Materials Science and Engineering C 32 (2012) 2169–2174
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Electrogenerated chemiluminescence sensor for formaldehyde based on Ru(bpy)32+-doped silica nanoparticles modified Au electrode Lin Chu, Guizheng Zou, Xiaoli Zhang ⁎ School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China
a r t i c l e
i n f o
Article history: Received 12 October 2011 Received in revised form 15 May 2012 Accepted 27 May 2012 Available online 1 June 2012 Keywords: Electrogenerated chemiluminescence Formaldehyde Ru(bpy)32+-doped silica nanoparticles (RuDSNPs) Sensor
a b s t r a c t A novel and sensitive electrogenerated chemiluminescence (ECL) sensor for formaldehyde was developed with the amine-functionalized Ru(bpy)32+-doped silica nanoparticles (Ru-DSNPs) as ECL emitter. Ru(bpy)32+ doped on the silica nanoparticle can maintain its electrochemical activities, which made silica nano-beads a excellent carrier of Ru(bpy)32+ species. The uniform Ru-DSNPs (about 75 nm) were conjugated with Au electrode using mercaptoacetic acid as the intermediate to fabricate an ECL sensor for formaldehyde. The ECL analytical performances of this ECL sensor for formaldehyde based on its enhancement ECL emission of Ru(bpy)32+ were investigated in details. Under the optimum condition, the ECL intensity was linear with the formaldehyde concentration in the range of 1.0 × 10 − 8 mol/L to 1.0 × 10 − 6 mol/L. The detection limit was 6.0 × 10− 9 mol/L (S/N = 3). This approach offered obvious advantages of being simpler, faster, and more stable compared with other sensors, and possessed great potential for formaldehyde detection which could be applied to determine directly the formaldehyde in real samples without pre-separation. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Recently, formaldehyde as one of the harmful volatile organic compounds (VOCs) have attracted considerable attention since it have been widely used in many areas such as chemicals, household products, building materials [1–7] and can even be found in fruits and vegetables [8]. It can increase the risk of impairing human health including cause cancer [9,10]. The maximum permitted concentration of formaldehyde vapor established by World Health Organization (WHO) is 80 ppb and this is lower than the detection limit (410 ppb) of the human sense of smell [2,11]. Although many methods have been reported for detecting formaldehyde, such as spectrophotometry [12], chromatography [13,14], fluorometry [15], mid-IR difference-frequency generation [16], piezoelectric sensor [17] and electrochemical biosensor [18], simple, rapid and sensitive detecting formaldehyde is still under urgent demand because most of the reported methods are restricted by the attainable sensitivity and the requirement of large, expensive, and elaborate laboratory equipment. As an analytical technique, electrogenerated chemiluminescence (ECL) assays possess several advantages such as low background noise, high sensitivity, as well as high versatility [19]. Among many of the electrogenerated systems, the Ru(bpy)32+ based ECL is of good selectivity, high stability, and it has been used for detecting
⁎ Corresponding author. Tel.: + 86 53188364446; fax: + 86 53188564464. E-mail address:
[email protected] (X. Zhang). 0928-4931/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.msec.2012.05.047
various samples [20]. Recently, ECL of Ru(bpy)32+ using formaldehyde as coreactants have been investigated by Hu et al. [21]. It can be used to determine formaldehyde in an aqueous solution. However, in this method relying on the Ru(bpy)32+, only a part of the Ru(bpy)32+ species in the solution, which reaches the electrode through diffusion, emits light. Thus, a large number of Ru(bpy)32+ in the solution are not used, decreasing the sensitivity. If the Ru(bpy)32+ molecules are immobilized on the electrode surface, the sensitivity of ECL would markedly increase. The reaction scheme for Ru(bpy)32+ ECL reveals that is regenerated at the electrode surface during the ECL reaction. Therefore, extensive efforts have been made to immobilize Ru(bpy)32+ onto electrode surface. The immobilizations of Ru(bpy)32+ onto a solid electrode surface are important for Ru(bpy)32+ ECL applications because it can simplify experimental design and reduce the expensive reagent. Dong's group developed an ECL sensor based on Ru(bpy)32+-doped silica nanoparticles (Ru-DSNPs) for