Yu, J. Yan, Y. Tu, Microchimica Acta, 175 (2011) 347.

Research, 1 (2008) 203.

us

[28] Z. Yu, X. Wei, J. Yan, Y. Tu, Analyst, 137 (2012) 1922.

cr

[27] X. Sun, Z. Liu, K. Welsher, J.T. Robinson, A. Goodwin, S. Zaric, H. Dai, Nano

[29] H. H. Chu, W. Y. Guo, J. W. Di, Y. Wu, Y. F. Tu, Electroanalysis, 21(2009) 1630.

an

[30] J. J. Zhao, W. Y. Guo, J. J. Li, H. H. Chu, Y. F. Tu, Electrochimica Acta, 61 (2012) 118

Ac ce p

te

d

M

[31] W.R. Algar, A.J. Tavares, U.J. Krull, Analytica Chimica Acta, 673 (2010) 1.

Page 12 of 18

Figure captions:

Fig. 1 The SEM images of (A) APTMS, (B) APTMS/GD, (C) APTMS/GO/GD, (D)

ip t

APTMS/GD/CdTe, (E) APTMS/GO/GD/CdTe on surface of ITO. Inserted are the

cr

enlarged part images.

us

Fig. 2 The AFM images of (A) APTMS/GD/CdTe, (B) APTMS/GO/GD/CdTe and the EIS of (C) APTMS/GD/CdTe, (D) APTMS/GO/GD/CdTe. Here (a) for bare ITO, (b)

an

for APTMS/(GO)/ITO, (c) for APTMS/(GO)/GD/ITO and (d) for APTMS/(GO)

M

/GD/CdTe/ITO in 0.1M NaCl containing 5mM K3Fe(CN)63+/4+ from 1 Hz to 100 kHz.

Fig. 3 (A) The effect of lower/upper limiting potential on the ECL of luminol on (1)

d

ITO, (2) APTMS/GD/CdTe/ITO and (3) APTMS/GO/GD/CdTe/ITO. (B)The effect of

te

pulse period on ECL of luminol on (a) APTMS/GD/CdTe/ITO or (b) APTMS/GO/GD /CdTe/ITO electrode (Cluminol=10-7M, pH=11.0). (C) The ECL signal of luminol on (1)

Ac ce p

ITO, (2) APTMS/GD/CdTe/ITO or (3) APTMS/GO/GD/CdTe/ITO electrode (Cluminol= 1.0×10-6M, pH=9.0, EU=0.9V, EL=-0.5V).

Fig. 4 (A) The effect of pH on ECL intensity of luminol on (a) ITO, (b) APTMS/GD/CdTe/ITO or (c) APTMS/GO/GD/CdTe/ITO. (B) The enhanced multiple of ECL intensity of luminol on (a) APTMS/GD/CdTe/ITO or (b) APTMS/GO/GD /CdTe/ITO within the pH range. (C, D) The ECL intensity of luminol on APTMS/(GO)/GD/CdTe/ITO in (a) oxygen equilibrated, (b) oxygen saturated or (c) deoxygenated solution within the pH range. Cluminol=1×10-7M.

Page 13 of 18

Ac ce p

te

d

M

an

us

cr

ip t

Fig. 1

Page 14 of 18

ip t

Fig. 2

D

C

45

cr

50

50

40

40

30

Z'' / ohm

25 20

20

d

15 10

a

5

c b

10

20

30

40

50

60

70

80

d

c

a

0

0 0

b

10

an

Z'' / ohm

30

us

35

0

10

20

30

40

50

60

Z' / ohm

Ac ce p

te

d

M

Z' / ohm

Page 15 of 18

Fig. 3

3

C

2.0

3

2

2

0.4

2 ECL Intensity

0.6

B

0.9

3 ECL Intensity

b

0.8

0.7

1.5

1.0

1

0.5

0.2

a

0.6

1

1

0.0 -0.9 -0.6 -0.3 0.0

0.3

0.6

0.9

1.2

0.0

1.5

1.5

2.0

Limiting potential / V

2.5

3.0

3.5

4.0

4.5

0

Period of pulse / s

200

400

600

800

1000

1200

Time / s

Ac ce p

te

d

M

an

us

cr

Relative ECL Intensity

0.8

A

ip t

1.0 1.0

Page 16 of 18

Fig. 4 18

B

c Enhancing mutiples

1.2

ECL Intensity

b

15

b 0.9 0.6

a 0.3

12

a

9 6 3

0.0

0 7

8

9

10

11

12

13

7

8

9

pH

b

1.8

D

12

0.9 0.6

c

a

us

ECL Intensity

a

1.2

1.2 0.9 0.6

c

0.3

0.3 0.0

13

b

1.5

1.5

ECL Intensity

11

cr

C

an

1.8

10

pH

ip t

A 1.5

0.0

7

8

9

10

11

12

13

7

8

9

10

11

12

13

pH

Ac ce p

te

d

M

pH

Page 17 of 18

Table 1 The detection limit for luminol and H2O2 on ITO, APTMS/GD/CdTe/ITO and

APTMS/GD /CdTe/ITO

11.0

5.01×10-7

5.30×10-8

6.47×10-9

7.31×10-9

1.09×10-6

9.94×10-8

5.61×10-8

3.25×10-9

5.57×10-8

6.37×10-9

1.49×10-9

7.94×10-10

3.51×10-8 2.18×10-8

ip t

10.0

7.36×10-10

9.97×10-10

1.32×10-11

1.13×10-11

2.78×10-9

4.71×10-10

9.03×10-10

1.96×10-8

3.15×10-10

2.45×10-10

Ac ce p

te

d

M

APTMS/GO /GD/CdTe/ ITO

9.0

us

ITO

For luminol (mol/L) For H2O2 (mol/L) For luminol (mol/L) For H2O2 (mol/L) For luminol (mol/L) For H2O2 (mol/L)

8.0

an

pH

cr

APTMS/GO/GD/CdTe/ITO electrode in different pH condition.

Page 18 of 18