detecting tripropylamine (TPA) [22]. Miao's group reported a double covalent coupling method to immobilie Ru(bpy)32+ for the fabrication of highly sensitive and reusable ECL sensors [23]. Yun et al. fabricated an ECL sensor for TPA based on the Ru-DSNPs/chitosan composite film modified electrode [24]. In this work, we provided a new strategy using silica nano-beads as the carrier of Ru(bpy)32+ species to bind up Ru(bpy)32+ and enhance ECL signal. We constructed an ECL sensor for formaldehyde based on the Ru-DSNPs modified Au electrode (Ru-DSNPs/Au electrode). Compared with the research of bounding Ru(bpy)32+ with the chitosan (CHIT) by H-bonding interaction, the proposed method of using mercaptoacetic acid as the intermediate by chemical bond
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to conjugate Ru-DSNPs with Au electrode yielded more Ru(bpy)32+ to be immobilized on the electrode, and showed a good sensitivity. Keeping in mind the importance of research for volatile organic compounds and the advantages of nanomaterials in the field of sensors, we developed this new ECL sensor for the detection of formaldehyde, which exhibited excellent sensitivity and stability for the determination of formaldehyde in real samples.
activate the carboxy group. Finally, 10 μL amine-functionalized RuDSNPs solution (2.8 mg Ru-DSNPs in 1 mL 0.1 mol/L Na2HPO4NaH2PO4 buffer solution) was dropped on the electrode and incubated for 5 h at 37 °C. The fabricating steps are outlined in Scheme 1.
2. Experimental
First, the 0.1 mol/L Na2HPO4-NaH2PO4 buffer solution containing formaldehyde was degassed with N2, Then the ECL measurement was performed using a self-made quartz cell and a three-electrode system that consisted of Ru-DSNPs modified Au working electrode, a saturated calomel reference electrode and a Pt wire auxiliary electrode. During measurement, the working electrode was scanned from 0.2 to 1.4 V at a scan rate of 50 mV/s in the anaerobic solution and the ECL intensity (IECL) versus applied potential (Ep) was recorded.
2.1. Apparatus and reagents The voltammetric and ECL measurements were performed using a CHI802 electrochemical analyzer (CH Instruments, Austin, TX, USA). A PMT (model H9305-04, Hamamatsu Photonics K. K., Japan) with a spectral width of 185–830 nm was used to measure ECL emission. During measurement, a potential was applied to the working electrode via a CHI 802 electrochemical analyzer (CH Instruments, Austin, TX, USA), and ECL emission was detected by a H9305-4 photomultiplier tube (Hamamatsu, Japan). Formaldehyde (HCHO, 37 wt.%) and mercaptoacetic acid (TGA) were obtained from Shanghai Chemical Reagents Co. Ltd. Tris (2, 2bipyridyl) ruthenium (II) chloride (Ru(bpy)32+) and Triton X-100 were acquired from Sigma-Aldrich (St. Louis, MO, USA). 3Aminopropyltriethoxysilane (APTS) was purchased from Acros (Belgium). Tetraethylorthosilicate (TEOS) was obtained from Damao Chemical Reagents Co. Ltd. (Tianjin, China). N-hydroxysuccinimide (NHS) was from Huifeng Chemical Industry Ltd. (Weinan, China). 1ethyl-3-(3-dimethyl-aminopropyl) carbodiimide hydrochloride (EDC) was from Shanghai Medpep Co. Ltd. (Shanghai, China). Other chemicals were obtained from standard reagent suppliers. Doubly distilled water was used to prepare the solution. 2.2. Preparation and surface modification of the Ru-DSNPs The Ru-DSNPs were prepared according to previously published work [25,26]. First, 1.77 mL of Triton X-100, 7.5 mL of cyclohexane, 1.8 mL of hexylalcohol, and 340 μL of Ru(bpy)32+ (40 mmol/L) were added into a 20 mL glass-vial with constant magnetic stirring for 30 min. Then, a polymerization reaction was initiated by adding 100 μL of TEOS and 60 μL of NH3·H2O (28–30 wt.%). After constant magnetic stirring for 24 h under 30 °C water bath, the RuDSNPs were isolated with acetone, washed successively with ethanol and water for three times each to remove any surfactant molecules, and dried in 37 °C incubator. Then the obtained Ru-DSNPs were functionalized according to the literature [26,27]. 0.01 g of RuDSNPs and 50 μL APTS were added into 5 mL anhydrous toluene. The mixture was refluxed under dry nitrogen for 3.5 h. The surface modified Ru-DSNPs were separated by centrifugation, followed by washing with toluene for three times and drying with nitrogen. Finally, the above amine-functionalized Ru-DSNPs were dispersed into the doubly distilled water and stored at 4 °C for later use.
2.4. Analytical procedure
3. Results and discussion 3.1. Characterization of the Ru-DSNPs The Ru-DSNPs prepared by a W/O microemulsion method result in the production of highly monodisperse dye-doped silica nanoparticles [28]. The as-prepared Ru-DSNPs are uniform in size, about 75 ± 5 nm as characterized by TEM shown in Fig. 1. In addition, SEM was also used to characterize the coating on the electrode surface. As seen from Fig. 1, inset, the Ru-DSNPs (2.8 mg/mL) dispersed evenly on the Au electrode is almost monolayer. As the as-prepared RuDSNPs are uniform in size with 75 nm, the thickness of the coating with monolayer is about 80–100 nm. The fluorescence emission spectra also show that Ru-DSNPs have characteristic emission at 610 nm when excited at 460 nm, similar to that of free Ru(bpy)32+, indicating the entrapped Ru(bpy)32+ uphold its optical properties. The fluorescence emission spectra of free Ru(bpy)32+ and Ru-DSNPs in 10 mmol/L PB is shown in Fig. A.1, appendix. 3.2. ECL behavior of Ru-DSNPs/Au electrode ECL study was performed to characterize the Ru-DSNPs modified Au electrode. Fig. 2 shows the ECL-potential curves of various Ru(bpy)32+ molecule. The peak potential for ECL of immobilized RuDSNPs (curve a) and free Ru-DSNPs (curve b) is around 0.9 V, which is similar to that of the free Ru(bpy)32+ ions (curve c). These results confirmed that Ru(bpy)32+ entrapped in the Ru-DSNPs maintained their ECL features. Besides, compared Ru-DSNPs immobilized on Au electrode with the free Ru-DSNPs in solution, the former have a stronger ECL intensity, indicating that the method of using mercaptoacetic acid as the intermediate to conjugate the uniform functional RuDSNPs with Au electrode yielded more Ru-DSNPs to participate in the reaction on the electrode. 3.3. ECL mechanism
2.3. Fabrication of the ECL sensor A gold disk electrode with diameter of 4 mm was polished carefully with 0.50 and 0.05 μm α-Al2O3 power on fine abrasive paper, respectively, followed by ultrasonic cleaning with distilled water and absolute ethanol for 5 min each. Then the electrode was activated in 0.5 mol/L sulfuric acid solution by several successive voltammetric scanning from 0 to 1.5 V until a steady voltammetric curve was obtained. After cleaning, the electrode was immersed in 10 mL 0.05 mol/L solution of TGA for 10 h. And TGA molecular can be self-assembly on Au electrode by gold-sulfur bond. Then being cleaned with water, 10 μL EDC (100 mg/mL in H2O) and 10 μL NHS (100 mg/mL in H2O) were dropped on the electrode for 2 h to
Fig. 3 shows the cyclic voltammetric (CV) curves of bare Au (Fig. 3A) and Ru-DSNPs/Au electrode (Fig. 3B) in the absence and presence of HCHO. As seen from Fig. 3, an irreversible redox couple
Scheme 1. The fabricating steps of the ECL senor.
L. Chu et al. / Materials Science and Engineering C 32 (2012) 2169–2174
RuðbpyÞ3
corresponding to the oxidation (Au-3e − → Au 3+) and reduction (Au 3++3e − → Au) of Au electrode was observed at 0.9 V and 0.3 V, respectively (curve a and b), and another reversible redox couple corresponding to the oxidation (Ru(bpy)32+ − e → Ru(bpy)33+) and reduction (Ru(bpy)33+ + e → Ru(bpy)32+) of Ru(bpy)32+/3+ at 1.0 V can be observed at Ru-DSNPs/Au electrode (curve c and d). Meanwhile, the oxidation currents at Au and Ru-DSNPs/Au electrode increase after adding HCHO, meaning the occurrence of oxidation of HCHO. In addition, the presence of HCHO does not change markedly the oxidation and reduction peak currents of Ru(bpy)32+, indicating that HCHO cannot electrochemically catalyze the oxidation and reduction of Ru(bpy)32+. The ECL-potential profiles of Ru-DSNPs/HCHO system are shown in Fig. 4. As can be seen, only one ECL peak was observed in potential of 0.9 V (first peak) in the absence of HCHO (Fig. 4, inset, curve a), indicating simple Ru(bpy)32+ generate the ECL in the aqueous solution. The possible reaction mechanism should be the same with literature [29], which included the following two steps: RuðbpyÞ3 RuðbpyÞ3
2þ
3þ
−e→RuðbpyÞ3
3þ
−
þ OH →RuðbpyÞ3
RuðbpyÞ3
•
2þ
→RuðbpyÞ3
0.8
•
þ OH
2þ
2þ
1 þ þ O2 þ H 2
ð3Þ
þ hν
ð4Þ
A
0.0
-0.8
a
-1.6
-2.4
ð1Þ 2þ
þ OH → RuðbpyÞ3
Hu et al. [21] observed that HCHO could greatly enhance the ECL of Ru(bpy)32+ at glassy carbon electrode, but not at Au and Pt electrode. In their study, the ECL of Ru(bpy)32+ at Pt or Au electrode only has the first ECL peak and does not have the second ECL peak. Their explanation was that the OH∙ radical generated could completely react with Au to form oxide films when using Au electrode. So, there was no active OH∙ radicals and could not generate the second ECL peak on Au electrode. In contrast, in our study, the Ru(bpy)32+/HCHO system showed another ECL peak (second ECL peak) around 1.2 V at Au electrode. This phenomenon indicated that there was a new intermediate generated on the Ru-DSNPs/Au electrode, which reacted with the oxidized Ru(bpy)32+ generating emitter. Therefore, the ECL process should be not coincident with that reported in literature [21]. It was known that oxidation of HCHO may produce strong reducing intermediates, ∙CHO radical, which was consistent with the electrocatalytic reaction mechanism as tripropylamine (TPA)-Ru(bpy)32+ system. So, we may conclude that the possible reaction mechanism at Ru-DSNPs/Au electrode could be described by the following reaction scheme (Eqs. (5)–(8)).
I / 10-4 A
Fig. 1. TEM image of Ru-DSNPs (the bar scale is 200 nm). Inset: SEM image of Au electrode modified with Ru-DSNPs.
3þ
2171
b 1.8
1.5
1.2
0.9
0.6
0.3
0.0
0.6
0.3
0.0
E/V
ð2Þ
B a
0
-1
-0.8
I / 10-4 A
ECL intensity a.u.
-1.0
-0.6
b
-0.4
-2
-3
c -0.2
c
-4
d
0.0 1.8 0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.5
1.2
0.9
E/V
E/V Fig. 2. ECL-potential curves for the immobilized Ru-DSNPs (curve a), free Ru-DSNPs (curve b) and free Ru(bpy)32+ ions (curve c) in 0.1 mol/L phosphate buffer solution (pH 8.0).
Fig. 3. (A) Cyclic voltammograms of bare Au electrode in the absence (solid) and presence (dash) of 5.0 × 10− 7 mol/L HCHO in 0.1 mol/L phosphate buffer solution (pH 8.0). (B) Cyclic voltammograms of Ru-DSNPs/Au electrode in the absence (solid) and presence (dash) of 5.0 × 10− 7 mol/L HCHO in 0.1 mol/L phosphate buffer solution (pH 8.0).
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-4
6
second peak
-0.8
5
-0.6
c
-0.2
-3 0.0
-2
0.2
0.4
0.6
0.8
1.0
1.2
b
4
-0.4
I ECL / a.u.
ECL intensity a.u.
-5
ECL intensity a.u.
a
-1.0
-6
1.4
3 2
E/V
b
-1
first peak
1
0
a
0 0.2
0.4
0.6
0.8
1.0
1.2
1.4
5
6
E/V Fig. 4. ECL-potential curves for the Ru-DSNPs/Au electrode in0.1 mol/L phosphate buffer solution (pH 8.0) (a) containing 1.0 × 10− 7 mol/L (b) and 5.0 × 10− 7 mol/L (c) HCHO.
RuðbpyÞ3
2þ
RuðbpyÞ3
3þ
−e→RuðbpyÞ3
3þ
ð5Þ
þ HCHO→RuðbpyÞ3 þ
2þ
þ
•
þ H þ HO
ð6aÞ
•
HCHO−e→H þ HO RuðbpyÞ3
3þ
RuðbpyÞ3
•
ð6bÞ
þ HO → RuðbpyÞ3
2þ
→RuðbpyÞ3
2þ
2þ
7
8
9
pH
þ products
ð7Þ
þ hν
ð8Þ
In addition, the ECL signal around 1.2 V increased considerably with the increasing concentration of HCHO (Fig. 4, curve b–c). Such ECL enhancement could used to determine HCHO. 3.4. Optimization of the conditions of fabricating ECL sensor and detecting HCHO
Fig. 6. Effect of pH on ECL intensity in 0.1 mol/L phosphate buffer solution with (b) and without (a) 5.0 × 10− 7 mol/L HCHO at the scan rate of 50 mV/s.
50 mV/s was investigated. As seen from Fig. 5, The ECL intensity increases accordingly with the increase of the Ru-DSNPs concentration from 0.4 to 2.8 mg/mL, which may be attributed to the fact that more Ru(bpy)32+ could be immobilized on the electrode with more Ru-DNSPs. But when the Ru-DSNPs concentration is higher than 2.8 mg/mL, the ECL reaches plateau regions. A possible reason might be owing to the increased Ru-DSNPs which led to an increase in thickness of the modifier which would prevent the HCHO from transferring from aqua solution to the interior of the films. Therefore, 2.8 mg/mL Ru-DSNPs was chosen for subsequent experiments. In order to obtain a higher sensitivity of the ECL sensor for HCHO, the influence of electrolyte pH level on ECL intensity was studied for the determination of HCHO. As can be seen from Fig. 6, the ECL intensity increase with increasing pH and gives a maximum at pH 8.0 in Ru-DSNPs/HCHO system (Fig. 6, curve b). The reason may be due to the difficult production of intermediates, ∙CHO radicals, in the acidic environment. Therefore, pH 8.0 was chosen in the following experiment.
Because Ru(bpy)32+ plays an important role in the process of ECL, the influence of Ru-DNSPs concentration on the ECL intensity in the presence of HCHO in PB (pH 8.0) at the scan rate of -12
A ECL intensity a.u.
-10
I ECL / a.u.
4.5
3.0
1.5
-8 -6
Log (ECL intensity a.u.)
6.0
2.0
7
1.6
1.2
0.8
0.4
-4
-8.0 -7.6 -7.2 -6.8 -6.4 -6.0
Log C
-2
1 0 0.0 0.2 0.0
0.8
1.6
2.4
3.2
4.0
0.4
0.6
0.8
1.0
1.2
1.4
1.6
E/V
C (mg/mL) Fig. 5. Influence of different Ru-DSNPs concentration to the ECL intensity in 0.1 mol/L phosphate buffer solution (pH 8.0) containing 5.0 × 10− 7 mol/L HCHO at the scan rate of 50 mV/s.
Fig. 7. Calibration of HCHO at the Ru-DSNPs/Au electrode. 1–7: 1.0 × 10− 8, 4.0 × 10− 8, 6.0 × 10− 8, 1.0 × 10− 7, 4.0 × 10− 7, 6.0 × 10− 7 and 1.0 × 10− 6 mol/L in 0.1 mol/L phosphate buffer solution (pH 8.0) at the scan rate of 50 mV/s. The ECL intensity was measured at the emission wave length of 1.2 V.
L. Chu et al. / Materials Science and Engineering C 32 (2012) 2169–2174
-6
Table 1 The interferences from some ions and organic compounds on the determination of 5.0 × 10− 7 mol/L HCHO. Content (mol/L)
RSD (%,n = 6)
Fe3+ Fe2+ Al3+ Cu2+ Mg2+ NO3− SO42− Methanol Formic acid
1.0 × 10− 2 1.0 × 10− 2 1.0 × 10− 2 1.0 × 10− 2 1.0 × 10− 2 1.0 × 10− 2 1.0 × 10− 2 5.0 × 10− 6 5.0 × 10− 6
2.7 1.4 1.9 2.1 3.3 1.5 3.7 4.2 3.9
A -5
ECL intensity (a.u.)
Interferences
2173
-4
-3
-2
-1
0
3.5. Calibration graphs and interferences
0
40
80
120
160
200
t/s 7
B
6
ECL intensity (a.u.)
The calibration graphs and detection limit were carried out under the optimal detection conditions with different concentrations of HCHO. As shown in Fig. 7, the ECL intensity increased gradually with the increasing concentrations of HCHO in the range of 1.0 × 10 − 8–1.0 × 10 − 6 mol/L with a detection limit of 6 ppb (at S/ N = 3) which is lower than the maximum permitted concentration of HCHO vapor established by WHO (80 ppb). The interferences from some ions and other organic compounds were also examined with 5.0 × 10 − 7 mol/L of HCHO. The results (shown in Table 1) indicated that they had no influence on the ECL potential. As a result, measurement of ECL intensity for three times and the average values were obtained. If the presence of some ions and organic compound altered the ECL intensity by less than ±5%, we considered that caused no interference. Some possible inorganic in the wastewater such as Fe 3+, Fe 2+, Al 3+, Cu 2+, Mg 2+, Co 2+, NO3− and SO42− (each of 1.0 × 10 − 2 mol/L) were added in Na2HPO4NaH2PO4 (pH 8.0) containing 5.0 × 10 − 7 mol/L HCHO, the results indicated that they had no influence on the ECL intensity. Further, some organic compounds which had the similar chemical structure with HCHO, such as methanol and formic acid, were investigated. The results indicated that 10-fold methanol and formic acid (5.0 × 10 − 6 mol/L for each) had no influence on the ECL intensity.
5
4
3
2 0
5
10
15
20
25
30
t / Day Fig. 8. (A) ECL intensity of the Ru-DSNPs/Au electrode in PB (pH 8.0) containing 5.0 × 10− 7 mol/L HCHO under continuous CVs for 8 cycles with the scan rate of 50 mV/s. (B) Stability of the Ru-DSNPs/Au electrode ECL sensor under storage.
3.6. Application of the sensor to real samples We also studied the applicability of the Ru-DSNPs/Au electrode by measuring local waste water, rain water and seafood. The quantitative determination was performed by standard-addition method. The results are summarized in Table 2 and 3. The recovery of the samples ranged between 94.5% and 101%, verifying the possibility of the method. 3.7. Stability of the Ru-DSNPs/Au electrode Both operational and storage stability are important from the practical application point of view. The IECL–time curves of RuDSNPs/Au electrode under continuously cyclic potential scanning from 0.2 to 1.4 V for 8 cycles in Na2HPO4-NaH2PO4 (pH 8.0) containing 5.0 × 10 − 7 mol/LHCHO is shown in Fig. 8A. The coincident
Table 2 Determination of formaldehyde in water samples. Samples
Waste water Sample 1 −5
−1
mol L ) Content (10 Added (10− 5 mol L− 1) −5 Found (10 mol L− 1) RSD (%, n = 6) Recovery (%)
2.6 5 7.5 3.4 98.7
7 10 17.1 3.6 101
Sample 1 0 20 18.9 3.2 94.5
4. Conclusion In this paper, the uniform amine-functionalized Ru(bpy)32+-doped silica nanoparticles were successfully applied in the field of ECL sensor to detect formaldehyde for the first time. This novel ECL sensor
Table 3 Determination of formaldehyde in real samples.
Rain Sample 2
ECL intensity was observed detectable change. The long-term storage stability of the present sensor was studied by storing it in 37 °C constant temperature when not in use, and by measuring its ECL response to 5.0 × 10 − 7 mol/L HCHO over a 30-day period with fitful usage of every five days. As can be seen from Fig. 8B, the ECL intensity changed slightly during this period. The reason may be due to the strong chemical bond between the amine-functionalized Ru-DSNPs and mercaptoacetic acid.
Sample 2 0 50 49 2.0 98
Samples −7
−1
Content (10 mol L ) Added (10− 7 mol L− 1) −7 Found (10 mol L− 1) RSD (%, n = 6) Recovery (%)
Seashell
Shrimp
Crab
2.6 5 7.3 7.9 94
7 10 17.1 3.6 101
0 20 18.9 3.2 94.5
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based on Ru-DSNPs showed significant advantages in sensitivity and stability due to: (1) a large number of Ru(bpy)32+ which were encapsulated in the silica shell maintained its electrochemical activities and generated strong electrochemiluminescence; (2) the exterior silica shell could effectively prevent the leakage of Ru(bpy)32+ due to the strong electrostatic interaction between them. Besides, mercaptoacetic acid was used as the intermediate to conjugate the Ru-DSNPs with Au electrode leading to the more stable immobilization, which resulting in a good reproducibility and stability of ECL sensor. Supplementary data to this article can be found online at http:// dx.doi.org/10.1016/j.msec.2012.05.047. Acknowledgments This project was supported by the National Natural Science Foundation of China (Grant No. 20975061) and the National Basic Research Program of China (Grant No. 2007CB936602). References [1] National Air Quality and Emission Trend Report: Air Toxics, US Environment Protection Agency, 1996 (Chapter 5). [2] World Health Organization, Environmental health criteria 89, Formaldehyde, WHO, Geneva, 1989. [3] P. Patnaik, Handbook of Environmental Analysis: Chemical Pollutants in Air, Water, Soil, and SolidWastes, CRC Press, Boca Raton, FL, 1997. [4] Y. Herschkovitz, I. Eshkenazi, C.E. Campbell, J. Rishpon, J. Electroanal. Chem. 491 (2000) 182–187. [5] J. Wang, L. Liu, S.Y. Cong, J.Q. Qi, B.K. Xu, Sens. Actuators B 134 (2008) 1010–1015. [6] J. Wang, P. Zhang, J.Q. Qi, P.J. Yao, Sens. Actuators B 136 (2009) 399–404.
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